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Decepticon
I hope this gets approved!

http://www.space.com/missionlaunches/05071...yby_future.html
gpurcell
QUOTE (Decepticon @ Jul 14 2005, 11:45 PM)


Hm. Indicates that it would need to be approved as a new Discovery project.

Not sure that would be the best use of resources...particularly with the messed up optics.
BruceMoomaw
Of course, they're talking about it as one of the little "Missions of Opportunity" -- consisting, up to now, of single instruments piggybacking on other nations' planetary spacecraft -- whose cost cap is $30 million. And the HRI's optics aren't THAT badly messed up -- it is, I think, still about 3 times higher resolution than the MRI. (Take a look at the difference between the HRI and MRI movies of the Tempel impact if you don't believe me.) I remain convinced that it is well worth doing for that cost.
djellison
Hell yes - they it would be madness to throw away a fantastic instrument in space with so much opportunity to do good science. Be it an Asteroid, Comet or BOTH flybys smile.gif

Genesis - granted - not much it could do ( and I believe it's now officially retired, and drifting into a slight earth leading solar orbit )

Stardust - it's going to be a tired, fuel-starved vehicle when it gets home.

But this is almost brand new smile.gif

Doug
BruceMoomaw
They came fairly close to assigning Genesis to an extended mission monitoring the solar wind (under the name "Exodus") -- but finally decided that its lack of a magnetometer made it non-cost-effective.
remcook
another stupid question of mine:
where does NASA get the money from for all extended missions? Does it affect any other missions? Does it have to go through congress?
tty
I remember that Carl Sagan once suggested in a book that some private foundation should "pick up" residual NASA missions as they were "turned off", and that this would be an extremely cost-effective way to conduct research. Perhaps an idea to explore. One problem is of course that access to the DSN will usually be required.

tty
dvandorn
Yeah -- and NASA controls the DSN. So, if you have a good idea to use left-over planetary probes, all well and good -- but if you need to use the DSN to communicate with them, you're SOL if NASA doesn't want to give you DSN privileges.

I think we need to figure out alternatives to the DSN before we can talk about private extensions of planetary probe missions. And since there *are* no alternatives to the DSN for communicating with planetary probes, that doesn't leave much in the way of alternatives...

-the other Doug
abalone
QUOTE (dvandorn @ Jul 17 2005, 07:47 PM)
Yeah -- and NASA controls the DSN.† So, if you have a good idea to use left-over planetary probes, all well and good -- but if you need to use the DSN to communicate with them, you're SOL if NASA doesn't want to give you DSN privileges.-the other Doug
*

There are quite a few radio telescopes that are not part of the DSN, example the radio telescope in Parkes, Australia. It does work for DSN like Apollo 11, attempts to re-establish contact with Pathfinder when it died and the Mars Polar Lander when it dissappeared, some of the Huygens downlink, but most of the time it does research. There are others around the world as well, it would just take some coordination to put together a useful syndicate. It would depend entirely if they could be convinced to give up a few hours of telescope time to do this work. There is no reason why NASA has a monopoly through its DSN on communication with probes.
Bob Shaw
Could a network of semi-amateur/student/small organisation stations be set up using apeture synthesis/phased array techniques and aggressive, SETI@Home-like signal processing to pick up data? We're talking about, in many cases, a very low bitrate for 99% of the time. Amateurs certainly picked up Apollo transmissions in the 1960s, and presumably could have listened to the ALSEPs until they fell silent.
djellison
I'm guessing you want at least an equiv to a 35m dish.

What's the pricetag on one of those anyway - and would an array of smaller dished adding up to a similar or larger size be a cheaper option

Doug
Phil Stooke
Re: Abalone's comment about other radio telescopes etc....

We are going to be hearing more about this in a little while! Too bad I can't say more right now but just wait. Things are bubbling away beneath the surface like... buried bubbling things.

