B Question re Webb telescope at L2

[Buzz Bloom]

TL;DR

The article https://jwst.nasa.gov/content/about/orbit.html describes the planned placing the Webb telescope in orbit near the L2 Lagrange point of the Earth-Sun system. But L2 is gravitationally unstable.

The diagram in the article seems to say that the Webb will orbit around the unstable L2 point. At any distance near L2 but not exactly at L2 the Webb will tend to move further from L2, unless Webb has an engine and fuel to maintain it in the special orbit. I was not able to find any description of such an engine, so I am asking the Physics Forums participants what they might know about this.

 

[anorlunda]

https://en.wikipedia.org/wiki/James_Webb_Space_Telescope#Orbit

The telescope will circle about the L2 point in a halo orbit, which will be inclined with respect to the ecliptic, have a radius of approximately 800,000 km (500,000 mi), and take about half a year to complete.[30] Since L2 is just an equilibrium point with no gravitational pull, a halo orbit is not an orbit in the usual sense: the spacecraft is actually in orbit around the Sun, and the halo orbit can be thought of as controlled drifting to remain in the vicinity of the L2 point.[146] This requires some station-keeping: around 2–4 m/s per year[147] from the total budget of 150 m/s.[148] Two sets of thrusters constitute the observatory's propulsion system.[