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Posted by: dvandorn Mar 28 2006, 07:58 AM

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

Posted by: Holder of the Two Leashes Mar 28 2006, 03:32 PM

Does anyone know how much it would cost to reinstate the magnetometer? A bit academic at this point, I'm afraid, but I am curious.

Posted by: Marz Mar 28 2006, 04:15 PM

yee haw!!

Has the mission timeline been changed at all?
Is it still scheduled for launch this year?

Posted by: J.J. Mar 28 2006, 04:27 PM

^
The launch has been pushed back to July 2007. That's better than nothing, but time will tell if it stays in-budget.

Posted by: AlexBlackwell Mar 28 2006, 04:49 PM

Hey, maybe Amir Alexander at TPS knows something we don't. Here's an excerpt from Alexander's latest story "http://www.planetary.org/news/2006/0327_A_New_Day_for_Dawn.html":

"For...9 months, Dawn will remain in orbit around Vesta, scanning it with an array of instruments including a camera, two spectrometers, an altimeter, and a magnetometer.

So, both the altimeter and magnetometer are back on the payload? That would certainly qualify as "news." Or is Alexander using outdated information?

Posted by: SFJCody Mar 28 2006, 04:58 PM

It would be great to have the altimeter back. Then we'd have complete (or nearly complete) topographic maps of every body in the inner solar system bigger than Pallas:

Mercury: Mercury Laser Altimeter
Venus: Magellen SAR altimetry
Earth: SRTM + many others
Moon: LOLA
Mars: MOLA
Vesta: Dawn Laser Altimeter
Ceres: Dawn Laser Altimeter

Excellent for comparative planetology.

Posted by: gpurcell Mar 28 2006, 05:40 PM

http://dawn.jpl.nasa.gov/science/technology.asp

Science Payload:
--------------------------------------------------------------------------------
Framing Camera : German Aerospace Center, DLR, Institute of Space Sensor Technology and Planetary Exploration, Berlin.

--------------------------------------------------------------------------------

Mapping Spectrometer : The Institute for Astrophysics in Space (IAFS), Rome

--------------------------------------------------------------------------------

Gamma Ray and Neutron Spectrometer : Los Alamos National Laboratory, Los Alamos NM

Posted by: elakdawalla Mar 28 2006, 05:45 PM

I notified Amir about the error and he corrected it. He said he got the information from Dawn's website...don't know where though; they seem to have scrubbed it pretty well for references to the altimeter and magnetometer.

--Emily

Posted by: peter59 Mar 28 2006, 05:46 PM

I checked my calendar but it is not April Fool's Day.
It is true ? I can't belive.

Posted by: JRehling Mar 28 2006, 05:58 PM

Shape from shading and stereography will yield some decent topographic maps of Vesta and Ceres in time, although I suspect that those analyses will take a while. Note that DEMs of Mercury based on Mariner 10 data came out in the late 1990s! Not that the analysis took that long to finish; I think it took about that long to start. Computers in 1996 being a bit more powerful than computers in 1975.

Note that a DEM of Mars that used some of the vast array of imaging data could really improve on the MOLA data, but it's almost incomprehensible that anyone would ever use ALL of the imagining data that exists. In the long run, combining MOLA with MEx and THEMIS would probably suffice for just about any imaginable geological purpose until we need to survey Mars for real estate.

Check out

http://webgis.wr.usgs.gov/mer/March_2002_presentations/Kirk/ISPRS_ComIV_2002_Kirk_MOC.pdf

...making high-res DEMs using MOC imagery. HiRise will become part of this capability.

Overall, I guess the techniques used on all of the Mars imagery coming in should allow the techniques to mature before Dawn gives us maps of Ceres and Vesta, and the resulting products might be quite good. They would only benefit from the laser altimeter data, but I'm not sure how much...

Posted by: AlexBlackwell Mar 28 2006, 06:02 PM

Shucks! And here I was hoping the two instruments had been restored and that Amir was merely burying the http://www.randomhouse.com/wotd/index.pperl?date=20001128.

Posted by: BruceMoomaw Mar 28 2006, 08:11 PM

It is, I imagine, well too late to reinstall either of them at this point.

