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The cost of launch is relatively low, meaning several hundred million out of a a $15-20B budget. But a given launch system is deeply intertwined with designing

by jmyeet 4y ago

The cost of launch is relatively low, meaning several hundred million out of a a $15-20B budget. But a given launch system is deeply intertwined with designing the mission. The size, the weight and the mass distribution. Moving parts are a nightmare for reliability. Every moving part is something that can cease up and go wrong. It's a motor that can fail and gears that can get jammed. JWST has two key components that involve a lot of moving parts: 1. The mirror. Hubble was smaller enough to be deployed fully constructed in the Space Shuttle so didn't have to deploy in space. JWST's mirror is 3-4x larger an there's no current launch vehicle that could launch it fully assembled. That's why you have all the beryllium hex mirrors that had to deploy the mirror once in orbit. These motors, actuators, assemblies, etc need to be incredibly precise and reliable; and 2. The heat shield. JWST has to be incredibly cold to operate (5K IIRC). The only way to get rid of heat in space is to radiate it away. The heat shield separates JWST from the Sun, the Earth and Moon (each of which reflect enough light to interfere with operations). The shield is several layers and it's large, like tennis-court sized. Obviously this too had to be deployed in space. There were like 10 technologies for JWST that had to be invented to make the mission possible. That's less than ideal. It adds to the cost, the complexity and the timelines. In hindsight it probably would've been worth having a stepping stone between Hubble and JWST that proved some of these technologies in a cheaper and less risky way, probably with a smaller mirror. But here we are.

