Webb telescope launch date slips again

We "don't have a lot of reserve" left.

Read the whole story

 

[Imbrium]

I will be very surprised if there isn't some USN assets in place to keep an eye on the cargo ship.

It is probably not really going to cost anything, cos if a Destroyer at sea cost X dollars daily, it doesnt matter where at sea it is at, since it's still going to cost that much money.

And I don't think USN has all it's current ships on "must do active duty" whereby they can't just redeploy a ship at a different location for a couple of weeks or so without it being a security issue elsewhere.

Much more likely would be a USCS cutter to escort it. If it needs anything, it would be protection against non-state pirates, not a state sanctioned and support seizure. Though in terms of size and crew, the WMECs are effectively the same size as a USNS frigate, though somewhat less capable in armament.

I don't think a pirate ship would mess with a USCS cutter with a 76mm deck gun, some 50s and a Dolphin or Jayhawk with a door gun.

Or honestly an armed US Coast Guard team or USMC team. That generally wouldn't be a concern even in pirate waters for the most part, but because of national restrictions, most ships don't sail with firearms on board or an armed security team. Less a cost prohibitive issue and some ships do sail with armed security details on them.

Most pirates are sailing real warships of any stripe. They are a few fast boats with AK-47s, RPKs and RPG-7. Which isn't going to seriously sink any real cargo ship, but can do some damage and of course if they can board...

But a security team with rifles and a GPMG or two is going to be some MASSIVE dissuasion for the pirates life choices. I might be wrong, but I am not aware of any civilian ships successfully seized by pirates in any waters that did have an armed security team onboard. And several instances where such ships successfully repelled pirates.

A stray bullet hitting the JWST would be a total disaster so a on-board security team is not a good idea. Ideally you would want to intercept would be pirates as far away from the cargo-ship as possible.

The seven Iranian fast missile boats being shipped to Venezuela on an Iranian ship right now could cause a big enough problem that something more substantial than a CG cutter might be appropriate. To be clear, I don't think it is likely that Venezuela or Iran would be stupid enough to attack the JWST in transit, but then again, they may figure that destroying it wouldn't be important enough to the US general public to elicit a call for war, or even serious retaliation.

When the shipment occurs, I imagine the USN will know where every one of those boats is located, and will make sure none of them enter weapons range. Fortunately, they carry fairly old short range ASMs, about 18 nm, so it should be a fairly easy task to keep them outside that range.

 

[azazel1024]

I will be very surprised if there isn't some USN assets in place to keep an eye on the cargo ship.

It is probably not really going to cost anything, cos if a Destroyer at sea cost X dollars daily, it doesnt matter where at sea it is at, since it's still going to cost that much money.

And I don't think USN has all it's current ships on "must do active duty" whereby they can't just redeploy a ship at a different location for a couple of weeks or so without it being a security issue elsewhere.

Much more likely would be a USCS cutter to escort it. If it needs anything, it would be protection against non-state pirates, not a state sanctioned and support seizure. Though in terms of size and crew, the WMECs are effectively the same size as a USNS frigate, though somewhat less capable in armament.

I don't think a pirate ship would mess with a USCS cutter with a 76mm deck gun, some 50s and a Dolphin or Jayhawk with a door gun.

Or honestly an armed US Coast Guard team or USMC team. That generally wouldn't be a concern even in pirate waters for the most part, but because of national restrictions, most ships don't sail with firearms on board or an armed security team. Less a cost prohibitive issue and some ships do sail with armed security details on them.

Most pirates are sailing real warships of any stripe. They are a few fast boats with AK-47s, RPKs and RPG-7. Which isn't going to seriously sink any real cargo ship, but can do some damage and of course if they can board...

But a security team with rifles and a GPMG or two is going to be some MASSIVE dissuasion for the pirates life choices. I might be wrong, but I am not aware of any civilian ships successfully seized by pirates in any waters that did have an armed security team onboard. And several instances where such ships successfully repelled pirates.

A stray bullet hitting the JWST would be a total disaster so a on-board security team is not a good idea. Ideally you would want to intercept would be pirates as far away from the cargo-ship as possible.

Sure, of course. That said, cargo ships are relatively bullet proof against what pirates are typically carrying (though not particularly RPG proof). So unless it was stored on deck or against the outer hall...

Mostly just pointing out that "pirate" isn't a serious threat to even just a few guys with guns on the ship. Out of an abundance of caution, a coast guard cutter should be able to more than handle any escort duties.

 

[azazel1024]

I will be very surprised if there isn't some USN assets in place to keep an eye on the cargo ship.

It is probably not really going to cost anything, cos if a Destroyer at sea cost X dollars daily, it doesnt matter where at sea it is at, since it's still going to cost that much money.

And I don't think USN has all it's current ships on "must do active duty" whereby they can't just redeploy a ship at a different location for a couple of weeks or so without it being a security issue elsewhere.

Much more likely would be a USCS cutter to escort it. If it needs anything, it would be protection against non-state pirates, not a state sanctioned and support seizure. Though in terms of size and crew, the WMECs are effectively the same size as a USNS frigate, though somewhat less capable in armament.

I don't think a pirate ship would mess with a USCS cutter with a 76mm deck gun, some 50s and a Dolphin or Jayhawk with a door gun.

Or honestly an armed US Coast Guard team or USMC team. That generally wouldn't be a concern even in pirate waters for the most part, but because of national restrictions, most ships don't sail with firearms on board or an armed security team. Less a cost prohibitive issue and some ships do sail with armed security details on them.

Most pirates are sailing real warships of any stripe. They are a few fast boats with AK-47s, RPKs and RPG-7. Which isn't going to seriously sink any real cargo ship, but can do some damage and of course if they can board...

But a security team with rifles and a GPMG or two is going to be some MASSIVE dissuasion for the pirates life choices. I might be wrong, but I am not aware of any civilian ships successfully seized by pirates in any waters that did have an armed security team onboard. And several instances where such ships successfully repelled pirates.

A stray bullet hitting the JWST would be a total disaster so a on-board security team is not a good idea. Ideally you would want to intercept would be pirates as far away from the cargo-ship as possible.