Posted by: AlexBlackwell Mar 28 2006, 09:30 PM

Undoubtedly so. Of course, there's also the "small" issue of there not being enough money.

Posted by: Marz Mar 28 2006, 10:01 PM

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?

Posted by: elakdawalla Mar 28 2006, 10:08 PM

Colleen Hartman said yesterday that the arrival dates were not changed by the one-year launch delay.

--Emily

Posted by: mchan Mar 28 2006, 10:39 PM

If the Dawn development team can't determine whether there is a subsurface ocean on Dawn, then the mission is doomed!

Posted by: AlexBlackwell Mar 28 2006, 10:55 PM

Of course the magnetometer and, to a lesser extent, the laser altimeter, both dropped during the descope, would have addressed this. As is stands now, the best bet for determining the internal structures of Ceres and Vesta, and possibly detecting a putative internal ocean, is by the Dawn radio science experiment. Alex Konopliv of JPL and his colleagues hope that this experiment can return data resulting in 12 degree or higher global gravity field solutions, determination of principal axes, bulk density, etc., thereby placing constraints on the asteroids' internal structures. Whether this is enough to determine the existence of an internal ocean (e.g., by getting a good value for the asteroids' Love numbers) is unclear to me.

Posted by: JRehling Mar 28 2006, 11:24 PM

Well, then, regardless of what happens with Dawn, the team behind it ought to consider opening an airline.




The plan to include an ocean on Dawn has been scrubbed due to mass considerations.

Posted by: ElkGroveDan Mar 28 2006, 11:39 PM

My sources tell me there were corrosion issues as well.

Posted by: mars loon Mar 29 2006, 12:47 AM

ah you beat me to this, My title was "DAWN reborn"

a new thread was overdue

sadly its too late for the magnetometer for technical reasons

on the budget,

many other recent missions, including our beloved rovers, NH, DI, MESSENGER,etc, have been far more overbudget. DAWN has been much closer to the target and the stand down added to the overrun


fortuneately due to the use of ion propulsion, there is a wide launch window extending to at least Oct 2007 and there is no delay in arrival to Ceres and Vesta.

Posted by: dvandorn Mar 29 2006, 02:26 AM

Awww... what if they descoped it? Just included a small sea on Dawn? That might work...



-the other Doug

Posted by: punkboi Mar 29 2006, 04:24 AM

All that matters is... The 'Send your name to the Asteroid Belt' feature has been reinstated on the Dawn website

Posted by: nprev Mar 29 2006, 06:40 AM

You know, all these "Dawn ocean" jokes are a bit salty for my taste...in fact, they tide my patience!

Okay, I await a wave of criticism for that egregious flotsam... well, perhaps "jetsam" is more apropos due to Dawn's selected means of propulsion...

Posted by: Myran Mar 29 2006, 11:34 AM

Ok great its back on track.
And no more ocean jokes? Ok I got a most serious question then.

I did send my spouse to Mars on one of the Mer rovers, so now Dawn will fly I might consider sending myself there instead.
But the distance between Mars and the Asteroid belt isnt that far.
So I worry somewhat, if this will still be within yelling distance?

Posted by: Bjorn Jonsson Mar 29 2006, 12:48 PM

AFAIK NH was on budget - the others were not.

Hopefully this near-cancellation will serve as a clear warning to future Discovery proposers. Otherwise the way to get a mission flown is going to be to purposefully underestimate costs, include lots of instruments when proposing a mission and once it's approved and spacecraft construction has started a few instruments can be dropped and NASA informed that "oops, we need more $$". If this happens the reinstatement of Dawn is actually bad news. So overall I guess I'm happy that Dawn has been reinstated - but happy with some reservations.

Posted by: antoniseb Mar 29 2006, 01:45 PM

I missed this thing getting started but is this a reference to the Ulysses mission, and Dawn and her fingertips of Rose igniting the clouds on the broad back of the wine dark sea?

Posted by: Bob Shaw Mar 29 2006, 02:21 PM

No.

