Potential servicing missions for the Webb

[su27k]

I'll just say this: If god forbid something happened during deployment, or the telescope runs out of fuel early than expected, you can bet NASA will suddenly come up with a way to save it by servicing, all the "But it can't do it because xyz" will magically disappear, and everybody who objected to servicing in this thread will pretend it was never an issue.

[Eric Hedman]

I'll just say this: If god forbid something happened during deployment, or the telescope runs out of fuel early than expected, you can bet NASA will suddenly come up with a way to save it by servicing, all the "But it can't do it because xyz" will magically disappear, and everybody who objected to servicing in this thread will pretend it was never an issue.

Do you have any idea of how long it would take to design a mission and a spacecraft to do a repair if it was possible?  You would need to build and test the hardware.  By the time you had it ready to launch you're probably talking 7 to 10 years if not more.  It would be a better use of money to work on the next telescope.

[DanClemmensen]

I'll just say this: If god forbid something happened during deployment, or the telescope runs out of fuel early than expected, you can bet NASA will suddenly come up with a way to save it by servicing, all the "But it can't do it because xyz" will magically disappear, and everybody who objected to servicing in this thread will pretend it was never an issue.

Do you have any idea of how long it would take to design a mission and a spacecraft to do a repair if it was possible?  You would need to build and test the hardware.  By the time you had it ready to launch you're probably talking 7 to 10 years if not more.  It would be a better use of money to work on the next telescope.

STS-49 salvaged Intelsat 603, which had failed to separate from the second stage of its launcher and was left in LEO. It took two years to plan the mission and build the needed hardware.
  https://en.wikipedia.org/wiki/STS-49
Hubble was launched with a defective optical system. While Hubble had been designed to be serviced by the shuttle, a fix for this defect was not an anticipated repair, so a repair mission had to be designed and implemented.
  https://en.wikipedia.org/wiki/Hubble_Space_Telescope#Flawed_mirror

Because Starship launches will be inexpensive and because Starship can reach any orbit, repairs will be more feasible in the future.

[Eric Hedman]

I'll just say this: If god forbid something happened during deployment, or the telescope runs out of fuel early than expected, you can bet NASA will suddenly come up with a way to save it by servicing, all the "But it can't do it because xyz" will magically disappear, and everybody who objected to servicing in this thread will pretend it was never an issue.

Do you have any idea of how long it would take to design a mission and a spacecraft to do a repair if it was possible?  You would need to build and test the hardware.  By the time you had it ready to launch you're probably talking 7 to 10 years if not more.  It would be a better use of money to work on the next telescope.

STS-49 salvaged Intelsat 603, which had failed to separate from the second stage of its launcher and was left in LEO. It took two years to plan the mission and build the needed hardware.
  https://en.wikipedia.org/wiki/STS-49
Hubble was launched with a defective optical system. While Hubble had been designed to be serviced by the shuttle, a fix for this defect was not an anticipated repair, so a repair mission had to be designed and implemented.
  https://en.wikipedia.org/wiki/Hubble_Space_Telescope#Flawed_mirror

Because Starship launches will be inexpensive and because Starship can reach any orbit, repairs will be more feasible in the future.

These were in LEO, not Sun Earth L2.  These were easily reachable with humans on the Shuttle.  There are thousands of possible failure modes for James Webb.  Most would more than likely require a human in the loop.  No space vehicle, not Orion and not Starship are going to go and do a mission anytime soon.  Orion is good for 21 days.  It takes a hell of lot longer than 21 days to get were the Webb telescope is going. The chance of being able to design and implement a successful unmanned mission is extremely low for most failure scenarios.  If the James Webb Telescope fails to deploy, it will be lost.

[DanClemmensen]

I'll just say this: If god forbid something happened during deployment, or the telescope runs out of fuel early than expected, you can bet NASA will suddenly come up with a way to save it by servicing, all the "But it can't do it because xyz" will magically disappear, and everybody who objected to servicing in this thread will pretend it was never an issue.

Do you have any idea of how long it would take to design a mission and a spacecraft to do a repair if it was possible?  You would need to build and test the hardware.  By the time you had it ready to launch you're probably talking 7 to 10 years if not more.  It would be a better use of money to work on the next telescope.

STS-49 salvaged Intelsat 603, which had failed to separate from the second stage of its launcher and was left in LEO. It took two years to plan the mission and build the needed hardware.
  https://en.wikipedia.org/wiki/STS-49
Hubble was launched with a defective optical system. While Hubble had been designed to be serviced by the shuttle, a fix for this defect was not an anticipated repair, so a repair mission had to be designed and implemented.
  https://en.wikipedia.org/wiki/Hubble_Space_Telescope#Flawed_mirror

Because Starship launches will be inexpensive and because Starship can reach any orbit, repairs will be more feasible in the future.

These were in LEO, not Sun Earth L2.  These were easily reachable with humans on the Shuttle.  There are thousands of possible failure modes for James Webb.  Most would more than likely require a human in the loop.  No space vehicle, not Orion and not Starship are going to go and do a mission anytime soon.  Orion is good for 21 days.  It takes a hell of lot longer than 21 days to get were the Webb telescope is going. The chance of being able to design and implement a successful unmanned mission is extremely low for most failure scenarios.  If the James Webb Telescope fails to deploy, it will be lost.

I agree that Orion cannot do this for both capability and cost reasons.

As I said: Starship will be able reach any orbit. It is not restricted to LEO. It can support a long-duration crewed mission: it is designed to carry crew to Mars and back. It  can carry as much repair equipment as needed. Intelsat 603 stayed in LEO unused and unusable for two years while the repair mission was negotiated and planned.

A crewed repair mission to Earth-sun L2 will be very expensive, but not as expensive as replacing JWST.  The trip would not happen before 2024, so I suspect it would include replenishment of consumables (helium and xenon?) and of course there is no guarantee of success.

[Lee Jay]

As I said: Starship will be able reach any orbit.

Its booster hasn't flown yet. Its spacecraft hasn't come close to being equipped with the needs of a crew yet. It may be so large that its propulsion will demolish the sun shield. It has no airlock. It has no arm. JWST doesn't have a docking or attachment point. Propulsion from Starship would likely contaminate JWST.

Do you have rational, economic, near-term solutions to those issues?

[DanClemmensen]

As I said: Starship will be able reach any orbit.

Its booster hasn't flown yet. Its spacecraft hasn't come close to being equipped with the needs of a crew yet. It may be so large that its propulsion will demolish the sun shield. It has no airlock. It has no arm. JWST doesn't have a docking or attachment point. Propulsion from Starship would likely contaminate JWST.

Do you have rational, economic, near-term solutions to those issues?

Nope. I'm not a space professional. I must trust that it will fly (NASA believes this: see the HLS contract), that it will be equipped for  crew (dearMoon, HLS, Elon's Mars plans), that it will have an airlock (HLS, Elon's Mars plans). I must also trust that a two-year effort by a rescue planning team (like the Intelsat 603 team) can solve the remaining problems if given, say, a $3 billion budget. Intelsat 603 had no docking or attachment point.

After about 5 minutes as a non-professional responding to a post on the Internet, my mission plan would be:
*arrive at a point 1000 meters away from target at 0 relative velocity using normal maneuvering thrusters and engines, with the trajectory computed to keep engines and thrusters pointed away from the target.
*use purpose-built inefficient wide-dispersion cold gas thrusters to maneuver to close proximity (10 meters?) at 0 relative velocity, taking 48 hours if needed.
*during multiple EVAs, crew will build purpose-designed scaffolding to connect the Starship to the JWST and act as the work platform.
*during further EVAs, crew undertakes repairs
*during further EVAs, crew detaches and retrieves scaffolding
*use the cold gas thrusters to very slowly move to 1000 meters
*go home on a trajectory that keeps the thrusters and engines pointed away from the target.


Do you believe that the US aerospace industry is incapable of planning and implementing this mission or planning a better one?

[M.E.T.]

As I said: Starship will be able reach any orbit.

Its booster hasn't flown yet. Its spacecraft hasn't come close to being equipped with the needs of a crew yet. It may be so large that its propulsion will demolish the sun shield. It has no airlock. It has no arm. JWST doesn't have a docking or attachment point. Propulsion from Starship would likely contaminate JWST.

Do you have rational, economic, near-term solutions to those issues?

Not commenting on the general viability of this plan, but I have to laugh at some of the specific objections raised to Starship in the above post.

No booster?
Cannot support crew?
No airlock?

That’s just lazy arguing. NASA’s entire Artemis program relies on the above three requirements as a given - among many other criteria.

Good time for a Joe Biden-style exasperated “Come on man!”

[Eric Hedman]

These were in LEO, not Sun Earth L2.  These were easily reachable with humans on the Shuttle.  There are thousands of possible failure modes for James Webb.  Most would more than likely require a human in the loop.  No space vehicle, not Orion and not Starship are going to go and do a mission anytime soon.  Orion is good for 21 days.  It takes a hell of lot longer than 21 days to get were the Webb telescope is going. The chance of being able to design and implement a successful unmanned mission is extremely low for most failure scenarios.  If the James Webb Telescope fails to deploy, it will be lost.

I agree that Orion cannot do this for both capability and cost reasons.

As I said: Starship will be able reach any orbit. It is not restricted to LEO. It can support a long-duration crewed mission: it is designed to carry crew to Mars and back. It  can carry as much repair equipment as needed. Intelsat 603 stayed in LEO unused and unusable for two years while the repair mission was negotiated and planned.

A crewed repair mission to Earth-sun L2 will be very expensive, but not as expensive as replacing JWST.  The trip would not happen before 2024, so I suspect it would include replenishment of consumables (helium and xenon?) and of course there is no guarantee of success.

