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Posted by: BruceMoomaw Feb 21 2006, 03:14 AM

I just caught this intriguing little note in a news release from the U. of Chicago on Stardust sample analysis.

http://www.spaceflightnow.com/news/n0602/20stardust/ :

" 'The Stardust spacecraft, meanwhile, may someday see further cometary action. "Stardust is still very healthy and has fuel left over,' [Thanasis] Economou said. 'After dropping the Space Return Canister, the spacecraft was diverted from entering the Earth's atmosphere and placed in an orbit around the sun that could bring it to another comet in February 2011.' "

Hmmm. Nice news, if true. Anyone have any idea which short-period comet this could be?



Meanwhile, another article on the first preliminary results from the dust analysis seems to show a surprise: a lack of hydrated silicates.

http://www.space.com/scienceastronomy/060220_stardust_update.html :

"While the samples appear to lack indicators of water, they do contain sulfides, a key component to life...

"The early results reveal that the 4.5 billion-year-old comet contains iron, sulfides, glassy materials, olivine, and what the scientists termed potentially interesting isotopic traces. These believe that these materials were also available during the formation of other objects in our solar system...

" 'We're confident that the things coming out [of Comet Wild 2] are the same as those that went in,' Brownlee told SPACE.com. 'We believe that we collected the most pristine samples of a comet, those that have never been warmed.'

"While further analysis of Tempel 1 revealed water ice on its surface, so far no evidence of water has been detected in the particles. The other sign of water would be the presence of hydrated silicates, which were present in Tempel 1, Brownlee said; but so far none of these have been found in the Stardust samples."

Now, what does THAT signify? Could the particles have been dehydrated by frictional heat when they plowed through the aerogel? But surely in that case they would still show clear structural and mineralogical evidence of having been water-modified?

Posted by: BruceMoomaw Feb 21 2006, 04:33 AM

It's possible that they may be hoping to fly Stardust by none other than Tempel 1, at its next perihelion -- which turns out to be in Feb. 2011! Such comparative studies of it by two spacecraft with different instruments -- perhaps even including an attempt by Stardust to photograph the Deep Impact crater -- would obviously be useful.

Posted by: ugordan Feb 21 2006, 08:22 AM

Is it even possible for Stardust to be slinghshot towards the comet by Earth? There's only so much delta-V a gravity assist can provide.
Note that even if Stardust were redirected to fly by Tempel 1, there's only about a 50% chance it would see the crater when it's facing the S/C during the closest approach.
It would be neat if it were able to see it, though - "Stardust called up once again to do what Deep Impact was supposed to do in the first place..."

Posted by: BruceMoomaw Feb 21 2006, 09:13 AM

I'm contacting Brownlee to see if this is indeed what they have in mind. Keep in mind that at this point they know the comet's speed and tilt of rotation pretty well, and could probably carry out a final midcourse correction to maximize the chances that the D.I. impact crater was on the side of the comet which Stardust was flying past.

Posted by: edstrick Feb 21 2006, 10:28 AM

General observation: Comet dust is probably a transcendentally heterogeneous mix from different sources with a few sources of material dominating and others much scarcer. If -- as appears probable in small comets -- there was never internal melting, the materials are likely to be in extreme chemical dis-equilibrium.

One thing very unclear theoretically and being hinted at observationally is that the eroded comet surface shows a comples accretional history, quite likely with different materials accreting at different times, or at least different mixes of material. The presence of water-ice-rich exposures does little to suggest that that water has ever been melted or even warm enough to do vapor transport over the age of the solar system... or recently, or when the comet was accreting. Yet there could have been.

That's the sort of GEOLOGY, even if the term is linquisticaly a disaster, that the Euro orbiter will really be able to tackle.

Posted by: antoniseb Feb 21 2006, 01:05 PM

That would be very interesting. I hope it's possible.

Posted by: BruceMoomaw Mar 20 2006, 04:42 AM

This just in: that IS what they're seriously considering for a Stardust extended mission:
http://www.spaceref.com/news/viewnews.html?id=1103

(I coudn't find anyone who knew anything about it at the Europa Focus Group meeting, and Don Brownlee never replied to my E-mail. According to Av. Week, they've been trying to keep this scheme under wraps.)

Posted by: Orlin Denkov Mar 20 2006, 06:40 AM

In the light of today's anouncement - I'm absolutely amazed from that precise supposition, made two months ago
I was reading carefully the article at the AviationNow, but I didn't uderstand the reasons for such a secrecy.
In any case it would be very important new target. Let's hope that they'll find the budget needed for the extansion of the Stardust mission.

Posted by: deglr6328 Mar 20 2006, 08:25 AM

Can we calculate the flyby velocity for a 2010 encounter?