The seven Iranian fast missile boats being shipped to Venezuela on an Iranian ship right now could cause a big enough problem that something more substantial than a CG cutter might be appropriate. To be clear, I don't think it is likely that Venezuela or Iran would be stupid enough to attack the JWST in transit, but then again, they may figure that destroying it wouldn't be important enough to the US general public to elicit a call for war, or even serious retaliation.

When the shipment occurs, I imagine the USN will know where every one of those boats is located, and will make sure none of them enter weapons range. Fortunately, they carry fairly old short range ASMs, about 18 nm, so it should be a fairly easy task to keep them outside that range.

I guess that might be in their minds. I don't see how it wouldn't be an act of war as it would likely be shipped on an actual US flagged ship, probably with a US crew. Especially if being escorted and it was attacked, pretty sure the US government would consider it an act of war.

40-50% of the US wants to blot Iran off the map. Probably not a whole lot smaller number would love to invade Venezuela. I don't think either one attacking or hijacking a US flagged ship carrying a major NASA payload to a foreign country for launch would be a heavy lift for a casus belli. Certainly an easy enough reason to provoke a forced regime change in Venezuela that I don't even think the US would consider a real "war" (for example, invasion of Grenada).

 

[thohac]

I will be very surprised if there isn't some USN assets in place to keep an eye on the cargo ship.

It is probably not really going to cost anything, cos if a Destroyer at sea cost X dollars daily, it doesnt matter where at sea it is at, since it's still going to cost that much money.

And I don't think USN has all it's current ships on "must do active duty" whereby they can't just redeploy a ship at a different location for a couple of weeks or so without it being a security issue elsewhere.

Much more likely would be a USCS cutter to escort it. If it needs anything, it would be protection against non-state pirates, not a state sanctioned and support seizure. Though in terms of size and crew, the WMECs are effectively the same size as a USNS frigate, though somewhat less capable in armament.

I don't think a pirate ship would mess with a USCS cutter with a 76mm deck gun, some 50s and a Dolphin or Jayhawk with a door gun.

Or honestly an armed US Coast Guard team or USMC team. That generally wouldn't be a concern even in pirate waters for the most part, but because of national restrictions, most ships don't sail with firearms on board or an armed security team. Less a cost prohibitive issue and some ships do sail with armed security details on them.

Most pirates are sailing real warships of any stripe. They are a few fast boats with AK-47s, RPKs and RPG-7. Which isn't going to seriously sink any real cargo ship, but can do some damage and of course if they can board...

But a security team with rifles and a GPMG or two is going to be some MASSIVE dissuasion for the pirates life choices. I might be wrong, but I am not aware of any civilian ships successfully seized by pirates in any waters that did have an armed security team onboard. And several instances where such ships successfully repelled pirates.

A stray bullet hitting the JWST would be a total disaster so a on-board security team is not a good idea. Ideally you would want to intercept would be pirates as far away from the cargo-ship as possible.

The seven Iranian fast missile boats being shipped to Venezuela on an Iranian ship right now could cause a big enough problem that something more substantial than a CG cutter might be appropriate. To be clear, I don't think it is likely that Venezuela or Iran would be stupid enough to attack the JWST in transit, but then again, they may figure that destroying it wouldn't be important enough to the US general public to elicit a call for war, or even serious retaliation.

When the shipment occurs, I imagine the USN will know where every one of those boats is located, and will make sure none of them enter weapons range. Fortunately, they carry fairly old short range ASMs, about 18 nm, so it should be a fairly easy task to keep them outside that range.

Wars have started over far less then destroying something that symbolizes the technical achievements and pride of 20 nations. The furthest I can possibly imagine Iran would go, is to try and harass the cargo ship with a unsafe approach, the way it often does with ships entering the Persian Gulf but given the international and scientific nature of the JWST project, even that would crate far more trouble for Iran than it would be worth.

 

[thohac]

I will be very surprised if there isn't some USN assets in place to keep an eye on the cargo ship.

It is probably not really going to cost anything, cos if a Destroyer at sea cost X dollars daily, it doesnt matter where at sea it is at, since it's still going to cost that much money.

And I don't think USN has all it's current ships on "must do active duty" whereby they can't just redeploy a ship at a different location for a couple of weeks or so without it being a security issue elsewhere.

Much more likely would be a USCS cutter to escort it. If it needs anything, it would be protection against non-state pirates, not a state sanctioned and support seizure. Though in terms of size and crew, the WMECs are effectively the same size as a USNS frigate, though somewhat less capable in armament.

I don't think a pirate ship would mess with a USCS cutter with a 76mm deck gun, some 50s and a Dolphin or Jayhawk with a door gun.

Or honestly an armed US Coast Guard team or USMC team. That generally wouldn't be a concern even in pirate waters for the most part, but because of national restrictions, most ships don't sail with firearms on board or an armed security team. Less a cost prohibitive issue and some ships do sail with armed security details on them.

Most pirates are sailing real warships of any stripe. They are a few fast boats with AK-47s, RPKs and RPG-7. Which isn't going to seriously sink any real cargo ship, but can do some damage and of course if they can board...

But a security team with rifles and a GPMG or two is going to be some MASSIVE dissuasion for the pirates life choices. I might be wrong, but I am not aware of any civilian ships successfully seized by pirates in any waters that did have an armed security team onboard. And several instances where such ships successfully repelled pirates.

A stray bullet hitting the JWST would be a total disaster so a on-board security team is not a good idea. Ideally you would want to intercept would be pirates as far away from the cargo-ship as possible.

Sure, of course. That said, cargo ships are relatively bullet proof against what pirates are typically carrying (though not particularly RPG proof). So unless it was stored on deck or against the outer hall...

Mostly just pointing out that "pirate" isn't a serious threat to even just a few guys with guns on the ship. Out of an abundance of caution, a coast guard cutter should be able to more than handle any escort duties.

You have bureaucratic issues to deal with as well. Most ports simply will not allows ships with armed personnel to dock. A private cargo vessel would also not allow armed personnel because their insurance would drop them like a hot-potato.