NASA would be crazy to spend money on a mission using Starship until it is proven with refueling and return from high speed trajectories.  It also needs to prove that it's life support system is reliable for a many months long mission out to L2 and back.  In addition, there also may be no way to fully assess the problems with the Webb before they get there.  What if they come out to fix one problem and discover it isn't the only one stopping the telescope from working?  I think it would be highly unlikely any repair mission would be mounted.  It would be better to concentrate on the next telescope.

[Paul451]

NASA would be crazy to spend money on a mission using Starship until it is proven with refueling and return from high speed trajectories.

And yet that's exactly what they are doing with Artemis. Crazy!

[Edit: That said, potential repair missions on that scale seem off-topic for this thread. Even discussing a MEV life-extension seems to be pushing the edges too far. Creating a new topic for "JWST life-extension and repair mission concepts and speculation" is just a matter of clicking a button.]

[LouScheffer]

This is a thread about potential servicing missions for the Webb telescope.

Perhaps the mods can pick out the serving mission posts and move them here, after which I'll delete this sentence.

The arguments for are:
  * Webb is quite expensive, and has unique capabilities
  * L2 orbit maintenance and momentum dumping require fuel, but there are no other consumables.  So an MEV-1 type addition (taking over attitude control only) might work.
  * Extending life might be cheaper than a new mission

The arguments against are:
  * Webb is not designed for servicing of any kind.  No place to attach, add fuel, etc.
  * A servicing mission would be too expensive for the benefit gained
  * It would take too long to develop
  * A servicing mission would damage Webb (hurt sunscreen, contaminate optics, etc.)
  * We should spend the money on a new mission, not fixing an old one

And here is a spot for Webb design documents that might shed light on the issues:  More can be added as found...
   * The paper "Status of the JWST sunshield and spacecraft" shows that the fill and drain valves are exposed. See Figure attached.
   * ...

[etudiant]

This seems like a useful test case of the impact of much lower cost/lb orbital access offered by SH/SS.
Is it cheaper to do a custom replenishment mission or to just do a JW2 reflight, taking advantage of the vastly increased volume and lift offered to eliminate the expensive origami aspects of the original?

[LouScheffer]

Here are some possible cost comparisons:

The DARPA "Orbital Express" project developed a refueler spacecraft and a target spacecraft for about $215 million (DARPA budget documents have
 2002: $5M
 2003: $40M
 2004: $55M
 2005: $47M
 2006: $37M
 2007: $31M
Though other sources put the total at $300M.

MEV-1 (comsat life extension) charges $13M a year for services, and the spacecraft is expected to last 15 years.  So the cost must be less than $195M, including launch.

[Jim]

, taking advantage of the vastly increased volume and lift offered to eliminate the expensive origami aspects of the original?

Really doesn't change much.  Only eliminates the mirror wings.  Secondary mirror still would need a deployment.  And the sun shield would still require packaging and deployment.  And it would be basically a compete redesign.

And the "origami" wasn't the expensive part.

[Jim]

The sunshield makes JWST unapproachable.

.  This is only 100lb thrusters

[DanClemmensen]

These were in LEO, not Sun Earth L2.  These were easily reachable with humans on the Shuttle.  There are thousands of possible failure modes for James Webb.  Most would more than likely require a human in the loop.  No space vehicle, not Orion and not Starship are going to go and do a mission anytime soon.  Orion is good for 21 days.  It takes a hell of lot longer than 21 days to get were the Webb telescope is going. The chance of being able to design and implement a successful unmanned mission is extremely low for most failure scenarios.  If the James Webb Telescope fails to deploy, it will be lost.

I agree that Orion cannot do this for both capability and cost reasons.

As I said: Starship will be able reach any orbit. It is not restricted to LEO. It can support a long-duration crewed mission: it is designed to carry crew to Mars and back. It  can carry as much repair equipment as needed. Intelsat 603 stayed in LEO unused and unusable for two years while the repair mission was negotiated and planned.

A crewed repair mission to Earth-sun L2 will be very expensive, but not as expensive as replacing JWST.  The trip would not happen before 2024, so I suspect it would include replenishment of consumables (helium and xenon?) and of course there is no guarantee of success.

NASA would be crazy to spend money on a mission using Starship until it is proven with refueling and return from high speed trajectories.  It also needs to prove that it's life support system is reliable for a many months long mission out to L2 and back.  In addition, there also may be no way to fully assess the problems with the Webb before they get there.  What if they come out to fix one problem and discover it isn't the only one stopping the telescope from working?  I think it would be highly unlikely any repair mission would be mounted.  It would be better to concentrate on the next telescope.

(Replying by copying from the other thread. Apologies if this is not the correct way to do this)

SpaceX clearly already plans to develop and demonstrate refueling, return from high-speed trajectories, and long-term life support, so no new spending is needed there. But spending a small amount of money on planning prior to completion of these demonstrations makes a lot of sense: the plan would allow NASA to fire up the rescue project design and implementation quickly as soon as the last demonstration is complete. This is not "instead of" the next telescope. Instead, it is an attempt to salvage some value from the $9.6 billion already spent on JWST. Sure sunk costs are sunk (we spent $9.9 B, but the current value of an operational JWST might be only $3 B or whatever) and sure, the rescue mission might not work. But it might work, so spending $2 million on an initial concept plan might be money well spent. It would at least be able to identify obvious show-stoppers (no possible solution) or major challenges (might be solvable but need real, in-depth analysis.)

[su27k]

Some official responses wrt servicing:

Scientists, engineers push for servicing and assembly of future space observatories

While JWST is not designed for servicing — Grunsfeld said it might be possible, but risky, to do some kind of robotic refueling mission for the telescope about 10 years after launch

Zurbuchen Taking One Last Look At Jwst Servicing Compatiblity

At a meeting of the NASA Advisory Council (NAC) today, Zurbuchen was asked by NAC member Mike Gold if NASA was ensuring some degree of JWST compatibility for servicing.  Gold works for Maxar Technologies.  Its Space Systems Loral business unit is one of the leading companies in developing satellite servicing technologies.

<snip>

Satellite servicing advocates have pointed out for years that although systems do not exist today that could robotically service JWST at L2, they might in the future.  They urged NASA to at least put stickers on the telescope to allow a future robotic system to locate it.

Zurbuchen confirmed today that NASA already has taken some steps and now is looking to see if there is anything else that can be done.

So it doesn't look to me that servicing is completely ruled out by NASA.

[Hobbes-22]

The sunshield makes JWST unapproachable.

  This is only 100lb thrusters

It certainly makes the approach more difficult.
On the other hand:
- this was something they hadn't accounted for in this flyaround, and may have been the first time the phenomenon was seen.
- they managed to dock Apollo to Skylab several times without blowing the sunshield away
- JWST has several thruster sets operating in the vicinity of the sunshield. So running a thruster with its thrust axis parallel to the sunshield seems to be possible if designed correctly.

There are ways to reduce the chance of damaging the sunshield:
- approach slowly, to minimize thruster use near JWST. The servicing vehicle is unmanned, so no problem if it takes 3 months to dock.
- to slow down when flying toward JWST, use thrusters set at a large angle to the velocity vector and accept the cosine losses.
- use a telescoping docking mechanism to absorb the remaining approach speed
- use thrusters mounted on a long boom to put their exhaust cone outside of the sunshield

You'd need a purpose-built vehicle rather than a standard MEV. We spent $9B on JWST to get 10 years of observation time.  We've paid $500M per servicing mission to extend Hubble's life several times.

IOW there's a gap between difficult and impossible.

[LouScheffer]

As far as contaminating the optics, the sunshade should largely prevent this, as exhaust will travel in straight lines.  After all, Webb has thrusters on the warm side (though angled away from the sunshade.)

If this is not enough, hydrogen or helium cold-gas thrusters would work.  The JWST optics are at about 50K, and neither hydrogen or helium will condense at that temperature.

[woods170]

As far as contaminating the optics, the sunshade should largely prevent this, as exhaust will travel in straight lines.  After all, Webb has thrusters on the warm side (though angled away from the sunshade.)

If this is not enough, hydrogen or helium cold-gas thrusters would work.  The JWST optics are at about 50K, and neither hydrogen or helium will condense at that temperature.

It is not about contamination. It is about physically shredding or tearing one or more layers of the sunshield via interaction with the RCS thrusters of an approaching servicing spacecraft.

[Jim]

- approach slowly, to minimize thruster use near JWST. The servicing vehicle is unmanned, so no problem if it takes 3 months

Not viable for many reasons such as JWST will moving during during such a long time period.

Other influences will over come such maneuvers

[John-H]

Could the service vehicle stop close by and the telescope use its station keeping thrusters for the final approach?  They should be harmless.  They will use some fuel, but you are going to refuel anyway.

John

[LouScheffer]

Could the service vehicle stop close by and the telescope use its station keeping thrusters for the final approach?  They should be harmless.  They will use some fuel, but you are going to refuel anyway.

I don't think this works, since I believe all the thrusters are oriented away from the heatshield, so Webb has no way to back up.  This induces complications, since each maneuver or momentum dump also then accelerates the spacecraft forward, even if that was not the intention.

I found this in an old paper (2002) but I don't think it's changed.

[DanClemmensen]

There must be a hundred viable ways to solve the approach problem. I have to believe the engineers on a rescue planning team will find one of them. Here is a simple plan that is probably suboptimal but will probably work. I don't know how important the approach problem is, but it has been raised as an issue, so let's demonstrate that it's solvable.

