WASHINGTON (AP) - Failure to convert English measures to metric values caused the loss of the Mars planet orbiter, a spacecraft that smashed into the planet instead of reaching a safe orbit, a NASA investigation concluded Wednesday. The Mars planet orbiter, a key craft in the space agency's exploration of the red planet, vanished after a rocket firing Sept. 23 that was supposed to put the spacecraft on station around Mars. An investigation board concluded that NASA engineers failed to convert English measures of rocket thrusts to newton, a metric system measuring rocket force. One English pound of force equals 4.45 newtons. A small difference between the two values caused the spacecraft to approach Mars at too low an altitude and the craft is thought to have smashed into the planet's atmosphere and was destroyed.