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The James Webb Space Telescope is generally considered to be in an unserviceable location at SEL2.

If servicing becomes necessary, is it possible for the JWST to use a low energy heteroclinic transfer to reposition itself at a more accessible repair location? Say the EML1 point? This location would make it accessible for diagnostic and repair missions from Gateway/Artemis resources. Once serviced and refueled, it could be returned to SEL2 using a separate booster attached to the launch mount ring.

JWST was deliberately placed in an unstable halo orbit which requires no reorientation for orbital maintenance burns. If these burns are discontinued, JWST will follow the unstable manifold (red in the diagram below) and could be guided into position for a stable manifold (blue in the diagram) transfer to EML1

enter image description here From:https://engineering.purdue.edu/people/kathleen.howell.1/Publications/Journals/2006_AA_HowKak.pdf

This NASA paper: https://ntrs.nasa.gov/api/citations/20190028906/downloads/20190028906.pdf studies the energy budget of transfers from Sun-Earth Halo orbits to Earth-Moon orbits (including Near Rectilinear Halo Orbit).

In the paper, several transfers were considered. See table on page 9 for delta-v estimates. The transfers required from 38.5 m/sec (SEL2 to EML2) to 128.5 m/sec (SEL2 to NRHO).

The total delta v budget for the JWST mission is widely stated (but unreferenced) as 150 m/sec. https://ntrs.nasa.gov/api/citations/20160001318/downloads/20160001318.pdf Mid Course Corrections were budgeted at 66.5 m/sec, but this was underused in the actual launch. https://ntrs.nasa.gov/api/citations/20140007519/downloads/20140007519.pdf mentions a station keeping budget of 25.5 m/sec for a planned 10 year mission. From these numbers, it looks like JWST’s remaining delta v is in the ball park for a low energy transfer

Question: Is the fuel supply on JWST adequate for a heteroclinic transfer to an EM libration point? And if so, at what point in JWST’s mission will the remaining fuel be inadequate for the transfer?

ET, come home.

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    $\begingroup$ The main issue with this plan is - there are no engines on JWST pointing in the right direction without turning it around and destroying parts of the equipment due to heat. $\endgroup$
    – asdfex
    May 8 at 16:48
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    $\begingroup$ Ahm, no. JWST only survived the launch and the LEO phase because it was folded and at the same time did a series of swing force-and-back maneuvers to prevent excess heating. $\endgroup$
    – asdfex
    May 8 at 18:38
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    $\begingroup$ @asdfex ... JWST is already in an escape orbit, so it would not need to "turn around" to aim towards the Sun. It's orbit on an unstable manifold was chosen to counter solar pressure on the sunshield. Station keeping burns do not require significant re-orientation. If station keeping burns are discontinued, JWST will continue on its escape orbit towards Earth. This may further reduce the delta v calculated in the OP reference. $\endgroup$
    – Woody
    May 8 at 18:41
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    $\begingroup$ If you cease station keeping, JWST will not come closer to Earth, it will drift away. It's not in an Earth-bound orbit after all. $\endgroup$
    – asdfex
    May 8 at 18:48
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2 Answers 2

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Moving the JWST is not practical. It's very limited in its maneuver capabilities because the thrusters do not point in the direction it looks (because either the sunshield would be in the way or it would contaminate the optics) and the sunshield must not turn around ever because the warmth from Sun, Moon and Earth would damage the sensors.

And why would we want to bring JWST to some other place? If we can move JWST to another place with low delta v, we can also move something from that point to JWST with low delta v.

Currently, a servicing mission does not seem very feasible. Not from a risk perspective not from an economical perspective. The lifetime of the telescope is now expected to be 20 years. We'll have to asses the situation down the road a few years (they are already thinking about that).

  • What are current technical capabilities?
  • What's the cost with current technology?
  • What's the risk associated?
  • What's the possible gain by such a mission?

Right now, assessing this questions tells us, that it's not worth the effort. But a few years in the future, the answer might be different. Cost to launch something towards L2 will probably be lower, technology and experience for automated servicing and refueling or other life extension missions will have grown significantly (we did the first life extension mission in GEO just recently in 2020).

