I gather that the James Web Space Telescope (JWST) has just deployed its "aft momentum flap". However I cannot find much other information. It is described as the "aft" momentum flap as if there might also be a "fore" momentum flap, but I don't think that's the case. It's also likened to a trim tab on an airplane which can be adjusted to keep the plane level in flight. But this trim tab appears to be fixed in position and not adjustable or retractable.
Presumably there is a set of detailed calculations that calculates the expected center of pressure on the sun shields in various telescope orientations. Is this documented anywhere?. The torque and build-up of angular momentum arises from the mismatch between the center of pressure and the center of mass. The momentum flap is set at a particular angle, is this to help keep the center of pressure and center of mass aligned over the wide range of orientations required for observations? What is the momentum flap made of? What are the moments of inertia of JWST? etc.
This is an interesting topic, so if anyone can point me to more detailed description, I'd appreciate it.
 added picture showing stability from solar sail with dihedral angle concave towards center of mass. For small angles this reduces to a restoring torque proportional to the rotation $\theta$. If the dihedral is the opposite, then it's a destabilizing torque.
I see there are some papers being published by SPIE that might be relevant, but they're behind a paywall.