Hershel operated 4 years and one month, but this was because it needed liquid helium coolant and it eventually ran out. Hershel was planned to operate 3.5 years.
btw. Hershel wast the first optical telescope placed in L2. It was also it was also the largest optical space telescope before JWST.
"though many factors could ultimately affect Webb’s duration of operation." JWST also needs helium coolant with no possibility to recharge therefore limiting its lifespan to ~10 years, I believe. Interesting about Herschel and L2.
It does use helium only as refrigeration fluid in closed cycle, it does not get depleted. Building a cryocooler capable of achieving so low temperatures without boiling helium off was a major hurdle in JWST development.
Also because it was imaging far infrared with wavelengths 100-1000 times that of visible light, the resolution of the optics was much lower and yielded kind of bla images (with a few notable exceptions):
I think a big reason Hubble managed to do that was that it captures in the visible spectrum due to being a repurposed spy satellite. That spectrum just isn't that interesting these days afaict, especially since ground based observatories have gotten a lot better at seeing through the earth's atmosphere. The false color images of most of today's missions are just a lot harder for the public to understand. It was also launched in a time where NASA desperately needed good publicity.
KH-11 ("Keyhole-class") spy satellites. It's generally believed that Hubble's optical technology came directly from that.
> KH-11s are believed to resemble the Hubble Space Telescope in size and shape, as the satellites were shipped in similar containers. Their length is believed to be 19.5 meters, with a diameter of up to 3 meters (120 in). A NASA history of the Hubble, in discussing the reasons for switching from a 3-meter main mirror to a 2.4-meter (94 in) design, states: "In addition, changing to a 2.4-meter mirror would lessen fabrication costs by using manufacturing technologies developed for military spy satellites".
And it seemed truly astounding. Like we were getting to journey across the universe. The visuals that Hubble presented, the variety and scale of that style of imagery (great for PR), and the way it cultivated the imagination of the mass public, is still unrivaled.
Infra-red is optical. Just not visible light but it uses lenses and mirrors like every other visible light telescope. The main difference is that those lenses are designed to be as transparent to IR as possible instead of accidentally filtering it out.
The big trick for Webb is that it will allow for extremely red shifted IR to be received, which translates into 'light from very long ago and very far away'. To be able to do that the sensors are cooled to extremely low temperatures to ensure that the instrument noise level is brought down as low as possible, allowing for extreme sensitivity.
That's a very good answer. A few more points, because the answer is a 2.5 years old.
- the docking adapter discussed in the answer did not make it. However, the answer offers a couple of alternatives, so +1.
- they painted some crosses on the JWST to make alignment easier.
- JWST's L2 location is really far from Earth. It's about 4X the distance from the moon. So a manned mission is currently infeasible. But maybe in the future.
- while fueling may be possible, any other sort of maintenance probably isn't. To save weight, the JWST is mostly glued together, unlike Hubble which used spacesuit accessible bolts.
It's also worth noting that much of JWST is now twenty year old technology. Assuming it isn't a total failure which needs to be salvaged for PR reasons, it will almost certainly make more sense to build a new observatory in ten years rather than rescuing this one. If Starship exists at that point it will also be a much less complex undertaking to get it into space, and it could likely use an even bigger mirror.
The complexity of the undertaking was not building the rocket. The complexity is the telescope itself. It would be interesting what the costs come down to if rather than starting from scratch they iterated on existing designs. Anyone know what the incremental cost of building the same telescope again would look like?
My understanding is that a lot of the complexity is making the telescope able to fit in limited space and then unfurl. That constraint is lifted significantly with Starship.
I think that the other commenter was referring to the relative complexity in JWST's unfolding/deployment. It might be possible to deploy something from Starship that doesn't need to be packed as tightly (and save on engineering costs there) and still get around the same performance.
A complicated sunshield deployment seems somewhat inevitable, personally, but I'd be happy to be proven wrong there.
> So a manned mission is currently infeasible. But maybe in the future.
Given the increased interest in manned missions and recent technology advancements/investments, I wouldn't be surprised if we could get there in 15-20 years, which sounds likely to be when it'd need to be refueled.
