Sources, including NASA and media, all emphasise that JWST at L2, is a million miles away, and therefore "if anything goes wrong, nothing can be done, it can't be serviced".

But over 50 years ago we could get a manned craft to 0.25M miles and back, which is far more demanding and constrictive on the vehicles (life support, human space, landing, reorbit, return,flight time due to life support duration). We have hugely more advanced technology for roboticised and remote controlled engineering. Space launch vehicles capable of reaching L2 are readily available, and allow enough payload capacity to contain a 6 ton roboticised servicer and enough fuel to deorbit L2 after.

I can't actually see any reason why exactly a servicing mission couldn't presently be done to JW, provided it at least had successfully inserted at L2? Or at least planned for future contingency.

Why are they so adamant in emphasizing that the capability isn't there?


According to @OrganicMarble, who links in a comment to this reply, "the party line may be changing". NASA may now be admitting exactly this, that robotic/remote servicing may indeed be something doable.

(It's clearly known, the announcement was the day of launch and clearly known or considered a long time, and seems settled opinion. And probably was quite a long time ago?)

But the question, I think, still stands. Maybe even more so, now. Why did they say so adamantly it wasn't, when now it seems obvious its viable, and was almost beyond doubt known (or believed likely) to be for a long time?

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    $\begingroup$ Because it isn't. What 'readily available vehicle' would you like to launch your non-existent 'servicer'? $\endgroup$ Commented Dec 25, 2021 at 12:50
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    $\begingroup$ Now you're talking "in 3 years time". Your question says presently. And "planned for future contingency" could have been done but it wasn't. Nothing you're asking about is physically or technically impossible, just fiscally improbable. $\endgroup$ Commented Dec 25, 2021 at 15:09
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    $\begingroup$ @Stilez - I assume your comments are simply because you don’t understand the complexities of space exploration. The economics absolutely make sense - it is incredibly expensive and requires years and years to prepare for any mission. $\endgroup$
    – Rory Alsop
    Commented Dec 25, 2021 at 16:51
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    $\begingroup$ @stilez Also wondering if that 'we can not' means 'we have spent all the money politicians gave us' rather than 'is impossible'. May also be some internal politics not wanting to trade say a mars mission for a JW service mission (local solar system science vs deep history science teams). $\endgroup$ Commented Dec 26, 2021 at 2:43
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    $\begingroup$ You skipped an important part in the comment about a servicing mission, "It might take a few years to pull all that together." $\endgroup$
    – Schwern
    Commented Dec 26, 2021 at 18:11

6 Answers 6


Looking at some of the repair missions to date may be informative. Hubble was repaired from the space shuttle. It was originally flown in the shuttle so size and fixtures were known. It was also due to the sun shield design far less susceptible to plume impingement from exhaust as the shuttle approached – any repair of JWST would need to work out how to approach without damaging the mirror or the massive foil heat shield. If the JWST could fold back up to protect itself this would be easier, but experience with ISS solar panels has been folding space exposed thin films is risky, and assumes every part of the deployment mechanism can be reversed/unlocked.

In terms of robots, Dextre has been on the ISS for 10 years but seems to have largely been used for moving and holding things rather than 'repair' type activities despite the risks and time involved in having humans do space walks and while a lot has changed in 10 years the fact an update has not been seen worth flying is possibly a data point. The Hubble repairs made extensive use of the human ability to adapt on the fly to get things lined up and connected – unsure if there are any robots that in a general purpose fashion can wiggle two parts around till the holes line up and detect if the fastener is started to cross thread without dedicated training. If we build a JWST test bed to train the repair robot, at what point does it get cheaper to just fly the test bed?

For actual successful robot repair missions to date, there is only MEV which worked by locking onto the nozzle of the target and taking over thruster control, which was successful but a long way from a 'repair' using manipulators or even connecting plumbing.

There is also the speed of light question at L2, which would force a fair degree of automation onto the whole process.

So the question becomes less 'it is not possible' and more 'a repair mission would involve a large number of new technologies working for the first time several light seconds from earth, where failure has high probability of destroying the JWST'.

What may have bearing on this is politics and funding – it is possibly unwise for NASA figures to be saying 'of course we will spend US taxpayer money to fix this international mission in the public conscience mostly for delays and over-runs'. What we may see instead is wording like 'A test of future Moon/Mars technology to extend life of JWST and improve value for money'.

