The spacecraft that has spent a quarter-century orbiting the Red Planet

Space · Published 17 October 2026 Swipe more like this →

In short: The 2001 Mars Odyssey remains the longest-running operation currently stationed on the planet. Launched in 2001, this robotic explorer has completed over 100,000 orbits, serving as a vital communication bridge and a pioneer in mapping the hidden water beneath the Martian surface.

Launched on April 7, 2001, from Cape Canaveral, Florida, 2001 Mars Odyssey arrived at Mars on October 24, 2001. Exceeding both Mars Express and the Pioneer Venus Orbiter, this craft is the most enduring active satellite orbiting a non-Earth world. The mission was famously named as a tribute to Arthur C. Clarke and the 1968 film 2001: A Space Odyssey, after the original candidate name, ARES, was deemed too aggressive.

The spacecraft serves as a critical communication relay, using an X-band radio system to talk to Earth and a UHF system to communicate with landers like the Mars Exploration Rovers and Phoenix. Beyond relaying data, its primary scientific goals involve using spectrometers and a thermal imager to detect water and ice, study geology, and assess the radiation environment for future human exploration. It operates at an altitude of about 250 miles (400 kilometers), providing views of the curving horizon and atmospheric layers similar to what astronauts see from the International Space Station.

One of its most significant discoveries occurred in May 2002, when its GRS instrument detected large amounts of hydrogen, indicating ice within a meter of the surface. This led to the mapping of vast water ice deposits in equatorial regions. While Mars is currently a sterile frozen desert, the spacecraft's data helps scientists understand a planet that was once much more Earth-like, featuring a denser atmosphere and liquid water billions of years ago.

Technologically, Odyssey is powered by a hydrazine propellant system and a radiation-hardened RAD6000 computer—a version of the chip once used in Macintosh computers. With 128 megabytes of RAM and three megabytes of non-volatile memory, it continues to collect data even as it approaches its estimated propellant limit at the end of 2025.

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