Micrometeoroid Noticeably Damaged One of Webb Telescope's Mirror Segments (space.com) 87
"A small space rock has proven to have a big effect on NASA's newly operational deep-space telescope," reports Space.com, causing "significant uncorrectable change" according to a new report from NASA engineers. But fortunately, "Seventeen mirror segments remain unblemished and engineers were able to realign Webb's segments to account for most of the damage."
A micrometeoroid struck the James Webb Space Telescope between May 22 and 24, impacting one of the observatory's 18 hexagonal golden mirrors. NASA had disclosed the micrometeoroid strike in June and noted that the debris was more sizeable than pre-launch modeling had accounted for. Now, scientists on the mission have shared an image that drives home the severity of the blow in a report released July 12 describing what scientists on the mission learned about using the observatory during its first six months in space.
Happily, in this case the overall effect on Webb was small....
Based on fuel usage, the telescope should last 20 years in space. But scientists aren't sure how much of an effect micrometeroid strikes will have upon its operations, the report authors stated. Micrometeroids are a known danger of space operations, and facing them is by no means new to scientists; the International Space Station and the Hubble Space Telescope are among long-running programs that are still operational despite occasional space rock strikes. However, Webb's orbit at Lagrange Point 2 about 1 million miles (1.5 million kilometers) away from the Earth may change the risk profile considerably....
In this case, however, the overall impact to the mission is small "because only a small portion of the telescope area was affected...." Engineers are still modeling how frequently such events will occur....
One remedy could be minimizing the amount of time Webb points directly into its orbital direction, "which statistically has higher micrometeoroid rates and energies," the team wrote.
Thanks to Tablizer (Slashdot reader #95,088) for sharing the article!
Happily, in this case the overall effect on Webb was small....
Based on fuel usage, the telescope should last 20 years in space. But scientists aren't sure how much of an effect micrometeroid strikes will have upon its operations, the report authors stated. Micrometeroids are a known danger of space operations, and facing them is by no means new to scientists; the International Space Station and the Hubble Space Telescope are among long-running programs that are still operational despite occasional space rock strikes. However, Webb's orbit at Lagrange Point 2 about 1 million miles (1.5 million kilometers) away from the Earth may change the risk profile considerably....
In this case, however, the overall impact to the mission is small "because only a small portion of the telescope area was affected...." Engineers are still modeling how frequently such events will occur....
One remedy could be minimizing the amount of time Webb points directly into its orbital direction, "which statistically has higher micrometeoroid rates and energies," the team wrote.
Thanks to Tablizer (Slashdot reader #95,088) for sharing the article!
Not occasional (Score:5, Interesting)
The ISS, Hubble and just about every other spacecraft in LEO are still operational despite daily space rock strikes. The debris environment in LEO is a lot worse than at L2, thanks to our littering: various explosions of expended stages and EOL satellites, one satellite collision and several ASAT weapon tests are the main culprits.
Re:Not occasional (Score:5, Interesting)
Worth noting the JWST has been hit by 19 meteoroids since launching. That is a *lower* than expected number. The issue here is that the one that the article is talking about was larger in magnitude than expected outside of a meteor shower. It was expected that such a meteoroid strike would be rare during the life of the JWST's mission.
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It probably is rare.
But rareness has nothing to do with the question "when does a 1 in 1000 year event happen?"
It can happen right now or in 1000 years, or two times in a row today and tomorrow again, and then not for another 2000 years at all.
Re:Not occasional [but still need solutions?] (Score:2)
Not a bad FP branch, but my fixation on solutions remains unsatisfied... In spite of having looked over several parts of the discussion...
So now I'm wondering if it might be possible in the future to repair one of the mirrors on the JWST. Could they send up a robot installer with a fresh mirror to replace a bad one? Pretty sure the answer is no, but it's possible they considered the idea. (Didn't they add a refueling capability rather late in the design process?)
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Could they send up a robot installer with a fresh mirror to replace a bad one? Pretty sure the answer is no
I think the same.
The whole design was about making it as compact as possible, and make it unfold when in place.
It is hard to imagine someone "flies there" and replaces a mirror in the middle of a pack of 18 mirrors with a screwdriver and a wrench.
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Well, now that I'm thinking about it... Maybe it wouldn't be that difficult. They have a number of actuators to control the shape of each mirror. If those actuators are also holding it in place, then you just need a "release mirror" setting for the actuators. The old mirror would float up and the repair robot would guide the new mirror into place until it engaged with the actuators.