*Use standard engines and thrusters to reach a station-keeping point at zero relative velocity at a safe distance on a tangential course that keeps the thrusters and engines pointed away from the JWST. "Safe" might be 1000 m or 5000 m. The team can compute this.
*Deploy a tug: a small vehicle on a long tether (1000 m? 5000 m? whatever) that has three cold gas thrusters mounted at angles that point at (say) 60 degrees away from the tether. If needed the tether itself can be made semi-rigid by pressurizing it after deployment. The system is deployed in the direction away from the JWST. Slowly move Starship toward JWST using Starship's thrusters, probably some specialized cold gas thrusters. These thrusters are pointed away from JWS. Starship is now dragging the tug along.
*As starship approaches JWST, use the tug's thrusters to bring Starship to a halt within a few meters of JSWT.
*Starship can orient itself using very large reaction wheels that were added as part of the rescue plan.
* After the repair and replenishment are complete, the tug will pull Starship slowly away from JWST.

The key concept is that Starship can slowly maneuver in any direction, but if it would otherwise need to point a thruster at JWST, it will instead use the tug's thrusters. The system allows Starship to navigate around JWST (e.g., circumnavigate for an inspection) if needed, but it gets complicated. If a great deal of such maneuvering is needed, it may be necessary to supply gas to the tug via the tether, but I think the nominal mission would rigidly connect the Starship via a custom scaffolding to one specific spot and leave it there for the duration of the repair and replenishment.

If I can think of something like this, presumably a team of professionals can do better.

[LouScheffer]

As far as contaminating the optics, the sunshade should largely prevent this, as exhaust will travel in straight lines.  After all, Webb has thrusters on the warm side (though angled away from the sunshade.)

If this is not enough, hydrogen or helium cold-gas thrusters would work.  The JWST optics are at about 50K, and neither hydrogen or helium will condense at that temperature.

It is not about contamination. It is about physically shredding or tearing one or more layers of the sunshield via interaction with the RCS thrusters of an approaching servicing spacecraft.

Absent a detailed analysis, it's hard to believe this a serious concern.  The sun facing layer is 2 mil (50 u) thick Kapton.  This is 4 times the thickness of the saran wrap you find in your home kitchen.  With a tensile strength of 34 MPa, it would take a force of 1700 N (173 Kg-force) to tear a 1 meter piece. 

And there is no need for high power thrusters in order to stop when you reach Webb.  The only maneuvering it is expected to do is momentum unloads once every 4-8 days.  In between it's drifting only, and you can predict exactly where it will be 4 days hence.  Approaching this location from a km away in a 4 day period needs only 3 mm/sec.  This video shows an ion thruster impinging on a piece of aluminum foil from about 2 cm away without damage.  This 0.006 newton thruster (surely small enough to not damage the sunshade) could remove this speed from a 1000 kg approaching satellite in 500 seconds, starting from less than a meter away.

[deadman1204]

Whats the point of this thead? The OP basically said "cons say its basically not possible", yet still wants to discuss it.
All of this also ignores that this is out in deep space at L2.

[deadman1204]

Nope. I'm not a space professional. I must trust that it will fly (NASA believes this: see the HLS contract), that it will be equipped for  crew (dearMoon, HLS, Elon's Mars plans), that it will have an airlock (HLS, Elon's Mars plans). I must also trust that a two-year effort by a rescue planning team (like the Intelsat 603 team) can solve the remaining problems if given, say, a $3 billion budget. Intelsat 603 had no docking or attachment point.

After about 5 minutes as a non-professional responding to a post on the Internet, my mission plan would be:
*arrive at a point 1000 meters away from target at 0 relative velocity using normal maneuvering thrusters and engines, with the trajectory computed to keep engines and thrusters pointed away from the target.
*use purpose-built inefficient wide-dispersion cold gas thrusters to maneuver to close proximity (10 meters?) at 0 relative velocity, taking 48 hours if needed.
*during multiple EVAs, crew will build purpose-designed scaffolding to connect the Starship to the JWST and act as the work platform.
*during further EVAs, crew undertakes repairs
*during further EVAs, crew detaches and retrieves scaffolding
*use the cold gas thrusters to very slowly move to 1000 meters
*go home on a trajectory that keeps the thrusters and engines pointed away from the target.


Do you believe that the US aerospace industry is incapable of planning and implementing this mission or planning a better one?

After all the planning, building, training, and huge costs of this, were looking at several billion and multiple years. The resources would be better spent towards a new telescope.

[Redclaws]

Whats the point of this thead? The OP basically said "cons say its basically not possible", yet still wants to discuss it.
All of this also ignores that this is out in deep space at L2.

“Yet still wants to discuss it”.  Huh, I wonder if that’s the point.

I think it’s very interesting to ask “how could we” and perhaps the answer is “we really can’t in practical terms”, but gosh, it sure is interesting to talk about.  Lots to be learned along the way.

[RotoSequence]

After all the planning, building, training, and huge costs of this, were looking at several billion and multiple years. The resources would be better spent towards a new telescope.

What new telescope? I am so tired of seeing this fallacy of "it'll all just go into the next one" when the next one takes ten years into the prime mission to get approved, 20 years to get made, and entire generations of researchers appear between now and the creation of "the new telescope." The entire paradigm of researcher question centered telescopes is so perversely made that I can't fathom why people keep endorsing the continuity of this Kafkaesque hellscape. The entire paradigm is wrong.

[faramund]

Whats the point of this thead? The OP basically said "cons say its basically not possible", yet still wants to discuss it.
All of this also ignores that this is out in deep space at L2.

“Yet still wants to discuss it”.  Huh, I wonder if that’s the point.

I think it’s very interesting to ask “how could we” and perhaps the answer is “we really can’t in practical terms”, but gosh, it sure is interesting to talk about.  Lots to be learned along the way.

And at least some parts of NASA seem to say they considered/have added elements to Webb to make potential servicing missions easier.

So it seems very odd that some seem say that servicing it is just an impossibility.

Granted its currently impossible, to prohibitively too expensive, to do such servicing in 2022 due to technology and development limits.

But Webb is designed for a 5.5 to possibly 10 year lifetime. Given the current rate of development of launch technology, I'd personally be surprised if a life extension mission in 10 years or so from now, was not possible.

[Zed_Noir]

After some thoughts  on how to service the JWST without damaging the sunshade by thruster plumes.


One could just grapple the JWST with a service arm on a long extendable fixture attracted to a servicing vehicle. Once grappled the extendable fixture retracts back to the servicing vehicle for servicing. Alternately some sort of remote operated mobile service robot (and/or Astronauts) could go to the JWST along the fixture to service the JWST.


Waiting for responses on why this is not practical.

[Redclaws]

After some thoughts  on how to service the JWST without damaging the sunshade by thruster plumes.


One could just grapple the JWST with a service arm on a long extendable fixture attracted to a servicing vehicle. Once grappled the extendable fixture retracts back to the servicing vehicle for servicing. Alternately some sort of remote operated mobile service robot (and/or Astronauts) could go to the JWST along the fixture to service the JWST.


Waiting for responses on why this is not practical.

How does using an arm avoid the issues?  How long are we suggesting it is?  How long does it need to be?

[DanClemmensen]

After some thoughts  on how to service the JWST without damaging the sunshade by thruster plumes.


One could just grapple the JWST with a service arm on a long extendable fixture attracted to a servicing vehicle. Once grappled the extendable fixture retracts back to the servicing vehicle for servicing. Alternately some sort of remote operated mobile service robot (and/or Astronauts) could go to the JWST along the fixture to service the JWST.


Waiting for responses on why this is not practical.

I have been assuming that the requirement is to not have any thruster exhaust at all impinge on any part of JWST, not because of kinetic damage but to avoid chemical contamination, especially to the mirror surfaces. (The actual requirement is probably less extreme than this.) This means no thrusters on a remote vehicle or an EVA suit, which means the the repair crew or remote will need to clamber around on a rigid scaffold or deploy an arm. But it also means that the main problem is how to get near the JWST without ever aiming a thruster anywhere near it, which is why I proposed a tethered tug (see above).

[Zed_Noir]

After some thoughts  on how to service the JWST without damaging the sunshade by thruster plumes.


One could just grapple the JWST with a service arm on a long extendable fixture attracted to a servicing vehicle. Once grappled the extendable fixture retracts back to the servicing vehicle for servicing. Alternately some sort of remote operated mobile service robot (and/or Astronauts) could go to the JWST along the fixture to service the JWST.


Waiting for responses on why this is not practical.

How does using an arm avoid the issues?  How long are we suggesting it is?  How long does it need to be?

The arm is on a fixture that is at least 100 meters long.

[Zed_Noir]

After some thoughts  on how to service the JWST without damaging the sunshade by thruster plumes.


One could just grapple the JWST with a service arm on a long extendable fixture attracted to a servicing vehicle. Once grappled the extendable fixture retracts back to the servicing vehicle for servicing. Alternately some sort of remote operated mobile service robot (and/or Astronauts) could go to the JWST along the fixture to service the JWST.


Waiting for responses on why this is not practical.

I have been assuming that the requirement is to not have any thruster exhaust at all impinge on any part of JWST, not because of kinetic damage but to avoid chemical contamination, especially to the mirror surfaces. (The actual requirement is probably less extreme than this.) This means no thrusters on a remote vehicle or an EVA suit, which means the the repair crew or remote will need to clamber around on a rigid scaffold or deploy an arm. But it also means that the main problem is how to get near the JWST without ever aiming a thruster anywhere near it, which is why I proposed a tethered tug (see above).

No thruster required. The repair crew and or remote operated robots travels to the end of the fixture on a trolley cart. Some of the robots will be mobile service arm segments.

[Lee Jay]

Whats the point of this thead? The OP basically said "cons say its basically not possible", yet still wants to discuss it.
All of this also ignores that this is out in deep space at L2.

“Yet still wants to discuss it”.  Huh, I wonder if that’s the point.

