A single missing character in a command sequence doomed Phobos 1, a Soviet satellite launched toward Mars in 1988. Weighing over six tons—about the same as four family cars—the probe was intended to study Mars and its moons, particularly Phobos, the largest of the planet’s two moons. On August 28, 29, and 30, 1988, the control center sent a long sequence of commands to the probe. However, one character was missing, causing the onboard computer to misinterpret the sequence. Instead of executing the intended commands, it triggered a test routine that was meant to be removed before launch. This routine disabled the probe’s attitude thrusters, which are crucial for maintaining orientation in space. Without the thrusters, Phobos 1 could no longer align its solar panels with sunlight, causing its batteries to drain. On September 2, 1988, the scheduled communication session never occurred, and contact with the probe was permanently lost. The probe was still several weeks away from its destination, Mars, and would never reach it. Soviet officials later informed the European Space Agency of a "command error" that caused the probe to lose orientation and stop responding to signals. However, Western sources had already reported issues as early as August 29. A dispute between the control centers in Yevpatoria, Crimea, and Moscow over mission direction may have contributed to the problem. Moscow took control of the mission, while Yevpatoria was responsible for verifying each command. This division complicated the process of sending valid commands. Some accounts suggest that a computer used to verify the command sequences was under maintenance, leading a technician to send the code without waiting for verification. This bypassed the usual checks, potentially contributing to the error. Despite the failure of Phobos 1, its twin, Phobos 2, successfully entered orbit around Mars in January 1989. It collected valuable data on the Sun, Mars, and Phobos. However, on March 27, 1989, communications with Phobos 2 also ceased due to a failure of its onboard computer. Neither probe managed to deploy landers on Phobos, which had been a major goal of the mission. Nevertheless, according to an article in Spaceflight in 1988, the plasma measurements around Mars and Phobos were largely successful. The forgotten test routine that caused the failure of Phobos 1 remains a frequently cited example of how critical it is to ensure that flight code is thoroughly tested and properly removed before launch.