 

[icarusKiD]

If it can survive the rigors of launch, how about the cargo bay of a C-5 Galaxy? Is there no airstrip at the ESA launch facility or something?

 

[icarusKiD]

Piracy? For something this expensive can't we get an escort??

If it can survive the rigors of launch, how about the cargo bay of a C-5 Galaxy? Is there no airstrip at the ESA launch facility or something?

 

[Bongle]

If it can survive the rigors of launch, how about the cargo bay of a C-5 Galaxy? Is there no airstrip at the ESA launch facility or something?

I guess the C-5 isn't big enough now that it is instrument + shield + spacecraft. Previously it has traveled the US in a C-5 for testing.

Here's more info from NASA: https://www.nasa.gov/feature/goddard/20 ... -telescope

For testing, it rode around in STTARS, a specialized 75-ton container. But once the spacecraft and sunshield are attached, it had to be upgraded to super-STTARS with a larger-size exterior.

I wonder if it could fit in the AN-225 or one of Airbus's or Boeing's guppies, but I'm going to assume the people whose fulltime jobs are to transport this thing have thought of that.

 

[Lagrange]

At least the next one can skip the "unfold the mirror" step if it fits through the starship door.
Reuse the mirror tiles, put more of them, remove part of the fragile moving parts...

We learnt enough with this prototype, can we order 4 or 6 of the cost-reduced version ?

The unfolding the mirror part actually isn’t the hard part; the sun shield is far more challenging.

The general rule of thumb with projects at this scale is you can get two for 1.7x the cost of the first one. (See Mars rover recent mission costs, for instance). Economies of scale don’t really kick in dramatically until much higher build numbers. Much of the cost is in integration and test, not initial design, and that work simply gets twice as big almost-linearly if you’re building and testing two of something.

In this case, the cost-reduced version is the one that launches on a Falcon Heavy with a sunshield that's 3x the mass. That would be a boat-load cheaper to make and test.

If the sunshield is such a problem they should just use the telescope at night instead. That's what I do with mine

 

[Lagrange]

I can't help but feel that system engineering has lead Nasa astray.

If your plan is a giant reflextive mirror, you have a couple of test telescopes you could have launched as intermediary steps. Atlas has been available for this time and things like the reflective tiles or heat shield are things crying out to be tested in space.

If instead of a flagship mission, Nasa had spun up a programme to deliver telescopes with increasing capability with a 10/20 year objective of reaching JWST. We would have gotten here faster and Nasa would have developed a department with real institutional memory.

With a 30 year project to deliver it is doubtful lessons from the project are really absorbed and from an engineering, technology or even process persoective they likely no longer apply.

But like with SLS it feels a great deal of time has been lost to paralysis by analysis, money spent on testing components in pure isolation and then running paper based excercises that sre only as good as your model and often not linked to the real world.

I get the value of system engineering, but the discipline doesn't seem to have evolved since the 1960's and as projects become increasingly complex the view is to entrench even more into requirements analysis or traceability matrix's.

Gradual evolution of design was done with other space telescopes as well as spy satellites so it's bizarre that NASA didn't think that was the way to go with JWST.

Mind you, they built Hubble to be similar to the KH-11 to save time and money and then gave the contract to produce its mirror to PerkinElmer who had never built space-qualified optics even close to that size (their largest was the 0.5m aperture camera for KH-9) rather than to Kodak who had track record of making the optics for the KH-11 as well as dozens of 1.2m aperture optical systems for the KH-7 and KH-8 series of recon sats. Kodak made the spare mirror which now sits in the Smithsonian and is optically perfect.

The original pitch for JWST was misleading to the point of being almost fraudulent. How anyone could claim with a straight face that a vastly larger and more challenging design than Hubble which was significantly different from any previous space telescope or spy satellite, could be built for only $500M is beyond me.

 

[jaminb]

Guys. Guys. The answer is simple. We deliver JWST to French Guiana in November using point-to-point Starship.

 

[Jenab6]

Consider the possibility that the James Webb Space Telescope won't deploy and/or wouldn't function properly even if it did deploy. It is known that the JWST suffered a number of mishandlings by inexperienced technicians at Northrop Grumman. Its propulsion system was damaged when someone used the wrong solvent to clean it. About seventy fasteners were improperly installed on the sun shield and fell off (some of them into the telescope's innards) when the instrument was moved. The program director did not (could not?) prevent these incidents. JWST is so far 14 years in delay and is over its original budget by a factor of twenty. We have gotten one excuse after another for more than a decade. This isn't your usual dose of incompetence. It is something more egregious. If JWST ever does launch, watch for who just happens to retire, switch jobs, or otherwise try to sneak away around that time.

 

[el_oscuro]

some quick websearching hasn't yielded much other than reddit crap,
and so I'm very seriously wondering about
the multiple comments over the years about how
once JWST is on station its "unmaintainable/unserviceable"

This is, presumably, by design given that HST was built to be deployed by shuttle,
and periodically visited by shuttle, and no one figured that a spacecraft capable
of getting to the Lagrange point would exist to go service JWST.

With new spaceflight capabilities coming online (Starship, even Orion if we want to believe
that SLS flies more than once) is JWST still "doomed" if the insanely complex,
nearly 200 step deployment process fails?

The obvious caveats that come to mind:
* money to fly "tbd" spacecraft to JWST at the lagrange point
* money to train astronauts to do whatever servicing is required
* money and time to develop whatever repair tools, systems are needed
* TBD spacecraft being able to station keep with JWST? (presumably no Canadarm grapple fixture anywhere on JWST
* spacecraft needs an airlock for cycling while repair crew goes in and out
* rad hardening for 'tbd' spacecraft, EVA suits because in 'deep space'

That's the first order list that comes to mind: but I still ask the question because
for the stake of just how much $$$ was spent on JWST, if deploy step
154 fails, and all the remote troubleshooting fails, does it really
just get thrown away ? ( sunk cost fallacy enters the rambling here too I suppose)


Does a, say, $150M repair mission to get the multi-billion dollar JWST back online
come into the conversation?

