[X] My Assistant

[Guest_BruceMoomaw_*]

Yeah, it is a worry -- they had a lot of trouble, even without the jet factor, in designing the Impactor's targeting software, since it must aim the Impactor not just for the center of the illuminated part of the nucleus, but for an area which isn't in any local shadow caused by terrain features. (Which helps explain why they couldn't just release the Impactor when the main craft was far away from the nucleus and let it fly -- although the distance at which the Impactor must be released is so far from the nucleus that it would be impossible to aim a passive Impactor for an impact with the tiny nucleus at that range anyway.)

This thing is a real gamble and always has been, even without the HRI problem. Its selection as a Discovery mission was something of a surprise, and I suspect that that choice was yet another of Dan Goldin's harebrained PR brainstorms -- big fireworks display on the 4th of July and all that.

[edstrick]

What is the phase angle on the approach to the comet. The simulatoins show a "gibbous" phase, maybe 70 degrees phase angle.

The dust plumes, as Giotto saw, (compared with the soviet VEGA images of Halley, and compared with Borelly and Stardust data at Wildt), are much brighter at high phase when backlit.

Some late afternoon, when the sun is maybe 20 degrees above the horizon, take a handfull of dusty dirt and throw it in the air between you and the sun. The dust is pretty bright. Now turn so the sun is behind you and repeat the experiment. Contrast between dust and the ground will be much lower.

Charcoal-black rough surfaces like a comet's nucleus show very strong phase angle effects. Looking upsun, you see mostly black shadows and surfaces that are on the average tilted away from the sun and not well illuminated. And since the surface is black, both macroscopic shadows, and the non-illuminated side of even microscropic dust grains will be nearly black, without bounce light adding much indirect illumination.

Having the impactor aim for a dust jet is possible, but it's probably less likely than some really unanticipated software or hardware glitch.

[Guest_BruceMoomaw_*]

It now seems that fdeep Impact's second destination is likely to be Comet Boethin:
http://www.space.com/businesstechnology/05...act_beyond.html

This is a change from what I was told by A'Hearn two years ago, which was
that the leading second destination was Comet Finlay.

Also note the latest conveniently vague comment on how well deconvolution
may correct the HRI problem: "[Ball Aerospace official] Henderson said
through this process, Deep Impact's picture taking can be 'massaged and
tweake' on the ground to greatly overcome the out-of-focus problem."

"Greatly overcome" it? Still nothing said lately on what kind of resolution
they're actually hoping for.

[dilo]

MRI gallery of last week images:

And a false color version to enhance both nucleus and faint coma (based on images I suspect a spacecraft orientation change after Jun,29):

[SFJCody]

It now seems that fdeep Impact's second destination is likely to be Comet Boethin:
http://www.space.com/businesstechnology/05...act_beyond.html

This is a change from what I was told by A'Hearn two years ago, which was
that the leading second destination was Comet Finlay.

Comet Boethin was also considered as a target for a CONTOUR extended mission. Is there any word yet on the possibility of retargeting Stardust after 2006?

[Guest_BruceMoomaw_*]

Unfortunately, I was told a couple of years ago by Don Brownlee that there is no chance of an extended mission for Stardust, because it simply won't have enough attitude-control and maneuvering fuel to make it worthwhile.

[SFJCody]

Unfortunately, I was told a couple of years ago by Don Brownlee that there is no chance of an extended mission for Stardust, because it simply won't have enough attitude-control and maneuvering fuel to make it worthwhile.

That's a pity. Do we know the targets of opportunity for Dawn yet?

[Guest_Sunspot_*]

JPL and the Deep Impact site have a link for viewing "near realtime mages" They're only thumbnails though

[edstrick]

I continue to be somewhat astonished by Stardust not having enough "consumables" for an extended mission.

I keep wondering if they used propellants at a higher than expected rate during the mission, or during design cut the supply margin too close for real comfort...?

[djellison]

Well - the difference between having a sensible margin, and having enough for an extended mission - is not inconsiderable

Doug

[edstrick]

We've lost missions, recent example being DART, which had a "reasonable" excess of propellant, and used it all up and failed.

Deep Impact's going to have <I think> do it all on it's own to retarget to an extended mission target.

Stardust releases the return capsule and then can do a deflection maneuver to do a range of earth swingby's, rather like Contour was going to do, giving a gravity assist magnified delta-V capability to retarget for an extended mission.

I'd like details I don't have on Stardust's performance.

[Guest_BruceMoomaw_*]

Brownlee told me they had taken into account the possibilities of an Earth gravity-assist flyby to retarget Stardust -- there was simply no way, even then, to maintain its maneuvering and attitude fuel supply long enough for another target.

[edstrick]

I'm wondering what the magnitude of the burn to deflect from the earth-impacting capsule release trajectory to a flyby trajectory is. While atmosphere entry doesn't have the same G limits Apollo astronauts had, it's not a vertical descent. But it could still be a very considerable deflection maneuver that would use almost the entire remaining propellant supply. Potentially considerably larger than Deep Impact's deflection burn.

Not every mission can get extended. Mariner 2 fried and died some 10 days or 2 weeks after Venus flyby.

Mariner 4 made it once around and got back into radio contact for some months of interplanetary weather study before attitude control gas ran out. Mariner 5 was flying at the same time, but when it came around and back into antenna range, it wasn't there. They FINALLY found it, way off frequency and wandering in frequency, carrier wave only, varying in amplitude with a slow spacecraft roll. They got it eventually to lock on to an uplink, but it was a "mindless reflex". Signal strength and behavior provided no indication it ever responded to any uplinked command. Nowdays, I'd call it a Persistant Vegetative State. They wanted simultaneous deep space solar wind observations with Mariner 4 but never got it.

Mariner 6 and 7 had brief extended missions as they flew out into the inner fringe of the asteroid belt. They'd been launched on fast-trajectory Mars flybys and had extra encounter speed and got a mild gravity assist from Mars during the flyby. The did engineering tests, post encounter and fired the midcourse engines a second time and watched the exhaust cloud's spectra with the short wave channel on the infrared spectrometers. No interplanetary science instruments onboard, so they couldn't do much else.

[abalone]

I'm wondering what the magnitude of the burn to deflect from the earth-impacting capsule release trajectory to a flyby trajectory is.

It all depends on how far out it's done and that depends on the battery life of the entry capsule. Far enough out and a small burn will do it. The difficult part is getting it on to a trajectory that will make it intercept another target.

[djellison]

And you dont want to do it too early - because you have no control of the entry capsule after you deploy it, so you want to be attached to the thing that can adjust your trajectory essentially until the last possible moment

PS - I dont think it's worth making a deep impact forum on its own - but i'll start a new threads after the 1800UT press conf (3:15 from now)

Doug