The James Webb Space Telescope (JWST) will be an incredible addition to the scientific community once it is launched and operational but the relative short planned mission time will make this a time critical operation.

The planned minimal mission time is 5 years with a projected 10 year life span of the spacecraft. Those 5 years seam quite short if you consider that the telescope is now delayed for longer than it supposed to be working. Those 5 years are also outshined by the 29 years Hubble has been operational (disregarding the optician consultation Hubble needed).

JWST may be in a considerably more "complicated" orbit than Hubble but launch cost as dropped significantly in the last few years. Therefore the price of a launcher for a planned refueling mission would only be a fraction of the whole JWST project.

Taking all this into account and the fact that Hubble was serviced every few years:

Why are there no plans to refuel JWST and is it even possible?

(Not asking about service mission such as the question: 1, 2, 3)

On the German Wikipedia article about the JWST I found a mention of the possibility of docking to the JWST for refueling.

Während der vorgesehenen Nutzungsdauer sind bisher keine Reparatur- und Wartungsmissionen vorgesehen; es gibt jedoch eine Vorrichtung, die eine nachträgliche Ergänzung der Treibstoffvorräte durch eine Robotermission ermöglichen würde.

Roughly translating to:

In the intended service life no repair and maintenance missions are planned; However, there is a mechanism that would allow for a subsequent supplementation of the fuel supplies by a robot mission.

There is no source for this information so it may well be outdated or outright false, but this gives me the hope that JWST may be refuel-able and will be if the necessary budget gets allocated.

Bottom (sun-facing side) of JWST Bottom (sun-facing side) of JWST; Wikipedia

Is the payload adapter for the Ariane 5 maybe useable as a docking mechanism for refueling or could a probe just dock with JWST and be used for station keeping without any fuel transfer?

I know there've been multiple question on the serviceability of JWST for example using Orion as a shuttle replacement, but I do not ask about changing instruments how it was done with Hubble but rather a "simple" reboost/refuel for station keeping.

This question ask about how the JWST will be serviced with the answer saying that it will not be serviced because:

There is currently no servicing capability that can be used for missions orbiting L2, and therefore the Webb mission design does not rely upon a servicing option.

This answers the other question about servicing but not mine about the refueling capabilities as it is something completely different to send a shuttle-like mission to JWST for servicing compared to sending something like an ATV launched from a Falcon 9/Ariane 6 for a refuel/reboost.

I just can't imagine that another 200 million USD for a launcher and automated probe wouldn't be justifiable if a spending of 2% of the overall project cost could mean a doubling of the life span.

  • $\begingroup$ @Hobbes I've already read your answer at the linked question but the quote with which you answer states:"There is currently no servicing capability that can be used for missions orbiting L2". But I do think that there is refueling capabilities for missions orbiting L2. $\endgroup$ – GittingGud Aug 27 '19 at 10:30
  • $\begingroup$ @Hobbes see the quote in the update at the beginning of Besides HST, JWST and stations, are there any examples of satellites designed for service in space?, though I see you have an answer there as well negating the idea, so maybe it's not so relevant. $\endgroup$ – uhoh Aug 27 '19 at 11:04
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    $\begingroup$ This question asks if it is possible. I think it really is a different question, especially after the revision, so voting to re-open. $\endgroup$ – uhoh Aug 27 '19 at 15:07
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    $\begingroup$ Especially because the question/answer this is supposed to be a duplicate of discusses servicing JWST which is considerably different to just refueling. $\endgroup$ – GittingGud Aug 27 '19 at 15:45
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    $\begingroup$ I'm going to guess this answer here is not technical enough for you. "In-space refueling of #JWST? Logically possible but difficult. It would require robots!" It was from a public-forum twitter Q&A, but kind of gives the impression that, no, we don't have a plan; but they said it's logistically possible ;). That was John Mather who said that. $\endgroup$ – Magic Octopus Urn Aug 27 '19 at 20:54

Theoretically possible, but not planned.

