NASA - James Webb Space Telescope - Discussion and Updates

[TripleSeven]

what got Webb was "to much" new technology (this is a theme song today...the Dreamliner, Ford CVN, F35 etc have all been snake bit by this) ....but no new technology to me is just as bad

Was it really "too much technology" that made JWST capsize like a clown in a circus?
I haven't followed it for long at all, but in these days it is the simple standard low tech stuff that fails. Northrup-Grumman fails to deliver what they have delivered to hundreds of working satellites in orbit. The space craft bus. Their thrusters leak after having been treated by abrasive chemicals. Their washers fall off in the standard vibration test and disappears into somewhere the rest of the spacecraft. They cannot even unfold their umbrella during the very last test without tearing it up and getting it stuck. What has N-G been doing with all their billions all of these years??? I cannot imagine any alternative to blatant corruption and an attempt to charge the tax payers for incompetence.

the failure on Galileo with the antenna was not a technology failure (as the TDRSS and "other" satellites have used that antenna) but with managing the technology, particularly in the endless "road" trips.

Didn't Galileo's antenna fail to unfold because it was delayed for several years (after a Shuttle disaster)? A stay in the storage that caused the lubrication of the unfolding mechanism to evaporate or change its properties. I remember reading something to that effect in the analysis following the failure. So every delay of the JWST sounds to me like a JWST even more prone to failures.

well NG management coupled with NASA is well near incompetent on the Webb...a failure from the start

the folks who built the LM and a great stretch of Naval fighters including my old ride...are long gone

Galileo's antenna failed for two maybe three reasons.  First it was transported several times across the country where the lubricant on it suffered our bumpy roads and I dont think that they ever inspected the lubricant again.  2) storage might have made that worse...and then there was a sunshield...but I would bet all the engineering and amateur radio creds I have that the first one did it

the antennas have worked flawlessly on a lot of TDRSS and well some other satellites as well.

there is nothing wrong with the design... and it only "weighs" 50 pounds...

if it had been on Cassini it would have changed the data time enormously

This interesting conversation started up on the Ice Giants' thread ( I mentioned JWST on that non-astronomy thread first, my fault )

I saw an ad for NG on SpaceNews awhile back just before the SMAP mission launched. It was advertising NG's experence with large-scale in-space deployments, claiming that after scores of deployments, not one that they built has failed (biased source, I know). So, I was just wondering, is there any company other than them who NASA with the experience required to perform a JWST-like mission? If NASA were to go for LUVOIR or Origins sometime in the future, who would they ask?

LOL it all depends on what one thinks happened with the NG payload on Falcon mileage might very

[Jim]

Of course a shield is needed, but the design is simplified greatly as you relax mass budgets and volume limits, or fairing constraints.

Wrong.  A FH would not have helped.  The extra mass would provide little improvement.  The FH uses the same fairing size and hence the issues would still be the same.  The issue isn't with the rocket.  It is the national infrastructure.

JWST is maxing out the airplanes, roads, factories, thermo-vac chambers in the US.  Have to spend a lot more to do bigger spacecraft.

[Jim]

If you have to fit a five layer 21*14m shield in a fairing that can't cope with an unfolded mirror, you're pretty much going to have to spend lots of effort making the shield actually fit.

A few meter large fairing is going to have little impact on the design of the sun shield, it would just have a few less folds.

[Jim]

The shield is simplified, I was imprecise, the remainder of the craft remains complex, I was attempting to keep it succinct.
If you remove the folding mirror, then the sunshade gets less complex, because it can obviously fit into the fairing better, if the mirror can.

Wrong, it doesn't "fit better". It still has to be deployable.

[Jim]

Some aspects of wavelength sensing and control (the mirror positioning related ones) are reduced. This whole field is undergoing a revolution in terms of design of adaptive optics and similar components, driven by searching for exoplanets - reducing distortions to retain massive contrast required.

Wrong, it still would be a segmented mirror and still need all the same support. The folding aspect of the mirror has little to do with this.

[Jim]

I saw an ad for NG on SpaceNews awhile back just before the SMAP mission launched. It was advertising NG's experence with large-scale in-space deployments, claiming that after scores of deployments, not one that they built has failed (biased source, I know). So, I was just wondering, is there any company other than NG with the experience required to perform a JWST-like mission for NASA? If NASA were to go for LUVOIR or Origins sometime in the future, who would they ask?

NG did not build the telescope, that was GSFC.  NG just built the spacecraft, sunshield and telescope tructural components for GSFC.