So in maybe 10 years, we'll have trivialized docking to old spacecraft to give them a life extension.. We'll see!

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  • $\begingroup$ Agreed that bringing lower mass and more maneuverable strap-on auxiliary propulsion to the JWST (assuming there's something to grab on to) is way easier and safer. But these two may not be the reasons; 1) "...very limited in its maneuver capabilities because the thrusters do not point in the direction it looks..." 2) "...and the sunshield must not turn around ever because the warmth from Sun, Moon and Earth would damage the sensors." Can you support them as reasons? JWST was warm on its way out there and didn't start cooling until later for example. $\endgroup$
    – uhoh
    Jul 29 at 12:15
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    $\begingroup$ While in Earth orbit before it could begin to unfold it did have to avoid over-heating but that's not the same thing. $\endgroup$
    – uhoh
    Jul 29 at 12:16
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    $\begingroup$ @TrySCE2AUX.... Thanks for the comments but they do not answer the question: Does fuel supply on JWST allow this option and, if it does, at what point in JWST service life would reduced fuel supply eliminate the option? The current end-of-service plan is to move JWST to a non- SEJ2 heliocentric graveyard orbit with the last of its fuel. A low energy heteroclinic transfer to EML2 would likely require about the same delta-v. And it would potentially allow extension of the service life. $\endgroup$
    – Woody
    Jul 29 at 21:23
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And what repair mission would you perform? JWST was given a grappling fixture, as that has no subsystems i. e., little added cost/mass/power/testing/etc. in the grand scheme. But what fuel would you add? JW, as field testing now indicates, has fuel margin for years- I assume, from the fuel margin I’ve heard, that micrometeoroid damage (sunshield punctures, or general degradation of exposed surfaces and their thermal properties) is now the life-limiting factor.

New instruments? ISIM not designed for instrument changeout… you should see the rat’s nest in there. New mirror segments? Ha. The alignment on the segments- or rather, on the interfaces to the multiple segment actuators- means you risk screwing it up as much as you gain from a new element. Replacement for some random bus component? As a megaproject, the S/C has redundancies on support systems… and redundancies on the redundancies. Some random part failure disabling JW is, statistically, as likely as it is on, say, Fermi (come on, ruby anniversary!) and less likely than Swift.

Then after you propose some (technically) worthy servicing requirement/result, propose for me the risk/benefit trade of that servicing, including (for one) a full FMEA (Failure Mode and Effects Analysis). Does an astronaut dropping (as such) a tool put a hole in something? Does a robot arm risk crunching something? Hard to come up with more examples, since… I can’t come up with some worthy servicing concept in the first place.

Are you musing forth on JW servicing because… Hubble was serviced, by shuttles? i. e., default to pattern? The Servicing Missions are an antipattern, and yet another thing the Shuttle program put forth as, not precedent, but a cautionary tale. We don’t plan on servicing post-Compton observatories (CGRO designed too late to reflect lessons learned) because of Shuttle Servicing Missions. They don’t make sense. Too much budget, too much schedule (itself budget-time is money), too much FME, too much opportunity cost in diverted resources. It’s better (whew… priviledge of hindsight) to have built it with margin and quality and minimized effects in the first place.

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    $\begingroup$ "'Is the fuel supply on JWST adequate for a transfer to an Earth Moon libration point to allow repairs?' seems yes/no answerable. OP isn't asking if it's a good idea or not." $\endgroup$
    – uhoh
    Aug 2 at 6:10
  • $\begingroup$ “is the question an astute question” is the FIRST question. Space missions- certainly JW- proceed by defining worthy investigations FIRST, then sticking to answering those requirements and ONLY those requirements. Spreading thinly to other notions is a waste of time and energy- mission creep- and the common path to failure for many a project, space or otherwise. We will NOT waste time, energy, or propellant on a notion. $\endgroup$ Aug 3 at 13:21
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    $\begingroup$ Okay, but this is Stack Exchange; answer posts should be used to answer the question as-asked. It's certainly understandable why you'd like to include this advice in addition to answering the question, but it shouldn't be in leu of answering it. $\endgroup$
    – uhoh
    Aug 3 at 13:29

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