I think it’s very interesting to ask “how could we” and perhaps the answer is “we really can’t in practical terms”, but gosh, it sure is interesting to talk about.  Lots to be learned along the way.

And at least some parts of NASA seem to say they considered/have added elements to Webb to make potential servicing missions easier.

So it seems very odd that some seem say that servicing it is just an impossibility.

Granted its currently impossible, to prohibitively too expensive, to do such servicing in 2022 due to technology and development limits.

That's what we're (we'll, at least I'm) saying is impossible. The idea of a rescue mission in case JWST has a deployment or commissioning issue happening near-term using Starship is just insane.

But Webb is designed for a 5.5 to possibly 10 year lifetime. Given the current rate of development of launch technology, I'd personally be surprised if a life extension mission in 10 years or so from now, was not possible.

Perhaps.

[Lee Jay]

As I said: Starship will be able reach any orbit.

Its booster hasn't flown yet. Its spacecraft hasn't come close to being equipped with the needs of a crew yet. It may be so large that its propulsion will demolish the sun shield. It has no airlock. It has no arm. JWST doesn't have a docking or attachment point. Propulsion from Starship would likely contaminate JWST.

Do you have rational, economic, near-term solutions to those issues?

Not commenting on the general viability of this plan, but I have to laugh at some of the specific objections raised to Starship in the above post.

No booster?
Cannot support crew?
No airlock?

That’s just lazy arguing. NASA’s entire Artemis program relies on the above three requirements as a given - among many other criteria.

Good time for a Joe Biden-style exasperated “Come on man!”

I'm consistently amazed that so many spacex fans take all this as a done deal when no test booster has flown yet, engines are still going through massive redesigns, the EDL system may or may not work, Starship has never been equipped with anything, in space refueling hasn't been tried and we don't even know what launch site will end up being used because BC is still under FAA review.

Long way to go with this ultra high risk project before counting on it.

[Robotbeat]

Whats the point of this thead? The OP basically said "cons say its basically not possible", yet still wants to discuss it.
All of this also ignores that this is out in deep space at L2.

“Yet still wants to discuss it”.  Huh, I wonder if that’s the point.

I think it’s very interesting to ask “how could we” and perhaps the answer is “we really can’t in practical terms”, but gosh, it sure is interesting to talk about.  Lots to be learned along the way.

And at least some parts of NASA seem to say they considered/have added elements to Webb to make potential servicing missions easier.

So it seems very odd that some seem say that servicing it is just an impossibility.

Granted its currently impossible, to prohibitively too expensive, to do such servicing in 2022 due to technology and development limits.

That's what we're (we'll, at least I'm) saying is impossible. The idea of a rescue mission in case JWST has a deployment or commissioning issue happening near-term using Starship is just insane.

But Webb is designed for a 5.5 to possibly 10 year lifetime. Given the current rate of development of launch technology, I'd personally be surprised if a life extension mission in 10 years or so from now, was not possible.

Perhaps.

I'll chalk you up on the long list of people who still don't take Starship seriously.

Of course a JWST rescue mission with Starship is just insane. EVERYTHING about Starship is insane, Artemis in particular.

[Lee Jay]

Whats the point of this thead? The OP basically said "cons say its basically not possible", yet still wants to discuss it.
All of this also ignores that this is out in deep space at L2.

“Yet still wants to discuss it”.  Huh, I wonder if that’s the point.

I think it’s very interesting to ask “how could we” and perhaps the answer is “we really can’t in practical terms”, but gosh, it sure is interesting to talk about.  Lots to be learned along the way.

And at least some parts of NASA seem to say they considered/have added elements to Webb to make potential servicing missions easier.

So it seems very odd that some seem say that servicing it is just an impossibility.

Granted its currently impossible, to prohibitively too expensive, to do such servicing in 2022 due to technology and development limits.

That's what we're (we'll, at least I'm) saying is impossible. The idea of a rescue mission in case JWST has a deployment or commissioning issue happening near-term using Starship is just insane.

But Webb is designed for a 5.5 to possibly 10 year lifetime. Given the current rate of development of launch technology, I'd personally be surprised if a life extension mission in 10 years or so from now, was not possible.

Perhaps.

I'll chalk you up on the long list of people who still don't take Starship seriously.

You're exaggerating. Starship will not be available for any mission near term. Long term, lots of possibilities exist but with a lot of risk.

Of course a JWST rescue mission with Starship is just insane.

Correct.  If JWST fails to deploy properly, a rescue mission with Starship would either take too long to plan and execute or be impossible.

EVERYTHING about Starship is insane, Artemis in particular.

Agreed, but not for the reason you probably think (has nothing to do with Starship).

[LouScheffer]

I have been assuming that the requirement is to not have any thruster exhaust at all impinge on any part of JWST, not because of kinetic damage but to avoid chemical contamination, especially to the mirror surfaces. (The actual requirement is probably less extreme than this.) This means no thrusters on a remote vehicle or an EVA suit, which means the the repair crew or remote will need to clamber around on a rigid scaffold or deploy an arm. But it also means that the main problem is how to get near the JWST without ever aiming a thruster anywhere near it, which is why I proposed a tethered tug (see above).

Nothing so extreme should be required.  Cold gas thrusters, using either helium or hydrogen, cannot contaminate the optics as they won't condense at JWST temperature.  They could in theory condense on some of the instruments, but these are dead center on the far side, the most protected spot for contamination.

Also, thrusters can easily be sized to not hurt the sunshield.  The sunshield is not built of magical fairy dust, it's built of 50 micron thick (2 mil) Kapton.  That's fairly tough stuff.  It would take many pounds of force to tear it.

[Lee Jay]

Am I the only one who has ever set up a tarp or tent?  They NEVER tear in the middle.  Loads across the area (from wind, usually) are concentrated at the corners and they tear at the grommets.  I've seen tarps 20 times thicker than 50 microns and 1/100th the size of JWST's sun shield tear (at the corners, where the loads are concentrated) in winds of 30mph.  Rocket exhaust, even from cold gas thrusters can be 10 times that velocity.  Yes, the density will be far lower but the loads could still add up at the corners and tear it.

2 mills is half the thickness of a standard sheet of printing paper and only the first layer is that thick. The rest are half that thick.  And the thing is the size of my entire back yard.

[redliox]

There could be some options, but not to the same extent as the Hubble-shuttle relationship.

Regardless of the Starship and Orion, a few companies are emerging to assist communication satellites. This however is limited to refueling, or perhaps more accurately acting like a jetpack to extend the life of a decent sat that simply ran out of gas. It is promising to see a series of small, pod-like satellites docking to large satellites and assisting.

Frankly I believe if the Webb screws up during deployment, it's dead. However I think mission extension is doable; something like a propulsion pod perhaps with gyroscopes. L2 would be further than usual, but it's not impossible. If Webb runs out of gas or gets an unwound gyroscope I'd advocate a minor servicing mission based off what's currently coming online. After all we've blown a few billion on it, may as well ensure the thing lasts two decades to get the most of it. Gold-plated beryllium doesn't grow on trees, even on Mars.

[Lee Jay]

Frankly I believe if the Webb screws up during deployment, it's dead.

Agreed.

However I think mission extension is doable; something like a propulsion pod perhaps with gyroscopes.

Maybe, but not with gyroscopes.  The JWST has special gyroscopes (they aren't what you'd normally think of when using that term) and those are integrated into the spacecraft pointing system (the gyroscopes are detectors, not actuators).  The external mission extension vehicle would have to integrate with the vehicle electrical system (probably not possible)  Further, it has 6 and needs 2.  Perhaps you are saying "gyroscopes" when you meant "reaction wheels" but I'd consider even that to be hard or impossible to do.  Propulsion for maintaining orbit (yes, JWST orbits) and desaturation of the reaction system might be possible, but it's not really designed for it.

I consider conserving fuel during operational use to be a more likely method of mission extension than attaching another vehicle.

[LouScheffer]

Maybe, but not with gyroscopes.  The JWST has special gyroscopes (they aren't what you'd normally think of when using that term) and those are integrated into the spacecraft pointing system (the gyroscopes are detectors, not actuators).  The external mission extension vehicle would have to integrate with the vehicle electrical system (probably not possible)  Further, it has 6 and needs 2.  Perhaps you are saying "gyroscopes" when you meant "reaction wheels" but I'd consider even that to be hard or impossible to do.  Propulsion for maintaining orbit (yes, JWST orbits) and desaturation of the reaction system might be possible, but it's not really designed for it.

I don't think a servicing craft would need to attach to the electrical system, even it has reaction wheels.  Webb obviously has a high-bandwidth radio system to communicate with Earth, and receiving this from a meter away through sidelobe leakage and scattering should be easy.  So Webb would just need to devote some packets to talking to the servicer.  The bandwidth requirements should not be large in any case, as Webb does detailed pointing with a tip/tilt mirror.
Talking the other way (servicer to Webb) would be lower bandwidth (space transponders are not built for high upload rates) but should be plenty fast.

I consider conserving fuel during operational use to be a more likely method of mission extension than attaching another vehicle.

I agree this is surely the first method that will be tried.  But I believe they already schedule observations to minimize usage, and it's not clear how much more can be done and still allow good science.

[Lee Jay]

Maybe, but not with gyroscopes.  The JWST has special gyroscopes (they aren't what you'd normally think of when using that term) and those are integrated into the spacecraft pointing system (the gyroscopes are detectors, not actuators).  The external mission extension vehicle would have to integrate with the vehicle electrical system (probably not possible)  Further, it has 6 and needs 2.  Perhaps you are saying "gyroscopes" when you meant "reaction wheels" but I'd consider even that to be hard or impossible to do.  Propulsion for maintaining orbit (yes, JWST orbits) and desaturation of the reaction system might be possible, but it's not really designed for it.