I've always wondered it they could do the deployment in LEO, then boost it to the desired orbit with ion engines once the deployment is complete. They could even have a Dragon capsule nearby with astronauts trained in its repair in orbit nearby during the deployment.

 

[JohnDeL]

some quick websearching hasn't yielded much other than reddit crap,
and so I'm very seriously wondering about
the multiple comments over the years about how
once JWST is on station its "unmaintainable/unserviceable"

This is, presumably, by design given that HST was built to be deployed by shuttle,
and periodically visited by shuttle, and no one figured that a spacecraft capable
of getting to the Lagrange point would exist to go service JWST.

With new spaceflight capabilities coming online (Starship, even Orion if we want to believe
that SLS flies more than once) is JWST still "doomed" if the insanely complex,
nearly 200 step deployment process fails?

The obvious caveats that come to mind:
* money to fly "tbd" spacecraft to JWST at the lagrange point
* money to train astronauts to do whatever servicing is required
* money and time to develop whatever repair tools, systems are needed
* TBD spacecraft being able to station keep with JWST? (presumably no Canadarm grapple fixture anywhere on JWST
* spacecraft needs an airlock for cycling while repair crew goes in and out
* rad hardening for 'tbd' spacecraft, EVA suits because in 'deep space'

That's the first order list that comes to mind: but I still ask the question because
for the stake of just how much $$$ was spent on JWST, if deploy step
154 fails, and all the remote troubleshooting fails, does it really
just get thrown away ? ( sunk cost fallacy enters the rambling here too I suppose)


Does a, say, $150M repair mission to get the multi-billion dollar JWST back online
come into the conversation?

I've always wondered it they could do the deployment in LEO, then boost it to the desired orbit with ion engines once the deployment is complete. They could even have a Dragon capsule nearby with astronauts trained in its repair in orbit nearby during the deployment.

That won't work because:
1) Deploying the telescope changes the center of mass, which means that it is much more difficult to lift to the LaGrangian point, and
2) The JWST has many, many parts that are glued together, which means that they simply cannot be fixed on-orbit.

 

[Wickwick]

some quick websearching hasn't yielded much other than reddit crap,
and so I'm very seriously wondering about
the multiple comments over the years about how
once JWST is on station its "unmaintainable/unserviceable"

This is, presumably, by design given that HST was built to be deployed by shuttle,
and periodically visited by shuttle, and no one figured that a spacecraft capable
of getting to the Lagrange point would exist to go service JWST.

With new spaceflight capabilities coming online (Starship, even Orion if we want to believe
that SLS flies more than once) is JWST still "doomed" if the insanely complex,
nearly 200 step deployment process fails?

The obvious caveats that come to mind:
* money to fly "tbd" spacecraft to JWST at the lagrange point
* money to train astronauts to do whatever servicing is required
* money and time to develop whatever repair tools, systems are needed
* TBD spacecraft being able to station keep with JWST? (presumably no Canadarm grapple fixture anywhere on JWST
* spacecraft needs an airlock for cycling while repair crew goes in and out
* rad hardening for 'tbd' spacecraft, EVA suits because in 'deep space'

That's the first order list that comes to mind: but I still ask the question because
for the stake of just how much $$$ was spent on JWST, if deploy step
154 fails, and all the remote troubleshooting fails, does it really
just get thrown away ? ( sunk cost fallacy enters the rambling here too I suppose)


Does a, say, $150M repair mission to get the multi-billion dollar JWST back online
come into the conversation?

I've always wondered it they could do the deployment in LEO, then boost it to the desired orbit with ion engines once the deployment is complete. They could even have a Dragon capsule nearby with astronauts trained in its repair in orbit nearby during the deployment.

That won't work because:
1) Deploying the telescope changes the center of mass, which means that it is much more difficult to lift to the LaGrangian point, and
2) The JWST has many, many parts that are glued together, which means that they simply cannot be fixed on-orbit.

No argument on (2). The telescope wasn't designed for repair so it can't be.

I'm not sure I follow on (1). Yes, the center of mass isn't located in the same place, but it's somewhere. No, the docking collar might not be in a straight line to the cg anymore, but one could apply the force elsewhere. You might not be able to accelerate as hard through such a secondary force path, but that doesn't make it any harder to lift to the Lagrange point, just slower.

 

[JohnDeL]

some quick websearching hasn't yielded much other than reddit crap,
and so I'm very seriously wondering about
the multiple comments over the years about how
once JWST is on station its "unmaintainable/unserviceable"

This is, presumably, by design given that HST was built to be deployed by shuttle,
and periodically visited by shuttle, and no one figured that a spacecraft capable
of getting to the Lagrange point would exist to go service JWST.

With new spaceflight capabilities coming online (Starship, even Orion if we want to believe
that SLS flies more than once) is JWST still "doomed" if the insanely complex,
nearly 200 step deployment process fails?

The obvious caveats that come to mind:
* money to fly "tbd" spacecraft to JWST at the lagrange point
* money to train astronauts to do whatever servicing is required
* money and time to develop whatever repair tools, systems are needed
* TBD spacecraft being able to station keep with JWST? (presumably no Canadarm grapple fixture anywhere on JWST
* spacecraft needs an airlock for cycling while repair crew goes in and out
* rad hardening for 'tbd' spacecraft, EVA suits because in 'deep space'

That's the first order list that comes to mind: but I still ask the question because
for the stake of just how much $$$ was spent on JWST, if deploy step
154 fails, and all the remote troubleshooting fails, does it really
just get thrown away ? ( sunk cost fallacy enters the rambling here too I suppose)


Does a, say, $150M repair mission to get the multi-billion dollar JWST back online
come into the conversation?

I've always wondered it they could do the deployment in LEO, then boost it to the desired orbit with ion engines once the deployment is complete. They could even have a Dragon capsule nearby with astronauts trained in its repair in orbit nearby during the deployment.

That won't work because:
1) Deploying the telescope changes the center of mass, which means that it is much more difficult to lift to the LaGrangian point, and
2) The JWST has many, many parts that are glued together, which means that they simply cannot be fixed on-orbit.

