In 1988, the Soviet Union launched two of its most ambitious spacecraft ever, not toward Mars itself, but toward one of its moons, a small, odd-shaped rock called Phobos. The mission was unlike anything attempted before.
One of the probes carried a jumping robot designed to literally jump across the surface of an alien moon. Scientists from 14 different countries participated. NASA was helping track the spacecraft from Earth. If everything had gone as planned, the Soviet Union would have made history. Instead, one spacecraft was killed by a single wrong command written from Earth, and the other fell silent just days before the big moment.
Neither probe ever touched Phobos.
What is Phobos and why did the Soviet Union want to explore the mysterious moon of Mars?
Phobos is one of the two moons of Mars, and it is an alien moon. It is small, only about 22 kilometers across, and its origin has long puzzled scientists. Some believe it is an asteroid captured by Mars’ gravity. Others believe it formed alongside the planet itself. Either way, studying Phobos up close could reveal important clues about how the solar system formed.
By the mid-1980s, Soviet space planners were looking to go beyond orbiters and simple flybys of Mars. They wanted to study Mars from its orbit, look at how the solar wind interacts with the planet, and, most ambitiously, actually land on the surface of Phobos. According to NASA’s HEASARC mission archive, the Phobos program was designed to study both Mars and its moon at the same time, in a way no mission has done before.
The Phobos spacecraft was the largest interplanetary probe ever built by the Soviets
Both spacecraft weighed more than 6,200 kilograms when fully fueled, making them among the largest interplanetary probes ever launched at the time.
It was filled with scientific instruments, cameras, spectrometers, x-ray and gamma-ray detectors, plasma analyzers, magnetometers, dust detectors, and more. These were not simple camera ships. They were essentially flying laboratories.But what made the mission truly special was what the probes were carrying to the surface of Phobos. One of the landers was a standard fixed science platform.
The other one called PROP-F was something completely new. Since Phobos has very weak gravity (about 2,000 times weaker than Earth’s), the wheeled spacecraft must have floated away. So engineers designed a robot that moved by jumping, hopping from place to place, and analyzing rocks, magnetic fields, and surface chemistry as it moved.
It would have been the first jumping robot to be operated in another world.
How did a faulty programming command kill Phobos 1 before it reached Mars?
Phobos 1 launched in July 1988, and everything seemed fine until an error occurred during a routine software load.
One incorrect command accidentally shut down the spacecraft’s attitude control system. This is the system that keeps the spacecraft oriented correctly in space, making sure the solar panels stay pointed toward the sun.Without it, Phobos 1 would slowly drift out of alignment. Its solar panels stopped receiving sunlight. Batteries drained. This is what happened, as the spacecraft stopped permanently, billions of kilometers from Earth, and was never heard from again.
It didn’t even reach Mars. This remains one of the most famous bugs in the entire history of spaceflight, and is a reminder that in space, a single line of bad code can kill a billion-dollar mission in minutes.
How Phobos 2 got to Mars and spent two months sending back valuable science
The second spacecraft was launched a few days after the first, and had much better luck, at least initially. After a seven-month journey, Phobos 2 successfully entered orbit around Mars in January 1989. For about two months, its science performance was truly impressive. It studied Martian dust, the interaction of the solar wind with the planet, and magnetic fields around Mars, and sent back 37 close-up images of Phobos, many of which were clear enough to reveal surface features as small as 40 meters across.
For years, these were the best pictures humanity had ever taken of the Moon.The mission also contributed to early mineral maps of Mars using infrared data and improved scientists’ understanding of how the solar wind strips molecules from the Martian atmosphere over time, a process linked to why Mars, which once had a thicker atmosphere, is a barren planet today.
The final days of Phobos 2 and how the mission ended before its greatest moment
The entire mission was aimed at one thing: getting close enough to Phobos to launch both probes.
The plan was for Phobos 2 to come within about 50 meters of the lunar surface before abandoning its landers. On March 27, 1989, just days before this happened, the spacecraft came to a complete stop.Investigations later concluded that the aircraft’s on-board computer was the most likely cause of the failure, although problems with the radio transmitter may also have played a role. By the time Phobos 2 reached Mars, many of the computers on board were already experiencing problems, and there were very few backups left. Neither probe was ever published.
The mission ended at the worst possible moment.
What the Phobos mission achieved and why it remains important in the history of space exploration
Although both spacecraft failed before they could complete their main objective, the Phobos program was not a total loss. The science brought back by Phobos 2 led to dozens of research papers in the early 1990s and contributed real knowledge about Mars’ atmosphere, magnetic environment, and the surface of its moon. Close-up images of Phobos have been the best available for many years.The mission is also a great example of international scientific cooperation during the Cold War, with researchers from 14 countries contributing, and even NASA providing tracking support. It was one of the broadest scientific collaborations of its time.But the Phobos program also reinforced a painful pattern in Soviet and later Russian planetary exploration: technically impressive spacecraft were repeatedly shot down due to software bugs, electronics failures, or bad luck. Neither the Mars 96 mission nor Phobos-Grunt were successful in the decades that followed, making Phobos one of the most tempting and least explored destinations in the solar system. The jumping robot that never got to jump, and the moon that was never touched, remain one of the most haunting questions in space history.
