NASA Dawn Asteroid Mission Told to "Stand Back Up", Reinstated! Options

[Bob Shaw]

Bruce:

'Harder metal cores?' That's an interesting one. If the proto-asteroids were differentiated, presumably by virtue of the radiactive decay of Al, then would hot cores be more or less likely to be disrupted than undifferentiated bodies after big impacts? Similarly, if the early asteroid belt saw many impacts, would that not mean that some bodies might still have been warm after the last whack when they ran into something else?

Obviously, these days, a monolithic lump of cold nickel-iron (or some variant thereof) is going to be hugely more robust than a rubble pile - but what about *warm* objects?

And that's got me wondering about the effect of T-Tauri solar winds on both icy and rocky/metallic bodies... ...induced currents in rotating irons, leading to poor structural cohesion, maybe?

Bob Shaw

[Guest_BruceMoomaw_*]

As a matter of fact, the fact that a lot of the asteroids may still have been partially melted when they ran into (or near) each other has immediate relevance to the most startling of the theories: Erik Asphaug's belief that a lot of the asteroids were broken apart, not by direct impacts, but by tidal forces when they happened to fly near the larger protoplanetary embryos that still existed in the Belt during its earliest days. (Apparently, for instance, a single such encounter would do a much neater job of pulling all the silicate mantle off an asteroid's already-solidified iron core than even a series of repeated impacts would do.) As I say, more on all this later.

[Bart]

A new edition of the Dawn's Early Light newsletter has just been posted:

http://www-ssc.igpp.ucla.edu/dawn/newslett...df/20060405.pdf

Bart

[gpurcell]

Looks like they whacked the program managers from JPL and Orbital.

[mchan]

The newsletter notes what was posted earlier in this thread -- the arrival times at Vesta / Ceres are not changed by the 1 year delay in launch due to the use of a Mars gravity assist (and SEP). However, it also noted that if the spacecraft doesn't launch by October 2007, the mission won't be possible for another 15 years.

It's good to have such a wide launch window, but watch that drop dead date!

[Marz]

So Oct 31, 2007 is a scary date indeed!

It's encouraging to see that the technical problems are gone (pending exhaustive testing), and heart-warming to see the other space-agencies offer support to get this mission going again. [hugs]

The only bummer is cutting 25kg of xenon, which isn't much, but does mean that the mission will end a tiny bit sooner.

[Guest_BruceMoomaw_*]

Andy Dantzler just provided an "explanation" for the reversal of Dawn's cancellation, in which he didn't really say that much -- except to try to warn scientists that this sort of thing will be "very, very rare" (maybe):

http://www.spaceref.com/news/viewnews.html?id=1112

[gpurcell]

The other thing is when you do overrun - if there is an overrun - we don't print money in the basement of Headquarters. The reason we have cost caps is so that we can plan our budgets. If there is an overrun that money will come from somewhere else. It will probably come from the next mission in that line - Scout, Discovery, New Frontiers - whatever. So ... not like any one ever intends to overrun - but I did at least want to clarify that and give everyone an opportunity to ask questions since I know that this is something of a new issue."

Well, that's really what we figured, isn't it? Goodbye Mission of Opportunity, maybe a year schedule slip for the Discovery competition....

[Guest_BruceMoomaw_*]

[quote name= quote in reply - removed
[/quote]

Not necessarily. Dantzler told the November COMPLEX meeting that the cancellation of any full-mission selection for the disastrous Discovery 11 AO had left him with a considerable amount of spare money, which he was determined (at the time) to use to select TWO full Discovery missions next time, although one of them might be minimum-cost. Even if Dawn's overruns have cut further into his kitty, I imagine this still leaves him enough to select one full mission this time, PLUS enough left over to fund not only Dawn's cost overrun but also one, or maybe even two, Missions of Opportunity (with reuse of Stardust and Deep Impact, I presume, being strong candidates for those).

[gpurcell]

Well, if he can still get two new vehicles out of the Discovery budget it would be great...make up a great deal for the gap in missions.

[Guest_Analyst_*]

What has been the problem with the Discovery 11 AO? There was no mission selection, but why?
Bruce, I am sure you know the story.

Analyst

[monitorlizard]

Without trying to provoke anger, I think Dawn was reinstated only because it is an international mission.
The US isn't on the best of terms with Europe in space cooperation, given the number of unilateral
things we've done on international missions (remember our half of the DUAL spacecraft Ulysses mission?).
After the significant science descope AND cost overrun of Dawn, I felt it might be a good life lesson
for Discovery participants for the mission to be cancelled. But the German and Italian contributors
would be understandably angered by that, so its good for international relations to keep Dawn alive.
But it's not a good precident for the future of the Discovery program. Not trying to offent anyone here.

[Bob Shaw]

Without trying to provoke anger, I think Dawn was reinstated only because it is an international mission.

Not to mention the ISS. Oh, no. Mustn't mention the ISS. Shan't. Won't. Can't make me.

Seriously, though, the US must have lost s-o-o-o-o much credibility with it's stop-start international missions, both manned and unmanned (I nearly wrote 'manned and scientific' there, which in retrospect might not have been a bad way of putting it!).

Sigh.

Bob Shaw

[tedstryk]

(remember our half of the DUAL spacecraft Ulysses mission?).

Given precedent such as Ulysses, I don't think this is the motivation in and of itself. I think a lot of it may have been due to how much of the cost is "sunk."

[Guest_BruceMoomaw_*]

What has been the problem with the Discovery 11 AO? There was no mission selection, but why?
Bruce, I am sure you know the story.

Analyst

Oh, yes. What happened was simply that the 2004 selection board concluded that the $350 million cost cap was seriously outdated, given (1) general inflation, (2) the more rapidly rising cost of Delta 2 boosters, and (3) the brutal fact that almost all the missions that can be cheaply done with present-day technology but are still scientifically worthwhile have already been done. They ended up saying that there was NO candidate within that cost cap for which they had enough faith in both its reliability and its scientific productivity.

The first meeting of the Solar System Strategic Roadmap Committee in December 2004 was bloody furious to hear about this -- and just last November, Mike Dantzler told the COMPLEX group that if the $350 million cap was maintained (as Sen. Mikulski was still insisting on at that point), he might be able to dredge up "one scientifically worthwhile finalist candidate from among the proposals that will be offered in response to the next AO, but I very much doubt I'll be able to find two". The planetary science community then made enough of a stink about this that Mikulski and the rest of Congress finally backed down and raised the cap to $425 million for the current selection.