However, that made me think of an option that might be cheaper and allow for semi-graceful loss of performance over a longer ti
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The graceful degradation option is available: use the actuators to move the damaged mirror to an orientation where it doesn't reflect light onto the secondary.
They decided against on-orbit assembly because it's very difficult to do that without contaminating the mirrors (by condensing thruster gases on them, for example).
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Thanks and you deserve an Informative mod.
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Well... it is being gracefully degraded. By the strikes. From the report: "After two subsequent realignment steps, the telescope was aligned to a minimum of 59 nm rms, which is about 5-10 nm rms above the previous best wavefront error rms values"
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I should have written "more gracefully" or "less ungracefully", but I'm not that sure about the optics involved. Or in the form of a question, "How much damage would it take before it would be better to entirely remove an imperfect mirror segment?" With additional complications as you consider that each of the segments is becoming more imperfect over time... Are these solvable engineering problems or do you just have to go with the statistics on meteor strikes and hope you don't get unlucky?
But if the mirro
Re: Not occasional [but still need solutions?] (Score:2)
It's possible, but at what cost? The engineering is going to have to be more complicated to allow for replacement of major components. Then you'll have to get the parts out there, then have robots sophisticated enough to make the swap. I suspect it's cheaper and better to always be launching a new vehicle every 10 years. Then retire the old craft, or have two until the older one has used it's fuel. Bonus is that you are sending the latest tech, or most desirable instruments up, rather than having to wait
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You're ignoring the techno-ignorati of the herd of lawyers-become-politicians that sets NASA's priorities and budget. Columbia was supposed to be the prototype space shuttle, to be retired after a decade and replaced with an updated model incorporating what was learned in practice. Instead NASA was forced to fly it for thirty years until it failed. Hubble was designed for your 10-year lifespan, again to be replaced by new and improved model. In 2012 the almost unknown National Reconnaissance Office scra
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Sadly informative.
Re:Not occasional (Score:4, Interesting)
The debris environment in LEO is a lot worse than at L2
Are we sure about that? Debris in LEO is dangerous only as long as it stays there. With the wrong trajectory, junk either re-enters Earth's atmosphere or exits our gravity well. Likewise, Lagrange points tend to be attractors for debris (man made or otherwise). Stuff collects there.
Along that line of thinking: Do we have a plan to de-orbit the JWST after 20 years? If not, it ends up being another piece of junk cluttering up L2 and reducing its utility.
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Likewise, Lagrange points tend to be attractors for debris (man made or otherwise). Stuff collects there
Kind of. As you can see [nasa.gov] L4 and L5 are stable like a ball on a hill top, or an inverted pendulum, while L1,2 and 3 are saddle shapes, stable like a ball on a horse saddle. 4 and 5 tend to push things away, but this increases speed and can send it into a tenuously stable orbit. With a saddle shape you can kind of orbit if you enter at the right speed range and direction, but it’s not really stable. With all of them, you can park a ship or satellite there and use very little fuel to maintain it if d
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Re: Not occasional (Score:2)
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This debris weighs less than a gram and has a speed of up to 50 km/s. We have no way to detect debris that small at a range long enough to move an interceptor into place.
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Do we have a plan to de-orbit the JWST after 20 years? If not, it ends up being another piece of junk cluttering up L2 and reducing its utility.
By then we'll probably have ways to help ease any L2 problems, like Space Chiropractors, etc...
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a: L2 is a huge area, not a single point
b: everything "floating" there is exactly that, floating - it wont hit anything particularly hard - unlike a meteorite coming from the outside of the solar system
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Do we have a plan to de-orbit the JWST after 20 years? If not, it ends up being another piece of junk cluttering up L2 and reducing its utility.
L2 is not a stable point. This is precisely why JWST's mission is limited to 20 years. It needs to burn fuel to stay at that point. Also L2's utility isn't very large. It's good for hyper expensive limited duration astronomy and not much else.
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Its mission is "limited to 20 years" the way that Hubble's mission was "limited" to a decade. As the science-deniers are rapidly taking over our government it's increasingly doubtful that there will ever be a replacement built for either of them. There just isn't enough money in a project like that for the weapons manufacturers to make it worth their while.