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    $\begingroup$ Thanks! It would be nice if there was a source, but I guess things like that don't really have them - its decided as you say. I'll hold off accepting an answer to see what else comes up, but this makes good sense. $\endgroup$
    – Stilez
    Commented Dec 26, 2021 at 4:21
  • $\begingroup$ Thanks :) Some good points by others, but mostly this feels more like the unarguable one. $\endgroup$
    – Stilez
    Commented Dec 26, 2021 at 20:19
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    $\begingroup$ "If the JWST could fold back up to protect itself this would be easier, but experience with ISS solar panels has been folding space exposed thin films is risky, and assumes every part of the deployment mechanism can be reversed/unlocked." Indeed. The moment that foil is unfolded it will no longer be perfectly clean. The mechanism is so incredibly precise that refolding and unfolding again afterwards could damage any of the exposed systems. It's a bit like having a bucket of sand poured over a bicycle chain, you won't know how much damage continuing to use it afterwards will do until you try. $\endgroup$
    – Mast
    Commented Dec 29, 2021 at 4:54

JWST is not designed to be serviceable

Sending a robot to JWST is moot, it is not designed to be serviceable by human or robot.

In the early days of the Webb project, studies were conducted to evaluate the benefits, practicality and cost of servicing Webb either by human space flight, by robotic missions, or by some combination such as retrieval to low-Earth orbit. Those studies concluded that the potential benefits of servicing do not offset the increases in mission complexity, mass and cost that would be required to make Webb serviceable, or to conduct the servicing mission itself.

Source: NASA

But why?

  • JWST was designed 20 years ago, a lot has changed.
  • JWST is already 20x over-budget and 15 years late.
  • JWST is already pushing the limits of mass and fairing size and complexity.
  • We barely do robotic service missions in LEO, nevermind L2.
  • NASA doesn't have Moon-landing era budgets.

JWST is late and over budget

Remember one important fact: JWST is 14 years late and 20 times over budget. JWST development began in 1996. It was supposed to be launched in 2007. The budget was supposed to be $500 million.

Look at JWST in that context, a $500 million mission began in 1996 and scheduled to launch in 2007. A lot changed during that period when JWST was being designed and built, and a lot has changed since 2007.

We didn't (and still don't) have the capability to get a manned mission to L2, a sixty day round trip. We didn't have cheap SpaceX launches. Robots were not up to the task, the first Mars rover wouldn't be until 2004.

During this time, US human space flight capability went through a roller coaster. JWST began development in the hey-day of the space shuttle, through the the 2003 Columbia disaster and subsequent retirement, through Constellation and its cancellation, and now still waiting for Orion and the SLS.

Meanwhile, commercial orbital vehicles went from being a long-shot to send cargo to the ISS to sending crew and cargo to orbit cheaper and like clockwork.

During all this change, the JWST team was trying to get their telescope into space. As each new (and usually prospective) technology became available it was considered for the JWST. Each of these adds change and change adds risk. Maybe we can use the Falcon Heavy; a different rocket with different fairing dimensions. Maybe Orion can reach and service it; a spacecraft which doesn't exist needing a docking ring which adds size and mass.

We're just starting to do basic robotic service missions

There's an assumption that a robotic servicing mission of a complex spacecraft at L2 would be easy. We've never done that. We barely do it with humans in LEO.

We've never done a servicing mission beyond LEO, robotic or human. While JWST was being designed we'd never done a robotic servicing mission. We've are now only just beginning to test robotic service missions in LEO. A robot in LEO can be controlled in real time. L2 is five light seconds away. A robotic servicing mission to L2 is a capability we do not have.

For more about that, read the NASA article Astronauts, Robots, and the History of Fixing Things In Space.

JWST is already pushing the limits

Like your laptop or cell phone, repairability comes at a cost.

The other answers go into the issues involved in making it repairable: protecting the mirrors, protecting the sun shield, points to grapple and stabilize the craft, panels which can be opened, modules which can be removed... Even turning a bolt in zero-G is complicated.

JWST is pushing the limits of mass and fairing size for a mission to L2. It's already folded up to cram it into the one of the largest fairings available and its unfolding is extremely risky. Making it repairable would add mass and size making it more expensive and more complex and add more risk.

When NASA says something is "infeasible", they do not mean it's impossible. They mean they looked at trying to do it not possible for the mass, size, risk, schedule, and budget. And if anyone can find those feasibility studies, please comment.

Going to the Moon is a poor analogy

But over 50 years ago we could get a manned craft to 0.25M miles and back...

Yes, for $150 billion. NASA doesn't have that kind of budget anymore. Space flight is not so much about "is it possible" as it is "do we want to pay for it".

Getting to L2 is rather different than the Moon. Going to the Moon you have the Moon there to capture you and it takes about three days. It's like rolling a ball over a up a hill and downhill into a dip; you can go a little faster and there's a larger margin for error.

Getting to L2 is more like rolling a ball uphill and having it coast to a stop perfectly on top. This takes much longer, 30 days. We've never had people in a spacecraft beyond LEO for 30 days.

When you think "if we could go to the Moon, why can't we..." remember they're different mission profiles, NASA doesn't have that kind of budget, and our capacities have changed.

