mfb said:
155,000 km, 10.7% - but that's 10% of the distance not the time. The telescope is fast early on and slows down as its distance to Earth increases.
The first mid-course correction should happen within the next hour. Doing it early in the flight improves the efficiency - both from a smaller accumulated position error and from the Oberth effect.
Correct.
One quick note though, performing maneuvers early on are only more efficient via the Oberth effect if they are prograde (in the direction of motion) or retrograde (in the opposite direction of motion). More-so, JWST has severe limitations concerning retrograde maneuvers at this point in its trajectory. If it accidentally overshoots its prograde maneuvers, it could potentially doom itself to zipping past L2 with little or no way to recover.*
For directions orthogonal to the direction of motion (e.g., "normal," "anti-normal," "radial-in," "radial-out"), the Oberth effect actually
hurts the efficiency, rather than helps. For maneuvers in these directions, it may be best to wait until the Earth's and Sun's gravitational tug slows it down a little. This competes with the idea that since a small change to an orbit now will have a large change to the orbital position later, that generally speaking, orbital adjustments should be done sooner rather than later. My point here is that the Oberth effect itself only helps the efficiency of prograde/retrograde maneuvers, and decreases the efficiencies of orthogonal maneuvers, in and of itself.
There's another mid-course correction scheduled in a couple of days (MCC1b).
*[Edit: And it is for this reason that Ariane-5's second stage
intentionally cut short of placing the JWST directly on a path to L2. Overshooting L2 could doom the mission. So JWST will make up the difference during its mid-course correction burns (in addition to its final insertion burn), where the JWST thrusters have more fine control.]
I will watch this later today!