No argument on (2). The telescope wasn't designed for repair so it can't be.

I'm not sure I follow on (1). Yes, the center of mass isn't located in the same place, but it's somewhere. No, the docking collar might not be in a straight line to the cg anymore, but one could apply the force elsewhere. You might not be able to accelerate as hard through such a secondary force path, but that doesn't make it any harder to lift to the Lagrange point, just slower.

It makes it much more complicated and much, much riskier. Do you really want to add more opportunities for things to go wrong?

Any lateral shift in the CoM from where it is means that the rocket moving the JWST to L₂ will have to compensate by firing at an angle. This means that it will use more fuel, upsetting the mass balance once again. It also means that small errors run a significant chance of accumulating, leading to oscillations, leading to losing the telescope.

 

[Wickwick]

some quick websearching hasn't yielded much other than reddit crap,
and so I'm very seriously wondering about
the multiple comments over the years about how
once JWST is on station its "unmaintainable/unserviceable"

This is, presumably, by design given that HST was built to be deployed by shuttle,
and periodically visited by shuttle, and no one figured that a spacecraft capable
of getting to the Lagrange point would exist to go service JWST.

With new spaceflight capabilities coming online (Starship, even Orion if we want to believe
that SLS flies more than once) is JWST still "doomed" if the insanely complex,
nearly 200 step deployment process fails?

The obvious caveats that come to mind:
* money to fly "tbd" spacecraft to JWST at the lagrange point
* money to train astronauts to do whatever servicing is required
* money and time to develop whatever repair tools, systems are needed
* TBD spacecraft being able to station keep with JWST? (presumably no Canadarm grapple fixture anywhere on JWST
* spacecraft needs an airlock for cycling while repair crew goes in and out
* rad hardening for 'tbd' spacecraft, EVA suits because in 'deep space'

That's the first order list that comes to mind: but I still ask the question because
for the stake of just how much $$$ was spent on JWST, if deploy step
154 fails, and all the remote troubleshooting fails, does it really
just get thrown away ? ( sunk cost fallacy enters the rambling here too I suppose)


Does a, say, $150M repair mission to get the multi-billion dollar JWST back online
come into the conversation?

I've always wondered it they could do the deployment in LEO, then boost it to the desired orbit with ion engines once the deployment is complete. They could even have a Dragon capsule nearby with astronauts trained in its repair in orbit nearby during the deployment.

That won't work because:
1) Deploying the telescope changes the center of mass, which means that it is much more difficult to lift to the LaGrangian point, and
2) The JWST has many, many parts that are glued together, which means that they simply cannot be fixed on-orbit.

No argument on (2). The telescope wasn't designed for repair so it can't be.

I'm not sure I follow on (1). Yes, the center of mass isn't located in the same place, but it's somewhere. No, the docking collar might not be in a straight line to the cg anymore, but one could apply the force elsewhere. You might not be able to accelerate as hard through such a secondary force path, but that doesn't make it any harder to lift to the Lagrange point, just slower.

It makes it much more complicated and much, much riskier. Do you really want to add more opportunities for things to go wrong?

Any lateral shift in the CoM from where it is means that the rocket moving the JWST to L₂ will have to compensate by firing at an angle. This means that it will use more fuel, upsetting the mass balance once again. It also means that small errors run a significant chance of accumulating, leading to oscillations, leading to losing the telescope.

The question related to sending the telescope from LEO to the LaGrange point with an ion engine. So the concern about needing more fuel is a non-starter. It was a question about a completely different way of deploying the instrument. Obviously, the direct-to-location system launching on Ariane cannot do that.

I asked about risks and your answer is basically that it's riskier without explanation. What's shifting once the sunshade is deployed and the mirror is open and locked? Nothing is. There would be no movement of the cg to have to worry about. The amount of force that could be applied could be measured in single-digit Newtons if you're of a mind. I guess the only limit is how long you want to take and how much force the sun shade actually generates.

 

[brionl]

some quick websearching hasn't yielded much other than reddit crap,
and so I'm very seriously wondering about
the multiple comments over the years about how
once JWST is on station its "unmaintainable/unserviceable"

This is, presumably, by design given that HST was built to be deployed by shuttle,
and periodically visited by shuttle, and no one figured that a spacecraft capable
of getting to the Lagrange point would exist to go service JWST.

With new spaceflight capabilities coming online (Starship, even Orion if we want to believe
that SLS flies more than once) is JWST still "doomed" if the insanely complex,
nearly 200 step deployment process fails?

The obvious caveats that come to mind:
* money to fly "tbd" spacecraft to JWST at the lagrange point
* money to train astronauts to do whatever servicing is required
* money and time to develop whatever repair tools, systems are needed
* TBD spacecraft being able to station keep with JWST? (presumably no Canadarm grapple fixture anywhere on JWST
* spacecraft needs an airlock for cycling while repair crew goes in and out
* rad hardening for 'tbd' spacecraft, EVA suits because in 'deep space'

That's the first order list that comes to mind: but I still ask the question because
for the stake of just how much $$$ was spent on JWST, if deploy step
154 fails, and all the remote troubleshooting fails, does it really
just get thrown away ? ( sunk cost fallacy enters the rambling here too I suppose)


Does a, say, $150M repair mission to get the multi-billion dollar JWST back online
come into the conversation?

I've always wondered it they could do the deployment in LEO, then boost it to the desired orbit with ion engines once the deployment is complete. They could even have a Dragon capsule nearby with astronauts trained in its repair in orbit nearby during the deployment.

That won't work because:
1) Deploying the telescope changes the center of mass, which means that it is much more difficult to lift to the LaGrangian point, and
2) The JWST has many, many parts that are glued together, which means that they simply cannot be fixed on-orbit.

No argument on (2). The telescope wasn't designed for repair so it can't be.

I'm not sure I follow on (1). Yes, the center of mass isn't located in the same place, but it's somewhere. No, the docking collar might not be in a straight line to the cg anymore, but one could apply the force elsewhere. You might not be able to accelerate as hard through such a secondary force path, but that doesn't make it any harder to lift to the Lagrange point, just slower.

