
I don't think a reboost exercise is analogous to a shuttle landing/launch
in terms of stresses/misalignments/etc.  I would think of the reboost as
a gentile push, where a landing, then launch as two JOLTS which would
put more mechanical stress on the instruments.  Additionally, there might
be a concern about landing loads to the shuttle in the event of a laden
landing.  Finally, probably some thought went into possible contamination 
problems if the instruments came back to earth.

Of course, the cost of two shuttle launches _is_ a good reason to avoid
something that might be done in one shuttle launch.  Here's hoping
Cepi's gang gets the job done right the first time.