[X] My Assistant

[djellison]

Massive solar arrays, lots of delicate instruments....if I was a PI on Rosetta, I'd be astonishingly wary of doing this at all. Even if the threat of a damaging impact because of a low impact speed isn't too bad - the potential to contaminate solar arrays and instruments remains high..even with near zero relative velocity.,

Maybe an impactor done a few months before arrival....but certainly nothing once it's arrived

Consider the HST images - that ejecta ended up covering a VAST area around the previous DI impact.

I would be astonished if the Rosetta guys were happy with this, even more so if the mission were selected.

Doug

[ugordan]

How does the usual, sublimation-driven ejection velocity compare to an impact-driven velocity? Is it also on the order of cca. hundred m/s? That's not peanuts either, so there would be risk of damage/contamination anyway, if a much lower one.
Granted, I don't know how active and far away from the sun the comet will be during Rosetta's mission, but we're just waving arms here anyway.

As far as HST images, it's conceivable only a small part was ejected at high velocities due to the impact itself, the majority being explosive sublimation of volatile material underneath. Still, a snowstorm is a snowstorm...

[Comga]

Massive solar arrays, lots of delicate instruments....if I was a PI on Rosetta, I'd be astonishingly wary of doing this at all.

I would be astonished if the Rosetta guys were happy with this,.

Actually the PI on Deep Impact and the deputy PI on DeepR Mike A'Hearn of UMd *IS* a co-I on an instrument on Rosetta, ALICE. The PI on ALICE, is in support of the idea. Some members of the Rosetta team in Europe are in favor of it, while some are said to oppose it, but for other reasons than risk to their instruments.

The concept is to hit the comet very late in the Rosetta mission, close to EOM. Comet Churumov-Gerasimenko crosses the ecliptic close to perihelion, so it is easiest to hit then. Rosetta's mission is supposed to end around that time. They will already have spent almost a year surveying the comet and seen all the activity as it approaches the Sun.

Note that flying alongside a very small body like a comet nucleus, with insignificant gravity, you can't just let the spacecraft drift along. Unless actively controlled, it will drift away from the comet. Think about the maneuvers of JAXS's Hayabus at Itokawa. Therefore, they can't put Rosetta into hybernation and wake it up every few years and look at the comet. Once the mission is over, its over. Why be so risk adverse that you have a 99% probability or retiring a healthy, but very old, spacecraft? They could pick a vantage where the solar panels are at right angles to the dust ejecta and not worry about a little very very fine dust bouncing off your lenses and mirrors.