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The JWST will not orbit Earth. It will be located near the second Lagrange point (L2) over 1,500,000 km away (The Moon is just 405,000 km from the Earth). Spa

• wyldfire 5y ago
  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.
• pklausler 5y ago
  It's not an orbit, per se, but... it will go around the Earth once per year.
  • phkahler 5y ago
    >> it will go around the Earth once per year. I think more accurately it will go around the sun once per year. The earth will provide the extra gravitational pull (toward the sun) needed to orbit the sun at a larger radius than the earth in the same amount of time as the earth.
    • pklausler 5y ago
      Sure, but it also goes around the Earth once per year, too, sidereally.
      • phkahler 5y ago
        Sure, but I doubt anyone would say that about some of the other lagrange points.
    • sp332 5y ago
      It equally orbits the sun and the earth. Normally, objects with smaller orbits take less time to make a circuit. But this is placed where the earth's gravity pulls it back, just enough to make it take one (earth) year to finish its smaller orbit. So gravity from the earth and the sun are involved.
  • nabla9 5y ago
    Only in the same sense as mars goes around the Earth. Meaningless concept. It never crosses inside Earth orbit. Maybe "co-orbits the Sun with the Earth using Earth's gravity"