A Costly Miscalculation
On December 11, 1998, NASA launched the Mars Climate Orbiter, a 638 kg robotic probe designed to study the Martian climate and act as a communications relay for the Mars Polar Lander. The mission was part of the Mars Surveyor ’98 program and aimed to measure atmospheric conditions, monitor surface changes, and map water distribution on Mars.
After a nine-month journey covering 669 million km, the spacecraft approached Mars on September 23, 1999. Minutes before orbital insertion, communication with the orbiter was lost, and it never responded again.
A Critical Navigation Error
The mission timeline showed all systems functioning until insertion began at 09:00 UTC. The probe was expected to enter orbit at about 226 km above the surface. However, data showed it approached Mars far lower than planned, at around 57 km.
At that altitude, the dense atmosphere likely destroyed the spacecraft or sent it hurtling into solar orbit. Initial trajectory checks, performed days earlier, had already hinted at a dangerously low approach. Calculations suggested an altitude between 150 and 170 km, later revised to 110 km — well below the safe threshold of 80 km.
The Units That Didn’t Match
The Mishap Investigation Board determined that the loss was caused by a mismatch between two measurement systems. Lockheed Martin supplied software that reported thruster impulse in pound-force seconds, but NASA’s navigation software expected the data in newton-seconds, a discrepancy of 4.45 times.
This error placed the orbiter on a much lower trajectory than intended. Despite early concerns raised by navigators, a planned corrective maneuver, TCM-5, was never executed.
Aftermath and Costs
NASA declared the mission lost on September 25, 1999. The failure occurred just months before the loss of the Mars Polar Lander, also part of the Mars Surveyor ’98 program. Officials concluded that insufficient cross-checks, inadequate documentation procedures, and funding limitations contributed to the outcome.
The total cost of the Mars Climate Orbiter and Mars Polar Lander missions reached $327.6 million, including development, launch, and operations.
On September 23, 1999, NASA’s Mars Climate Orbiter vanished during its approach to Mars.
A $327.6 million mission ended in silence within minutes, leading to one of NASA’s most costly navigation errors and a discovery that two systems used different measurement units…🧵👇 pic.twitter.com/FDvKIu20Fi
— Fascinating True Stories (@FascinatingTrue) August 27, 2025