capableweb 4y ago
> In hindsight it probably would've been worth having a stepping stone between Hubble and JWST that proved some of these technologies in a cheaper and less risky way, probably with a smaller mirror. But here we are. That doesn't really seem to be in NASAs DNA, to do smaller incremental improvements. Instead, they really upgrade big, in chunks with long time in-between. I don't know why they do it, but in their webcasts it been mentioned a couple of times related to James Webb.
- KerrAvon 4y ago
  My (minimally educated) guess is the funding model: they need to give lots of congresspeople stuff for their districts. Big projects provide much more stuff and are easier to sell if everyone can get a piece at once rather than Alabama getting this one piece one year and Colorado getting this other piece the next year.
  - swores 4y ago
    Seems a reasonable guess, but I'd hope that if that were the main stumbling block then it wouldn't be too hard to still sell it as a multi-state project that's also multi-stage, either sharing the work at each stage or signing off up front which stage goes where.
    - mrguyorama 4y ago
      Remember that for congresscritters, it's infinitely easier to cull $20m from NASA's budget than $5 from the DOD. Also remember that a non-trivial amount of Americans believe the moon landing was faked, or that the earth is flat and NASA is part of some conspiracy. Or that a certain political party has spent literally three decades saying "the nerds at NASA are lying, there is no global warming" and you might start to understand the complete lack of political will to give NASA the funding to do even literally the basics.
- gammarator 4y ago
  We have more ideas for telescopes than money to build them. So to get funded, a new telescope needs to be a substantial improvement over what already exists: 10x or more, typically. There’s typically only a chance to build a flagship every ten years or so.
WalterBright 4y ago
A while back I raised a bit of a furor here saying that a duplicate could be made and launched at a tenth of the cost. A lot of people said I don't know what I'm talking about, that little money would be saved. But it seems patently obvious. After all, 10 technologies don't have to be reinvented. No research would need to be redone. No test rigs would need to be redesigned and duplicated. And on and on. The most bizarre argument against building a duplicate was there wouldn't be anything extra worth looking at. Yet I watched the NOVA episode on the scope last night, and everywhere they look where we thought there was "nothing" turns out to be crammed with 10,000 galaxies and stars.
- baxtr 4y ago
  We could probably deploy 100k of them and still see only a tiny fraction of the universe.
  - skykooler 4y ago
    Taking pictures the level of the first image released, it would take about 3700 years for JWST to image the entire sky.
- zabzonk 4y ago
  I take your point, but it does seem to have actually worked.
  - WalterBright 4y ago
    Obviously a great deal of the cost also came from making sure it would work, because there wouldn't be another. What if 10 were built, each with only a 10% chance of success? What would that have cost? After all, it doesn't need the expense of being man-rated.
    - zabzonk 4y ago
      > What would that have cost? No idea. Do you? Genuinely interested, particularly regarding methodology. Not intending at all to be insulting.
ars 4y ago
> These motors, actuators, assemblies, etc need to be incredibly precise and reliable Is it impossible to build to a lower level of reliability then have humans available to fix/adjust things in orbit? Then once it's fully assembled in place, move it to its final location?
- WalterBright 4y ago
  Don't we also have 60 years of experience with motors, actuators, and assemblies in space?
- HideousKojima 4y ago
  Some of the parts are so sensitive them weren't deployed until the telescope got into its final position at the moon's L2 Lagrange point. If you had humans assemble it in orbit it would still have to undergo the stresses of acceleration to get to the L2 Lagrange point.
- UmYeahNo 4y ago
  I don't think that's possible because, if I understand correctly, many of the parts need to be adjusted periodically to maintain accuracy. It's not a set-once-and-forget type situation. Those parts need to be able to make extraordinarily precise adjustments repeatedly for the life of the mission. "Aligning the primary mirror segments as though they are a single large mirror means each mirror is aligned to 1/10,000th the thickness of a human hair. This alignment has to be done at 50 degrees above absolute zero! [0] [0]https://www.nasa.gov/topics/technology/features/webb-actuator.html https://www.nasa.gov/topics/technology/features/webb-actuato...
- jmyeet 4y ago
  Yes and no. It raises a bunch of questions/problems, wuch as: 1. Where doe the telescope deploy? Ideally in LEO so you have a chance fo fix things but then that complicated the launch. You have to park in orbit and restart th eengine at a later point. AFAIK JWST didn't enter a parking orbit so would've required additional fuel. That might not have been possible; 2. What if the launcher itself fails? Do you want to have the capacity to launch another rocket, have it rock with JWST and then go on? If so, that's a whole new level of complexity and a set of problesm you have to solve as well as things that can go wrong; 3. If you look at the flight plan there are a bunch of turns. How would the G-forces affect, say, the deployed heat shield? 4. JWST actually had to rotate during launch to point the instruments away from the Sun so as not to destroy them. This already added complexity. Doing this with the deployed spacecraft would probably only further complicate this.
l1tany11 4y ago
My understanding is that not only did the heat shield have to unfurl, but construct a particular geometry such that it created a waveguide to channel the light out the sides and avoid too much entrapment or too slow of transport. Being the material it is, there’s also no way to model exactly how it will unfurl so it’s difficult to develop. Just the metrology effort on the ground to validate the shape was quite great. The sun shield is held up as this big challenge but I don’t think they do a good job explaining why it was so difficult. There’s a popular YouTube whose father was a metrologist working on the sun shield. https://youtu.be/Pu97IiO_yDI https://youtu.be/Pu97IiO_yDI
motoboi 4y ago
With really cheap space access you can do assembling in space. No motors, just plain old human hands in space. Tennis court sized shield? Take it up like a long and precious Persian mat and let the humans rig the thing in orbit. From there, attach fuels tanks and you are good to go for your insertion burns.
Brian_K_White 4y ago
I like that idea of breaking the job up. Seems like the heat shield could have been it's own seperate launch that just provides the platform, and a bigger/better one, that the scope comes along later and attaches to. Maybe the main reflectors could be like that too. One or more packages that are just the reflector, maybe not even all of it but just sections. I think the adjustable array of smaller sections is simply necessary to get and maintain the focus anyway, so the adjustability is not an expensive extra. Hubble actually went up with a botched main reflector and couldn't be corrected directly. The replacement secondary optics was only a terrible patch, and really only even possible because the scope is within human reachable space to do that level of heart surgury in-situ like that. So if the reflector has to be adjustable anyway just to work at all, then it's not a crazy extra fundamentally, and only a bit extra to have the pieces be able to be shipped individually and self-assemble on site. The inherent adjustability which was required anyway, allows for the inherent inaccuracy of connecting two parts vs one solid part. With 2 or 3 or more smaller component missions, each project becomes not only less critical and more tolerable of a failure, but also less complex and less likely to suffer a failure. And it seems like this project does have at least 2 or 3 natural major building block boundaries. The shield vs everything else is one for sure. That could be turned into a platform, maybe for more than one instrument added or replaced over time, and could maybe supply power as well. Then maybe also the main reflector vs the actual instruments. And the main reflector itself could be in simpler discrete sections instead of having to fold and unfold.

