Printable Version of Topic

Click here to view this topic in its original format

Unmanned Spaceflight.com _ Dawn _ Dawn Cruise

Posted by: SkyeLab Sep 27 2007, 12:31 PM

Pushing out of Earth orbit now...........

biggrin.gif

Posted by: elakdawalla Sep 27 2007, 02:39 PM

loon reports from the Cape that AOS happened about 2 hours after launch, at 9:44 EDT. Yay!

Emily

Posted by: ustrax Sep 27 2007, 02:55 PM

Horst Uwe Keller, Dawn's FC Team Leader reported to spacEurope an hour ago:

"Now we have telemetry! Everything looks OK.
Looks good. Cameras are responding (heaters)."

He added:

"We just talked about it. We (MPS) are now in charge of 6 cameras operating currently in space!
2 on Rosetta, 2 on DAWN, 1 on VEX, 1 on Phoenix and in addition the detector for the microscope on Phoenix.
Looks like a record to me."

He's happy... smile.gif

Posted by: climber Sep 27 2007, 04:10 PM

May be little OT...and that's the reason of this post actualy !
We have 8-11 spacecrafts that can be considered in "Cruise phase" at this time (including 2 bound for Mars : Phoenix and Dawn)
Do I miss any?

New Horrizons
Phoenix
Dawn
Roseta
Messenger
Hayabusa
Deep Impact
Stardust
and may be as well :
Voyager 1
Voyager 2
Ulyses

That's quite an achievment. smile.gif I'm wondering if we ever had as many at the same time.
I'm also wondering if, instead of keeping them in their proper section (Mercury,Mars, Pluto, etc…), it'll not be worth to have a section in the Forum that'll show "Cruise phase Spacecrafts".

Advantage will be that we could go there and check down all status instead of having to remember which Spacecraft is where.
Just a thought.

BTW : Go Dawn, Go mars.gif

Posted by: punkboi Sep 27 2007, 04:18 PM

Godspeed, Dawn!

Posted by: dvandorn Sep 27 2007, 05:18 PM

Well -- I missed the launch (6:34 am is a little early for me these days, and that's when she lofted by my clock), but I just saw a quick replay of the launch at the beginning of the post-launch news conference, and I have to say, that thing heeled over to the left (from the camera angle I saw) pretty good before straightening out and angling to the right onto its correct trajectory. Took off like a bat out of hell, though...

Four issues were just mentioned -- the RCS switched itself from the primary to the secondary system, for reasons yet unknown; the RCS thrusters are running colder than anticipated, which is making the software controls lock them out, but reversion to hardware controls is keeping them running -- the fix is a minor re-set of the software's criteria values; the RCS brackets are running a little warmer than normal, but are cooling down; and there is a slight difference in electricity being generated between the two solar panels.

Those are the only issues that have been discussed.

-the other Doug

Posted by: stevesliva Sep 27 2007, 05:39 PM

Amazing! Given the incredible complexity of the post-launch deployments and sequencing in the Planetary Society Blog post by Marc Rayman, I'm amazed that so much goes on without human intervention...
http://planetary.org/blog/article/00001153/

That post has got to be one of the more informative discussions of autonomous operation that I've read. (Other than perhaps the explanations of the incidents when they have gone wrong)

Posted by: Rakhir Sep 27 2007, 08:49 PM

QUOTE (climber @ Sep 27 2007, 04:10 PM) *
We have 8-11 spacecrafts that can be considered in "Cruise phase" at this time (including 2 bound for Mars : Phoenix and Dawn)
Do I miss any?

Already forget Kaguya ? wink.gif
She is still in cruise phase.
(As well as VRAD and Relay sat. unless you count them as part of Kaguya until they are released)

Posted by: Toma B Sep 28 2007, 07:33 AM

Just as I thought...nobody in the press conference asked question that I am most interested in... blink.gif
Dawn is going to visit two biggest asteroids Ceres and Vesta. It is going to enter orbit around these two but there was some words before that it can do few close flybys of some small asteroids as well.
I guess that planed flybys are all canceled because slips in launch but there should be new ones.
Does anybody know if there are any candidates?

Posted by: ugordan Sep 28 2007, 07:36 AM

QUOTE (Toma B @ Sep 28 2007, 09:33 AM) *
I guess that planed flybys are all canceled because slips in launch but there should be new ones.

IIRC, there never were any planned flybys. It will be determined in flight (based on current trajectory, fuel and ion engine performance) what is feasibly reachable and if it's worth the trouble. One of TPS blog entries mentions something about it as I recall.

Posted by: elakdawalla Sep 28 2007, 04:35 PM

QUOTE (Toma B @ Sep 28 2007, 12:33 AM) *
I guess that planed flybys are all canceled because slips in launch but there should be new ones.

Gordan's right, there were no flybys planned in advance, not only because of the uncertainty in launch date but because of uncertainty in performance of the ion engines. And there may well not be any flybys of any real quality unless they get very lucky. Unlike a flyby mission, Dawn can directly translate fuel reserves into a much longer mission at its primary targets. Which is a better use of the xenon, a relatively distant view of a small asteroid or another week spent in orbit at Ceres, or a closer orbit, or a different orbit, etc. etc.? It sounds to me like unless the orbital mechanics gods smile upon them with a really great opportunity that lies fortuitously close to the trajectory, the economics won't work out for any other flybys.

(The answer to this question was on a http://planetary.org/radio/show/00000236/.)

--Emily

Posted by: stevesliva Sep 28 2007, 04:57 PM

QUOTE (ugordan @ Sep 28 2007, 03:36 AM) *
IIRC, there never were any planned flybys. It will be determined in flight (based on current trajectory, fuel and ion engine performance) what is feasibly reachable and if it's worth the trouble. One of TPS blog entries mentions something about it as I recall.
I recall that as well, nothing was planned or expected until launch. Similar to the New Horizons Jupiter flyby... they didn't plan the launch to coincide with anything but the primary targets.But I am definitely curious to see what they will pass by, and whether the instruments can do useful science on more distant fly-bys.

Posted by: jabe Sep 29 2007, 02:10 AM

QUOTE (abalone @ Jul 21 2007, 03:00 PM) *
If specific impulse reigns supreme then why do they use Xenon instead of hydrogen

I believe it is the ionization energy as well as storage issues..An ion engine needs ions..Xenon ionization energy is lower than hydrogen so if you can use a little energy to ionize it the rest of the available energy can be used to "spit" the ions out...(As well hydrogen is a diatomic gas so electrons are used in the bonds..no free ones available to excite if my chemistry is right smile.gif ) Helium would be next best but still ionization energy is high)

Posted by: Greg Hullender Sep 29 2007, 05:46 AM

jabe: No, that's not it, but this has already been discussed at length here, and the actual answer is well worth reading.

http://www.unmannedspaceflight.com/index.php?showtopic=3274&st=300

--Greg

Posted by: jabe Sep 29 2007, 11:56 AM

QUOTE (Greg Hullender @ Sep 29 2007, 05:46 AM) *
jabe: No, that's not it, but this has already been discussed at length here, and the actual answer is well worth reading.

http://www.unmannedspaceflight.com/index.php?showtopic=3274&st=300

--Greg

Thanks for the link..always wondered why they didn't use helium smile.gif

Posted by: Del Palmer Oct 2 2007, 05:14 PM

Latest Dawn journal:

http://dawn.jpl.nasa.gov/mission/journal_9_30_07.asp

Posted by: punkboi Oct 2 2007, 05:41 PM

Interesting journal. Hopefully, a "Where is Dawn now?" page will be posted on the mission website soon.

Posted by: Stephen Oct 3 2007, 02:38 AM

QUOTE (punkboi @ Oct 3 2007, 03:41 AM) *
Interesting journal. Hopefully, a "Where is Dawn now?" page will be posted on the mission website soon.

Speaking of "Where is Dawn now?", where the "Dawn" subforum on UMSF.com? Or are we going to continue working out of this present thread from now until it reaches the asteroid belt?

=====
Stephen

Posted by: djellison Oct 3 2007, 06:59 AM

It doesn't need a subforum until it starts doing science in a few years. It has ONE thread right now...maybe it'll get another - but a thread on it's own in a subforum would be a tumble-weed like situation. On that basis, the front page of the C & AM subforum would need to be split into 6 subforums which would be a pointless overcomplication.

Doug

Posted by: volcanopele Oct 3 2007, 07:09 AM

I could see the creation of a new thread though wink.gif

Posted by: ugordan Oct 3 2007, 08:47 AM

QUOTE (volcanopele @ Oct 3 2007, 09:09 AM) *
I could see the creation of a new thread though wink.gif

That might be a good idea, seeing as how it's finally happening and on its way. 30 pages to go through just to read the current news is a bit of an overkill smile.gif

Posted by: Stephen Oct 4 2007, 02:03 AM

QUOTE (djellison @ Oct 3 2007, 04:59 PM) *
It doesn't need a subforum until it starts doing science in a few years. It has ONE thread right now...maybe it'll get another - but a thread on it's own in a subforum would be a tumble-weed like situation.

I notice Phoenix isn't "doing science" thus far either yet it has a subforum all its very own.

And then there's MSL, which last I checked hasn't even been built yet, much less launched.

And of course there's New Horizons which will be spending much of the next decade in hiberation before it starts doing science at Pluto, and Messenger which is still heading Mercury-ward. True, both did do a teensie bit of science at Jupiter and Venus, respectively. On the other hand I do seem to recall them getting their own sub-forums (sub-fora?) even before they got that far.

On the other hand I notice Kayuga hasn't got a subforum of its own yet either so I guess that puts Dawn in good company. rolleyes.gif

=====
Stephen

Posted by: Greg Hullender Oct 4 2007, 04:57 AM

I think it's simpler than that; it's because there is no "Where is Dawn" link on the page yet. Until then, they haven't officially lanched, as far as I'm concerned, and they don't deserve a subforum yet.

Perhaps we should start a new thread titled "Where is Dawn?"

--Greg :-)

Posted by: jamescanvin Oct 4 2007, 08:50 AM

QUOTE (Stephen @ Oct 4 2007, 03:03 AM) *
I notice Phoenix... MSL... New Horizons...


Yeah, but look at how many threads are in each of those forums, too many for me to count!

Once the threads start mounting then a case for keeping them all together in a sub-forum can be made, but that time isn't now.

James

Posted by: CAP-Team Oct 4 2007, 10:00 AM

Here's where Dawn is now:




Earth as seen from Dawn:



Posted by: djellison Oct 4 2007, 10:54 AM

QUOTE (Stephen @ Oct 4 2007, 03:03 AM) *
rolleyes.gif



Yeah - that pretty much sums it up. Subforums get made when they're required - not becaue of some line in the sand or event that takes place. They're made because one topic dominates another forum.

Doug

Posted by: punkboi Oct 4 2007, 05:27 PM

QUOTE (CAP-Team @ Oct 4 2007, 03:00 AM) *
Here's where Dawn is now:




Earth as seen from Dawn:




Cool- Did you create that yourself? Or which website did you get that from?

EDIT: Interesting that Phoenix has been near Earth ever since launch... I think the second TCM later this month should change that

Posted by: ugordan Oct 4 2007, 05:56 PM

QUOTE (punkboi @ Oct 4 2007, 07:27 PM) *
I think the second TCM later this month should change that

No, it won't. TCMs are correction maneuvers, not huge boosts.

Posted by: CAP-Team Oct 4 2007, 09:20 PM

QUOTE (punkboi @ Oct 4 2007, 07:27 PM) *
Cool- Did you create that yourself? Or which website did you get that from?

EDIT: Interesting that Phoenix has been near Earth ever since launch... I think the second TCM later this month should change that


Yes, I created the image with a program called xplanet (by Hari Nair) and you can use spice kernels you can download from the NASA NAIF site.
It's a bit like Celestia but for still images.

Phoenix is still relatively close to Earth because it went inwards first (thus moving faster than Earth) , it's just since last week Phoenix is starting to move out.
Phoenix and Dawn will stay relatively close to each other till Phoenix reaches Mars.

Posted by: volcanopele Oct 4 2007, 09:27 PM

Wow, you're right, Dawn is available on the NAIF site smile.gif Which means I can import it into Celestia, sweetness! Wish New Horizons was available...

Posted by: Stephen Oct 5 2007, 01:49 AM

QUOTE (djellison @ Oct 4 2007, 08:54 PM) *
Yeah - that pretty much sums it up. Subforums get made when they're required - not becaue of some line in the sand or event that takes place. They're made because one topic dominates another forum.

Glad to hear there's a defensible logic behind such things. As opposed to ad hoc rules of a more arbitrary kind. smile.gif

=====
Stephen

Posted by: belleraphon1 Oct 9 2007, 11:56 PM

Sweetness and LIGHT.....

First ion thruster test......

http://www.planetary.org/blog/article/00001186/

Craig

Posted by: Marz Oct 10 2007, 04:32 AM

Marc cracks me up!!!

"The drama was captured in the stirring name of the file that was transmitted to the spacecraft: dz002e.scmf"

Truly excellent and enjoyable reading, and great news everything's checking out ship-shape. I hope he can continue keeping me entertained in the 7.4 years to Ceres... are we there yet?

Posted by: peter59 Oct 20 2007, 07:40 AM

Science Instruments Checked Out
October 15 - 19
Dawn's science instruments were powered on and given their first health checks this week. The gamma ray and neutron spectrometer, imaging camera, and visible and infrared mapping spectrometer all operated perfectly.

Posted by: peter59 Oct 27 2007, 06:36 AM

Second Ion Thruster Checkout Completed Successfully
October 22 - 26
The mission operations team completed the checkout of a second ion thruster this week. In one of the tests, the thruster was operated for 27 hours continuously at 5 different throttle levels, and in two other tests it was operated at maximum power for 4 hours each time. All spacecraft systems performed extremely well.

Posted by: nprev Oct 27 2007, 01:32 PM

Thanks for the update, Peter. Green bird, baby, green bird...GO DAWN!!! smile.gif

Slightly OT here, but has anyone else noticed that, provided that VEX, Chang'e and/or Kaguya survive, we should have active missions happening on or around all the major bodies of the inner Solar System in 2011? If the hangtime for them all extends to Dawn's arrival at Ceres, then that envelope gets pushed out to the Belt. What a heady time for UMSF!

EDIT: Forgot about Juno going to Jupiter...if everything converges right, then we've got it covered all the way out to Saturn at that time!!!

Posted by: brellis Oct 27 2007, 02:06 PM

QUOTE (nprev @ Oct 27 2007, 06:32 AM) *
has anyone else noticed that, provided that VEX, Chang'e and/or Kaguya survive, we should have active missions happening on or around all the major bodies of the inner Solar System in 2011? If the hangtime for them all extends to Dawn's arrival at Ceres, then that envelope gets pushed out to the Belt. What a heady time for UMSF!

EDIT: Forgot about Juno going to Jupiter...if everything converges right, then we've got it covered all the way out to Saturn at that time!!!


