<p>There are no plans in place to fix JWST. It has to work.</p>

CC BY-SA 4.0
2021-12-10T18:51:00.793Z
Oh, my... I hope the JWST will work without problem.
pdh0710
CC BY-SA 4.0
2021-12-10T18:54:53.483Z
@pdh0710 That's what the entire field of astronomy&astrophysics is hoping...
AtmosphericPrisonEscape
CC BY-SA 4.0
2021-12-10T23:34:10.660Z
@pdh0710 that's also one of the cost drivers in space business: quality assurance. The other is documenting that so that the blame can be assigned, if it doesn't work ;)
planetmaker
CC BY-SA 4.0
2021-12-11T04:02:46.417Z
@planetmaker you mean armies of lawyers to ensure contracts are written so as to ensure no blame can be assigned
jwenting
CC BY-SA 4.0
2021-12-10T18:37:10.073Z
2021-12-10T18:37:10.073Z
ProfRob
<p>The same question applies to practically all space probes that leave a near Earth orbit. If one of the Mars rover breaks, you can't call your local service station to send an engineer and get it repaired. Or think of New Horizons that went to Pluto.</p>
<p>Basically, the probes get designed and tested as much on Earth as possible to withstand all the forces of the launch and the environmental conditions in space (radiation, heating/cooling cycles etc) and by now the engineers have a lot of experience.</p>
<p>A sonde consists of many different components and some are redundant (i.e. there are several systems that can take over each other's function), so when something fails, the sonde is still usable with possibly limited functionality. It's not like a car breakdown where you're really stuck in the middle of nowhere and can't move until it's repaired.</p>
<p>For space probes, there are certain ways of &quot;repairing&quot; by uploading new software that e.g. disables malfunctioning instruments or modifies their function.</p>
<p>In the past, there are many examples of probes where certain components failed and the sonde continued to be used, often long beyond the original design life.</p>
<p>An instructive example is the Kepler space telescope. Two of the four reaction wheels failed in 2012; they stabilise the sonde so that it points precisely in the desired direction (this is called &quot;attitude control&quot;), so their failure is a serious problem for a space telescope as it becomes useless if you can't point it to where you want.</p>
<p>So they put it into powersaving mode for a while and designed a new mission using the remaining capabilities, which started 2013 and run for another 5 years until 2019, so this is pretty good for a failure that is almost as bad as you can get. For this second mission, they didn't need any actual &quot;repairs&quot; but uploaded software so it could be stabilisied with the two remaining reaction wheels (by turning it such that the radiation pressure from the sun provided some force). It was more restricted and could only observe certain parts of the sky, but it still delivered a lot of data even the failure.</p>
<p>So for Webb, we hope it works of course, but if something breaks, they will analyse the problem and work around the failed components to continue a useful mission.</p>
<p>A more frequent experience is that probes have worked perfectly fine for the planned design life, and still continued to work afterwards with perhaps some components failing one after another many years after the original design life. So the missions get extended, redesigned and modified to get as much out of the instruments as long as they are somewhat functional. I guess the record are the Voyager and Pioneer probes that were designed for 3 or 4 years but worked (at least) ten times as long.</p>

CC BY-SA 4.0
2021-12-11T22:22:14.290Z
Good point! I was worried about the failure of Webb telescope compared to the case of Hubble telescope. Now I can understand that  Webb telescope should be compared with the case of Kepler telescope.
pdh0710
CC BY-SA 4.0
2021-12-11T23:47:24.743Z
Yeah, the lens in Hubble was quite something. But engineers (hopefully) also learned from this mistake and improved the test procedures to catch such mistakes before the launch.
uUnwY
CC BY-SA 4.0
2024-12-27T09:16:19.673Z
I changed the French word *sonde* to "probe".
James K
CC BY-SA 4.0
2021-12-11T21:47:59.923Z
2024-12-27T09:15:53.550Z
2024-12-27T09:15:53.550Z
uUnwY
<p>Fix covers many things.  Once the telescope is on station it will be too far away for a manned mission to fix it unless that is judged extremely important and worth developing new capabilities.  There are a surprising number of things that can be fixed by command or by uploading new software.  Without some definition of what needs to be fixed there is no better answer.  NASA has spent a lot of effort trying to ensure that nothing needs to be fixed.</p>

CC BY-SA 4.0
2021-12-11T09:25:20.487Z
Yes. `fix` is a easy but ambiguous word. I wanted to express my question in easy and everyday language. Because I think the JWST will be of ordinary people's interest, like the Hubble space telescope.
pdh0710
CC BY-SA 4.0
2021-12-11T11:53:56.473Z
You make a good point! There are several kinds of remote fixes, from reprogramming to a series of instructions with the goal of "shaking something that's stuck loose".  But changes of crewed repair are low. However there are also robotic repairs imaginable in the future.
uhoh
CC BY-SA 4.0
2021-12-11T14:14:11.217Z
Except they designed jwst knowing it won't be repairable. A robotic mission would have a very hard time doing anything. Also any craft approaching jwst is likely to damage the extremely fragile sunshield with its thrusters.
Rob
CC BY-SA 4.0
2021-12-11T05:06:36.780Z
2021-12-11T05:06:36.780Z
Ross Millikan
<p>(Please excuse my English)</p>
<p>The James Webb space telescope(JWST) will be launched in 11 days. I've always wondered, how do we fix the JWST if it breaks? The JWST will be too far away. According to <a href="https://en.wikipedia.org/wiki/James_Webb_Space_Telescope" rel="nofollow noreferrer">Wikipedia</a>, it will be about 1.5 million km from Earth, circling about 370,000 km from the Sun-Earth L2 point.</p>

<james-webb-space-telescope>
How to fix James Webb space telescope?
pdh0710
# How to fix James Webb space telescope?

