TROUBLESHOOTERS investigating the loss of the Mars Climate Orbiter spacecraft
have uncovered a potentially critical flaw in the Mars Polar Lander, now nearing
its destination. NASA engineers believe they can fix the problem. But if it
hadn鈥檛 been noticed, the craft would probably have smashed into the Red Planet鈥檚
surface.
Following the Mars Climate Orbiter鈥檚 loss, engineers have been reviewing the
Mars Polar Lander鈥檚 systems, hoping to catch any errors before its scheduled
landing on 3 December. Arthur Stephenson, who led the Mars Climate Orbiter
Mission Failure Investigation Board, says that a propulsion expert on his team
discovered a serious error in the thrusters that will control the lander鈥檚
descent.
The lander鈥檚 descent engine was too cold for comfort, the team found. In the
chill of interplanetary space, its fuel lines were in danger of freezing solid.
鈥淭he fuel flow might be inhibited if it had any frozen lines,鈥� Stephenson told a
press conference in Washington DC last week.
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However, Edward Stone, director of the Jet Propulsion Laboratory (JPL) in
Pasadena, believes the problem will be easy to fix. 鈥淲e鈥檝e done that reanalysis,
and will turn on the heaters earlier,鈥� he told the press conference.
Stephenson鈥檚 investigation board confirmed that Mars Climate Orbiter was the
victim of confusion over metric and imperial units
(快猫短视频, 9 October, p 6).
The push of sunlight and the solar wind on the probe鈥檚 solar
panel tended to make it spin. To counteract the spin, the craft had to fire its
thrusters from time to time.
Technicians used a computer program to estimate the effect on the craft鈥檚
trajectory. But while the program expected the figures for the strength of these
periodic firings to be in newton-seconds, the figures actually entered were in
pound-seconds.
The error meant the orbiter entered Martian orbit at an altitude of 57
kilometres, rather than the planned 226 kilometres. It either burnt up in the
planet鈥檚 atmosphere, or bounced off into deep space like a stone skimming the
surface of a lake.
Stephenson鈥檚 report blames the Mars Climate Orbiter team鈥攚hich was
split between NASA headquarters in Washington DC, JPL and the contractor
Lockheed Martin鈥攐n several counts, including inadequate training and poor
communications. Furthermore, staff were badly overworked, as they had to cover
other Mars missions as well. 鈥淚t may have been too much to ask of them,鈥�
Stephenson told last week鈥檚 press conference.
NASA is promising better management in future. But it can鈥檛 hide from the
uncomfortable fact that the latest thruster problem with Mars Polar Lander was a
near disaster, and would probably not have been discovered had scrutiny not been
stepped up in the wake of the orbiter鈥檚 loss.