Refuelling in the sense of replacing expended fuel in the propulsion system is possible in theory. This answer provides a nice schematic of the propulsion system, and according to the legend at least there is a valve for filling up the propellant tanks. Presumably, you could "top it off" again once the fuels is depleted.

JWST propulsion system

However, this would be extremely difficult and dangerous: I doubt that the risks of an astronaut handling hydrazine in space would be acceptable, so a robot needs to do this. This would require a very advanced robot and I don't think we have this technology yet. I doubt undertaking such a mission would be feasible with technology and budgets available.

At some point in time it was apparently decided to add a dedicated docking ring to JWST for this exact purpose, but I'm unable to confirm if this docking ring still exists:

NASA is adding a docking ring to the James Webb Space Telescope (JWST) just in case a visit by astronauts aboard a future Orion Crew Exploration Vehicle is needed to complete deployment of the multibillion-dollar orbiting observatory.

(from: NASA Adds Docking Capability For Next Space Observatory, space.com, 2007)

However, the launch vehicle interface ring, which mates the JWST with the Ariane 5 launcher, can potentially be used as alternative to dock an autonomous spacecraft for providing attitude and orbit control:

There are, however, modest efforts being made to make JWST “serviceable” like Hubble, according to Scott Willoughby, JWST’s program manager at Northrop Grumman Aerospace Systems in Redondo Beach, California. The aerospace firm is NASA’s prime contractor to develop and integrate JWST, and has been tasked with provisioning for a “launch vehicle interface ring” on the telescope that could be “grasped by something,” whether astronaut or remotely operated robot, Willoughby says. If a spacecraft were sent out to L2 to dock with JWST, it could then attempt repairs—or, if the observatory is well-functioning, simply top off its fuel tank to extend its life.

(from: Is the James Webb Space Telescope "Too Big to Fail?", Scientific American, 2017)

In any case, if a spacecraft docks with JWST, this would require some reconfiguring of the JWST control software, since it would need to delegate the attitude control to the docked spacecraft. Depending on how the control software is designed, this may be trivial or very complicated.

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    $\begingroup$ "This would require a very advanced robot and I don't think we have this technology yet. " Well we have cartoons of one at least! Is Landsat-7's propellant resupply port “robot-ready”? (Restore-L mission) $\endgroup$ – uhoh Aug 28 '19 at 11:37
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    $\begingroup$ I did my Ph.D. in robotics in the area of physical interaction: it's hard. Not at all a solved problem. Even if you did it with some remote control, you'd need some haptic feedback, which at those distances is really tricky. $\endgroup$ – Ludo Aug 28 '19 at 11:47
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    $\begingroup$ @Ludo It wouldn't be that bad--just take it extremely slowly. To make a robot reach over and grab something is hard. To move it a millimeter at a time and observe the result might require days but isn't hard. It's an unmanned mission, so what if it takes days? $\endgroup$ – Loren Pechtel Aug 30 '19 at 15:30
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    $\begingroup$ @LorenPechtel the problem is in the contact: at the moment you go from free-moving to in-contact, the dynamics of the system change dramatically and you need to account for this in the control loops, which is not trivial. Moving slowly has nothing to do with it. If you add haptics to it, the time delay comes into the equation which makes it even harder. A fellow PhD student in my lab spent his Ph.D. trying to implement stable haptic feedback over a link from Netherlands to Australia, imagine doing it at distance to L2. $\endgroup$ – Ludo Aug 30 '19 at 15:57
  • $\begingroup$ @Ludo So you're talking about the initial docking? Simply have a clamp that can go around a protrusion--line it up without any contact, then clamp. The slower your movement the more lag you can tolerate in your feedback system. Make it slow enough and you can make it work. In this sort of situation it doesn't matter if it takes days to line them up. $\endgroup$ – Loren Pechtel Aug 30 '19 at 22:11

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