If it's worth it or too dangerous to send an astronaut to deal with the dangerous refueling operation are whole other questions. But actually getting there? I think we can do it in 15-20 years.
Maybe but it might be obsolete by then, especially considering how much lift capacity Starship will bring online. Will be a lot cheaper to just replace Webb.
I've read that optical tracking/docking markers were added around mating ring that connected JWST to Ariane upper stage. It does not mean that docking to it will be easy but it was at least considered.
I am not familiar with the station keeping needed for maintaining an L2 orbit; would it be possible to use an Earth orbiting laser to apply photonic force against JWST's solar shield (turning it into a laser sail) to balance it "falling back" towards Earth without onboard propellant? My understanding is that it has a gravitational weighting towards Earth to prevent slipping away.
Is it enormously expensive because of physics or because of bureaucracy and politics?
Like, serious question: how much cost are the raw materials for the fuel and spacecraft/rocket, and how much are the costs like human labor and ground transportation to the launch site?
It's also interesting to me that the mirror appears to be fully exposed to space unlike Hubbell. If anyone knows something about that design choice I've like to hear it.
Cooldown has already started with the deploying of the sunshield from it's launch position, even before it is unfolded fully and stacked properly the delta is already a whopping 60 degrees Celsius across a bit over two meters.
Hubble needed to hide mirror because it is passing from sunlight into shadow every 47 minutes and mirror has to be protected from thermal stress. Also Earth emits some light even on night side that would interfere with observations.
JWST's mirror is always in shadow and stray light from sides will not be a problem at L2.
The explore all deployments section is worth a read too. Wealth of info on the whole site and it's designed really well. Clearly catering to the education / general public good will with this site. https://jwst.nasa.gov/content/webbLaunch/deploymentExplorer....
Fascinating that it's already covered 40% of the distance, but it's only on day 4 out of 30. That makes sense once you realize that its radial velocity needs to slow to zero when it reaches L2. I'd love to see the shape of how the velocity curve slows.
i've been checking for the past few days and it looks like JWST is available now in NASA's little 3D space model. you can literally it in the solar system model now too!
And think about how many layers of safety margins. If there are ten subsystems each with a 20% safety margin to say that their designers did their jobs right, then you might have an overall system with as much as 200% safety margin. (yeah not everything is linear like that, but illustrating the point.)
I never understood how we launch to earth sun langrange points?
By starting from earth we’re already at the correct orbital velocity around the sun so do we just cruise out there and cancel out the delta v we used to get there?
Remember that no matter how far from the earth you get, you're always being pulled by it, decreasing velocity. The Webb left earth moving at 7km/s, but now is going less than 1km/s.
It's going to let Earth's gravity slow it down so that it reaches (effectively) zero at exactly the right spot.
It's literally rocket science to do the equations to make it work, but by God we've gotten pretty good at it.
As the OP alludes to, JWST's operational life is hard-limited by its fuel capacity. L2 (like L1 and L3, but unlike L4 and L5) is an unstable orbit, and without regular corrections it will drift out of position. This means that you want to save ALL your fuel for making those corrections, and thus spend as little of it as possible on getting there in the first place. So over the next month it's going to slowly crawl into place, cruising on no power other than what the Ariane initially gave it, getting continually slower and slower via the effect of the earth and sun's gravity until it stops perfectly in position.
> cruising on no power other than what the Ariane initially gave it
Webb has already done multiple burns to get to L2 after being released from the Ariane upper stage. Preserving time on orbit is important but the bigger issue is that Webb can only fire its thrusters in one direction (because it can't point the optics at the sun) so any overshoot is catastrophic. Ariane thus was set to intentionally undershoot L2 and Webb is making up the difference with its fuel.
> and without regular corrections it will drift out of position
How significant is that drift? Over 1 year how far out of position would it get? How many days/months/years would it take before it started being too far from earth or had an orbit that was dangerous?
I've never been able to find any answers to this question. The internet is covered in people repeating that L1, L2 and L3 are unstable, but never explain the impact.