New Horizons and the Voyagers will still be humming too smile.gif

Posted by: punkboi Oct 27 2007, 06:45 PM

New journal up:

http://dawn.jpl.nasa.gov/mission/journal_10_24_07.asp

Posted by: peter59 Nov 20 2007, 08:59 PM

More Ion Thrusting Tests Completed
November 12 - 16
The week-long systems test of interplanetary cruise thrusting completed successfully on Monday. The third ion thruster was tested this week, and like the other two, it performed perfectly. The thruster operated at 4 throttle levels, including full power. In a separate activity, the mission operations team powered off the reaction wheels to test pointing control with hydrazine thrusters during ion thrusting.

Posted by: punkboi Nov 20 2007, 09:04 PM

A week late, but whatever:

http://dawn.jpl.nasa.gov/mission/journal_11_13_07.asp

Still no "Where is Dawn now?" page on the official website, eh? wink.gif

Posted by: peter59 Nov 24 2007, 07:35 AM

Main Antenna Checked Out and New Software Uploaded
November 19-23
This week the spacecraft was commanded to use its main antenna for the first time and measurements showed that it is in fine condition. New software was installed in one of Dawn's computers (and its backup), correcting a minor bug that was discovered shortly after launch.

Posted by: punkboi Nov 29 2007, 06:48 PM

"Where is Dawn now?" page finally up:

http://dawn.jpl.nasa.gov/mission/live_shots.asp

Posted by: peter59 Dec 19 2007, 09:56 PM

"Dawn has started IPS cruise thrusting to Vesta. The thrust came on at
4:08 PM pacific. We are on our way."—Project Manager, Keyur Patel 12/17/07

Posted by: punkboi Dec 20 2007, 09:15 AM

http://www.planetary.org/blog/article/00001266/

New Dawn Journal up... Planetary.org posted calibration photos taken by the spacecraft's Framing Camera

Posted by: IM4 Jan 8 2008, 09:33 PM

Good news everyone!
Extended version of the Dawn trajectory is now available at HORIZONS (two additional segments till April 2008). I did some simulations and found that Dawn will pass within 0.048 AU from comet 79P/du Toit-Hartley somewhere around March 17, 2008. Exact date and distance depends on actual thrusting, nevertheless, upcoming event will be the closest of this kind till EPOXI encounter with comet Hartley-2.
Comet 79P was rediscovered last November in its 5th apparition and will pass perihelion in May 2008. That's a faint comet, but I hope not a smallest one. Even with coma/tail size of 20-30 thousands km Framing Camera and VIR spectrometer will be able to distinguish some details. I think that's a good opportunity to test and calibrate instruments on the real object, especially for VIR, which is a relative of Rosetta's VIRTIS spectrometer.

PS Attached image features comet orbit, Dawn trajectrory and planets positions on March 17, 2008.

 

Posted by: tedstryk Jan 9 2008, 11:53 AM

That is still 7 million miles, but it could be done, at least as a test. It also flies by a really big object in February 2009. mars.gif

Ted

Posted by: elakdawalla Feb 1 2008, 07:28 PM

The latest Dawn Journal is now up at http://dawn.jpl.nasa.gov/mission/journal_1_31_08.asp and http://planetary.org/blog/article/00001315/ websites. In it, Marc reports that Dawn did go into safe mode on January 14, 2008, the same day as the MESSENGER flyby and when Ulysses went haywire, but Marc told me that the Dawn safing at least had nothing to do with any of the other drama in the solar system; it was a routine, well-understood event, and the spacecraft is fine.

--Emily

Posted by: JTN Feb 10 2008, 09:17 PM

(I'm not normally into fields'n'particles, so forgive my ignorance...)
So, we lost the magnetometer. Is there any way, from science or engineering data, that we'll be able to tell anything at all about the magnetic environment of Ceres/Vesta? Not quantitative, just enough to spot Mercury-level surprises.
I know they don't put those awkward booms on spacecraft for the fun of it... just asking.

Posted by: Holder of the Two Leashes Feb 14 2008, 07:28 PM

In a word, no.

If Vesta appears unusually bright, it could be guessed that deflection of the solar wind by a field might have prevented weathering, at least over a significant portion of past history. If gravity data indicates a very dense core for Vesta, that would also be an indication that a magnetic field is more likely, but won't tell you anything about whether it is really there. Any realistic value for what you could expect at Vesta will not affect high energy cosmics rays very much, those which provide part of the signature for GLAST.

For Ceres, it was speculated that salty underground water reservoirs might have a magnetic signature, like they do on Ganymede. If they are there, and they do, then there is no way now for DAWN to know about it.

Posted by: ugordan Feb 14 2008, 07:31 PM

QUOTE (Holder of the Two Leashes @ Feb 14 2008, 08:28 PM) *
deflection of the solar wind by a field might have prevented weathering

Isn't the majority of space weathering related to micrometeoroid impacts?

Posted by: Holder of the Two Leashes Feb 14 2008, 07:51 PM

The weathering being referred to here is the general darkening of an airless surface by the implantation of solar wind particles. Local areas of relatively high magnetic strength on the moon are lighter colored than their surroundings because they prevent this weathering.

But you make a good point. Vesta might have more gardening from impacts, since it is in the main belt. That could lighten up the surface, too. Which might make it even harder to guess about the cause.

Edit - Wait, wait. Sorry. You were talking about micrometeorites. Yes, they do darken the surface. I really don't know by what proportion. However, if you look at a picture of Reiner Gamma on the moon, you can see what a difference a magnetic shield can make.

Posted by: punkboi Mar 5 2008, 02:09 AM

New Dawn journal up:

http://dawn.jpl.nasa.gov/mission/journal_2_29_08.asp

Posted by: peter59 Mar 20 2008, 04:34 PM

I nearly forgot about these cancelled missions.

http://spacefiles.blogspot.com/2007/11/pre-dawn-french-soviet-vesta-mission.html

Very interesting three proposed trajectory for two spacecrafts.

Trajectory 1:
-launch from Earth
-Mars gravity assist
-flyby of 2335 James (a 10 km X-type asteroid) (an Amor-asteroid)
-Mars gravity assist
-109 Felicitas (C-type, 76 km)
-739 Mandeville (EMP(?) type, 110 km)
-4 Vesta (V-type, or Vestoid. Has a diameter of 570 km) flyby with 3.5 km/s. A penetrator is released.
Total delta-v: 450 m/s

Trajectory 2:
-launch from Earth
-Mars gravity assist
-flyby of the P/Tritton short period comet
-Mars gravity assist
-2087 Kochera (30 km?)
-1 Ceres (flyby & releasing a penetrator)
Total delta-v: 1150 m/s

Trajectory 3:
-launch from Earth
-Mars gravity assist
-1204 Renzia (10 km?) (an Amor-asteroid)
-Mars gravity assist
-435 Ella (U type, 30 km)
-46 Hestia (F type, 165 km)
-135 Hertha (M type, 80 km)
Total delta-v: 350 m/s

Posted by: peter59 Apr 1 2008, 03:38 PM

Dawn Completes Another Month of Thrusting
March 31, 2008
Dawn thrust with its ion propulsion system for most of March, stopping once each week to point its main antenna to Earth. Almost 96% of the month was devoted to thrusting.

Posted by: Stu Apr 1 2008, 04:11 PM

QUOTE (peter59 @ Apr 1 2008, 04:38 PM) *
Dawn Completes Another Month of Thrusting
March 31, 2008


What is this, "Carry On Spaceflight"?!?!?! I could swear I heard Sid James laughing when I read that title... tongue.gif

Posted by: Greg Hullender Apr 30 2008, 04:01 AM

I just noticed that Dawn has substantially upgraded their "Where is Dawn" page.

http://www.dawn-mission.org/mission/live_shots.asp

Now I have something to keep me entertained for the next 1213 days. :-)

--Greg

Posted by: Holder of the Two Leashes May 1 2008, 04:26 PM

Yes, the diagrams are much better now, especially compared to the earlier monochome ones where you could barely tell the different orbits apart.

And ... the latest monthly thrusting report.

http://dawn.jpl.nasa.gov/mission/journal_4_22_08.asp

Carry on ... smile.gif

Posted by: mps May 30 2008, 11:46 AM

Meanwhile somewhere on the vicinity of Mars...

http://dawn.jpl.nasa.gov/mission/journal_5_27_08.asp

quote: be sure to visit the cool new feature "Where is Dawn Now?" at http://dawn.jpl.nasa.gov/mission/live_shots.asp. The site includes depictions not only of the craft's trajectory and location but also of its attitude

Posted by: punkboi Jun 30 2008, 03:17 AM

New Dawn journal up:

http://dawn.jpl.nasa.gov/mission/journal_6_26_08.asp

Posted by: dmuller Jun 30 2008, 06:41 AM

QUOTE (peter59 @ Mar 21 2008, 02:34 AM) *
http://spacefiles.blogspot.com/2007/11/pre-dawn-french-soviet-vesta-mission.html


I noticed the following paragraph in the above article:
QUOTE
I've heard it's not ruled out that Dawn will be directed to rendezvous with 2 Pallas (for a slow flyby) in 2018, after the main mission at Vesta and Ceres is completed and enough fuel is left.

Is that possibly still on the cards?

Posted by: nprev Jun 30 2008, 11:11 AM

laugh.gif ...Dr. Rayman is a hoot! He sure can write an entertaining update.

Posted by: ilbasso Jun 30 2008, 12:10 PM

He is indeed quite an entertaining writer.

Maybe during the relatively quiet years of the cruise phase, ESA could contract out to him to write mission updates of the probes they purportedly have deployed around the solar system.

Posted by: Greg Hullender Jun 30 2008, 12:41 PM

QUOTE (nprev @ Jun 30 2008, 04:11 AM) *
laugh.gif ...Dr. Rayman is a hoot! He sure can write an entertaining update.


A joke or two can be funny, but not one or two in every paragraph. It's hard to tell sometimes what's serious and what's not. Also, for my tastes, very little of his humor is actually funny.

--Greg

Posted by: ugordan Jun 30 2008, 12:48 PM

QUOTE (Greg Hullender @ Jun 30 2008, 02:41 PM) *
Also, for my tastes, very little of his humor is actually funny.

Sadly, this is often the case for me as well which is a shame because it distracts from otherwise detailed status reports he makes.

Posted by: MahFL Jun 30 2008, 01:01 PM

He sounds like a typical slightly nutty scientist type.........

Posted by: djellison Jun 30 2008, 01:11 PM

See this...

----------------------

That's a line being drawn under the debate regarding Marc's writing. Some like it. Some don't. End of debate.

Posted by: jasedm Jul 1 2008, 10:30 AM

I'm just pleased that we get regular updates on the mission.
The possible post-main mission rendezvous with Pallas hasn't been mentioned for a while, but IIRC the mechanics of setting it up are difficult due to Pallas' orbit being appreciably out of ecliptic.
Maybe the mission planners are going to present the relevant trajectories as a fait accompli when they're lobbying for that mission extension... wink.gif

Posted by: 3488 Jul 1 2008, 03:42 PM

QUOTE (jasedm @ Jul 1 2008, 11:30 AM) *
I'm just pleased that we get regular updates on the mission.
The possible post-main mission rendezvous with Pallas hasn't been mentioned for a while, but IIRC the mechanics of setting it up are difficult due to Pallas' orbit being appreciably out of ecliptic.
Maybe the mission planners are going to present the relevant trajectories as a fait accompli when they're lobbying for that mission extension... wink.gif


I hope so. In December 2018, 2 Palles is on the descending node. In fact DAWN would not even have to leave the plane of 1 Cere's orbit to do this, as 2 Pallas will intersect that plane. The biggest issues will be the supply of Xenon, & the state of the solar arrays, will they still be producing enough power?

I really, really hope that the 2 Pallas option stays open. To bag all three of the Asteroid Belt's largest members would be a real accomplishment. However 2 Pallas would not be orbited, but could be a slow encounter, enabling much of the giant asteroid to be seen at a fairly high resolution.

Whilst 4 Vesta & 1 Ceres are primary mission aims, I think to not lose sight of 2 Pallas as an encore right at the very end, would be worthwhile.

No decent Hubble Space Telescope images exist of 2 Pallas do they, or have I not been able to find them?

Andrew Brown.

Posted by: ElkGroveDan Jul 1 2008, 04:55 PM

QUOTE (3488 @ Jul 1 2008, 07:42 AM) *
No decent Hubble Space Telescope images exist of 2 Pallas do they, or have I not been able to find them?


from http://www.lpi.usra.edu/meetings/lpsc2008/pdf/2502.pdf

"Figure 1: Pallas imaged by HST in 336nm UV filter."

 

Posted by: Del Palmer Jul 1 2008, 04:56 PM

QUOTE (3488 @ Jul 1 2008, 04:42 PM) *
No decent Hubble Space Telescope images exist of 2 Pallas do they, or have I not been able to find them?


Depends what you mean by "decent." wink.gif I don't recall seeing any press release images of Pallas from STScI, but there is a set of WFPC2 images in the http://archive.stsci.edu/xcorr.php archive. Looks like they were taken using gyro-guiding, and so the targeting was a little off...


Posted by: Del Palmer Jul 1 2008, 05:01 PM

QUOTE (ElkGroveDan @ Jul 1 2008, 05:55 PM) *
"Figure 1: Pallas imaged by HST in 336nm UV filter."


Dan, great find! smile.gif Have not seen that in the raw data archives...


Posted by: 3488 Jul 1 2008, 06:47 PM

QUOTE (ElkGroveDan @ Jul 1 2008, 05:55 PM) *
from http://www.lpi.usra.edu/meetings/lpsc2008/pdf/2502.pdf

"Figure 1: Pallas imaged by HST in 336nm UV filter."


Thank you very much Dan,

I tried, high & low to find HST imagery of 2 Pallas. I had heard before that the triaxial shape had been determined from rotational light curves. That is a very good image & quite clearly shows a rounded triangular profile, the best I've ever seen of this gigantic asteroid.

I've downloaded the image.

QUOTE (Del Palmer @ Jul 1 2008, 05:56 PM) *
Depends what you mean by "decent." wink.gif I don't recall seeing any press release images of Pallas from STScI, but there is a set of WFPC2 images in the http://archive.stsci.edu/xcorr.php archive. Looks like they were taken using gyro-guiding, and so the targeting was a little off...


Thank you very much Del also for your help.

The scientific case for DAWN to go onto 2 Pallas after the end of the primary mission is compelling.

It's great to be back here, hopefully I can contribute something of interest at some point.

Andrew Brown.

Posted by: tedstryk Jul 3 2008, 06:21 PM

This is another Hubble view. During the 2001 observations, the Hubble missed Pallas with its Planetary Camera chip, getting the image with its lower-resolution wide field portion of WFPC2.


Posted by: Del Palmer Aug 27 2008, 02:00 PM

Latest Dawn update:

http://dawn.jpl.nasa.gov/mission/journal_8_24_08.asp



Posted by: Greg Hullender Aug 27 2008, 03:35 PM

Hmmm. He raises the point that Dawn will cross Mars' orbit before the gravitational assist but doesn't seem to explain why. Obviously this happens with Venus gravitational assists, but that's unavoidable. I'm trying to think why it would be better to do the assist from the far side of Mars, but I can't think of any -- other than the question-begging one of "it wouldn't work the other way".

Does anyone know?

--Greg

Posted by: djellison Aug 27 2008, 04:20 PM

The Mars flyby is mainly about changing the orbital inclination of Dawn iirc.

