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LOSS OF WEATHER SATELLITE BLAMED ON TOO-LONG SCREW

The nation's next polar-orbiting weather satellite is being fixed to prevent a failure like that of NOAA-13 last year - a loss being blamed on a screw that was just a little bit too long.

A 12-member investigating board concluded last week that the long screw penetrated through a layer of insulation, causing an electrical short circuit that doomed the $77 million satellite.An inspection of the next planned weather satellite found that 10 of the 12 mounting screws in the same area were long enough to penetrate the insulation layer.

That satellite, scheduled for launch in December, has been modified to fix the problem, said Charles Thienel of NASA.

The NOAA-13 satellite was launched Aug. 9, 1993, from Vandenberg Air Force Base in California. It operated as expected until Aug. 21, when an electrical short occurred in the solar array that powered the craft, followed by loss of signal when the batteries were depleted.

The investigators reported that the most probable cause of the loss is that a 1.25-inch screw extended too far below an aluminum plate designed to dissipate heat. The screw penetrated a layer of insulation and made contact with a radiator plate, causing the short circuit, the investigators concluded.

"The board concluded that the design of the charge assembly is prone to a failure of this type," said Jeremiah Madden of NASA'S Goddard Space Flight Center, chairman of the panel.

The design of the battery charge assembly cannot be checked or easily X-rayed once it is assembled, the group noted.

Poor packaging design of the battery assembly and poor processing and inspection of the charge assembly were contributors to the failure, the board added.

The National Aeronautics and Space Administration supervises design and construction of the weather satellites, which are then operated by the National Oceanic and Atmospheric Administration. Prime contractor for the project was Martin Marietta Astro Space, East Windsor, N.J.

The NOAA satellites orbit the Earth from pole to pole at an altitude of 540 miles, passing over each part of the Earth twice a day to collect weather information. Two similar satellites, NOAA-11 and NOAA-12, remain in operation.

The satellite weather photos seen on television are provided by a different type of satellite in a higher 22,000-mile orbit, hovering in a fixed position above the Earth.