Phil
abalone
QUOTE (Bob Shaw @ Jul 18 2005, 12:27 AM)
Could a network of semi-amateur/student/small organisation stations be set up using apeture synthesis/phased array techniques and aggressive, SETI@Home-like signal processing to pick up data?
*

It is not enough to just pick up data, you have to be able to transmit commands as well. Parkes has two dishes the larger being about 64m, the same as the larger dishes in the DSN.
If you have not seen the movie, there is one called "The Dish" starring Sam Neil that give quite a good account of its contributuion to the first Moon landing.
Bob Shaw
QUOTE (abalone @ Jul 18 2005, 01:06 PM)
It is not enough to just pick up data, you have to be able to transmit commands as well. Parkes has two dishes the larger being about 64m, the same as the larger dishes in the DSN.
If you have not seen the movie, there is one called "The Dish" starring Sam Neil that give quite a good account of its contributuion to the first Moon landing.
*


For some high percentage of the time, listening is probably acceptable - especially with semi-dormant spacecraft, and I still wonder whether big dishes are required for that. Obviously, you *do* need a big dish to wake 'em up and tell them to perform, because they only have little titchy antennae on 'em and they just wouldn't hear you otherwise.

I wonder what the post-encounter cruise bitrate(s) for New Horizons is(are), and what the long-term strategy for the vehicle is (if you're not running cameras or other warm things, and are prepared to accept a c-o-l-d vehicle) assuming there's cash to fund it? We have a decade plus of computational advancement to prepare for the Pluto encounter, assuming that a distributed reception network is feasible, and potentially decades more of operation thereafter (I hope!).
abalone
QUOTE (Bob Shaw @ Jul 18 2005, 11:17 PM)
For some high percentage of the time, listening is probably acceptable - especially with semi-dormant spacecraft, and I still wonder whether big dishes are required for that.
*

My recollection is that it does not quite wark this way. The Voyager craft for example I believe still have several hours of com time each week. This must be followed by a ground transmission of an aknowledgement of receipt otherwise it would just keep repeating the transmission and wasting power. In sleep mode the craft still need to maintain attitude, charge batteries, regulate temp and constant self diagnosis and be regularly monitored by com with the ground.
Bob Shaw
QUOTE (abalone @ Jul 18 2005, 01:39 PM)
My recollection is that it does not quite wark this way. The Voyager craft for example I believe still have several hours of com time each week. This must be followed by a ground transmission of an aknowledgement of receipt otherwise it would just keep repeating the transmission and wasting power. In sleep mode the craft still need to maintain attitude, charge batteries, regulate temp and constant self diagnosis and be regularly monitored by com with the ground.
*


See my comment within the 'Interstellar Probe' thread re the conceptual DSN 11m antenna 'Farm'.
Bob Shaw
Space.com article which includes details of a trajectory change for the extended mission:

http://www.space.com/missionlaunches/05072...yby_update.html

And Space Daily's take on it:

http://www.spacedaily.com/news/deepimpact-05o.html
gpurcell
The Decadal Survey places a flyby of Trojan/Centaur asteroids as a medium priority.

Would it be possible to get DI out to the Centaurs?
tedstryk
QUOTE (gpurcell @ Jul 21 2005, 05:42 PM)
The Decadal Survey places a flyby of Trojan/Centaur asteroids as a medium priority.

Would it be possible to get DI out to the Centaurs?
*


Being solar powered, even if some gravity assists could be rigged, which I doubt, the spacecraft wouldn't operate out there.
Decepticon
QUOTE
"Personally, I donít understand the fuss over whether the crater will be visible."


This comment made me mad. mad.gif
edstrick
"Personally, I donít understand the fuss over whether the crater will be visible."

