Discovery Program 2006 and Missions Of Opportunity Options

[djellison]

Yup - we had that discussion a while back about star scanners being out of focus to produce a little ring of the star which is easier to identify with software than a sharp star and cosmic ray hits etc.

[monitorlizard]

Concerning the Discovery program selection this round, I remember (but can't find) an article where the head of Discovery said that, because there was no mission selected in the previous Announcement of Opportunity, the program had extra money and he would fight hard for two missions to be selected this time. However, it might be more realistic to expect one new mission and the Stardust and Deep Impact extensions to be funded.

All of this is dependent on the NASA manned program not raiding Discovery's extra funds, of course.

[Mariner9]

I remember that also. I'm fairly sure that was Andy Dantzler who said it, and he is now gone. It would be nice to see two Discovery missions selected (considering the 5 year gap since the last selection) but I'm not holding my breath.

Given the events of the last couple years, I just hope we still get the New Frontiers #3 AO in 2008. That program started out as an "every 3-4 years" and turned into "every 5 years" by the second mission. This does not bode well.

[ugordan]

we had that discussion a while back about star scanners being out of focus to produce a little ring of the star which is easier to identify

Actually, I was the one who suggested that in both cases so it should be taken with a grain of salt. I do, however, seem fairly certain I read that somewhere -- most likely a writeup on Cassini.

[Floyd]

There are some Cassini sky shots from Sept 30, 2006 where they seem to do long exposures with camera drift. It makes the real star track very different from the cosmic rays. Photo

I assume the streaked star images were intentional??

Floyd

[JRehling]

"...would return a sample of an enigmatic asteroid,..."

The <derogatory-scatalogical-term-deleted>-wits in the PR office were too stupid to indicate what asteroid or (equally important) what KIND of asteroid in the press release.

That's just how enigmatic it is.

[Comga]

Actually, I was the one who suggested that in both cases so it should be taken with a grain of salt. I do, however, seem fairly certain I read that somewhere -- most likely a writeup on Cassini.

Yes, indeed, star trackers and star cameras do blur the images of the stars. As you said, this does enable the system to find the "centroid" or center-of-gravity so to speak of the spot, to a small fraction of the pixel dimension.

Defocus is one way to do this blurring, and is definitely used on commercial products. Others have (and may still) use a camera that just doesn't form a good image, although the blur still has to be round (to a first approximation). Using focus requires very stable systems, so that the blur spot doesn't grow or shrink too much.

There are papers in the professional literature (AIAA proceedings for instance) on the software that determines orientation in space from an image of stars. Extremely clever programing, although some are even more clever than others.

[Phil Stooke]

For the comment by Dantzler about funding two missions if possible, check out post # 13 in this thread (page 1). The information came from Bruce Moomaw.

Phil

[Comga]

As for MOs, he (Dantzler) hinted that more than one might be picked -- in fact, he said that there may be more than one simultaneous MO picked associated with the Deep Impact extended mission! He made a vague reference to the possibility of "interplanetary observations" for one such Deep Impact MO, along with a comet flyby for another. But I have some trouble seeing what kind of interplanetary observations they could make with DI that would be worth the trouble -- ..

Well, now you know: EPOCh ! Exosolar Planet Observation & Characterization. Using the defocused 30cm telescope as a photometer and spectrophotometer for transits of very large exoplanets.

and from nprev and Phil Stooke:

..what does DI have that Hubble doesn't? Are we just talking availability here, or does DI's HRC have better resolution for such a task?"

The only thing Deep Impact can have that Hubble doesn't is time. It could stare at a transiting exoplanet for long periods, monitoring multiple eclipses - well, not stare presumably, but take lots of pics, or maybe do a deliberately blurred and offset image like Galileo with Comet SL9 - whereas Hubble time is far too valuable to deploy like that.
Phil

Generally correct. It can take long sequences of small images taken rapidly. In addition, the blur, while not originally intentional, would be a benfit here. It will spread the star light out so that the detector can use much longer exposures with much improved radiometry (Can Hubble be defocused significantly and was this done when they observed transits by HD 149026b?) The amount of blurring can be more important than the aperture for these measurements of bright stars. Plus Deep Impact was designed to take small images rapidly, which could be used to determine the time profile of the transits, which is important for determining size. It also has an imaging spectrometer that goes out to 4.8 microns.

Not only is Hubble's time too valuable to stare for days or weeks, but it gets interrupted by orbiting so close to the Earth, which blocks much of the sky for up to half of each orbit.

Note that DIXI (Deep Impact eXtended Investigation of comets), EPOCh, and the Stardust extended mission actually won only $250K for further studies. This surprised people. Weren't previous MoOs fully awarded at this point?

[Mariner9]

I haven't researched this, but I also thought that the MOs were just announced, and not awarded study money.

Still, 250K for study isn't all that much.... that's something on the order of 2-3 man years (or, I suppose, 5-10 grad-student years, since they pay those folk dirt).

[volcanopele]

Are EPOHc and DIXI (clever ) necessarily mutually exclusive? Is it possible both could be approved, with DI targeted to a new comet and "EPOHc" running during the "dead" time before and after the comet encounter?

[djellison]

That's what I was wondering - will an observation program during cruise consume fuel to a point that might leave little or no margin for the DIXI encounter?

Doug

[elakdawalla]

Generally correct. It can take long sequences of small images taken rapidly. In addition, the blur, while not originally intentional, would be a benfit here. It will spread the star light out so that the detector can use much longer exposures with much improved radiometry...

Comga's right here. I asked for an explanation from Drake Deming, the PI, and that's pretty much what he said; see the blog entry...
http://www.planetary.org/blog/article/00000756/

--Emily

[Comga]

Are EPOHc and DIXI (clever ) necessarily mutually exclusive? Is it possible both could be approved, with DI targeted to a new comet and "EPOHc" running during the "dead" time before and after the comet encounter?

Yes they are. EPOCh can observe practically any time. DIXI needs to target the spacecraft for Earth fly-by and then observe Comet Boethin for a few months. Having already done the bulk of the retargeting just after the flyby of Tempel 1, there is not that much velocity change needed for DIXI, and EPOCh shouln't take much propellant at all. Other than that, as long as nothing wears out, they don't interfere with each other, and the two should cost less than the sum of the separate programs. You only have to wake up and check out the spacecraft once. The spacecraft was healthy last time it was contacted.

[stevesliva]

Yes they are.

Don't you mean, no they're not mutually exclusive?