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Dawn Cruise
SkyeLab
post Sep 27 2007, 12:31 PM
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Pushing out of Earth orbit now...........

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"There are 10 types of people in the world - those who understand binary code, and those who don't."
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Greg Hullender
post Aug 27 2008, 04:44 PM
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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
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3488
post Aug 27 2008, 07:25 PM
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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.


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"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.
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Greg Hullender
post Aug 29 2008, 06:02 PM
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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
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dmuller
post Aug 30 2008, 09:37 AM
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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


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Posts in this topic
- SkyeLab   Dawn Cruise   Sep 27 2007, 12:31 PM
- - elakdawalla   loon reports from the Cape that AOS happened about...   Sep 27 2007, 02:39 PM
|- - ustrax   Horst Uwe Keller, Dawn's FC Team Leader report...   Sep 27 2007, 02:55 PM
- - climber   May be little OT...and that's the reason of th...   Sep 27 2007, 04:10 PM
|- - punkboi   Godspeed, Dawn!   Sep 27 2007, 04:18 PM
|- - Rakhir   QUOTE (climber @ Sep 27 2007, 04:10 PM) W...   Sep 27 2007, 08:49 PM
- - dvandorn   Well -- I missed the launch (6:34 am is a little e...   Sep 27 2007, 05:18 PM
- - stevesliva   Amazing! Given the incredible complexity of t...   Sep 27 2007, 05:39 PM
- - Toma B   Just as I thought...nobody in the press conference...   Sep 28 2007, 07:33 AM
|- - ugordan   QUOTE (Toma B @ Sep 28 2007, 09:33 AM) I ...   Sep 28 2007, 07:36 AM
||- - stevesliva   QUOTE (ugordan @ Sep 28 2007, 03:36 AM) I...   Sep 28 2007, 04:57 PM
|- - elakdawalla   QUOTE (Toma B @ Sep 28 2007, 12:33 AM) I ...   Sep 28 2007, 04:35 PM
- - Greg Hullender   jabe: No, that's not it, but this has already ...   Sep 29 2007, 05:46 AM
|- - jabe   QUOTE (Greg Hullender @ Sep 29 2007, 05:4...   Sep 29 2007, 11:56 AM
- - Del Palmer   Latest Dawn journal: http://dawn.jpl.nasa.gov/mis...   Oct 2 2007, 05:14 PM
|- - punkboi   Interesting journal. Hopefully, a "Where is ...   Oct 2 2007, 05:41 PM
|- - Stephen   QUOTE (punkboi @ Oct 3 2007, 03:41 AM) In...   Oct 3 2007, 02:38 AM
- - djellison   It doesn't need a subforum until it starts doi...   Oct 3 2007, 06:59 AM
|- - Stephen   QUOTE (djellison @ Oct 3 2007, 04:59 PM) ...   Oct 4 2007, 02:03 AM
|- - jamescanvin   QUOTE (Stephen @ Oct 4 2007, 03:03 AM) I ...   Oct 4 2007, 08:50 AM
|- - djellison   QUOTE (Stephen @ Oct 4 2007, 03:03 AM) ...   Oct 4 2007, 10:54 AM
|- - Stephen   QUOTE (djellison @ Oct 4 2007, 08:54 PM) ...   Oct 5 2007, 01:49 AM
- - volcanopele   I could see the creation of a new thread though   Oct 3 2007, 07:09 AM
|- - ugordan   QUOTE (volcanopele @ Oct 3 2007, 09:09 AM...   Oct 3 2007, 08:47 AM