(Asked by: username_0 on 2021-12-10)

(Please excuse my English)

The James Webb space telescope(JWST) will be launched in 11 days. I've always wondered, how do we fix the JWST if it breaks? The JWST will be too far away. According to [Wikipedia](https://en.wikipedia.org/wiki/James_Webb_Space_Telescope), it will be about 1.5 million km from Earth, circling about 370,000 km from the Sun-Earth L2 point.

**Tags:** james-webb-space-telescope

---

## 3 answers

### Answer by username_1 on 2021-12-10. Score: 10

There are no plans in place to fix JWST. It has to work.

> **Comments:**
> **username_0**: Oh, my... I hope the JWST will work without problem.  
> **username_2**: @pdh0710 That's what the entire field of astronomy&astrophysics is hoping...  
> **username_3**: @pdh0710 that's also one of the cost drivers in space business: quality assurance. The other is documenting that so that the blame can be assigned, if it doesn't work ;)  
> **username_4**: @planetmaker you mean armies of lawyers to ensure contracts are written so as to ensure no blame can be assigned  

---

### Answer by username_5 on 2021-12-11. Score: 5

The same question applies to practically all space probes that leave a near Earth orbit. If one of the Mars rover breaks, you can't call your local service station to send an engineer and get it repaired. Or think of New Horizons that went to Pluto.

Basically, the probes get designed and tested as much on Earth as possible to withstand all the forces of the launch and the environmental conditions in space (radiation, heating/cooling cycles etc) and by now the engineers have a lot of experience.

A sonde consists of many different components and some are redundant (i.e. there are several systems that can take over each other's function), so when something fails, the sonde is still usable with possibly limited functionality. It's not like a car breakdown where you're really stuck in the middle of nowhere and can't move until it's repaired.

For space probes, there are certain ways of "repairing" by uploading new software that e.g. disables malfunctioning instruments or modifies their function.

In the past, there are many examples of probes where certain components failed and the sonde continued to be used, often long beyond the original design life.

An instructive example is the Kepler space telescope. Two of the four reaction wheels failed in 2012; they stabilise the sonde so that it points precisely in the desired direction (this is called "attitude control"), so their failure is a serious problem for a space telescope as it becomes useless if you can't point it to where you want.

So they put it into powersaving mode for a while and designed a new mission using the remaining capabilities, which started 2013 and run for another 5 years until 2019, so this is pretty good for a failure that is almost as bad as you can get. For this second mission, they didn't need any actual "repairs" but uploaded software so it could be stabilisied with the two remaining reaction wheels (by turning it such that the radiation pressure from the sun provided some force). It was more restricted and could only observe certain parts of the sky, but it still delivered a lot of data even the failure.

So for Webb, we hope it works of course, but if something breaks, they will analyse the problem and work around the failed components to continue a useful mission.

A more frequent experience is that probes have worked perfectly fine for the planned design life, and still continued to work afterwards with perhaps some components failing one after another many years after the original design life. So the missions get extended, redesigned and modified to get as much out of the instruments as long as they are somewhat functional. I guess the record are the Voyager and Pioneer probes that were designed for 3 or 4 years but worked (at least) ten times as long.

> **Comments:**
> **username_0**: Good point! I was worried about the failure of Webb telescope compared to the case of Hubble telescope. Now I can understand that  Webb telescope should be compared with the case of Kepler telescope.  
> **username_5**: Yeah, the lens in Hubble was quite something. But engineers (hopefully) also learned from this mistake and improved the test procedures to catch such mistakes before the launch.  
> **username_6**: I changed the French word *sonde* to "probe".  

---

### Answer by username_7 on 2021-12-11. Score: 4

Fix covers many things. Once the telescope is on station it will be too far away for a manned mission to fix it unless that is judged extremely important and worth developing new capabilities. There are a surprising number of things that can be fixed by command or by uploading new software. Without some definition of what needs to be fixed there is no better answer. NASA has spent a lot of effort trying to ensure that nothing needs to be fixed.

> **Comments:**
> **username_0**: Yes. `fix` is a easy but ambiguous word. I wanted to express my question in easy and everyday language. Because I think the JWST will be of ordinary people's interest, like the Hubble space telescope.  
> **username_8**: You make a good point! There are several kinds of remote fixes, from reprogramming to a series of instructions with the goal of "shaking something that's stuck loose".  But changes of crewed repair are low. However there are also robotic repairs imaginable in the future.  
> **username_9**: Except they designed jwst knowing it won't be repairable. A robotic mission would have a very hard time doing anything. Also any craft approaching jwst is likely to damage the extremely fragile sunshield with its thrusters.  

---