I don't think a servicing craft would need to attach to the electrical system, even it has reaction wheels.  Webb obviously has a high-bandwidth radio system to communicate with Earth, and receiving this from a meter away through sidelobe leakage and scattering should be easy.  So Webb would just need to devote some packets to talking to the servicer.  The bandwidth requirements should not be large in any case, as Webb does detailed pointing with a tip/tilt mirror.

I don't know the electrical system on Webb, but I've designed many control systems and none of them had the capability to externalize the control loop to the communications system with the outside world.  All the control stuff (data from sensors, data and power sent to actuators) was internal and the external communications didn't include the ability to integrate sensors or actuators into that stream.

[LouScheffer]

I don't think a servicing craft would need to attach to the electrical system, even it has reaction wheels.  Webb obviously has a high-bandwidth radio system to communicate with Earth, and receiving this from a meter away through sidelobe leakage and scattering should be easy.  So Webb would just need to devote some packets to talking to the servicer.  The bandwidth requirements should not be large in any case, as Webb does detailed pointing with a tip/tilt mirror.

I don't know the electrical system on Webb, but I've designed many control systems and none of them had the capability to externalize the control loop to the communications system with the outside world.  All the control stuff (data from sensors, data and power sent to actuators) was internal and the external communications didn't include the ability to integrate sensors or actuators into that stream.

I completely agree it's not designed to do this.  On the other hand, I'd be surprised if the attitude target and current gyro readings are not included in the downlink telemetry.  Given this, Webb could potentially turn off its own attitude control and let the attached package handle it.  Webb or the ground would also have to tell the pointing package when it's between observations and OK to desaturate. 
   However, I doubt that exporting reaction wheel control will be needed.   As you said, Webb has 6 and needs at most 3, and reaction wheels seem to be pretty reliable (now that the space-ion-charging problem is fixed, even the low cost wheels are doing well, and Webb likely has fancy no-contact wheels anyway.)

[Lee Jay]

I don't think a servicing craft would need to attach to the electrical system, even it has reaction wheels.  Webb obviously has a high-bandwidth radio system to communicate with Earth, and receiving this from a meter away through sidelobe leakage and scattering should be easy.  So Webb would just need to devote some packets to talking to the servicer.  The bandwidth requirements should not be large in any case, as Webb does detailed pointing with a tip/tilt mirror.

I don't know the electrical system on Webb, but I've designed many control systems and none of them had the capability to externalize the control loop to the communications system with the outside world.  All the control stuff (data from sensors, data and power sent to actuators) was internal and the external communications didn't include the ability to integrate sensors or actuators into that stream.

I completely agree it's not designed to do this.  On the other hand, I'd be surprised if the attitude target and current gyro readings are not included in the downlink telemetry.

Oh, I'm sure it can be.  However, not necessarily in real-time.  It probably just saves the data to internal storage and includes it in a stream to Earth when that's available, minutes, hours or days later.

The same is true in my systems.  The sensor and actuator data is included in the storage loop but the storage loop can't be included in the real-time control loop.  This is intentional so that the real-time loop is never held up by or dependent on the storage loop timing.

[Barley]

I don't know the electrical system on Webb, but I've designed many control systems and none of them had the capability to externalize the control loop to the communications system with the outside world.  All the control stuff (data from sensors, data and power sent to actuators) was internal and the external communications didn't include the ability to integrate sensors or actuators into that stream.

I've worked on many control systems and all of them had the ability to externalize control loops.  Very common to see vehicles driving around the lab being controlled by an external laptop through a serial port, USB port or Bluetooth.

On most modern systems a general purpose micro controller (or FPGA) reads all the inputs, does some calculations and then sets the outputs.  As long as the micro is reprogrammable and has some communications capability (which is almost always there for debugging) the only problem is if the comm system has too much delay for the needed frequency response.

The systems were not designed to do this.  But it's actually quite hard to design a system that prevents it, you've got to hardwiring things and not giving a micro controller access.  The hardcore EEs who believe all PID loops should be implemented in op amps balk when they realize that they won't be able to fix things in software.

[Lee Jay]

I don't know the electrical system on Webb, but I've designed many control systems and none of them had the capability to externalize the control loop to the communications system with the outside world.  All the control stuff (data from sensors, data and power sent to actuators) was internal and the external communications didn't include the ability to integrate sensors or actuators into that stream.

I've worked on many control systems and all of them had the ability to externalize control loops.  Very common to see vehicles driving around the lab being controlled by an external laptop through a serial port, USB port or Bluetooth.

When a control-system failure results in a multi-million dollar machine crumbling to the ground, you generally don't do that.  I can unplug my HMI and the system stays running.

[deadman1204]

Whats the point of this thead? The OP basically said "cons say its basically not possible", yet still wants to discuss it.
All of this also ignores that this is out in deep space at L2.

“Yet still wants to discuss it”.  Huh, I wonder if that’s the point.

I think it’s very interesting to ask “how could we” and perhaps the answer is “we really can’t in practical terms”, but gosh, it sure is interesting to talk about.  Lots to be learned along the way.

Except the "discussion" ignores basically EVERYTHING that makes it improbable. It resets back to the start every couple days ignoring all the problems that were raised again. Its literally a couple people who are unhappy they are told its not possible just saying the same stuff over and over ad naseum.

[LouScheffer]

Except the "discussion" ignores basically EVERYTHING that makes it improbable. It resets back to the start every couple days ignoring all the problems that were raised again. Its literally a couple people who are unhappy they are told its not possible just saying the same stuff over and over ad naseum.

OK, to improve the discussion, please state WHAT makes it improbable, and WHY the solutions proposed here cannot work.  If you can do so with numbers, or references to documents, that's even better.  That's the point of this discussion, to look at the obstacles and see if any workarounds or solutions can avoid them.   A statements of "it can't be done", without reasoning and (better yet) numbers, is not helpful here.

[Lee Jay]

Except the "discussion" ignores basically EVERYTHING that makes it improbable. It resets back to the start every couple days ignoring all the problems that were raised again. Its literally a couple people who are unhappy they are told its not possible just saying the same stuff over and over ad naseum.

OK, to improve the discussion, please state WHAT makes it improbable, and WHY the solutions proposed here cannot work.

Starship won't be ready in time for a mission to repair a problem with deployment.
No other spacecraft will either.
JWST may not be approachable due to limitations on loads on the sun shade.
JWST may not be approachable due to contamination from the visiting vehicle.
JWST's location, assuming it gets there, isn't an easy place to get to for humans (remember, it's 4 times farther away than the moon is, so much further than any human has ever been away from Earth before).
A repair to what is broken may not be possible in space (depends on what is broken).
JWST wasn't designed for in-space service like Hubble was.

[ulm_atms]

Except the "discussion" ignores basically EVERYTHING that makes it improbable. It resets back to the start every couple days ignoring all the problems that were raised again. Its literally a couple people who are unhappy they are told its not possible just saying the same stuff over and over ad naseum.

OK, to improve the discussion, please state WHAT makes it improbable, and WHY the solutions proposed here cannot work.  If you can do so with numbers, or references to documents, that's even better.  That's the point of this discussion, to look at the obstacles and see if any workarounds or solutions can avoid them.   A statements of "it can't be done", without reasoning and (better yet) numbers, is not helpful here.

Let me help.  You can't land a booster...it's impossible and not worth trying.  Or at least that was what was said ~10 years ago...

deadman1204 question...Why are you so worked up that you have to shut everyone else down?  If you think it is impossible that is fine...but these people want to work through the problems and discuss....which is what the forum is for.  I guess I am trying to understand why you keep coming back to this thread instead of just leaving it be and letting the people who want to discuss...um well....discuss. 

This topic is strange though here...you got two sides.  One side is 100% no...why bother discussing and the other going "This is a problem if a service mission was considered...so how could we get around it?"  Why are you no trying so hard to shut this convo down?  If you don't agree, state it, state why, and then go about your business.  Coming back over and over to state the same "it's impossible" is well......confusing...and will get this thread locked eventually....which I hope is not the reason as that is bad taste IMO.

[DanClemmensen]

Except the "discussion" ignores basically EVERYTHING that makes it improbable. It resets back to the start every couple days ignoring all the problems that were raised again. Its literally a couple people who are unhappy they are told its not possible just saying the same stuff over and over ad naseum.

OK, to improve the discussion, please state WHAT makes it improbable, and WHY the solutions proposed here cannot work.

Starship won't be ready in time for a mission to repair a problem with deployment.
No other spacecraft will either.
JWST may not be approachable due to limitations on loads on the sun shade.
JWST may not be approachable due to contamination from the visiting vehicle.
JWST's location, assuming it gets there, isn't an easy place to get to for humans (remember, it's 4 times farther away than the moon is, so much further than any human has ever been away from Earth before).
A repair to what is broken may not be possible in space (depends on what is broken).
JWST wasn't designed for in-space service like Hubble was.

Thank you for this concise list of objections, all of which may very well be valid. This thread has been attempting to address or at least discuss each of them. A careful preliminary engineering and programatic analysis may very well conclude that a repair mission should not be attempted, if in fact it is needed. I think the "advocates", including me, are suggesting that such an analysis should be done before the mission is dismissed out of hand.  Here is an attempt to summarize the "answers" to each of your points:

*Starship won't be ready in time for a mission to repair a problem with deployment.
No other spacecraft will either.
       This depends on the useful life after repair of the JWST and of the amount of time it can spend in an unrepaired state before it becomes unrepairable. If the mission could be mounted in 2024 and JWST can then operate for six years, the mission might be cost-effective.

JWST may not be approachable due to limitations on loads on the sun shade.
JWST may not be approachable due to contamination from the visiting vehicle.
      This thread has proposed several possible solutions that do not load or contaminate the shade or JWST at all. One of them might be feasible.