They should have built it differenly. (Score:1)
Hubble is pretty well protected since all optics are sheathed in a tube, like any terrestrial telescope. They should have done the same with JWST. We have plenty of junk floating up there that could have done the job (Like spent Saturn boosters) We've gotten pretty good at making robots that can do things remotely. I don't think making robots to cut-prep an old Saturn booster is outside the realm of possibility.
Re:They should have built it differenly. (Score:5, Insightful)
Hubble is pretty well protected since all optics are sheathed in a tube, like any terrestrial telescope.
So far so good.
They should have done the same with JWST.
Hold on cowboy. That's what we call a one-stop. One step too far. Unless you can show us your degree in this field (and your volume of work showing authority) that is, I'd have to assume NASA knows far more about this than you do and what should be done.
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Unless you can show us your degree in this field (and your volume of work showing authority) that is, I'd have to assume NASA knows far more about this than you do and what should be done.
Don't worry, they did their research.
Before Apollo, Surveyor landers tested (Score:2)
Unless you can show us your degree in this field (and your volume of work showing authority) that is, I'd have to assume NASA knows far more about this than you do and what should be done.
Don't worry, they did their research.
Folks said the same about space shuttle o rings before the challenger disaster.
What kind of research? Paper? Or did we send a probe to the lagrange point to measure conditions? Before Apollo landed on the moon we landed robotic Surveyor missions to test that conditions would be safe for a Lunar Module and astronauts. I'd hope we did the same for Webb.
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The Shuttle booster O-rings only existed because of Congress. NASA's design called for them to be built close enough to Cape Canaveral that they could be constructed in one piece and just moved to the Vertical Assembly Building. Morton Thiokol could make more money just building them at their ICBM factory, so that's what the herd of lawyers in Congress decided should be done, since they're so much better at designing spacecraft than a rocket scientist ever would be.
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The Shuttle booster O-rings only existed because of Congress.
Good thing Congress kept its hands off during Webbs' nearly 30 years of development and did not consider how it could benefit their district. Good thing Congress was accepting of and hands off during delays and cost overruns and never put any pressure on the project. Good thing there were never Congressional plans to kill the project, deals made to keep it going. Good thing Congressional opponents of Webb did not have allies in the scientific community who opposed Webb because they thought Webb was sucking
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Which factory made the o-rings does not seem relevant.
The original design did not call for 0-rings, they were added by Thiokol because the SRB had to be cut into chunks to be transported from the Midwest to the Cape.
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Which factory made the o-rings does not seem relevant.
The original design did not call for 0-rings, they were added by Thiokol because the SRB had to be cut into chunks to be transported from the Midwest to the Cape.
That is interesting and sad. Thank you.
Lost one mirror in one month ... not promising (Score:3)
Hold on cowboy. That's what we call a one-stop. One step too far. Unless you can show us your degree in this field (and your volume of work showing authority) that is, I'd have to assume NASA knows far more about this than you do and what should be done.
And that is what is called the fallacy of appeal to authority.
We don't need no degree in rocket surgery to note that Webb has been on station at the lagrange point only ONE MONTH and one mirror has been damaged. While it may be an outlier, it is a cause for concern at this moment. IFF tubes protected previous space born telescopes to some degree it is not unreasonable to ask why Webb has no comparable (though not necessarily tubular) shield, or plans for one. What do NASA previous probes to lagrange poin
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A degree in statistics might help though.
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A degree in statistics might help though.
I've only had one undergrad and two graduate level statistics classes, but my amateur understanding is that statistics is only as good as the data. We have data collected at the lagrange point?
Or were you attempting to point out the obvious, IFF not an outlier, the current rate will not take out all mirrors in 18 months because every mirror has an equal probability of being hit, those already hit and those yet unit. The dice have no memory so to speak.
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You noted a single datapoint, then proceeded to draw conclusions from it. That's a very human thing to do, and completely irrational. If you expand your dataset to include not just a single unexpectedly large impact you do indeed have more observations. Webb was hit more than a dozen times just on its way out, which is pretty unremarkable.
The OP noted a singular event and jumped to the conclusion the thousands of scientists who worked on JWST don't know what they're doing. The original reply correctly point
"IFF" = If and only if. (Score:2)
You noted a single datapoint, then proceeded to draw conclusions from it.
Have you had a statistics 101? When you do you will learn the abbreviation "IFF" = If and only if.
