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How long can it stay stable at that point? Does it have thrusters to keep a station there? If so, how long is the fuel for them provisioned for? Does use of

How long can it stay stable at that point? Does it have thrusters to keep a station there? If so, how long is the fuel for them provisioned for? Does use of the thrusters impact the sensors that the telescope uses?

pageandrew 5y ago
The orbit needs to be actively maintained. The telescope was designed for a 5.5 year mission, but NASA says it could last up to 10.5 years with proper fuel management. It has two different types of thrusters under the "Propulsion Subsystem". > One kind is called "Secondary Combustion Augmented Thrusters" (SCAT), and they are used for orbit correction (like applied changes in velocity for each maneuver the spacecraft makes and also for orbit station-keeping). The SCATs are bi-propellant thrusters, using hydrazine (N2H4) and dinitrogen tetroxide (N2O4) as fuel and oxidizer, respectively. > The other kind of thruster on Webb is called a MRE-1, or mono-propellant rocket engine, since it only uses hydrazine. There are eight MRE-1s on Webb, and they are used for attitude control and momentum unloading of the reaction wheels Ref: https://jwst-docs.stsci.edu/jwst-observatory-hardware/jwst-spacecraft-bus/jwst-propulsion https://jwst-docs.stsci.edu/jwst-observatory-hardware/jwst-s...
spywaregorilla 5y ago
> Does use of the thrusters impact the sensors that the telescope uses? The point of sitting in a lagrange point is that you can stay there without moving due to two gravitational forces. That's not perfectly accurate, but I don't think it needs constant thrust, just occasional taps.
deleted 5y ago
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hguant 5y ago
The L2 point is unstable with a period of 23 days? I believe, so the JWT needs a course correct burn to stay positioned correctly (called station keeping). It does have thrusters - a ring of 16 hydrazine "burning" units that can produce thrust on 3 axis. The fact that the L2 point is unstable and that thrusters are required puts a lifetime on the telescope - I think NASA plans for a minimum of 5 1/2 years and are hoping to get up to 10. That's entirely reliant on the fuel supply. The use of thrusters does impact the sensors the telescope uses. NASA et al schedule usable telescope time around burns, and general attitude shifts/correction. The telescope uses a bunch of gyroscopes/flywheels to point itself in the proper direction, during maneuvers like that the sensors aren't operable.
- wyldfire 5y ago
  > The fact that the L2 point is unstable and that thrusters are required puts a lifetime on the telescope - I think NASA plans for a minimum of 5 1/2 years and are hoping to get up to 10. That's entirely reliant on the fuel supply. So when the fuel is exhausted the orbit decays and the unshielded telescope disintegrates on re-entry into Earth's atmosphere?
  - lmm 5y ago
    > So when the fuel is exhausted the orbit decays and the unshielded telescope disintegrates on re-entry into Earth's atmosphere? Or drifts off into its own orbit around the Sun, but essentially yes.

pageandrew 5y ago

The orbit needs to be actively maintained. The telescope was designed for a 5.5 year mission, but NASA says it could last up to 10.5 years with proper fuel management. It has two different types of thrusters under the "Propulsion Subsystem". > One kind is called "Secondary Combustion Augmented Thrusters" (SCAT), and they are used for orbit correction (like applied changes in velocity for each maneuver the spacecraft makes and also for orbit station-keeping). The SCATs are bi-propellant thrusters, using hydrazine (N2H4) and dinitrogen tetroxide (N2O4) as fuel and oxidizer, respectively. > The other kind of thruster on Webb is called a MRE-1, or mono-propellant rocket engine, since it only uses hydrazine. There are eight MRE-1s on Webb, and they are used for attitude control and momentum unloading of the reaction wheels Ref: https://jwst-docs.stsci.edu/jwst-observatory-hardware/jwst-spacecraft-bus/jwst-propulsion https://jwst-docs.stsci.edu/jwst-observatory-hardware/jwst-s...

spywaregorilla 5y ago

> Does use of the thrusters impact the sensors that the telescope uses? The point of sitting in a lagrange point is that you can stay there without moving due to two gravitational forces. That's not perfectly accurate, but I don't think it needs constant thrust, just occasional taps.

deleted 5y ago

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hguant 5y ago

The L2 point is unstable with a period of 23 days? I believe, so the JWT needs a course correct burn to stay positioned correctly (called station keeping). It does have thrusters - a ring of 16 hydrazine "burning" units that can produce thrust on 3 axis. The fact that the L2 point is unstable and that thrusters are required puts a lifetime on the telescope - I think NASA plans for a minimum of 5 1/2 years and are hoping to get up to 10. That's entirely reliant on the fuel supply. The use of thrusters does impact the sensors the telescope uses. NASA et al schedule usable telescope time around burns, and general attitude shifts/correction. The telescope uses a bunch of gyroscopes/flywheels to point itself in the proper direction, during maneuvers like that the sensors aren't operable.

wyldfire 5y ago
> The fact that the L2 point is unstable and that thrusters are required puts a lifetime on the telescope - I think NASA plans for a minimum of 5 1/2 years and are hoping to get up to 10. That's entirely reliant on the fuel supply. So when the fuel is exhausted the orbit decays and the unshielded telescope disintegrates on re-entry into Earth's atmosphere?
- lmm 5y ago
  > So when the fuel is exhausted the orbit decays and the unshielded telescope disintegrates on re-entry into Earth's atmosphere? Or drifts off into its own orbit around the Sun, but essentially yes.