- - Greg Hullender   I think it's simpler than that; it's becau...   Oct 4 2007, 04:57 AM
- - CAP-Team   Here's where Dawn is now: Earth as seen fro...   Oct 4 2007, 10:00 AM
|- - punkboi   QUOTE (CAP-Team @ Oct 4 2007, 03:00 ...   Oct 4 2007, 05:27 PM
|- - ugordan   QUOTE (punkboi @ Oct 4 2007, 07:27 PM) I ...   Oct 4 2007, 05:56 PM
- - CAP-Team   QUOTE (punkboi @ Oct 4 2007, 07:27 PM) Co...   Oct 4 2007, 09:20 PM
- - volcanopele   Wow, you're right, Dawn is available on the NA...   Oct 4 2007, 09:27 PM
- - belleraphon1   Sweetness and LIGHT..... First ion thruster test...   Oct 9 2007, 11:56 PM
- - Marz   Marc cracks me up!!! "The drama ...   Oct 10 2007, 04:32 AM
- - peter59   Science Instruments Checked Out October 15 - 19 Da...   Oct 20 2007, 07:40 AM
- - peter59   Second Ion Thruster Checkout Completed Successfull...   Oct 27 2007, 06:36 AM
- - nprev   Thanks for the update, Peter. Green bird, baby, gr...   Oct 27 2007, 01:32 PM
|- - brellis   QUOTE (nprev @ Oct 27 2007, 06:32 AM) has...   Oct 27 2007, 02:06 PM
|- - punkboi   New journal up: http://dawn.jpl.nasa.gov/mission/...   Oct 27 2007, 06:45 PM
- - peter59   More Ion Thrusting Tests Completed November 12 - 1...   Nov 20 2007, 08:59 PM
|- - punkboi   A week late, but whatever: http://dawn.jpl.nasa.g...   Nov 20 2007, 09:04 PM
- - peter59   Main Antenna Checked Out and New Software Uploaded...   Nov 24 2007, 07:35 AM
|- - punkboi   "Where is Dawn now?" page finally up: h...   Nov 29 2007, 06:48 PM
- - peter59   "Dawn has started IPS cruise thrusting to Ves...   Dec 19 2007, 09:56 PM
|- - punkboi   http://www.planetary.org/blog/article/00001266/ N...   Dec 20 2007, 09:15 AM
- - IM4   Good news everyone! Extended version of the D...   Jan 8 2008, 09:33 PM
|- - tedstryk   That is still 7 million miles, but it could be don...   Jan 9 2008, 11:53 AM
- - elakdawalla   The latest Dawn Journal is now up at JPL and TPS w...   Feb 1 2008, 07:28 PM
- - JTN   (I'm not normally into fields'n'partic...   Feb 10 2008, 09:17 PM
- - Holder of the Two Leashes   In a word, no. If Vesta appears unusually brigh...   Feb 14 2008, 07:28 PM
|- - ugordan   QUOTE (Holder of the Two Leashes @ Feb 14 200...   Feb 14 2008, 07:31 PM
- - Holder of the Two Leashes   The weathering being referred to here is the gener...   Feb 14 2008, 07:51 PM
|- - punkboi   New Dawn journal up: http://dawn.jpl.nasa.gov/mis...   Mar 5 2008, 02:09 AM
- - peter59   I nearly forgot about these cancelled missions. P...   Mar 20 2008, 04:34 PM
|- - dmuller   QUOTE (peter59 @ Mar 21 2008, 02:34 AM) P...   Jun 30 2008, 06:41 AM
|- - 3488   QUOTE (jasedm @ Jul 1 2008, 11:30 AM) I...   Jul 1 2008, 03:42 PM
|- - ElkGroveDan   QUOTE (3488 @ Jul 1 2008, 07:42 AM) No de...   Jul 1 2008, 04:55 PM
||- - Del Palmer   QUOTE (ElkGroveDan @ Jul 1 2008, 05:55 PM...   Jul 1 2008, 05:01 PM
|- - Del Palmer   QUOTE (3488 @ Jul 1 2008, 04:42 PM) No de...   Jul 1 2008, 04:56 PM
|- - 3488   QUOTE (ElkGroveDan @ Jul 1 2008, 05:55 PM...   Jul 1 2008, 06:47 PM
|- - tedstryk   This is another Hubble view. During the 2001 obse...   Jul 3 2008, 06:21 PM
- - peter59   Dawn Completes Another Month of Thrusting March 31...   Apr 1 2008, 03:38 PM
|- - Stu   QUOTE (peter59 @ Apr 1 2008, 04:38 PM) Da...   Apr 1 2008, 04:11 PM
- - Greg Hullender   I just noticed that Dawn has substantially upgrade...   Apr 30 2008, 04:01 AM
