NASA Dawn Asteroid Mission Told to "Stand Back Up", Reinstated! |
NASA Dawn Asteroid Mission Told to "Stand Back Up", Reinstated! |
Mar 28 2006, 07:58 AM
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Senior Member Group: Members Posts: 3419 Joined: 9-February 04 From: Minneapolis, MN, USA Member No.: 15 |
Just 'cause I said I would...
Hopefully, though, this whole episode has made its point -- NASA isn't afraid to tell overbudget missions to stand down. I just *really* wish we could get the magnetometer back on the beastie, though... -the other Doug -------------------- “The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
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Mar 28 2006, 04:27 PM
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#2
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Junior Member Group: Members Posts: 94 Joined: 22-March 06 Member No.: 722 |
^
The launch has been pushed back to July 2007. That's better than nothing, but time will tell if it stays in-budget. -------------------- Mayor: Er, Master Betty, what is the Evil Council's plan?
Master Betty: Nyah. Haha. It is EVIL, it is so EVIL. It is a bad, bad plan, which will hurt many... people... who are good. I think it's great that it's so bad. -Kung Pow: Enter the Fist |
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Mar 28 2006, 10:01 PM
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#3
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Member Group: Members Posts: 311 Joined: 31-August 05 From: Florida & Texas, USA Member No.: 482 |
^ The launch has been pushed back to July 2007. That's better than nothing, but time will tell if it stays in-budget. Oh, I have no complaints delaying launch a year, so long as it flies. So does this mean we can just add 1 year to the arrival times? (2012=Vesta and 2016=Ceres?) Ugh... these mission timelines are so painful! I'm beginning to loathe the "efficiency" of ion propulsion. Other questions: 1. did the recent keck/hubble observations of Ceres place a size limit boundary on any possible moons? 2. are Vesta and Ceres expected to both have at least one moon? (seems like most main-belt 'roids have companions, right?) 3. aside from visual clues, are there any instruments on Dawn that can determine if there is a subsurface ocean on Ceres? Is this completely unlikely, without tidal heating... or has Enceledus taught us a sound lesson to expect the unexpected? 4. Is EVE simply a Dawn clone to visit Pallas and other big 'roids? Should a lander mission be in the works for Ceres (dare I say, sample return)? 5. any likelyhood of the Pentagon being told to "stand down" as we review their incredible cost overruns and in the meantime use that budget to fund EVE and Dawn's Early Flight? |
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Mar 29 2006, 04:08 PM
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#4
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Member Group: Members Posts: 624 Joined: 10-August 05 Member No.: 460 |
Oh, I have no complaints delaying launch a year, so long as it flies. So does this mean we can just add 1 year to the arrival times? (2012=Vesta and 2016=Ceres?) ... 3. aside from visual clues, are there any instruments on Dawn that can determine if there is a subsurface ocean on Ceres? Is this completely unlikely, without tidal heating... or has Enceledus taught us a sound lesson to expect the unexpected? ... Can somebody provide me with a good reference on the scientific objectives and why-fors? I don't dare Google "Dawn Love Numbers" |
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Guest_BruceMoomaw_* |
Apr 1 2006, 12:48 AM
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#5
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Guests |
Can somebody provide me with a good reference on [Dawn's] scientific objectives and why-fors? I don't dare Google "Dawn Love Numbers" One of the references Alex provided -- "Dawn: A Journey in Space and Time" -- is absolutely terrific for that purpose ( http://www-geodyn.mit.edu/russell.dawn_space_time.pdf ). It's dated mid-2003, but is still up to date in practically every respect. (It was written at a time when Dawn still had its magnetometer, and of course the launch date has since been changed, presumably with detailed effects on the schedule and duration of orbital activities around Vesta and Ceres.) Alas, there is no reference to "Love numbers". I'm currently trying to accumulate information on just how likely it is that Ceres might have a subsurface liquid-water ocean, given that it undergoes almost no tidal heating. Apparently McCord and Sotin did a piece in the May 2005 "JGR-Planets" ( http://www.agu.org/pubs/crossref/2005/2004JE002244.shtml ) concluding that the heat from the radioisotopes in Ceres' rocky core were probably adequate to keep some of its ice layer liquid for about 2 billion years -- and if Ceres also has a significant amount of ammonia in its interior (there's one extremely tentative hint of possible ammoniated clays in its near-IR surface spectra), they say it might have a liquid-water layer to this day, but that the odds are against it. Two notes about Russell's article: (1) The table on page 41 lists some possible asteroid flyby targets for Dawn's mission as it was then planned. Three of them are tiny things only a few km across; the fourth was 197 Arete, 30 km wide. The distances by which Dawn would have missed them if it expended none of its ion-drive fuel for minor course corrections to make close flybys of them are listed in "Gm" -- presumably "gigameters", or "millions of km". But page 12 notes: "Because of the efficiency of SEP, the number of candidate flyby targets is expected to be large, with many opportunities for low-velocity encounters. Groundbased observations of these targets will be critical to a selection of targets on the basis of science return as opposed to simple dynamical convenience." Even with Dawn's fuel load reduced, we can still hope for a fair number of such flybys. (2) The minimum "performance floor" version of the Dawn mission (pg. 13-14) called for it to orbit Vesta, but just to fly by one hydrated C-type asteroid similar in overall composition to Ceres -- perhaps the 100-km wide "50 Virginia". This confirms something I said earlier: where asteroids are concerned, size matters a lot less than composition. During the quarter-century in which I've been reading proposals for asteroid exploration, Vesta has always been right at the top of every list because of its unique composition, which seems to be right at the far end of the spectrum of asteroid differentiation levels. But, until Dawn came along, I had NEVER seen Ceres listed as any kind of high- or even medium-priority target, despite the fact that it's the unquestioned King of the Asteroid Belt -- the reason being simply that, compositionally, it was regarded as just one of a fairly large number of hydrated C-type asteroids. It was starting to look as though, by 2020, Ceres would be by far the biggest object in the Solar System anywhere this side of the Kuiper Belt to be unreconnoitered. |
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