They need a firm launch date because of the cascading research windows already allocated, but there are 344 single points of failure, and it will be virtually impossible to fixed once launched. I'm terribly excited for the advancements this telescope will bring, but I'm very nervous about the launch and deployment.
It seems like they could start scheduling windows for say June 2022, and then if it happens to be ready before that, have a lottery for slots that you have to use within a day or two of getting the slot. So basically for the folks who just happen to be ready to go and what they're looking at isn't time dependent.
Since the telescope has to always point its shielding toward the sun, won't there be certain windows of opportunity to view things depending on where they are located in relation to the sun?
The good news is that the trajectory of timeline slip is less than one week per week, and if that holds true, the two will eventually rendezvous.
In 1996, it was estimated for 2007, fast forwarding a bit to 2018, it slipped one year from an estimated launch in 2020 to 2021, in 2020 it slipped from March 2021 to July, by January 2021 it slipped to October 31st, and it's been known since June, 14 weeks ago, that it wasn't likely to meet that date.
At this rate, I estimate the current date will intercept the target date in early 2022.
It still works in that case, actually; you just have to pass through a singularity where the timeline is delayed infinitely many times, but the total amount of each of those infinite delays is finite. 1/2 + 1/4 + 1/8 + 1/16 + 1/32 + ... = 1.
This is the answer to Zeno's paradox. A sports reporter gives an update every time Hercules catches up to where the tortoise was the last time he gave an update. All that happens is the sports reporter eventually needs to talk faster and faster and faster, and eventually try to give infinite updates right as Hercules passes the tortoise. Then the reporter's vocal chords explode, but otherwise the race proceeds as you would expect. (That is, just because a description of an event is infinitely long, does not mean the event itself is infinitely long in any sense.)
Lol yeah, that was a goof. I had Zeno’s paradox in mind and intended to choose a divergent series but accidentally used the textbook convergent one. Let’s swap it out for the harmonic series.
Although tragic, it would be a fitting end to this boondoggle of a project. JWST was originally marketed as a quick, cheap win for NASA, but it turned into the polar opposite of that.
Most of the time and money was spent on design. If it blows up they should be able to build a second one for a fraction of the time/cost of the first one.
Wasn't a major part of the problem that the design kept changing based on the pushed timeline? So what we are getting now is completely different from what was planned in 1996 to be launched in 2007? If that's the case, and the JWST fails to deploy, we probably wouldn't just build another copy of it - we would build a completely new/reworked space telescope that would take another 25 years to design/launch.
There are about 50 deployment actions that have to occur. If everything works perfectly, great. But if something hangs up or gets tangled, the people running the mission are blind when trying to debug the problem
To learn from what went wrong. Even if it cannot be corrected for the telescope, we can hopefully see enough about what went wrong to be able to prevent the same thing from happening on future complex satellites.
>"trajectory of timeline slip is less than one week per week, and if that holds true, the two will eventually rendezvous."
Not mathematically certain. If the timeline slip is a sequence like [1-1/2^k]_{k=1...} = {1/2 week, 3/4 weeks, 7/8 weeks, 15/16 weeks...}, then it's possible the project timeline could diverge forever. (This is just a restatement of Zeno's paradox).
The act of delaying launch takes non-zero amount of time in the real world, so at some point the slippage fraction gets so small that the launch will happen while being about to be rescheduled.
I thought Zeno's paradox was caused by lack of understanding of infinitesimal calculus by Ancient Greeks? That is, in situations where a series converges despite an having infinite number of elements. Divergent series like yours shouldn't constitute such a paradox, since they both have an infinite number of elements AND diverge.
An infinite number of mathematicians walk into a bar. The first one orders a pint. The second one orders half a pint. When the third orders a quarter of a pint, the bartender rolls his eyes, places two beers on the bar, and says "you all need to learn your limits!"
An infinite number of mathematicians walk into a bar. The first orders a beer. The second orders half a beer. The third orders a quarter of a beer. Before the next one can order, the bartender says, "You're all assholes," and pours two beers.
They got lucky to have a bartender who knows his customer's limits.
