Has JWST done its first station keeping yet? The last burn I know about was the MCC2 burn on Jan24; more than 21 days ago; and that was a pretty long burn with a $\Delta v$ of 1.6 m/sec or 160 cm/sec, which is much larger than the 12cm/sec minimal so I would assume they would want another burn at 21 days just because JWST must always stay on the Earth side of the halo orbit, and there had to be some reasonable margin in the MCC2 burn.

This question is somewhat inspired by uhoh's answer to How frequent are (or will be) JWST station keeping burns at L2? which quotes the Monte Carlo Paper:

Stationkeeping (SK) maneuvers will be performed every 21 days to keep JWST in an LPO around the unstable SEM L2 point... a planned maneuver that would be smaller than 12 cm/sec would be skipped for efficiency... so in most cases an SK maneuver would be performed every 42 days, not every 21 days.

A second somewhat related question is how close does JWST get to the top of the hill/saddle, from which JWST would escape, including the solar radiation? The closer JWST is to the saddle, the less fuel is used for station keeping, but JWST must always stay on the Earth side of the saddle since the station keeping engines only fire in one direction, towards the sun.

For the 2nd half of the question, take JWST's current position and velocity, and only change the distance to the sun. The if JWST is a few hundred kilometers further from the sun, or at most a few thousand kilometers early in the project, then JWST is on the wrong side of the saddle and will irrevocably escape Earth's pull and go into orbit around the sun instead.

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    $\begingroup$ As of the JPL Horizons data updated on 2022-Feb-25, there have been no more burns since MCC2. See ssd.jpl.nasa.gov/api/… $\endgroup$
    – PM 2Ring
    Mar 1, 2022 at 6:03
  • $\begingroup$ The top of the saddle is the L2 point. Over the timespan covered by the projected data currently on Horizons, the minimum distance from JWST to L2 is usually around 500,000 km, although it gets as low as 450,000 km at the end of 2023. You can use my script at space.stackexchange.com/a/55061/38535 to make a plot. Use JWST for the target, and @32 (which is the Sun-EMB L2 point) for the center. $\endgroup$
    – PM 2Ring
    Mar 1, 2022 at 8:15
  • $\begingroup$ @PM2Ring The physical distance to L2 doesn't matter as L2 is not a point in space. It's a point in 6-dimensional phase space of position and velocity. JWST could be exactly at L2 (or even behind) and still be on "the Earth side of the saddle". $\endgroup$
    – asdfex
    Mar 1, 2022 at 14:10
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    $\begingroup$ @asdfex Fair point. Being exactly at the designated L2 location is only "on the saddle" if your velocity in the corotating frame is zero. Still, it is nice to stay on this side of L2, and JWST certainly does (will do) that. $\endgroup$
    – PM 2Ring
    Mar 1, 2022 at 14:22
  • $\begingroup$ @PM2Ring The top of the saddle: Take JWST's current velocity and position, and only change the distance to the sun. Then I think if JWST is a few hundred km further from the sun, or perhaps a few thousand km in the early mission, then JWST is on the wrong side of the saddle and will irrevocably escape Earth's pull and go into orbit around the sun instead. $\endgroup$
    – Sheldon
    Mar 1, 2022 at 15:00

1 Answer 1


Yes. The "Characterization of JWST science performance from commissioning" document says in section 2.1:

Orbit around L2 is maintained through regular station-keeping burns, which are scheduled every three weeks. As of July 12, 2022, there have been four station-keeping burns, with typical durations of tens of seconds. During commissioning, three station-keeping burns were skipped because the computed correction was negligibly small.

Source: https://www.stsci.edu/files/live/sites/www/files/home/jwst/documentation/_documents/jwst-science-performance-report.pdf

  • $\begingroup$ Thanks @filo, if I can get a little more info and the individual station keeping burns that would be cool. Unless someone else provides such detail, you get the bonus. I'll wait a couple of days before awarding the bonus. $\endgroup$
    – Sheldon
    Jul 21, 2022 at 12:16

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