2. Basically any satellite in use today uses spinning masses which it can speed up or down to change the direction it's looking. Angular momentum is conserved, but direction pointing isn't. Eventually due to uneven forces (eg, from the sun), these reaction wheels become "saturated" and some propellant is used slow the wheels down. Current estimates put the fuel running out in more than a decade.
3. It's an orbit in L2, past the Earth from the Sun's view. This orbit is unstable, and some of the fuel will also be used to maintain this orbit.
4. There is no refilling mechanism built in. It's likely once the propellant is out the mission will be done. There is the possibility of another spacecraft grabbing onto James Webb and pushing it for station keeping, but it wouldn't be able to refill it. One major innovation with the James Webb though is that it's refrigerator is closed loop, as otherwise running out of coolant would be the mission limiting factor.
2. Basically any satellite in use today uses spinning masses which it can speed up or down to change the direction it's looking. Angular momentum is conserved, but direction pointing isn't. Eventually due to uneven forces (eg, from the sun), these reaction wheels become "saturated" and some propellant is used slow the wheels down. Current estimates put the fuel running out in more than a decade.
3. It's an orbit in L2, past the Earth from the Sun's view. This orbit is unstable, and some of the fuel will also be used to maintain this orbit.
4. There is no refilling mechanism built in. It's likely once the propellant is out the mission will be done. There is the possibility of another spacecraft grabbing onto James Webb and pushing it for station keeping, but it wouldn't be able to refill it. One major innovation with the James Webb though is that it's refrigerator is closed loop, as otherwise running out of coolant would be the mission limiting factor.