James Frysinger wrote in USMA 16936: That's not quite it either, Joe. NASA was going to send up signals to >the MCO to burn certain engines for a certain number of seconds. To >calculate those times, they needed data from L-M in the form of computer >files. The contract specified that those files would be in metric units. >L-M supplied the data but in non-metric equivalent units. Since the >computer files contained only numbers, this was not apparent to NASA, >who took the numbers to be metric quantities. The engine firings were >conducted on those unconverted numbers and that put MCO off course.
Agreed. >A simplified analogy would be this. Assume NASA asked L-M how much to >change in velocity of the MCO was needed. L-M provides the number 10 >[feet per second] and NASA interprets that as 10 [meters per second] >because the contract said that meters per second were the specified >units. Note that L-M merely says "10" and NASA hears "10", but both are >thinking in terms of different units. The result would be that the >orbiter would be given orders to change velocity by about 3.3 times as >much as it should have. L-M was culpable because the contract specified >the use of (certain) metric units for the provided data and they failed >to comply. I can't agree with Jim's explanation. When the Mars Climate Orbiter was launched its main thruster rockets burned out in a few seconds. From then on the speed of the orbiter was determined. The snafu was with instructions to the side-acting jets whose function was to steer the orbiter. The orders from NASA to the orbiter were to control its direction, not its speed. NASA ordered newtons to steer the orbiter into an orbit around Mars The orbiter, built by Lockheed Martin, interpreted the orders as pounds-force, and the orbiter crashed into the back side of Mars. >AAAS probably toned down the wording in that article and mentioned only >NASA by name to keep from stirring up another round of finger-pointing >and yelling. > >Jim > >"Joseph B. Reid" wrote: >> >> James Frysinger in USMA 16919 quoted Science magazine of December 21 as >>saying: >> : >> > In an epic snafu, the controllers of the Mars Climate >> > Orbiter failed to convert English units of force into >> > metric ones >> >> My understanding of the snafu was exactly the reverse of Science's. The >> NASA flight controllers ordered the Orbiter to make course corrections in >> newton seconds and the Orbiter, built by Lockheed Martin, interpreted the >> orders to be in pound-force seconds Hence the Orbiter over-reacted. My quarrel with Science was not because they omitted reference to Lockheed Martin. It was because Science said that the orbiter failed to convert English units of force into metric ones. Actually, the controllers of the Orbitor issued metric orders and the Orbiter assumed that they were in English units. Joseph B.Reid 17 Glebe Road West Toronto M5P 1C8 TEL. 416-486-6071