Aesop: "he grapes were probably sour, anyway."
Comga
QUOTE (tedstryk @ Jul 21 2005, 11:57 AM)
Being solar powered, even if some gravity assists could be rigged, which I doubt, the spacecraft wouldn't operate out there.
*


Correct. The spacecraft is designed for a maximum of about 1.5AU from the sun. Much futher out and it couldn't generate enough power to operate or keep its internal components warm. The Centaurs are a long, long way out, and there are other interesting things to observe in the inner solar system, like Comet Boethin. As each of the four imaged comet nuclei have been distinct, adding a fifth is a good idea.
Bob Shaw
On Spaceflight Now today:

http://www.spaceflightnow.com/news/n0605/16deepimpact/

A clone mission, and a new target for Deep Impact. Pity NH2's was made so artificially expensive by the bean counters...

Bob Shaw
BruceMoomaw
I don't think that DI clone mission has a chance in hell of being picked for Discovery -- notice that the DI people just shot themselves in the foot by cheerfully stating in the same release that "half of the science return from DI came before the impact". That is, a CONTOUR-type mission that makes non-impact flybys of several comets for comparative studies will provide far more scientific bang for the buck than smashing another impactor into one more comet and getting the same (highly ambiguous) results.
Analyst
The engineering aspect of Deep Impact (hitting a small speeding comet etc.) has been (and has to be) the focus of development and testing. Science has almost been secondary, more so after the out of focus HRI and the (predictable?) dust cloud.

This "engineering bias" has also been a problem of MPF (EDL) and Dawn (ion engine, descope with even less instruments) and to some extent Stardust and Genesis (entry capsule). The reason is the limited Discovery budget: it's barely enough to built a special spacecraft (to land somethere etc.) and launch it, there is not much left for science instruments. Compare this with Rosetta, MEX and VEX or Cassini, MGS, MER and MRO. That's imo the better approach: if you go there, why not carry "all" you have.

I like the European approach: less missions, but with a full instrument suite. And missions with a longer time to observe. Even without a lander, Rosetta will tell us much more about comets than Deep Impact, Stardust and Contour (which failed, I know) did. Rosetta will see changes over time, can revisit interesting areas etc.

Btw, NEAR, Contour and Messenger (over budget) have a better instrument suite. I'm not sure about the very small Lunar Prospector and Kepler. Bruce, I understand more and more the problem of the 11th AO to find a mission within the budget.

Analyst
BruceMoomaw
Actually, Deep Impact is the only comet mission so far whose science rationale I have serious doubts about. Stardust, by dint of actually returning samples to Earth (even if they are small samples exposed to high temperature by the friction of their passage through the aerogel) will allow many extremely sensitive analyses which are simply impossible to the in-situ instruments on Rosetta, and a CONTOUR-type survey of multiple comets is vital because of the major differences in both morphology and composition that clearly exist among comets. (The difference in composition between Oort and Kuiper comets, given their formation in different parts of the initial solar nebula, is perhaps the single most important scientific subject for comet studies right now.)

I have always suspected that Dan Goldin, given his obsession with PR stunts, had something to do with the unexpected selection of Deep Impact -- but even if that is true, just try proving it at this point.
Mariner9
I don't think DI 2 has much chance either. I recall one of the project scientists in an interview a couple years ago saying that Deep Impact wouldn't be a very logical mission if we knew much about comets, but it was useful since we knew so little.

So now we have flown such a mission, have completed the Stardust sample return, flown by several comets, and will probably do close flybys of one and maybe two more before DI 2 would be launched. And DI 2 would then plow into a comet that is being studied by a long lived orbiter, and a lander, each with a full suite of instruments.

Methinks not.

As for Deep Impact being a publicity stunt? I would certainly wager that people at least had that on their mind when selecting it. I remember NEAR: the flyby of Mathilda was a blip on the news radar. Orbiting Eros for a year was the occasional 15 second news story. But the "landing", followed by the one week operation on the surface with the only instrument left that could actually return any useful data from that position .... well that made the news for several days. On every channel. International even.

