Columbia’s White External Fuel Tanks

The white external tank used in NASA's STS-1 mission is jettisoned after launch. CREDIT: NASA/JSC.

Many SPACE.com readers have written letters asking about the white external fuel tanks that fed NASA's first two orbiter test flights - STS-1 and STS-2 - and whether the paint job added any additional protection against the type of foam shedding that led to the 2003 Columbia accident.

John Chapman, NASA's external tank project manager at the Marshall Space Flight Center (MSFC) in Huntsville, Alabama, said the white paint was initially added to protect shuttle fuel tanks from the damaging effects of exposure to ultraviolet rays during extended periods on the launch pad.

While tests were unfinished as NASA prepared STS-1 for its maiden flight, engineers painted the first two tanks to be on the safe side, Chapman said.

"Because you just don't go up to the external tank on the pad with a can of paint and a roller," Chapman told SPACE.com, adding that he, former shuttle tank project manager Sandy Coleman and Kennedy Space Center (KSC) director Jim Kennedy watched Columbia's April 12, 1981 launch debut from the roof of a Winnebago the trio had driven to KSC with three other coworkers from MSFC.

Subsequent tests found that the paint wasn't vital for shuttle launches and it was abandoned to free up weight - about 600 pounds (272 kilograms) - for additional payload, NASA officials said.'

The paint also did not prevent foam from popping free of Columbia's fuel tank during its first two launches, Chapman added.

Following the Feb. 1, 2003 loss of Columbia during reentry, which investigators found was due to heat shield damage caused by tank foam insulation debris at launch, NASA revisited the white paint approach, as well as a myriad other schemes to reduce foam shedding.

But adding additional protection measures, such as a nylon covering or chicken wire mesh, could not only add another debris source during launch, but also lead to larger pieces pulling free from anchored spots, Chapman said.

"The biggest thing for us would be to make sure that anything we do doesn't cause more harm than good," Chapman said.

Since the 2003 Columbia accident - and NASA's subsequent July-August 2005 STS-114 return to flight mission in which unacceptably large chunks of foam were also shed during launch - tank engineers have focused on reducing the amount of foam insulation on future tanks.

Engineers are also replacing a set of engine cut-off sensors inside the next tank to fly, and preparing for large-scale wind tunnel tests to evaluate the removal of a large foam ramp that shed unacceptably large pieces of debris during the STS-114 flight.

"We do a lot of subscale wind tunnel tests, but this will be a closer to a full-size test," Chapman said of the upcoming checks.

The wind tunnel tests will aid NASA's second return to flight mission - STS-121aboard the Discovery orbiter - slated to launch no earlier than July 1.

• Faulty Fuel Tank Sensors Prompt Launch Delay for NASA's Next Shuttle Mission
• Next Shuttle Fuel Tank to Fly Arrives at NASA Spaceport
• Return to Flight: NASA's Road to STS-121
• Fixing NASA: Returning to Flight with STS-114
• Columbia Accident Special Report