Metric mishap caused loss of nasa orbiter

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Metric mishap caused loss of NASA orbiter

NASA's Climate Orbiter was lost September 23, 1999


September 30, 1999
Web posted at: 4:21 p.m. EDT (2021 GMT)

By Robin Lloyd
CNN Interactive Senior Writer

(CNN) -- NASA lost a $125 million Mars orbiter because a Lockheed Martin engineering team used English units of measurement while the agency's team used the more conventional metric system for a key spacecraft operation, according to a review finding released Thursday.

The units mismatch prevented navigation information from transferring between the Mars Climate Orbiter spacecraft team in at Lockheed Martin in Denver and the flight team at NASA's Jet Propulsion Laboratory in Pasadena, California.

Lockheed Martin helped build, develop and operate the spacecraft for NASA. Its engineers provided navigation commands for Climate Orbiter's thrusters in English units although NASA has been using the metric system predominantly since at least 1990.

No one is pointing fingers at Lockheed Martin, said Tom Gavin, the JPL administrator to whom all project managers report.

"This is an end-to-end process problem," he said. "A single error like this should not have caused the loss of Climate Orbiter. Something went wrong in our system processes in checks and balances that we have that should have caught this and fixed it."

The finding came from an internal review panel at JPL that reported the cause to Gavin on Wednesday. The group included about 10 navigation specialists, many of whom recently retired from JPL.

"They have been looking at this since Friday morning following the loss," Gavin said.

The navigation mishap killed the mission on a day when engineers had expected to celebrate the craft's entry into Mars' orbit.

After a 286-day journey, the probe fired its engine on September 23 to push itself into orbit.

The engine fired but the spacecraft came within 60 km (36 miles) of the planet -- about 100 km closer than planned and about 25 km (15 miles) beneath the level at which they could function properly, mission members said.

The latest findings show that the spacecraft's propulsion system overheated and was disabled as Climate Orbiter dipped deeply into the atmosphere, JPL spokesman Frank O'Donnell said.

That probably stopped the engine from completing its burn, so Climate Orbiter likely plowed through the atmosphere, continued out beyond Mars and now could be orbiting the sun, he said.

Climate Orbiter was to relay data from an upcoming partner mission called Mars Polar Lander, scheduled to set down on Mars in December. Now mission planners are working out how to relay its data via its own radio and another orbiter now circling the red planet.

Climate Orbiter and Polar Lander were designed to help scientists understand Mars' water history and the potential for life in the planet's past. There is strong evidence that Mars was once awash with water, but scientists have no clear answers to where the water went and what drove it away.

NASA has convened two panels to look into what led to the loss of the orbiter, including the internal peer review panel that released the Thursday finding. NASA also plans to form a third board -- an independent review panel -- to look into the accident.

Metric system used by NASA for many years

A NASA document came out several years ago, when the Cassini mission to Saturn was under development, establishing the metric system for all units of measurement, Gavin said.

The metric system is used for the Polar Lander mission, as well as upcoming missions to Mars, he said.

That review panel's findings now are being studied by a second group -- a special review board headed up by John Casani, which will search for the processes that failed to find the metric to English mismatch. Casani retired from JPL two months ago from the position of chief engineer for the Lab.

"We're going to look at how was the data transferred," Gavin said. "How did it originally get into system in English units? How was it transferred? When we were doing navigation and Doppler (distance and speed) checks, how come we didn't find it?"

"People make errors," Gavin said. "The problem here was not the error. It was the failure of us to look at it end-to-end and find it. It's unfair to rely on any one person."

Lockheed Martin, which failed to immediately return a telephone call for comment, is building orbiters and landers for future Mars missions, including one set to launch in 2001 and a mission that will return some Mars rocks to Earth a few years down the line.

It also has helped with the Polar Lander mission, set to land on Mars on December 3 and conduct a 90-day mission studying martian weather. It also is designed to extend a robotic arm that will dig into the nearby martian soil and search for signs of water.

NASA managers have said the Polar Lander mission will go on as planned and return answers to the same scientific questions originally planned -- even though the lander will have to relay its data to Earth without help from Climate Orbiter.

Error points to nation's conversion lag

Lorelle Young, president of the U.S. Metric Association, said the loss of Climate Orbiter brings up the "untenable" position of the United States in relation to most other countries, which rely on the metric system for measurement. She was not surprised at the error that arose.

"In this day and age when the metric system is the measurement language of all sophisticated science, two measurements systems should not be used," Young said.

"Only the metric system should be used because that is the system science uses," she said.

She put blame at the feet of Congress that she said has squeezed NASA's budget to the point that it has no funds to completely convert its operations to metric.

"This should be a loud wake-up call to Congress that being first in technology requires funding," she said, "and it's a very important area for the country."

Nov. 10, 1999: Metric Math Mistake Muffed Mars Meteorology Mission

A NASA review board found that the problem was in the software controlling the orbiter’s thrusters. The software calculated the force the thrusters needed to exert in pounds of force. A separate piece of software took in the data assuming it was in the metric unit: newtons.

“The units thing has become the lore, the example in every kid’s textbook from that point on,” Cook said. “Everyone was amazed we didn’t catch it.”

