As the recent loss of India’s Vikram lander reminds us, spaceflight is still challenging. Sending a spacecraft across millions of kilometers to reach a precise position at a precise velocity in order to orbit another planet is a daunting task, and programming a spacecraft to pull off that feat and then land neatly on the surface of another world is an even greater challenge. Orbiters and landers don’t always make it, but they often manage to send home useful data – and images from their final weeks, days, or moments.
The Soviet Union’s Phobos 2 probe settled into orbit around Mars in January 1989 to study the planet’s two moons, Phobos and Deimos, and for the first few days, everything seemed to be going well. Phobos 2 took 37 photos of Phobos, and it managed to gather some data on the Martian atmosphere in the process. But just as the orbiter made its closest approach to Phobos to release a pair of landers, it lost contact with Earth.
NASA lost contact with Mars Observer in August 1993 just three days before it was scheduled to enter Martian orbit. 26 years later, the agency still isn’t entirely sure whether the orbiter managed to enter orbit successfully or if it missed its Martian rendezvous and kept orbiting the Sun, lost and alone in interplanetary space. But in early 1994, an investigation suggested that the orbiter’s fuel pressurization tank had probably ruptured, setting the spacecraft spinning out of control and disrupting its programmed commands. Before the fateful moment, Mars Observer sent home a few images of Mars.
Mars Climate Orbiter
We’re still not sure if Mars Climate Orbiter broke up in Mars’ thin atmosphere or skimmed past it and vanished into an orbit around the Sun. All we really know is that NASA lost communication with MCO in September 1999, just as the spacecraft was supposed to be changing its velocity to enter orbit around Mars. The mission’s ground control software was using customary units to calculate the spacecraft’s momentum, but it was supposed to be using metric units — and since the rest of the spacecraft’s systems were expecting metric units, MCO ended up flying much too close to Mars and skimming through the red planet’s atmosphere. MCO’s mission was to study the weather on Mars and the distribution of water and dust in the planet’s atmosphere, but instead the doomed orbiter managed to send home a single photo of the planet.
Japan’s Nozomi spacecraft was supposed to orbit Mars for a whole Martian year (about 2 Earth years), but a problem with a valve on its first Earth flyby in December 1998 left it short on fuel. As a result, the spacecraft’s main thruster didn’t fire 5 years later during an important orientation manuver on Nozomi’s last Earth flyby, in preparation for entering Mars orbit. Nozomi’s human team on Earth decided not to risk contaminating the planet with Earth bacteria, so Nozomi only got to do a single Mars flyby before vanishing into orbit around the Sun. But during its lonely interplanetary flights en route to Mars, the failed Mars orbiter managed to return some useful data on Lyman-alpha light, a type of radiation emitted by neutrally-charged hydrogen in certain distant galaxies. It also sent home this image of the Earth and the Moon, the first photograph of the mission.