[X] My Assistant

[edstrick]

Bruce Moomaw: ...." there are variations on it in the "Hera" and "Hummingbird" proposals for collecting surface material from a near-Earth asteroid and a comet nucleus, although they use a sticky pad or a short high-speed drill instead, to obtain bigger samples.) "

On one of the later Apollo missions, they took a special lunar sample with a special single-use instrument: They had a handle and something like a piece of velvet free-floating in a wire frame but attached at the edges. They pressed it flat against a flat spot of undisturbed regolith so that the very uppermost grains of soil would be caught by the fibers in the velvet. Then they detached the velvet from the frame, rolled it up on a rod or pin (probably pre-attached to the side of the fabric) and stuffed it neatly in a tube and capped the tube.

I never heard any results of analysis or inspection of the sample and have wondered if it's still in the sample tube somewhere in the bowls of the lunar sample storage facility, lost like the ark in "Raiders"

[Guest_BruceMoomaw_*]

That was either Apollo 16 or 17, and I have a very faint and possibly false memory that they DID analyze it. The sticky pads on the proposed "Hera" (which I think may well be picked as the next Discovery mission) would be coated with 1 cm of silicone grease to pick up a much bigger sample -- about 100 grams from each of nine sites on three different near-Earth asteroids:
http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1032.pdf
http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1047.pdf
http://www.lpi.usra.edu/meetings/lpsc2004/pdf/1716.pdf
http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1452.pdf
http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1464.pdf



Meanwhile, there are some excellent descriptions of the Hayabusa mission at http://www.lpi.usra.edu/meetings/lpsc2004/pdf/1521.pdf and http://www.lpi.usra.edu/meetings/lpsc2004/pdf/2161.pdf -- including a description of the curation procedures for the returned samples. And there are detailed descriptions of the Minerva hopper at http://www.lpi.usra.edu/meetings/lpsc2004/pdf/1517.pdf and http://www.lpi.usra.edu/meetings/lpsc2005/pdf/2289.pdf .

Finally, http://www.lpi.usra.edu/meetings/lpsc2004/pdf/2058.pdf notes that Earth-based studies already suggested that there might be something unusual about Itokawa's surface. While its color curve resembles that of a standard S-type asteroid, its albedo is distinctly higher -- and it is a less diffuse scatterer, suggesting to me that it may indeed have a rocky surface mostly bare of ejecta (which would mesh nicely with the lack of craters, both suggesting that it may be a fragment quite recently broken off a bigger asteroid). However, the little Q-type asteroids, whose spectra resemble ordinary-chondrite meteorites and which are also believed to be relatively fresh pieces broken off bigger asteroids and so exposed to little "space weathering" (which would give them an S-type coloring), are a distinctly different color. Tune in for our next exciting chapter...

[dvandorn]

I never heard any results of analysis or inspection of the sample and have wondered if it's still in the sample tube somewhere in the bowls of the lunar sample storage facility, lost like the ark in "Raiders"

NASA has top men working on it...



I only have one other thing to add to this -- the sampler was indeed flown on Apollo 16, and the description of the sampling process that Young and Duke gave during the EVA was that only one corner of the velvet actually touched the surface, because the surface was very uneven, even at small scales.

So, they did get a sample and it was returned, but it covered less than a quarter of the collector cloth. I *seem* to recall a description of the time the very top layer of the regolith at that location had been in place, based on this sample, but I'd be at a loss to tell you where I might have read that, or when.

-the other Doug

[RNeuhaus]

I have the curiosity about the long distance iwhere Hayabusa remains as gateway at 20 km from Itokawa. Why it so far instead of closer distance? I have many suppositions; these are:

1) Better control for approaching with long time for adjusting the propulsion.
2) Better picture focus according to the camera photography.
3) Outside of Itokawa gravity's attraction.

Any comments?