Posted by: Greg Hullender Aug 27 2008, 04:44 PM

That makes sense -- I'd wondered why the projected path didn't seem to show much change after the assist -- but it still seems you could just as easily change inclination on an outbound flyby as an inbound one.

Again, I'm sure there's a reason why this works out to be superior -- I'm just not seeing what it is. Why is this outer-planet flyby different from all others?

--Greg

Posted by: 3488 Aug 27 2008, 07:25 PM

Also as Doug before you said, it is about changing inclination & also speed. The Mars encounter IIRC also prevents DAWN from coming much closer to the Sun again.

Andrew Brown.

Posted by: Greg Hullender Aug 29 2008, 06:02 PM

QUOTE (3488 @ Aug 27 2008, 12:25 PM) *
Also as Doug before you said, it is about changing inclination & also speed. The Mars encounter IIRC also prevents DAWN from coming much closer to the Sun again.


I wasn't wondering "why is there a Mars flyby." I was wondering "why is this an 'inbound' (toward the Sun) flyby not an 'outbound' one."

Given the way ion propulsion works (long-term but weak), I'm actually surprised Dawn can do this maneuver at all. I'd have thought the thrust would always be close to parallel to the velocity vector and that the orbit (if they turned the engines off) would be nearly circular at any given point. But Dawn is actually falling back towards the Sun (a little) in order to make this flyby.

Maybe that explains it; the angle between the velocity vector of the spacecraft and the velocity vector of the planet needs to get smaller during the flyby or else energy will be lost, not gained. Perhaps it's easier to lift Dawn above the orbit of Mars and then drop it than it would be to get it to rise past it at any significant angle. In that case, though, I do wonder why they quit thrusting entirely for a few months before and after the assist. It'd seem you could get a steeper angle that way.

Of course I know you plan your orbits with the planets you have -- not the planets you'd like to have. :-) At a certain point, I suppose the answer is just "Yeah, you'd go faster, but you wouldn't get to Vesta."

--Greg

Posted by: BrianJ Aug 29 2008, 09:15 PM

QUOTE (Greg Hullender @ Aug 29 2008, 06:02 PM) *
I wasn't wondering "why is there a Mars flyby." I was wondering "why is this an 'inbound' (toward the Sun) flyby not an 'outbound' one."

Hi, just wanted to point out that for earlier launch windows, the flyby was indeed "outbound", as per this image http://upload.wikimedia.org/wikipedia/commons/2/2d/Dawn_Trajectory_as_of_2006.jpg

Also, just out of interest, here's a graphic comparing the orbit of Dawn to the orbit of Mars, before and after the (current trajectory) flyby.
http://img169.imageshack.us/img169/3606/dawn1copyzs2.gif

Regards,
Brian

Posted by: dmuller Aug 30 2008, 01:36 AM

My two cents worth:

Dawn is picking up speed from the flyby. As this happens halfway between periapsis (closest point to sun) and apoapsis (farthest point to sun), both are raised. It also rotates the apsises clockwise, so Dawn will be at periapsis shortly after the Mars encounter. By thrusting then, it efficiently raises the apoapsis further. It also increases the inclination from 1.9 to 6.5 degrees, which I think would be costly to do without a gravity assist.

I dont think it makes a difference whether the flyby is inbound or outbound, you gain speed w.r.t. sun as long as you fly behind Mars.

Horizons gives the following orbital elements w.r.t. solar system barycenter (Mars flyby as inferred from Horizons data is around Feb 12):

CODE
                  1 Feb 2009     28 Feb 2009     Change
Eccentricity        0.160521        0.132016     orbit gets rounder
Periapsis (km)   180,738,278     203,950,288     +23 million km
Apoapsis (km)    249,858,224     265,989,955     +16 million km
Inclination           1.9249          6.5018     gets steeper

Posted by: tasp Aug 30 2008, 06:04 AM

I will reiterate my ignorance about such matters, but will still post a question.

Let's say the Dawn ion drive accels the craft nominally at .001 G right now (neglecting slow increase in accel with fuel mass depletion) and let's say every one in the front office monitoring the engine is happy to sign off at running it in the range of .00085 to .00115 G.

And the office crew is ok with adjusting the throttle from time to time, so long as Mars encounter and Vesta arrival (or was Ceres first ? no matter) happen on schedule, and the average accel is .001 for optimal fuel utilization.

So, by tweaking the throttle only, in the narrow approved range, with a minimum impact to our amazing flight of discovery to Vesta and Ceres, how far off the 'nominal track' can the probe get, and does this resulting 'lens' shaped area in the graph (assuming frame of reference w/ Dawn) take us near anything known and interesting ??

For example, from Mars to Vesta, we accel at lower approved G limit 1/2 way and then go rest of the way at higher approved rate (allowing for the trajectory smiths to approve limits, of course) or we accel 1/2 way at higher G limit, then at lower limit the rest of the way. This gives us an area (instead of a line) along the way to Vesta we can explore for interesting objects to encounter for 'free'. (other than the brain wear and tear it takes to figure this out)

So is this already obvious to everyone and has been found to be undesirable for some reason I haven't figured out yet, or does this put a toe in the door for a free extra object to look at ??

( I am assuming the area potentially available with this technique compared to the known number of asteroids yields a figure of >1 for # of objects on average expected to be in an area of that size, but if it is more like .001, then it looks like I have my answer . . . )


blink.gif




Posted by: dmuller Aug 30 2008, 09:37 AM

QUOTE (Greg Hullender @ Aug 30 2008, 04:02 AM) *
that the orbit (if they turned the engines off) would be nearly circular at any given point.

Greg, that does not seem to be the case. To start with, the original post-launch (pre-ion thrusting) was nowhere near a circle (150m km x 246m km). And the Mars flyby boosts both the periapsis and apoapsis quite a lot (as compared to the thrusting)

Again from Horizons:
CODE
Date        Periapsis         Apoapsis
1-Oct-07     150,019,330      246,071,890
1-Nov-07     150,128,927      244,454,659
1-Jan-08     151,655,060      246,166,277
1-Jul-08     165,446,119      251,548,401
1-Jan-09     180,583,781      250,621,283
1-Jul-09     204,715,862      269,844,671
1-Jan-10     224,351,731      293,297,300
1-Jul-10     260,729,882      309,582,209
1-Jan-11     299,787,522      326,511,305
1-Jul-11     317,551,998      368,001,819
1-Jan-12     320,554,935      382,753,035
1-Jul-12     319,854,770      382,797,552
1-Jan-13     338,984,080      382,275,315
1-Jul-13     363,921,049      408,392,742
1-Jan-14     364,440,390      457,493,646
1-Jul-14     364,604,289      449,257,439
1-Jan-15     378,673,307      445,436,420
1-Feb-15     382,279,514      445,557,925

Posted by: siravan Aug 30 2008, 03:19 PM

QUOTE (tasp @ Aug 30 2008, 01:04 AM) *
So, by tweaking the throttle only, in the narrow approved range, with a minimum impact to our amazing flight of discovery to Vesta and Ceres, how far off the 'nominal track' can the probe get, and does this resulting 'lens' shaped area in the graph (assuming frame of reference w/ Dawn) take us near anything known and interesting ??


IIRC, the ion engines of Dawn are not exactly throttlable. In fact, they have such a low thrust that the main way to control them is to simply turn them on and off. Dawn has periods of "powered flight", separated by periods of cruise. I think each powered segment (days or weeks in a row) has essentially a fixed attitude. Then, then turn off the engine, determine the exact location, turn Dawn to a new attitude and turn on the engine again...

But, back to your main question. Essentially, Dawn does not have one fixed route from where it is to Vesta and in theory it possible to target it to some interesting object en route. However , there are two complications: the low thrust means that everything should be planned way ahead of time and Mars encounter. The exact time and location of the Mars encounter is still not determined, so there is still lots of uncertainty in the post encounter orbit. I believe that it is only after the encounter that Dawn will have a constrained orbit and the team can start planning for any possible extra targeting.

Posted by: djellison Aug 30 2008, 03:36 PM

QUOTE (siravan @ Aug 30 2008, 04:19 PM) *
IIRC, the ion engines of Dawn are not exactly throttlable.


They are - dramatically.

http://dawn.jpl.nasa.gov/mission/journal_10_07_07.asp - lots of detail of the 112 different throttle levels they can use.

Posted by: Hungry4info Aug 30 2008, 04:12 PM

@ tasp

They may not due that so as to conserve fuel. According to Wikipedia (which I realise may not be accurate), if the Vesta and Ceres investigations are successful, DAWN may go on to Pallas -- something I would really love to see.

Posted by: vjkane Aug 30 2008, 04:58 PM

QUOTE (Hungry4info @ Aug 30 2008, 05:12 PM) *
They may not due that so as to conserve fuel. According to Wikipedia (which I realise may not be accurate), if the Vesta and Ceres investigations are successful, DAWN may go on to Pallas -- something I would really love to see.

Per the Dawn Q&A page: "Q: Will there be opportunities to visit other asteroids, either en route to Ceres or as part of an extended mission?
Answer: Unlikely, because there is greater return by spending more of our resources on Vesta and Ceres." http://dawn.jpl.nasa.gov/mission/faqs.asp#

I personally have my doubts about this answer. If at the end of the *extended* Ceres investigations, there is still meaningful amounts of fuel left, I strongly suspect that Dawn will either 1) be sent to orbit another asteroid (a fairly expensive option because of mission ops) or 2) be sent to flyby one or more other bodies in similar solar orbits as Ceres (a less expensive option). NASA is really good at getting the most bang out of a working spacecraft. On the other hand, I don't think that anyone is working really hard on the question of what to do after Ceres -- that event is 7 years away and lots of things can happen to fuel levels, spacecraft and instrument health, and NASA budgets.

Posted by: Greg Hullender Aug 30 2008, 06:01 PM

QUOTE (BrianJ @ Aug 29 2008, 01:15 PM) *
Hi, just wanted to point out that for earlier launch windows, the flyby was indeed "outbound", as per this image http://upload.wikimedia.org/wikipedia/commons/2/2d/Dawn_Trajectory_as_of_2006.jpg

Also, just out of interest, here's a graphic comparing the orbit of Dawn to the orbit of Mars, before and after the (current trajectory) flyby.
http://img169.imageshack.us/img169/3606/dawn1copyzs2.gif


Well, I think the first graphic actually shows an inbound, not an outbound flyby. Did you mean to give a different link?

The second graphic is really cool, though. Does look like a pretty good bang for the buck from this flyby!

dmuller: On the question of the orbit always being circular, I didn't mean to imply that I thought that was the case with Dawn -- it's that it seemed to me that that would be the optimal way to use a low-thrust engine, and I'm curious why that's not the case in practice. Is it solely to make the Mars flyby work?

EDIT

Should have checked Vallado (Fundamentals of Astrodynamics and Applications) first. In Chapter 6.7 (Continuous Thrust Transfers) he works out that this type of transfer returns to circular only on integral numbers of orbits.

--Greg

Posted by: tasp Aug 30 2008, 10:40 PM

Just wanted to comment how much fun it is to have a new 'toy' (ion drive) to 'play' with on the Dawn mission (I wasn't paying attention during Deep Space 1).

I think for folks brought up during the space age we all mostly have a 'feel' for Hohmann transfer orbits and their permutations, but 'learning the ropes' with an ion drive is new and exciting.

No shortage of ideas on things to try with it, and probably some good caution being exercised by the mission planners.

I really appreciate all the interest in this mission.

And of course, future applications of this drive technology seem to be promising all kinds of exciting possibilities. I'd love to wire up an ion drive to an RTG and see what we could get going . . .





Posted by: BrianJ Aug 30 2008, 11:09 PM

QUOTE (Greg Hullender @ Aug 30 2008, 06:01 PM) *
Well, I think the first graphic actually shows an inbound, not an outbound flyby. Did you mean to give a different link?
Erm...I don't think so. I would call it "outbound" since Dawn approaches the flyby from within the orbit of Mars (assuming the link I gave shows you the same as it shows me!) I only comment since I spent quite some time trying to figure out the flyby trajectory for the earlier June launch window (as an "interested layman" who finds these things fascinating smile.gif )

Best regards,
Brian

Posted by: dmuller Aug 31 2008, 02:08 AM

QUOTE (Greg Hullender @ Aug 31 2008, 04:01 AM) *
On the question of the orbit always being circular, I didn't mean to imply that I thought that was the case with Dawn -- it's that it seemed to me that that would be the optimal way to use a low-thrust engine, and I'm curious why that's not the case in practice. Is it solely to make the Mars flyby work?

Greg, if you have the Orbiter simulator (http://www.orbitersim.com) you can simulate this in Earth orbit. Get a scenario where your ship is docked to the ISS, set your Orbit display to PRJ ship and DST altitude (will look more or less like a circle), undock, hit "prograde", get your engines on the lowest thrust setting (i.e. press and hold "Ctrl" and then literally hit your "+" button on the Numpad as short as possible), speed up the simulation to 100x (unless you have a lot of time - but dont go over 100x), and watch the PeA (perigee altitude) and ApA (apogee altitude) increase ... everytime you nearly get a circle (circle: PeA = ApA), youl'll find the ApA running away, half an orbit later the PeA starts to catch up.

Posted by: siravan Aug 31 2008, 02:59 AM

Regarding ion engines and circular orbits, one may make a qualitative non-mathematical argument why that is the case. We all know that for an elliptical orbit, firing engines at periapsis modifies the apoapsis (rising or dropping the apoapsis depending on the direction of the thrust), whereas firing the engines at apoapsis changes the periapsis. Now, for the case of a continuous low-thrust ion engine, it affects both apoapsis and periapsis. Let assume the case where both increase (as in Dawn). The spacecraft spends more time in the vicinity of the apoapsis that periapsis, as it is slower farther in its orbit from the center. Therefore the effect on periapsis is larger than the periapsis. The net effect is that with continuous thrusting, periapsis starts to catch up with apoapsis, i.e. the orbit becomes more circular.

Posted by: dmuller Aug 31 2008, 03:31 AM

BTW, whilst getting the Dawn data from the Horizons system, I noticed the following description of the propulsion system. I particularly love the bold part, leaves every high-performance car lover drooling!

PROPULSION
Dawn uses 3 ion thrusters to reach Vesta once separated from the Delta II. It
will use the thrusters to spiral to lower altitudes on Vesta, leave Vesta,
cruise to Ceres, and spiral to a low altitude orbit at Ceres.

Weight : 8.9 kg each
Dimensions : 33 cm long, 41 cm diameter
Specific impulse : 3100 s
Thrust : 19-91 mN
Acceleration : 0-60 mph in 4 days
Operational time : 2000 days of thrust (entire mission)


Posted by: dmuller Aug 31 2008, 04:37 AM

Since there is much talk about the Dawn cruise, I have finally uploaded the Dawn Realtime simulation onto my website at http://www.dmuller.net/dawn

That's been 4 posts to this thread in 24 hours ... I'll give it a break now for a while

Posted by: Greg Hullender Sep 1 2008, 05:57 PM

QUOTE (BrianJ @ Aug 30 2008, 04:09 PM) *
Erm...I don't think so. I would call it "outbound" since Dawn approaches the flyby from within the orbit of Mars (assuming the link I gave shows you the same as it shows me!) I only comment since I spent quite some time trying to figure out the flyby trajectory for the earlier June launch window (as an "interested layman" who finds these things fascinating smile.gif )



I see it now. The graphic is a bit confusing because sometimes the dotted line is Dawn's trajectory and other times it's a planetary orbit. I was seeing the solid line as Mars' orbit -- but it's actually Dawn.