JWST's location, assuming it gets there, isn't an easy place to get to for humans (remember, it's 4 times farther away than the moon is, so much further than any human has ever been away from Earth before).
      It's energetically closer that Mars, and Starship is designed to go to Mars.

A repair to what is broken may not be possible in space (depends on what is broken).
JWST wasn't designed for in-space service like Hubble was.
      True. A careful analysis might determine that repair is impossible or highly likely to fail. If so the mission would not be mounted. The analysis should be done. Intelsat 603 was not designed for repair, but a repair process was designed and successfully implemented.

I am not advocating that a mission should be mounted. I am suggesting that a study should be funded as soon as possible if a failure occurs.

[LouScheffer]

Except the "discussion" ignores basically EVERYTHING that makes it improbable. It resets back to the start every couple days ignoring all the problems that were raised again. Its literally a couple people who are unhappy they are told its not possible just saying the same stuff over and over ad naseum.

OK, to improve the discussion, please state WHAT makes it improbable, and WHY the solutions proposed here cannot work.

Thank you for this list.  I'll discuss each objection in turn:

Starship won't be ready in time for a mission to repair a problem with deployment.  No other spacecraft will either.

Absolutely true.  A deployment failure is doom for the mission.  The missions being discussed here are life extension, assuming Webb works as designed, and the main problem is that it is running out of fuel.  Starship is not needed for for a mission like this; the servicing spacecraft can be launched just like JWST itself.  A recoverable Falcon 9 can put about 3300kg to L2; commercially available life extension vehicles mass less than 2900 kg.  Also, the running-out-of-fuel scenario gives several years of warning - enough to construct a JWST specific vehicle, as will be required.

JWST may not be approachable due to limitations on loads on the sun shade.

Needs detailed analysis, but controlled approach appears possible.  Only low relative speeds are needed, and thrusters of well under a Newton will suffice.  Assuming the thruster is designed with a diffuse exhaust (hurts efficiency, but not a concern here) this should put very survivable forces on the subshield.

JWST may not be approachable due to contamination from the visiting vehicle.

If the visiting vehicle uses cold-gas thrusters with helium, there should be no contamination problems.  Easier solutions may be possible as the subshield also shields the optics, but cold helium thrusters should work if nothing else does.

JWST's location, assuming it gets there, isn't an easy place to get to for humans (remember, it's 4 times farther away than the moon is, so much further than any human has ever been away from Earth before).

True, but why would you want humans?  The life extension already commercially available for comsats does not use humans.  It approaches, clamps on, then assumes attitude control.  These are all relatively simple tasks that do not require human presence.

A repair to what is broken may not be possible in space (depends on what is broken).

True, but a life extension mission looks very possible.

JWST wasn't designed for in-space service like Hubble was.

Neither were the comsats that are the current customers of life extension missions.  To my knowledge, MEV-1 and MEV-2 simply approach and clamp on to various sturdy points (such as the engine bell) that are guaranteed to have capable load paths for satellite maneuvering.  Webb has such locations, with two main maneuvering engines on the spacecraft body.

[Lee Jay]

JWST may not be approachable due to limitations on loads on the sun shade.

Needs detailed analysis, but controlled approach appears possible.  Only low relative speeds are needed, and thrusters of well under a Newton will suffice.  Assuming the thruster is designed with a diffuse exhaust (hurts efficiency, but not a concern here) this should put very survivable forces on the subshield.

Really? Show your work.  That "detailed analysis" you mentioned.

[su27k]

Some thoughts:
1. Why would JWST be lost if it fails during deployment? Why can't it be put into a safe state, waiting a few years for a servicing mission? Note Hubble waited 3.5 years for its first serving mission.
2. If a servicing spacecraft will be permanently docked to JWST similar to Northrop Grumman's MEV, how feasible it is for the servicing vehicle to bring its own sunshade (a more sturdy one hopefully, using the larger mass margin provided by Starship) to replace the existing one in case the existing one was torn or just failed to deploy? Note Skylab 2 mission brought a replacement sunshade to fix Skylab, so it's not unprecedented either.

[LouScheffer]

JWST may not be approachable due to limitations on loads on the sun shade.

Needs detailed analysis, but controlled approach appears possible.  Only low relative speeds are needed, and thrusters of well under a Newton will suffice.  Assuming the thruster is designed with a diffuse exhaust (hurts efficiency, but not a concern here) this should put very survivable forces on the subshield.

Really? Show your work.  That "detailed analysis" you mentioned.

OK.  Let's model a patch of the sunshield as a 1 meter square, constrained on all edges (to account for stresses being concentrated at corners). Assume the thruster impingement creates a force of 10N/m^2 (this should be quite conservative).  We know the membrane is 50u thick Kapton.
From Dupont, we know the tensile modulus of Kapton is 2.48 x 10^9 Pascal.

Then using the "Stress Analysis Manual," Air Force Flight Dynamics Laboratory, October 1986, section 7.5.3, we can find the deflection and stress on the membrane.  Here is the calculation in Python:

n1 = 0.35  # Coefficients for a square panel
n6 = 0.35
p = 10     # Pressure of 10 N/m^2
E = 2.48e9 # From Dupont Kapton spec
t = 50e-6  # From Webb description
a = 1      # Assumed membrane panel size (meters)
print(f"deflection (meters) = {n1*a*pow(p*a/(E*t), 1/3):5.3f}" )
print(f"stress  (Mpa) = {n6*pow(p**2*E*(a/t)**2, 1/3)/1e6:5.3f}" )

When we run this we get:

deflection (meters) = 0.015
stress  (Mpa) = 1.620

We compare this to the allowable stress of Kapton of 234 MPa and conclude we are in no danger of rupturing the membrane.  We can re-run this with a 7 meter square (not realistic, you would not get this much pressure over such a large area), and get:

deflection (meters) = 0.202
stress  (Mpa) = 5.929

Still well under the strength of the Kapton film.

So overall, the force of a small thruster should not rupture the sunshade.

[Lee Jay]

JWST may not be approachable due to limitations on loads on the sun shade.

Needs detailed analysis, but controlled approach appears possible.  Only low relative speeds are needed, and thrusters of well under a Newton will suffice.  Assuming the thruster is designed with a diffuse exhaust (hurts efficiency, but not a concern here) this should put very survivable forces on the subshield.

Really? Show your work.  That "detailed analysis" you mentioned.

OK.  Let's model a patch of the sunshield as a 1 meter square, constrained on all edges (to account for stresses being concentrated at corners).

I think the edge constraint is wrong. The edges are unconstrained and the resulting analysis is complex for two reasons. First, the resulting system is non-linear (wrinkles can and will form). Second, the impingement isn't steady, it's dynamic (the plume isn't steady and there will be flow over the edges).  If I'm right, your numbers are wrong by orders of magnitude.

[edzieba]

Taking the Gordian option: 'damn the torpedoes sunshield, full speed ahead!'. Send a vehicle (Starship or otherwise) to L2 with sufficient Delta-V to haul JWST back to an Earth orbit (or another one more conducive to a subsequent manned or real-time-remote-controlled servicing mission). Assume the sunshield will be torn to shreds during rendezvous and capture and will need to be replaced later during servicing. Assume JWST and its instruments and structure will heat up to unacceptable temperatures and assume they will need to go through recomissioning later (along with any new instruments installed).
The major stumbling block - beyond a vehicle with sufficient delta-V to shuttle JWST around, and cost/benefit of the dual mission architecture - is mirror and instrument contamination. A copious inert cold-gas supply for use during rendezvous minimises reaction product contamination, and the subsequent heating aids in boiling of any volatiles, but servicing (and especially any interaction that releases particulates like having to go poking around in the instrument section) is going to be the hard part whilst avoiding contaminating the optics and instruments and rendering the servicing pointless. A vacuum is not automatically a cleanroom especially once you start generating local contaminants.
If a clean handling system ends up of similar complexity to design, test, and build as a new telescope, a servicing mission is not an ideal option vs. a follow-up telescope unless there is some time-critical task it is needed for (it's a scientific instrument, so almost certainly not).

[LouScheffer]

JWST may not be approachable due to limitations on loads on the sun shade.

OK.  Let's model a patch of the sunshield as a 1 meter square, constrained on all edges (to account for stresses being concentrated at corners).

I think the edge constraint is wrong. The edges are unconstrained and the resulting analysis is complex for two reasons. First, the resulting system is non-linear (wrinkles can and will form). Second, the impingement isn't steady, it's dynamic (the plume isn't steady and there will be flow over the edges).  If I'm right, your numbers are wrong by orders of magnitude.

I agree an analysis with the real geometry and real constraints would be needed before any mission.

That said, a lack of edge constraints in general reduces forces, as under load,  the edges move in rather than the plastic stretching.  I think wrinkles are unlikely under small forces, as the sunshield is deployed under tension.  Also the sunshield is designed to withstand dynamic forces.  When it's sitting on the launch pad, there is atmospheric pressure (about 100,000 N/m^2) on both sides of each piece of membrane.   During the first few minutes of launch this pressure is reduced to zero.  The air will not escape equally fast from all the pockets of the folded sunscreen, and so induce dynamic forces.  If the escape rate is different by even 0.1% or so, the dynamic forces will exceed the dynamic forces induced by a small thruster.

Many people think of the sunscreen as being made of some enormously fragile material, but it's not.  The typical space blanket you might carry while camping is 1 mil (25 micron) mylar.  The sunshade is 2 mil (50 micron) Kapton, and Kapton is stronger than mylar.  So yes it's a giant pain to unfold it without snags or tears, but once it's unfolded it should be quite robust.

[Jim]

OK.  Let's model a patch of the sunshield as a 1 meter square, constrained on all edges (to account for stresses being concentrated at corners). Assume the thruster impingement creates a force of 10N/m^2 (this should be quite conservative). 