Bob Shaw

Posted by: The Messenger Mar 29 2006, 04:08 PM

Can somebody provide me with a good reference on the scientific objectives and why-fors? I don't dare Google "Dawn Love Numbers"

Posted by: BruceMoomaw Mar 29 2006, 06:52 PM

There's a great deal on this subject scattered around in various places (including both the official website and a lot of recent conference abstracts). Once again, as soon as I get the chance (I'm trying to do several things at once), I'll try to dig up the best summaries for you.

Posted by: AlexBlackwell Mar 29 2006, 07:04 PM

A couple of slightly outdated (from an instrument standpoint) references are "http://www-spc.igpp.ucla.edu/dawn/pdf/Dawn_JourneySpaceTime.pdf" by Russell et al. and "http://www-spc.igpp.ucla.edu/dawn/pdf/ACMConferencePaper" by Russell et al.

If you have access to Planetary and Space Science, then a slightly more detailed mission description can be found http://dx.doi.org/10.1016/j.pss.2003.06.013.

I also http://www.unmannedspaceflight.com/index.php?s=&showtopic=1645&view=findpost&p=44352 a recent Dawn-related article in Eos.

Posted by: SFJCody Mar 29 2006, 08:01 PM

Magnetometer or not, 2015 will put a significant capstone on humanity's exploration of the solar system: reconnaissance of the first KBO and the first main belt asteroid in the same year. 2016/2017 would be a good time to revise planetary textbooks.

Posted by: The Messenger Mar 29 2006, 08:05 PM

Thanks - these references are prefect. It will be interesting to compare these surfaces with Tempel I and Itowana.

Posted by: AlexBlackwell Mar 29 2006, 08:08 PM

You're welcome. And I presume you meant "Itokawa"?

Posted by: SFJCody Mar 29 2006, 08:10 PM

Perhaps Luna, Mars, Ganymede and Callisto will make better points of reference...

Posted by: Mariner9 Mar 29 2006, 08:45 PM

I second SFJCody's comment about a capstone event, but I would give it a slightly different slant.

With NEAR we got a look at the lower end of the mid-sized asteroids.

With Hayabusa we got a look at the smallest end of asteroids, and saw our first flying rubble pile

With Dawn, we will see 2 of the largest asteroids.

We will have completed our inital sampling of the asteroid belt.

Posted by: BruceMoomaw Mar 29 2006, 09:51 PM

Actually, we still won't have done that. We have already seen three Main Belt asteroids -- one, Mathilde, fairly large, and two more (Gaspra and Ida) quite small; and Rosetta by 2010 should have flown by both little Steins and the quite large (100-km) Lutetia -- but that's still quite a limited set composition-wise. For instance, we will not yet have seen any M-types, or any of the distant D-types that are thought to be even richer in water and organics than the C types are (indeed, on the borderline between asteroids and comets).

Granted that this is assuming that Dawn -- which, at least earlier in its planning, had the potential to fly by several other asteroids during its cruises to Vesta and then to Ceres -- doesn't visit any of these types. But there is clearly such great compositional variety in the Belt (including WITHIN the overall asteroid "types") that it will be some time before we can honestly claim that we've seen a good sampling of it.

Posted by: SFJCody Mar 29 2006, 09:51 PM

...and Rosetta will give us a look at the upper end of the mid-sized asteroids.

Posted by: JRehling Mar 29 2006, 10:19 PM

Now this is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning.

-- Winston Churchill

Posted by: Mariner9 Mar 29 2006, 11:00 PM

Sigh. I considered putting in a caveate about the diversity of the asteroid belt, and just how many types of asteroids there are, and how a mere handful of asteroids does not fully represent the belt...

but I thought when I said "initial sample" that I might be conveying .. uh, "initial sample" as opposed to "exhaustive survey" or "good statistical representation of all major types"

Pardon me for not fully explaining that yes, I have indeed read several good texts and articles on asteroids, and yes, I know there are quite a lot of different types.

I suppose though, you just are not a full member of this forum until you've been corrected by the Moomaw.

Do I get my pin and certificate now?

Posted by: dvandorn Mar 29 2006, 11:01 PM

Myran -- in space, no one can hear you yell...

