When NASA returns astronauts to the Moon, mission operations on the lunar surface will be measured entirely in kilometers rather than miles, according to reporting on the agency’s metric commitment. The stated goal is to standardize parts, tools, and calculations across the mission — eliminating the kind of unit mismatch that has caused serious problems before.

The costly mistake behind the decision

NASA has technically used the metric system since around 1990, but English units have persisted on some missions, occasionally within the same program. That inconsistency had catastrophic consequences once: the 1999 loss of the Mars Climate Orbiter was directly traced to a contractor providing thruster-firing data in English units (pound-force seconds) while NASA’s own team was calculating the spacecraft’s trajectory in metric (newton-seconds), sending the orbiter off course and destroying it.

A mistake that isn’t unique to space missions

Unit-conversion errors happen far outside aerospace — in cooking, construction, medicine dosing, or any situation where a measurement crosses between metric and imperial systems without being carefully converted. The consequences are rarely as dramatic as losing a spacecraft, but the underlying failure mode is identical: treating two different units as if they were interchangeable without converting between them.

Convert carefully, every time

Whether you’re working with length, weight, or temperature, our unit converter handles the exact conversion factors between metric and imperial units, precisely because “close enough” conversions are exactly how mistakes like NASA’s happen.