Environmental Engineering Reference
In-Depth Information
which they were developed at GSFC and examined relative to the contribu-
tions they made for specific spacecraft on which the FSW functionality was
flown. General time periods reviewed are the 1970s, 1980s, 1990s, and 2000s.
3.2.1 1970s and Prior Spacecraft
During the 1970s, NASA made the first attempt to standardize onboard flight
data systems with the creation of the NASA Standard Spacecraft Computer
(NSSC), versions I and II. The NSSC-I, a derivative of that flown on the
Orbiting Astronomical Observatory-3 (OAO-3) in 1972 and IUE in 1978, was
scheduled for launch in 1979). Compared to modern flight computers, the
NSSC-I was slow, had very limited memory, was cumbersome when performing
mathematical functions due to its small word size and lack of floating point
arithmetic, and was awkward to program due to the exclusive use of assembly
language. However, it was extremely reliable and was used successfully to
support the onboard needs of many missions, from SMM in 1980 to the HST
payload in 1990.
The NSSC computers and other OBCs with comparable capabilities such
as those used on the HEAO series were employed successfully in the 1970s
to support a basic foundation of spacecraft autonomy, including stored com-
manding, telemetry generation, FDC, orbit propagation, and pointing control.
Stored commanding capabilities included the (now) standard set of absolute-
timed, relative-timed, and conditional commands, as discussed previously. A
degree of FDC (for constraints such as bright object avoidance and minimum
power levels) also was present in the form of limit checks on key onboard
Fig. 3.1.
Solar maximum mission (SMM) (image credit: NASA)