-the other Doug

Posted by: BruceMoomaw Mar 30 2006, 02:52 AM

Actually, the Moomaw was just trying to point out that you can't even rightfully call it an "initial survey" until you've gotten at least one look at all the major types of asteroids -- and the M and D types definitely fall into that category. Asteroid size is less important than their composition.

Posted by: JRehling Mar 30 2006, 03:47 PM

I have a long-standing belief that I haven't heard expressed explicitly, so I'll say it here: If we ever get to perform a close flyby of a very large number of asteroids, we would seem to be bound to find some interesting anomalies out there, even though most of those worlds are far too small to have their own dynamic thermal history. But with some permutation of parent bodies, impacts, and just plain the unexpected, and 10,000 chances, there have GOT to be some interesting freaks out there. Maybe an asteroid made primarily of some very rare element, like silver. Maybe a surface that has by statistical chance avoided taking any major impacts in 4 billion years. Maybe an asteroid that was last resurfaced by a single massive electrical discharge. Or one that is highly magnetized.

The above is specific-to-general thinking, but given the surprises you see just in the Saturnian satellites, it seems like a collection of bodies 1,000 times as numerous has got to have some inCREDible freaks among it.

Maybe one day we'll see some sort of solar powered/solar sail craft that has enough autonomy to go on arbitrary numbers of flybys and a fleet of them could visit a very large number of asteroids for not very much money; with longevity on their side, doing so for decades.

Some of those freaky finds would be just curiosities that don't tell us much about anything except the freak itself, but the right kind of find could be a major score for science; in principle, something like this could be more valuable than a mission to a major planet. The hitch is that any such discovery would be rear-loaded: It would probably come with no warning, and hence no opportunity for the given asteroid to ever be assessed by a boardroom full of planners as a worthy target. That's potentially a blindspot of planning methodology.

Posted by: Myran Mar 30 2006, 05:06 PM

You havnt heard us two when we begin one argument and start yelling, its loud! So I worry that even 1 AU of vaccum would be a safe distance.

Back to being serious and re BruceMoomaw & JRehling, yes it would be interesting to have a look at avariety of asteroids and lest one of each type to see if our ideas derived from meteorites found on earth are correct or not.
Are these parts of a once larger 'moon sized' asteroid with a molten core that differentiated and broke up and gave us the various types. Yes moon sized meaning one smaller than Earths Moon, its unlikely it was larger, the total mass of the asteroid belt is to low to think a really larg object existed there.

Or was it another process in smaller asteroids like heating from impacts that caused some asteroids to be carbenous and others to have a high nickel iron content? The latter is perhaps less likely but cant be ruled out. A good survey might settle the question, so Dawn are a good start on doing that.

Posted by: JRehling Mar 30 2006, 05:12 PM

The total mass of the main belt asteroids is less than the Moon, but it is still clear from meteorites (remember, we have tons of samples: in fact, some of the samples themselves weigh tons!) that there were larger parent bodies that were broken up significantly by impacts. I'd like to know how clear the picture is on which now-destroyed parent bodies may have existed. I know that it seems that Vesta is the (by far?) largest piece of a shatter event that has created some smaller named asteroids and no end of meteorites. And Vesta is large enough to have differentiated. But I don't know if we have a jigsaw-puzzle-solver's clue as to whether there were originally three such bodies, or five, or twelve, or ???

Posted by: BruceMoomaw Mar 30 2006, 06:31 PM

One of the major mysteries of the belt is how Vesta -- which is pretty obviously one of the originally differentiated protoplanets in the Belt -- could have survived almost intact while almost everything else in the Belt was smashed into very small pieces by collisions. There was a recent piece of work by (I believe) Erik Asphaug proposing a time history of the Belt, and of the statistical distribution of different-sized fragments within it, that could explain how this happened. I'll track it down. (There is also Eric Nimmo's recent theory that Vesta may actually be a protoplanet from the inner-planet zone that wandered out into the Belt later on.)