by jmyeet 4y ago

capableweb 4y ago

> In hindsight it probably would've been worth having a stepping stone between Hubble and JWST that proved some of these technologies in a cheaper and less risky way, probably with a smaller mirror. But here we are. That doesn't really seem to be in NASAs DNA, to do smaller incremental improvements. Instead, they really upgrade big, in chunks with long time in-between. I don't know why they do it, but in their webcasts it been mentioned a couple of times related to James Webb.

KerrAvon 4y ago
My (minimally educated) guess is the funding model: they need to give lots of congresspeople stuff for their districts. Big projects provide much more stuff and are easier to sell if everyone can get a piece at once rather than Alabama getting this one piece one year and Colorado getting this other piece the next year.
- swores 4y ago
  Seems a reasonable guess, but I'd hope that if that were the main stumbling block then it wouldn't be too hard to still sell it as a multi-state project that's also multi-stage, either sharing the work at each stage or signing off up front which stage goes where.
  - mrguyorama 4y ago
    Remember that for congresscritters, it's infinitely easier to cull $20m from NASA's budget than $5 from the DOD. Also remember that a non-trivial amount of Americans believe the moon landing was faked, or that the earth is flat and NASA is part of some conspiracy. Or that a certain political party has spent literally three decades saying "the nerds at NASA are lying, there is no global warming" and you might start to understand the complete lack of political will to give NASA the funding to do even literally the basics.
gammarator 4y ago
We have more ideas for telescopes than money to build them. So to get funded, a new telescope needs to be a substantial improvement over what already exists: 10x or more, typically. There’s typically only a chance to build a flagship every ten years or so.

WalterBright 4y ago

A while back I raised a bit of a furor here saying that a duplicate could be made and launched at a tenth of the cost. A lot of people said I don't know what I'm talking about, that little money would be saved. But it seems patently obvious. After all, 10 technologies don't have to be reinvented. No research would need to be redone. No test rigs would need to be redesigned and duplicated. And on and on. The most bizarre argument against building a duplicate was there wouldn't be anything extra worth looking at. Yet I watched the NOVA episode on the scope last night, and everywhere they look where we thought there was "nothing" turns out to be crammed with 10,000 galaxies and stars.

baxtr 4y ago
We could probably deploy 100k of them and still see only a tiny fraction of the universe.
- skykooler 4y ago
  Taking pictures the level of the first image released, it would take about 3700 years for JWST to image the entire sky.
zabzonk 4y ago
I take your point, but it does seem to have actually worked.
- WalterBright 4y ago
  Obviously a great deal of the cost also came from making sure it would work, because there wouldn't be another. What if 10 were built, each with only a 10% chance of success? What would that have cost? After all, it doesn't need the expense of being man-rated.
  - zabzonk 4y ago
    > What would that have cost? No idea. Do you? Genuinely interested, particularly regarding methodology. Not intending at all to be insulting.

ars 4y ago

> These motors, actuators, assemblies, etc need to be incredibly precise and reliable Is it impossible to build to a lower level of reliability then have humans available to fix/adjust things in orbit? Then once it's fully assembled in place, move it to its final location?