Lunar Prosepector. Who in the general public even knew it existed? Yet dollar for dollar, it was probably the most cost effective Discovery mission ever flown.

Same thing with Mars Global Surveyor VS Mars Pathfinder. From a scientific standpoint, MGS is vastly more signifigant. Hell, even from an exploration "look at the pictures" standpoint I think MGS did more. Yet Mars Pathfinder got more internet hits over the first few days than had ever happened up to that point.

Try explaining to the average person the value of the gravity field mapping experiment on JUNO. We are talking about a measurment that might help nail down Gas Giant formation theory. That's pretty big from a pure science standpoint. But even if the person follows your explanation, I bet he puts it out of his mind five minutes later, never to care again.

But that same person probably remembers the Sojourner rover. People on the street really get, on a gut level, what a landing is. Exploration to most people means "being there". They can live vicariously through the exploits of Sojourner and MER. Lots of people know what Huygens was. Far fewer would remember that Cassini is still out there.

So yes, people were excited when we slammed into Temple 1. They felt like mankind reached out and touched something.

I vote for a strong Discovery program with the occasional Publicity Stunt mission. I think it helps pay the bills.
monitorlizard
A Deep Impact 2 probably won't be approved, but what about a Stardust 2? Getting samples from
a different type of comet ought to be worth the effort. The infrastructure for sample analysis
already exists, and sample return missions give you the most science for the buck IMO. Anybody
know if this is being considered for Discovery? Or does it make too much sense for NASA to go
for it?
BruceMoomaw
This is a real possibility -- especially if you jazz it up further: what about combining Stardust and CONTOUR to produce a comet-sampling mission that flies by several comets before returning to Earth (as a CONTOUR-type mission will do periodically anyway, in order to make gravity-asist flybys to set it up for its next comet encounter)? We already have the right spacecraft design -- the "Aladdin" concept for sampling Mars' moons, which twice became a Discovery finalist, used a conveyor-belt type aerogel strip to take separate samples from a total of five different flyby encounters.

The one problem is that most or all of these comet flybys would be at much higher speed than Stardust's flyby of Wild 2, thus damaging the dust particles -- that mission took so long only because of the careful sequence of maneuvers used to minimize its flyby speed at Wild 2 -- but the samples would still be scientifically useful, especially if taken from several comets for comparative purposes.
mars loon
Both the DI extended mission, nicknamed "DIXI", and the DI clone nicknamed "DeepR for Deep Rosetta" are absolutely worth doing and funding. DeepR would impact Comet 67P/Churyumov-Gerasimenko as the ESA Rosetta spacecraft watches nearby with a suite of 11 science instruments.

Contrary to some earlier posts, there are no currently approved NASA follow-on missions to comets, making these proposals as well as the Stardust extended mission even more crucial for cometary research.
Analyst
Not every mission is useful only because there are no other missions. Why do you need a flyby spacecraft and not only the impactor, if you have the Rosetta orbiter with 11 instruments watching? As for the extended missions: Both spacecraft have degraded cameras and only one or two other instruments. It is a matter of additional costs: 20 or 30 million are probably o.k., more is not.

Analyst
tedstryk
QUOTE (Analyst @ May 19 2006, 07:09 AM) *
Not every mission is useful only because there are no other missions. Why do you need a flyby spacecraft and not only the impactor, if you have the Rosetta orbiter with 11 instruments watching? As for the extended missions: Both spacecraft have degraded cameras and only one or two other instruments. It is a matter of additional costs: 20 or 30 million are probably o.k., more is not.

Analyst


Well, two angles are better than one. And the impactor will likely need a bus to get there anyway. And Rosetta has a great suite of instruments, but it is by no means comprehensive.
BruceMoomaw
Actually, Mars Loon was completely correct in pointing out something that I had stupidly overlooked: the value of a repeat of Deep Impact is massively increased if it produces a fresh crater that Rosetta can examine close up. The impact had better be carried out considerably before Rosetta's arrival, though, or the dust cloud thrown out by it is likely to be disastrous to Rosetta.
Bob Shaw
Why not use the Deep Impact bus as an impactor? Then Rosetta can look at the hole it makes... ...assuming that DI could make it at all to Rosetta's target, that is!

