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Posted by: John M. Dollan Jan 31 2006, 07:50 PM

Hi folks...

I read today that Stardust has been placed in hibernation, while in an orbit that reaches out substantially further than Mars. No mention was made regarding future plans.

I was curious... since the Dawn mission has been put on hold, is it possible that Stardust will be used to explore any bodies in the Belt?

...John...

Posted by: AlexBlackwell Jan 31 2006, 07:54 PM

Note that potential proposers for the Discovery 2006 and Missions of Opportunity AO are being http://discovery.larc.nasa.gov/dpl.html#libsec8 the option to propose uses for both Stardust and Deep Impact.

Posted by: John M. Dollan Jan 31 2006, 08:09 PM

Thanks much for the information!

...John...

Posted by: BruceMoomaw Jan 31 2006, 09:57 PM

I'm rather skeptical about an extended mission for Stardust. First, unless they can find another comet for it to fly by (as opposed to near-Earth asteroids), the only usable science instrument it has is a black and white camera. Second, it's much lower on remaining delta-V than Deep Impact is.

Posted by: djellison Jan 31 2006, 10:22 PM

The Stardust people seemed quite bold and confident when suggesting such a follow on. I agree - DI is more likely to get an extension that Stardust, but given it's shielding, Stardust could be sent on a fairly do-or-die flyby of another nucleus in a few years. No reason why they can't just hibernate the thing as they have now for 4, 5 years, and wake it up in the way they did for Giotto for another flyby. Even just an imaging sequence would be another set of images of a small body.

Doug

Posted by: tedstryk Feb 1 2006, 12:29 AM

As for instruments, that is simply not true. First, it has the Cometary and Interstellar Dust Analyzer (CIDA), a mass spectrometer, and it also has the Dust Flux Monitor Instrument (DFMI). On top of that, it is only a black and white camera due to the stuck filter wheel. I remember reading that they thought they could likely free it, but didn't want to risk it later getting stuck on a less favorable filter during the main flyby. But at this point, they could risk it.

Posted by: BruceMoomaw Feb 1 2006, 07:23 AM

Well, I specified "unless they can find another comet" -- in which case of course those other two instruments do become relevant. It's if they fly it by an asteroid (a lot easier to do, given the number of them) that only the camera would be of any use.

Posted by: tedstryk Feb 1 2006, 05:15 PM

Oops..missed that part

Posted by: AlexBlackwell Feb 1 2006, 05:24 PM

I would only add that the radio system could be used during a flyby (e.g., for mass determination and/or occultation science).

Posted by: ugordan Feb 1 2006, 07:32 PM

That would only work if the spacecraft was reaction wheel stabilized.
Does Stardust use reaction wheels or regular attitude thrusters?

Posted by: AlexBlackwell Feb 1 2006, 07:38 PM

Huh?? 3 axis-stabilized (and spin-stabilized) spacecraft have long carried out radio science experiments. Have you ever heard of, say, Voyager?

Posted by: ugordan Feb 1 2006, 07:45 PM

Yeah, but you're talking about radio occultations. Mass determination requires long periods of radio tracking WITHOUT any perturbations such as attitude thruster firings as they would trash the effect. Similar to the problem of measuring the Pioneer anomalous acceleration with the Voyagers - impossible.
Granted, I forgot about spin-stabilized craft, but Stardust isn't one such craft, is it?

Posted by: AlexBlackwell Feb 1 2006, 07:52 PM

I ain't talkin' about "the Pioneer anomalous acceleration"; I'm talking about standard flyby mass determinations which, by definition, are not "long periods." Are you aware that 3-axis and spin-stabilized spacecraft have routinely done this over the decades? For example, Galileo (Galileans), Viking (Phobos/Deimos), etc.

Posted by: ugordan Feb 1 2006, 08:12 PM

I'm aware Galileo did mass determinations of either/both Gaspra and Ida, but it was spin stabilized craft. As for the Vikings, I'm not aware of the extent of their measurements, but a couple of hours of tracking data before and after the flyby might have probably done the trick.
However, any attitude maneuvers during the measurement will likely destroy any gravitational effect, especially if a small target body is concerned.
Another thing, determining a comet's mass might prove to be a bigger problem than that. Cometary particles impacting the S/C would also trash the the effect of the body's gravity.

Posted by: AlexBlackwell Feb 1 2006, 08:53 PM

Which is precisely why attitude maneuvers are not planned when acquiring gravity data, regardless of spacecraft type.

Posted by: ugordan Feb 1 2006, 09:59 PM

Correct me if I'm wrong, but Stardust doesn't have a scan platform. Meaning that if one wanted to actually image the comet nucleus during the flyby, one would have to constantly track and retarget the pointing after each dust impact. Hence the velocity perturbation.
I just don't see how the requests for mass determination and optical imaging can be reconciled. And that's ignoring the dust hits themselves.

Posted by: AlexBlackwell Feb 1 2006, 10:00 PM

Maybe we should clarify things a bit. Attitude maneuvers can happen during precise radio tracking, as long as the spacecraft rolls about the antenna boresight to Earth. In this instance, the spacecraft is spin-stabilized and remains Earth-pointed. On the hand, as you allude to, propulsive, delta-V maneuvers are not desirable.

Posted by: ugordan Feb 1 2006, 10:03 PM

Yes, but even in this case the thrust vectors from the thrusters aren't perfectly aligned in on the three axes. While such small uncertainties can be dismissed when measuring the mass of, say, Europa, a small cometary nucleus already has a very weak effect and it would really be desirable if NO maneuvers occured.