Two other notes:

(1) The "EVE" mission Russell's team is proposing as a follow-up of Dawn would look at Hygeia -- which may be the biggest of the D-type asteroids -- and Psyche or some other M-type. This really WOULD allow us to complete our initial survey of the Belt.

(2) Even among the M types, however, there is currently a knock-down fight as to whether they really are all metallic. Some of them show signs of hydration, which implies that we may have wildly misinterpreted what they're made of -- they may be made not of nickel-iron, but of relatively low-temperature hydrated minerals. Others, however, DO seem from their near-IR spectra and radar reflectivity to be metallic.

Posted by: Myran Mar 30 2006, 06:36 PM

Thats correct, though the asteroid belt could have been more massive in the past with many bodies ejected, perturbed by Jupiter or broken up from collsions the ejecta in chaotic orbits etc. But I dont have any impression theres any consensus on how much more massive it might have been. But feel free to correct me on that if im mistaken.

Yes Vesta are interesting since it is special in more than one way, yes it have taken a huge impact, and spectroscopy hints it have had some volcanism so its should have undergone differentiation.

But you cut to the core (oops) of what I was thinking there, the question if most meteorites comes from one or few bodies. Or if they are offsprings of a wide range of parent bodies.

Posted by: tedstryk Mar 30 2006, 08:39 PM

I think that it depends on how one defines samples...if you just want a main belt asteroid, we have done that. And heck, if we operate on that level, Pluto, even with its new neighbors in the outer solar system, would round out our exploration. But in reality a much broader sampling of worlds is needed.

Posted by: JRehling Mar 30 2006, 11:39 PM

It seems that Vesta is one proto-planet that survived (mainly) and Ceres, which is considerably bigger, is one proto-planet that never lost too much matter to impact. Pallas is another. Those three were never all-in-one, so there was no "Pangaea" of the asteroid belt, and the number of parent-worthy bodies (Ceres and Pallas having never been seriously fissioned) must have been at least four or five. The question is how many others were there? Was five the grand total? Or was it twelve? I was wondering if meteoritics had constrained this, but no one is piping up.

I would think that isotopic analysis might cluster the massive collection of meteorites into a few groups, but I could easily imagine that this hope would be dashed by reality. Just wondering if anyone had pointers to results along these lines.

Posted by: Mariner9 Mar 31 2006, 03:47 PM

I remember in one of the earlier Discovery mission proposals I read about a mission similar to CONTOUR which would flyby multiple asteroids. It wouldn't seem all that cost effective to only fly by 2-3 asteroids, but I know that in the early days of DAWN they were suggesting that they could fly past as many as 10-12 targets on the way there. I always found that number as overly optimistic, Dawn will have enough on it's plate just getting there, so if they manage 1-2 extra flybys it would be impressive enough. Something I read recently suggested they were now using lower numbers whenever the topic came up.

But has anyone given any serious consideration to taking a Dawn type ion propelled spacecraft and using all of the delta-vee specifically for as many fly-bys as possible? I would think with a couple Earth, Venus, or Mars flybys thrown in to make the orbit more elipitcal, they could potentially survey a very large number of targets.

It occurs to me that the instrumentation on DAWN might not be the best for fast flybys, but with the right package this might yield a lot more targets and results than a simple ballistic probe like CONTOUR. And that might make it worth it.

All of this is assuming that the Discovery office at NASA isn't really gun shy about ion drive missions right now.

Posted by: JRehling Mar 31 2006, 05:47 PM

Yeah, if you pick targets according to trajectories that net the highest sheer number, without any particular targets offering constraints, I would expect some fantastic possibilities.

Thinking outside the box, I wonder about using a Jupiter gravity assist to create a retrograde orbit that could be later circularized or near-circularized with propulsion and/or Earth gravity assists. It seems to me that flying backwards through the asteroid belt would very much increase the number of flyby possibilities, the same way that you would pass close to a LOT more cars on the highway driving 70 mph against traffic than you would driving 90 mph with traffic. In fact, this would mean no propellant would be needed to catch up to asteroids, or to lag behind them, and all of the propellant (once you achieve that orbit) could be used in "lateral" motion to create flybys. With 10,000 targets, and a full lap relative to the field taking place in about 2.5 years, the craft in retrograde orbit would fly by the radial vector of another asteroid every 2.5 hours! Assuming the asteroid belt is 1 AU wide, totally planar and with uniform distribution of the asteroids within it, the craft would fly within 0.001 AU (149,000 km) of an asteroid about three times a year even if you did nothing to aim for any targets! I would think that a campaign of lateral manuevers aiming for targets well in advance could lead to a mission ultimately achieving hundreds of flybys in a main mission of ten years.

