TDRS Satellites

I don't know if this is the right group to post this question to, but I'll
give it a try. Is there any way of knowing which two TDRS satellites are
being used at any given time for communications? I use STS Plus to track
satellites and the Space Shuttle, but have never known which two TDRS
satellites to select as the active ones--I just go with what was set in the
program originally. Any help will be appreciated.

Thanks,
Paul