Designing, building and launching a spacecraft is enormously expensive. That is why NASA missions to Mars are designed in the hope that they will last as long as possible, like the famous rover Opportunity, which was supposed to last 90 days and managed to go on for 15 years. The longer a mission can continue to run, the more data it can collect and the more we can learn from it.
That’s true for orbiters that travel around Mars, as well as rovers that explore its surface, like the Mars Odyssey spacecraft, which launched in 2001 and has been in orbit around Mars for more than 20 years. But the orbiter can’t keep running forever, as it will eventually run out of fuel, so determining exactly how much fuel is left is important, but it also turned out to be more complicated than NASA engineers expected.
Odyssey started with nearly 500 pounds of hydrazine fuel, though last year it appeared the spacecraft was running on much less fuel than anticipated.
The problem is that there’s no easy way to tell how much fuel is left, so engineers use methods like heating the tank and seeing how long it takes to reach a temperature that indicates how much mass is inside. This method had been used to calculate the low amount of fuel left, so there was a leak in the spacecraft or the measurement was wrong.
“First, we had to verify that the spacecraft was OK,” Joseph Hunt, Odyssey project manager at NASA’s Jet Propulsion Laboratory, said in a statement. “After ruling out the possibility of a leak or that we were burning more fuel than estimated, we began looking at our measurement process.”
After examining the systems, the team discovered that the problem had to do with the way the spacecraft heats up and cools down. Because electronic components must be kept warm to function properly in the cold space environment, Odyssey uses heaters to keep parts, including fuel tanks, warm. But these heaters were also heating the fuel inside the tanks, so when the team made their thermal measurements to estimate the remaining fuel, it appeared there was less fuel inside than there really was.
“Our measurement method was fine. The problem was that the fluid dynamics that occur aboard Odyssey is more complicated than we thought,” said Jared Call, Odyssey’s mission manager.
The good news is that, accounting for the heat, Odyssey has at least 9 pounds of fuel left, which should last until at least the end of 2025. Odyssey will therefore be able to continue observing Mars and may even make it to its 25-year anniversary. of year
“It’s a bit like our scientific discovery process,” Call said. “You explore an engineering system without knowing what you will find. And the more you look, the more you find what you didn’t expect.”
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