Hayabusa - The Return To Earth, The voyage home Options

[odave]

...starting a new thread for Hayabusa's sampling feedback and the return voyage.

After its nail-biting success in November, will there be enough fuel for the Falcon to make it home?

[edstrick]

Holder of the Two Leashes:
"...One other thing I don't understand, though, is what your whole point is. ..."

I guess my points is that NEAR was the first of the Smaller, Cheaper, Faster, Better missions, but there is an ongoing debate on whether it was even good enough to accomplish what I thought was it's primary mission objective: determining whether S-type asteroids are or are not the parent bodies of ordinary chondrite meteorites. While the indications of a space-weathering modified surface were at least somewhat expected to cause potential problems in linking the two, the mission that was flown carried instruments that simply did not have the signal-to-noise ratio AND the resolution to clearly sort out what appear to be end-members of the weathering sequence. It was good, but like Boris, it wasn't good-enough.

Where NEAR really shined is in photo-geology, where it mostly made up for it's dinky camera with scads and scads of images that can be mosaiced into global coverage, and revolutionized our understanding of geologic processes on asteroids.

[JRehling]

Both missions were successful. Note that they were quite different operationally in that NEAR orbited Eros, while Hayabusa more or less "escorted" Itokawa, and so far as I have seen, ended up with mainly high phase angle images. Of course, this was part of the mission design.

I would think that in retrospect, one might try to emulate NEAR again staying rather close to the mission's goals/money ratio, whereas Hayabusa was a bit too far over the edge for a novel spacecraft... perhaps with legacy components a future mission could be as ambitious and as cheap, but clearly the mission had more than one failure to execute -- the blessing is that it suceeded in every way needed to produce good science. Was it by design or luck that the "optional" portions of the mission were the ones to fail? Contrast Nozomi, which had lots of systems operational, but the one that failed to execute meant no Mars encounter at all.

NEAR had the advantage of treating Eros like it was a planet, but alternately easier (since light thrusters could perform the manuevers) and harder (strange gravity field made it). Hayabusa had a different challenge, and one felt as though it was awkwardly dancing with the asteroid. We can divide future asteroid missions between those that can orbit their worlds and those that must undertake many, frequent propulsive manuevers to execute. Given speed-of-light time, an autonomous system that was foolproof in gracefully dancing with its target would be a tremendous accomplishment.

One accomplishment of Hayabusa was in showing us an entirely new kind of world, at the smallest-yet end of the spectrum, whereas Eros looks on the whole like Gaspra, and is not too different from Phobos, the first "small" world seen by spacecraft. In a sense, Hayabusa "finished" the size spectrum, because yet smaller "worlds" are likely to be boulder heaps like Hayabusa in every way but the reading on the tape measure -- Hayabusa is clearly at the point where gravity ceases to rework the "world" in any way except to hold it together and pool its dust.