In accordance with NASA Management Instruction (HQMI 6810.1B), we provide the enclosed MOR for the mid-January 1993 TDRS launch on the Space Shuttle (STS-54). At least two full capability TDRS s are required, one over the Atlantic Ocean and the other over the Pacific to meet the minimum requirements of the TDRS- dependent missions now operating in space. In addition, a third orbiting TDRS is required in a "ready reserve" status. Without this reserve capacity, should either of the-two operating satellites fail, up to 50 percent of each TDRS-dependent mission s communications requirements could not be satisfied for at least a year while waiting for another full capacity satellite to be launched and activated. The concept of a minimum constellation of three full capability spacecraft remains as valid today as at its conception over two decades ago. Of those now in space, only TDRS-4 and -5 can provide the complete range of customer-required capabilities. While TDRS-5 enjoys redundancy in all of its systems, TDRS-4 has lost some primary bus system redundancy. Should similar l DRS-4 failures occur, it could be rendered totally inoperable. The two other on- orbit spacecraft, TDRS-1 and -3, have both suffered numerous subsystem failures. Neither can replace TDRS-4 or -5. We could have risked the consequences of in-space TDRS failures by delaying the launch of the sixth TDRS. But, our own studies and the experience of similar programs conclude that maintaining reserve capacity on the ground is neither technically prudent nor cost effective. Once in orbit, the spacecraft is less susceptible to damage, less expensive to maintain and its useful life is undiminished as compared to storage on the ground. More importantly, an additional full capability TDRS is needed in orbit now to protect the tens of billions of dollars in space missions that are TDRS-dependent for mission success.
Mission Operations Report (MOR) for the Sixth Tracking and Data Relay Satellite (TDRS)
1992
28 pages
Report
No indication
English