> > Douglas Isbell > Headquarters, Washington, DC June 25, 1999 > (Phone: 202/358-1547) > > Lynn Jenner > Goddard Space Flight Center, Greenbelt, MD > (Phone: 301/286-8982) > > RELEASE: 99-74 > > INVESTIGATION FINDS DESIGN ERRORS > CAUSED WIRE SPACECRAFT FAILURE > > NASA's Wide-Field Infrared Explorer (WIRE) failed because of an > incorrectly designed electronics box that prematurely fired explosive > devices, causing early ejection of the instrument's telescope cover, a > NASA board has found. > > The WIRE Mishap Investigation Board found that the design of the > instrument's electronics box did not take into account subtle, but > known, start-up characteristics of one component within the box. > Electrical power created at the start-up of this component reached > explosive devices, called pyrotechnics, meant to eject the telescope's > cover later in the mission. The power reached the pyrotechnics within a > fraction of a second after the box was turned on, and the cover was > ejected. > > With the premature loss of the telescope's cover, the frozen > hydrogen used to cool the telescope's sensitive infrared detectors was > exposed to the Sun. As the telescope warmed, the hydrogen converted into > a gas and vented entirely into space within 48 hours of launch. Without > the frozen hydrogen, the instrument could not conduct its scientific > mission. > > "There was no component failure," said Darrell Branscome, chairman > of the eight-member WIRE Mishap Board and Deputy Associate Administrator > (Enterprise Development) for NASA's Office of Space Flight, Washington, > DC. "This was simply a case of a design error that allowed power to get > to the explosive charges before it should have. The system operated the > way it was designed. Unfortunately, the design was flawed." > > The report added that simulators and other support equipment used > for design and verification tests lacked the fidelity required to detect > this potential failure. > > "A significant contributing cause of the anomaly was the failure to > identify, understand, and correct the electronic design of the pyro > electronics box," the report said. "Design errors in the circuitry, > which controlled pyro functions, were not identified. The pyro > electronics box design was not peer reviewed, and other system reviews > conducted by the instrument design team did not focus on the electronics > box." > > WIRE was launched from Vandenberg Air Force Base, CA, March 4 > aboard a Pegasus XL launch vehicle. WIRE's mission was to detect > infrared light in the background cosmos to learn more about the > formation of stars, galaxies and the current state of the universe. > > NASA has already taken additional steps to ensure that design > engineers are aware of this condition. A NASA Parts Advisory was issued > on May 27 at the request of the Mishap Board informing design engineers > of the need to consider the startup behavior of electronic devices to > prevent unwanted or unexpected power discharges. > > The team's report also included recommendations for future > spacecraft designers. These include the use of independent, separate > inhibiting devices for pyrotechnics for mission-critical or irreversible > events; additional testing for anomalous start-up behavior; detailed, > independent reviews to assess the system design; and consideration of > the design, location and mounting of external vent hardware in the event > of a worst-case venting scenario. > > The WIRE spacecraft is now in a stable orbit with its other systems > and electronics in good working order. Ground controllers will proceed > with tests on new flight-control technology aboard the spacecraft. > > The WIRE mission was the latest in a series of Small Explorers, a > project under the Explorers Program managed by NASA's Goddard Space > Flight Center, Greenbelt, MD. Goddard also built the WIRE spacecraft. > The Jet Propulsion Laboratory, Pasadena, CA, managed development of the > WIRE instrument, which was constructed by the Space Dynamics Laboratory > at Utah State University, North Logan, Utah. > > The full text of the executive summary of the report is available > on the World Wide Web > at: > > ftp://ftp.hq.nasa.gov/pub/pao/reports/1999/wire_summary.pdf > > -end- > > * * * > -- 41.087N 80.714W 305 meters Mike DiMuzio mdimuzio@cisnet.com