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Presumably the Ariane 5 rocket launched the James Webb Space Telescope into an elliptical orbit with its apogee at the L2 point. Such an orbit’s period is about 70 days, i.e. the journey to L2 should take 35 days. Is the reason for it taking only 30 days due to the Coriolis Effect or is the trajectory something other than a simple orbit?

I am of course, for simplicity, viewing the above orbit in a rotating frame of reference centred on the Sun-Earth barycentre and rotating at the Earth’s orbital angular velocity.

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JWST has thrusters for station keeping during its lifetime. These thrusters will also be used to execute several mid-course manoeuvres over the next month - see Timeline of Events After Launch at this NASA page. So, no, JWST’s trajectory from Earth to L2 is not a simple ballistic orbit.

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  • $\begingroup$ So I guess I’m trying to understand the reasons why a simple ballistic trajectory wasn’t sufficient. Is it because of the requirement to so accurately position the apogee so that the telescope can be ‘captured’ by the Lagrangian point? And this would have been beyond the predictive capabilities of NASA at launch? $\endgroup$
    – adlibber
    Commented Dec 28, 2021 at 8:33
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    $\begingroup$ @adlibber The L2 doesn't capture at all. It is fully unstable in the radial direction, the coriolis effect is much less significant than for L4/5. That's why JW will be parked a little before L2, with thrusters stabilizing it against dropping back to earth. $\endgroup$
    – tobalt
    Commented Dec 28, 2021 at 9:14
  • $\begingroup$ Perhaps I should have said 'landed' on the L2 plateau, tobalt, rather than 'captured'. But I'm still trying to reason where the 'lost' five days have gone. $\endgroup$
    – adlibber
    Commented Dec 28, 2021 at 9:42
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This question made an incorrect assumption of orbit eccentricity leading to the period of seventy days mentioned. The answer is of course that a suitable choice of orbital energy will achieve the necessary eccentricity to produce an orbital period of sixty rather than seventy days. My apologies.

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