ISS Risk Mitigation

Test of Portable Computer System (TPCS) Hardware

TPCS Hardware


The TPCS experiment was designed to determine the quantity of Single Event Upsets (SEUs) that occur on small, portable computers due to the radiation environment at the International Space Station (ISS) orbital inclination and alititude.

Shuttle-Mir Missions
STS-86, NASA-6, NASA-7, STS-91

NASA currently flies IBM ThinkPad 755C laptop computers as Payload and General Support Computers (PGSCs). This system provides the Space Shuttle crews with a small, inexpensive way of controlling small experiments, viewing data not available from the primary flight computers, and performing standard personal computer tasks such as email, word processing and viewing digital imagery. A modified version of these computers, the IBM ThinkPad 760ED is planned for use on the International Space Station (ISS). The radiation environment of space can cause what appears to the user as "software bugs", but in reality is a single bit upset (SBU) or multiple bit upset (MBU). These upsets tend to be increased at higher orbits, with higher upsets in the South Atlantic Anomoly (SAA) and at the polar regions. Because these upsets could potentially cause a system malfunction or loss of data, an upgraded system was developed and tested both prior-to and during the NASA-Mir program.

The TPCS hardware consisted of a IBM ThinkPad 760ED laptop computer, an Intel 133 Mega Hertz Pentium Processor with 48 Megabytes of RAM, a four speed CD-ROM, a power supply unit, a 1.44 Megabyte floppy disk drive, two 1.2 Gigabyte hard drives, and associated power, data and video cables. A notation should be made that the memory used in these computers was not previously radiation hardened.

During the NASA-Mir program, crewmembers operated the Super Memory Checker software and ran the software for approximately 8 hours per session. Upsets were recorded by both the internal software and crewmember visual observations.

The initial data show that the 760ED computer is much less susceptible to SEUs than its predecessor, the IBM ThinkPad 755C.

The overall system was much more effective than previous models. However, two susystems were recommended for improvements prior to flight on the International Space Station. The I533 card and its interface cable proved that in some cases, this connection is not reliable and will likely lead to loss of data since the cable disconneced easily when jarred. Alternatively, strong consideration should be made to battery type that is flown.

Overall, the IBM ThinkPad 760ED notebook computer had near-perfect space flights for an off-the-shelf computer. Based on the data gathered, the computer and its associated systems are ready to support both Space Shuttle and International Space Station operations.

"Results of Risk Mitigation Experiment 1332 for Space Shuttle and Space Station Mir Missions", Final Report 1998.

Principal Investigators
Rodney L. Lofton
NASA/Johnson Space Center

Andrew L. Klausman

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Page last updated:07/16/1999

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