-----------------
An infinite number of mathematicians walk into a bar
The first mathematician orders a beer
The second orders half a beer
"I don't serve half-beers" the bartender replies
"Excuse me?" Asks mathematician #2
"What kind of bar serves half-beers?" The bartender remarks. "That's ridiculous."
"Oh c'mon" says mathematician #1 "do you know how hard it is to collect an infinite number of us? Just play along"
"There are very strict laws on how I can serve drinks. I couldn't serve you half a beer even if I wanted to."
"But that's not a problem" mathematician #3 chimes in "at the end of the joke you serve us a whole number of beers. You see, when you take the sum of a continuously halving function-"
"I know how limits work" interjects the bartender "Oh, alright then. I didn't want to assume a bartender would be familiar with such advanced mathematics"
"Are you kidding me?" The bartender replies, "you learn limits in like, 9th grade! What kind of mathematician thinks limits are advanced mathematics?"
"HE'S ON TO US" mathematician #1 screeches
Simultaneously, every mathematician opens their mouth and out pours a cloud of multicolored mosquitoes. Each mathematician is bellowing insects of a different shade. The mosquitoes form into a singular, polychromatic swarm. "FOOLS" it booms in unison, "I WILL INFECT EVERY BEING ON THIS PATHETIC PLANET WITH MALARIA"
The bartender stands fearless against the technicolor hoard. "But wait" he interrupts, thinking fast, "if you do that, politicians will use the catastrophe as an excuse to implement free healthcare. Think of how much that will hurt the taxpayers!"
The mosquitoes fall silent for a brief moment. "My God, you're right. We didn't think about the economy! Very well, we will not attack this dimension. FOR THE TAXPAYERS!" and with that, they vanish.
A nearby barfly stumbles over to the bartender. "How did you know that that would work?"
"It's simple really" the bartender says. "I saw that the vectors formed a gradient, and therefore must be conservative."
Why does the launch date keep slipping? I've been looking forward to this launch for a very long time and I'm getting pretty irked at the teams sending this up, to the point where even if they are completely successful I hope they don't get put on another big project like this again. Hopefully the delays have been because it's a lot harder to send this to L2 successfully than anyone thought or could have known, and now we do.
This is complete hearsay but I was sat next to a engineer working on the project on a recent flight. He mentioned to me that 1.) it would be delayed past October till December, and probably early into next year, and 2.) COVID, like any good excuse, was being used because it was there and not necessarily because it caused the delays.
Maybe the engineer was just telling a story with a bit of flair but I believed him.
Why? Time estimation is hard and you’re a pretty bad PM of a scientific missions primary goal is to launch by a date. You keep working until you are confident you can do it right.
Failures happen when delivery dates are more important than quality.
Being in a shadow area would mean it would be in orbit of something, and at best it would be in shadow 50% of the time and still need the same amount of shielding for daylight operations. Being in orbit would also mean its position would be much less stable than it will be at the L2 point.
There aren't any permanent shadows in space. Every orbit goes "around" eventually -- and there's no configuration where some combination of objects works to permanently shadow you.
(A technical exception is a planetary solar L2 Lagrange point [0], *if* it would occur close enough to a planet to be totally eclipsed. But that doesn't happen (AFAIK) -- they're generally far enough away that although the planet is always in front of the sun, the planet's disk is much smaller than the solar disk. Like a partial eclipse).
With cryogenic cooling, you have an even more difficult challenge: the light of a planet's infrared radiation emission is something you also have to shield. That's a major reason JWST (and similar cryogenic telescopes) go to solar L2: its sunshield doesn't only block out the sun -- it simultaneously blocks out the sun and the Earth. That's the unique advantage of the solar L2 point: the sun and Earth are always in the same direction.
Why it's not made serviceable? Or at least able to be serviced, with non-herculean efforts? Manned missions to L2 would both maintain the truly unique device and move forward the manned space capabilities and experience. It's just - what? - four time farther than the Moon?
At the time the design was locked in, there was nothing even planned that would be capable of supporting a crewed servicing mission. They have however included a grapple bar so that there is something to connect to should there be something in the future. SpaceX's Starship is the most likely vehicle at this stage, but that is still substantial development away from being capable of a James Webb servicing mission.