Can anyone with knowledge provide a rough estimate of how much would it cost to manufacture a second telescope considering all the research cost is assigned to first one.
It is a hypothetical question to understand if we had lost it in launch would it have been a complete loss or can we have 2nd one within couple of billions and 3 years.
A lot of the core research wouldn't have to be repeated, but the build and verification costs would not go away, and to do proper verification takes many many years.
Modular telescopes? Couldn't the whole manufacturing of the module (semi-)automated? (So no need for so much testing, verification, etc.) Bring unit costs down, and launch a few of the modules each year. Eventually they'll have as big a mirror as they want.
I suspect it wouldn't be easy to incrementally build up a single large aperture because the secondary optics needed would be different at each size.
If we build telescopes for optical vlbi we could build a fleet to have the resolution of a telescope kilometers across... I believe VLBI has been accomplished experimentally at MWIR wavelengths.
From my experience the cost breakdown of a typical [0] satellite is on the order of 60% recurring engineering, 40% non-recurring engineering. I don't have a good sense of the breakdown for JWST but the assembly and verification campaign is huge compared to most satellites and they would have to do that again so I would expect the recurring engineering to be higher. Coupled with the fact that it wouldn't be directly build-to-print due to parts obsolescence and technology upgrades they would want to make the cost would probably be higher still. So its not going to be a huge cost savings but you could maybe do it for something like 70-80% of the original cost.
As for the timeline, that's going to be a hard one to change. Consider that all of the mirror segments and optics were delivered by the end of 2013. So the integration and test campaign of the spacecraft took 8 years. There would definitely be some optimization and lessons learned from that and you could likely shave off a couple years. However, if we are also looking at building it "now" the supply chain issues also hit the aerospace industry. There are typical things that you would expect like chip shortages, but also random things like its difficult to buy the epoxy we normally use to glue solar cells on to panels.
[0] "Typical" varies wildly here. So for typical I am assuming something like a large NASA earth science mission with building one spacecraft of a relatively unique design.
NASA may be the greatest engineering organization in human history; I can't think of any competitors. They are also masters at consulting: Underpromise, overdeliver.
'The rover is planned to last one year.' 'Amazingly, it is still working after three years!'
* NASA Curiosity: "2 years" -> 9.5 years, and counting.
* NASA Spirit: "90 days" -> Just over 6 years, ending in 2010.
* NASA Opportunity: "90 days" -> Over 14 years, ending in 2018.
NASA has had some failures too, of course. These stats are cherry-picked but still impressive.
My point is that it's not impressive, it's just an old sales technique. Curiosity could have been designed for 20 years, but all NASA needs to do is say '2 years' and the project sounds like a resounding success if it fails in 10.
(It is extremely impressive to have rovers and helicopters traversing Mars.)
In each of the above cases, the mission end date was extended because the hardware was capable of doing more science (or for more time) than it was designed for (and budgeted for).
Like JWST, some of the procedures required for a successful mission had never been done before, and could not be tested fully on Earth. Many of those procedures have implications on mission longevity. Very smart and dedicated people make their most educated guesses, build in what they know, try to handle the unknowns, and hope and pray -- and more often than not, are proven correct. That's pretty close to my personal definition of "impressive engineering".
There's a political angle too, of course. We don't know what NASA's "estimate fudge factor" is. I'd be amazed to learn that it is 5x, 24x, or 56x.
> the mission end date was extended because the hardware was capable of doing more science (or for more time) than it was designed for (and budgeted for)
That is circular, it assumes that the announced end date isn't just underpromising what they know will be a later date. Neither of us is there when these dates are chosen, so we don't know what they are thinking. Arguably, NASA should be better able to estimate project lifetimes by now.
The announced end date is the goal. It just so happens that making the system reliable enough to last x days means it also has a high, but not sure, chance that it will last 10x days.
Easier to just say it's NASA's high percentage confidence interval. Maybe it's the 95% mark. They are 95% certain it will last 5 years. They likely also have lower confidence intervals with longer times.
