Potential servicing missions for the Webb

[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.