Mars Probe Lost Due to Simple Math Error
October 01,
1999|ROBERT LEE HOTZ | TIMES SCIENCE WRITER
NASA
lost its $125-million Mars Climate Orbiter because spacecraft engineers failed
to convert from English to metric measurements when exchanging vital data
before the craft was launched, space agency
officials said Thursday.
A navigation team at the Jet Propulsion Laboratory used the metric system of millimeters and
meters in its calculations, while Lockheed Martin Astronautics in Denver, which
designed and built the spacecraft, provided crucial acceleration data in the
English system of inches, feet and pounds.
As a result, JPL engineers mistook acceleration
readings measured in English units of pound-seconds for a metric measure of
force called Newton-seconds.
In a sense, the spacecraft was lost in
translation.
"That is so dumb," said John Logsdon,
director of George Washington University's space policy institute. "There
seems to have emerged over the past couple of years a systematic problem in the
space community of insufficient attention to detail."
None of JPL's rigorous quality control procedures
caught the error in the nine months it took the spacecraft to make its 461-million-mile flight to Mars.
Over the course of the journey, the miscalculations were enough to throw the
spacecraft so far off track that it flew too deeply into the Martian atmosphere
and was destroyed when it entered its initial orbit around Mars last week.
John Pike, space policy director at the
Federation of American Scientists, said that it was embarrassing to lose a spacecraft to such a simple math error.
"It is very difficult for me to imagine how such a fundamental, basic
discrepancy could have remained in the system for so long," he said.
"I can't think of another example of this
kind of large loss due to English-versus-metric confusion," Pike said.
"It is going to be the cautionary tale until the end of time."
At the Jet Propulsion Lab, which owes its
international reputation to the unerring accuracy it has displayed in guiding
spacecraft across the shoals of space, officials did not flinch from
acknowledging their role in the mistake.
"We know this error is the cause," said
Thomas R. Gavin, deputy director of JPL's space and earth science directorate,
which is responsible for the JPL Mars program. "And our failure to detect
it in the mission caused the unfortunate loss of Mars Climate Orbiter.
"It is ironic," Logsdon said,
"that we can cooperate in space with the Russians and the Japanese and the
French but we have trouble cooperating across parts of the United States.
Fundamentally, you have partners in this enterprise speaking different
languages."
In
your science notebook, on
the right side, respond to the following question:
Why
is it important to measure things accurately in science and use the correct
units? Can you think of other
examples where careful measurement and correct units would be important in your
life? EXPLAIN (HINT: Think about
if all amounts and measurements were random. What would life be like?)