(If anyone knows what percentage the confidence interval actually is, I would be curious to know)
It's pretty much expected, these sorts of complex systems follow a bathtub curve. Failures either happen very early or after a very long time. If you design something so that it has a 99% of lasting 1 year, there's pretty good odds that it'll make it to 5 years since the riskiest time is the first weeks/months.
I guess it's that way for budgeting reasons. Probably easier to get funding for mission extension for rover that's already on Mars than budgeting 15 year mission at the beginning. And when it does actually fail earlier there's no hassle with reallocating funds.
For some things like the rovers it seems like the "design life" was just the minimum required to justify the mission. It would be silly to call a mission a failure if it died after a year when the mission would have been justified with just 90 days of operation simply because we had expected it to last two years.
A key thing is that several years ago they realised that the reaction wheels were failing earlier than planned, some nifty deep analysis found the issue and I hope that this means they’ll last long enough.
The Reaction wheels are used to rotate the space craft without the use of fuel, and Scott Manly, as ever did a great video on this:
I wonder if Webb having a longer life won't be bad for us in the long run. Webb was designed a long time ago, with tech that is now pretty old. It's a design that was heavily compromised by the limits on what we could lift into space at the time.
It seems likely to me that in ten years time we could build and lift a much better instrument. But if Webb is still working will we have the political will to do so?
By then low hanging science that could be done with this instrument will probably be done (or they would have engineered it for more than 5 years...). There are plenty of older prestige instruments that no longer get used for much important science because it is career suicide to invest your time on an instrument where other people have already found all of the easy and medium difficulty discoveries reachable from it. (e.g. as was the case for arecebo before it collapsed)
It's not hard for me to imagine that ten or fifteen years from now Webb isn't being very effectively used because the scientists attention are elsewhere and where we could build a vastly superior instrument, but we don't because webb still works.
Maybe someone more aware of the realpolitik of astronomy projects will tell me that I'm being pessimistic for no good reason. :)
103 comments
[ 3.3 ms ] story [ 170 ms ] threadbtw. Hershel wast the first optical telescope placed in L2. It was also it was also the largest optical space telescope before JWST.
https://webb.nasa.gov/content/about/innovations/cryocooler.h...
Hershel took awesome images. For example:
Galactic outflow with the Suzaku X-ray astronomy satellite https://www.esa.int/var/esa/storage/images/esa_multimedia/im...
Herschel’s view of new stars and molecular clouds https://www.esa.int/var/esa/storage/images/esa_multimedia/im...
The Little Fox and the Giant Stars https://www.esa.int/var/esa/storage/images/esa_multimedia/im...
Star formation on filaments in RCW106 https://www.esa.int/var/esa/storage/images/esa_multimedia/im...
Feathery filaments in Mon R2 https://www.esa.int/var/esa/storage/images/esa_multimedia/im...
https://www.herschel.caltech.edu/images
What? Where did this come from?
> KH-11s are believed to resemble the Hubble Space Telescope in size and shape, as the satellites were shipped in similar containers. Their length is believed to be 19.5 meters, with a diameter of up to 3 meters (120 in). A NASA history of the Hubble, in discussing the reasons for switching from a 3-meter main mirror to a 2.4-meter (94 in) design, states: "In addition, changing to a 2.4-meter mirror would lessen fabrication costs by using manufacturing technologies developed for military spy satellites".
https://en.wikipedia.org/wiki/KH-11_KENNEN
https://i.imgur.com/Go5VDi1.jpg
And it seemed truly astounding. Like we were getting to journey across the universe. The visuals that Hubble presented, the variety and scale of that style of imagery (great for PR), and the way it cultivated the imagination of the mass public, is still unrivaled.
The big trick for Webb is that it will allow for extremely red shifted IR to be received, which translates into 'light from very long ago and very far away'. To be able to do that the sensors are cooled to extremely low temperatures to ensure that the instrument noise level is brought down as low as possible, allowing for extreme sensitivity.
JWST is also primarily infrared telescope. It as some capability in red and the yellow part of the visible spectrum.
Is there something qualitatively different about infrared and ultraviolet that they share with visible, that they are all grouped into 'optical'?