- - Holder of the Two Leashes   Yes, the diagrams are much better now, especially ...   May 1 2008, 04:26 PM
- - mps   Meanwhile somewhere on the vicinity of Mars... Da...   May 30 2008, 11:46 AM
|- - punkboi   New Dawn journal up: http://dawn.jpl.nasa.gov/mis...   Jun 30 2008, 03:17 AM
- - nprev   ...Dr. Rayman is a hoot! He sure can write an ...   Jun 30 2008, 11:11 AM
|- - Greg Hullender   QUOTE (nprev @ Jun 30 2008, 04:11 AM) .....   Jun 30 2008, 12:41 PM
|- - ugordan   QUOTE (Greg Hullender @ Jun 30 2008, 02:4...   Jun 30 2008, 12:48 PM
|- - MahFL   He sounds like a typical slightly nutty scientist ...   Jun 30 2008, 01:01 PM
- - ilbasso   He is indeed quite an entertaining writer. Maybe ...   Jun 30 2008, 12:10 PM
- - djellison   See this... ---------------------- That's a ...   Jun 30 2008, 01:11 PM
- - jasedm   I'm just pleased that we get regular updates o...   Jul 1 2008, 10:30 AM
- - Del Palmer   Latest Dawn update: http://dawn.jpl.nasa.gov/miss...   Aug 27 2008, 02:00 PM
- - Greg Hullender   Hmmm. He raises the point that Dawn will cross Ma...   Aug 27 2008, 03:35 PM
- - djellison   The Mars flyby is mainly about changing the orbita...   Aug 27 2008, 04:20 PM
- - Greg Hullender   That makes sense -- I'd wondered why the proje...   Aug 27 2008, 04:44 PM
|- - 3488   Also as Doug before you said, it is about changing...   Aug 27 2008, 07:25 PM
|- - Greg Hullender   QUOTE (3488 @ Aug 27 2008, 12:25 PM) Also...   Aug 29 2008, 06:02 PM
|- - BrianJ   QUOTE (Greg Hullender @ Aug 29 2008, 06:0...   Aug 29 2008, 09:15 PM
||- - Greg Hullender   QUOTE (BrianJ @ Aug 29 2008, 01:15 PM) Hi...   Aug 30 2008, 06:01 PM
||- - BrianJ   QUOTE (Greg Hullender @ Aug 30 2008, 06:0...   Aug 30 2008, 11:09 PM
|||- - Greg Hullender   QUOTE (BrianJ @ Aug 30 2008, 04:09 PM) Er...   Sep 1 2008, 05:57 PM
||- - dmuller   QUOTE (Greg Hullender @ Aug 31 2008, 04:0...   Aug 31 2008, 02:08 AM
|- - dmuller   QUOTE (Greg Hullender @ Aug 30 2008, 04:0...   Aug 30 2008, 09:37 AM
- - dmuller   My two cents worth: Dawn is picking up speed from...   Aug 30 2008, 01:36 AM
- - tasp   I will reiterate my ignorance about such matters, ...   Aug 30 2008, 06:04 AM
|- - siravan   QUOTE (tasp @ Aug 30 2008, 01:04 AM) So, ...   Aug 30 2008, 03:19 PM
|- - djellison   QUOTE (siravan @ Aug 30 2008, 04:19 PM) I...   Aug 30 2008, 03:36 PM
- - Hungry4info   @ tasp They may not due that so as to conserve fu...   Aug 30 2008, 04:12 PM
|- - vjkane   QUOTE (Hungry4info @ Aug 30 2008, 05:12 P...   Aug 30 2008, 04:58 PM
- - tasp   Just wanted to comment how much fun it is to have ...   Aug 30 2008, 10:40 PM
- - siravan   Regarding ion engines and circular orbits, one may...   Aug 31 2008, 02:59 AM
- - dmuller   BTW, whilst getting the Dawn data from the Horizon...   Aug 31 2008, 03:31 AM
- - dmuller   Since there is much talk about the Dawn cruise, I ...   Aug 31 2008, 04:37 AM
- - Toma B   I still haven't found what I was looking for.....   Sep 1 2008, 09:08 PM
- - Phil Stooke   Earlier discussions of this mission, before launch...   Sep 1 2008, 09:39 PM
|- - kwp   QUOTE (Phil Stooke @ Sep 1 2008, 01:39 PM...   Sep 2 2008, 04:01 AM
|- - Marz   QUOTE (kwp @ Sep 1 2008, 11:01 PM) I aske...   Oct 3 2008, 06:20 PM
- - djellison   Yes - an extensive campaign is planned for Dawn at...   Oct 3 2008, 06:28 PM
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