TO LOSE one Martian orbiter may be regarded as a misfortune. To lose a second
looks like carelessness鈥攅specially when the craft was lost not through
some unfortunate malfunction, but because human error or a software bug caused
it to be steered to its destruction.
The loss of the Mars Climate Orbiter, presumed to have broken up in the
planet鈥檚 atmosphere on 23 September, is acutely embarrassing for NASA, coming as
the agency is battling to stave off budget cuts. Worse, some researchers suggest
that the error is a result of NASA鈥檚 policy of launching 鈥渇aster, better,
cheaper鈥� missions.
The Mars Climate Orbiter was supposed to enter an orbit that would have
brought it no closer than 155 kilometres from the surface, after a
course-altering rocket burn on 15 September. The burn went according to plan.
Yet the craft descended to within 57 kilometres of the planet鈥檚 surface, where
it could not withstand the friction caused by the Martian atmosphere. This is
NASA鈥檚 second Mars probe to be lost on arrival, and joins a list of failed
missions in the 1980s and 1990s (see Table).
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Having ruled out a malfunction on the probe, NASA officials say that the
problem must have been with the calculation of its trajectory. This was plotted
by feeding tracking data from NASA鈥檚 Deep Space Network antennas into a computer
program that takes account of the changing positions of the Earth and
Mars鈥攊nformation that was generated by another software package, called
the ephemeris model.
When navigators at NASA鈥檚 Jet Propulsion Laboratory (JPL) in Pasadena
calculate a trajectory they also make an error estimate, which might be 10
kilometres either side of the projected path. But a 100-kilometre error is
unprecedented鈥攁nd points to either a software bug, or someone entering the
wrong data. 鈥淚t鈥檚 unbelievable that they made this mistake,鈥� says Francis
Rocard, an astrophysicist with the French space agency in Paris.
Troubleshooters are scrambling to pin down the source of the error before
December, when another craft must rely on the same software. 鈥淲e need to
understand because Mars Polar Lander is two months away from Mars,鈥� says Phil
Knocke, a JPL mission controller.
NASA officials are putting a brave face on the loss. 鈥淚t is not devastating
to the Mars Surveyor programme as a whole,鈥� claims Carl Pilcher, science
director for Solar System exploration at the agency鈥檚 headquarters in Washington
DC. But in addition to studying the Martian atmosphere and climate, the missing
craft was supposed to relay data from the Mars Polar Lander. This will study
surface weather and probe the soil near the planet鈥檚 south pole for three
months. Now the data must be sent directly to Earth鈥攊n which case half
will be lost鈥攐r be relayed back via Mars Global Surveyor, forcing that
craft to cut its own observations short.
NASA鈥檚 previous Mars mishap, the loss of the $1 billion Mars Observer
in 1993, was instrumental in causing the switch to more frequent, cheaper
missions. But some scientists wonder if the pendulum has swung too far. 鈥淲e鈥檝e
been saying all along they were going to lose one of these things,鈥� says one.
鈥淲ith `faster, better, cheaper鈥� you work your people to death,鈥� agrees Peter
Smith of the University of Arizona, principal investigator for Mars Polar
Lander.
Such signs of dissent are not what NASA wants to hear right now. As New
Scientist went to press, Congress was negotiating the agency鈥檚 budget for
2000. NASA expects its space science budget to be cut by at least $184
million, or 8.3 per cent.
