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dvandorn
Just 'cause I said I would... biggrin.gif biggrin.gif biggrin.gif biggrin.gif biggrin.gif biggrin.gif

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
Holder of the Two Leashes
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.
Marz
yee haw!!

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

biggrin.gif
J.J.
^
The launch has been pushed back to July 2007. That's better than nothing, but time will tell if it stays in-budget.
AlexBlackwell
QUOTE (dvandorn @ Mar 28 2006, 07:58 AM) *
I just *really* wish we could get the magnetometer back on the beastie, though...

Hey, maybe Amir Alexander at TPS knows something we don't. Here's an excerpt from Alexander's latest story "A New Day for Dawn":

"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 Or is Alexander using outdated information?
SFJCody
QUOTE (AlexBlackwell @ Mar 28 2006, 05:49 PM) *
So, both the altimeter and magnetometer are back on the payload? That would certainly qualify as "news." Or is Alexander using outdated information?


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.
gpurcell
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
elakdawalla
QUOTE (AlexBlackwell @ Mar 28 2006, 08:49 AM) *
Hey, maybe Amir Alexander at TPS knows something we don't. Here's an excerpt from Alexander's latest story "A New Day for Dawn":

"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?

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
peter59
I checked my calendar but it is not April Fool's Day.
It is true ? I can't belive. biggrin.gif
JRehling
QUOTE (SFJCody @ Mar 28 2006, 08:58 AM) *
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:


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_p...02_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...
AlexBlackwell
QUOTE (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.

Shucks! And here I was hoping the two instruments had been restored and that Amir was merely burying the lede. biggrin.gif
BruceMoomaw
It is, I imagine, well too late to reinstall either of them at this point.
AlexBlackwell
QUOTE (BruceMoomaw @ Mar 28 2006, 08:11 PM) *
It is, I imagine, well too late to reinstall either of them at this point.

Undoubtedly so. Of course, there's also the "small" issue of there not being enough money. biggrin.gif
Marz
QUOTE (J.J. @ Mar 28 2006, 10:27 AM) *
^
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. ph34r.gif

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

--Emily
mchan
QUOTE (Marz @ Mar 28 2006, 02:01 PM) *
3. aside from visual clues, are there any instruments on Dawn that can determine if there is a subsurface ocean on Dawn?


If the Dawn development team can't determine whether there is a subsurface ocean on Dawn, then the mission is doomed! smile.gif
AlexBlackwell
QUOTE (Marz @ Mar 28 2006, 10:01 PM) *
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?

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.
JRehling
QUOTE (elakdawalla @ Mar 28 2006, 02:08 PM) *
Colleen Hartman said yesterday that the arrival dates were not changed by the one-year launch delay.

--Emily


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


QUOTE (mchan @ Mar 28 2006, 02:39 PM) *
If the Dawn development team can't determine whether there is a subsurface ocean on Dawn, then the mission is doomed! smile.gif


The plan to include an ocean on Dawn has been scrubbed due to mass considerations.
ElkGroveDan
QUOTE (JRehling @ Mar 28 2006, 11:24 PM) *
The plan to include an ocean on Dawn has been scrubbed due to mass considerations.

My sources tell me there were corrosion issues as well.
mars loon
QUOTE (dvandorn @ Mar 28 2006, 07:58 AM) *
Just 'cause I said I would... biggrin.gif biggrin.gif biggrin.gif biggrin.gif biggrin.gif biggrin.gif

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


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.
dvandorn
QUOTE (JRehling @ Mar 28 2006, 05:24 PM) *
The plan to include an ocean on Dawn has been scrubbed due to mass considerations.

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

blink.gif

-the other Doug
punkboi
All that matters is... The 'Send your name to the Asteroid Belt' feature has been reinstated on the Dawn website biggrin.gif
nprev
You know, all these "Dawn ocean" jokes are a bit salty for my taste...in fact, they tide my patience! rolleyes.gif

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

QUOTE
punkboi said: The 'Send your name to the Asteroid Belt' feature has been reinstated on the Dawn website.


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? laugh.gif
Bjorn Jonsson
QUOTE (mars loon @ Mar 29 2006, 12:47 AM) *
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.
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.
antoniseb
QUOTE (dvandorn @ Mar 28 2006, 09:26 PM) *
Awww... what if they descoped it? Just included a small sea on Dawn?


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?
Bob Shaw
QUOTE (antoniseb @ Mar 29 2006, 02:45 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?


No.

Bob Shaw
The Messenger
QUOTE (Marz @ Mar 28 2006, 03:01 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?)
...

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" wink.gif
BruceMoomaw
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.
AlexBlackwell
QUOTE (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" wink.gif

A couple of slightly outdated (from an instrument standpoint) references are "Dawn: A Journey In Space and Time" by Russell et al. and "DAWN: A JOURNEY TO THE BEGINNING OF THE SOLAR SYSTEM" by Russell et al.

If you have access to Planetary and Space Science, then a slightly more detailed mission description can be found here.

I also mentioned a recent Dawn-related article in Eos.
SFJCody
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.
The Messenger
QUOTE (AlexBlackwell @ Mar 29 2006, 12:04 PM) *
A couple of slightly outdated (from an instrument standpoint) references are "Dawn: A Journey In Space and Time" by Russell et al. and "DAWN: A JOURNEY TO THE BEGINNING OF THE SOLAR SYSTEM" by Russell et al.

If you have access to Planetary and Space Science, then a slightly more detailed mission description can be found here.

I also mentioned a recent Dawn-related article in Eos.

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

You're welcome. And I presume you meant "Itokawa"?
SFJCody
QUOTE (The Messenger @ Mar 29 2006, 09:05 PM) *
It will be interesting to compare these surfaces with Tempel I and Itowana.


Perhaps Luna, Mars, Ganymede and Callisto will make better points of reference...
Mariner9
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.
BruceMoomaw
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.
SFJCody
QUOTE (Mariner9 @ Mar 29 2006, 09:45 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.


...and Rosetta will give us a look at the upper end of the mid-sized asteroids.
JRehling
QUOTE (Mariner9 @ Mar 29 2006, 09:45 PM)
With NEAR we got a look at the lower end of the mid-sized asteroids.



QUOTE (SFJCody @ Mar 29 2006, 01:51 PM) *
...and Rosetta will give us a look at the upper end of the mid-sized asteroids.


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
Mariner9
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?
dvandorn
QUOTE (Myran @ Mar 29 2006, 05:34 AM) *
...I worry somewhat, if this will still be within yelling distance? laugh.gif

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

-the other Doug
BruceMoomaw
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.
JRehling
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.
Myran
QUOTE
dvandorn said: in space, no one can hear you yell...


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. tongue.gif

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.
JRehling
QUOTE (Myran @ Mar 30 2006, 09:06 AM) *
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.


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 ???
BruceMoomaw
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.
Myran
QUOTE
JRehling wrote: The total mass of the main belt asteroids is less than the Moon,


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.
tedstryk
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.
JRehling
QUOTE (Myran @ Mar 30 2006, 10:36 AM) *
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.


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.
Mariner9
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.
JRehling
QUOTE (Mariner9 @ Mar 31 2006, 07:47 AM) *
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.


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.

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