With this new kowledge interpret what I wrote: " IFF not an outlier"
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You can construct all the elaborate hypothetical scenarios you want, but it's pretty pointless. We have a bunch of spacecraft at the Langrange points and a bunch of research on how to use them to record impacts. JWST was hit 19 times on it's way to it's target orbit. The big one is an outlier, which is why it attracted attention.
It's not surprising you didn't know that, because it doesn't make a good news story. That's why the original reply is correct: experts actually do know things you don't pick up fro
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You can construct all the elaborate hypothetical scenarios you want, but it's pretty pointless.
Unless ... wait for it ... its not an outlier.
We have a bunch of spacecraft at the Langrange points and a bunch of research on how to use them to record impacts.
That was something I asked about in the first post. Had we sent probes to **this** lagrange point to collect collision data, or were we using theoretical estimates. Collecting meaningful data as we did with Surveyor before Apollo. What is the data for **this** lagrange point?
JWST was hit 19 times on it's way to it's target orbit.
Not entirely relevant. The relevant data is what happens on station at this particular lagrange point. What happened at transit is just the regular hazards of spaceflight. For long term oper
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And that is what is called the fallacy of appeal to authority.
Wrong.
Appeal to Authority means, you appeal to someone who has some random authority.
It is not an appeal to authority if one mentions: the experts abut that topic know more about it than a random stranger.
We don't need no degree in rocket surgery to note that Webb has been on station at the lagrange point only ONE MONTH and one mirror has been damaged. by a Meteorite ...
IFF tubes protected previous space born telescopes to some degree it is no
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And that is what is called the fallacy of appeal to authority. Wrong.
Appeal to Authority means, you appeal to someone who has some random authority.
It is not an appeal to authority if one mentions: the experts abut that topic know more about it than a random stranger.
Actual appeal to authority includes any authority. Using your logic it would be OK to say, well, he's an expert I will accept his statement without asking him to offer any evidence. That's now how it works. As I wrote earlier, what did the probes sent to the Lagrange point find? We sent probles first? We collected data first? As we did with Apollo when we sent the Surveyor mission before Apollo.
We don't need no degree in rocket surgery to note that Webb has been on station at the lagrange point only ONE MONTH and one mirror has been damaged. by a Meteorite ...
IFF tubes protected previous space born telescopes to some degree it is not unreasonable to ask why Webb has no comparable (though not necessarily tubular) shield, or plans for one. Wow - you are a complete idiot, right?
Do you actually even know how immense awesome big the James Webb Telescope is? It is not big, it is not large, it is huge. Dumb idiot.
Sorry, you just have low reading comprehension and a lack of imagination. For the former did you read "comparable
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Actual appeal to authority includes any authority.
No, it does not.
The flood is coming! What should we do?
Ask the Sherriff! He must know!
Ask the Judge! He was on university!
Ask the Doctor! He has studied!
Ask the Monk, he knows about floods!
That is appeal to authority.
It is not appeal to authority of the expert in question actually is an expert about the topic.
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Actual appeal to authority includes any authority. No, it does not.
It is not appeal to authority of the expert in question actually is an expert about the topic.
Wrong. It not simply about expertise, its about evidence. In science, in court, we often have experts making contradictory claims. It only gets sorted out when you add evidence. See first definition below.
You seem to be referring to a different fallacy, "Appeal to False Authority". See second definition below.
"Appeal to Authority"
"Insisting that a claim is true simply because a valid authority or expert on the issue said it was true, without any other supporting evidence offered."
https://www.logical [logicallyfallacious.com]
Re: (Score:2)
Appeal to authority always meant: someone who has an office is cited as "fallacy evidence" to support the case of the guy arguing.
Simplest example, I'm against abortion, and I cite the pope with the words "did the pope not say you shall not sin?".
So I appeal to his authority to support my argument. And obviously there is no connection between my argument and the citation about the pope.
That: is appeal to authority. And hence a fallacy.
Your first citation is wrong, imho.
And your second one is exactly what I
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Appeal to authority always meant: someone who has an office is cited as "fallacy evidence" to support the case of the guy arguing.
There is a general fallacy that does not distinguish between true and false offices. Either can be wrong, though for different reasons. A more specialized fallacy limits itself to only false offices.
And your second one is exactly what I explain above, and what I explained in my previous post.