This just over ran the reaction wheels

[LouScheffer]

OK.  Let's model a patch of the sunshield as a 1 meter square, constrained on all edges (to account for stresses being concentrated at corners). Assume the thruster impingement creates a force of 10N/m^2 (this should be quite conservative). 

This just over ran the reaction wheels

This is certainly a concern.  The total momentum storage of Webb is about 40 Nms, so a 1N thruster impinging 2 meters from the axis would saturate the wheels within 20 seconds.

To avoid this, you would want to approach along the axis, and have symmetrical thrusters.  If symmetry can be maintained within 5% (a typical value) then you have 20 times as long before you saturate the wheels.  This should be more than enough.  A 1N thruster, acting on a 3000Kg servicing spacecraft,  could stop it from a 1 cm/sec approach velocity in 30 seconds.

[deadman1204]

Except the "discussion" ignores basically EVERYTHING that makes it improbable. It resets back to the start every couple days ignoring all the problems that were raised again. Its literally a couple people who are unhappy they are told its not possible just saying the same stuff over and over ad naseum.

OK, to improve the discussion, please state WHAT makes it improbable, and WHY the solutions proposed here cannot work.  If you can do so with numbers, or references to documents, that's even better.  That's the point of this discussion, to look at the obstacles and see if any workarounds or solutions can avoid them.   A statements of "it can't be done", without reasoning and (better yet) numbers, is not helpful here.

Please read basically the entire thread before this point, PLUS the jwst thread this branched off of. There are MANY MANY descriptions about the problems.

[Barley]

I don't know the electrical system on Webb, but I've designed many control systems and none of them had the capability to externalize the control loop to the communications system with the outside world.  All the control stuff (data from sensors, data and power sent to actuators) was internal and the external communications didn't include the ability to integrate sensors or actuators into that stream.

I've worked on many control systems and all of them had the ability to externalize control loops.  Very common to see vehicles driving around the lab being controlled by an external laptop through a serial port, USB port or Bluetooth.

When a control-system failure results in a multi-million dollar machine crumbling to the ground, you generally don't do that.  I can unplug my HMI and the system stays running.

If you are trying to rescue or life extend a non-functional Webb, it's not a multi-billion dollar machine, it's a zero dollar piece of space junk.

NASA has a history of reprogramming space probes in ways you would not do on the ground, where the alternative is
loss of mission.  For example, deep sleep mode on Opportunity was a work around for broken heater switch.

[LouScheffer]

Thinking about this more, it seems quite plausible to dock with Webb without ever firing any thrusters in its direction.  For example, you can set up rendezvous 100 meters away.  The thrusters in the Webb direction can be canted 45^o from the Webb, so their thrust will miss Webb by a large distance.  The shuttle used a similar strategy when approaching ISS.

Then start closing on Webb at about 3 cm/sec (about the shuttle speed when docking with ISS).  Keep aligned with the target point (if needed) by using side thrusters only.  It will take about an hour to close in.

When you get close, extend a springy apparatus (perhaps modeled on the Shuttle ODS below)  to contact Webb.  I'd suggest contacting the main engines - since these are 10 N engines, 10 N of force applied here will cause no mechanical problems for Webb.  Applying 10N of force will decelerate the 3000 Kg life extension craft at  (10/3000) m/s.  This will stop it in about 9 seconds.   During this time it will move about 1/2(10/3000)9^2 = 13.5 cm closer.  The docking apparatus must allow for this much travel.

At the end of this, the two spacecraft are at rest compared to each other, and can be hard docked.

[AstroWare]

I know this conversation is specifically about servicing missions...

But if the problem is low fuel, and the consequences of low fuel are inability to desaturate momentum, are there other ways to do that?

Specifically, we have a giant solar sail (and a trim tab too). Could the observatory desaturate momentum by specifically orienting itself in such a way that the solar pressure would induce a torque that could be used to offload the wheels?

(In the future, could a JWST successor be designed such that there are no limiting consumables?)

Sent from my Pixel 5a using Tapatalk

[LouScheffer]

I know this conversation is specifically about servicing missions...

But if the problem is low fuel, and the consequences of low fuel are inability to desaturate momentum, are there other ways to do that?

Specifically, we have a giant solar sail (and a trim tab too). Could the observatory desaturate momentum by specifically orienting itself in such a way that the solar pressure would induce a torque that could be used to offload the wheels?

(In the future, could a JWST successor be designed such that there are no limiting consumables?)

I think this could work in pitch and yaw.  It's not obvious to me how this would help cancel any momentum built up around the anti-sunward axis (though it's also not obvious why momentum would build up around this axis either).

If you simply paired each observation with an opposite observation, this would only lose a factor of 2 in efficiency.  Much better than no observing at all.  And I suspect there are so many candidates for observations that you could almost always find one that would help unload the wheels.  Maybe not the best one science wise, but better than no observation at all.

With a slightly more articulated flap, I see no reason, in principal, that you could not (slowly) keep the wheels unloaded without using thrusters.  Hubble accomplishes this by acting against the local magnetic field, but the field is too weak at L2.

[AstroWare]

I know this conversation is specifically about servicing missions...

But if the problem is low fuel, and the consequences of low fuel are inability to desaturate momentum, are there other ways to do that?

Specifically, we have a giant solar sail (and a trim tab too). Could the observatory desaturate momentum by specifically orienting itself in such a way that the solar pressure would induce a torque that could be used to offload the wheels?

(In the future, could a JWST successor be designed such that there are no limiting consumables?)

I think this could work in pitch and yaw.  It's not obvious to me how this would help cancel any momentum built up around the anti-sunward axis (though it's also not obvious why momentum would build up around this axis either).

If you simply paired each observation with an opposite observation, this would only lose a factor of 2 in efficiency.  Much better than no observing at all.  And I suspect there are so many candidates for observations that you could almost always find one that would help unload the wheels.  Maybe not the best one science wise, but better than no observation at all.

With a slightly more articulated flap, I see no reason, in principal, that you could not (slowly) keep the wheels unloaded without using thrusters.  Hubble accomplishes this by acting against the local magnetic field, but the field is too weak at L2.

This site is full of interesting pages. Looks like they are already planning to use target selection to minimize total momentum gain during observation periods.

"Momentum changes can be managed at some level by the way a sequence of observations is planned; this is done by observing at an orientation that builds momentum in a particular reaction wheel, followed by an observation at an orientation that removes momentum from that wheel."

https://jwst-docs.stsci.edu/jwst-observatory-hardware/jwst-momentum-management

Also interesting that desaturation firing phases are required every couple weeks. Orbital maintenance firings are required every few months.

(Also the trim flap is fixed position. I didn't mean to imply otherwise, just that it adds to the total solar 'drag')

Sent from my Pixel 5a using Tapatalk

[su27k]

https://twitter.com/marinakoren/status/1474367236244750345

Unlike Hubble, Webb isn't designed to be fixed by astronauts. But it can be refueled robotically. Zurbuchen says that "once this telescope is deployed, I'm going to put all the effort towards developing that technology, and so within the 10-year lifespan, we can go refuel it."


A few days ago I asked Bill Ochs, JWST's project manager at NASA, what he would say if Elon Musk offered to try to refuel JWST someday, which would be a very Musk thing to say. Ochs said, "Yeah, go for it."

[su27k]

https://twitter.com/wingod/status/1474522449911840769

I was around during some of the debates about this.  Dr. John Grunsfeld had Zurbuchen's job then and tried to get a grappling fixture added.  He was vociferously opposed, and the science community when JWST was designed did not want crew near it.


The science community hated that Hubble was astronaut upgradable and many of them hated the servicing missions.  There is a huge gulf between many in the science community and human spaceflight.

[Star One]

https://twitter.com/wingod/status/1474522449911840769

I was around during some of the debates about this.  Dr. John Grunsfeld had Zurbuchen's job then and tried to get a grappling fixture added.  He was vociferously opposed, and the science community when JWST was designed did not want crew near it.


The science community hated that Hubble was astronaut upgradable and many of them hated the servicing missions.  There is a huge gulf between many in the science community and human spaceflight.

Well that’s disappointing to hear. It’s not something I’ve seen commented on before and sounds from a lay persons prospective hugely un-constructive.

[Yiosie]

Incidentally, the AP article on the launch has this corroborating tidbit:

Space telescope launched on daring quest to behold 1st stars

NASA is shooting for 10 years of operational life from Webb. Engineers deliberately left the fuel tank accessible for a top-off by visiting spacecraft, if and when such technology becomes available.

[su27k]

Q&A: NASA Administrator Bill Nelson talks big moments of 2021 and what's next in 2022

FLORIDA TODAY: If everything goes well with Webb's incredibly complex deployment process, do you see continued participation from the public and Congress when it comes to future space telescopes? We saw something similar when Hubble came online and delivered the riveting Hubble Deep Field image with thousands of galaxies.

Nelson: Yes, but mind you, this thing has a design life of up to 10 years. But we are also developing the capability of on-orbit servicing. That includes refueling. We have the capability in the next 10 years, before Webb runs out of fuel, to go up there and refuel. So instead of a 10-year life, it could continue to give us information on and on just like Hubble has.

[tibber]

Like so many things in life, the answer to the original question is a mix of yes and not likely now.

Yes, JWST was designed to be serviceable robotically, specifically to refuel.
Not likely now to be visited by a human service team to service or repair. Surely at some point we will be more than capable of visiting JWST...

But would we choose to? As described in this thread, there would be some serious cost/benefit analysis. Replacing JWST would not cost $10 billion in 2000 dollars, much of the original cost was the R&D and engineering that was created for the first one. For instance, we wouldn't need to completely redesign the actuators all over again.

