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NASA Dawn asteroid mission told to ‘stand down’
Bob Shaw
post Mar 5 2006, 12:28 AM
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QUOTE (mcaplinger @ Mar 5 2006, 12:17 AM) *
Deep Impact's aphelion is at about the orbit of Mars, so it's got no chance of getting to the main belt. Stardust's is at 2.7 AU and Ceres' orbit is from 2.55 to 2.99 AU, so it's a much better prospect; of course, the orbits are unlikely to be in phase to allow a close approach, and Stardust only has ~140 m/sec of delta-v left.

http://discovery.larc.nasa.gov/discovery/dpl.html has some information on these spacecraft.


Although Ceres looks highly improbable, a bit of orbital tweaking via the Earth might yet make something feasible... ...asuming the spacecraft has the oomph!

Bob Shaw


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mcaplinger
post Mar 5 2006, 01:00 AM
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QUOTE (Bob Shaw @ Mar 4 2006, 04:28 PM) *
Although Ceres looks highly improbable, a bit of orbital tweaking via the Earth might yet make something feasible... ...asuming the spacecraft has the oomph!

DI has only about 340 m/s of delta-v left. I think it would need many km/sec to get to the main belt, even with an Earth gravity assist. I'd be happy to be proved wrong, though.


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Disclaimer: This post is based on public information only. Any opinions are my own.
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Bob Shaw
post Mar 5 2006, 01:55 AM
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QUOTE (mcaplinger @ Mar 5 2006, 01:00 AM) *
DI has only about 340 m/s of delta-v left. I think it would need many km/sec to get to the main belt, even with an Earth gravity assist. I'd be happy to be proved wrong, though.


No:

The word is *delighted*!

The simple facts may conspire against us, though - it's great if a spacecraft can do more than we asked, but by no means a failure if it doesn't! If, by any chance, there's some funny trajectory, then let's be *very* happy!

Bob Shaw


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Guest_AlexBlackwell_*
post Mar 6 2006, 09:30 PM
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Not to beat a dead horse but here are a couple of new references pertinent to this thread:

An article from the March 7, 2006, issue of Eos:

Ceres, Vesta, and Pallas: Protoplanets, Not Asteroids
This article points out that, although Ceres, Vesta, and Pallas have been classified as either fragments or asteroids, they instead appear to be small planets, or protoplanets.
T. B. McCord, L. A. McFadden, C. T. Russell, C. Sotin, and P. C. Thomas
Eos, Trans., AGU, 87, 105 & 109, (2006).
http://www.agu.org/journals/eo/eo0610/2006...0002.pdf#anchor

Given the normal lead time required for articles, I imagine the authors had to make some hasty, last-minute revisions, namely by adding a passage at the very end: "In 2001, NASA had selected the Dawn mission, which would have visited and investigated Vesta and Ceres starting in 2010. The mission was scheduled for launch in June 2006, but NASA cancelled the project on 2 March."

And there was an article posted last Friday on Spaceflight Now, which I haven't seen anyone mention:

Probe built to visit asteroids killed in budget snarl
BY STEPHEN CLARK
SPACEFLIGHT NOW
Posted: March 3, 2006
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Guest_AlexBlackwell_*
post Mar 6 2006, 10:04 PM
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QUOTE (AlexBlackwell @ Mar 6 2006, 09:30 PM) *
And there was an article posted last Friday on Spaceflight Now, which I haven't seen anyone mention...

I stand corrected.
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gpurcell
post Mar 7 2006, 04:32 PM
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From the Spaceflight Now article:

In the period leading up to the stand down, worries also spread concerning several key spacecraft issues. Relying on a solar electric ion propulsion system, Dawn was to have carried a tank for the xenon gas propellant required by the three cutting edge engines. The xenon tank - composed of a titanium liner covered with composite wrapping - is located deep inside the spacecraft bus, and other pieces were added around it during the manufacturing process.

The flight tank inside Dawn passed pre-flight tests that included taking it to pressures far above those necessary for ground or space operations. Yet when similar tanks were put through more stringent tests, they ruptured at pressures lower than the expected design limits. By finding that the tank was not as strong as first thought, engineers were forced to compensate the weakness by forming a new strategy that included not filling the tank to its full capacity.


I think this might have been the straw that broke the camel's back. I wonder if the Ceres encounter was going to be descoped as a result of the reduction in fuel.

One descope too many, I suspect.
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djellison
post Mar 7 2006, 04:37 PM
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I just hope there is a thorough investigation into why the mission ended up being scrubbed - as it is a mission failure. Just because it failed on the ground doesnt mean is should escape a mission failure review board. A root cause should be identified, and if it was a contractor - then the contractor should be penalised for it.

Doug
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Guest_AlexBlackwell_*
post Mar 7 2006, 07:05 PM
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QUOTE (djellison @ Mar 7 2006, 04:37 PM) *
I just hope there is a thorough investigation into why the mission ended up being scrubbed - as it is a mission failure. Just because it failed on the ground doesnt mean is should escape a mission failure review board. A root cause should be identified, and if it was a contractor - then the contractor should be penalised for it.

I think "failure" is too harsh. When you strip away most of the rhetoric, it appears, to me at least, the entire cancellation issue revolved around risk management. NASA SMD didn't seem convinced the Dawn team could manage the risk within the cost caps. The Dawn team, while conceding the cost overrun, felt that, through no fault of their own, the bar had been raised for them. In other words, they felt the mission was doable under the original cost caps but that NASA SMD erected more hurdles and then axed the mission when the team couldn't clear them. Sykes may have had a point when he claimed that NASA was "negative" about Dawn "for years." That may be true. On the other hand, it also may be justified. Maybe there was a negative trend after selection (e.g., the science descope) and that contributed to a case of "buyer's remorse." If true, it couldn't have happened at a worse point in time.

