Each of the testbed computers is a standalone version of the flight computers on board the SLS. As contractor, Boeing provides the computer hardware and low-level software, such as the operating system, while NASA develops the software to fly the vehicle.
NASA describes the new systems as real-time, embedded computers capable of executing programs on a fixed schedule measured in milliseconds. "These are the most capable flight computers ever developed for human spaceflight," said Dane Richardson, manager of Boeing's SLS avionics and software team.
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The testbed computers each have three redundant processors, which interpret data separately and "vote" to be sure they all agree on a response to be sent. Three flight computers on the rocket compare answers, then send commands for execution.
"The triple redundant processors make each computer reliable in the harsh radiation environment," Richardson said. "Similarly, the three computers working in concert make the vehicle reliable." The configuration is referred to as the flight computer operating group.
NASA has legacy flight software and modeling and simulation software from other programs, such as the canceled Constellation program and recently concluded Space Shuttle program, that can be used in developing the SLS software. The arrival of the testbed computers signals the start of development of the application software and advanced modeling and simulation of space flight conditions.
The SLS is a heavy-lift rocket capable of boosting a 70 metric ton payload by its first launch, targeted for 2017, and eventually a payload of 130 metric tons, needed to enable manned missions beyond the Earth's orbit.
Other aspects of SLS development include an upcoming test on the J-2X upper stage engine at the Stennis Space Center in Mississippi. Another NASA program is focused on development of the Orion Multi-Purpose Crew Vehicle, the capsule to be lifted by the SLS rocket, which is slated for a 2014 test flight.
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