As part of its effort to return the space shuttle to flight, NASA has selected a new design for the bipod that attaches the orbiter to the external tank (ET) and is contemplating other changes to mitigate or eliminate foam strikes.

The bipod and other critical areas of the ET are insulated with foam to prevent the formation of ice on the outside of the tank, which holds cryogenic fuel. The shuttle Columbia is believed to have been doomed by a piece of foam that broke loose from the bipod and damaged the orbiter's left wing shortly after launch Jan. 16.

The ET has been a source of such "liberating debris" throughout the history of the shuttle program, according to Michael Greenfield, associate deputy administrator for technical programs. The shuttle's return to flight team currently is scrutinizing various "foam liberation sites" and assessing dangerous foam strikes from those areas might be, Greenfield said.

NASA recently chose a new bipod design in an effort to remove foam insulation from that area altogether. Changes from the previous design include replacing the bipod's aluminum end caps with inconel covers and installing heaters to prevent ice formation.

"Whereas that is easy enough to do, and there's electrical power there, a real challenge is to understand ... what happens if our heaters go out at ... T-minus nine minutes, or something like that," Greenfield said in a presentation to the NASA Advisory Council (NAC) in Washington June 10. "Do you in fact scrub the launch? There's a lot of study on how long the heaters have to be on."