NSSC-1
Encyclopedia
The NASA Standard Spacecraft Computer-1 (NSSC-1) was a computer
developed as a standard component for the MultiMission Modular Spacecraft at the Goddard Space Flight Center
(GSFC) in 1974. The basic spacecraft
was built of standardized components and modules, for cost reduction. The computer had 18 bits of core memory or plated wire memory
; up to 64 k. 18 bits was chosen because it gave more accuracy (x4) for data over a 16 bit machine. Floating point
was not supported.
The NSSC-1 was used on the Solar Maximum Mission
, Space Telescope, and Landsat-D Missions, among others. The hardware was developed by Westinghouse
and GSFC. The machine used diode-transistor logic
, the lowest power parts available at the time on the preferred parts list; initially fabricated from 1700 SSI (NOR gate
) packages, it was later moved to 69 MSI (medium-scale integration) chips.
/loader
/simulator toolset hosted on Xerox XDS 930 (24- bit) mainframe
. An associated simulator ran at 1/1000 of real time. The Xerox computer was interfaced to a breadboard
OBP in a rack. (Which, of course, operated at room temperature ambient conditions). Later, the Software Development and Validation Facility (SDVF) added a flight dynamics simulator hosted on a PDP-11/70 minicomputer
.
A purpose-built NSSC-1 Flight Executive was developed and used on the Solar Maximum Mission (SMM) and subsequent flights. It time sliced tasks at 25 ms. It included a stored command processor that handled both absolute time and relative time commands. It included a status buffer that could be telemetered back to the ground. It required a lot of memory, typically more than half of that available, leaving the rest for applications and spare.
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
developed as a standard component for the MultiMission Modular Spacecraft at the Goddard Space Flight Center
Goddard Space Flight Center
The Goddard Space Flight Center is a major NASA space research laboratory established on May 1, 1959 as NASA's first space flight center. GSFC employs approximately 10,000 civil servants and contractors, and is located approximately northeast of Washington, D.C. in Greenbelt, Maryland, USA. GSFC,...
(GSFC) in 1974. The basic spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
was built of standardized components and modules, for cost reduction. The computer had 18 bits of core memory or plated wire memory
Plated wire memory
Plated wire memory is a variation of core memory developed by Bell Laboratories in 1957. Its primary advantage was that it could be machine-assembled, which potentially led to lower prices than the hand-assembled core....
; up to 64 k. 18 bits was chosen because it gave more accuracy (x4) for data over a 16 bit machine. Floating point
Floating point
In computing, floating point describes a method of representing real numbers in a way that can support a wide range of values. Numbers are, in general, represented approximately to a fixed number of significant digits and scaled using an exponent. The base for the scaling is normally 2, 10 or 16...
was not supported.
The NSSC-1 was used on the Solar Maximum Mission
Solar Maximum Mission
The Solar Maximum Mission satellite was designed to investigate solar phenomenon, particularly solar flares. It was launched on February 14, 1980....
, Space Telescope, and Landsat-D Missions, among others. The hardware was developed by Westinghouse
Westinghouse Electric (1886)
Westinghouse Electric was an American manufacturing company. It was founded in 1886 as Westinghouse Electric Company and later renamed Westinghouse Electric Corporation by George Westinghouse. The company purchased CBS in 1995 and became CBS Corporation in 1997...
and GSFC. The machine used diode-transistor logic
Diode-transistor logic
Diode–transistor logic is a class of digital circuits that is the direct ancestor of transistor–transistor logic. It is called so because the logic gating function is performed by a diode network and the amplifying function is performed by a transistor .- Implementations :The DTL circuit shown in...
, the lowest power parts available at the time on the preferred parts list; initially fabricated from 1700 SSI (NOR gate
NOR gate
The NOR gate is a digital logic gate that implements logical NOR - it behaves according to the truth table to the right. A HIGH output results if both the inputs to the gate are LOW . If one or both input is HIGH , a LOW output results. NOR is the result of the negation of the OR operator...
) packages, it was later moved to 69 MSI (medium-scale integration) chips.
Programming and support
The NSSC-1 had an assemblerAssembly language
An assembly language is a low-level programming language for computers, microprocessors, microcontrollers, and other programmable devices. It implements a symbolic representation of the machine codes and other constants needed to program a given CPU architecture...
/loader
Loader (computing)
In computing, a loader is the part of an operating system that is responsible for loading programs. It is one of the essential stages in the process of starting a program, as it places programs into memory and prepares them for execution...
/simulator toolset hosted on Xerox XDS 930 (24- bit) mainframe
Mainframe computer
Mainframes are powerful computers used primarily by corporate and governmental organizations for critical applications, bulk data processing such as census, industry and consumer statistics, enterprise resource planning, and financial transaction processing.The term originally referred to the...
. An associated simulator ran at 1/1000 of real time. The Xerox computer was interfaced to a breadboard
Breadboard
A breadboard is a construction base for prototyping of electronics. The term is commonly used to refer to solderless breadboard ....
OBP in a rack. (Which, of course, operated at room temperature ambient conditions). Later, the Software Development and Validation Facility (SDVF) added a flight dynamics simulator hosted on a PDP-11/70 minicomputer
Minicomputer
A minicomputer is a class of multi-user computers that lies in the middle range of the computing spectrum, in between the largest multi-user systems and the smallest single-user systems...
.
A purpose-built NSSC-1 Flight Executive was developed and used on the Solar Maximum Mission (SMM) and subsequent flights. It time sliced tasks at 25 ms. It included a stored command processor that handled both absolute time and relative time commands. It included a status buffer that could be telemetered back to the ground. It required a lot of memory, typically more than half of that available, leaving the rest for applications and spare.