NASA’s Kepler space telescope is running out of fuel

Solar wouldn’t power the jets used to orient it

It was only supposed to be in orbit a few years then some issues arose and NASA altered the mission statement. Now it’s more of a “stick it out there and see how much we can find” type of mission.

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Shouldn’t NASA be able to pretty accurately guess how much fuel has been burned? Or is this thing just kind of doing whatever it wants?

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You'd be shocked how much these probes vary from how much power they consume. The Voyager probes are still active, and no one thought they'd last past the 80s.

Don’t worry, she has a plan

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Shouldn’t NASA be able to pretty accurately guess how much fuel has been burned?

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Found this regarding NASA link

Why is measuring fuel supply in space so difficult?

On the ground, measuring fuel supply in a vehicle is easier, but it’s still difficult to be accurate. Gravity keeps all the fuel at the bottom of the tank and a float sensor can measure how high the tank is filled. But as the fuel level drops, uncertainties in the fuel height, amount of fuel in the lines between the tank and the engine, and how completely the tank will drain, means predicting when an engine will stop running is inherently uncertain.

In space, the problem is exacerbated. Without gravity, the fuel doesn’t “drain out the bottom,” and a simple float doesn’t work. Kepler’s fuel system uses a common approach in which the fuel tank includes an internal air bladder that is pressurized before launch to “push” the fuel into the lines. As the fuel is consumed, the bladder expands to take up more space and keep the fuel under pressure. The pressure is monitored and is used as an indicator of how much fuel remains as the expansion of the bladder results in a predictable drop in pressure. But as that remaining fuel drops and the expansion of the bladder is impeded by the walls of the tank, that predictability begins to degrade.

Another approach is to monitor the duration of each thruster firing — how long the fuel is allowed to flow through the engine with each use — and compare the accumulated time with an estimate of the total time it would take to empty the tank. The Kepler team uses this approach as well, measuring the firing times of each thruster when they are used. But this approach also has limitations. An automobile engine doesn’t use the same amount of fuel for each revolution — for example, you use more fuel when accelerating than you do coasting, even if the engine is turning at the same speed — and a spacecraft thruster’s performance also changes depending on how it’s used.

There are even more difficult ways to estimate fuel usage by analyzing how the spacecraft’s momentum has changed over its lifetime. Accounting for all the environmental disturbances, the unexplained leftover momentum must have been accounted for by fuel usage, and that usage can be estimated.

All these approaches are used, and the team generates a consensus estimate of the remaining fuel, along with the uncertainty. In the end, what we end up with is this estimate, not a precise knowledge.

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DavidTheGnome

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Your threads suck