An Expensive Silence
On September 23, 1999, NASA’s Mars Climate Orbiter vanished without a trace. The spacecraft, designed to study the Martian atmosphere and relay communications for a lander mission, had completed a 9.5-month journey across 669 million kilometers.
As it approached Mars, ground controllers lost contact. The probe was never heard from again. Within weeks, investigators discovered the cause: a simple error in unit conversion. One engineering team used metric units, while another used U.S. customary units—causing the orbiter to fly fatally close to the Martian surface.
A Mission Built for Efficiency
The Mars Climate Orbiter was part of NASA’s cost-efficient Mars Surveyor ’98 program, conceived in response to rising expenses and past mission failures. The spacecraft, weighing 638 kg, carried two instruments: the Pressure Modulated Infrared Radiometer (PMIRR) and the Mars Color Imager (MARCI).
Its objectives included mapping temperature, water vapor, and dust across the Martian atmosphere. It also had a high-gain antenna, UHF radio, and solar array to support data relay from the Mars Polar Lander. The orbiter’s IBM RAD6000 computer managed operations with 128 MB of RAM and 18 MB of flash memory.
Approach and Disappearance
On September 8, 1999, NASA performed its final trajectory correction maneuver. Days later, calculations showed the spacecraft was headed toward an insertion altitude much lower than planned—potentially as low as 110 km, with survival limits estimated at 80 km.
NASA decided not to conduct a final correction. At 09:00 UTC on September 23, the spacecraft began its Mars orbital insertion burn. Communication was lost at 09:04:52, just as the orbiter slipped behind Mars. NASA never regained contact.
Root Cause: A Unit Conversion Error
Post-mission analysis revealed the fatal flaw: Lockheed Martin engineers had used pound-force seconds in their software when the interface required newton-seconds. This mismatch—an error by a factor of 4.45—misled navigation calculations.
The result placed the orbiter on a dangerously low trajectory, ultimately causing its destruction in the Martian atmosphere. Two NASA navigators had flagged inconsistencies but were ignored due to procedural oversights. NASA accepted responsibility, citing inadequate checks and poor communication between teams.
Consequences and Cost
The Mars Climate Orbiter cost NASA $327.6 million, equivalent to over $570 million in 2023. The incident occurred just months before the loss of Mars Polar Lander, which never reported back after its December 1999 descent. Both missions were part of the same underfunded program.
Following the failures, NASA restructured its Mars exploration strategy, emphasizing better systems engineering and clearer protocols. The objectives of the lost orbiter were later achieved by Mars Reconnaissance Orbiter, launched in 2005.
In 1999, NASA lost a $327 million spacecraft because one team used metric units and another used imperial.
The Mars Climate Orbiter, meant to study weather and relay data from a lander, vanished after entering Mars’ atmosphere on a fatally low trajectory…🧵👇 pic.twitter.com/Klfm6fwned
— Detective Tiger's Stories (@TigerDetective) June 13, 2025