[jbenton]

I saw an ad for NG on SpaceNews awhile back just before the SMAP mission launched. It was advertising NG's experence with large-scale in-space deployments, claiming that after scores of deployments, not one that they built has failed (biased source, I know). So, I was just wondering, is there any company other than NG with the experience required to perform a JWST-like mission for NASA? If NASA were to go for LUVOIR or Origins sometime in the future, who would they ask?

NG did not build the telescope, that was GSFC.  NG just built the spacecraft, sunshield and telescope tructural components for GSFC.

I guess I did just say "deployments", that would include the telescope. I guess I didn't make clear what I was asking, my bad.
I was asking about the sunshield, who else can do it?

[Star One]

Inferring the Composition of Disintegrating Planet Interiors from Dust Tails with Future James Webb Space Telescope Observations

Disintegrating planets allow for the unique opportunity to study the composition of the interiors of small, hot, rocky exoplanets because the interior is evaporating and that material is condensing into dust, which is being blown away and then transiting the star. Their transit signal is dominated by dusty effluents forming a comet-like tail trailing the host planet (or leading it, in the case of K2-22b), making these good candidates for transmission spectroscopy. To assess the ability of such observations to diagnose the dust composition, we simulate the transmission spectra from 5-14 μm for the planet tail assuming an optically-thin dust cloud comprising a single dust species with a constant column density scaled to yield a chosen visible transit depth. We find that silicate resonant features near 10 μm can produce transit depths that are at least as large as those in the visible. For the average transit depth of 0.55% in the Kepler band for K2-22b, the features in the transmission spectra can be as large as 1%, which is detectable with the JWST MIRI low-resolution spectrograph in a single transit. The detectability of compositional features is easier with an average grain size of 1 μm despite features being more prominent with smaller grain sizes. We find most features are still detectable for transit depths of ~0.3% in the visible range. If more disintegrating planets are found with future missions such as the space telescope TESS, follow-up observations with JWST can explore the range of planetary compositions.

https://arxiv.org/abs/1808.07043

[TrevorMonty]

While not serviceable as such, plan is to make it easy for robotic service vehicles to locate and grabble it.

https://spacepolicyonline.com/news/zurbuchen-taking-one-last-look-at-jwst-servicing/

If service vehicle could grabble JWST  then shouldn't be problem to tow it back to the Gateway for an attempting at repairing it. Both NG (Orbital) and SSL will vehicles capable of doing this in near future.

[speedevil]

While not serviceable as such, plan is to make it easy for robotic service vehicles to locate and grabble it.

https://spacepolicyonline.com/news/zurbuchen-taking-one-last-look-at-jwst-servicing/

If service vehicle could grabble JWST  then shouldn't be problem to tow it back to the Gateway for an attempting at repairing it. Both NG (Orbital) and SSL will vehicles capable of doing this in near future.

In principle it may be possible to top off the propellant tank, if the appropriate external fitting is there, or to deorbit it and put it in a museum.
Actually servicing it in meaningful ways pretty much has to be designed into it from the start.
Note for example the large cost implications of the misconnection of a power supply - sensors had to be removed and replacements re-welded, after a lot of tearing down. The enormous complexity in the compact volume makes servicing of any involved sort sound basically impossible without an infrastructure comparable to the ground facilities.

[freda]

While not serviceable as such, plan is to make it easy for robotic service vehicles to locate and grabble it.

https://spacepolicyonline.com/news/zurbuchen-taking-one-last-look-at-jwst-servicing/

If service vehicle could grabble JWST  then shouldn't be problem to tow it back to the Gateway for an attempting at repairing it. Both NG (Orbital) and SSL will vehicles capable of doing this in near future.

In principle it may be possible to top off the propellant tank, if the appropriate external fitting is there, or to deorbit it and put it in a museum.
Actually servicing it in meaningful ways pretty much has to be designed into it from the start.
Note for example the large cost implications of the misconnection of a power supply - sensors had to be removed and replacements re-welded, after a lot of tearing down. The enormous complexity in the compact volume makes servicing of any involved sort sound basically impossible without an infrastructure comparable to the ground facilities.

Did I hear that the JWST mirrors would be damaged by the reaction motors emissions of any approaching vehicle, hence none of the conventional ideas for servicing are possible?  (Basically that the cloud of exhaust from the thrusters would deposit nasty stuff on the mirrors surfaces).

[Johnnyhinbos]

While not serviceable as such, plan is to make it easy for robotic service vehicles to locate and grabble it.

https://spacepolicyonline.com/news/zurbuchen-taking-one-last-look-at-jwst-servicing/

If service vehicle could grabble JWST  then shouldn't be problem to tow it back to the Gateway for an attempting at repairing it. Both NG (Orbital) and SSL will vehicles capable of doing this in near future.