Feasible?

Posted by: BruceMoomaw Mar 31 2006, 08:12 PM

It's certainly an idea. One might even combine it with a few small passive impactors and a flash spectrometer on the main craft to try to get element measurements during the flyby (which, unfortunately, are just about impossible to get any other way during flybys -- gamma rays are inherently too weak for the purpose without an orbiter, and out in the Belt solar radiation is too weak to generate adequate fluorescent X-rays for meaningful element data during a flyby).

Posted by: Bob Shaw Mar 31 2006, 10:57 PM

Now *that* is a really clever idea!

Simple, cheap, and (almost) free.

Any serious orbital dynamics guys out there? Or girls, I care not which!

Bob Shaw

Posted by: David Apr 1 2006, 12:06 AM

Not me, but one thing occurs to me: aren't these byflights going to be awfully fast?

Posted by: BruceMoomaw Apr 1 2006, 12:16 AM

Oh, yes. Might be worth doing anyway, though, if you can't get element measurements even during regular slower prograde flybys. By contrast, near-IR mineral spectrometers (along with cameras) could probably get good mineralogical data even during such a high speed flyby, and as John says you might get a much larger number of them during the probe's operating lifetime.

Perhaps the most important question is the extent to which near-Earth asteroids (which are so much more easily accessible and samplable) provide an adequate sample of the different types of Main Belt asteroids. They seem to be diverted from the Main Belt into the inner System only when they wander into one of the narrow zones in which Jovian gravitational resonances divert them inward -- but the Yarkovsky Effect seems to have moved a substantial number of the smaller asteroids (and their meteoric fragments) inward or outward from their original orbits over the Solar System's lifetime, and so has presumably provided these "escape hatches" from the Belt with a hefty shovelful of asteroid samples from all sorts of different zones in the Main Belt. There is apparently still some debate over just how well Yarkovsky works, though -- and it does not work on significantly larger asteroids.

Posted by: JRehling Apr 1 2006, 12:32 AM

Yeah. About 50 km/s, which is about 3 times the relative velocity of, say, New Horizons at Pluto. But these worlds are pretty small, too, so you could aim for a daytime-side flyby, and reliably get a good "full asteroid" view during the minute or so that you have to squeeze off some multicolor frames. Looks like short exposure time, probably a pushbroom design, etc... we see some mission design specs that the high speed would require. Operational precision would be required. All told, though, if you're getting hundreds of flybys and a few are botched, you're still doing pretty well.

Posted by: BruceMoomaw Apr 1 2006, 12:48 AM

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.

Posted by: AlexBlackwell Apr 1 2006, 01:36 AM

Actually, after having read it, I realize this particular link is a preprint/postprint of the Planetary and Space Science paper.

Posted by: BruceMoomaw Apr 1 2006, 02:22 AM

I've considered trying to look into the question of what really lay behind the reinstatement of Dawn -- but the more I think about it, the more such a project strikes me as an exercise in futility. Every single person I talked to would be cheerfully willing to lie for their own reasons about what actually went on, and -- not having access to any instruments of torture -- there would be no conceivable reliable source I could track down on what really happened.

Posted by: tedstryk Apr 2 2006, 04:53 PM

I think the recent HST data changes a lot of that. It is the only main belt asteroid that, were it a moon of one of the outer planets, not be one of the "irregulars." Thus, there is the possibility that it is differentiated, which would also be unique - asteroids like Vesta might be fragments of what used to be a larger world, but Ceres seems to be more than a fragment.

