Scientists Solve Mystery of Mars Orbiter’s Lack of Fuel

For nearly two years, NASA engineers had worried that the fuel supply for the Mars Odyssey orbiter was running out, brings a tragic end to the precious spacecraft. But as it turns out, they had miscalculated what’s left in the orbiter’s gas tank and that it’s good to go for another two years, according to NASA.

Mars Odyssey has orbited the red planet for more than two decades, covering a distance equivalent to 1.37 billion miles (2.21 billion kilometers) in space. When it was launched in 2001, the orbiter had 500 pounds (225.3 kg) of hydrazine propellant to propel it through its orbital. travels around Mars. What Odyssey doesn’t do though has is a fuel gauge, making it difficult for mission controllers determining exactly how much fuel the orbiter has left in its tank.

To check the orbiter’s fuel supply, the mission team would heat up the spacecraft’s two propellant tanks and see how long it takes for them to reach a certain temperature. “As with a teapot, a nearly empty fuel tank would heat up faster than a full one,” NASA wrote. It’s not perfect, but it still gave mission control a good estimate of how much gas was left in the tank, so to speak.

By the summer of 2021, fuel estimates appeared to indicate that the Odyssey was running low with about 11 pounds (5 kg) of propellant remaining. Later in January 2022, the team’s calculations showed that only 2.8 kg of hydrazine remained, according to NASA. That meant the mission would run out of fuel in less than a year, sooner than the team had expected.

Odyssey captured this image of Martian sand dunes in 2006.
Image: NASA/JPL-Caltech/ASU

Mission engineers were shocked; either the spacecraft was leaking fuel or their calculations were simply off. They spent months figuring it out before bringing in an outside consultant, Boris Yendler, who specializes in spacecraft propellant estimation.

After studying the inner workings of the Odyssey, Yendler pinpointed the reason behind the disappearing fuel. The orbiter uses heaters to prevent its parts from freezing in the depths of space, and one of its heaters, which connects the fuel tanks, caused the propellant to heat up at a faster rate than expected. As a result, the team’s attempts to estimate how much fuel was left in the Odyssey were thwarted when the propellant heated up faster than they expected, leading them to believe that there was less fuel in the orbiter’s tank.

“Our measurement method was fine. The problem was that the fluid dynamics occurring on board the Odyssey are more complicated than we thought,” Jared Call, of NASA’s Jet Propulsion Laboratory in Southern California, said in the statement. I mean, it seems a little defensive, but okay.

The mission team went back to the drawing board and calculated how much fuel was left in the Odyssey while accounting for the extra heat. It turns out that the orbiter is good to go until 2025. But that doesn’t mean it is guaranteed, as the team is still working on refining the measurements.

“It’s kind of like our process for scientific discovery,” Call said. “You explore an engineering system not knowing what you’re going to find. And the further you look, the more you find out that you didn’t expect.”

Odyssey is a crucial member of NASA’s Mars fleet. The orbiter not only relays data between NASA’s ground control and its rovers on Mars, it has also aided in the discovery of minerals, ice deposits and potential landing sites on the Red Planet. Hopefully the spacecraft still has some gas left in the tank, continuing its 22-year legacy.

More: Curiosity Rover finds clear evidence of ancient water on Mars

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