--Greg

Posted by: Toma B Sep 1 2008, 09:08 PM

I still haven't found what I was looking for....can anybody help me?
Will there be any "non-targeted" flyby of any known asteroid or comet on the way to Vesta or Ceres?

Posted by: Phil Stooke Sep 1 2008, 09:39 PM

Earlier discussions of this mission, before launch, suggested there could be several other flybys, but now they are not emphasized. Saving fuel is probably the big reason.

Phil

Posted by: kwp Sep 2 2008, 04:01 AM

QUOTE (Phil Stooke @ Sep 1 2008, 01:39 PM) *
Earlier discussions of this mission, before launch, suggested there could be several other flybys, but now they are not emphasized.


I asked a mission specialist a few weeks ago and was told that, sadly (my word, not hers), no en route flybys are planned.

-Kevin

Posted by: Marz Oct 3 2008, 06:20 PM

QUOTE (kwp @ Sep 1 2008, 11:01 PM) *
I asked a mission specialist a few weeks ago and was told that, sadly (my word, not hers), no en route flybys are planned.

-Kevin


The Mars gravity assist is coming up in a few months (Feb 09). Are any observations or kodak-moments planned?

Only 2.8 more years until Vesta is reached! wheel.gif

Posted by: djellison Oct 3 2008, 06:28 PM

Yes - an extensive campaign is planned for Dawn at the mars flyby

http://cosis.net/abstracts/EPSC2008/00442/EPSC2008-A-00442-1.pdf

One extra detail I discovered at Europlanet is a colour movie of a full mars day on the departure leg.

Doug

Posted by: ugordan Oct 3 2008, 06:41 PM

QUOTE (djellison @ Oct 3 2008, 08:28 PM) *
One extra detail I discovered at Europlanet is a colour movie of a full mars day on the departure leg.

That will make for a great companion to MESSENGER's Earth departure movie!

Posted by: tedstryk Oct 3 2008, 09:35 PM

QUOTE (ugordan @ Oct 3 2008, 07:41 PM) *
That will make for a great companion to MESSENGER's Earth departure movie!


It will also be fun to compare with the Rosetta images (given the recent flurry of activity, I am guessing that the psa release will be soon).

Posted by: Greg Hullender Oct 8 2008, 04:57 PM

Someone apparently asked the Dawn team our earlier question about Dawn's "inbound" gravitational assist, and the Dawn people actually posted a very nice response in their FAQ section.

QUOTE
http://dawn.jpl.nasa.gov/mission/faqs.asp#: I see that a gravitational trajectory assist is scheduled for February 2009 (angular momentum transfer) with Mars. Normally, outward-bound probes pass by the planet while closer to the sun than the planet. The Dawn probe seems to be further away from the sun than Mars, so it would be traveling faster than Mars before the transfer. Wouldn't that slow the probe down, instead of speeding it up with respect to the sun? A more succinct question would be: How much delta V are you expecting from the Mars encounter (heliocentric velocity).

http://dawn.jpl.nasa.gov/mission/faqs.asp#: There is a wide range of geometries that can make planetary gravity assists effective, and while approaching from outside the orbit of the planet may appear unusual, Dawn is not unique in doing so. The specifics of the gravity assist include not only the relative speed between the probe and the planet but also the direction each one is moving at the time of the encounter. In our case, the principal benefit of the gravity assist is to change the plane of Dawn's orbit around the Sun. Based on your choice of words, you seem to have some understanding already of the key principles, so you probably already know that most planets orbit the Sun close to the plane of Earth's orbit, also known as the ecliptic. You may also know that changing the plane of an orbit can be energetically very expensive. Vesta and Ceres orbit farther from the ecliptic than most planets do.

If we had launched in 2006, the ion propulsion system could have achieved the plane change by itself. The mission is a little more difficult with a 2007 launch, because there is less time to complete the required ion thrusting before the relative alignment of Vesta and Ceres makes the trip between them inconveniently long. Therefore, we take advantage of the gravity of Mars to change Dawn's inclination. The delta-v is about 1.1 km/s, providing a plane change of less than 5°, but that significantly reduces the time Dawn needs to thrust, allowing it to reach Vesta at about the same time, even after launching a year later.

This certainly answered all of my questions! I don't usually look at the FAQ sections for space missions because most of them are too elementary to interest me, but this was a welcome exception.

Their whole FAQ list is here: http://dawn.jpl.nasa.gov/mission/faqs.asp

--Greg


Posted by: peter59 Nov 27 2008, 07:59 PM



27 November 2008 - 1001 days to Dawn's arrival at Vesta.

Posted by: Juramike Dec 1 2008, 05:48 PM

"We may be humbled by our own insignificance in the universe, yet we still undertake the most valiant adventures in our attempts to comprehend its majesty."

-Dr. Marc D. Rayman, Dawn Journal entry for November 30, 2008 posted in the Planetary Society website : http://www.planetary.org/blog/article/00001755/

Posted by: Del Palmer Dec 1 2008, 11:46 PM

You know you're a UMSFer when you're not just marveling at the Universe, but the fact that they deliberately pointed the solar arrays 60 degrees away from the Sun. blink.gif


Posted by: peter59 Jan 3 2009, 06:41 PM

How images might be acquired at Vesta during the High Altitude Mapping Orbit.
http://dawn.jpl.nasa.gov/feature_stories/soa.asp
I can't wait.

Posted by: peter59 Jan 4 2009, 07:09 PM

Somebody knows something about the geometry of the Mars flyby ? I found a out of date drawing showing the flyby scheduled for March 23, 2009.


Dawn should leave the plane of the planets (Vesta's orbital inclination: 7.133 degrees), so geometry of flyby scheduled for February 12, 2009 must be very similar.

Posted by: mps Jan 5 2009, 01:29 PM

QUOTE (peter59 @ Jan 4 2009, 09:09 PM) *
geometry of flyby scheduled for February 12, 2009 must be very similar.

You mean, February 17, like described in http://dawn.jpl.nasa.gov/mission/journal_12_30_08.asp?

Posted by: dmuller Jan 14 2009, 11:26 AM

According to the Dawn ops team, the best estimate of the closest approach to Mars is February 17 at 16:28:55 PST +/- 35 seconds (Spacecraft Event Time). They will continue to refine the time over the coming weeks, with the principal uncertainty being the effect of RCS activity to desaturate reaction wheels. Also there will be no high resolution images of Mars during closest approach, and no observations of Mars are possible whilst Dawn approaches Mars because the Sun is at too close an angle to Mars. After all, the Mars flyby is just a means to reach Vesta, and would not have been in the flight plan had the mission launched earlier.

EDIT: The source of the above information was provided by Marc Rayman, Chief Engineer of the Dawn mission.

Posted by: ngunn Jan 19 2009, 03:06 PM

I thought people might be interested in this website, aimed at coordinating amateur observations 'in support of NASA missions'. I link straight to the calendar page because the upcoming OPPOSITION OF CERES next month is to be the most favourable for THOUSANDS OF YEARS!! Even I will be getting off my couch for that. My binoculars should show a distinct and surprisingly mobile dot in Leo over the next month or two, an experience I look forward to all the more in the knowledge that there is a spacecraft on the way there as I watch. Does anybody know if any time on the big professional 'scopes is set aside to take advantage of this viewing opportunity?
http://dawn-aop.astro.umd.edu/calendar.shtml

Posted by: dmuller Jan 26 2009, 12:21 PM

QUOTE (peter59 @ Jan 5 2009, 06:09 AM) *
about the geometry of the Mars flyby ? I found a out of date drawing showing the flyby scheduled for March 23, 2009.

The SPICE kernels seem to indicate a flyby altitude of 568km

Posted by: jekbradbury Jan 27 2009, 02:18 AM

It would be amazing if HiRISE were to snap a picture of Dawn as it passes Mars. I guess I'm just spoiled from the Phoenix descent image. laugh.gif

Posted by: stevesliva Jan 27 2009, 04:09 AM

QUOTE (jekbradbury @ Jan 26 2009, 09:18 PM) *
It would be amazing if HiRISE were to snap a picture of Dawn as it passes Mars. I guess I'm just spoiled from the Phoenix descent image. laugh.gif

I imagine it'd be a matter of how big and bright you want your streak to be.

Posted by: Hungry4info Jan 27 2009, 10:48 PM

QUOTE (jekbradbury @ Jan 26 2009, 08:18 PM) *
It would be amazing if HiRISE were to snap a picture of Dawn as it passes Mars. I guess I'm just spoiled from the Phoenix descent image. laugh.gif


IIRC, HiRISE imaged another spacecraft, was it Odyssey?

Posted by: djellison Jan 27 2009, 11:04 PM

MOC imaged Odyssey and Mars Express. Not seen any HiRISE attempts to do the same though.

Dawn will, iirc, be swooping over the south pole - not sure if any orbiting spacecraft will have an opportunity to image it.

Doug



Posted by: dmuller Feb 10 2009, 01:21 PM

2 1/2 days until Dawn enters the Martian Hillsphere ... and a minor trajectory update in the kernels: closest approach on 18 Feb 00:29:06 UTC at an altitude of 549 km.

I have now implemented the notional DSN tracking for Dawn (or to be more precise: for Mars) for the next 16 days at http://www.dmuller.net/dawn




Posted by: Steve G Feb 15 2009, 12:53 AM

I know this is way too premature, but has there been any musings about an extended mission after Ceres? Will Dawn have any fuel reserves for new adventures?

Posted by: dmuller Feb 15 2009, 01:04 AM

I have corrected the event times (from ET to UTC) and added whatever I could extract from the Dawn journal to come up with the following timeline for the http://www.dmuller.net/dawn:

CODE
13 Feb 05:01:13   Enters Mars Hillsphere
17 Feb 13:01:33   Gravitational attraction of Mars exceeds that of the Sun
17 Feb 17:47      Visible and infrared mapping spectrometers switched on
17 Feb 21:21      Primary science camera switched on
17 Feb 21:57      Slew to Mars observation attitude. Loss of main antenna signal.
17 Feb 22:26:58   Deimos closest approach (16,031 km)
17 Feb 23:53:47   Phobos closest approach (8,014 km)
18 Feb 00:28:00   Mars Flyby. Altitude 549 km
18 Feb 11:53:30   Gravitational attraction of the Sun exceeds that of Mars
19 Feb 11:09      Slew to point main antenna to Earth
20 Feb 15:48      Slew to Mars observation attitude to practice Vesta arrival.
20 Feb 19:28      Slew to point main antenna to Earth. End of Mars flyby observations.
22 Feb 23:51:20   Exits Mars Hillsphere

Posted by: Hungry4info Feb 15 2009, 01:53 AM

QUOTE (Steve G @ Feb 14 2009, 06:53 PM) *
I know this is way too premature, but has there been any musings about an extended mission after Ceres? Will Dawn have any fuel reserves for new adventures?


Can't say how accurate it is, but I've heard musings about, if indeed everything goes as plan and there is sufficient fuel reserves, an extended mission to Pallas.

Posted by: K-P Feb 15 2009, 09:20 PM

QUOTE (Hungry4info @ Feb 15 2009, 03:53 AM) *
Can't say how accurate it is, but I've heard musings about, if indeed everything goes as plan and there is sufficient fuel reserves, an extended mission to Pallas.


A FLY-BY of Pallas, to be exact.
(which of course is a great thing too if happens)

There is no rational reason to use all capitals here. Also, flyby is one word. - Moderator

edit: Just wanted to point out the type of exploration in this case, since Dawn is orbiting every other target it visits, so some might assume by default that possible Pallas -extension includes also orbiting of that object. ...and sorry for my bad English.

Posted by: Hungry4info Feb 16 2009, 01:10 AM

I don't suppose there's any pictures of Mars yet?

Posted by: elakdawalla Feb 16 2009, 01:24 AM

There aren't going to be any distant-approach ones because of the high phase (which would result in unacceptable heating of the instrument, pointing too close to Sun). According to Marc's latest Dawn Journal, the science camera will be powered on at 21:21 UTC Feb 17.

--Emily

Posted by: volcanopele Feb 16 2009, 10:17 PM

Dawn at Mars Closest Approach:



 

Posted by: volcanopele Feb 16 2009, 10:21 PM

And here is the global view post encounter:




 

Posted by: CAP-Team Feb 16 2009, 10:49 PM

Volcanopele,

What ephemeris do you use in Celestia? I use the most recent kernels from the NAIF site, and with that, the flyby occurs on 11 february.

Posted by: volcanopele Feb 16 2009, 10:54 PM

I used dawn_ref_081031-090601_090213_dc024p1_v1.bsp.

The problem is... for some reason, I broke it... Now I get February 11...

Posted by: dmuller Feb 17 2009, 02:22 AM

I am currently using "dawn_ref_081031-090601_090209_mga_c2_v1.bsp" for my realtime simulation which gives the correct C/A time. Prior to that file being available I used "dawn_ref_081031-090601_090129_dc023p2_v1.bsp" which was also yielding the correct flyby time.

Posted by: Holder of the Two Leashes Feb 18 2009, 10:16 PM

The Mars to Vesta leg of the journey should now be much better determined as to the exact path. Add to this the fact that the number of main belt asteroids with well determined orbits is exploding, and I'm wondering if the DAWN team might revisit the idea of doing a target-of-opportunity flyby?

Hope so.

Posted by: Paolo Feb 23 2009, 05:30 AM

On arXiv today http://arxiv.org/abs/0902.3579

Posted by: Holder of the Two Leashes Jun 11 2009, 07:10 PM

After a long time coasting, DAWN has fired up its ion thrusters again. They will be firing for most of the time from now on, with only short interruptions, until Vesta arrival. This begins the final leg towards Vesta.

http://www.nasa.gov/mission_pages/dawn/news/dawn-20090608.html

Posted by: peter59 Aug 21 2009, 11:08 AM

Great opportunity to see Vesta through their own eyes.


The positions of Venus and Vesta are shown by crosses when they are closest on the morning of August 26.

Posted by: Holder of the Two Leashes Sep 29 2009, 03:40 PM

Good news. DAWN will arrive at Vesta earlier and stay longer, due to higher power margins from its solar panels. Here is a http://dawn.jpl.nasa.gov/mission/journal_9_27_09.asp to the latest DAWN journal. Also, Emily's blog over at the Planetary Society web site has some details on this.

Arrival is now set for July 2011 rather than September.

Posted by: Poolio Sep 29 2009, 04:09 PM

What an entertaining and informative read! Thanks for pointing it out. And great news about the extended stay at Vesta. An increase from 9 months to 12 months is quite significant.

Posted by: tedstryk Sep 29 2009, 06:22 PM

Yay! Glad to hear this.

Posted by: Holder of the Two Leashes Nov 3 2009, 02:49 AM

The latest http://dawn.jpl.nasa.gov/mission/journal_10_31_09.aspcan be interpreted to kinda sorta hint that they might be targeting one or more additional asteroids on the way. More on the topic next month (or later).

