Possible Date Is Set For Atlantis to Launch

But Sensor Problem Could Delay Mission

NASA set a tentative date yesterday of Jan. 24 to launch the space shuttle Atlantis, which will carry a long-delayed European space laboratory to the international space station, while saying that additional troubleshooting may be necessary to repair a nagging problem with the external tank's backup fuel gauges. That could force a further delay until next month, officials said.

John Shannon, the deputy shuttle program manager, said the agency thinks it knows what caused the problem and how it can be solved. Engineers will begin making repairs next week at the Kennedy Space Center in Florida, but 10 to 14 days of additional testing will be needed to make sure they fully understood the problem.

"To make the 24th, everything has to go right," Shannon said. "But we're also looking at February 2 if things go like we expect they'll go."

Erratic electrical readings from four sensors that measure levels of super-cold liquid hydrogen fuel in the shuttle's huge external tank halted two attempted launches last month. The problem has shown up numerous times in recent years.

After the two failures, the agency sent parts of the malfunctioning sensors to the Marshall Space Flight Center in Huntsville, Ala., where they will be tested in a bath of gaseous helium starting next week. While NASA engineers now believe they have figured out why the problem occurred, Shannon left open the possibility that the launch could be further delayed if the testing at Marshall does not confirm their analysis.

Shannon called the proposed repair -- which involves soldering together parts of an electrical cable rather than relying on a pin-and-plug system -- "a simple and elegant change." A similar problem on the Atlas-Centaur rocket was solved with soldering, he said.

Atlantis has been stuck on a launchpad since Dec. 6, when the fuel sensors first failed. The sensors are a backup safety system designed to shut down the shuttle's three main engines if their fuel supply runs out, to avoid the extreme danger of running the engines and their massive fuel pumps on a dry tank.

Engineers think the problem is in an electrical connector and plug that route wires through the wall of the tank to the sensors. After similar malfunctions with the sensors in 2005 and 2006, engineers thought they had solved an electrical problem in the gauges themselves, not in the connectors.

William H. Gerstenmaier, NASA's director of space operations, said yesterday that the agency now thinks there may have been problems with the gauges and the connectors.

The Columbus space lab, which cost its European builders $2.1 billion, was ready to be added to the international space station before the 2003 space shuttle Columbia disaster. The lab will greatly increase the amount of research that can be conducted on the station once it is fully operational and the space station crew doubles to six.

Even if the shuttle is ready to launch next month, it may not have an open docking port at the space station because a Russian cargo ship is scheduled to arrive there Feb. 7. Shannon said NASA officials are discussing the schedule with the Russians.

Despite the delays in the Atlantis launch, Shannon said he is confident that NASA will be able to launch the final 13 shuttle missions by September 2010, when the remaining three space shuttles are scheduled to be retired.