No. 010 · Cabinet of Wrong Numbers

Pounds, Meet Newtons

· a 10-month trip, lost on arrival

  1. 1Ground software reports thruster impulse in pound-force seconds
  2. 2Navigation software expects newton-seconds
  3. 3Every small trajectory correction is off by a factor of about 4.45
  4. 4Orbiter arrives far too low over Mars
  5. 5It is lost in the atmosphere ✕

Units belong in the interface contract, not in someone's head.

Source: NASA Mishap Investigation Board, November 1999

Mars Climate Orbiter loss, 1999. Duration: a 10-month trip, lost on arrival. 5 hops from the first change to the failure.