Mike DiMuzio (mdimuzio@cisnet.com)
Fri, 25 Jun 1999 18:08:16 +0000

> 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
>         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 electronics box design was not peer reviewed, and other system reviews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