Not sure if intentional or not, but you just gave me a new word. I had to look it up...

“grabble”

[Blackstar]

I think that this is a case of NASA performing due diligence. The last time they looked at servicing for JWST was many years ago. NASA has worked on "non-cooperative" servicing for awhile. Maybe they learned something. And maybe they could do something if, for instance, the spacecraft lost attitude control but was otherwise operational.

That said, I doubt that they're going to come to any different conclusions than before. It was never designed for servicing, and it's not the kind of telescope that probably could have been designed for servicing if they wanted to. It was designed to get very cold and stay very cold, and it is unlikely that it could have been designed to be messed with and still achieve its goals.

[speedevil]

Did I hear that the JWST mirrors would be damaged by the reaction motors emissions of any approaching vehicle, hence none of the conventional ideas for servicing are possible?  (Basically that the cloud of exhaust from the thrusters would deposit nasty stuff on the mirrors surfaces).

You may have heard this, but it's superficially correct only.

Standard hypergolic rocket engine exhaust will of course contain water (and other things) that will condense on even a slightly cold mirror, and not evaporate at an appreciable rate.

However, nitrogen from cold gas thrusters has a significant vapour pressure (~0.005 bar) at 50K, and will evaporate.

This is even without going to helium/hydrogen cold gas thrusters, or exotics like Neon.

In the context of a JWST servicing mission, cold gas thrusters in the microgee range are the very least issue. Other trace gasses from non propellant emissions from a servicing mission could be a concern.


Note that JWST does have hypergolic engines.

[ncb1397]

Did I hear that the JWST mirrors would be damaged by the reaction motors emissions of any approaching vehicle, hence none of the conventional ideas for servicing are possible?  (Basically that the cloud of exhaust from the thrusters would deposit nasty stuff on the mirrors surfaces).

You may have heard this, but it's superficially correct only.

Standard hypergolic rocket engine exhaust will of course contain water (and other things) that will condense on even a slightly cold mirror, and not evaporate at an appreciable rate.

However, nitrogen from cold gas thrusters has a significant vapour pressure (~0.005 bar) at 50K, and will evaporate.

This is even without going to helium/hydrogen cold gas thrusters, or exotics like Neon.

In the context of a JWST servicing mission, cold gas thrusters in the microgee range are the very least issue. Other trace gasses from non propellant emissions from a servicing mission could be a concern.


Note that JWST does have hypergolic engines.

If the cold mirror is the issue, they could likely heat it back up to normal temperature. They already did a complete thermal cycle on the ground. It doesn't have to stay cold. And if the problem they are fixing is with the sun shield, it may not be cold to begin with.

[jbenton]

While not serviceable as such, plan is to make it easy for robotic service vehicles to locate and grabble it.

https://spacepolicyonline.com/news/zurbuchen-taking-one-last-look-at-jwst-servicing/

If service vehicle could grabble JWST  then shouldn't be problem to tow it back to the Gateway for an attempting at repairing it. Both NG (Orbital) and SSL will vehicles capable of doing this in near future.

I've been thinking about the possibility of servicing JWST ever since this conversation came up:

the big question here is what happens if Webb turns out to be a Hubble...ie there is some flaw in it that makes it less "generational"

then what?

Much loud noises, fingerpointing, and little else.
It is if not impossible to service JWST - practically so, without getting it back to earth which would be expensive and damaging.
If it is impacted seriously enough, there would be a modest saving due to no operations budget.

a total failure will be catastrophic for the agency in my view

While not designed to be serviceable, I do wonder what is possible if it could be returned to LOP-G for investigation.

I remember years ago (this mission has been in development for sooo long) that they were considering adding a docking ring like the soft capture mechanism on Hubble, in case NASA may try to make do with an Orion-centric servicing mission; then they deleted it, then they reconsidered it, and I don't know what happened  since.

In any case I found this Jeff Foust article from 2006:
http://www.thespacereview.com/article/759/1

I find it interesting that the leader of this study was thinking on the same line of reasoning as the proposers of the "Flexible Path" considered by the Augustine Commission three years later.

[jbenton]

Did I hear that the JWST mirrors would be damaged by the reaction motors emissions of any approaching vehicle, hence none of the conventional ideas for servicing are possible?  (Basically that the cloud of exhaust from the thrusters would deposit nasty stuff on the mirrors surfaces).

You may have heard this, but it's superficially correct only.

Standard hypergolic rocket engine exhaust will of course contain water (and other things) that will condense on even a slightly cold mirror, and not evaporate at an appreciable rate.

However, nitrogen from cold gas thrusters has a significant vapour pressure (~0.005 bar) at 50K, and will evaporate.