Orion ( https://en.wikipedia.org/wiki/Orion_(spacecraft) ) - "Capable of supporting a crew of six beyond low Earth orbit, Orion can last up to 21 days undocked". Can be used, especially with booster which can be launched by e.g. Falcon-9 Heavy, or if more mass required, by SLS (!) or Big Falcon Rocket.
Orion is not viable. They haven't even launched Artemis 1, let alone Artemis 2 (which is scheduled for 2023!) which would be the _first_ crewed launch.
I'm not sure why we would plan to service JWT when we have nothing to service it with.
One reason (of many) is that when the telescope was designed there was no way to know if we'd have capability to send anyone (or anything) to service it.
Even today we don't have a proven platform that could pull off a manned mission to L2, let alone a mission that would then fix an insanely complex telescope in-situ. (There are a few that could try, but no one's done it.)
Sending a manned mission to L2 for repair just doesn't make sense. You might as well just build a new telescope and send it out again, that probably would be cheaper. Just look at the massive effort that it took to go to the moon. Sure we are now more advanced, but if it was easy to go there now Elon would've already flown. As you said L2 is 4 times further, and you need to stop and restart at each point.
Re: stopping and restarting: there's a trade-off to be made here between flight time and necessary delta-V for arriving at a Lagrange point (and an independent one for departing). If you're willing to take the time (and consumables), you could use a slow trajectory that arrives with negligible relative velocity. And you can go there fast, arrive nearly dry, and still get back by "falling out of the sky". It's an interesting optimization problem.
Note that if you send a human crew you don’t really want to go slow because of cosmic rays (not to mention being locked in a can). Autonomous robotics have come a long way but I don’t think they’re ready for state of the art telescope repair.
Soviet spaceship TKS ( https://en.wikipedia.org/wiki/TKS_spacecraft ) was a whole orbital station module together with return capsule, developed up to mid-1980-s. It was supposed to be launched manned, and crew members - up to 3 - would have a lot of space available to them right after getting to orbit. So it could be considered as a long-range mission spacecraft; it would need to have a booster module, but that's solvable (i.e. Agena for Gemini-10 flight https://en.wikipedia.org/wiki/Agena_target_vehicle ).
Right, but the timeline of getting a human certified flight vehicle for a mission of that duration, carrying the amount of fuel needed for the "back again" portion of the trip is probably equivalent to the (delayed and prolonged) development time of the JWT.
We're on track for a manned moon mission in approximately 10 years, and the 'best minds' view building a robotic refueling station in cis-lunar space as the ideal means of making the launch realistically happen, owing to the issues of fuel weights. The rocket to do this mission doesn't exist, the space craft to go there doesn't exist, and the designs we do have (crew dragon, soyuz) aren't easily retrofitted to the mission requirements of going out to L2.
Theoretically solvable, yes. Practically impossible, especially when building another JWT would cost less, take less time (just do it again, but better!), and most importantly, risk fewer lives (0, by my count).
Yes, most likely it won't be done, but that doesn't mean impossible. Just four times farther than the Moon. Flight to the Moon - 4 days, so maybe a couple of weeks here - at most. Getting to Moon orbit from translunar - about 1 km/s, getting back - about the same, here it won't be more.
> especially when building another JWT would cost less,
I highly doubt. JWT is a unique device - telescope at the bleeding edge of capabilities of humanity. And in comparison we had close to 300 manned flights, about 10 of which - above LEO, and more than half a dozen of space tourists - no offense intended, just in case. So, no, I don't believe a manned spacecraft for a longer-duration mission can't be created in a few years.
And the space tech capabilities are actually higher than in 1960-s - look at the SpaceX progress.
> take less time (just do it again, but better!),
Less maybe than those 2,5 decades it took first. But less than 5 years? Unlikely. And in 5 years you may have Starship flying, Starliner flying, Dream Chaser flying, SLS/Orion in a better shape, Falcon-9 Heavy with more flights, possibly Vulcan getting ready - Vulcan has some advanced booster stage, by the way, suitable for more complex missions.
> and most importantly, risk fewer lives (0, by my count).
Possibly - again, in L2 we don't need to land or lift off, while we're still going to to that with the Moon, so I'm not sure if L2 mission would be riskier than a Moon landing flight. But in exchange we'll have those two benefits:
I was typing up a response, but "space enthusiast" on your profile sums it up - you're statements show your enthusiasm, but not any real understanding of the problem space.