The first citation is a more general version. The second citation is a specialized variant that only considers false experts.
if I point to NASA and exclaim, well we are talking about rocket science, they are the experts. then: I'm right, because they are the authority regarding the facts of space travel.
No you are engaging in a fallacious argument. NASA is indeed experts in space travel but you cited none of NASA's evidence. You are saying trust NASA, more on "trust" below. NASA has and w
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Hence true experts being part of the general fallacy, since if they offer an opinion without evidence they are essentially asking you to trust them
That was not the discussion.
It was opposite around.
A random yerk was arguing that NASA can not be right, because, he has deeper knowledge (for which he did not provide evidence). Then another yerk claimed "trusting NASA" in this topic is an "appeal to authority" fallacy.
Which it was/is not.
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Hence true experts being part of the general fallacy, since if they offer an opinion without evidence they are essentially asking you to trust them That was not the discussion.
Yes it was. You simply did not understand, you failed to consider true experts. I was referring to both true and false experts. Hence your reaction.
It was opposite around ...
Nope. One side engaging in fallacy does not make the other correct. Both could engage in fallacy and both be wrong.
Yes, it is. Trust is not evidence. The true expert part of the fallacy is about opinion without evidence. The entire point of the fallacious statement is to persuade without evidence. That's not how science works, science needs data. We often have h
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Yes it was. You simply did not understand, you failed to consider true experts. I was referring to both true and false experts. Hence your reaction.
My answer was not to you, but some of our parents. Then we got sidetracked.
So: no it was not the topic.
No idea about the NASA stuff you mention here. I probably did not read anything of it ... and after skimming over your post: no idea why it is relevant.
I corrected/tried to correct the wrong usage of a name of a logical fallacy. I do not care what NASA tested o
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I'd have to assume NASA knows far more about this than you do and what should be done.
You must be new here; welcome to /. :-)
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Are you joking man? The rest of you joking too?
43 replies to this dimwit who is asking for my credentials. I'm only seeing one or two good responses here. Of note by hackertourist who provides a pretty good pros and cons to the approach. [slashdot.org] The rest is just debate team jibberish which I doubt any of us have ever been on a debate team (Maybe NewYorkCountryLawyer, but he's not in the thread)
Sign of the times I suppose because there's a lot of idiots out there these days trying to apply logical fallacies to
Re:They should have built it differenly. (Score:4, Funny)
riiight, and you're going to have deployable sunscreen system and cooling system for that massive Sat V tube?
We look forward to seeing your design. Well actually we're laughing at you, put the crayons away.
Flat shielding panels shipped separately ... (Score:2)
riiight, and you're going to have deployable sunscreen system and cooling system for that massive Sat V tube? We look forward to seeing your design. Well actually we're laughing at you, put the crayons away.
Those of us who have moved beyond crayons tend to think beyond just making the last thing bigger.
I would expect it to be separate missions delivering flat panels. Webb could have had attachment points, panels rendezvous and attach. Perhaps now they just maintain formation around Webb. Replacements sent as fuel runs low or damage excessive. Ambitious, yes, but Webb was pretty damn ambitious too. It would be a damn shame for it to take a mirror hit once a month. That's where we are at, one month on station
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Shielding becomes less realistic as things you want to shield get bigger. JWST had to unfold. A shield for JWST would have to unfold even more. And then it would have to be useful for shielding stuff. Or you'd have to send a whole bunch of pieces on a whole bunch of launches, and then assemble them. Either way the scope of the project is dramatically larger than JWST itself.
What we learn here may be that it's not realistic to have something like JWST without expecting to send new parts to it periodically
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Shielding becomes less realistic as things you want to shield get bigger. JWST had to unfold. A shield for JWST would have to unfold even more.
And that is why I described something different. Did you read?
Or you'd have to send a whole bunch of pieces on a whole bunch of launches, and then assemble them.
And here too I described a different option. Did you read?
Either way the scope of the project is dramatically larger than JWST itself.
No, rendezvous and formation flying is 1960s NASA capabilities.
What we learn here may be that it's not realistic to have something like JWST without expecting to send new parts to it periodically
Sending new parts, I mentioned that. Did you read?
What we may lean here is to send probes ahead of the real mission to evaluate the environment. As we did with Apollo.