Posted by: Greg Hullender Nov 3 2009, 04:47 PM

Unless you have inside information (in which case, please share!) :-) I don't get that impression. When he talks about other things Dawn will do between now and the Vesta encounter, I think he's just talking about routine maintenance activities, such as he's posted about in the past.

For my money, the most significant milestone in the new Dawn Journal is that, on November 13, Dawn enters the main asteroid belt for good. One day before I turn 51.

--Greg

Posted by: tedstryk Nov 3 2009, 08:04 PM

"They are also preparing to give it some additional tasks before the year is out, and inside sources reveal that these may be described in an upcoming log." It is certainly possible that it is targeting an asteroid or taking advantage of a serendipitous flyby, but I wouldn't put money on it.

Posted by: Holder of the Two Leashes Nov 3 2009, 08:13 PM

Nope, no inside information. If I did have inside information, I'd be keeping it inside, and wouldn't be posting anything that would hint that I did know something. wink.gif

Here is the part that caught my attention: "They [mission controllers] are also preparing to give it some additional tasks before the year is out, and inside sources reveal that these may be described in an upcoming log." And that little tidbit is imbedded in an update that celebrates at some length DAWN's arrival in the main belt.

This may or may not have anything to do with other asteroids in the area (I stressed the word might smile.gif ), but it does sound a little more than just routine, as in true "inside sources reveal ..." Unless, of course, Dr. Rayman is teasing everyone with trying to build some excitement over additional voltage margin checks of the ion engines. And that is not totally out of the question.

Posted by: Greg Hullender Nov 3 2009, 09:22 PM

Oh I can't imagine he'd write anything to tease his readers!

--Greg :-)

Posted by: charborob Dec 1 2009, 04:55 PM

The latest Dawn journal quashes any hope that anyone might have entertained about Dawn making a flyby of an asteroid on the way to Vesta or Ceres. It seems that Dawn will not come closer to 1 million km from a 5 km asteroid.
Read the journal http://dawn.jpl.nasa.gov/mission/journal_11_27_09.asp.
No wonder it is titled "Dawnticlimaxes".

Posted by: nprev Dec 1 2009, 06:16 PM

Well, no worries. Who cares about a few crumbs in the big picture; we're going for full cakes, here! smile.gif

Posted by: djellison Dec 1 2009, 08:01 PM

I've deleted two rather pathetic and childish rants.

Posted by: brellis Dec 1 2009, 10:43 PM

I dusted off my copy of the Feb 2008 issue of Discover Magazine, which has a nice article on DAWN for a layman like myself. It traces the stories of Russel and McCord, the two lead investigators. You really have to take care of your health and live a long, long time to see a mission like this come to fruition from its inception!

I'm excited all over again about Ceres, with its possible underground ocean. Adding to that tantalizing notion, the following article in that Feb 2008 issue is one postulating that life may have originated in extreme cold, rather than warm conditions.

Posted by: TritonAntares Jan 31 2010, 11:34 AM

Hi,
as Dawn is now 0,1821 AU ( ~27 Mio. km) behind Mars I wonder if there will be any images taken from there ?
http://neo.jpl.nasa.gov/orbits/fulltraj.jpg

Any information on this available ?
What about its camera resulotion from this distance ? Is there any senseful imagery possible at all?

Thanks & bye.

1200 x 900 in-line image removed. Please link to, do not embed, images of that size - ADMIN

Posted by: brellis Jan 31 2010, 12:04 PM

From that p.o.v. - looks like they can get a Mars-Earth 2-shot! Perhaps "cruise mode" doesn't let her wake up for these Kodak moments, though.

Posted by: ugordan Jan 31 2010, 12:28 PM

QUOTE (brellis @ Jan 31 2010, 01:04 PM) *
From that p.o.v. - looks like they can get a Mars-Earth 2-shot!

Hardly, it looks like the lines of sight to the two are separated by some 20 degrees or so.

Posted by: brellis Jan 31 2010, 01:19 PM

I meant in the coming weeks/months. Sorry for the vagueness.

Posted by: dmuller Jan 31 2010, 01:58 PM

QUOTE (brellis @ Jan 31 2010, 11:04 PM) *
From that p.o.v. - looks like they can get a Mars-Earth 2-shot! Perhaps "cruise mode" doesn't let her wake up for these Kodak moments, though.

Not really ... straight line is around 10 March 2010, but the inclination is off by a lot:
http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=399&vbody=-203&month=3&day=10&year=2010&hour=00&minute=00&fovmul=1&rfov=60&bfov=30&porbs=1&showsc=1

They're not gonna stop thrusting and re-orient the spacecraft for that, I reckon.

Posted by: Hungry4info Jan 31 2010, 02:08 PM

Additionally, how will the cameras handle being aimed ~at the sun?

Posted by: Greg Hullender Feb 1 2010, 01:52 AM

But the cool thing is that, from here on, although Mars will gradually move farther and farther away, Dawn will steadily close on Vesta, until it meets it on the other side of the Sun eighteen months from now. It looks like it's chasing it down.

And it is.

--Greg

Posted by: Paolo Feb 26 2010, 07:06 PM

24 February Dawn Journal http://dawn.jpl.nasa.gov/mission/journal_02_24_10.asp

Posted by: dmuller Mar 1 2010, 05:11 PM

Dawn has published the first arrival trajectory kernels. They're likely to change, but still it is very interesting to see how different the approach to a "traditional" orbit insertion will be, mainly due to the lack of a short and decisive orbit insertion burn. According to that trajectory data:

1) Dawn is captured by Vesta (i.e. orbit eccentricity < 1) on 21 July 2011 05:08:35 whilst still 15,756km away from (the center of) Vesta, and at a relative speed of 0.048km/s

2) Dawn achieves its initial orbit (near-circular 3003x2994km) on 04 August 2011 17:29:53. Ion thrusting ceases at around the same time (otherwise the resulting orbit wouldnt be circular). Relative speed then is 0.077km/s

Posted by: Explorer1 Mar 1 2010, 05:59 PM

How close can Dawn's orbit come to Vesta and still be able to leave once it's time to rendezvous with Ceres? They have to balance between getting good date by being close and being able to escape by being far, correct?

Posted by: ilbasso Mar 1 2010, 06:04 PM

QUOTE (dmuller @ Mar 1 2010, 12:11 PM) *
...
1) Dawn is captured by Vesta (i.e. orbit eccentricity < 1) on 21 July 2011 05:08:35 whilst still 15,756km away from (the center of) Vesta, and at a relative speed of 0.048km/s

2) Dawn achieves its initial orbit (near-circular 3003x2994km) on 04 August 2011 17:29:53. Ion thrusting ceases at around the same time (otherwise the resulting orbit wouldnt be circular). Relative speed then is 0.077km/s


For us Americans, the capture speed is 107 mph, and the relative speed in orbit is 177 mph. That's pretty darned slow!

Posted by: charborob Mar 1 2010, 06:55 PM

QUOTE (dmuller @ Mar 1 2010, 12:11 PM) *
initial orbit (near-circular 3003x2994km)

Do these numbers represent the distance from the center of Vesta, or the overall size of the orbit?

Posted by: dmuller Mar 2 2010, 02:51 AM

QUOTE (charborob @ Mar 2 2010, 05:55 AM) *
Do these numbers represent the distance from the center of Vesta, or the overall size of the orbit?

That's an apogee of 3,003km and perigee of 2,994km measured from the "center" of Vesta. Vesta isn't round (it's 578×560×458 km), so altitude above Vesta will vary to some extent.

Explorer1, I haven't seen any figures on how close Dawn will go to Vesta. The initial orbit is at a safe distance to explore and refine models, they may only decide later as to how much to reduce the orbit. I think (but I may be wrong) that the main criteria for the lowest orbit are instrument constraints, comms and safe altitude (no point crashing) ... I think Dawn should be able to escape Vesta from any orbit.

Posted by: charborob Mar 2 2010, 05:32 AM

I found some information about the mapping orbits at Vesta and Ceres on the http://www.mps.mpg.de/projects/dawn/ (click on the "Mission" tab and then on the "Orbital scenarios" tab). But I suspect that the actual orbits may differ from the proposed orbits.

By the way, what do you call "perigee" and "apogee" relative to Vesta and Ceres? Or do we simply use the generic terms "periapse" and "apoapse"?

Posted by: nprev Mar 2 2010, 06:18 AM

I definitely would. There's no need to torture the language of spaceflight any further by mandating new pseudo-Latin nouns for the same orbital concepts around each world.

Posted by: stevesliva Mar 2 2010, 07:23 AM

QUOTE (nprev @ Mar 2 2010, 01:18 AM) *
There's no need to torture the language of spaceflight any further by mandating new pseudo-Latin nouns


They use the greek root, because peri and apo are greek. So, just to torture you: Perihestion and apohestion from (I think) Hestia for Vesta. Demeter is the greek Ceres. So Peridemeter and apodemeter, perhaps.

I insist you use these ridiculous terms. I may even suggest them to Marc Rayman to make you squirm. ::duck::

Posted by: dmuller Mar 2 2010, 07:41 AM

QUOTE (stevesliva @ Mar 2 2010, 06:23 PM) *
So Peridemeter and apodemeter, perhaps.

Mmm yeah and if you can't remember those you definitely have peridementia and apodementia

Posted by: Greg Hullender Mar 2 2010, 12:10 PM

I'd suggest "aphestion" since the 'h' is just a signal that the following 'e' is a "breathy" vowel. Of course, "apoapsis" ought to be "apapsis" by the same logic -- apo- drops the 'o' before a vowel.

Not that we're actually speaking Greek, of course.

--Greg

Posted by: Vultur Mar 3 2010, 12:38 AM

Are any of those specific terms actually used besides peri/apogee and peri/aphelion? ("periastron" does get use for binary stars I guess).

I mean, the Cassini stuff I've seen talks about periapse and not "pericronon" or whatever, and you don't normally see "periareon"/"apareon" for Mars, or "periaphrodite" for Venus.

(Perihestion/aphestion sounds really cool, though, and *should* get used ... but won't.)

Posted by: stevesliva Mar 3 2010, 12:52 AM

Perilune gets used. Might have heard Messenger use Periherm. These terms are fairly clear in their meaning. So is something like periareon if you think about it. As you get towards lesser dieties, it's not so clear, and the best reason to use a big word is for clarity.

Posted by: dmuller Mar 7 2010, 08:51 AM

Received a kind and very detailed email from Marc Rayman which answers quite a few questions raised regarding Vesta arrival and subsequent science orbits. Main focus is that all these information pertain to planned and reference orbits etc. Reality will be different because of so many unknowns at Vesta. His email, slightly edited ...

QUOTE
We have constraints on the orbit we want to achieve based on the plans for acquiring and returning the data, but the details will depend on Vesta's gravity field and higher order gravity terms. So I hope you understand the 3003 x 2994 km orbit is just our current design. As I wrote in my latest Dawn Journal, we are beginning the detailed sequence design, and this is the reference orbit we use, but we are making the design tolerant to significant changes that will be dictated by what we find there. Planning for orbital operations at a massive body with a highly uncertain gravity field is very complicated.

That first orbit is called "survey orbit." The first ~ 5 days we are there will be used to tweak the sequences based on the actual orbit, updates to instrument parameters (e.g., integration times based on data acquired during approach), etc.

With our current design, the next science orbit will be at a radius of 950 km, and the third and lowest science orbit will be at a radius of about 460 km. Of course, we will not proceed from one orbit to the next without verifying we can do so safely, but unless we discover a problem, we will not change our plans once we are at Vesta. We will not choose to go to a lower orbit (apart, again, from what is needed based on the actual gravity field).

We have no concern about accidental impact with Vesta, even in the lowest orbit. The choice of the lowest radius is a trade-off between the need to go low for the benefit of GRaND on the one hand vs. the time required to travel there and the difficulty of operating so deep in the gravity field. When we are thrusting to low orbits, we are not acquiring the highest quality science data, and at some point it simply isn’t worth the time to continue flying down rather than devoting the time to getting the nuclear spectra. We have a lot to learn about the field, and while the risk of crashing is truly negligible, we still can get a very wild ride. Moreover, with our very large solar arrays, accommodating the gravity gradient torque at low altitude will be a challenge.

We can escape from any orbit we can fly to. The total delta-v for Vesta operations is a very small fraction of the flight system’s total capability. We spiral down, and then we spiral out!



Posted by: nprev Mar 7 2010, 09:38 AM

Possibly a silly question, but at what inclination is this reference orbit? Wondering if they intend to (or even can) try for a polar/near-polar for full mapping.

Posted by: peter59 Mar 8 2010, 05:46 PM

QUOTE (peter59 @ Nov 27 2008, 08:59 PM) *


27 November 2008 - 1001 days before Dawn's arrival at Vesta.


08 March 2010 - 500 days before Dawn's arrival at Vesta.

Posted by: dmuller Mar 9 2010, 12:30 AM

QUOTE (nprev @ Mar 7 2010, 08:38 PM) *
Possibly a silly question, but at what inclination is this reference orbit? Wondering if they intend to (or even can) try for a polar/near-polar for full mapping.

I do NOT know the answer but I would expect it to be polar / polarish (assuming Vesta's rotational tilt is 29 deg or so) ... not just to get a global (hestial?) map, but also to ensure the solar panels are sun bathing all the time. I doubt they can thrust on batteries "behind" Vesta when they spiral in / spiral out. On the upside, this allows for more easy comms as well.
A quick look at the trajectory state vectors (Dawn as seen from Vesta) shows that the z-axis goes from +2960km to -2960km during the survey orbits. AFAIK that z-axis is perpendicular to the ecliptic. So that looks pretty polar if Vesta's tilt is indeed 29deg.
I'll have a closer look in due course.

Posted by: tasp Mar 9 2010, 12:45 AM

Just curious, but the apparent 'stuff' orbiting Rhea found by Cassini's MIMI instrument has me wondering if Dawn might find something similar at Vesta or Ceres. Are there any dynamical constraints on the possibility of boulder type satellites?

Posted by: peter59 Mar 9 2010, 10:58 AM

Due to propulsion, Dawn will be approached very slowly to Vesta. Does anyone know when will be at distance which allows the observation of Vesta' surface? It can be assumed that half a million kilometers is the appropriate distance. It must be assumed that this will be a few weeks before arrival ?

Posted by: dmuller Mar 9 2010, 04:13 PM

QUOTE (peter59 @ Mar 9 2010, 09:58 PM) *
... half a million kilometers ...

Distance from Vesta of 500,000km is achieved late in the day on 31 May 2011 (UT) according to that reference trajectory. Velocity relative to Vesta at that time is around 810 km/h.

Posted by: Paolo Apr 22 2010, 05:11 AM

Today in arXiv http://arxiv.org/abs/1004.3610

Posted by: Explorer1 May 3 2010, 06:20 AM

New Dawn Journal entry:

http://www.planetary.org/blog/article/00002468/

Includes the usual great info and usual puns, with a real groaner near the end. wink.gif

Posted by: Hungry4info May 3 2010, 10:30 AM

QUOTE
While spacecraft have flown past a few asteroids in the main belt (although none as large as the behemoth Vesta nor the still more massive dwarf planet Ceres), no probe has ever attempted to orbit one, much less two.