Posted by: BruceMoomaw Apr 2 2006, 08:13 PM

That, in turn returns us to the question I mentioned a bit earlier: to what extent have all the asteroids, including the biggest ones, been busted up by impacts? Especially during the Belt's earliest days, when it is generally thought to have had MUCH more material in it -- perhaps including dozens of large protoplanetary "embryos", some of them perhaps as big as the Moon or Mars? Most of that material was eventually completely ejected from the Belt by Jupiter's gravitational perturbations, but in the meantime the situation there must have been wild indeed.

The trouble is that the evidence seems contradictory. The existence of a fair number of M-type asteroids -- some of which still appear to be iron-nickel, even in the latest revised near-IR compositional studies -- suggests that they were created from small, initially differentiated asteroids whose outer silicate mantles were completely stripped away, leaving their harder metal cores. There are also the asteroid "families" whose trajectories clearly show that they are the fragments of a bigger original body that got blasted to hellandgone at some point -- and eight of those families are big enough that they must have come from bodies over 200 km wide. But at the same time Vesta seems mostly covered by a basalt crust -- which must be the product of a particularly strong and complete differentiation process -- and most of that outer crust is still on it, instead of having been blasted away by impacts to expose the asteroid's underlying non-basalt mantle. (There are also the other really big remaining asteroids -- Ceres, Pallas, Hygeia. Did they also avoid a large number of impacts, or were they bashed into rubble but were still big enough that their gravity recompressed them again into solid material and spherical forms? If so, then the original ice in them could have been melted by those impacts, and the large part of it that they retained would then have refrozen again as their upper layer.)

There seem to be at least three different theories to explain this seeming contradiction on the Belt's collisional environment, and I'm currently trying to slog through abstracts and papers on the subject to try and get everyone's views properly sorted out. Once I get this done -- on top of the other things I'm trying to do right now -- I'll have more comments.

Posted by: Bob Shaw Apr 2 2006, 08:57 PM

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

Posted by: BruceMoomaw Apr 2 2006, 11:34 PM

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.

Posted by: Bart Apr 6 2006, 10:23 PM

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

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

Bart

Posted by: gpurcell Apr 7 2006, 04:23 PM

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

Posted by: mchan Apr 8 2006, 02:16 AM

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!

Posted by: Marz Apr 9 2006, 02:58 PM

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.

Posted by: BruceMoomaw Apr 11 2006, 08:37 PM

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

Posted by: gpurcell Apr 11 2006, 10:38 PM

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

Posted by: BruceMoomaw Apr 12 2006, 12:05 AM

[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).

Posted by: gpurcell Apr 12 2006, 03:07 PM

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.

Posted by: Analyst Apr 18 2006, 10:59 AM

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

Posted by: monitorlizard Apr 18 2006, 12:38 PM

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.

Posted by: Bob Shaw Apr 18 2006, 01:12 PM

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

Posted by: tedstryk Apr 18 2006, 02:48 PM

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."

Posted by: BruceMoomaw Apr 18 2006, 09:48 PM

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.

Posted by: Analyst Apr 20 2006, 08:00 AM

Thank you, Bruce.

Posted by: ugordan Apr 20 2006, 09:31 AM

Interesting. Why are Delta 2s becoming more expensive? Does the same go for all boosters out there, being a result of increased demand or something else?

Posted by: Analyst Apr 20 2006, 03:17 PM

I guess it's not rising but falling demand. A large fraction of the costs (workforce, machines, management, launch pad maintaining etc.) are fixed, this means they are the same if you built and launch 4 boosters or 10 each year. Air Force demand is zero after the last GPS 2R launch in aboaut two years and commercial missions are zero right now. This leaves NASA as the only customer. The per unit costs are rising because they must cover all fixed costs.

I believe Delta II will be retired anyway in a couple of years in favour of the EELVs (Atlas V and Delta IV): More powerful (even if not needed for Scout or Discovery or EOS) BUT more expensive too. I don't see a replacement for the Delta II (Falcon 5 doesn't count). Will it be still around in 2011 for Mars Scout 2?

Analyst

Posted by: BruceMoomaw Apr 20 2006, 08:31 PM

"Analyst" is correct -- as the demand for Delta 2 falls, it costs more per booster to keep the assembly line going. The problem of what to do when Delta 2 production finally shuts off completely has been a problem for some time in NASA's space science division, and as far as I know they're still squabbling about it.