It makes it much more complicated and much, much riskier. Do you really want to add more opportunities for things to go wrong?

Any lateral shift in the CoM from where it is means that the rocket moving the JWST to L₂ will have to compensate by firing at an angle. This means that it will use more fuel, upsetting the mass balance once again. It also means that small errors run a significant chance of accumulating, leading to oscillations, leading to losing the telescope.

The question related to sending the telescope from LEO to the LaGrange point with an ion engine. So the concern about needing more fuel is a non-starter. It was a question about a completely different way of deploying the instrument. Obviously, the direct-to-location system launching on Ariane cannot do that.

I asked about risks and your answer is basically that it's riskier without explanation. What's shifting once the sunshade is deployed and the mirror is open and locked? Nothing is. There would be no movement of the cg to have to worry about. The amount of force that could be applied could be measured in single-digit Newtons if you're of a mind. I guess the only limit is how long you want to take and how much force the sun shade actually generates.

It's finally finished. They aren't going to make a major change at the last minute, just to please "Some Guy on the Internet™".

 

[Wickwick]

It's finally finished. They aren't going to make a major change at the last minute, just to please "Some Guy on the Internet™".

I don't think I was suggesting any such thing. The original question seemed, to my eye, to ask why the telescope couldn't have been designed for LEO check-out followed by a transfer to its operational spot. Such a decision was made long ago, but even then there were electric propulsion systems that could have been employed.

 

[Christopher James Huff]

some quick websearching hasn't yielded much other than reddit crap,
and so I'm very seriously wondering about
the multiple comments over the years about how
once JWST is on station its "unmaintainable/unserviceable"

This is, presumably, by design given that HST was built to be deployed by shuttle,
and periodically visited by shuttle, and no one figured that a spacecraft capable
of getting to the Lagrange point would exist to go service JWST.

With new spaceflight capabilities coming online (Starship, even Orion if we want to believe
that SLS flies more than once) is JWST still "doomed" if the insanely complex,
nearly 200 step deployment process fails?

The obvious caveats that come to mind:
* money to fly "tbd" spacecraft to JWST at the lagrange point
* money to train astronauts to do whatever servicing is required
* money and time to develop whatever repair tools, systems are needed
* TBD spacecraft being able to station keep with JWST? (presumably no Canadarm grapple fixture anywhere on JWST
* spacecraft needs an airlock for cycling while repair crew goes in and out
* rad hardening for 'tbd' spacecraft, EVA suits because in 'deep space'

That's the first order list that comes to mind: but I still ask the question because
for the stake of just how much $$$ was spent on JWST, if deploy step
154 fails, and all the remote troubleshooting fails, does it really
just get thrown away ? ( sunk cost fallacy enters the rambling here too I suppose)


Does a, say, $150M repair mission to get the multi-billion dollar JWST back online
come into the conversation?

I've always wondered it they could do the deployment in LEO, then boost it to the desired orbit with ion engines once the deployment is complete. They could even have a Dragon capsule nearby with astronauts trained in its repair in orbit nearby during the deployment.

That won't work because:
1) Deploying the telescope changes the center of mass, which means that it is much more difficult to lift to the LaGrangian point, and
2) The JWST has many, many parts that are glued together, which means that they simply cannot be fixed on-orbit.

No argument on (2). The telescope wasn't designed for repair so it can't be.

I'm not sure I follow on (1). Yes, the center of mass isn't located in the same place, but it's somewhere. No, the docking collar might not be in a straight line to the cg anymore, but one could apply the force elsewhere. You might not be able to accelerate as hard through such a secondary force path, but that doesn't make it any harder to lift to the Lagrange point, just slower.

It makes it much more complicated and much, much riskier. Do you really want to add more opportunities for things to go wrong?

Any lateral shift in the CoM from where it is means that the rocket moving the JWST to L₂ will have to compensate by firing at an angle. This means that it will use more fuel, upsetting the mass balance once again. It also means that small errors run a significant chance of accumulating, leading to oscillations, leading to losing the telescope.

That's nonsense: it wouldn't use any more fuel, the telescope would just accelerate with another direction being "forward". And control of oscillations is a problem we have plenty of experience with. All of the problems and complications are things you have to deal with anyway to handle stationkeeping activities after arrival.

 

[Wickwick]

some quick websearching hasn't yielded much other than reddit crap,
and so I'm very seriously wondering about
the multiple comments over the years about how
once JWST is on station its "unmaintainable/unserviceable"

This is, presumably, by design given that HST was built to be deployed by shuttle,
and periodically visited by shuttle, and no one figured that a spacecraft capable
of getting to the Lagrange point would exist to go service JWST.

With new spaceflight capabilities coming online (Starship, even Orion if we want to believe
that SLS flies more than once) is JWST still "doomed" if the insanely complex,
nearly 200 step deployment process fails?

The obvious caveats that come to mind:
* money to fly "tbd" spacecraft to JWST at the lagrange point
* money to train astronauts to do whatever servicing is required
* money and time to develop whatever repair tools, systems are needed
* TBD spacecraft being able to station keep with JWST? (presumably no Canadarm grapple fixture anywhere on JWST
* spacecraft needs an airlock for cycling while repair crew goes in and out
* rad hardening for 'tbd' spacecraft, EVA suits because in 'deep space'

That's the first order list that comes to mind: but I still ask the question because
for the stake of just how much $$$ was spent on JWST, if deploy step
154 fails, and all the remote troubleshooting fails, does it really
just get thrown away ? ( sunk cost fallacy enters the rambling here too I suppose)


Does a, say, $150M repair mission to get the multi-billion dollar JWST back online
come into the conversation?

I've always wondered it they could do the deployment in LEO, then boost it to the desired orbit with ion engines once the deployment is complete. They could even have a Dragon capsule nearby with astronauts trained in its repair in orbit nearby during the deployment.

