On 8/7/2011 9:44 AM, Giulio P. AOL wrote:

what could be the critical height (closest to the earth) for the satellite, where the temperatures will degrade the operation?

By the time we see significant heating, we only have 10's of hours left in orbit. Take a look at the temperatures of RAFT on:

http://www.usna.edu/Users/aero/bruninga/craft/save-raft.html

You can't really see a clear temperature rise until about 2 days before reentry.

-Joe KM1P