I'm still curious, though, about the independent asseessment team report. That both NASA SMD and the Dawn team could come away with opposite conclusions is, to put it charitably, interesting, even when factoring in the inevitable spin from both sides. If this is true, then the report was worthless.
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Guest_BruceMoomaw_*
post Mar 7 2006, 08:59 PM
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At the COMPLEX meeting, Dantzler mentioned the problem with the xenon tank (although I don't remember him going into any detail), but added that the craft was still supposed to go to both asteroids because it had been concluded that sending it just to Vesta wasn't cost-effective enough to justify the mission. He emphasized that the mission had had a whole rash of seemingly unconnected technical problems with things that were supposed to be routine, and that the stand-down was to determine whether this was just bad luck or whether there was some kind of systematic incompetence involved. I suspect the latter turned out to be the case, and that any ass-covering going on right now is coming from the Dawn team itself rather than from NASA HQ (despite the fact that, if the latter were blamed for the murder of Abraham Lincoln, I would regard the matter as being at least worth further inquiry).
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dvandorn
post Mar 7 2006, 09:58 PM
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You also have to remember that NASA HQ has ben steeling themselves to cancel a mission that's blown its cost cap for a while, now. Recall that HQ told Steve Squyres that Spirit and Opportunity would look great sitting in a museum -- it came very close on the MERs.

It was bound to happen to someone, eventually. NASA HQ was looking to make an example of someone, and now they have.

-the other Doug


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mars loon
post Mar 8 2006, 01:08 AM
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There is alot of misinformation being spread here and in some of the news reports in Spaceflightnow.com and Space.com.

There are NO TECHNICAL ISSUES preventing DAWN from launching. This nonsensical cancellation is based on funding shortfalls at NASA and politics

This mission is NOT a failure, but there appears to be a failure of WILL to launch a virtually complete spacecraft that is GOOD to GO. Sadly this can be traced to certain higher-ups at NASA and lack of White House budgetary support for NASA which has resulted in many cutbaks in space science missions in addition to DAWN. I find this and the growing anti-science attitude in this country to be very troubling.

ken
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Bob Shaw
post Mar 8 2006, 11:22 AM
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What was that French phrase? 'Pour encourage les autres'

The Romans did it, too - they decimated their legions to punish failure. Not in the sense we use it now, but by executing one in ten of the members of the failing groups.

I bet there are some fevered examinations going on right now by project managers and PIs who thought they might have to go back to the cash cow for another bucket of moolah!

Bob Shaw


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Guest_BruceMoomaw_*
post Mar 8 2006, 01:36 PM
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Assuming that this cancellation was due to the new science funding cutbacks at NASA doesn't really make sense -- the craft, after all, was almost finished, and had they cancelled it for that reason they'd be flushing several hundred million in already-spent money down the toilet just to avoid spending an additional $50 million or so. I imagine it really was cancelled because NASA finally did decide to get tough on their cost-cap policy (as they did with the Clark satellite). And I wouldn't be surprised to learn that Griffin played a strong personal role in that decision.
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pilotpirx
post Mar 8 2006, 03:59 PM
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QUOTE (BruceMoomaw @ Mar 8 2006, 01:36 PM) *
Assuming that this cancellation was due to the new science funding cutbacks at NASA doesn't really make sense -- the craft, after all, was almost finished, and had they cancelled it for that reason they'd be flushing several hundred million in already-spent money down the toilet just to avoid spending an additional $50 million or so. I imagine it really was cancelled because NASA finally did decide to get tough on their cost-cap policy (as they did with the Clark satellite). And I wouldn't be surprised to learn that Griffin played a strong personal role in that decision.

How much was Dawn's launch vehicle - $150-200M?.

Too bad there is no cost cap policy on the Shuttle and Station program.

Has the unmanned vs. manned debate become politically incorrect? A few years ago that was a hot topic.
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JRehling
post Mar 8 2006, 06:36 PM
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QUOTE (AlexBlackwell @ Mar 7 2006, 11:05 AM) *
Maybe there was a negative trend after selection (e.g., the science descope) and that contributed to a case of "buyer's remorse." If true, it couldn't have happened at a worse point in time.


I have an overwhelming urge to use a sports analogy.

Watching a track race once, I saw a runner who was going to be in multiple races running his third of the day. He was in second place near the end of that race, well ahead of third, and could have eased up to save some energy for the fourth race. But the runner in first fell back to tempt him to finish this race hard. As soon as he took the bait, the leader sped up, and the race ended with a furious finish but with the guy still finishing second, by a tiny margin. A lot of unnecessary effort for nothing. And I beat that guy in his next race. wink.gif

Dawn was a lot like that guy's third race.

I remained heartened that before decades past, we'll probably see the same science as a non-descoped Dawn, and maybe a better eventual outcome than if some descoped version had flown. It's been mentioned that Discovery may be running out of missions. Well, this is a flyable mission, and it's going to stay near the top of priorities. In one form or another, it'll fly. I doubt very much if five new Discovery selections will occur before something taking on some or all of Dawn's science goals is selected. Mercury is "done", barring a smash-and-grab sample return. Venus probably won't get more than one Discovery mission. The Moon and Mars have their own programs, and Phobos/Deimos definitely wouldn't get more than one Discovery mission. If Contour is reflown, that would do the comet matter into the ground. I doubt if Genesis will be reflown. Outer SS options exist, but at the margins. It seems obvious that the asteroids are going to stay near the front of the queue, and the big asteroids aren't likely to be "shut out" by the small ones.
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