On March 27, 1989, the Soviet Union's Phobos 2 mission to Mars' moons ended in failure. [‘On This Day in Space’ Video Series on Space.com](https://www.space.com/39251-on-this-day-in-space.html)

But the whole mission was definitely not a failure. Phobos 2 arrived in Mars orbit two months earlier and had been studying Mars and Phobos, the larger of the planet's two moons. During that time, it beamed 37 pictures of Phobos back to Earth. For the final phase of its mission, the spacecraft was getting ready to drop off two small landers on Phobos. One lander was actually something called a "hopper" that could move around on the moon's surface. As Phobos 2 made its way over to Phobos to deploy the landers, mission control suddenly lost contact with it, and the mission was lost. The cause of this failure was determined to be a computer error.