In the era when the decision was made, what you're proposing was a capability that was speculative at best. We are still not capable of a robotic servicing mission to L2, we are barely exploring them in LEO; JWST is already extremely complex, crammed into its fairing, and pushing the mass limits of heavy lift vehicles. For the original budget, it didn't seem worth it to add the expense and complexity and mass of making JWST serviceable by a speculative capability we still do not have.

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    $\begingroup$ Small suggestion: rather than can we afford it, it's rather a question of do we want to afford it. The world could decide to spend $150 billion on a new space project, but we choose to have other priorities today. $\endgroup$
    – gerrit
    Commented Dec 27, 2021 at 9:15
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    $\begingroup$ @gerrit I can see how "afford" could be ambiguous, ok. $\endgroup$
    – Schwern
    Commented Dec 27, 2021 at 20:17
  • $\begingroup$ If anyone can find the feasibility studies for servicing JWST, please post them below. I know they looked into adding a spot to grapple the spacecraft, and there is a report from 2007 they were adding a docking ring from Orion, but I guess that went away with Orion. $\endgroup$
    – Schwern
    Commented Dec 27, 2021 at 20:29
  • $\begingroup$ With laptops and cell phones, lack of repairability comes with a cost. $\endgroup$
    – Vikki
    Commented Dec 28, 2021 at 8:25
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    $\begingroup$ @Vikki Rather, both repairability and lack of repairability come with cost. Not just the obvious ones of it costs x more but you can save y by extending the life through repair... For example, to make a cell phone easily repairable requires being able to open it up easily, which makes it very hard to make it waterproof. Plus it will either be larger or have lesser hardware, because phone manufacturers are already reducing size as much as possible for the given hardware so adding non-welded connectors, screws, etc., can only increase size. $\endgroup$ Commented Dec 28, 2021 at 20:59

Honestly, it would likely be cheaper to build a fixed JWST than to launch a dedicated robotic mission there, aside from minor things like refueling. Sure, the cost was \$10 billion to build the first copy, but I bet a second one could be built for \$1 billion or so.

The only spacecraft being designed that could remotely fix JWST in the event of a major issue is Starship, and that won't be operating for a while.

The Space Shuttle was a fantastic vehicle for satellite operations and such, but it isn't flying today, and nothing similar for some time. Also, it couldn't operate in deep space. It allowed for servicing by humans, which adds a lot more flexibility. A dedicated robotic mission would require much work.

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    $\begingroup$ A robotised remote repair drone (if that's the term) doesn't need Shuttle or.Starship to deliver it to L2. Theres no obvious or stated reason in this answer why another current launch vehicle couldn't (Ariane 5 was fine for a far more complex and probably more massive L2 delivery and L2 is fixed location/orbit w.r.t. earth, for practical purposes). The JW v2. cost is speculative, and the launch risk of a robotic drone vs an entire new unfolding telescope is probably very much less and i suspect cheaper. Sorry but this answer seems speculative on all points, is there's more solid explanation? $\endgroup$
    – Stilez
    Commented Dec 25, 2021 at 15:55
  • $\begingroup$ How long would it take for Starship to get to L2, assuming tanker refueling (if helpful) in orbit? I imagine it would be less difficult than flying Starship to the moon .... $\endgroup$
    – Sheldon
    Commented Dec 25, 2021 at 16:58
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    $\begingroup$ @Stilez The human factor allows for a lot more flexibility. Building the robot drone to fix it would likely cost at least $2 billion $\endgroup$
    – PearsonArtPhoto
    Commented Dec 25, 2021 at 21:44
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    $\begingroup$ This. Anything you could send to fix it would be equally or more complicated and/or heavy than the original thing itself. It's not that we can't fix it, it just wouldn't be worth it. $\endgroup$
    – J...
    Commented Dec 26, 2021 at 23:37
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    $\begingroup$ @Stilez The principle that a second specimen would be much cheaper than the original JWST is not speculative. All the design decisions, materials testing, parts testing, basically all the engineering has happened already and doesn't have to be paid for again. Granted, you will (have to) re-design a few things because they are not available any longer, or much better solutions are available today, but still. It was not the machining of the parts that took 20+ years and billions of dollars; it was the development. $\endgroup$ Commented Dec 28, 2021 at 23:15

Impossible is a bit to strong a word -- very, very, difficult -- to the point of making it infeasible is a better description.

JWST is fragile and thus susceptible to damage from thruster firings of approaching spacecraft (In particular, the mirrors and the sun shields). Note that the Hubble had a "lens cap" that could be closed to protect its mirrors when approached by the shuttle. It's would be very, very difficult to design and build a servicing spacecraft that could maneuver in the vicinity of JWST without damaging it.