Fused silica is falls off in the mid IR and is opaque for long wave IR, and optimizing for UV costs you IR response. ( https://escooptics.com/pages/materials-fused-silica-quartz )
The main optical path of JWST is all reflective for this reason.
There are refractive optics in some the instruments, but those are more wavelength specific.
E.g. NIRcam uses refractive elements made from LiF, BaF2, and ZnSe ( http://ircamera.as.arizona.edu/nircam/pdfs/5904-9_Ryder.pdf ) while I don't think MIRI ( https://arxiv.org/pdf/1508.02488.pdf ) uses any refractive components at all except a ZnS-GE double prism ( https://orbi.uliege.be/bitstream/2268/95768/1/DPA%20v8.pdf ) which is opaque to visible light.
- the docking adapter discussed in the answer did not make it. However, the answer offers a couple of alternatives, so +1.
- they painted some crosses on the JWST to make alignment easier.
- JWST's L2 location is really far from Earth. It's about 4X the distance from the moon. So a manned mission is currently infeasible. But maybe in the future.
- while fueling may be possible, any other sort of maintenance probably isn't. To save weight, the JWST is mostly glued together, unlike Hubble which used spacesuit accessible bolts.
A complicated sunshield deployment seems somewhat inevitable, personally, but I'd be happy to be proven wrong there.
Given the increased interest in manned missions and recent technology advancements/investments, I wouldn't be surprised if we could get there in 15-20 years, which sounds likely to be when it'd need to be refueled.
If it's worth it or too dangerous to send an astronaut to deal with the dangerous refueling operation are whole other questions. But actually getting there? I think we can do it in 15-20 years.
Like, serious question: how much cost are the raw materials for the fuel and spacecraft/rocket, and how much are the costs like human labor and ground transportation to the launch site?
It's also interesting to me that the mirror appears to be fully exposed to space unlike Hubbell. If anyone knows something about that design choice I've like to hear it.
1. Bigger mirror = better. Enclosing a mirror requires mass and volume, limiting mirror size.
2. The L2 orbit is unstable. Far less risk of being hit by debris than low Earth orbit.
3. Webb's sun shield blocks the primary light pollution angle. Hubble would need more protection from all angles due to the Sun, Earth, and Moon.
I also had no idea L2 was unstable and found a little discussion on it. https://space.stackexchange.com/questions/284/why-should-the...
https://youtu.be/7PHvDj4TDfM
JWST's mirror is always in shadow and stray light from sides will not be a problem at L2.
No idea if what they're saying is true however, I've no knowledge about the domain.
https://youtu.be/aICaAEXDJQQ
In the end it will be several hundred degrees difference, which given the distances involved is extremely impressive.
https://upload.wikimedia.org/wikipedia/commons/3/36/Lagrangi...
https://solarsystem.nasa.gov/solar-system/our-solar-system/o...
In other words, it should be the norm and not the exception. But of course the vast majority of us work in fields where overpromising is the norm.
By starting from earth we’re already at the correct orbital velocity around the sun so do we just cruise out there and cancel out the delta v we used to get there?
It's going to let Earth's gravity slow it down so that it reaches (effectively) zero at exactly the right spot.
It's literally rocket science to do the equations to make it work, but by God we've gotten pretty good at it.
Right now it's traveling at about 0.55 miles per second. When I checked the other day that was over 0.7, and a bit after launch it was over 1.
Putting JWST into L2 is essentially the world's biggest curling toss ( https://en.m.wikipedia.org/wiki/Curling ).
As the OP alludes to, JWST's operational life is hard-limited by its fuel capacity. L2 (like L1 and L3, but unlike L4 and L5) is an unstable orbit, and without regular corrections it will drift out of position. This means that you want to save ALL your fuel for making those corrections, and thus spend as little of it as possible on getting there in the first place. So over the next month it's going to slowly crawl into place, cruising on no power other than what the Ariane initially gave it, getting continually slower and slower via the effect of the earth and sun's gravity until it stops perfectly in position.
