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Mars Climate Orbiter was lost in 1999 because software mixed up which units?

Pound-seconds and newton-seconds: one team used English units, the other metric.

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  1. Miles and kilometers
  2. Pound-seconds and newton-seconds ✔
  3. Degrees Fahrenheit and Celsius

Why: Thruster impulse data in a ground file called Small Forces was in pound-seconds, but the navigation software expected newton-seconds. The trajectory errors sent the craft too close to Mars.

Huh, didn't know that: NASA lost contact on September 23, 1999, nine months after launch.

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Why did the engineer label every result? So the units would never feel left out.
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References

Answer: Pound-seconds and newton-seconds. Thruster impulse data in a ground file called Small Forces was in pound-seconds, but the navigation software expected newton-seconds. The trajectory errors sent the craft too close to Mars.

  1. NASA Science: Mars Climate Orbiter science.nasa.gov/mission/mars-climate-orbiter
    Ground software used English units, while onboard software worked in metric.
    Checked 2026-10-10.
  2. NASA Mars Climate Orbiter Mishap Investigation Board Phase I Report llis.nasa.gov/llis_lib/pdf/1009464main1_0641-mr.pdf
    the data was reported in English units of pound-seconds (lbf-s)
    Checked 2026-10-10.

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