Wednesday, January 10, 2007

NASA goes metric for the moon

NASA announced that any future missions to the moon will be done in metric. This will simplify communications with companies and organizations from other countries, and it will allow things like metric hand tools — used by the Russian space agency — to be used on the NASA missions.

Besides simplifying tools and making communication easier between countries, it also avoids a particular form of disaster. NASA has used the metric system since 1990, but to make it easier for American contractors they used a dual system, with both metric and imperial units in play. This had disastrous consequences in 1999. The Mars Climate Orbiter was destroyed on insertion into Mars orbit because of a metric conversion error. A thruster contractor gave NASA thrust data in imperial measurements (pounds of thrust per second, or pound-seconds). Most of the data was in metric, since the programs came from the Mars Global Surveyor. There was a conversion factor for converting pound-seconds to newton-seconds, but it was buried in a formula... and was left out of the Mars Climate Orbiter's software.

A pound-second is the amount of force produced by a thruster in pounds of force per second. The metric equivalent is a newton-second. A newton is the amount of force it takes to accelerate a kilogram at 1 metre per second per second (or metre/second2. There are 4.45 pounds in a newton.

When the Mars Climate Orbiter had to make an engine thrust to put it into Mars orbit, it was told to fire its thrusters for a certain length of time. The program thought that the thrusters were less powerful than they were. Instead of putting the robotic orbiter at an altitude of between 140 and 150 kilometres, the orbiter was thrown into an orbit 57 km high. Before it had a chance to slow down. Friction and forces tore the orbiter apart.

NASA also says they will use standard Internet protocols for communicating with moon missions. This will make it easier for private companies and smaller organizations to get involved.

This is assuming that a moon mission actually happens in my lifetime. There's some question as to whether or not a moon mission will get off the ground, or if it was just thrown out there for the sake of politics, or for the sake of the current administration's legacy.

Here's the story about NASA and the metric system:

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