Do engineers use metric or english system of units to command the Phoenix spacecraft on its trip to Mars?
NASA uses the metric system to design the Trajectory Correction Maneuver (TCM). They specify the desired maneuver in terms of a change in velocity (delta-V) which is in meters/second. The Lockheed Martin spacecraft team is responsible for implementing the maneuver given the performance characteristics of the Phoenix spacecraft. Lockheed Martin also works in the metric system and ensures that all measures and reference frames are consistent. There will always be some error between the ideal maneuver design and the actual implementation of a TCM. Phoenix’s first TCM was on August 10th and the resulting error in total delta-V was less than 1 centimeter/sec for the desired magnitude of approximately 18.5 meters/second. That represents less than 0.054% magnitude error. Five more TCMs are planned to further refine the spacecraft’s trajectory.
