If the James Webb Space Telescope fails, how much and how long to replace it?

The James Webb Space Telescope was originally slated to cost $1 billion but rang in at $10 billion by launch date. If any of its 300 single points of failure cause it to fail today, how much would it cost us to replace it?

I’m thinking it wouldn’t be the whole $10 billion because presumably we could rely on some of the technology that was designed for JSWT Sr. without reinventing the wheel. But then again, if we’re starting over, maybe NASA wouldn’t be able to resist a few upgrades (in addition to repairing whatever failed the first time) along with the new telescope. Plus inflation probably means paying more for at least some of the things. So how much to start over today with a replacement? And how long would it take us to get Jr. into space?

I agree with your thinking, except the decision to replace it would be a slow decision, and it would have to look fairly different for voters to trust the design.

I read yesterday that with the completion of the sun shield, 75% of the 344 single points of failure “have been retired”. That is, the telescope is safely past them.

I’m glad to hear about the success and I hope we don’t have to find out how much a replacement mission would cost. But there are factors that success a cheaper second go-around and factors that suggest a more expensive one. Do you think a new JWST would cost more or less than the first?

I am certain it would not be replaced.

The secondary mirror has been successfully deployed. That is a very important step.

I’d like to believe that with Hubble failing we would do something to make sure we have a nice space telescope. After all, once we went to the moon we were always sure to preserve our ability to send people into space, right? No, you’re probably right. Perhaps we’d build a cheaper regular Earth orbit telescope with scaled backed ambitions.

A SpaceX Starship, even if it fails as a reusable launch system, could launch a heavy payload in a much larger fairing. A replacement/successor telescope could have a much more forgiving design.

Or it could use the more ample payload dimensions to implement an automated-origami telescope of stupendous size.

How practical would it have been to launch JWST to Earth orbit, where it could have been checked out, and then boost it to L2?

For that matter, how practical would it be to launch 2 or 3 sections to Earth orbit for assembly and checkout there, and then boost it to L2? Or even make the boost rocket one of the sections? Is there any hard and fast limit to how big a telescope we could have that way?

A critical aspect of launching the JWST is that right from the start it could not be pointed at a heat source, and it has stayed pointed in the much the same direction (away from the sun) for the entire journey. Putting into Earth orbit would make this near impossible.
In order to boost the telescope form orbit to L2 it would need a much more capable system than its internal engine. It would really need to stay attached to its launch second stage. Which would make deployment a seriously difficult affair. Whether an unfolded telescope could survive the boost from Earth orbit is another matter. It is vasly more energetic than the insertion burn that will place it into L2 orbit.

Finally, what help does having the telescope in LEO provide? The only reason for deploying in orbit is if you can send someone up to fix it. The telescope was not designed for fixing. Unlike Hubble which was designed from the outset to be captured and man handled, opened up and have bit replaced. JWST was zipped up tight and just trying to dock with it would probably wreck it.

We sent the Apollo astronauts into LEO for a couple of orbits to check out the spacecraft before the TLI burn. But there was no idea about fixing stuff, rather if the spacecraft didn’t checkout they came back down again. Very nearly happened to Apollo 12.

Eventually we probably will assemble telescopes in LEO. But they will be designed from the outset to be so built.

It remains to be seen what NASA does with its two spare Hubble telescopes. So far there has been little mention of anything planned. So they are just sitting in storage.

There is the Nancy Roman Grace Telescope planned for later this decade. More similar in size to the Hubble, but also going to L2.

Right. An Earth orbit telescope would likely have similar capabilities as Hubble. That’s what I meant by scaled back ambitions.

I’ve never heard of spare Hubbles. Are you referring to these two telescopes? It seems like they are basically tubes with mirrors. No sensor package. And they may not be optimized for the field of view NASA wants. I’m not sure they will ever take those out of storage.

Yes, but the key is “single point of failure”. Watch, we’ll get through 343 of them and then … … :flushed:

Yes. I was being trifle evil by calling them spare Hubbles. But for all intents they are the same tech and design as the HST. A lot came out of the same factory. It was the misassembly of the test jig the civilian team borrowed from the classified side that was the result of the famed out of focus main mirror. But the spy sats were more advanced than Hubble. Another scandal was that the spy sat guys knew head of time that the solar arrays would not work properly, and differential heating would mean that pointing stability was compromised. The spy sats use more advanced solar panels that were not retro-fitted to Hubble for another decade. The scandal being that the HST designers were not told about the problem.
So yes, they need a sensor package. It remains curious that there is much made about how valuable the HST is, and how we can longer fix it. But we do have two brand new sats that contain the lions share of the value and effort in storage. They will almost certainly not be configured as HST replacements. But there is other science to be done.

