Monday, August 24, 2015

Why are Measurement and Correct Units Important in Science?

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?)