In regards to the James Webb telescope(congrats, NASA!): How does the solar shield NOT act like a solar wind sail, which would cause the telescope to be steadily pushed away from us and require frequent re-alignment?

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In regards to the James Webb telescope(congrats, NASA!): How does the solar shield NOT act like a solar wind sail, which would cause the telescope to be steadily pushed away from us and require frequent re-alignment?

In: 143

It does… There is an aft flap that serves to counter balance that rotation keeping the telescope oriented correctly

Very good question! JWST has an “aft momentum flap” which works to counter this effect. It lets it, sort of surf or sail on the pressure from the sun’s radiation to steer it in the right angle.

You can read more about it here: https://blogs.nasa.gov/webb/2021/12/30/webbs-aft-momentum-flap-deployed/

Secondary question because I’m too lazy to make a new post. How does it orbit a point in space at L2? What I’m referring to is the vertical orbit it makes to keep in line of the sun around the earth while it’s in its stationary orbit.

Good question. You gotta see which force is acting against that pressure. The telescope is not at the L2 exactly, but slightly “before” so it has the ever slightest tendency to get pulled towards the sun. This gravitational force is bigger than the solar wind pressure, so you need fuel to ever stay as close to L2 as possible, not overshot.

The aft momentum flap is to counteract rotation caused by the wind pressure, and not to act against the outward force of the wind pressure: the shield is rarely perpendicular to the sun rays, which causes a rotation as the sun beam is reflected off.

If I remember correctly the L2 orbit is always behind the earth in relation to the sun. So the James Webb will be in shadow and not have as much solar wind. Just that deflected by Earth’s field.

It does, to a degree. But the spacecraft has fuel the inertia wheels to allow maneuvering to compensate. The sail force is very small.

First, solar light has many many many times more effect than solar wind. Then, the shield acts as a light sail, but it’s rather small force (at this distance from the Sun the force is about 1/100th pound per acre or about 1kg per square kilometer) but it’s accounted for in orbital positioning (the orbit would be slightly shifted towards the Sun to counter that).

The main effect is that solar radiation would try to rotate the craft to “topple” it, as the mass behind the shield isn’t symmetrically distributed. But this is accounted for too, as the craft has special solar radiation “rudder” which allows countering this.