Engineers keep an eye on fuel supply of NASA’s oldest Mars orbiter

Measuring the gas provide on Odyssey, a decades-old spacecraft with no gas gauge, isn’t any straightforward process.

Since NASA launched the 2001 Mars Odyssey Orbiter to the Pink Planet nearly 22 years in the past, the spacecraft has looped round Mars greater than 94,000 occasions. That is concerning the equal of 1.37 billion miles (2.21 billion kilometers), a distance that has required extraordinarily cautious administration of the spacecraft’s fuel supply. This feat is all of the extra spectacular on condition that Odyssey has no gas gauge; engineers have needed to depend on math as an alternative.

Their work has helped Odyssey construct a scientific legacy: The spacecraft has mapped minerals throughout the Martian floor, permitting scientists to raised perceive the planet’s historical past. Odyssey has discovered ice deposits that could possibly be utilized by future astronauts. It is studied radiation that would hurt those self same astronauts. And it is scouted potential touchdown websites for missions to come back. Odyssey can also be amongst a small constellation of orbiters that relays information again to Earth from NASA’s rovers and landers (nearly 150 gigabytes up to now, and counting).

However final yr, Odyssey appeared as if it is perhaps working out of fuel: Calculations indicated its hydrazine gas was a lot decrease than anticipated.

Odyssey launched in 2001 with nearly 500 kilos (225.3 kilograms) of hydrazine propellant. As a result of there is no gas gauge, engineers have used quite a lot of methods to deduce how a lot hydrazine the spacecraft has consumed over time. One strategy to measure Odyssey’s gas is to use heat to the spacecraft’s two propellant tanks and watch how lengthy they take to achieve a sure temperature. As with a teapot, a virtually empty gas tank would warmth up sooner than a full one.

That’s, in actual fact, what appeared to happen with a gas estimate carried out on Odyssey in the summertime of 2021. The mathematics appeared to point out that about 11 kilos (5 kilograms) of propellant remained out there—lower than the mission’s modeling had predicted. One other estimate in January 2022 indicated solely 6 kilos (2.8 kilograms) of hydrazine remained.

If the figures have been correct, Odyssey can be working on empty in lower than a yr. Both the spacecraft had skilled some form of failure, like a leak, or one thing was off within the staff’s measurements.

Months of testing and intense investigation ensued. After finding out the thriller of the “lacking” gas, mission engineers have realized new issues about how the getting old spacecraft’s advanced gas system behaves in flight. Their conclusion: The orbiter ought to even have sufficient to final a minimum of via the tip of 2025.

How Odyssey makes use of hydrazine

Odyssey does not want loads of hydrazine to get by on any given day. Photo voltaic panels energy its methods, whereas three strategically positioned response wheels assist the orbiter level its science devices on the Martian floor. Because the response wheels spin contained in the spacecraft bus, or physique, they create torque that causes Odyssey to maneuver in the wrong way.

“These response wheels need to work collectively to keep up the spacecraft’s pointing,” stated Odyssey’s mission supervisor, Jared Name of NASA’s Jet Propulsion Laboratory in Southern California. “However with Odyssey finishing a full loop each orbit, you want a strategy to unload the rising momentum.”

That is the place Odyssey’s hydrazine is available in. The spacecraft’s thrusters launch this propellant in small, calculated bursts to counter the response wheels’ constructing momentum.

Teamwork

So when the staff’s calculations confirmed that their propellant provide was decrease than anticipated, engineers at JPL set to work with these at Lockheed Martin Area, which constructed Odyssey, maintains mission operations, and supplies spacecraft engineering assist.

“First, we needed to confirm the spacecraft was okay,” stated Joseph Hunt, Odyssey’s undertaking supervisor at JPL. “After ruling out the potential for a leak or that we have been burning extra gas than estimated, we began taking a look at our measuring course of.”

The staff agreed that they wanted some recent eyes to evaluate the state of affairs. They introduced in Boris Yendler, an out of doors marketing consultant who additionally focuses on spacecraft propellant estimation.

Like all spacecraft, Odyssey depends on heaters to maintain numerous elements, together with the gas tanks, working within the chilly of space. Yendler puzzled whether or not warmth was being added to the propellant from another supply on the spacecraft, complicating the gas measurement. After numerous experimentation, the staff confirmed that was the case: Heaters alongside a gas line connecting the tanks have been warming them sooner than anticipated, making it appear as if the tanks have been practically empty.

“Our methodology of measurement was nice. The issue was that the fluid dynamics occurring on board Odyssey are extra difficult than we thought,” Name stated.

After determining how a lot warmth wasn’t being accounted for of their calculations, the staff concluded that Odyssey has about 9 kilos (4 kilograms) of hydrazine left. It is sufficient to final the mission for a number of extra years. Though the quantity might change because the staff works to refine the measurements and enhance their accuracy, the staff is resting simpler now that they higher perceive their spacecraft.

“It is a bit like our course of for scientific discovery,” Name stated. “You discover an engineering system not understanding what you will discover. And the longer you look, the extra you discover that you just did not count on.”