The statements above are wildly optimistic, and don't actually take into account the actual capabilities and capacities of the launch vehicles in question. Furthermore, you're showing an extreme disregard for the actual engineering problems at hand here. It's a multi-decade process to design, build, and certify a launch vehicle _for LEO_. Handwaving "we can do it in 5 years" because the sales teams at SpaceX said so is, frankly, not a real answer. Talking about the "good state" the SLS/Orion are going to be in is, frankly, optimistic to the point of being naive.
Spewing factoids about spacecraft that don't actually exist beyond a "we blew it up on a launch pad" isn't an answer - it's a pipe dream.
Furthermore, you've deftly evaded even acknowledging the core problem - we don't have a space craft with an engine that can do the "back again" part of an L2 mission. That capacity literally doesn't exist right now. You can't just whistle up a rocket that works a few million miles from home.
It reminds me a lot some conversations with Energomash back in the days of particularly young SpaceX. Since then most players in world space market acknowledged that progress is possible. Some, unfortunately, didn't.
I'd say the real issue isn't even getting people there, but being properly prepared for the repair. Would we be able to know 100% everything that went wrong? Would we be sure that the right tools and parts for repair were aboard the repair craft? Maybe to be sure of a successful repair, we'd have to bring most of a whole new satellite anyways. Maybe it's easier to just send an actual whole new satellite up instead.
There actually is a docking adapter, but its utility is limited for a few reasons
* If you're futzing with hydrazone, you want to avoid sending humans to mess with it
* Any mission to repair it risks damaging the sensors just from the reaction mass that it takes to rendezvous
* There is currently no path forward to actually doing this servicing mission, in terms of equipment and vehicles. The technology will almost definitely exist in the future, but by the time it does why not just send a new mission?
* Designing the spacecraft to make it serviceable imposes new limitations on it
Inspiration 4, the private mission scheduled to launch next week, will be the furthest a manned mission has gone from earth since the last space shuttle Hubble servicing mission over a decade ago. Hubble is only about 100km higher than ISS.
To visit L2 you basically need a a vehicle and rocket capable of performing a moon mission which hasn't been available since 1972.
> To visit L2 you basically need a a vehicle and rocket capable of performing a moon mission which hasn't been available since 1972.
You don't need to land on anything - and that's a quite large delta-V saving, about 5 km/s for Apollo-style missions. So you save on mass, and you can spend savings elsewhere.
NASA keep calling SLS block 1 a moon rocket and it can't land anything on the moon either. All it can do is transfer crew to a halo orbit and back. And Orion clearly isn't a very capable vehicle for satellite refurbishing. Without an airlock EVAs would require depressurising the whole vehicle and it can't carry any big payloads or a robotic arm.
My guess is after mass is added for all the capabilities shuttle had for spacecraft servicing you probably do need a real moon rocket.
I mean, technically they were available after '72. There were a couple Saturn V's and Command/Service Modules (and at least one Lunar Module) left over (and mostly repurposed).
It would be interesting to know when the last time the hardware existed in working order that would have allowed a lunar mission.
Well, the Moon is some 1+ light second from Earth, with average orbital radius of 384,400 km. L2 in Sun-Earth system is roughly 1.5 millions kilometers. That roughly makes four times difference.
73 comments
[ 3.0 ms ] story [ 118 ms ] threadIn 1996, it was estimated for 2007, fast forwarding a bit to 2018, it slipped one year from an estimated launch in 2020 to 2021, in 2020 it slipped from March 2021 to July, by January 2021 it slipped to October 31st, and it's been known since June, 14 weeks ago, that it wasn't likely to meet that date.
At this rate, I estimate the current date will intercept the target date in early 2022.
Not if the timeline slips such that at each slip the delta between the current time and the launch time decreases by 50%.
This is the answer to Zeno's paradox. A sports reporter gives an update every time Hercules catches up to where the tortoise was the last time he gave an update. All that happens is the sports reporter eventually needs to talk faster and faster and faster, and eventually try to give infinite updates right as Hercules passes the tortoise. Then the reporter's vocal chords explode, but otherwise the race proceeds as you would expect. (That is, just because a description of an event is infinitely long, does not mean the event itself is infinitely long in any sense.)