Did NEAR orbit Eros?

Posted by: dmuller May 3 2010, 12:31 PM

NEAR orbited Eros apparently 230 times: http://near.jhuapl.edu/intro/faq.html

Posted by: nprev May 3 2010, 12:50 PM

Eros is not a main-Belt asteroid, though; think that's what he was referring to.

Posted by: ElkGroveDan May 3 2010, 01:29 PM

QUOTE (dmuller @ May 3 2010, 05:31 AM) *
NEAR orbited Eros apparently 230 times:

A lot more than that. It's been in a very low geosynchronous orbit since EOM. biggrin.gif

Posted by: climber May 3 2010, 02:37 PM

Erosynchronous it is! I'm wondering...well, no.

Posted by: elakdawalla May 3 2010, 03:58 PM

Yeah, and Hayabusa orbited Itokawa too, but neither are main belt asteroids, they're both near Earth asteroids. (I asked Marc the same question and he pointed out the distinction that he made, which I'd also missed.) It may seem like a fine distinction but remember if you're sending a spacecraft to a NEA from Earth you, by definition, are starting out with an orbit pretty similar to the asteroid's, so it's not so hard to match velocities. To enter orbit around a main belt asteroid have to do a LOT more work.

Posted by: ugordan May 3 2010, 04:08 PM

QUOTE (elakdawalla @ May 3 2010, 05:58 PM) *
Yeah, and Hayabusa orbited Itokawa too

I thought it "only" performed station-keeping maneuvers at certain vantage points? Something I wouldn't call orbit.

Posted by: Paolo May 3 2010, 05:10 PM

Hayabusa only did station keeping at various distances over the day "hemisphere" of Itokawa

Posted by: MarkG May 19 2010, 12:58 AM

Dawn is now closer to Vesta than to Mars. A small thing, but it marks the cruise approach to Vesta. Go Dawn!

Posted by: dmuller May 23 2010, 03:56 AM

I had another look at the SPICE kernel for the nominal arrival timeline (planning) and can infer the following key events:

CODE
01-Jun-2011          500,000km from Vesta. First observations?
29-Jun-2011          Enters Vesta Hillsphere (488radii x 265km?)
21-Jul-2011 05:08:35 Orbit capture
04-Aug-2011 17:00    Achieves survey orbit (~3000km)
27-Aug-2011 23:00    Starts Ion drive to lower orbit
14-Sep-2011 08:00    Achieves first science orbit (~950km)


I have also plotted the apohestion & perihestion distances during the descent from the survey orbit to the first science orbit (pdf file attached below). Very interesting to see the 'bouncing' of the lines as a result of continuous low thrust (compared to two bursts that would be needed with chemical propulsion).

Will update my realtime simulations with the above events in a couple of days

 Dawnarr_1.pdf ( 32.53K ) : 305
 

Posted by: dmuller Jun 8 2010, 12:30 AM

NASA's Dawn Spacecraft Fires Past Record for Speed Change:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-192&cid=release_2010-192

Posted by: punkboi Jun 30 2010, 07:27 AM

New Dawn Journal is up

http://www.dawn-mission.org/mission/journal_06_27_10.asp

Posted by: punkboi Jul 28 2010, 05:54 AM

New Dawn Journal is up

http://dawn.jpl.nasa.gov/mission/journal_07_26_10.asp

Posted by: brellis Jul 28 2010, 07:31 AM

What is the analogous OS of Dawn? Is it like Windows XP?

Posted by: Pavel Jul 28 2010, 01:25 PM

More importantly, where is Dawn-tan? http://musasi12.blog.ocn.ne.jp/blog/images/2010/06/18/hayabusatan.jpg has one and so does http://en.wikipedia.org/wiki/OS-tan.

Posted by: PDP8E Jul 28 2010, 05:51 PM

Brellis,

Dawn uses the RAD6000 computer.
It is a space qualified, radiation hardened, well behaved, and characterized computer.
It is a 25MHZ PowerPC. It is used in almost 200 active spacecraft (look up the RAD6000 in Wiki)
The OS is space qualified and called: VxWorks (from Wind River). It is a flavor of UNIX, has a C compiler, libs and is tuned for real time control. I use VxWorks on a kludge at work that tests printed circuit boards.

I've always said that given the right transceiver, I could hack into Spirit or Oppy through the backdoor username 'Guest' and password 'Guest'

<dream_mode>

CODE
trying to transmit and receive..... < snap ... crackle....pop....whiz....bang....>

****VxWorks Ver 4.1C

Username> GUEST
Password> *****

-_-_-_-_ Welcome to MER-A -_-_-_-_-_
-_-_-_-_ Welcome to MER-A -_-_-_-_-_

VxWorks Version 4.1C Kernel: WIND version 2.2
Copyright Wind River Systems Inc, 1990-2003
CPU: PowerPC Memory: 128Mb WDB: Ready

********* enter debug commands or scripts to 'drive' MER-A **********
********* do not reformat drive **********
>

</dream_mode>

Posted by: nprev Jul 28 2010, 10:08 PM

Ah, good ol' VxWorks...also used on numerous modern aircraft computers!

Posted by: punkboi Sep 2 2010, 07:17 AM

New Dawn Journal is up

http://dawn.jpl.nasa.gov/mission/journal_08_30_10.asp

Posted by: YesRushGen Sep 8 2010, 08:11 PM

Hi everyone, two questions please:

1. At what point will Dawn begin snapping pictures of Vesta?

2. At what point will the resolution of those pictures exceed the best Hubble images?

Thanks,

Kelly

Posted by: alan Sep 8 2010, 11:20 PM

Optical navigation images will be taken during the approach phase which begins in May 2011.

QUOTE
The first optical navigation images will be acquired when Dawn is about 1.2 million kilometers (750 thousand miles) from Vesta...
When these first optical navigation images are taken, distant Vesta will appear to be only about 5 pixels across.


QUOTE
By early June 2011, the images will surpass the best that can be obtained with the Hubble Space Telescope.

http://dawn.jpl.nasa.gov/mission/journal_03_28_10.asp

Posted by: punkboi Oct 1 2010, 07:11 AM

New Dawn Journal is up

http://dawn.jpl.nasa.gov/mission/journal_09_27_10.asp

Posted by: Marz Nov 3 2010, 09:59 PM

Another entry in the journal:

http://dawn.jpl.nasa.gov/mission/journal_10_31_10.asp

255 days till Vesta!

Posted by: punkboi Dec 6 2010, 10:50 PM

New Dawn Journal is up

http://dawn.jpl.nasa.gov/mission/journal_11_30_10.asp

Posted by: Greg Hullender Dec 11 2010, 05:04 AM

Did anyone catch this comment?

QUOTE
To rotate from one attitude to another requires firing some jets to start the huge ship (the largest NASA has ever sent on an interplanetary voyage) turning and then others to stop it.

Is Dawn really the largest interplanetary probe ever sent by NASA? Or just the largest past Mars?

--Greg

Posted by: ElkGroveDan Dec 11 2010, 05:12 AM

Not sure, but we all know by now that Cassini is "school-bus-sized"

Posted by: elakdawalla Dec 11 2010, 05:25 AM

The physical span of its solar panels is probably the biggest, but I'm confident that Cassini is heavier (yup, just checked, Cassini had almost double Dawn's mass at launch). Which is more important, diameter or mass? wink.gif (Be careful not to ask any Pluto fans this question, now that there's evidence that Eris may be smaller but is still more massive.....)

Posted by: Explorer1 Dec 11 2010, 05:42 AM

The sentence talks about size, which is technically dimensions, not mass or weight. In that case, yeah, Dawn is really large!
The Dawn fact sheet says 19.7 meters tip to tip.

Rosetta's solar panels are 32 meters tip to tip, according to the ESA site I just checked. In that case it's Rosetta with the largest!
(which it needs, out at Jupiter orbit, but does it actually cross farther during hibernation? I can't tell from the simulation on their site; that would be a first if true.)

Posted by: nprev Dec 11 2010, 05:50 AM

I think what Dr. Rayman probably really means is that controlling Dawn's attitude is challenging due to its mass distribution from those long arrays.

So, yeah, size matters. wink.gif

That's gotta be quite a bit of inertia to overcome (...very carefully) by thrusters mounted on the spacecraft bus.

Posted by: Paolo Dec 11 2010, 05:53 AM

QUOTE (Explorer1 @ Dec 11 2010, 06:42 AM) *
Rosetta's solar panels are 32 meters tip to tip, according to the ESA site I just checked. In that case it's Rosetta with the largest!


do antennae contribute to "size"? Lunar orbiter Explorer 49 (RAE 2) was almost 500 m across when it deployed its wire antennae

Posted by: ZLD Dec 11 2010, 06:11 AM

Found this on Wiki Commons. I honestly hadn't ever even considered how large the solar array must be. Wow...



Isn't Rosetta an ESA only mission as well, making this really the biggest probe (length wise) NASA has sent up?

Posted by: Decepticon Dec 11 2010, 06:47 AM

Whoa Rosetta is a moving target with those panels. I wonder what impact the particles of the comet will have on the probes solar panels.

Posted by: djellison Dec 11 2010, 06:58 AM

Remember - Rosetta isn't doing a 12km/sec flyby of Chary-Gary... it's a rendezvous and orbit... and orbits around small bodies are amazingly slow.

Posted by: centsworth_II Dec 11 2010, 12:51 PM

Here is a discussion by Marc Rayman on the comparison between Dawn's and Rosetta's panels.
http://blogs.jpl.nasa.gov/?p=70

Posted by: Greg Hullender Dec 12 2010, 11:20 PM

Marc Rayman sent Emily and me a very nice e-mail on the size question.

Since we're a sophisticated bunch here, here is his message in its entirety.

QUOTE
Hi Emily and Greg,
I noted the recent discussion at unmannedspaceflight.com about Dawn's size. I don't want to post there because I don't have time to be a reliable participant in discussions, but since I know both of you, I thought I'd send you some more (wordy) information in case it's of interest. Feel free to do with it what you like. If you want to post any of it, that's fine, and you certainly can attribute it to me. If it's not worth your time, that's fine too.

I measure the size of the spacecraft by rigid, primary spacecraft components. Certainly deployed flexible antennas, dampers, booms, and other components on other spacecraft may extend farther. If Paolo or someone else prefers to use those to measure the size of the spacecraft, I won't disagree.

This may be obvious to one or both of you, but turning with thrusters requires imparting a torque, and that depends on the product of the thrust with the moment arm (the distance from the line of thrust to the center of mass). Then the resulting angular acceleration of the spacecraft is the torque divided by the moment of inertia. So, high moment of inertia means low response from the spacecraft.

Then to your specific question, Emily, about which is more important between mass and size, for the purposes of attitude control (which is what I was writing about), they cannot be separated. The moment of inertia, as you may recall, is the integral of {the mass as a function of distance from the center times the square of the distance}. Because of the squaring, moments of inertia often are dominated by mass at large distance, even if that mass is relatively small. Mass at the center of the spacecraft doesn't matter as much as mass at greater distances. Certainly Dawn's moment is dominated by the solar arrays. Turning those huge arrays requires a significant torque, and that is very important in our hydrazine budget. It also drove the selection of our reaction wheels.

As an aside, as an illustration of the effect of the arrays, we spent a fair amount of effort before launch analyzing the contingency case of what would happen if the spacecraft "thought" the arrays had deployed and they had not. Sensors to indicate deployment might fail, so although we had them, we could not rely on them for a function that was truly critical for the success of the mission. We needed to ensure that the spacecraft would be in control under all circumstances. But the moments were so different before and after deployment that the algorithms had to account for the mass distribution. Essentially we had one control system before deployment and another after. As it turned out, we were able to prove that, while the performance would not be beautiful, it would be adequate if the spacecraft switched to post-deployment control even if the deployment had been unsuccessful or was incomplete.

Back to the UMSF discussion, I intended no comparisons with the mass or moment of inertia of other spacecraft. Cassini and other spacecraft certainly are more massive than Dawn. Just Cassini's propellant at launch exceeded Dawn's total mass at launch by more than a factor of two. Moreover, contrary to what nprev posted, I did not mean that controlling Dawn's attitude is challenging due to its mass distribution from those long arrays. It's true, but that wasn't my point. I was simply explaining for readers less technically astute than those at UMSF that slewing the spacecraft requires expending hydrazine. That was all I meant. Of course I avoid the use of terms like "moment of inertia" or "torque" that most readers won't understand, and since I was recovering from the stomach flu, I didn't feel like providing any more detail. I made no effort to be quantitative (which would serve to illustrate how challenging it is) nor to compare Dawn's actuators (thrusters or reaction wheels) with those on other spacecraft. I just threw in the comment about the size (which I have mentioned in several other Dawn Journals as far back as June 2, 2007) for color.

I hope some of that's of interest.

Best regards,
Marc


Thanks, Marc. I'm sure we all appreciate it. In my opinion, one of the best things about UMSF (second only to looking at the cool pictures) is the fact that real scientists actually read and occasionally post here.

--Greg

Posted by: nprev Dec 12 2010, 11:34 PM

Yep; we're a very lucky group of space enthusiasts! smile.gif

Thanks for your response, Dr. Rayman, and thanks for posting it, Greg; much interesting information there!

Posted by: hendric Dec 13 2010, 09:35 PM

Anyone who has turned a merry-go-round with the participant...er, victim...in the center vs on the edge is very aware of the moment of inertia! Also, conservation of angular momentum as well, but we don't have very many spaceships with parts moving to that degree. Does remind me though of the launch video of the MERs, when the two weights were released and flew off to dampen the spin.

Posted by: punkboi Dec 14 2010, 01:40 AM

QUOTE (Decepticon @ Dec 10 2010, 10:47 PM) *
Whoa Rosetta is a moving target with those panels. I wonder what impact the particles of the comet will have on the probes solar panels.


Are you referring to the photo ZLD posted? That's Dawn.

Posted by: cotopaxi Dec 14 2010, 02:03 PM

QUOTE (Explorer1 @ Dec 11 2010, 06:42 AM) *
Rosetta's solar panels are 32 meters tip to tip, according to the ESA site I just checked. In that case it's Rosetta with the largest!
(which it needs, out at Jupiter orbit, but does it actually cross farther during hibernation? I can't tell from the simulation on their site; that would be a first if true.)


The expected aphelion distance during hibernation is 5.29 AU.

Posted by: Greg Hullender Dec 25 2010, 10:54 PM

New stuff in the are-we-there-yet department. Looking at the full-trajectory map: http://neo.jpl.nasa.gov/orbits/fulltraj.jpg

I see we're just a little under one Ceres-year from end-of mission, and we're coming up on one Mars-year since the gravity assist. Still 203 days to get to Vesta.

For the first time it "dawns" on me that we'll be spending a LOT more time at Vesta than at Ceres. Perhaps that means there's likely to be an extended mission to observe Ceres a bit longer.

--Greg

Posted by: nprev Dec 25 2010, 11:18 PM

I wonder when we'll get our first peeks at Vesta. Looks like Dawn is around five million miles (8 million km) away at this time.