Bob Shaw
Comga
QUOTE (Bob Shaw @ May 20 2006, 10:50 AM) *
Why not use the Deep Impact bus as an impactor? Then Rosetta can look at the hole it makes... ...assuming that DI could make it at all to Rosetta's target, that is!

Bob Shaw



It can't. The orbit is all wrong. Also, I believe the targeting software was in the Impactor, which was designed to point its camera right at the target. Besides, while it is a sturdy and healthy craft, it would have to survive for another eight years for Rosetta to observe the impact.

Besides, a large fraction (50%?) of the science return was said to have come from the pre-impact images. The Flyby spacecraft can do this again, at Comet Boethin, and such an extended mission has been proposed.

I respectfully disagree with Bruce on impacting Comet C-G before Rosetta arrives. If they were really worried about the dust, they could always "hide" behind the nucleus. More likely, they would just sit back a good safe distance and still be able to see. It would be interesting to see an estimation of the dust flux as a function of distance, assuming this nucleus is as dusty as Tempel 1.
mars loon
QUOTE (Comga @ May 21 2006, 04:26 AM) *
It can't. The orbit is all wrong. Also, I believe the targeting software was in the Impactor, which was designed to point its camera right at the target. Besides, while it is a sturdy and healthy craft, it would have to survive for another eight years for Rosetta to observe the impact.

Besides, a large fraction (50%?) of the science return was said to have come from the pre-impact images. The Flyby spacecraft can do this again, at Comet Boethin, and such an extended mission has been proposed.

I respectfully disagree with Bruce on impacting Comet C-G before Rosetta arrives. If they were really worried about the dust, they could always "hide" behind the nucleus. More likely, they would just sit back a good safe distance and still be able to see. It would be interesting to see an estimation of the dust flux as a function of distance, assuming this nucleus is as dusty as Tempel 1.

Actually the back-up plan for Deep Impact was to use the flyby as an impactor on Comet Temple-1 if the impactor missed. The newly proposed "DIXI" extended mission plan, as i mentioned above, is to fly by Comet Boethin in 2008. A funding decison will be announced around September 2006.

Bob, as comga wrote, this DI cant fly to Comet 67P/Churyumov-Gerasimenko. A DI target burn to enable the Comet Boethin flyby has already been completed last July 2005 shortly after the July 4 impact.

Bruce, thanks for the complement above. I am glad we can agree on this new Discovery DI clone proposal to impact Comet 67P/Churyumov-Gerasimenko. In fact 2 teams have proposed this concept.

Analyst, the Deconvolution has achieved the full image resolution expected with the DI HRI and all the instruments are working perfectly.....

and tedstryks follow-up comments are right on target
Comga
QUOTE (mars loon @ May 21 2006, 07:02 AM) *
Actually the back-up plan for Deep Impact was to use the flyby as an impactor on Comet Temple-1 if the impactor missed.


I believe that may have been a contingency if the Impactor died early in the flight. By the time the Impactor hit or missed, it was well too late to retarget the Fly-by.

"I am glad we can agree on this new Discovery DI clone proposal to impact Comet 67P/Churyumov-Gerasimenko. In fact 2 teams have proposed this concept. "

I must be falling behind. Which two groups proposed this concept?

Impactor-only missons to Churumov-Gerasimenko have been discussed, but I don't know if anyone proposed it or will propose it.