Rodolfo

[djellison]

It'll take less fuel to hover at 20km that it would at say, 5km

Doug

[volcanopele]

Nothing special, but I made an animated gif out of their rotation sequence:

http://pirlwww.lpl.arizona.edu/~perry/images/Itokawa.gif

[Bob Shaw]

Nothing special, but I made an animated gif out of their rotation sequence:

http://pirlwww.lpl.arizona.edu/~perry/images/Itokawa.gif

Some of those sticky-out-bits (a technical term, I'm sure!) really *do* stick out! The closeups will be great...

...I hope!

[RNeuhaus]

It'll take less fuel to hover at 20km that it would at say, 5km

Doug

Less fuel with greater distance?

At 5 km from Itokawa, Hayabusa will need to adjust its position from Itokawa more often due to the gravity attraction or not?

Rodolfo

[JRehling]

At any rate, we still are not seeing any major craters whatsoever, but we're
seeing what looks like a VERY rough, textured surface.

Remember, the skinniest dimensions of Itokawa are only about 250 meters -- half a pixel in ISS's best images of Titan! It's about 1/50th the size of Eros! It's tiny.

Look at the limb of Itokawa in the JAXA releases and think of the horizon in snapshots Apollo astronauts took on the Moon -- those are similar scales. You don't see many craters on the near-horizon of the Apollo photos, either.

I'm not sure if a world Itokawa's size *can* show much in the way of craters. It may be in that all asteroids this small will have surfaces completely flattened by to saturation, like a World War I battlefield.

[djellison]

At 5 km from Itokawa, Hayabusa will need to adjust its position from Itokawa more often due to the gravity attraction or not?

I think it would take more fuel to maintain a station keeping posititon at 5km, because gravity decreases with r^2 - so going to 5km would increase the gravitational attraction ( however small ) by 8x

I'm sure they'll do lots of observations from closer in - but it's like a field geologist. Find high ground and look around first...THEN tackle the target.

Doug

[abalone]

I think it would take more fuel to maintain a station keeping posititon at 5km, because gravity decreases with r^2 - so going to 5km would increase the gravitational attraction ( however small ) by 8x

If you are comparing 20km to 5km , its 16X the force for 1/4 of the distance.

[djellison]

Opps - yup - it's GM1M2/r^2 - I knew that, just didnt have my maths hat on before breakfast

If I was feeling brave - I'd calculate the actual gravitational attraction between asteroind and spacecraft.

Doug

[Bob Shaw]

Opps - yup - it's GM1M2/r^2  - I knew that, just didnt have my maths hat on before breakfast

If I was feeling brave - I'd calculate the actual gravitational attraction between asteroind and spacecraft.

Doug

Doug:

It's just over .005 of a Tad (3/8 of a Smidgeon in Old Money).

Bob Shaw

[abalone]

The force is so pathetically small whether you are at 5km or 20km I wonder if this is really the reason or is it simply a convenient staging distance to gather visual info without the danger of some small error sending it smashing into it. If they go too close too soon the camera is not capable of taking full global images ( if that is not an overstatement for this small gravel patch in space)

[RNeuhaus]

Doug, Hope that with a coffee drinking, the brain will work much better with maths.

It is very interesting to know the comments relating to the selection of the distance: 20 km from Itokawa. The gravity attraction between the space and the asteroide is almost nil at 5 km.

Maybe, the distance selection of 20 km, is due to approaching command control reasons. This large distance gives the electronic instruments to control better the feedback in order to adjust with very high precision the point of landing. On the other hand, the maneuver of approach to Itokawa does not rely to Earth control command unless the Hayabusa will perform its automatic control approach.

All at all, I think that the distance is somewhat exaggerated. but this approaching maneuver is the first ones of this kind. Hence Hayabusa might be taking this extra room (distance) in order to know better the interaction behaviour between the hardware and software of approach command and also give the spacecraft the needed time to adjust if anything goes wrong.

Rodolfo