The $193 million dollar mistake caused by a unit conversion: The Mars Climate Orbiter

The Mars Climate Orbiter was a robotic space probe launched by NASA on December 11th, 1998 to study Mars’ atmosphere. At the time, it was NASA’s most ambitious Mars project yet, one that was set to study the climate and atmosphere of the Red planet and provide us the first true weather satellite for another world.

For the first year and a half after launch, the orbiter encountered relatively few problems. Although it had to make more adjustments while flying than expected, it arrived at Mars on September 23rd, 1999 ready to go into orbit. Or so it seemed.

Just two days later, on September 25th, the mission was declared a failure. The space craft had flown 105 miles lower than expected and tore up in the Martian atmosphere.

What had happened?

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 system: newtons. One pound of force is about 4.45 newtons of force.

With that simple unit conversion error, the orbiter arrived at Mars and drastically underestimated its own orbiting distance, eventually veering as close as 37 miles away to the surface. Just for reference, project scientists had determined beforehand that the craft would tear up in the atmosphere at any distance closer than 53 miles. An internal investigation afterward found that NASA’s JPL engineers had simply forgotten to check the units.

As if to add insult to injury, another NASA Mars Craft, the Mars Polar Lander, failed soon after. The Polar Lander was launched three weeks after the Climate Orbiter; while this mistake was not as careless as the other, between the two crafts, NASA lost ~$300 million in technology.

Richard Cook, a NASA engineer at the time, recalled:

In essence, NASA was trying to perform too much with too little, rushing projects to completion and exhibiting a careless streak that came to fruition with these two rovers.

Luckily, NASA would go on to make some sweeping changes. Several planned missions, including a mission that was to bring Mars rocks back to Earth, were scrapped. The space agency went back to basics, rebuilding its Mars program based on conservative strategies and concepts that had already been tested.

As a result, NASA has had three tremendously successful rovers grace Mars since: Spirit, Opportunity, and, most recently, Curiosity. These new missions were and still are showcases in longevity; Opportunity functioned for nearly a decade despite having a 90-day mission time and Curiosity is still active today despite having a 2-year mission time.

While the Climate Orbiter may be one of the most careless, costly mistakes of all time, it has hopefully paved the way for a brighter future in our space program!

Photo by NASA on The Commons

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