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DATE=2/14/2000 TYPE=CORRESPONDENT REPORT TITLE=SHUTTLE MAST (L) NUMBER=2-259133 BYLINE=DAVID MCALARY DATELINE=WASHINGTON CONTENT= VOICED AT: INTRO: Space agency engineers are analyzing a problem with the orbiting space shuttle Endeavour's long radar mast. The problem could shorten the mission. Science Correspondent David McAlary reports a tiny thruster at the end of the mast is not properly stabilizing the structure. TEXT: A small valve at the end of the 60-meter mast emits nitrogen to hold the boom steady as the antenna bombards Earth with radar signals that are used to generate a three-dimensional map. But despite a constant nitrogen flow, the valve is not providing enough steadying pressure. Ground technicians suspect a leak in the gas line. Keeping the mast from moving is important for sharp radar images, so NASA spokesman Doug Peterson says Endeavour's pilots are compensating by firing the shuttle's thrusters more frequently than planned. But this burns fuel at rate that could shorten the mission by up to one-day. // PETERSON ACT // When the nitrogen thruster is working, the orbiter itself still has its thrusters shooting every two minutes. Because the nitrogen thruster is not working, we are having to use the orbiter's thrusters every 90-seconds. So we are using them more than expected and therefore we are looking at the problem with the potential overuse of propellant. // END ACT // Shuttle managers say it may take two-days to calculate how much extra fuel the shuttle's thruster firings are using and to determine if the mapping exercise has to be shortened. The mapping part of the flight had been shortened one- day before Endeavour took off, and scientists in charge of the shuttle radars do not want to lose any more time. What was supposed to have been 10-days of radar mapping to cover 90-percent of the Earth's terrain became nine-days covering less than 80-percent when NASA reassessed the flight plan. Doug Peterson says the space agency wanted extra time during the flight for astronauts to be able deal with a technical problem they feared could arise with the mast, the longest rigid structure ever flown in space. // PETERSON ACT // People were looking at the possibility of the mast that the antenna is on being unable to be retracted into the payload bay. We looked at that and said it may be the case that we would have to do a spacewalk to go out and crank it in. If that was the case, that would require us to have another day to do that. So in order to have enough time, we decided to back off on the number of days for mapping so that we would have enough time to pull it in, if necessary. // END ACT // Despite the problem with the mast's nitrogen thruster, scientists analyzing the radar data say the first results are sharp, showing topographic features that are completely invisible in the best existing radar maps. (SIGNED) NEB/DEM/RAE 14-Feb-2000 09:29 AM EDT (14-Feb-2000 1429 UTC) NNNN Source: Voice of America .