WalterBright 4y ago
Don't we also have 60 years of experience with motors, actuators, and assemblies in space?
HideousKojima 4y ago
Some of the parts are so sensitive them weren't deployed until the telescope got into its final position at the moon's L2 Lagrange point. If you had humans assemble it in orbit it would still have to undergo the stresses of acceleration to get to the L2 Lagrange point.
UmYeahNo 4y ago
I don't think that's possible because, if I understand correctly, many of the parts need to be adjusted periodically to maintain accuracy. It's not a set-once-and-forget type situation. Those parts need to be able to make extraordinarily precise adjustments repeatedly for the life of the mission. "Aligning the primary mirror segments as though they are a single large mirror means each mirror is aligned to 1/10,000th the thickness of a human hair. This alignment has to be done at 50 degrees above absolute zero! [0] [0]https://www.nasa.gov/topics/technology/features/webb-actuator.html https://www.nasa.gov/topics/technology/features/webb-actuato...
jmyeet 4y ago
Yes and no. It raises a bunch of questions/problems, wuch as: 1. Where doe the telescope deploy? Ideally in LEO so you have a chance fo fix things but then that complicated the launch. You have to park in orbit and restart th eengine at a later point. AFAIK JWST didn't enter a parking orbit so would've required additional fuel. That might not have been possible; 2. What if the launcher itself fails? Do you want to have the capacity to launch another rocket, have it rock with JWST and then go on? If so, that's a whole new level of complexity and a set of problesm you have to solve as well as things that can go wrong; 3. If you look at the flight plan there are a bunch of turns. How would the G-forces affect, say, the deployed heat shield? 4. JWST actually had to rotate during launch to point the instruments away from the Sun so as not to destroy them. This already added complexity. Doing this with the deployed spacecraft would probably only further complicate this.

l1tany11 4y ago

My understanding is that not only did the heat shield have to unfurl, but construct a particular geometry such that it created a waveguide to channel the light out the sides and avoid too much entrapment or too slow of transport. Being the material it is, there’s also no way to model exactly how it will unfurl so it’s difficult to develop. Just the metrology effort on the ground to validate the shape was quite great. The sun shield is held up as this big challenge but I don’t think they do a good job explaining why it was so difficult. There’s a popular YouTube whose father was a metrologist working on the sun shield. https://youtu.be/Pu97IiO_yDI https://youtu.be/Pu97IiO_yDI

motoboi 4y ago

With really cheap space access you can do assembling in space. No motors, just plain old human hands in space. Tennis court sized shield? Take it up like a long and precious Persian mat and let the humans rig the thing in orbit. From there, attach fuels tanks and you are good to go for your insertion burns.

Brian_K_White 4y ago

I like that idea of breaking the job up. Seems like the heat shield could have been it's own seperate launch that just provides the platform, and a bigger/better one, that the scope comes along later and attaches to. Maybe the main reflectors could be like that too. One or more packages that are just the reflector, maybe not even all of it but just sections. I think the adjustable array of smaller sections is simply necessary to get and maintain the focus anyway, so the adjustability is not an expensive extra. Hubble actually went up with a botched main reflector and couldn't be corrected directly. The replacement secondary optics was only a terrible patch, and really only even possible because the scope is within human reachable space to do that level of heart surgury in-situ like that. So if the reflector has to be adjustable anyway just to work at all, then it's not a crazy extra fundamentally, and only a bit extra to have the pieces be able to be shipped individually and self-assemble on site. The inherent adjustability which was required anyway, allows for the inherent inaccuracy of connecting two parts vs one solid part. With 2 or 3 or more smaller component missions, each project becomes not only less critical and more tolerable of a failure, but also less complex and less likely to suffer a failure. And it seems like this project does have at least 2 or 3 natural major building block boundaries. The shield vs everything else is one for sure. That could be turned into a platform, maybe for more than one instrument added or replaced over time, and could maybe supply power as well. Then maybe also the main reflector vs the actual instruments. And the main reflector itself could be in simpler discrete sections instead of having to fold and unfold.