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Engineers watch shuttle leak for possible landing problem

HOUSTON -- While astronauts set a possible record for using robotics in space, NASA engineers yesterday focused on a slow leak aboard the space shuttle Discovery that, if it worsens, could cause a first-of-its-kind shutdown of one of three hydraulic systems during Monday's landing attempt.

John Shannon, the shuttle program's deputy manager, said the problem was unlikely to affect the shuttle's return to Earth, but engineers were closely monitoring the leak in the pipeline of an auxiliary power unit that controls hydraulic steering and braking maneuvers.

It is leaking at a rate of ``about six drops per hour" and could be leaking harmless nitrogen or flammable hydrazine fuel, Shannon said.

The leak is more likely nitrogen, but there is no way of knowing that, so National Aeronautics and Space Administration is treating the problem as if the leak were fuel, he said. If it is fuel, the current rate is still 100,000 times slower than what would cause a fire, he said.

So if nothing changes, the shuttle will land normally, he said.

Just in case, NASA will turn on the power unit with the leak early tomorrow as part of its normal testing and then see whether the leak-rate changes. If it does, NASA may burn off the hydrazine and shut down the power unit before the shuttle returns to Earth to eliminate any fire hazard, Shannon said.

If that happens, the shuttle would land with just its two other power units for the first time in the spacecraft's history.

The shuttle is certified to land normally with two power units, with the only change requiring pyrotechnics to lower landing gear, Shannon said. The shuttle could land with only one power unit, but that would be more difficult, he said.

Also yesterday, the shuttle and the International Space Station set an informal record for robotic activity during a mission. Discovery's robot operators, Stephanie Wilson and Lisa Nowak, used the shuttle's robotic arm to examine the shuttle heat shield.

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