Thankfully the deployments have all been successful. Today the primary mirror is all one unit with the wings unfolded. JWST is considered fully deployed.

Next the mirrors are unstowed and aligned, likely over the next couple of days.

Cheers,
Tom

[MattMason]

Except the "discussion" ignores basically EVERYTHING that makes it improbable. It resets back to the start every couple days ignoring all the problems that were raised again. Its literally a couple people who are unhappy they are told its not possible just saying the same stuff over and over ad naseum.

OK, to improve the discussion, please state WHAT makes it improbable, and WHY the solutions proposed here cannot work.

Starship won't be ready in time for a mission to repair a problem with deployment.
No other spacecraft will either.
JWST may not be approachable due to limitations on loads on the sun shade.
JWST may not be approachable due to contamination from the visiting vehicle.
JWST's location, assuming it gets there, isn't an easy place to get to for humans (remember, it's 4 times farther away than the moon is, so much further than any human has ever been away from Earth before).
A repair to what is broken may not be possible in space (depends on what is broken).
JWST wasn't designed for in-space service like Hubble was.

Now that JWST is fully deployed, this thread's discussion is thankfully academic.

But I wanted to note one point.

Any failure that would support any kind of servicing mission would be under the assumption that JWST's optic systems were able to keep its orientation pointed away from the sun before such a mission arrived.

As noted in launch coverage, JWST was deliberately launched with less velocity so it would not overshoot its L2 point. It could not rotate itself to slow down or it would compromise its optics from solar exposure by overheating and end its mission.

Through deployment or spacecraft bus failure, a servicing mission will be pointless if the telescope's optics can't be preserved. Those instruments are way more complicated than any servicing mission could repair.

[Jorge]

A space.com story in 2007 reported that JWST would have a passive docking ring for Orion. Don't know if they followed through on that, though. There are no updates to this story. The Orion design at the time used the LIDS docking system, which is not compatible with the NDS used now by Orion and Starliner, or the SpaceX docking system used by Dragon.

https://www.space.com/3833-nasa-adds-docking-capability-space-observatory.html

[arachnitect]

A space.com story in 2007 reported that JWST would have a passive docking ring for Orion. Don't know if they followed through on that, though. There are no updates to this story. The Orion design at the time used the LIDS docking system, which is not compatible with the NDS used now by Orion and Starliner, or the SpaceX docking system used by Dragon.

https://www.space.com/3833-nasa-adds-docking-capability-space-observatory.html

There is no docking adapter or grapple fixture on JWST

[Bob Shaw]

To dock with JWST no docking adapter is required. There have been several demonstrations of dockings by means of 'stingers' inserted into rocket nozzles aboard semi-defunct communications satellites. Adding a support module in GEO is already state of the art.

[deadman1204]

With NASA saying there are up to 20 years of fuel onboard web, I think that also obviates the need for a servicing mission.

[Lee Jay]

With NASA saying there are up to 20 years of fuel onboard web, I think that also obviates the need for a servicing mission.

If everything works and stays working.

[deltaV]

With NASA saying there are up to 20 years of fuel onboard web, I think that also obviates the need for a servicing mission.

NASA's previous 11-digit-dollar space telescope (Hubble) has lasted for 31+ years. So a servicing mission in ~2040 to refill JWST's propellant tanks seems plausible.

[Jim]

With NASA saying there are up to 20 years of fuel onboard web, I think that also obviates the need for a servicing mission.

NASA's previous 11-digit-dollar space telescope (Hubble) has lasted for 31+ years. So a servicing mission in ~2040 to refill JWST's propellant tanks seems plausible.

Bad logic.  HST lasted because it was serviced.

[deltaV]

The Chandra X-ray Observatory has been active for 22 years without any servicing (https://en.wikipedia.org/wiki/Chandra_X-ray_Observatory). I'm not saying that a refueling mission is probable, just that it's plausible.

[deadman1204]

With NASA saying there are up to 20 years of fuel onboard web, I think that also obviates the need for a servicing mission.

NASA's previous 11-digit-dollar space telescope (Hubble) has lasted for 31+ years. So a servicing mission in ~2040 to refill JWST's propellant tanks seems plausible.

One of these was designed for servicing - to have instruments changed and other stuff. The other simply wasn't....

[maxtout]

Astroscale, who had their own demonstrator for servicing OOS satellites in LEO, bought IP and assets for a previous venture called Space Drone. This was being developed in a joint partnership between a UK and an Israeli company, the former being around since 2013 and the deal signed 2018.
The sale of Space Drone was in 2020.

The reason this is interesting is because the main idea behind Space Drone is to use its manipulators to grapple payload rings (spacecraft separation rings) for docking.

This allows you to grapple OOS spacecraft who do not have a rocket nozzle available in that position that MEV and many others require.
With multiple arms instead of just one, which most solutions feature (DARPA's Orbital Express / RSGS), this makes it a much more stable solution.

JWST falls into that position of not having a centralized rocket motor nozzle to launch a stinger down it, and also does not feature a prominent marman ring which is often used as a grapple. 
Bur it does have a payload ring, bolted on to the bus cone as part of the structure.
The inner ring, aside from having the two small thruster nozzles to one side, also features absorption and reflective tile covered radiators and the ring is similarly tile covered itself.

From concept work it seems that Space Drone grappled on the outer rim edge of the spacecraft separation ring and a variation of this would be most useful. Anything beyond that of course is another matter.

Although i know of the position of the fill/drain valves it is very hard to see them in most photographs of the bus.
A robotic system at the current level would similarly find it difficult I suspect, although they have been experimenting on this for many years. .

[Jim]

The payload ring is a Marman ring.

[tibber]

The payload ring is a Marman ring.

Thanks.

Is it held away from the rest of the bus by standoffs or something that would give enough clearance for an arm to grab the ring?
I guess I should also ask if the ring is strong enough for such a grab?

Cheers,
Tom

[Jim]

The payload ring is a Marman ring.

Thanks.

Is it held away from the rest of the bus by standoffs or something that would give enough clearance for an arm to grab the ring?
I guess I should also ask if the ring is strong enough for such a grab?

Cheers,
Tom

it connected the spacecraft to the launch vehicle

[maxtout]

I see marman ring, spacecraft separation ring and payload adapter used interchangeably for the same collection of hardware.
Same goes for the clamp.

In this context, most material stated payload ring and adapter and clamp for JWST.
The guideline for the Marman Ring standard was substantially different in profile when compared to JWST so in most cases I leave it at payload ring.

Is it held away from the rest of the bus by standoffs or something that would give enough clearance for an arm to grab the ring?

https://svs.gsfc.nasa.gov/14052
Shows that it is not proud, and doesn't have to be for its job.
JWST's complication is that there are boxes covered in OSR (as is the ring itself) arrayed around the inside of the ring, so if you 'just' grabbed it, you would damage those parts.

For the way Space Drone seemed to indicate (more delicate than most current grabbers that also grip both sides of the ring profile), yes it is, which is why I mentioned it.
As it is, other existing grabbers have been designed for more prominent ring profiles.

I guess I should also ask if the ring is strong enough for such a grab?

forged rolled aluminium, yes it is strong enough, it has to be when mounted on the launcher, supporting the payload and its connection.

[tibber]

The payload ring is a Marman ring.

Thanks.

Is it held away from the rest of the bus by standoffs or something that would give enough clearance for an arm to grab the ring?
I guess I should also ask if the ring is strong enough for such a grab?

Cheers,
Tom

it connected the spacecraft to the launch vehicle

Well, yeah.  That was assumed as part of the definition.

What I'm asking is the ring so closely attached to the space craft that a drone would be unlikely to have room to grab onto?
The second question related to the strength of the ring for the drone to grab and then connect the two together? In the launching position the whole ring would share in the load, which I presume is mostly pushing toward the spacecraft, whereas a grab would be one or two attachments subject to (I presume) vastly different force vectors.

Of course, I also expect any grab action would be programmed to be a gentle as possible so Webb isn't pushed significantly.

Cheers,
Tom

[maxtout]

The telescope backbone is connected to the core inside of the bus.

The bus is visibly square, but inside it is actually a cone. So it is very strong for the role it serves.

A  graphite-epoxy composite cone that the payload ring is bolted on to.

[tibber]

...

https://svs.gsfc.nasa.gov/14052
Shows that it is not proud, and doesn't have to be for its job.
JWST's complication is that there are boxes covered in OSR (as is the ring itself) arrayed around the inside of the ring, so if you 'just' grabbed it, you would damage those parts.

...

Thanks for the link to the videos! Very helpful.

And for your explanations.

Cheers,
Tom

[LouScheffer]

Although i know of the position of the fill/drain valves it is very hard to see them in most photographs of the bus.
A robotic system at the current level would similarly find it difficult I suspect, although they have been experimenting on this for many years.

According to this diagram, the drain and fill valves project out of the spacecraft bus, supposedly to make any hypothetical refueling easier.  So they should not be hard to spot.

[Jim]

They are covered in MLI

[maxtout]

They are covered in MLI

Precisely. Anyone have a good photo of it?

[JulesVerneATV]

robotic support repair, maintenance and rescue of older spacecraft

NASA 'Swift' but with the private sector getting involved maybe relevant for Hubble and future Webb

Private mission to save NASA space telescope will launch in 2026 on a rocket dropped from a plane
https://www.space.com/space-exploration/missions/katalyst-space-technologies-swift-observatory-rescue-mission-pegasus-rocket


Spacecraft to Boost NASA Telescope's Orbit for the First Time
https://www.extremetech.com/aerospace/private-spacecraft-to-boost-nasa-telescopes-orbit-for-the-first-time
It's another example of NASA relying more on private enterprise for its orbital infrastructure and maintenance.