There had been warning signs, the mishap board found. En route to Mars, the spacecraft had to make 10 to 14 times more minor adjustments than engineers expected. And the last few signals from the orbiter indicated that it was dipping dangerously low into the Martian atmosphere, about 105 miles lower than it was supposed to go.

Ultimately, the Mars Climate Orbiter came within 37 miles of the Martian surface. Simulations showed that, at any altitude lower than 53 miles, atmospheric friction would tear the fragile craft apart.

The whole thing could be written off as a miscommunication. Propulsion engineers, like those at Lockheed Martin who built the craft, typically express force in pounds, but it was standard practice to convert to newtons for space missions. One pound of force is about 4.45 newtons. Engineers at NASA’s Jet Propulsion Lab assumed the conversion had been made, and didn’t check.

But there was an underlying issue in the culture of NASA’s space exploration at the time, Cook said.

“‘Better, faster, cheaper’ was the mantra at the time,” Cook said. “Certainly that project was trying to do a whole lot for a limited amount of money.”

Six Unit Conversion Disasters

Think you had a bad day at work? At least you didn't lose equipment worth hundreds of millions of dollars (at least, I'm assuming you didn't). Forgetting to convert units can result in big-time disasters like these six examples.

1. Can you imagine losing $125 million thanks to a little metric system error? That’s exactly what happened in 1999 when NASA lost a Mars orbiter because one team used metric units for a calculation and the other team didn’t. Guess they didn’t learn from their previous mistake…

2. … just the year before, NASA lost equipment worth millions thanks to shoddy conversion practices. SOHO, the Solar Heliospheric Observatory, a joint project between NASA and the ESA (European Space Agency), lost all communications with Earth. After about a week of trying various things, communication was restored and everyone breathed a sigh of relief. Among the problems thought to have caused the sudden blackout?

There was an error in the spacecraft’s navigation measurements of nearly 100 km, which resulted in a much lower altitude than expected and led to the vehicle’s break-up in the atmosphere.

• The conversion factor from English to Metric units was erroneously left out of the AMD files.
• Interface Specification required that the impulse-bit calculations should be done using Metric Units.

3. In 1983, an Air Canada plane ran out of fuel in the middle of a flight. The cause? Not one but two mistakes in figuring how much fuel was needed. It was Air Canada’s first plane to use metric measurements and clearly not everyone had the hang of it yet. Luckily, no one was killed and only two people received minor injuries. That’s amazing considering the flight crew thought they had double the fuel they actually had.

4. In 1999, the Institute for Safe Medication Practices reported an instance where a patient had received 0.5 grams of Phenobarbital (a sedative) instead of 0.5 grains when the recommendation was misread. A grain is a unit of measure equal to about 0.065 grams… yikes. The Institute emphasized that only the metric system should be used for prescribing drugs.

5. An aircraft more than 30,000 pounds overweight is certainly no laughing matter. In 1994, the FAA received an anonymous tip that an American International Airways (now Kalitta Air, a cargo airline) flight had landed 15 tons heavier than it should have. The FAA investigated and discovered that the problem was in a kilogram-to-pounds conversion (or lack thereof).

6. Even Columbus had conversion problems. He miscalculated the circumference of the earth when he used Roman miles instead of nautical miles, which is part of the reason he unexpectedly ended up in the Bahamas on October 12, 1492, and assumed he had hit Asia. Whoops.

Name: Date: Period:

Let’s Fix Some Famous Unit Conversion Errors!
Story 1: On September 23, 1999 NASA lost the $125 million Mars Climate Orbiter spacecraft after a 286-day journey to Mars. Miscalculations due to the use of English units instead of metric units apparently sent the craft slowly off course. Thrusters used to help point the spacecraft had, over the course of months, been fired incorrectly because data used to control the wheels were calculated in incorrect units. Lockheed Martin, which was performing the calculations, was sending thruster data in English units (pounds) to NASA, while NASA's navigation team was expecting metric units (Newtons).
Problem 1 - A solid rocket booster is ordered with the specification that it is to produce a total of 10 million pounds of thrust. If this number is mistaken for the thrust in Newtons, and is built to have 10 million Newtons of thrust, how many pounds is 10 million Newtons? (1 pound = 4.5 Newtons) Did the rocket have too little or too much thrust?

Problem 2 - The Mars Climate Orbiter was meant to stop about 160 km away from the surface of Mars, but it ended up within 36 miles of the surface. How far off was it from the surface? How large was the difference from its target distance (in km)? (1 mile = 1.6 km)

Story 2: On January 26, 2004 at Tokyo Disneyland's Space Mountain, an axle broke on a roller coaster train mid-ride, causing it to derail. The cause was a part being the wrong size due to a conversion of the master plans in 1995 from English units to Metric units. In 2002, new axles were mistakenly ordered using the pre-1995 English specifications instead of the current Metric specifications.
Problem 1 - A bolt is ordered with a thread diameter of 1.25 inches. What is this diameter in millimeters? If the order was mistaken for 1.25 centimeters, by how many millimeters would the bolt be in error? (25.4 mm = 1 inch)

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