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Posted by: Paolo Oct 11 2009, 08:49 AM

no one seems to have noticed this
http://www.sciencemag.org/cgi/content/abstract/326/5950/275

Posted by: nprev Oct 11 2009, 08:57 AM

Well, well, well! Guess it's extremely premature to start lobbying for an XM for Dawn, but hopefully some wheels are turning in that regard already.

Posted by: Paolo Oct 11 2009, 10:55 AM

I discussed about this with Mark Rayman a few weeks ago and he told me that

Posted by: vjkane Oct 12 2009, 05:03 AM

Ancient memory suggest that 2 Pallas orbits in an inclined orbit. If the memory chips are still functioning, this would make it hard...

Posted by: nprev Oct 12 2009, 05:11 AM

I was thinking that it was maybe a few degrees off the ecliptic, but it's actually 35(!) freakin' degrees! Good trace memory, VJ.

Guess a flyby by Dawn might still be technically possible if Pallas is doing a plane crossing at the right time & place with respect to the spacecraft, but the whole thing sounds unlikely to the point of ain't-gonna-happen. Oh, well.

Posted by: Paolo Oct 12 2009, 05:38 AM

From http://en.wikipedia.org/wiki/2_Pallas

Posted by: tedstryk Oct 12 2009, 02:54 PM

There was a blurb about a Pallas encounter that briefly appeared on Astronomy Now's website back before DAWN launched, but it was pulled within a few hours of being posted.

Posted by: vjkane Oct 12 2009, 04:19 PM

There has been talk from time to time about Dawn extended missions. The official blurb put out awhile ago is that any planning now is premature. The team will want to see how long they spend at Ceres, how much fuel is left, and what the efficiency of the engines will be at that distance from the sun. Very different than normal ballistic missions.

Posted by: PaulM Oct 12 2009, 07:34 PM

I wonder if the Indians or Chinese have considered a flyby of 2 Pallas? Indian and Chinese missions to the Moon and Mars will never generate the public interest that would result from sending a spacecraft past a new Solar System body.

2 Pallas is one of the biggest objects in the Asteroid belt and so I am sure would have interesting and varied landscapes. For me the mission that really put the Japanese Space Agency on the map was Hayabusa because Itokawa was unlike any Solar System body visited before.

Posted by: Paolo Oct 14 2009, 06:17 PM

Note also this LPSC paper http://www.lpi.usra.edu/meetings/lpsc2009/pdf/2421.pdf
and its thanks to "STSCI and the Dawn mission for supporting this work."

Posted by: djellison Oct 15 2009, 07:01 AM

A series of barely funny but fairly inappropriate posts have been culled.

Posted by: Paolo Dec 21 2009, 06:43 AM

On ArXiv today: http://arxiv.org/abs/0912.3626

Posted by: nprev Dec 21 2009, 06:55 AM

Huh. Almost the same average density as Mars.

Hate to say it, but it's probably dry as a bone....metal-rich, though.

Posted by: elakdawalla Dec 22 2009, 06:05 PM

Thanks very much for the pointer to that article, Paolo.

Of interest to some of the 3D modeling types here might be this website mentioned in the article, which has a database that currently includes 179 shape models for 112 asteroids.

http://astro.troja.mff.cuni.cz/projects/asteroids3D/web.php

--Emily

Posted by: HSchirmer Apr 24 2016, 12:06 AM

Since there is already a 2 Pallas thread, so I'm putting thoughts about a Dawn extended mission to Pallas here.

If Dawn leaves Ceres, could it rendezvous with Pallas? Could it orbit it?
I'm beginning to suspect it could; if Dawn can catch Pallas as Pallas crosses Ceres' orbit then it would
appear that Dawn could use a gravity assist from Pallas to match the inclination of Pallas' orbit to the ecliptic.
Once Dawn is heading in the same general direction as Pallas, it could chase down Pallas the same way
it chased down Ceres.

I think this might work because I noticed a few very interesting things about the orbits of Ceres and Pallas-
They have an almost exact 1:1 orbit resonance. Not locked exactly, but the same orbital period
Ceres = 1680 days. Pallas = 1686 days They also have essentially identical mean motion (speed).
And, yes, Pallas is at 35 degrees inclination to the ecliptic, however, Ceres is at 10 degrees.
We were able to achieve a 10 degree inclination to rendezvous with Ceres without breaking the spacecraft,
so conceptually we can do 10 degrees again, and again, and then 5 degrees.

url="http://nssdc.gsfc.nasa.gov/planetary/factsheet/asteroidfact.html"]http://nssdc.gsfc.nasa.gov/planetary/facts...teroidfact.html[/url]
Asteroid Diameter ~Mass Rotation Orbital Spectral Semimajor Orbital Orbital Number
Name (km) 1015 kg Period Period Class Axis Eccentricity Inclination and Name
1 Ceres 965 x 961 x 891 939,300 9.074 hrs 4.60 yrs C 2.768 AU 0.0758 10.59 deg
2 Pallas 582 x 556 x 500 205,000 7.813 hrs 4.61 yrs U 2.772 AU 0.2310 34.84 deg

That makes this VERY interesting- Ceres and Pallas have essentially identical orbital period and semimajor axis.
The eccentricity and inclination are different, but if I recall my physics and mechanics correctly (not guaranteed)
then the energy of the two orbits is essentially the same, it is the direction and the shape of the orbits that is different.
Essentially, the total energy of the two orbits is the same, but the eccentric orbit exchanges
gravitational potential energy for kinetic energy as Pallas goes from perihelion to aphelion and back again.

