The Shuttle Projects Information Frontier (SPIF) Telemetry and Command Processor (TAC) is a personal-computer-based data-handling system that serves as part of an interface for transfer of data between Johnson Space Center and Goddard Space Flight Center (see figure). The data in question pertain to and/or are acquired by payloads that are carried, launched, deployed, repaired, retrieved, or returned by the Space Shuttle Program.

The SPIF TAC receives and transmits NASA communications (NASCOM) blocks encapsulated in user datagram protocol (UDP) packets. The SPIF TAC receives payload data interleaver (PDI), calibrated ancillary system (CAS), and command acceptance pattern (CAP) data from the mission control center (MCC) at Johnson Space Center and performs limited processing before passing the data to the advanced carrier customer equipment support system (ACCESS) in the Attached Shuttle Payloads Center (ASPC) at Goddard Space Flight Center. In turn, the ACCESS sends commands to the SPIF TAC for validation before transmission to the MCC. Should errors arise in the commands, the command response block (CRB) is returned to the ACCESS.

The SPIF TAC performs limited processing of data that it transmits between Johnson Space Center and Goddard Space Flight Center. (CMD is command and PTP is programmable telemetry processor.)

The SPIF TAC supplants an older system called the "SPIF RS" (RS meaning replacement system). It became necessary to replace the SPIF RS with the SPIF TAC because the SPIF RS will not be able to function after the beginning of the year 2000 and cannot handle the transition to NASCOM Internet Protocol (IP). Because of considerations of cost and schedule, it was decided to design a new system (the SPIF TAC) rather than modify the SPIF RS.

UNIX workstations in the SPIF RS were replaced with relatively inexpensive, low-maintenance desktop personal computers in the SPIF TAC. The software for the SPIF TAC was developed by use of Microsoft Visual C++ 5.0. Because of this use of commercial off-the-shelf software, the total cost of development was one-tenth of the cost of replacing the old UNIX computers with new UNIX computers. In addition, the development was completed in one-fourth of the projected time.

The SPIF TAC is ready for the year 2000 and uses IP to communicate with NASCOM. As an added bonus, the SPIF TAC outperformed the SPIF RS while being tested during the STS-87 space shuttle mission.

This work was done by John A. McQueen, Matthew J. Erb, and Amit K. Singh of AlliedSignal Technical Services Corp. for Goddard Space Flight Center.No further documentation is available. GSC-14011

NASA Tech Briefs Magazine

This article first appeared in the June, 1999 issue of NASA Tech Briefs Magazine.

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