In December 1998, NASA launched the Mars Climate Orbiter, a 638-kilogram spacecraft designed to study the climate and atmosphere of Mars. The mission aimed to place the probe in orbit around the planet, but it failed to do so. It is believed the spacecraft either burned up in Mars' atmosphere or crashed onto its surface. This failure was due to a critical error in unit conversions between two engineering teams working on the mission. The Jet Propulsion Laboratory (JPL), responsible for the spacecraft’s navigation, used the metric system, which is standard in most scientific fields. However, Lockheed Martin, the company that built the probe, used imperial units, commonly used in the United States. This discrepancy led to an error factor of 4.45, which significantly affected the spacecraft’s trajectory. Specifically, a software module called SM_FORCES, developed by Lockheed Martin, calculated angular momentum in pound-seconds, while the JPL navigation system expected newton-seconds. The mission’s technical requirements called for metric units, but the Lockheed Martin software continued using imperial units throughout the nine-and-a-half-month journey to Mars without being detected. As the spacecraft approached Mars, the JPL team noticed that the trajectory data did not match their predictions. They reported the issue, but it was not given high priority due to unclear communication and lack of traceability between the two teams. Over time, the frequency of maneuvers to adjust the spacecraft’s angular momentum became higher than expected, causing a gradual deviation in its path. A final check was performed shortly before the planned orbital insertion, but by then, it was too late to correct the course. An investigation later confirmed that the primary cause of the failure was the absence of a unit conversion from imperial to metric in the navigation software. In response, NASA implemented several changes, including stronger cross-checks between teams, more consistent documentation, and improved attention to weak or ambiguous signals from field teams. The Mars Climate Orbiter failure is now a well-known case study in system failures, emphasizing the critical need for unit consistency across all components of a mission, especially in complex engineering projects involving multiple teams.