The Devil's Advocate

How does is it feel to have your satellite in space? Please let us know your feelings and anecdotes! YES2 has been orbiting Earth with Foton over 30 times now. Since we are switched off, we are not absolutely sure what is the status of YES2. But it will be tough in vacuum and cold of space! For several years now my task has been to go over the design again and again, imagine the mission and everything that could possibly go wrong. Probably I have overlooked things, but almost all my doubts have been resolved in the preparations and tests that led up to launch. We definitely launched a well-tested system with tether deployment system in excellent state and ready to succeed, and this is great, because I felt very happy to see YES2 lift off in to space: we have done all we could possibly do to secure its success. Yet I say almost, because there are a few things that keep haunting me these days - but the satellite is out of reach and I can only think not act!

I wake up in the morning early because I imagine the YES2 computer to be in extreme cold. Foton is in a random attitude, and if we are unlucky, YES2 will not see any Sun at all, and could get extremely cold. The YES2 on-board computer (OBC) was not originally designed to deal with extreme cold, as it was meant to be placed inside the thermally controlled Foton capsule. After it was moved to the vacuum of space, to reduce interfacing issues with the Russian collegues, -this was July 2004, after the PDR-, we still had in the thermal design a good thermal link with the Foton battery pack, which was supposed to keep us warm. Only in February 2006 it was decided that this thermal link was to be removed, in order to make Foton independent from YES2. At this time we had to redo our thermal analysis and a lot of MLI, a heater and a thermostat was added to YES2. To make things worse, early this year the OBC did not pass the thermal test of the expected temperatures in the new situation. It can only be switched on if it is warmer than about -15 C. In most simulations cases we have done, we should be ok, but not in the most extreme and unlikely ones, that are still possible. So this is what we are focussing on right now: to find out if we are warm or cold, based on attitude data we get from the DIMAC experiment tomorrow.

The second thing I see in my dreams is the safety system we implemented recently going off even in nominal case, i.e. cutting the tether for security reasons even if all is well. There is a passive and an autonomous safety system on-board protecting the Foton satellite from being wrapped in the tether in case of a tether jam. If it is triggered, the tether is released to end the mission safely. But the problem is that the most unlikely failure cases are difficult to distinguish from the most unlikely -but still acceptable- nominal cases. Better to be on the safe side, so for such extreme cases of doubt we have to assume failure and make the system release the tether. But it would be a shame to lose the mission this way...

Well, these are my bad dreams,  and others may have their own, I hope they are and remain only dreams. We worked hard to make such failures improbable and left the satellite with confidence, so why worry? Can't wait to switch on YES2 and get going for real.