-Contact
Not mathematically certain. If the timeline slip is a sequence like [1-1/2^k]_{k=1...} = {1/2 week, 3/4 weeks, 7/8 weeks, 15/16 weeks...}, then it's possible the project timeline could diverge forever. (This is just a restatement of Zeno's paradox).
I thought Zeno's paradox was caused by lack of understanding of infinitesimal calculus by Ancient Greeks? That is, in situations where a series converges despite an having infinite number of elements. Divergent series like yours shouldn't constitute such a paradox, since they both have an infinite number of elements AND diverge.
A crate of beer is standing in the end of a magical room; each step towards the crate is half as short as the preceding one.
A mathematician and an engineer enter the room. The engineer starts walking towards the chest, while the mathematician stands still.
M: Why are you doing this? You can't reach it in finite time anyway!
E: But in a few hundred steps I'll be close enough for all practical purposes!
An infinite number of mathematicians walk into a bar. The first one orders a pint. The second one orders half a pint. When the third orders a quarter of a pint, the bartender rolls his eyes, places two beers on the bar, and says "you all need to learn your limits!"
They got lucky to have a bartender who knows his customer's limits.
-----------------
An infinite number of mathematicians walk into a bar
The first mathematician orders a beer
The second orders half a beer
"I don't serve half-beers" the bartender replies
"Excuse me?" Asks mathematician #2
"What kind of bar serves half-beers?" The bartender remarks. "That's ridiculous."
"Oh c'mon" says mathematician #1 "do you know how hard it is to collect an infinite number of us? Just play along"
"There are very strict laws on how I can serve drinks. I couldn't serve you half a beer even if I wanted to."
"But that's not a problem" mathematician #3 chimes in "at the end of the joke you serve us a whole number of beers. You see, when you take the sum of a continuously halving function-"
"I know how limits work" interjects the bartender "Oh, alright then. I didn't want to assume a bartender would be familiar with such advanced mathematics"
"Are you kidding me?" The bartender replies, "you learn limits in like, 9th grade! What kind of mathematician thinks limits are advanced mathematics?"
"HE'S ON TO US" mathematician #1 screeches
Simultaneously, every mathematician opens their mouth and out pours a cloud of multicolored mosquitoes. Each mathematician is bellowing insects of a different shade. The mosquitoes form into a singular, polychromatic swarm. "FOOLS" it booms in unison, "I WILL INFECT EVERY BEING ON THIS PATHETIC PLANET WITH MALARIA"
The bartender stands fearless against the technicolor hoard. "But wait" he interrupts, thinking fast, "if you do that, politicians will use the catastrophe as an excuse to implement free healthcare. Think of how much that will hurt the taxpayers!"
The mosquitoes fall silent for a brief moment. "My God, you're right. We didn't think about the economy! Very well, we will not attack this dimension. FOR THE TAXPAYERS!" and with that, they vanish.
A nearby barfly stumbles over to the bartender. "How did you know that that would work?"
"It's simple really" the bartender says. "I saw that the vectors formed a gradient, and therefore must be conservative."
Maybe the engineer was just telling a story with a bit of flair but I believed him.
Failures happen when delivery dates are more important than quality.
Question - they have a ton of shielding for solar radiation - can they not locate this thing in a shadow area somewhere?
https://news.ycombinator.com/item?id=10462349 ("NASA's last original Voyager engineer retires at 80")
(A technical exception is a planetary solar L2 Lagrange point [0], *if* it would occur close enough to a planet to be totally eclipsed. But that doesn't happen (AFAIK) -- they're generally far enough away that although the planet is always in front of the sun, the planet's disk is much smaller than the solar disk. Like a partial eclipse).
With cryogenic cooling, you have an even more difficult challenge: the light of a planet's infrared radiation emission is something you also have to shield. That's a major reason JWST (and similar cryogenic telescopes) go to solar L2: its sunshield doesn't only block out the sun -- it simultaneously blocks out the sun and the Earth. That's the unique advantage of the solar L2 point: the sun and Earth are always in the same direction.
