Status Executive And Buffer Stored Command Processor

SUBSYSTEM FUNCTIONS ACS POWER THERMAL OBSERVATORY SAFETY OBSERVATORY OPERATIONS MISSION—UNIQUE FUNCTIONS

Fig. 6-51. NSSC-I Memory Layout Tor the MMS Spacecraft The MMS attitude control system core requirements are 10 K. to 16 K. words of program and data storage; 10 to 1000 stars at 4 words per star; and 100 to 3000 words for 72 hours of ephemeris data

NSSC-II. This computer is a microprogrammed general-purpose computer that is compatible with the standard instruction set of IBM S/360 ground-based computer systems [NASA, 1977]. The machine microcode implements a total of 171 instructions including 16-, 32-, and 64-bit fixed-point and 32-bit floating point instructions. In addition, the design accommodates 512 words of microcode memory capacity for special instructions or routines programmed or specified by the user. The semiconductor memory is expandable in 16 K-byte (8-bit byte) increments.

The NSSC-II uses 8-, 16-, 32- or 64-bit fixed-point data words at the user's option. The basic cycle time for the machine is 440 ns. The system has 16 general registers. The word size allows 20-bit operand addresses in instructions; thus, NSSC-II programs can address directly up to 1 M-byte words of data.

HEAO Computer. The digital processor employed for the HEAO spacecraft will process gyroscope data and compute jet commands (every 320 ms) for

* Eighteen-bit words.

HEAO-1 and -C and will process both gyroscope and star tracker data to compute jet commands for HEAO-B [Hoffman, 1976]. The specifications for the HEAO

digital processor are given in Table 6-13.

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