The NASA Standard Spacecraft Computer-1 (NSSC-1) is a computer developed as a standard component for the

MultiMission Modular Spacecraft Multi-mission Modular Spacecraft, also known as the MMS, was originally designed by NASA to serve the largest array of functions for the space program possible to decrease the cost of space missions. It was designed to operate in four distinct are ...

at the

Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C. in Greenbelt, Maryland, United States. Established on May 1, 1959 as NASA's first space flight center, GSFC emp ...

(GSFC) in 1974. The basic

spacecraft A spacecraft is a vehicle or machine designed to spaceflight, fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including Telecommunications, communications, Earth observation satellite, Earth ...

was built of standardized components and modules, for cost reduction. The computer had 18 bit wide

core memory Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (manufacturing), used in casting and molding * Core (optical fiber), the signal-carrying portion of an optical fiber * Core, the centr ...

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 In computing, floating-point arithmetic (FP) is arithmetic that represents real numbers approximately, using an integer with a fixed precision, called the significand, scaled by an integer exponent of a fixed base. For example, 12.345 can be r ...

arithmetic was not supported.

Usage

The NSSC-1 was used on the * Solar Maximum Mission *

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most ver ...

(for spacecraft control, not image data handling which initially used the DF-224) *

Landsat The Landsat program is the longest-running enterprise for acquisition of satellite imagery of Earth. It is a joint NASA / USGS program. On 23 July 1972, the Earth Resources Technology Satellite was launched. This was eventually renamed to L ...

-D,D' Missions, renamed

Landsat 4 Landsat 4 is the fourth satellite of the Landsat program. It was launched on July 16, 1982, with the primary goal of providing a global archive of satellite imagery. Although the Landsat Program is managed by NASA, data from Landsat 4 was coll ...

and Landsat 5 and other missions that were mostly limited to the solar system, eg Gamma Ray Observatory, and UARS. The prior OBP hardware was developed by Westinghouse and GSFC. The machine used

diode–transistor logic Diode–transistor logic (DTL) is a class of digital circuits that is the direct ancestor of transistor–transistor logic. It is called so because the logic gating function (e.g., AND) is performed by a diode network and the amplifying functio ...

, the lowest power parts available at the time on the preferred parts list; initially fabricated from 1700 SSI (

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 (1) results if both the inputs to the gate are LOW (0); if one or both input is HIGH (1), a LOW output (0 ...

) packages, the later AOP was implemented using 69 MSI ( medium-scale integration) TTL chips from Harris. The NSSC-1 was implemented by IBM using TRW versions of the Harris chips.

Programming and support

The NSSC-1 had an

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/ loader/simulator toolset hosted on Xerox XDS 930 (24- bit)

mainframe A mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for tasks such as censuses, industry and consumer statistics, enterpris ...

. An associated

simulator A simulation is the imitation of the operation of a real-world process or system over time. Simulations require the use of models; the model represents the key characteristics or behaviors of the selected system or process, whereas the ...

ran at 1/1000 of real time. The Xerox computer was interfaced to a

breadboard A breadboard, solderless breadboard, or protoboard is a construction base used to build semi-permanent prototypes of electronic circuits. Unlike a perfboard or stripboard, breadboards do not require soldering or destruction of tracks and ar ...

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 Flight dynamics in aviation and spacecraft, is the study of the performance, stability, and control of vehicles flying through the air or in outer space. It is concerned with how forces acting on the vehicle determine its velocity and attitude ...

simulator hosted on a PDP-11/70

minicomputer A minicomputer, or colloquially mini, is a class of smaller general purpose computers that developed in the mid-1960s and sold at a much lower price than mainframe and mid-size computers from IBM and its direct competitors. In a 1970 survey, ...

. A purpose-built NSSC-1 Flight Executive was developed for use on the Solar Maximum Mission (SMM) and subsequent flights. It switched tasks at intervals of 25 ms and included a stored command processor that handled both

absolute time Absolute space and time is a concept in physics and philosophy about the properties of the universe. In physics, absolute space and time may be a preferred frame. Before Newton A version of the concept of absolute space (in the sense of a prefer ...

and relative time commands. It had a status buffer that could be transferred back to a ground receiver station and thus required a lot of memory, typically more than half of that available, leaving the rest for applications and spare.Stakem, Patrick H. The History of Spacecraft Computers from the V-2 to the Space Station, 2010, PRB Publishing, ASIN B004L626U6

Historical context

Prior to NSSC-1

The Advanced Onboard Processor (AOP) was used on Landsat B & C, International Ultraviolet Explorer (IUE), and OSS-1. It used

medium scale integration An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny M ...

transistor-transistor logic (TTL).

Subsequent to NSSC-1

In the 1980s the

RCA 1802 The COSMAC (Complementary Symmetry Monolithic Array Computer) is an 8-bit microprocessor family introduced by RCA. It is historically notable as the first CMOS microprocessor. The first production model was the two-chip CDP1801R and CDP1801U, w ...

was used for many missions—like Galileo. This mission and other missions started the trend away from custom built NASA CPUs in spacecraft. The exploration of the inner and outer parts of the solar system would have to be done with existing (civilian and military-aerospace) CPUs. Before the RAD family of 32 bit CPUs were used in space missions, the MIL-STD-1750A (a CPU that could run modern applications) saw substantial use. Since the arrival of the IBM RAD6000 in the 2000s and the RAD750 in the 2010s, using the NSSC-1 has become unthinkable. Its computing power was not great, and most modern space missions require flight computers to have substantial and substantive computing power.

References