So, remember Ulysses? No it's not Bloomsday...
Ulysses the spacecraft was redirected into an out-of-the-ecliptic orbit by using a gravitational slingshot around Jupiter.
That was able to redirect the spacecraft's orbit out of the ecliptic, not much of a change in delta-V IIRC, but change in direction.

Seems that when Pallas crosses [edit the ecliptic] the plane of ceres' orbit, Dawn could do a slingshot manoeuvre to
redirect it from a Ceres-like 1686 day 10 degree orbit into an inclined Pallas-like 1680 day 35 degree orbit.

Posted by: Explorer1 Apr 24 2016, 01:26 AM

It would be amazing to get Dawn to a 3rd object, I agree, but Pallas is a lot less massive than Jupiter, so a slingshot would be far less effective.
And Dawn would be running on (xenon) fumes by that point so if anything goes wrong, it's over.

Posted by: Paolo Apr 24 2016, 07:02 AM

and don't forget that changing the inclination of an orbit is very delta-V consuming. much more so than is usually appreciated

Posted by: nprev Apr 24 2016, 09:29 AM

Pallas is not nearly massive enough to effect a significant change in Dawn's velocity nor change its inclination. Recall that the only moon in the Saturn system massive enough to affect Cassini's trajectory is Titan...and Pallas is only about twice as massive as Enceladus.

If this happens at all, it's gonna be a flyby.

Posted by: HSchirmer Apr 24 2016, 12:45 PM

Ahh, good point, interesting point actually, seems that gravity assist maneuvers are limited to about 70% of the escape velocity of the object.
While Pallas is moving fast, (relative to Dawn) it's weak gravity only lets you take small bites of that gravity assist capability.

So, Pallas escapeV is 324 m/s, so the maximum deltaV from any single assist is around 230 meters per second.
As compared to Titan, the reported gravity assist numbers I could find for Cassini had a deltaV of 1,100 meters per second.
That initially seems promising, Dawn at Pallas might get around 1/4 of the slingshot effect of Cassini at Titan,
but part of the benefit to Cassini is that Titan has a 16 day orbit, so get to do multiple slingshot encounters.
Interesting that Titan's orbit has a relative motion available for slingshot manoeuvres of around 5.6km/s.
For Dawn in a solar orbit, the relative motion of Pallas around the Sun is much higher, around 17.6km/s,
but the orbit takes so much longer, 16 hundred days, you're not getting many slingshot opportunities.

So, at first glance, it seemed like Pallas' high speed might balance out its low gravity for gravity assist,
but the way the equations work out, the speed of Pallas doesn't translate into higher deltaV, at least for single passes.
With each orbit taking 4.6 years, it would take a long while to do multiple passes.

Posted by: jasedm Apr 24 2016, 07:01 PM

It would be fantastic to think it would be on the cards to 'do' a flyby of Pallas by extending an existing mission - this is the largest remaining object unstudied at close range within the orbit of Pluto, but my feeling is that budget constraints along with shortage of consumables and required deltaV will nix the idea.

Would love to be wrong though.....

Posted by: TheAnt Apr 24 2016, 11:41 PM

It's not calibration of instruments, we would get even higher resolution for the neutron measurements from GRaND for example. But that bad flywheel which have to be compensated by Dawn using fuel to aim at the surface then to realign itself to send data back to Earth.
The craft would use up the remaining fuel in such an orbit. And as already pointed out, that's now something that can be allowed to happen.

Dawn have to be put in a safe orbit that will not pose any risk of collision in the foreseeable future at least.
Pallas would be the grand price on one already excellent mission, since that small world appear to be an eroded proto planet.
And we know that they did at least look into the possibility of such a flyby earlier. Pallas will pass trough the plane of the ecliptic in just a few years, it might be the reason for the wish to approve a mission extension soon.

Though I agree with Nprev, this appear to be a means to get a little more of the spacecraft that by necessity will have to do a final flight anyway.
Regardless of object it won't be anything but a flyby, but it's good enough in my book, even though it might not be Pallas.
So if not, lets hope they have identified something with odd properties, carbonates or minerals or something else that deserves a closer look where even just images might give us an insight.

Posted by: HSchirmer Apr 25 2016, 12:00 AM

Well, it could be a fly into, like LCROSS or the end of GRAIL.

Edit, quick check shows that Pallas crosses Cere's orbital plane in late Feb '19, nice timing as Earth's closes approach occurs in April '19.

Posted by: nprev Apr 25 2016, 01:58 AM

Landing or crashing is not considered an option since the spacecraft is not sterilized. Apparently, this would violate NASA Planetary Protection Protocols for Ceres.

Of course, that begs the question of what the plan is should a flyby of any target of opportunity not be possible. I'd guess that would leave just escaping Ceres in a non-targeted way or at the very least raising the orbit as high as possible before the xenon is exhausted and/or a critical failure occurs that renders the spacecraft uncontrollable.

Posted by: HSchirmer Apr 25 2016, 02:30 AM

Sorry, should have been clearer, impact on Pallas, not Ceres.
Get all the photos you can from the spacecraft before Dawn impacts on Pallas.
Then Earth-based telescopes coordinate to do spectroscopy of the ejecta.

Hmm, now that I'm thinking of it, not sure if Dawn would have enough bandwidth
to offload the data or be able to point the main antenna to stream all the date live.

Posted by: nprev Apr 25 2016, 03:33 AM

I think that's about ten deep in "ifs" right there. Let's just see what they decide to do.