This is even without going to helium/hydrogen cold gas thrusters, or exotics like Neon.

In the context of a JWST servicing mission, cold gas thrusters in the microgee range are the very least issue. Other trace gasses from non propellant emissions from a servicing mission could be a concern.


Note that JWST does have hypergolic engines.

Right. And astronaut's MMUs would use nitrogen.

the article I mentioned above said that a heavily modified Orion (same capsule, super-powered, reusable SM) could launch from an Ares I (the SM had drop tanks to increase delta-v) and have "a 35-day round-trip" including a 5-day stay at SE-L2 (15 days there and 15 days back). This makes sense because Apollo took 3 days to reach the Moon, and SE-L2 is about three times the distance (the Moon is about 400,000 km; SE-L2 is at about 1,500,000 km). Given that the delta-v requirement is only slightly higher than going to the Moon, a SLS Block IA or IB can certainly send the distance, but today's Orion can only keep the crew alive for 21 days. I thought of two potential solutions:

one was a complex plan involving LOP-G using it's propulsion stage to move to EM-L2 prior to the mission. Doesn't work if it is not possible to refuel Orion while there. Also, LOP-G won't be open for business soon enough.

the other would be to have a SLS Block IB to send Orion with a 4-segment Cygnus to act as a small DSH. Cygnus would use its own thruster to start the trans-Earth Injection and Orion would finish the job (after jettisoning Cygnus). I also supposed that the mission could be shortened if the launch would be timed in such a way as to have a Lunar gravity assist, either on the way there or the way back. On the other hand, SLS Block IB also won't be available any earlier than 2024 (IIRC)

In either case, I imagined Orion i a halo orbit of SE-L2 away standing off from JWST. The astronauts would get in close using MMUs (or they'd get in close in a SEV and get in closer with MMUs)

[jbenton]

While not serviceable as such, plan is to make it easy for robotic service vehicles to locate and grabble it.

https://spacepolicyonline.com/news/zurbuchen-taking-one-last-look-at-jwst-servicing/

If service vehicle could grabble JWST  then shouldn't be problem to tow it back to the Gateway for an attempting at repairing it. Both NG (Orbital) and SSL will vehicles capable of doing this in near future.

I think that this is a case of NASA performing due diligence. The last time they looked at servicing for JWST was many years ago. NASA has worked on "non-cooperative" servicing for awhile. Maybe they learned something. And maybe they could do something if, for instance, the spacecraft lost attitude control but was otherwise operational.

That said, I doubt that they're going to come to any different conclusions than before. It was never designed for servicing, and it's not the kind of telescope that probably could have been designed for servicing if they wanted to. It was designed to get very cold and stay very cold, and it is unlikely that it could have been designed to be messed with and still achieve its goals.

The study above focuses on robotic servicing. I was thinking about human servicing. If they can do robotic servicing, then more power to them!
It would mean a cheaper and smaller rocket than for humans. Any rocket only slightly larger than the one they intend to use to launch a RSM to GEO could probably make it to SE-L2, cutting costs substantially.

The second easiest mission for robotic servicing is simply refilling a satellite's tanks (the easiest is docking to said said sat and providing RCS itself by pushing the sat - see the mission extension vehicle. I don't think such a design will work for as complex a ship as JWST)

Speaking of Chandra, that thing has been up there for over 20 years, and it still works. Assuming that everything goes right with JWST, How long could it possibly last past it's 5-year primary mission? I mean to say how long before it runs out of propellant, or some other consumable? How long do large space observatories usually last on there with out servicing?

Propellant is its only consumable (one of the technical breakthroughs on JWST is the closed-loop cryocooler). It was designed with enough propellant for 10.5 years of operation. Estimates of propellant usage for station keeping and pointing at a Lagrange point vs actual usage tend to be quite pessimistic, so it would not be surprising if the propellant allows for longer than that. I have heard that system failures are the more likely cause of EOM than propellant, however.

This got me thinking: even if everything goes 100% right (including the propellant subsystem and RCS), robotic servicing could still be quite useful. Suppose that it finishes it's 5-yr primary mission and NASA approves a 5-yr extended mission. Perhaps then, if nothing is broken, a RSM could come in at the start of year 11, refill the tanks and JWST could do 20 years of science operations!

[jbenton]

BTW, does this thing have reaction wheels?

If so, do they have metal or ceramic ball bearings?

[russianhalo117]

BTW, does this thing have reaction wheels?

If so, do they have metal or ceramic ball bearings?

Metal bearings are used on spacecraft currently in orbit for several years. Ceramic bearings are being used on newer spacecraft. Not sure what is planned on JWST.