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I read you making stupid fucking suggestions like having all the parts do stationkeeping next to one another so precisely that they work as one piece
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I read you making stupid fucking suggestions like having all the parts do stationkeeping next to one another so precisely that they work as one piece
You think stationkeeping for satellites or spacecraft is something new? As I wrote: "Ambitious, yes, but Webb was pretty damn ambitious too." Even if the precision is loose enough to allow some gaps, or we have gaps due to insufficient panels, its still an improvement over the current vulnerability.
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No, nor do I think having things dock up is new. But the pieces you want to have do all that stuff are currently extremely simple and low in mass, and you want to make them spacecraft in their own right. As a means of avoiding the complexity or mass involved in another solution, they therefore don't make anything like sense.
If this sort of thing keeps happening, then probably the sanest thing to do would be to expect to have to resupply. And then the result doesn't look like either thing. You're going to wa
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But the pieces you want to have do all that stuff are currently extremely simple and low in mass, and you want to make them spacecraft in their own right.
Not quite. Going back to the first post, IFF the tube on Hubble provided some protection from micro-meteors than we are not necessarily talking about exotic nor high mass stuff. If not that then various parts of the ISS have different types of shielding to evaluate.
Regarding spacecraft. Yes, a shield panel would need thrusters, fuel, sensors and a computer for control and comms. That's not a terribly exotic spacecraft. Delivery vehicle, well what got Webb to lagrange?
New software. Networking of shiel
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All those things would be like million watt searchlights to the Webb., congrats now you have a menagerie of things that would have to be kept crygenic. No, you're not an engineer and are just talking out of your ass, crayon level.
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All those things would be like million watt searchlights to the Webb., congrats now you have a menagerie of things that would have to be kept crygenic.
You mean like the sunshield that Webb itself deploys. A shielding panel would deploy its own sunshield between itself and Webb.
No, you're not an engineer and are just talking out of your ass, crayon level.
LOL - you speak about engineering and yet you fail to see that the solution is staring you in the face. The vey same simple and elegant solution that Webb employs to solve the same problem for itself.
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"A shielding panel would deploy its own sunshield between itself and Webb."
So your thing's sunshield is reflecting sunlight onto the Webb, nice going. Oh you forgot besides your gizmos the Sun was also there and all is orbiting the L point?
Ain't gonna work, what the Webb needs is a whole lot of nothing nearby.
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"A shielding panel would deploy its own sunshield between itself and Webb."
So your thing's sunshield is reflecting sunlight onto the Webb, nice going. Oh you forgot besides your gizmos the Sun was also there and all is orbiting the L point?
No, what I was describing would be the panels on the side of Webb Closer to the Sun. Where the order would be Sun, sunshield, panel, sunshield, Webb. Now for the other side, where we have the ordering you describe one would angle the sunshield so that it reflects away from Webb. Yes a larger sunshield would be needed to cast a large enough shadow.
Or we have one larger sunshield closer to the sun that casts a shadow for Webb and its constellation of micro-meteor shields.
Ain't gonna work, what the Webb needs is a whole lot of nothing nearby.
The fact that Webb can get sufficie
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Pretty well protected you say? Sorry to impact your mirror but...
https://spaceref.com/press-rel... [spaceref.com]
Re:They should have built it differenly. (Score:5, Informative)
There are good reasons not to enclose the telescope.
1. You'd need a rigid enclosure consisting of two layers (a Whipple shield). This would add a lot of complexity: it would have to unfold along with the telescope.
2. The telescope is limited by the available payload and volume. Adding a heavy enclosure means the mirror would have had to be smaller.
3. An enclosure would increase the temperature by making it more difficult to radiate away the heat, making the telescope less sensitive. We've operated telescopes without an enclosure before: Herschel has a 3.5 m unprotected mirror. That's already close to the limit of what fits on current rockets. A mirror that small is too small for the science goals of JWST, making the mission pointless.
4. We've operated spacecraft at L2 for decades, so we have a pretty good idea of the average frequency of impacts. Outliers are hard to plan for.
Your idea of salvaging an enclosure would solve 2.. But it adds a lot of weight to the telescope, which means it takes more energy to rotate the telescope between observations, and more energy for course corrections. That means carrying more fuel and a larger solar panel. There was no payload margin to do that, so you're stuck launching a second mission to bring these up.
Another problem is that rocket fuel tanks don't make good shields: they're single-walled. You want a Whipple shield (two walls with space between them). This is rapidly becoming a very complex mission to assemble a decent shield in orbit.
