[X] My Assistant

[John M. Dollan]

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...

[Guest_BruceMoomaw_*]

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.

[Guest_AlexBlackwell_*]

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.

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

[ugordan]

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

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

[Guest_AlexBlackwell_*]

That would only work if the spacecraft was reaction wheel stabilized.

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

[ugordan]

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

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?

[Guest_AlexBlackwell_*]

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.

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.

[ugordan]

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.

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.

[Guest_AlexBlackwell_*]

However, any attitude maneuvers during the measurement will likely destroy any gravitational effect, especially if a small target body is concerned.

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

[Guest_AlexBlackwell_*]

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

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.

[ugordan]

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.

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.