For nearly two years, NASA engineers had been worried that the fuel supply of the Mars Odyssey orbiter was running low, bringing 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.
The Mars Odyssey has been orbiting the Red Planet for over two decades, traveling a distance equivalent to 1.37 billion miles (2.21 billion kilometers) in space. When it launched in 2001, the orbiter had 500 pounds (225.3 kilograms) of hydrazine propellant to power it through its orbital journeys around Mars. However, what Odyssey doesn’t have is a fuel gauge, making it difficult for mission controllers to determine exactly how much fuel the orbiter has left in its tank.
In order to check on the orbiter’s fuel supply, the team behind the mission 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.
In the summer of 2021, fuel estimates seemed to indicate that Odyssey was running low with about 11 pounds (5 kilograms) of propellant remaining. Later in January 2022, the team’s calculations showed that only 6 pounds (2.8 kilograms) of hydrazine remained, according to NASA. That meant that the mission would run out of fuel in less than a year, sooner than the team had anticipated.
Mission engineers were stumped; either the spacecraft was leaking fuel or their calculations were simply off. They spent months trying to figure it out before bringing in an outside consultant, Boris Yendler, who specializes in spacecraft propellant estimation.
After studying the inner workings of Odyssey, Yendler pinpointed the cause behind the disappearing fuel. The orbiter uses heaters to keep its parts from freezing in the depths of space, and one of its heaters, which connects the fuel tanks, was causing the propellant to warm at a faster rate than expected. As a result, the team’s attempts to estimate how much fuel was left in Odyssey were foiled as the propellant heated up faster than they anticipated, leading them to think there was less fuel in the orbiter’s tank.
“Our method of measurement was fine. The problem was that the fluid dynamics occurring on board Odyssey are more complicated than we thought,” Jared Call, from NASA’s Jet Propulsion Laboratory in Southern California, said in the statement. I mean, that seems a little defensive, but okay.
The team behind the mission went back to the drawing board, calculating how much fuel was left in Odyssey while accounting for the extra heat. It turns out, the orbiter is good to go until 2025. But that’s not to say it’s guaranteed, as the team is still working towards refining the measurements.
“It’s a little like our process for scientific discovery,” Call said. “You explore an engineering system not knowing what you’ll find. And the longer you look, the more you find that you didn’t expect.”
Odyssey is a crucial member of NASA’s Martian fleet. The orbiter not only relays data between NASA’s ground control and its rovers on Mars, it has also helped in the discovery of minerals, ice deposits, and potential landing sites on the Red Planet. Hopefully the spacecraft still has some gas left in its tank, continuing its 22-year-old legacy.
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