"Analyst, the Deconvolution has achieved the full image resolution expected with the DI HRI and all the instruments are working perfectly..... "

Yes, indeed. There is a heck of a difference between the Stardust Nav-Cam and the Deep Impact High Resolution Instrument, which met its resolution and SNR requirements after deconvolution. Not to mention the IR spectrometer and the filter wheels AND the Medium Resolution Instrument, which alone is more powerful than the Nav Cam.
BruceMoomaw
QUOTE (Comga @ May 21 2006, 10:12 PM) *
I believe that may have been a contingency if the Impactor died early in the flight. By the time the Impactor hit or missed, it was well too late to retarget the Fly-by.

"I am glad we can agree on this new Discovery DI clone proposal to impact Comet 67P/Churyumov-Gerasimenko. In fact 2 teams have proposed this concept. "

I must be falling behind. Which two groups proposed this concept?

Impactor-only missons to Churumov-Gerasimenko have been discussed, but I don't know if anyone proposed it or will propose it.

"Analyst, the Deconvolution has achieved the full image resolution expected with the DI HRI and all the instruments are working perfectly..... "

Yes, indeed. There is a heck of a difference between the Stardust Nav-Cam and the Deep Impact High Resolution Instrument, which met its resolution and SNR requirements after deconvolution. Not to mention the IR spectrometer and the filter wheels AND the Medium Resolution Instrument, which alone is more powerful than the Nav Cam.



(1) The plan to hit Tempel 1 with the main craft was indeed an emergency expedient to be carried out if the Impactor failed to pass its functioning tests before release.

(2) I'm very far from saying that a repeat of DI should be the next Discovery selection -- I'm just saying that it would be considerably more scientifically useful than I initially thought. If I had to make a guess as to the two front-runners for the next Discovery selection, I should say a CONTOUR repeat (maybe jazzed-up with a different spacecraft), or the U. of Arkansas' "Hera" scheme for a large-scale sample return from 3 different near-Earth asteroids.

(3) Even with deconvolution, the resolution on Deep Impact's HRI was only about half as good as had been planned -- although this still made it far better than the MRI, let alone the Stardust camera (which had some troubles of its own, since they were never able to completely clean all the early contamination off its optics).
djellison
QUOTE (BruceMoomaw @ May 22 2006, 03:46 AM) *
I'm just saying that it would be considerably more scientifically useful than I initially thought. I


ohmy.gif You were all OVER the selection of DI after the mission was done, saying that the science return was poor because they said that seing the crater was the important part of the science and everyone should have known it would have been obscured by ejecta.

Why the change of tune?

Doug
BruceMoomaw
Because, my dear Douglas, in this case we have another spacecraft hanging around to take a good close (in fact, VERY close) look at the impact crater after the new DI leaves -- which we didn't have last time. No doubt, if this second mission is flown, the new DI main spacecraft won't be able to get a good look (or ANY look) at its impact crater, any more than the first one was (although that was its most important scientific goal) -- but Rosetta will be able to examine it in exquisite detail. It might even be able to touch down its lander on the nearby ejecta blanket.

I don't know if this is enough to justify picking this mission as a Discovery selection, but it certainly greatly strengthens the case for it compared to the first DI.
Comga
QUOTE (BruceMoomaw @ May 22 2006, 07:51 PM) *
Rosetta will be able to examine it (the crater) in exquisite detail. It might even be able to touch down its lander on the nearby ejecta blanket.


Only if the Europeans become so interested in the manmade crater that they change their plans. The Philae lander is scheduled to be deployed well before an impact is feasible. However, after seeing what JAXA did with Hayabusa, Rosetta itself should be able to get close enough to examint it, as you say, exquisite detail.

Anyone care to estimate the limiting resolution of the Rosetta instruments and the standoff distance for that resolution? (Actually, if Rosetta were to get too close, one could push the resolution and recover some of the defocus blur through deconvolution. Ironic isn't it?)
djellison
Is NASA HQ is really going to select a mission from which the bulk of the science is done by a foreign spacecraft with foreign instruments and foreign PI's? I'm sure there's plenty of US involvement within Rosetta - but I can't see the cheque-writers going for it in any way.