The JWST team decided against on-orbit assembly because that increased the risk:
1. you have to do it in LEO, no current manned spacecraft can go to L2, so you end up in the much worse space debris environment of LEO during assembly.
2. having a manned spacecraft near JWST means thruster firings etc. that can contaminate the optics.
3. manned operations near fragile parts like the mirrors and sunshield increase the risk.
Finally, we have no experience with robotic large-scale machining in Earth orbit.
Another problem is that
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Wasn't the whole idea behind the JWST not to get a telescope with a much larger diameter, essential for looking further into space than the Hubble is capable of?
While I agree that it would have been nice to have an extra layer of protection by shielding it with a tube like construction, just like Hubble. I don't think that would have been feasible.
The tube should than also be fold-able and that would make it structurally weak, to the point of it becoming useless against mini-meteor strikes. So it would intr
Wouldn't L2 act like a centrifuge? (Score:2)
Pardon my ignorance but wouldn't L2 act as a gravitational "vortex" capturing random space debris? Thus making that area relatively dense with particles? Thanks
Re: Wouldn't L2 act like a centrifuge? (Score:3, Informative)
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Thanks
20 years (Score:2)
>Based on fuel usage, the telescope should last 20 years in space.
Wait wait, what? They took over 20 years to design this thing and it'll run out of fuel and burn up in 20 years!?
Hubble was funded in 1978 and planned for launch 8 years later (until the Challenger disaster), and launched in 1990 (12 years). Hubble was serviced and upgraded five times with more capabilities. It was designed to last 15 years but it's been going for 32, and some of its most significant discoveries happened after its expected
Re:20 years (Score:4, Insightful)
Webb isn't a replacement for Hubble. It's a replacement for Spitzer. Spitzer was planned for 2.5-5 years, but managed to keep doing some observing at it's shortest wavelengths for another decade. Before that were ISO (3 years) and IRAS (10 months).
Observing in the infrared is hard because you have to keep the telescope cold. Webb was planned for 2-4x Spitzer and it looks like it's actually going to be capable of twice that. A 20 year lifespan is remarkable, and achieving it is a triumph of engineering.
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Why didn't they plan for this thing to live for decades? We'll have nothing to replace it with once it craps out--and Hubble will probably still be alive! Boosted back into high orbit by Elon Musk or something.
Diminishing returns?
The added cost for additional redundancies, fuel, weight, hauling it into orbit, etc. could potentially exceed the cost of launching a brand new one with even better optics/whatever by the time the projected lifespan of the current model runs out. I'm think it's pretty safe to assume that NASA at least crunched the numbers for the various options before greenlighting project.
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Why didn't they plan for this thing to live for decades?
You realize that 20 years is 2 decades -- right?
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Fine, more than two decades
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Why didn't they plan for this thing to live for decades?
Because then you would need (have) to launch it with enough fuel for decades.
That amount did not fit into the launch vehicle.
Your question is like: why did they not use a warp drive to get it to L2 and why does it not have a main deflector array and shields ... just saying.
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Wait until you find out that earth based telescopes have operated and continue to operate far longer than Hubble as well. If your goal is to make something last a long time, then have an argument with your wife. The goal here is for specific science, not mission duration.
Comparing anything at L2 to the Hubble is stupid. The Hubble telescope doesn't need to burn fuel to remain operational. L2 is an unstable point hence it has a limited mission life as the telescope needs a mechanism to course correct.
We'll have nothing to replace it with once it craps out
And? Th
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>Comparing anything at L2 to the Hubble is stupid. The Hubble telescope doesn't need to burn fuel to remain operational.
Hubble has been boosted five times.
>And? The JWST wasn't built just to be a telescope in space. It was built to do specific things, with the plan for those specific things to occur in the expected mission time.
So was HST
>Anything else is a bonus, not part of the plan.
Plans change, like it did with HST. HST conducted its best observations after its originally planned mission expire
Protection from debris.. (Score:1)
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You're not going to use compressed air to deflect a micrometeoroid approaching at 10 kilometers per second. That's like proposing that warships use a desk fan to deflect incoming missiles. The compressed air would also contaminate the mirrors/instruments.
Biggest telescope ever! (Score:2)
And it didn't see this coming?
The slow death of slashdot (Score:2)
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They really should just sell the commenting and moderation system to other sites. That's really what drove the growth back in the day be bubbling up the good stuff.