The spacecraft attitude during thrust might not be favorable for approach imaging, though; I confess my ignorance of Dawn's architecture.

Posted by: Holder of the Two Leashes Dec 26 2010, 12:16 AM

http://dawn.jpl.nasa.gov/mission/journal_03_28_10.asp

"Approach begins in early May 2011 ..."
"The first optical navigation images will be acquired when Dawn is about 1.2 million kilometers (750 thousand miles) from Vesta ..."
" When these first optical navigation images are taken, distant Vesta will appear to be only about 5 pixels across."
"By early June 2011, the images will surpass the best that can be obtained with the Hubble Space Telescope."

Posted by: Greg Hullender Dec 26 2010, 01:33 AM

Yeah, it's surprising how far a probe needs to go before it gets pics competitive with ground-based scopes, but it makes a certain amount of sense. If an instrument has (say) 5% the power of an Earth-based scope, it needs to be 5% of the distance from a target to be competitive--all other things being equal. For most probes, the last 5% of the distance seems to come around the last 1% or so of the transit time.

Now if we could only figure out how to launch something with instruments the size of the Hubble . . .

--Greg

Posted by: tasp Dec 26 2010, 02:18 AM

Maybe we get lucky and an NEA drifts by James Web Space Telescope.

Probably would not be able to track such an object anyhow . . .


(little bit of holiday levity)



In defense of cameras in space, IIRC, the pixels on Cassini are less than 4 arc seconds on a side, and that's pretty good. What are Hubbles', 0.1 or so? And aiming Hubble at Saturnian objects while in Saturnian orbit would be quite a feat. The view of Enceladus from 28 km would be pretty dramatic though, and orbiting Vesta at any height with that resolution would be sublime.

Posted by: ZLD Dec 27 2010, 03:10 PM

QUOTE (Greg Hullender @ Dec 25 2010, 10:54 PM) *
For the first time it "dawns" on me that we'll be spending a LOT more time at Vesta than at Ceres. Perhaps that means there's likely to be an extended mission to observe Ceres a bit longer.


I think that's the hope. They had to look for some easy areas to trim down costs to pass the review board or face getting cut. Originally, the mission planned for 11 months for each. I think we'll likely see that happen anyway, should Ceres turn out to be as interestng as it seems from Earth.

Posted by: Greg Hullender Dec 28 2010, 02:53 AM

Dr. Marc Rayman, Dawn's Chief Engineer/Mission Manager sent us the following note. As he's told us before, he can't really read UMSF often enough to participate in threads directly, but we're fortunate enough to have got his attention this month.

QUOTE
You are quite right that we spend more time at Vesta than Ceres.



The planned times were indeed reduced between the proposal and the project's "confirmation." So since January 2003, we had intended to spend about seven months at Vesta and five months at Ceres. (It's not unusual to see sources that continue to quote the outdated durations from the proposal, but those values were only that -- proposed.) Now we have increased the time at Vesta to 12 months, thanks largely to better performance than expected from the solar arrays. That extra time has allowed us to devise a more robust plan and to conduct observations that had not previously been planned. That should be cool!



It is also worth noting that we do not need as much time at Ceres as at Vesta. Actually, there are several reasons for this, including the difference in planned spatial resolutions of the images, but there is one that perhaps should be obvious but yet seems to surprise people. We have to escape from Vesta, but we do not depart from Ceres. While the exact duration will depend upon details of Vesta's gravity field and other physical effects we cannot refine until we are in the protoplanet's vicinity, it will take almost three months to travel from the lowest altitude orbit back to interplanetary cruise in which the spacecraft is no longer gravitationally bound to Vesta. (We could do it a little faster, but we devote some of the time to flying to a particular orbital geometry from which to acquire certain bonus observations with the new solar geometry at that time. The time for that doesn't change the basic story.) In contrast, the primary mission concludes in orbit at Ceres, so we do not need to allocate time for the spacecraft to go anywhere after the end of its observations in the lowest altitude orbit there. Obviously an extended mission still would be of neat!



With regard to spatial resolution, Dawn's redundant cameras are designed for mapping these worlds. The pixel scale is just under 100 microradians (a bit over 20 arcsec), quite different both from HST and from Cassini. (In my March 28, 2010 Dawn Journal, I described the camera as having the equivalent of a magnification of about 3 compared to our unaided eyes.) But with its nearly 0.1-radian (5.5 degree) field of view, it is well suited to covering the bodies with multiple filters and at multiple angles (for stereo) from orbit.

Posted by: ElkGroveDan Dec 28 2010, 03:51 AM

QUOTE (Dr. Marc Rayman @ Dec 27 2010, 06:53 PM) *
We have to escape from Vesta, but we do not depart from Ceres.

I'm curious as to what the planned ultimate fate of the craft is after end of mission.

Posted by: Hungry4info Dec 28 2010, 04:11 AM

From what I've heard, it will ultimately depend on the condition of the spacecraft and amount of fuel when it gets there.

The idea of a Pallas flyby was discussed, but of course anything decided will have to be weighed against the option of continued orbital investigation of Ceres.

Posted by: DFinfrock Dec 28 2010, 11:30 PM

Or perhaps as fuel runs low, the orbit can be lowered again and again, giving higher resolution views of the surface, until it ultimately impacts the surface of Ceres.

Posted by: Explorer1 Dec 29 2010, 01:36 AM

An end-game like NEAR would be quite a treat, but of course that's still half a decade away, so let's not get ahead of ourselves. wink.gif

Posted by: nprev Dec 29 2010, 01:44 AM

I doubt that it will be possible for Dawn to land safely on Ceres. That's a much more massive body than Eros, and since the spacecraft would have to use its thrusters for the descent (main drive wouldn't be much help) I would be surprised if enough RCS fuel will remain by then even if the thrusters' performance is up to the task.

I would bet that any XM will involve one or more opportune flybys of accessible Main Belt objects. Personally, I'd love to see a flyby of one of these suspected volatile-rich 'dead comets' if that turns out to be at all possible.

Posted by: Greg Hullender Dec 30 2010, 04:55 AM

A couple more tidbits from Marc. I'll just paraphrase this time.

There's concern that Ceres may have enough ice on it to make it worth protecting. We won't know that until we get there, but if that's the case, Dawn will stay at least 700 km up to avoid biological contamination. If not, she'll almost certainly go for a closer look.

That makes the starting conditions for an XM extremely uncertain. Add to that how far in the future it is, and you can see why no one wants to spend a whole lot of time trying to plan one yet.

Lots of people seem to be confused about Pallas. Someone did an analysis at one point of sending a copy of Dawn to Pallas, but that would have been a different mission. No one has studied the feasibility of sending Dawn itself there.

--Greg

Posted by: vjkane Dec 30 2010, 06:19 AM

QUOTE (Greg Hullender @ Dec 29 2010, 08:55 PM) *
That makes the starting conditions for an XM extremely uncertain. Add to that how far in the future it is, and you can see why no one wants to spend a whole lot of time trying to plan one yet.

Early in the mission, the official line was that extended missions would depend on the exact time the XM would start (uncertain at that time until the engines and solar arrays were fully characterized), the amount of time spent at Ceres, and the remaining fuel. An equally important factor would be the extended mission budget that might be available.

My guess is that it will be several years before we hear anything solid about XM.

Pallas has a significant orbital inclination that would make a flyby dicey (only crosses the elliptic at two specific points) and a rendezvous difficult probably impossible with this spacecraft.

Posted by: ElkGroveDan Dec 30 2010, 07:40 AM

QUOTE (Greg Hullender @ Dec 29 2010, 08:55 PM) *
... from Marc. .... There's concern that Ceres may have enough ice on it to make it worth protecting.

That's what I was getting at in my question above. I know NASA has a high priority on that kind of thing. I guess a 700km orbit would be considered stable then?

Posted by: Greg Hullender Dec 30 2010, 02:52 PM

My guess would be that, if they do decide Ceres needs protection, then they'd move Dawn out of orbit at EOM. Lacking solid data, there is probably even less enthusiasm for planning EOM than XM. :-)

Van: I can't resist. :-) Name an asteroid that does NOT cross the ecliptic at exactly two points. More seriously, it's hard for me to believe there would be enough science in a quick flyby of Pallas to justify the effort. On the other hand, if someone looks hard, I'll bet there's at least one or two reasonable asteroid targets much easier to reach that might be worth a look. Depending on how much fuel is left and how patient we are, Dawn might manage to get a good look at a half a dozen big rocks. Now THAT would be a cool XM!

--Greg

Posted by: charborob Dec 30 2010, 04:12 PM

QUOTE (Greg Hullender @ Dec 30 2010, 09:52 AM) *
get a good look at a half a dozen big rocks.

There are also Ni-Fe asteroids out there somewhere. Wouldn't that be an interesting target?

Posted by: vjkane Dec 30 2010, 04:15 PM

QUOTE (Greg Hullender @ Dec 30 2010, 06:52 AM) *
Van: I can't resist. :-) Name an asteroid that does NOT cross the ecliptic at exactly two points.

--Greg

Greg - You got me. :-)

Pallas' 34.8 degree inclination means that it's hard to encounter it anywhere but where it does cross the ecliptic (unless you dedicate a mission to it). So an extended mission will likely miss this interesting world (7% of the asteroid belt's mass per Wikipedia) to encounter asteroids that keep closer to the ecliptic.

I looked up Vesta (7.1 degree incline) and Ceres (10.5 degree incline). We're lucky that the technology for Dawn's engines was available to take advantage of this opportunity. Turns out that the average asteroid orbital inclination is 8.2 degrees; there's a nice plot here: http://burro.astr.cwru.edu/stu/advanced/asteroid.html

Does anyone know how the orientation of these three asteroid's inclinations match up?

Marc Raymondman devoted a portion of the following log to the discussion of inclination http://dawn.jpl.nasa.gov/mission/journal_09_27_10.asp

Posted by: Hungry4info Dec 30 2010, 04:45 PM

QUOTE (vjkane @ Dec 30 2010, 11:15 AM) *
Does anyone know how the orientation of these three asteroid's inclinations match up?

Not particularly well.

Ascending nodes (Ω)
Ceres Ω = 80.399°
Pallas Ω = 173.134°
Vesta Ω = 103.91°

Posted by: Greg Hullender Jan 1 2011, 04:10 AM

It turns out (per Marc) that there's going to be lots of great science to do at Ceres after the nominal end of mission. This has already been published in “Dawn: A mission in development for exploration of main belt asteroids Vesta and Ceres” at https://pod51000.outlook.com/owa/redir.aspx?C=150a87e543ed437896959b0f8104b336&URL=http%3a%2f%2fwww.dawn-mission.org%2fmission%2fDawn_overview.pdf so I guess it's not really news. :-)

Here are some specifics he mentioned:

QUOTE
I don’t think there is any doubt Ceres will merit further study. It’s a big place, and in the time Dawn has there for the primary mission, it will not be possible to make as many measurements as are likely to be of high value. We will make global maps from the survey orbit and high altitude mapping orbit, but just as at Vesta, imaging from the low altitude mapping orbit will cover only a small portion of the surface. Mineralogical mapping with VIR will cover even a smaller fraction at high spatial resolution, as is inevitable with the high data volume inherent in a mapping spectrometer. In addition, gamma-ray and neutron spectrometry could benefit significantly from longer integration times, both to increase the spatial resolution and to improve the accuracy of elemental abundances. I would also expect there to be great interest in the possibility of seasonal changes.

Once the gravity field is mapped, it is likely the planetary protection constraints could be satisfied from a lower orbit, so that would offer even more possibilities.

Even if the planetary protection requirements disappeared, I don’t see any value in an intentional contact with the surface. I mentioned in a Dawn Journal in 2006 that the spacecraft can’t survive landing. The surface gravity is about 3% of Earth’s, so even the dry spacecraft mass of about 800 kg would require a thrust of more than 200 N! Our RCS thrusters provide less than 1 N each. An impact would probably be valueless; Ceres is too far away for anything else to observe it, and for other technical reasons, it would be difficult to target a particular location anyway.

Other destinations always remain a possibility, but a flyby of almost anything is likely to be of lower value than further study of Ceres. Nevertheless, if the spacecraft remained healthy and propellant margins remained good, I wouldn’t be surprised if at some point, there were a study of what bodies might be reached.


My personal guess: they'll get an XM to study Ceres in more detail, and they'll stay there until the fuel runs out.

--Greg

Posted by: kwp Jan 2 2011, 03:26 PM

With less than 200 days to go (Vesta or bust!) do we have a precise estimate yet of when orbital insertion will occur? Or is that still remain to be defined/refined? I see nothing more precise than "July 2011" on the Dawn mission website.

-Kevin

Posted by: Hungry4info Jan 2 2011, 04:21 PM

It may be kinda hard to actually define that well. Dawn, using ion propulsion, slowly matches it's heliocentric velocity with Vesta. This is a far cry different from the typical screaming toward a planet, then blasting the engines to suddenly slow down to get captured into orbit.
Dawn's orbit insertion may be rather gradual, and difficult to pin down to a specific day.

Anyone's free to correct me on that.

Posted by: tasp Jan 2 2011, 06:51 PM

Would the date of entering the Vestonian (Vestian?) Hill sphere be more appropriate for the answer to the question, are we there yet?

Or perhaps when the approach velocity is under the escape speed for the current actual altitude would be better?

Fun contemplating how different the ion drive makes us think about these matters.

blink.gif

Posted by: siravan Jan 2 2011, 07:08 PM

QUOTE (tasp @ Jan 2 2011, 01:51 PM) *
Would the date of entering the Vestonian (Vestian?) Hill sphere be more appropriate for the answer to the question, are we there yet?


I guess it is not that easy. Vesta is not spherical, its mass uncertainty is large and its gravity field unmapped (after all, these are some of the things Dawn is going to measure), so any definition of a Hill sphere at this time would be rather arbitrary. Maybe even a "Hill ellipsoid" might be a better concept.


Posted by: Phil Stooke Jan 2 2011, 08:29 PM

I think we have to get away from trying to specify exact times and dates in these circumstances. It's not like the start of the orbit insertion burn (or other specified moment in time) that we have with standard rockets. Pick an arbitrary date if you need one, but don't worry about trying to impose it as the correct answer.

Phil

Posted by: Greg Hullender Jan 2 2011, 09:15 PM

I suspect the problem is with the term "Orbit Insertion." For an ion-powered vehicle, as Hungry4Info says, this doesn't seem to be a sharply defined event.

Perhaps a more interesting stat would be the date when Dawn first goes retrograde with respect to the Sun.

Or, a more complicated idea, when does it switch from thrusting to add energy to thrusting to subtract it? Maybe that's the real date we care about.

--Greg

Posted by: centsworth_II Jan 2 2011, 09:52 PM

So, no tense minutes spent nervously munching peanuts?
I think I like that, not being an adrenalin junkie.
Slow and steady as she goes, that's for me. smile.gif

Posted by: kwp Jan 3 2011, 12:31 AM

Perhaps I should have asked the question differently (or, more precisely, asked a different question): when will the ion propulsion be turned off because "we're there!"?

-Kevin

Posted by: volcanopele Jan 3 2011, 12:33 AM

It begins in my mind when Dawn's view of Vesta is better than Hubble's. Or twice as good as Hubble's.

