Safety Concerns Delay NASA Shuttle Launch

NASA has decided to delay the launch of the first shuttle flight after the Columbia disaster by two months, citing continuing concerns about the buildup of ice on the external fuel tanks and other problems observed during a recent fueling test.

The earliest the Discovery launch could now occur would be the afternoon of July 13, NASA Administrator Michael D. Griffin said Friday. The launch from Kennedy Space Station in Cape Canaveral, Fla., had been scheduled for May 22.

“We’re going to return to flight, not rush to flight,� said Griffin, who has been on the job for two weeks. “We’re going to do it right.�

The announcement follows a series of engineering reviews over the last two weeks to ensure that engineers have addressed all of the concerns raised in the aftermath of Columbia’s destruction. Columbia broke up on reentry in 2003 because its wing heat shield had been damaged during takeoff when it was struck by a piece of insulating foam that fell off the external fuel tank. All seven crew members died.

In the two years since the accident, NASA scientists have been examining other potential debris sources that might produce similar damage.

“After a great deal of testing and analysis, we have been able to cross about 175 potential debris sources off our concerned list,� said N. Wayne Hale Jr., deputy manager of the space shuttle program. But, he added, “there are still three or four more items to work on.... We’ll take a few more weeks to deal with them.�

The decision to delay the launch was made by the shuttle managers, but Griffin said he fully supported them. “It is prudent to have additional verification and validation of our extensive engineering work to ensure a safe flight,� Griffin said in a prepared statement.

Two of the key problems that must be solved before Discovery can be launched involve ice buildup on fuel lines on the external fuel tank and malfunctions of hydrogen sensors in the tank.

The external fuel tank is 154 feet long and 28 feet in diameter. It carries 535,000 gallons of liquid oxygen (at minus 297 degrees Fahrenheit) and liquid hydrogen (at minus 423 degrees).

The primary area of concern involves bellows or expansion joints on the external lines, which allow the lines to expand and contract in response to temperature changes during the fueling process.

Because of that motion, the bellows cannot be insulated with foam to prevent ice formation. The foam would crack and fall off, producing debris that could damage the leading edge of the orbiter wing.

Engineers have already installed what they call a “drip lip,� a foam skirt around the joints that wicks condensed moisture away before it can freeze. The team thinks the drip lips can prevent as much as 70% of the ice buildup.

Future shuttle tanks will also have a heater built into the bellows to further reduce ice buildup.

William Readdy, a former astronaut who now heads NASA’s space operations, said NASA probably would take advantage of the postponement to install a heater kit on this external tank as well. The kit can be installed while the vehicle is in the upright position, but the shuttle will have to be moved back into the Vehicle Assembly Building for the work to be done.

There are also brackets and other small exposed areas of the lines that are susceptible to the same type of ice buildup, Hale said, and NASA is exploring ways to slow or eliminate the accumulation.

One possibility that is likely to be adopted, he said, is to install infrared lights on the launch pad to warm the exposed areas. That would be helpful, he noted, but the lights cannot reach all the areas at risk.

During a recent fueling test, engineers also observed intermittent malfunctions of two of the four hydrogen sensors in the tank. The sensors show when the hydrogen supply is exhausted so that the engines on the shuttle can be shut off. Mission rules require all four to be functioning at launch time.

Readdy said the sensors themselves had been found to be functional. Engineers are now checking out the electrical lines that connect them -- in effect, wiggling junctions to see if they can find a loose connection. So far, they have not, he said.

The repairs will probably not take the full six weeks, but July 13 marks the first available launch window when the mission -- designed to resupply the International Space Station -- can be conducted during daylight hours.

NASA officials want the first two post-Columbia missions to launch in the daytime so that the flight can be exhaustively filmed to check for potential damage from foam or other debris.

The new launch window ends July 31. If Discovery cannot be launched then, the next window is Sept. 9 to Sept. 24.

William H. Gerstenmaier, the Johnson Space Center official coordinating the space station program, said the delay would not adversely affect the station. Russia’s unmanned Progress cargo rocket is scheduled to launch June 19, he said, and officials planned two potential cargos -- one for if the shuttle was launched in May and one for if it was not.

Because the shuttle is not launching next month, Progress will carry extra oxygen and water to the station, more than enough to last it until the next Progress mission in August.

Griffin said that he was also ordering researchers at the Goddard Space Flight Center in Maryland to begin planning for a Hubble servicing mission with the shuttle, even though such a mission had not yet been approved.

Using a gambling term to describe the potential Hubble mission, Griffin said: “We are betting on the come a little bit that we can do the mission.... But there are questions about [using] the shuttle that we simply cannot answer until we return to flight.