Furthermore - the ejecta would surely be a big risk for Rosetta, look at the HST images from the first DI, and any damage caused would of course have been entirely predictable and obvious eh Bruce. smile.gif

Doug
BruceMoomaw
Once again, the latter would depend (as "Comga" points out) on whether Rosetta was at a safe distance from Comet C-G during the impact itself, and closed in for the closeup view only after the coast had (literally) cleared.

I'll agree that the odds are against the selection of this mission -- and one reason (connected with what you said) is that, for proper science return, it depends on the success of two spacecraft, both of them carrying out complex assignments. Still, it can't be ruled out completely -- especially because it would utilize an virtually exact copy of a spacecraft design which we already know works.
edstrick
Rosetta could well stand off from the comet several thousand kilometers to watch an impact from safe distance.

Also..... Note that impact ejecta would hit a station-keeping spacecraft at zero-relative-velocity-plus-ejection-velocity. Fine dust ejecta might be travelling (armwaving guess here) a kilometer per second, while coarse ejecta would be travelling much slower, much of it not escaping the comet at all.
ugordan
Plus, at several hundred km distance, the impact ejecta would probably be very diluted and would not pose any real hazard to the S/C. Even a kilometer per second sounds to be on the high side here, I wonder if fluffy, dusty and compressible material would readily reach supersonic velocities like those.
djellison
Massive solar arrays, lots of delicate instruments....if I was a PI on Rosetta, I'd be astonishingly wary of doing this at all. Even if the threat of a damaging impact because of a low impact speed isn't too bad - the potential to contaminate solar arrays and instruments remains high..even with near zero relative velocity.,

Maybe an impactor done a few months before arrival....but certainly nothing once it's arrived

Consider the HST images - that ejecta ended up covering a VAST area around the previous DI impact.

I would be astonished if the Rosetta guys were happy with this, even more so if the mission were selected.

Doug
ugordan
How does the usual, sublimation-driven ejection velocity compare to an impact-driven velocity? Is it also on the order of cca. hundred m/s? That's not peanuts either, so there would be risk of damage/contamination anyway, if a much lower one.
Granted, I don't know how active and far away from the sun the comet will be during Rosetta's mission, but we're just waving arms here anyway.

As far as HST images, it's conceivable only a small part was ejected at high velocities due to the impact itself, the majority being explosive sublimation of volatile material underneath. Still, a snowstorm is a snowstorm...
Comga
QUOTE (djellison @ May 23 2006, 05:52 AM) *
Massive solar arrays, lots of delicate instruments....if I was a PI on Rosetta, I'd be astonishingly wary of doing this at all.

I would be astonished if the Rosetta guys were happy with this,.



Actually the PI on Deep Impact and the deputy PI on DeepR Mike A'Hearn of UMd *IS* a co-I on an instrument on Rosetta, ALICE. The PI on ALICE, is in support of the idea. Some members of the Rosetta team in Europe are in favor of it, while some are said to oppose it, but for other reasons than risk to their instruments.

The concept is to hit the comet very late in the Rosetta mission, close to EOM. Comet Churumov-Gerasimenko crosses the ecliptic close to perihelion, so it is easiest to hit then. Rosetta's mission is supposed to end around that time. They will already have spent almost a year surveying the comet and seen all the activity as it approaches the Sun.

Note that flying alongside a very small body like a comet nucleus, with insignificant gravity, you can't just let the spacecraft drift along. Unless actively controlled, it will drift away from the comet. Think about the maneuvers of JAXS's Hayabus at Itokawa. Therefore, they can't put Rosetta into hybernation and wake it up every few years and look at the comet. Once the mission is over, its over. Why be so risk adverse that you have a 99% probability or retiring a healthy, but very old, spacecraft? They could pick a vantage where the solar panels are at right angles to the dust ejecta and not worry about a little very very fine dust bouncing off your lenses and mirrors.
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