Yes, just to add to this point, the JWST L2 orbit will be a large, elliptical, slow orbit with a period of about 6 months. The orbital insertion burn will hardly be more than a gentle nudge, as opposed to the fiery violence involved in leaving earth orbit.

Right. If you’re sending something to a place where fixes are basically impossible, it would make little sense to devote time / effort / mass / money to fixability.

But we hear some rumblings that, as fuel starts to runs short some 10 years from now, it might be possible for a robotic probe to deliver more. Is that actually in the cards?

There was talk about putting a docking ring on the bottom, but I think it never got added.

There has been a lot of recent work on ideas to allow geostationary sats to be refuelled. Also work on support sats that go up and dock with them and take over station keeping duties with their own fuel and thrusters. This can work even for sats not designed for it - the support sat uses the other sats engine bell as the docking target, and essentially uses a barbed probe stuck into the engine bell to make a hard dock.
There has also been work on seeing whether some sats can be refuelled by various other physical means, up to and including drilling holes in their fuel tanks and squirting fuel in. Needless to say it is a lot more hair raising than this. In the middle are designs for refuelling connections explicitly intended for in-orbit refuelling.

However I have not seen any mention that the JWST has any designed in capability to support any life extending missions. Doesn’t mean it doesn’t. But it a very old design, and NASA would have been under immense pressure not to mess with the telescope.

I will bet there will be lots of pressure mounting in a few years to put some effort into scoping out a life extending mission. Something like a support sat that grapples itself on, and then provides some control capability might work. Complicating things is that the JWST is rather autonomous. The distances involved, and a general desire to not have to control its every minute action, means that the telescope runs itself, scheduling tasks, changing direction as needed, and generally getting on with things, without needing outside help. So how it interfaces with a new support system and uses it for general operations is an open question. Not insoluble, but a whole new level of tricky.

For a long time repair or replenishment of satellites simply wasn’t economical, because launch was so expensive and payload so limited that for the cost and complexity of a servicing mission you could simply boost a replacement; especially if degradation of components limited the lifetime of a satellite anyway. The Hubble was designed for servicing when the Shuttle was expected to make round trip to LEO frequent and economical; plus high-precision optical mirrors are one of the few things expensive enough to want to keep in service. The Shuttle missions were probably barely economical but were practice for the sort of LEO operations space enthusiasts had hoped would become routine. With the lowering of launch costs pioneered by SpaceX, servicing missions are approaching viability again.

Wth Starship, I think we could eventually see the payload being built into Starship itself for stuff that doesn’t have to be up there for a long time.

Consider Sofia, the 747-based optical telescope. It has done a lot of good science.

I could imagine a Starship outfitted with a huge telescope or other insteumentation, taking off and flying for two weeks while taking a whole bunch of images, then landing again. Repeat as needed. Or even just fit one out, fly it into a high orbit and leave it there. If the telescope breaks, either service it in orbit or send up a tanker to fill the landing tanks on the Starship if necessary and land the thing back on Earth for repairs and upgrades.

Likewise, instead of orbiting hotels perhaps the model for tourism will be the equivalent of a ‘cruise’ today. Take off for four weeks aboard a luxurious Starship! No need for a hotel at all when you have a spaceship big enough to put 100 people in it.

There’s a little bit.

“Though a human servicing mission is not feasible for JWST, NASA did make one small design tweak in case the agency wants to give the telescope a tuneup someday. Included on the back of JWST are stickers in the shapes of crosses. They’re meant to serve as targets, to help guide a potential robotic spacecraft visitor to JWST in the future. Over the last decade, various space companies have been working on “servicing satellites,” designed to catch up with satellites already in space and grab hold of them, either to refuel their tanks or to tweak aging components. It’s possible that one day, NASA may want to send a servicing satellite to JWST to add more propellant to the telescope’s tanks, extending its time in space. If that happens, the targets will provide a reference point for where the visiting spacecraft should attach to fill up JWST’s tank.”

Side note: what is the fuel for the telescope?