NASA's Mars Odyssey reached the Red Planet on October 24, 2001, and it is still operating today, according to WIRED. Alongside its sibling, the Mars Reconnaissance Orbiter (MRO), it has now run far longer than anyone involved in the launches expected, and the two missions have together reshaped the scientific picture of water on Mars, both in the past and in the present.
Keeping the pair alive this long has taken careful engineering, steady troubleshooting and, by WIRED's account, a measure of luck. Both craft were originally built to last only a few years.
Why it matters
Briony Horgan, a planetary scientist at Purdue University who is not affiliated with either mission, told WIRED that Odyssey and MRO rank among the most productive spacecraft ever built and described them as essential to NASA's Mars research as a whole. Odyssey's surveys of Martian ice and MRO's ability to track how surface features shift over time have each given researchers a far richer view of Mars as an active world rather than an inert mass of rock, according to WIRED.
The orbiters also serve a practical role: they relay communications between Earth and every NASA rover on the surface, since those rovers cannot talk to Earth directly. WIRED reports that this is a notable legacy for two spacecraft that were meant to operate for only a few years.
Surviving a harsh environment
Space is an unforgiving place, and lasting decades there requires both resilience and good fortune. WIRED reports that high-energy particles constantly strike spacecraft hardware, and a strong enough hit on a sensitive instrument can end it. Ground teams also cannot watch over a Mars orbiter the way they can monitor satellites circling Earth. Rob Lillis, a planetary and space physicist at the University of California, Berkeley, who has worked on more recent Mars orbiters, told WIRED that bandwidth to Mars is limited, so science craft may check in only once or twice a week.
Losing a single instrument is a setback, but losing power or computing systems can disable the entire spacecraft. To guard against that, NASA routinely installs duplicate copies of critical components, so a mission can keep running on a backup while engineers work out a fix, according to WIRED.
MRO has run into a problem that stems directly from its longevity. The orbiter fixes its position and orientation by matching what its cameras see against a star map stored onboard. Paul Fieseler, an engineer at NASA's Jet Propulsion Laboratory and MRO's chief engineer, told WIRED that the spacecraft is old enough that some of those stars have drifted slightly across the sky. Those small discrepancies confused the craft, and last year engineers uploaded a revised map to keep it oriented correctly going forward.
Odyssey's main vulnerability is different: it is running low on the propellant used for small adjustments that hold its orientation in space. WIRED reports that the spacecraft has no fuel gauge, because without gravity to settle the liquid there is no volume to measure, so NASA cannot say how much remains. Engineers have devised new procedures that let the craft operate fully on very small amounts of propellant in an effort to stretch out its life.
Lessons from earlier failures
WIRED reports that both missions benefited from failures during NASA's "faster, better, cheaper" period. In 1999 the agency lost two spacecraft as they arrived at Mars. The Mars Climate Orbiter burned up in the atmosphere, and months later the Mars Polar Lander crashed into the surface. Investigations traced the first to a unit mismatch between a ground system using imperial measurements and a flight system using metric, and the second to a software error that testing had not caught.
Glen Havens, an engineer at JPL and project and mission manager for Mars Odyssey, told WIRED that those losses weighed heavily on the team assembling Odyssey. With the failures fresh, NASA put more resources into refining Odyssey and MRO before launch, designing both for maximum durability and testing every component and system configuration.
A central design principle was what NASA calls margin, the spacecraft equivalent of packing an extra snack in case of need. Nilton Renno, a spaceflight engineer at the University of Michigan who has not worked on either mission, told WIRED that unexpected problems arise and a spacecraft must be built to survive them. Fieseler noted that MRO launched with a bigger battery and more propellant than its requirements demanded, and that reserve is what keeps it flying now, with NASA hoping for another decade of operation.
What comes next
Nothing in orbit around Mars can be taken for granted. WIRED reports that last year NASA lost the Mars Atmosphere and Volatile Evolution mission, its youngest orbiter at 11 years old, after it unexpectedly lost power on the planet's far side.
As Odyssey and MRO age, questions remain about their successors. NASA has contracted Blue Origin to build a dedicated communications satellite that will relay large volumes of data to Earth for at least five years, but unlike the earlier orbiters, which started as science missions before taking on communications work, this one will only pass along signals from other spacecraft, according to WIRED.
The agency's Mars science plans are relatively modest. One mission led by Lillis involves two orbiters already traveling to Mars to study how the planet reacts to the continuous flow of charged particles from the sun, though he told WIRED it sits "right on the edge of being too small to do good science." WIRED also notes Skyfall, a set of three small helicopters intended to launch aboard the first nuclear-powered spacecraft, though the source material does not describe that mission further.
What to watch: whether NASA commits to another large science orbiter at Mars, or whether Odyssey and MRO end up as the last of their line.