That won't work because:
1) Deploying the telescope changes the center of mass, which means that it is much more difficult to lift to the LaGrangian point, and
2) The JWST has many, many parts that are glued together, which means that they simply cannot be fixed on-orbit.

No argument on (2). The telescope wasn't designed for repair so it can't be.

I'm not sure I follow on (1). Yes, the center of mass isn't located in the same place, but it's somewhere. No, the docking collar might not be in a straight line to the cg anymore, but one could apply the force elsewhere. You might not be able to accelerate as hard through such a secondary force path, but that doesn't make it any harder to lift to the Lagrange point, just slower.

It makes it much more complicated and much, much riskier. Do you really want to add more opportunities for things to go wrong?

Any lateral shift in the CoM from where it is means that the rocket moving the JWST to L₂ will have to compensate by firing at an angle. This means that it will use more fuel, upsetting the mass balance once again. It also means that small errors run a significant chance of accumulating, leading to oscillations, leading to losing the telescope.

That's nonsense: it wouldn't use any more fuel, the telescope would just accelerate with another direction being "forward". And control of oscillations is a problem we have plenty of experience with. All of the problems and complications are things you have to deal with anyway to handle stationkeeping activities after arrival.

I can see that you wouldn't want to subject the telescope to the full transfer acceleration it's going to experience with the current launch. If it were deployed, the sun shade might become damaged. Perhaps not - it was tested at 1 g, but for argument's sake let's take that as a given.

Now that we have to make the transfer at lower accelerations it's possible we lose some Oberth effect. So our fuel consumption would be slightly higher. But the discussion also hinged on electric propulsion for this transfer. With that, we're back to winning the propellant mass argument again thanks to a much higher Isp.

 

[JohnDeL]

some quick websearching hasn't yielded much other than reddit crap,
and so I'm very seriously wondering about
the multiple comments over the years about how
once JWST is on station its "unmaintainable/unserviceable"

This is, presumably, by design given that HST was built to be deployed by shuttle,
and periodically visited by shuttle, and no one figured that a spacecraft capable
of getting to the Lagrange point would exist to go service JWST.

With new spaceflight capabilities coming online (Starship, even Orion if we want to believe
that SLS flies more than once) is JWST still "doomed" if the insanely complex,
nearly 200 step deployment process fails?

The obvious caveats that come to mind:
* money to fly "tbd" spacecraft to JWST at the lagrange point
* money to train astronauts to do whatever servicing is required
* money and time to develop whatever repair tools, systems are needed
* TBD spacecraft being able to station keep with JWST? (presumably no Canadarm grapple fixture anywhere on JWST
* spacecraft needs an airlock for cycling while repair crew goes in and out
* rad hardening for 'tbd' spacecraft, EVA suits because in 'deep space'

That's the first order list that comes to mind: but I still ask the question because
for the stake of just how much $$$ was spent on JWST, if deploy step
154 fails, and all the remote troubleshooting fails, does it really
just get thrown away ? ( sunk cost fallacy enters the rambling here too I suppose)


Does a, say, $150M repair mission to get the multi-billion dollar JWST back online
come into the conversation?

I've always wondered it they could do the deployment in LEO, then boost it to the desired orbit with ion engines once the deployment is complete. They could even have a Dragon capsule nearby with astronauts trained in its repair in orbit nearby during the deployment.

That won't work because:
1) Deploying the telescope changes the center of mass, which means that it is much more difficult to lift to the LaGrangian point, and
2) The JWST has many, many parts that are glued together, which means that they simply cannot be fixed on-orbit.

No argument on (2). The telescope wasn't designed for repair so it can't be.

I'm not sure I follow on (1). Yes, the center of mass isn't located in the same place, but it's somewhere. No, the docking collar might not be in a straight line to the cg anymore, but one could apply the force elsewhere. You might not be able to accelerate as hard through such a secondary force path, but that doesn't make it any harder to lift to the Lagrange point, just slower.

It makes it much more complicated and much, much riskier. Do you really want to add more opportunities for things to go wrong?

Any lateral shift in the CoM from where it is means that the rocket moving the JWST to L₂ will have to compensate by firing at an angle. This means that it will use more fuel, upsetting the mass balance once again. It also means that small errors run a significant chance of accumulating, leading to oscillations, leading to losing the telescope.

The question related to sending the telescope from LEO to the LaGrange point with an ion engine. So the concern about needing more fuel is a non-starter.

Is it your understanding that ion engines don't use fuel? Because I can assure you that they do.

I asked about risks and your answer is basically that it's riskier without explanation. What's shifting once the sunshade is deployed and the mirror is open and locked? Nothing is.

The fuel for the ion thruster (it is a gas, but still vulnerable to sloshing). The liquid helium onboard the JWST. Both of which can create dangerous oscillations.

Then there are the much smaller but non-neglible effects of light pressure on the opened canopy.

some quick websearching hasn't yielded much other than reddit crap,
and so I'm very seriously wondering about
the multiple comments over the years about how
once JWST is on station its "unmaintainable/unserviceable"

This is, presumably, by design given that HST was built to be deployed by shuttle,
and periodically visited by shuttle, and no one figured that a spacecraft capable
of getting to the Lagrange point would exist to go service JWST.

With new spaceflight capabilities coming online (Starship, even Orion if we want to believe
that SLS flies more than once) is JWST still "doomed" if the insanely complex,
nearly 200 step deployment process fails?

The obvious caveats that come to mind:
* money to fly "tbd" spacecraft to JWST at the lagrange point
* money to train astronauts to do whatever servicing is required
* money and time to develop whatever repair tools, systems are needed
* TBD spacecraft being able to station keep with JWST? (presumably no Canadarm grapple fixture anywhere on JWST
* spacecraft needs an airlock for cycling while repair crew goes in and out
* rad hardening for 'tbd' spacecraft, EVA suits because in 'deep space'

That's the first order list that comes to mind: but I still ask the question because
for the stake of just how much $$$ was spent on JWST, if deploy step
154 fails, and all the remote troubleshooting fails, does it really
just get thrown away ? ( sunk cost fallacy enters the rambling here too I suppose)


Does a, say, $150M repair mission to get the multi-billion dollar JWST back online
come into the conversation?