1: https://www.smithsonianmag.com/smart-news/curly-curling-robo...
Webb has already done multiple burns to get to L2 after being released from the Ariane upper stage. Preserving time on orbit is important but the bigger issue is that Webb can only fire its thrusters in one direction (because it can't point the optics at the sun) so any overshoot is catastrophic. Ariane thus was set to intentionally undershoot L2 and Webb is making up the difference with its fuel.
How significant is that drift? Over 1 year how far out of position would it get? How many days/months/years would it take before it started being too far from earth or had an orbit that was dangerous?
I've never been able to find any answers to this question. The internet is covered in people repeating that L1, L2 and L3 are unstable, but never explain the impact.
It is a hypothetical question to understand if we had lost it in launch would it have been a complete loss or can we have 2nd one within couple of billions and 3 years.
He estimates that a second would cost about 90% of the first.
Modular telescopes? Couldn't the whole manufacturing of the module (semi-)automated? (So no need for so much testing, verification, etc.) Bring unit costs down, and launch a few of the modules each year. Eventually they'll have as big a mirror as they want.
If we build telescopes for optical vlbi we could build a fleet to have the resolution of a telescope kilometers across... I believe VLBI has been accomplished experimentally at MWIR wavelengths.
As for the timeline, that's going to be a hard one to change. Consider that all of the mirror segments and optics were delivered by the end of 2013. So the integration and test campaign of the spacecraft took 8 years. There would definitely be some optimization and lessons learned from that and you could likely shave off a couple years. However, if we are also looking at building it "now" the supply chain issues also hit the aerospace industry. There are typical things that you would expect like chip shortages, but also random things like its difficult to buy the epoxy we normally use to glue solar cells on to panels.
[0] "Typical" varies wildly here. So for typical I am assuming something like a large NASA earth science mission with building one spacecraft of a relatively unique design.
'The rover is planned to last one year.' 'Amazingly, it is still working after three years!'
(It is extremely impressive to have rovers and helicopters traversing Mars.)
In each of the above cases, the mission end date was extended because the hardware was capable of doing more science (or for more time) than it was designed for (and budgeted for).
Like JWST, some of the procedures required for a successful mission had never been done before, and could not be tested fully on Earth. Many of those procedures have implications on mission longevity. Very smart and dedicated people make their most educated guesses, build in what they know, try to handle the unknowns, and hope and pray -- and more often than not, are proven correct. That's pretty close to my personal definition of "impressive engineering".
There's a political angle too, of course. We don't know what NASA's "estimate fudge factor" is. I'd be amazed to learn that it is 5x, 24x, or 56x.
That is circular, it assumes that the announced end date isn't just underpromising what they know will be a later date. Neither of us is there when these dates are chosen, so we don't know what they are thinking. Arguably, NASA should be better able to estimate project lifetimes by now.
NASA is doing amazing things; I'm not so cynical.
(If anyone knows what percentage the confidence interval actually is, I would be curious to know)
Also called sandbagging. :)
For some things like the rovers it seems like the "design life" was just the minimum required to justify the mission. It would be silly to call a mission a failure if it died after a year when the mission would have been justified with just 90 days of operation simply because we had expected it to last two years.
The Reaction wheels are used to rotate the space craft without the use of fuel, and Scott Manly, as ever did a great video on this:
https://youtu.be/KibT-PEMHUU
It seems likely to me that in ten years time we could build and lift a much better instrument. But if Webb is still working will we have the political will to do so?
By then low hanging science that could be done with this instrument will probably be done (or they would have engineered it for more than 5 years...). There are plenty of older prestige instruments that no longer get used for much important science because it is career suicide to invest your time on an instrument where other people have already found all of the easy and medium difficulty discoveries reachable from it. (e.g. as was the case for arecebo before it collapsed)
It's not hard for me to imagine that ten or fifteen years from now Webb isn't being very effectively used because the scientists attention are elsewhere and where we could build a vastly superior instrument, but we don't because webb still works.
Maybe someone more aware of the realpolitik of astronomy projects will tell me that I'm being pessimistic for no good reason. :)