There is a lot that the two missions you mentioned--Stardust and Hayabusa--have taught us about sample return.
- Sample Contamination: Serious measures were taken with Stardust to control for the possibility of sample contamination, but notable problems were still encountered:
However, despite these precautions the
Stardust spacecraft outgassing was sufficient to degrade
camera operations, and the aerogel capture media
was significantly contaminated during manufacture.
We also never completely solved the problem of
defining useful limits for organic contaminants of
spacecraft hardware, which haunts us as we rather unexpectedly
captured primitive cometary organics.
Landing Conditions and Sample Recovery: The landing site for Stardust in the Utah Test and Training Range was unexpectedly wet and the lack of a canister seal for the samples became an issue.
Sample Curation: The necessary preparations for managing the returned sample take a long time--longer than expected:
More than two full years
were required to prepare curation facilities for Stardust.
Despite this seemingly adequate lead time, major
changes to curation procedures were required once the
actual state of the returned samples became apparent.
Two years of Curation preparation are insufficient.
The Stardust sample database was not fully implemented
before sample return –we did not adequately
think through all of the possible sub-sampling and
analytical activities before settling on a database design.
Remote storage of a sample subset is critical, for
Stardust the remote samples are in a vault in New
- Unknown Surface Conditions: Hayabusa had to be designed without knowing what the surface of its target was like:
We didn't know what Itokawa's surface would be like before the spacecraft actually arrived there. Indeed, the assignment given to us was quite broad. We were to build a device that, no matter what the surface was like, would grab samples, ranging from monolithic bedrocks to powdery regolith, in the brief instant of each of the spacecrfat's [sic] touchdowns.
- Touchdown Time: Hayabusa had to ascend immediately after touchdown, forcing the retrieval to occur quickly:
Because the sampler horn is attached to the edge of the spacecraft, if the horn were to contact the surface of the asteroid for too long, the spacecraft would start tumbling on its center of mass. In other words, if the spacecraft did not ascend right after the touchdown, it would lose its balance and fall on its rear. Thus samples would have to be collected in less than one second, by firing a bullet at a speed of 300 meters per second.