[0] https://en.wikipedia.org/wiki/Lagrange_point
I'm not sure why we would plan to service JWT when we have nothing to service it with.
Even today we don't have a proven platform that could pull off a manned mission to L2, let alone a mission that would then fix an insanely complex telescope in-situ. (There are a few that could try, but no one's done it.)
We're on track for a manned moon mission in approximately 10 years, and the 'best minds' view building a robotic refueling station in cis-lunar space as the ideal means of making the launch realistically happen, owing to the issues of fuel weights. The rocket to do this mission doesn't exist, the space craft to go there doesn't exist, and the designs we do have (crew dragon, soyuz) aren't easily retrofitted to the mission requirements of going out to L2.
Theoretically solvable, yes. Practically impossible, especially when building another JWT would cost less, take less time (just do it again, but better!), and most importantly, risk fewer lives (0, by my count).
Yes, most likely it won't be done, but that doesn't mean impossible. Just four times farther than the Moon. Flight to the Moon - 4 days, so maybe a couple of weeks here - at most. Getting to Moon orbit from translunar - about 1 km/s, getting back - about the same, here it won't be more.
> especially when building another JWT would cost less,
I highly doubt. JWT is a unique device - telescope at the bleeding edge of capabilities of humanity. And in comparison we had close to 300 manned flights, about 10 of which - above LEO, and more than half a dozen of space tourists - no offense intended, just in case. So, no, I don't believe a manned spacecraft for a longer-duration mission can't be created in a few years.
And the space tech capabilities are actually higher than in 1960-s - look at the SpaceX progress.
> take less time (just do it again, but better!),
Less maybe than those 2,5 decades it took first. But less than 5 years? Unlikely. And in 5 years you may have Starship flying, Starliner flying, Dream Chaser flying, SLS/Orion in a better shape, Falcon-9 Heavy with more flights, possibly Vulcan getting ready - Vulcan has some advanced booster stage, by the way, suitable for more complex missions.
> and most importantly, risk fewer lives (0, by my count).
Possibly - again, in L2 we don't need to land or lift off, while we're still going to to that with the Moon, so I'm not sure if L2 mission would be riskier than a Moon landing flight. But in exchange we'll have those two benefits:
1) service a unique device
2) gain important experience in human spaceflight
Those aren't small benefits.
The statements above are wildly optimistic, and don't actually take into account the actual capabilities and capacities of the launch vehicles in question. Furthermore, you're showing an extreme disregard for the actual engineering problems at hand here. It's a multi-decade process to design, build, and certify a launch vehicle _for LEO_. Handwaving "we can do it in 5 years" because the sales teams at SpaceX said so is, frankly, not a real answer. Talking about the "good state" the SLS/Orion are going to be in is, frankly, optimistic to the point of being naive.
Spewing factoids about spacecraft that don't actually exist beyond a "we blew it up on a launch pad" isn't an answer - it's a pipe dream.
Furthermore, you've deftly evaded even acknowledging the core problem - we don't have a space craft with an engine that can do the "back again" part of an L2 mission. That capacity literally doesn't exist right now. You can't just whistle up a rocket that works a few million miles from home.
* If you're futzing with hydrazone, you want to avoid sending humans to mess with it
* Any mission to repair it risks damaging the sensors just from the reaction mass that it takes to rendezvous
* There is currently no path forward to actually doing this servicing mission, in terms of equipment and vehicles. The technology will almost definitely exist in the future, but by the time it does why not just send a new mission?
* Designing the spacecraft to make it serviceable imposes new limitations on it
To visit L2 you basically need a a vehicle and rocket capable of performing a moon mission which hasn't been available since 1972.
You don't need to land on anything - and that's a quite large delta-V saving, about 5 km/s for Apollo-style missions. So you save on mass, and you can spend savings elsewhere.
My guess is after mass is added for all the capabilities shuttle had for spacecraft servicing you probably do need a real moon rocket.
I mean, technically they were available after '72. There were a couple Saturn V's and Command/Service Modules (and at least one Lunar Module) left over (and mostly repurposed).
It would be interesting to know when the last time the hardware existed in working order that would have allowed a lunar mission.
https://en.wikipedia.org/wiki/Canceled_Apollo_missions#Cance...
Oh, is that all?