Posted by: Hungry4info Jan 3 2011, 02:03 AM

QUOTE (volcanopele @ Jan 2 2011, 06:33 PM) *
It begins in my mind when Dawn's view of Vesta is better than Hubble's.

Agreed (and the same with the Pluto encounter in 2015). Up until that point, the mission doesn't really provide a lot of new information.

Posted by: stevesliva Jan 3 2011, 02:12 AM

QUOTE (tasp @ Jan 2 2011, 02:51 PM) *
Vestonian (Vestian?)


Vestal.

Posted by: centsworth_II Jan 3 2011, 02:26 PM

QUOTE (kwp @ Jan 2 2011, 07:31 PM) *
...when will the ion propulsion be turned off because "we're there!"?
As I understand this http://dawn.jpl.nasa.gov/mission/journal_04_28_10.asp#spacecraft, the ion thrust will be turned off a little over two weeks after entering orbit around Vesta.

"In late July 2011, as the probe follows its approach trajectory to Vesta, their paths will be so similar they will be moving at nearly the same direction and speed around the Sun... That combination of distance and velocity will allow Vesta to take gentle hold of Dawn. The spacecraft will not even notice the difference, but it will be in orbit around its first celestial target, even as it continues ion thrusting to reach the planned orbit more than 2 weeks later.

....Dawn’s first loop around Vesta will be about 10 days, and its second will take 4. It will stop thrusting when it is in 'survey orbit,' where one revolution takes just under 3 days."

Posted by: tasp Jan 3 2011, 03:11 PM

Wow, a 10 day orbit around such a low mass (compared to Mars or Mercury) object. That is interesting. I assume while the drive is on maneuvering the craft for 'Kodak moments' won't happen. But if an interesting shot 'drifts by' where ever the camera is pointed at the time (crescent Vesta with Saturn in the background for instance) are there plans to click a few?

Also, are scans for possible satellites scheduled?



Posted by: djellison Jan 3 2011, 03:54 PM

It reminds me of NEAR and Eros. Long orbits, very slow etc etc.

Posted by: Greg Hullender Jan 4 2011, 03:24 AM

QUOTE (stevesliva @ Jan 2 2011, 06:12 PM) *
Vestal.

Well, "Vestian" if you want to derive it from the Latin Genitive, like most of the other planets do, but it'll really depend (I think) on what the Dawn team does, since whatever they write will quickly constitute 90%+ of all actual uses in English. "Vestal" ought to refer to the astrological effect of Vesta--whatever that is.

Then we'll see if anyone is brave enough to use "Cererean" when we get to Ceres. Or "Cereal," for those who insist on "Vestal." :-)

--Greg

Posted by: ilbasso Jan 4 2011, 03:33 AM

And here's hoping the photos at Ceres won't be grainy.

(ducks and runs)

Posted by: brellis Jan 4 2011, 05:01 AM

Ya hear that? That's the sound of a hundred puns left in my head, not in this post, lol

It's fascinating to consider the propulsive decisions made in years past that will result in such a gentle arrival.

Posted by: stevesliva Jan 4 2011, 06:52 AM

QUOTE (brellis @ Jan 4 2011, 01:01 AM) *
Ya hear that? That's the sound of a hundred puns left in my head, not in this post, lol


I totally teed up "Vestal" during a conversation about insertion. Really, who cares if it's quite right? wink.gif

Posted by: tanjent Jan 4 2011, 12:26 PM

QUOTE (Greg Hullender @ Jan 3 2011, 05:15 AM) *
Perhaps a more interesting stat would be the date when Dawn first goes retrograde with respect to the Sun.

--Greg


Will this ever happen? Back of the envelope calculation:
Vesta's semimajor axis (treat it as the radius of a circle) = 2.361 AU
Orbital circumference will be approximately 15 AU (close enough)
1 AU = about 150 million km.
Vesta's orbital period is listed as 1325 days, or 31800 hours
(15 x 150) million km in 31800 hours gives Vesta a prograde motion of about 70K km/hr.
Unless Dawn moves this fast in its orbit relative to Vesta, it seems it can't move retrograde relative to the sun.
Vesta's escape velocity is listed as 0.35 km/sec, which would be (x3600) 1260 km/hr.
(Sorry Greg, my chances to make a substantive contribution here come so rarely, I just couldn't resist.) rolleyes.gif

Posted by: Greg Hullender Jan 5 2011, 04:28 AM

QUOTE (tanjent @ Jan 4 2011, 04:26 AM) *
Unless Dawn moves this fast in its orbit relative to Vesta, it seems it can't move retrograde relative to the sun.
Vesta's escape velocity is listed as 0.35 km/sec, which would be (x3600) 1260 km/hr.

No apologies! :-) It's nice to see someone doing the math--and I definitely said the wrong thing. :-) Let's see if I can fix it. I want the point where Dawn's angular velocity with respect to the Sun is less than Vesta's angular velocity. In other words, Dawn is catching up to Vesta. I want the point at which it turns around and moves behind it.

--Greg

Posted by: punkboi Jan 5 2011, 06:42 AM

New Dawn journal is up

http://dawn.jpl.nasa.gov/mission/journal_12_30_10.asp

Posted by: Greg Hullender Jan 7 2011, 02:00 AM

I see he included a reference to a previous Dawn Journal with a fairly detailed description of how Dawn will enter Vestian orbit. It also talked about scans for satellites.

http://dawn.jpl.nasa.gov/mission/journal_04_28_10.asp#spacecraft

--Greg


Posted by: ZLD Jan 7 2011, 04:20 AM

Thought this may be of interest to this topic:
http://www.mpg.de/english/illustrationsDocumentation/documentation/pressReleases/2011/pressRelease20110106/index.html

I don't have access to Icarus at the moment but for those that do, here is the link to the http://www.sciencedirect.com/science/article/B6WGF-51MJYPX-1/2/3b6a44e744f2b695555443e8aaff999e.

Posted by: PDP8E Jan 7 2011, 05:28 AM

Dr. Rayman uses a nice big fat word: Brobdingnagian
(see: Gulliver's Travels)
very entertaining Dawn log

Posted by: siravan Jan 7 2011, 11:03 PM

I have found it interesting that a consequence of using ion propulsion is that Dawn is already pretty close to Vesta (just 0.06 AU) and slowly approaching it. A quick back-of-envelop calculation shows that the apparent magnitude of Vesta as seen from Dawn is already -0.5, which rivals Canopus. If it wasn't for the fact that Dawn is going to get close to Vesta in few months, it would have been possible to do some good science from even this distance.

Posted by: MarkG Jan 10 2011, 03:55 PM

Dawn thoughts...
It is one Martian year since the Martian fly-by and orbit boost.
Dawn would need to be within about 2 million kilometers of Vesta for Vesta to appear bigger that a point to a human eye observer at that distance. It is about 3 times that distance now.
Question: What will be Dawn's velocity relative to Vesta when it enters Vesta's Hill sphere? (An approximation will do...a bit too complex to figure out myself on just one cup of coffee...)

Posted by: punkboi Jan 30 2011, 02:45 AM

The Dawn website has been re-designed. Pretty cool.

http://dawn.jpl.nasa.gov/

Posted by: ElkGroveDan Jan 30 2011, 05:19 AM

QUOTE (punkboi @ Jan 29 2011, 06:45 PM) *
The Dawn website has been re-designed.

Very nice. Looks like they put a CERES amount of time into that new design. I wonder if they also had to inVESTA lot of money.

Posted by: eoincampbell Jan 30 2011, 06:31 AM

I didn't get it at first...then it dawned on me smile.gif

Posted by: punkboi Jan 30 2011, 07:11 AM

All right folks... Let's leave it to Marc Rayman to make such witty/corny wordplay in his Dawn journals tongue.gif

Posted by: climber Jan 30 2011, 09:31 AM

You'll never stop elkgroveDAWN biggrin.gif

Posted by: lyford Jan 30 2011, 03:59 PM

Yes, we will have to keep our ION him. rolleyes.gif

Posted by: centsworth_II Jan 30 2011, 04:50 PM


Posted by: nprev Jan 30 2011, 05:48 PM

<goes to UMSF>
<reads this thread>
<groans>
<begins drinking early today>...

Posted by: Greg Hullender Jan 30 2011, 05:57 PM

I think this is caused because the new layout has accidentally made the Dawn Journal inaccessible. The law of conservation of asteroid puns is causing the excess to spill over.

I sent an e-mail asking them to investagate--I mean LOOK AT it.

--Greg (It may already be too late) :-)

Posted by: tasp Jan 30 2011, 06:51 PM

I am enjoying the levity here today.

(translation: drat, all the good puns are already used)




The slow approach vector from the ion drive is allowing too much time for everyone to belt out GRaND puns.

BTW, does high solar activity have any effect on the gamma ray and neutron detector on the craft? Either making it work better with more flux, or does it hinder it because of the increased background noise? Or do the two effects cancel ?







Posted by: punkboi Feb 3 2011, 06:52 AM

New Dawn Journal is up

http://dawn.jpl.nasa.gov/mission/journal_01_30_11.asp

Posted by: antoniseb Feb 16 2011, 06:43 AM

Dawn is about 5 million kilometers away now. How close will it have to be before its highest magnification cameras will be able to get the best ever images (so far) of Vesta? I don't know much about the imaging systems on this craft.

Posted by: ups Feb 16 2011, 04:32 PM

Can we please keep the discussion sirius in this forum?



Posted by: machi Feb 16 2011, 04:51 PM

QUOTE (antoniseb @ Feb 16 2011, 07:43 AM) *
Dawn is about 5 million kilometers away now. How close will it have to be before its highest magnification cameras will be able to get the best ever images (so far) of Vesta? I don't know much about the imaging systems on this craft.


I don't know exact resolution of HST or 8-10m class telescopes. My guess is about 50 km/pix. Framing Cameras onboard Dawn have resolution 1 km from distance 10 750 km. So Dawn must be more closely than ~500 000 km to Vesta.

Posted by: Holder of the Two Leashes Feb 16 2011, 05:27 PM

As was discussed earlier on this thread, DAWN will begin to match the resolution of the best Hubble images around early June. The best from Hubble was from May of 1996, when approximately 35 km/pixel resolution on the .04 arcsec per pixel camera was achieved. You will have to get closer (as machi said) than about half a million km from Vesta to match this. The two identical framing cameras on DAWN only have about three times the resolution of normal human eyes.

Posted by: antoniseb Feb 17 2011, 01:23 AM

QUOTE (Holder of the Two Leashes @ Feb 16 2011, 11:27 AM) *
... The two identical framing cameras on DAWN only have about three times the resolution of normal human eyes.

Alas, I've been spoiled by MRO's HiRES. I start now trying to regain realistic hopes for what Dawn will show.


Posted by: qraal Mar 7 2011, 03:55 AM

Hurry up! (said like Blackboard from Mr. Squiggle... a uniquely Australian children's show)

Vesta will, no doubt, be a fascinating little world, but I'm hanging out for amazing scenes from Ceres. Both are rather odd, even so. Basalt! On an asteroid, no less.

Posted by: Holder of the Two Leashes Mar 7 2011, 06:25 AM

A little bit of trivia to pass the time while we're waiting.

In the first week of December 2012, about five months after DAWN leaves Vesta, and around twenty-six months before it arrives at Ceres, while it is enroute from one to the other, Ceres and Vesta will be having their own close encounter with each other. At that time they will be 0.390 a.u. (58,300,000 km or 36,200,000 miles) apart. Ceres as seen from Vesta will be a 3.9 magnitude object in the constellation Ursa Major, and Vesta as seen from Ceres will be magnitude 4.2 (41 percent phase) in Piscis Austrinus.

Ceres, however, will not be in opposition to Vesta at that time. That will occur fully fifteen months later in March 2014, when they will be 0.401 a.u.apart.

The 2012 close approach will be the closest the two have been since November 1892, when they were separated by 0.373 a.u. They will not be this close again until November 2081, when they will pull within 0.284 a.u.

All this according to "Starry Night", anyway.

Posted by: Stefan Mar 21 2011, 06:40 PM

http://www.mps.mpg.de/en/aktuelles/pressenotizen/pressenotiz_20110321.html

Posted by: MarkG Mar 22 2011, 06:25 PM

At its current distance from Dawn, Vesta is only maybe about 3 pixels wide in the framing cameras, not much fun yet. At some point, there will be navigational benefit from the cameras, but I'm unsure when that starts.

It is indeed encouraging to see that the cameras are operational again after all this time in the cold irradiated vacuum of space. Congrats to the Dawn teams!

Posted by: Greg Hullender Apr 2 2011, 10:38 PM

New Dawn Journal: http://www.dawn-mission.org/mission/journal_03_31_11.asp


Apparently their big task for March was to calibrate the thusters. Since the thust is so gentle, they cannot measure it directly, so there's a trick to it.

--Greg

Posted by: stevesliva Apr 9 2011, 01:09 AM

This is cute:

http://dawn.jpl.nasa.gov/news/vesta_fiesta.asp

Clickable for info.

Posted by: Decepticon Apr 9 2011, 03:08 AM

All I can find in terms of arrival is July 2011.

Is there a projected date plus or minus?

Posted by: elakdawalla Apr 9 2011, 03:26 AM

The date of "arrival" is still kind of up in the air, though I think it's unlikely to be more than a few days before or after July 16. It depends on a lot of factors -- thrusting time trades off with other useful activities on the spacecraft. They may know internally by now but haven't specified a date publicly. Anyway, Dawn doesn't so much arrive as it wanders into Vesta's neighborhood; pictures from orbit won't really look much different from pictures from approach until they start spiraling down.

Posted by: Greg Hullender Apr 9 2011, 03:52 PM

Not final for a week or two, but the current plan looks something like this:

First optical images: May 3 (5 pixels wide, but up to 12 by end of month)

Arrival: July 17

Survey Orbit: August 8

--Greg

Posted by: bagelverse Apr 18 2011, 05:56 PM

Yeah, just in time for my birthday. rolleyes.gif

Full inline quote removed - ADMIN

Posted by: elakdawalla May 3 2011, 07:38 PM

New topic for the Vesta Approach phase of Dawn's mission http://www.unmannedspaceflight.com/index.php?showtopic=6957...

Posted by: belleraphon1 Sep 17 2014, 11:29 AM

Dawn Operating Normally After Safe Mode Triggered 09/11/2014
http://www.nasa.gov/jpl/dawn/operating-normally-after-safe-mode-triggered/

Engineers immediately began working to restore the spacecraft to its normal operational state. The team determined the source of the problems, corrected them, and then resumed normal ion thrusting on Monday night, Sept. 15.

As a result of the change in the thrust plan, Dawn will enter into orbit around dwarf planet Ceres in April 2015, about a month later than previously planned. The plans for exploring Ceres once the spacecraft is in orbit, however, are not affected.

Posted by: Superstring Nov 2 2014, 02:14 AM

We're less than 3 months away from getting better-than-Hubble images of Ceres!

http://dawnblog.jpl.nasa.gov/2014/10/31/dawn-journal-october-31/

Powered by Invision Power Board (http://www.invisionboard.com)
© Invision Power Services (http://www.invisionpower.com)