Nothing on JWST is designed for servicing. There is no good way to grapple it, no reasonable way to access the instruments, no reasonable way to attach to its communication, electrical or plumbing. It's like trying to repair plumbing under a concrete slab; access implies destruction of the original item.

It would be easier and cheaper to build a new telescope.

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    $\begingroup$ I think the word that applies here is impractical. $\endgroup$ Commented Dec 27, 2021 at 3:59
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    $\begingroup$ @Joshua. I can't find any current references to a docking attachment point. See webb.nasa.gov/content/observatory/bus.html. Any pointers to current info would be interesting. $\endgroup$
    – Freddo411
    Commented Dec 28, 2021 at 2:35
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    $\begingroup$ @JeremyFriesner. Yes, that's a synonym for infeasible $\endgroup$
    – Freddo411
    Commented Dec 28, 2021 at 2:36
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    $\begingroup$ @Joshua: THE KLAW!!! $\endgroup$
    – Vikki
    Commented Dec 28, 2021 at 8:27
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    $\begingroup$ @Joshua I believe that is the ring to connect JWST to the upper stage. You can see it during upper stage separation in this video at 1m50s. If so, in theory something could reattach to that, but it's not designed to do so. It would require very careful maneuvering and potentially spraying propellant meters away from the very, very vulnerable sun shield. Since it's at L2, there would be a 10 second round-trip delay requiring this very tricky maneuver to be semi-autonomous. $\endgroup$
    – Schwern
    Commented Jan 6, 2022 at 23:29

Maybe it would have been possible to design JWST so it could be serviced by robotic missions in some specific ways. Only – we don't know what kind of specific servicing may turn out to be necessary. After all, we have never attempted unfurling anything remotely like JWST in outer space.

In case of Hubble, if they had foreseen the calibration error of the mirror, they would simply not have launched it with the faulty mirror but instead given it a further grind to install the corrective elements right with the launch. Likewise, for any automatised servicing capabilities that could have been installed in JWST, it would have probably been much more effective to fix the problem right there and then instead of adding even more complexities and failure points by considering docking of a separate probe.

If there was some element in the telescope that we know would have to be replaced after some time, and would have to be fresh (something like an RTG that inevitably decays), then NASA would probably have figured out a way to install it on a long boom or so, such that docking spacecraft wouldn't interfere with the sunshield etc.. Maybe even with some kind of conveyor belt or what not. But all of that would add mass, fragility, and add more items to the deployment process. It's just not worthwhile.

Even so: I personally believe NASA would try hard to conceive a robotic repair mission, in case it turns out that e.g. some boom just won't unfold without external help. It would get extremely expensive, but surely still cheaper than building a new space telescope. But they certainly won't plan for that now: for one thing, nobody wants to hear annoncements of “the telescope's launched, but don't balk: we've already thought about how to have some more billions of cost overrun...”, nor suggest that if something goes wrong they have a chance to fix it – because for many things that could plausibly fail, there's just really no chance a robotic mission could do it.


The JWST was not designed to be served or repaired by a robot in space. We got no experience at all with robotic service or repair in space.

  • $\begingroup$ We have huge experience - the mars rover has its own earth side duplicate to test commands on, due to signal time. And, if we didn't, we've had 10+ years to develop it, which is a far lesser step technologically than the JW itself - we have decades of spaceside mechanisms and handlers, and remote control systems. Plenty of time to blend the 2 if we didn't have the experience and wanted it, or consider how to make key systems and one point or many other issues serviceable, contrary to what this answer suggests. So not really a reason at all "why not". $\endgroup$
    – Stilez
    Commented Dec 25, 2021 at 20:41
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    $\begingroup$ @Stilez so we have no experience at all about robotic repair in zero gravity..... $\endgroup$
    – Uwe
    Commented Dec 25, 2021 at 23:04
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    $\begingroup$ @Stilez did you come here to ask a question or to promote your ideas on the subject? All you have done is argue with all the answerers and commenters. Consider posting your own answer. $\endgroup$ Commented Dec 25, 2021 at 23:41
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    $\begingroup$ @Stilez vacuum or air is much the same, but gravity on a planet like Mars is much different to zero gravity in an orbit. $\endgroup$
    – Uwe
    Commented Dec 25, 2021 at 23:48
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    $\begingroup$ @OrganicMarble - to ask a question,and to find hard data rather than personal views in the replies. So far, the 3 answers+your comment state "it would be cheaper to rebuild from scratch" (unsourced), "the only solution is the defunct shuttle" (no supporting source given, sounds dubious), "we have no experience" (no supporting source, other missions suggest not an issue, sounds dubious as heck), and "hours after launch its been suggested it perhaps isn't a big problem to service remotely at L2" (sourced). ... $\endgroup$
    – Stilez
    Commented Dec 26, 2021 at 0:59

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