The on-orbit TDRS network was rearranged and included two fully operational spacecraft occupying the TDRS East and West slots, one on-orbit fully functional spare, TDRS-1, which was nearly depleted having exceeded its planned lifetime, and the partially operational TDRS-3 spacecraft dedicated to supporting the Compton Gamma Ray Observatory and providing coverage an area that can't be seen by the other satellites known as the Zone of Exclusion.