Posted by: collectSPACE Mar 20 2006, 09:03 AM

In January, Tom Duxbury http://www.collectspace.com/archive/archive-0106.html#0127060015 in an interview with John McGauley, albeit it was only a brief mention as the focus of his questions were on the http://collectspace.com/ubb/Forum33/HTML/000336.html.

Posted by: BruceMoomaw Mar 20 2006, 06:10 PM

Ah. I missed that one.

Posted by: BruceMoomaw Mar 21 2006, 11:25 PM

More on this plan at http://www.newscientistspace.com/article/dn8874-stardust-part-ii-deep-impact-comet-revisited.html . (It is called -- I kid you not -- "ScarQuest".)

Posted by: ElkGroveDan Mar 22 2006, 01:22 AM

Can someone give me rough pencil outline as to how this mission could reach $30 miilion in costs? Would it not just be man hours and DSN (or some other big ears) tracking time?

Posted by: AlexBlackwell Mar 22 2006, 01:31 AM

Without access to their cost breakdown data, we can do no more than speculate. However, the average person would be surprised to see how much personnel costs (i.e., "man hours") and DSN antenna time can amount to in a typical proposal, especially under the "full cost accounting" methodology that NASA requires proposers to utilize. ~$30 million for a Discovery MOO does not surprise me in the slightest.

EDIT: I should have added that the "~$30 million" figure almost certainly includes the NASA-mandated cost reserves that others (e.g., Dawn) have complained about.

Posted by: Phil Stooke Mar 22 2006, 04:34 AM

I'm surprised that mission planners think they can predict when the impact crater would be illuminated and facing the camera during the flyby. I would not have expected that the rotation rate was known well enough to know the nucleus orientation at a specific time five years from now. I'm all in favour of a new flyby but as a cartographer I'd rather see the other side!

Phil

Posted by: BruceMoomaw Mar 22 2006, 05:11 AM

It's probably something of a gamble, involving a last-minute course correction utilizing long-range photos of the nucleus' orientation just before the flyby. (You'll notice that the New Scientist article says that just observing the changes in surface features since the DI flyby would be useful as well. Also, of course, we'd get some dust compositional data to go with that for Halley and Wild 2.)

Posted by: Phil Stooke Mar 22 2006, 01:57 PM

Hmmm... if the flyby is at a typical speed for such things there would be no chance to delay the closest approach a few hours to allow the crater to rotate into sunlight. That's what I'm chiefly questioning - the kind of last-minute redirection Bruce mentions would allow only a small positional change in the flyby point, but not the timing. If Stardust - sorry, Scarquest (isn't that a diet?) can turn and view the departing side we might get about 50% coverage, as at Wild-2, but that gives us a 50% chance of not seeing the crater.

Phil

Posted by: AlexBlackwell Mar 22 2006, 05:40 PM

This is a good question for both the Discovery 2006 science and TMC review panels to "sanity check." I could easily see the ScarQuest science being a little seductive, especially given that it would be "re-using" a spacecraft.

Posted by: Phil Stooke Mar 23 2006, 07:47 PM

Well, I can answer my own question now, because I just had lunch with Don Brownlee and asked him this very question. It turns out that they do indeed think they know the rotation rate of the nucleus well enough to predict where the crater will be at flyby time, and they plan to image some new territory plus see the crater clearly.

I'm surprised about the presumption that they know the rotation rate so well, but I guess I have to accept that.

Phil

Posted by: ugordan Mar 23 2006, 07:51 PM

Perhaps it's got to do with the Deep Impact observations well before the flyby so they got good light curves. Still, I remain skeptical as you the rotation can be nailed down in such a short observational span.
Any uncertainties now will lead to large rotational offsets 4 years in the future.

Posted by: tty Mar 23 2006, 10:41 PM

You would only have to know the rotation period with enough precision to know that the crater is somewhere on the lighted side at flyby time. Tweaking the orbit a little "sideways" to pass over either the "morning", "midday" or "evening" side of the comet could be made quite late based on images taken during the approach.

tty

Posted by: Phil Stooke Mar 24 2006, 03:55 AM

Well, tty, your first sentence is absolutely correct - it's just that I'm surprised they know the rotation period that well. But your second is more doubtful, I think. These flybys are so fast that there's no time to get early images, figure out where the crater is, and adjust the flyby position. Their only hope would be to plan a Wild-2 type flyby, on the sunlit side, turning to view both approach and departure sides so the entire sunlit surface is seen.

Anyway, it sounds as if they are reasonably confident that they can see the crater. And from my point of view, if I can see some more of the surface too, I'll be quite happy.

Phil

Posted by: Bob Shaw Mar 24 2006, 08:53 AM

Report on Space Daily regarding an article in Science (23 March 2006) on 'main belt' comets - objects in asteroid-like orbits but with comet-like characteristics.

http://www.spacedaily.com/reports/Main_Belt_Comets_May_Have_Been_Source_Of_Earths_Water.html

Bob Shaw