Posted by: Bob Shaw Apr 20 2006, 08:40 PM

Bruce:

SeaLaunch on Zenit-2.

Bob Shaw

Posted by: djellison Apr 20 2006, 10:36 PM

Sea Launch is 5200kg to GTO
Delta II Heavy - 2064 to GTO

Sea Launch is more like a low end Delta IV in terms of performance ( at one point I believe it held the outright commercial payload mass record )

Doug

Posted by: edstrick Apr 21 2006, 10:40 AM

The europeans ran into the same "oops.... how do we launch mid-sized payloads" trap when the nuked the Ariane 1-4 series production line. Gee... Wonder why they're building a Soyuz launch pad in Guyana?

Posted by: Bob Shaw Apr 21 2006, 07:43 PM

Doug:

Dual launches, anyone? Ariane 5 does it as standard!

SeaLaunch is more-or-less American, and could launch not only from equatorial regions but also from Florida or California, making use of all the existing range infrastructures.

Bob Shaw

Posted by: BruceMoomaw Apr 22 2006, 02:06 AM

Yeah, but most Solar System launches have limited launch windows -- and with a dual launch, you have two payloads instead of just one that might run into technical problems serious enough to make your probe miss its window.

Posted by: RNeuhaus Apr 22 2006, 02:19 AM

I haven't heard that new rocket model: SeaLaunch. Are you referring it to Soyuz?

Rodolfo

Posted by: tedstryk Apr 22 2006, 02:21 AM

[quote name='RNeuhaus' _quote in reply -removed
[/quote]

No, SeaLaunch is a cooperative project between the russians (RKK Energia I think) and Boeing which launches satellites from the ocean - hence "sealaunch."

Posted by: remcook Apr 22 2006, 03:46 PM

zenit is the rocket model

Posted by: tty Apr 22 2006, 05:13 PM

How about Long March 2 - 3370 kg to GTO

tty

Posted by: Jim from NSF.com Apr 22 2006, 07:57 PM

Sealaunch is at the higher end of the EELV medium class..

US gov't payloads can't use Sealaunch.

So far only 3 companies have vehicle that are certified to launch NASA payloads.

Posted by: ljk4-1 Apr 27 2006, 01:54 PM

Mark Rayman has created his first log of the renewed DAWN mission.
He did the same for Deep Space 1.


STELLAR CHEMISTRY

- The DAWN Of A New Mission Marks Log Entry Number One

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

Pasadena CA (SPX) Apr 27, 2006 - NASA's next planned venture into the solar
system, Dawn is a collaborative effort of scientists, engineers and people in
other disciplines at JPL, UCLA, Orbital Sciences Corp., the space agencies of
Germany and Italy, and other universities and private companies in the United
States and elsewhere.

Posted by: Rakhir Jun 1 2006, 08:38 AM

Dawn Team Looking Good For Launch Next Year

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

Posted by: Marz Jun 1 2006, 03:50 PM

Fun and interesting article!

"Following the tradition nearly as ancient and revered as nerdiness itself, these tests are generally referred to by an acronym: CPTs."

Posted by: PhilHorzempa Jun 29 2006, 03:43 AM

Some recently posted images on DAWN website showing us
a living, breathing spacecraft. Here is one example.

Another Phil

Posted by: punkboi Jun 29 2006, 05:42 PM

Nice to see Dawn taking shape.

Posted by: PhilHorzempa Aug 1 2006, 03:38 AM

There have been several very good photos of DAWN released lately.
Here is a view of DAWN's ion propulsion system xenon-feed assembly.
Shades of Star Trek.

Another Phil

Posted by: djellison Aug 1 2006, 08:53 AM

Is it really necessary to attach these images to the forum when a link would suffice?

Posted by: punkboi Sep 13 2006, 07:46 AM

Last day to send your name to the asteroid belt is November 4.

http://www.dawn-mission.org/DawnCommunity/Sendname2asteroid/nameEntry.asp