A Superalloy Solution
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THE MAGAZINE DEVOTED TO NICKEL AND ITS APPLICATIONS |
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When Discovery blasts off again in 2005, it will carry newly designed bipod fitting end covers
made of superalloy S66286. |
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BIPOD FITTING COVERS (silver) have been made of superalloy S66286, containing 24-27% nickel, to withstand
the high temperature created by aerodynamic heating. |
NASA’s fix for the Space Shuttle. By Carroll McCormick
Nickel Magazine, November 2004 -- When the U.S. space shuttle Discovery flies again, in May 2005, the area where insulating foam broke away, causing fatal damage to Columbia, will be redesigned to include high-temperature superalloy S66286 (alloy 286) end covers.
The affected area is in the forward bipod area, where struts join the giant external fuel tank to the shuttle. In the old design, the two bipod fittings, which are the attachment points for the 135-centimeter-long struts, were covered with wedge-shaped foam structures called bipod ramps. These prevented the build-up of ice on the fittings caused by the minus 253°C cryogenic liquid hydrogen fuel in the external tank. The bipod ramps, which measured 76 centimetres (cm) long by 36 cm wide by 31 cm tall, also protected the bipod fittings from aerodynamic stresses.
When Columbia left the launch pad in January 2003, a piece of one of the bipod ramps broke free, striking and breaching the leading edge of the shuttle’s left wing. On re-entry, superheated gases entered the hole made by the foam chunk, causing Columbia to break apart, killing all seven astronauts on board.
In the new design, the bipod ramps have been eliminated. Instead, the bipod fittings will be left exposed, with rod heaters beneath them to prevent ice buildup. Since the bipod fitting end covers will be exposed to much higher temperatures, they have been redesigned using S66286 (containing 24-27% nickel), which can withstand temperatures of up to 1,093°C. The covers will reach a temperature of 510°C at the highest point of aerodynamic heating when the shuttle hits a top speed of four times that of sound (Mach 4).
The redesign, with the S66286 end covers, will be retrofitted on the fleet’s eight exisitng external tanks and all new tanks. Discovery will be the first space shuttle to be launched since the Columbia disaster.
Carroll McCormick is a Montreal-based freelance writer.
PHOTO: NASA
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Lynette Madison |