I've always wondered it they could do the deployment in LEO, then boost it to the desired orbit with ion engines once the deployment is complete. They could even have a Dragon capsule nearby with astronauts trained in its repair in orbit nearby during the deployment.

That won't work because:
1) Deploying the telescope changes the center of mass, which means that it is much more difficult to lift to the LaGrangian point, and
2) The JWST has many, many parts that are glued together, which means that they simply cannot be fixed on-orbit.

No argument on (2). The telescope wasn't designed for repair so it can't be.

I'm not sure I follow on (1). Yes, the center of mass isn't located in the same place, but it's somewhere. No, the docking collar might not be in a straight line to the cg anymore, but one could apply the force elsewhere. You might not be able to accelerate as hard through such a secondary force path, but that doesn't make it any harder to lift to the Lagrange point, just slower.

It makes it much more complicated and much, much riskier. Do you really want to add more opportunities for things to go wrong?

Any lateral shift in the CoM from where it is means that the rocket moving the JWST to L₂ will have to compensate by firing at an angle. This means that it will use more fuel, upsetting the mass balance once again. It also means that small errors run a significant chance of accumulating, leading to oscillations, leading to losing the telescope.

That's nonsense: it wouldn't use any more fuel, the telescope would just accelerate with another direction being "forward". And control of oscillations is a problem we have plenty of experience with. All of the problems and complications are things you have to deal with anyway to handle stationkeeping activities after arrival.

The problem with "another direction being 'forward'" is that if you don't compensate for that, you end up not going to L₂ today.

 

[wagnerrp]

The question related to sending the telescope from LEO to the LaGrange point with an ion engine. So the concern about needing more fuel is a non-starter.

Is it your understanding that ion engines don't use fuel? Because I can assure you that they do.

But it’s an ion thruster. The ~7.5km/s needed to spiral out to SEL-2 only takes around 1.5t of extra propellant. The problem is going to be time, not all the extra propellant mass.

I asked about risks and your answer is basically that it's riskier without explanation. What's shifting once the sunshade is deployed and the mirror is open and locked? Nothing is.

The fuel for the ion thruster (it is a gas, but still vulnerable to sloshing). The liquid helium onboard the JWST. Both of which can create dangerous oscillations.

Then there are the much smaller but non-neglible effects of light pressure on the opened canopy.

At the extremely low acceleration of an ion thruster, why would any of that matter?

 

[JohnDeL]

The question related to sending the telescope from LEO to the LaGrange point with an ion engine. So the concern about needing more fuel is a non-starter.

Is it your understanding that ion engines don't use fuel? Because I can assure you that they do.

But it’s an ion thruster. The ~7.5km/s needed to spiral out to SEL-2 only takes around 1.5t of extra propellant. The problem is going to be time, not all the extra propellant mass.

And the current mass balance is such that they don't have an extra 1.5t to spare.

I asked about risks and your answer is basically that it's riskier without explanation. What's shifting once the sunshade is deployed and the mirror is open and locked? Nothing is.

The fuel for the ion thruster (it is a gas, but still vulnerable to sloshing). The liquid helium onboard the JWST. Both of which can create dangerous oscillations.

Then there are the much smaller but non-neglible effects of light pressure on the opened canopy.

At the extremely low acceleration of an ion thruster, why would any of that matter?

Because it is simpler and safer not to take those risks in the first place. At this point any risk that can be avoided must be avoided, lest we lose the ten billion dollar investment.

 

[wagnerrp]

The question related to sending the telescope from LEO to the LaGrange point with an ion engine. So the concern about needing more fuel is a non-starter.

Is it your understanding that ion engines don't use fuel? Because I can assure you that they do.

But it’s an ion thruster. The ~7.5km/s needed to spiral out to SEL-2 only takes around 1.5t of extra propellant. The problem is going to be time, not all the extra propellant mass.

And the current mass balance is such that they don't have an extra 1.5t to spare.

Totally false. They can’t spare another 1.5t because the Ariane 5 can’t lift that much on a transfer to SEL-2, but the Ariane 5 would only be lifting to LEO, and it can most definitely do 7.5t to LEO.

 

[Wickwick]

The question related to sending the telescope from LEO to the LaGrange point with an ion engine. So the concern about needing more fuel is a non-starter.

Is it your understanding that ion engines don't use fuel? Because I can assure you that they do.

But it’s an ion thruster. The ~7.5km/s needed to spiral out to SEL-2 only takes around 1.5t of extra propellant. The problem is going to be time, not all the extra propellant mass.

And the current mass balance is such that they don't have an extra 1.5t to spare.

I asked about risks and your answer is basically that it's riskier without explanation. What's shifting once the sunshade is deployed and the mirror is open and locked? Nothing is.

The fuel for the ion thruster (it is a gas, but still vulnerable to sloshing). The liquid helium onboard the JWST. Both of which can create dangerous oscillations.

Then there are the much smaller but non-neglible effects of light pressure on the opened canopy.

At the extremely low acceleration of an ion thruster, why would any of that matter?

Because it is simpler and safer not to take those risks in the first place. At this point any risk that can be avoided must be avoided, lest we lose the ten billion dollar investment.

You forgot to subtract the 7.5 km/s from the propellant needed to reach L2 using chemical rockets. If it's a hypergolic insertion stage is going to have < half the Isp of an ion engine (and yes, I am aware reaction mass is necessary). If it's not an insertion stage and you're using the Ariane second stage, you're also lifting all the mass of the second stage while doing the insertion. In either case, not inserting directly isn't a performance cost.

The "it's more dangerous to do it staged" is classic Old Space groupthink. Actually, it's not even groupthink. It was Boeing's mantra to maintain existence in the launch market. It is simply a political slogan - something that sounds great and means nothing.

You do understand that liquids sloshing at 0.05 g is a really minor concern, right? If that's a problem, good luck station keeping when the helium tank is at 15% liquid volume.

 

[Wickwick]

The problem with "another direction being 'forward'" is that if you don't compensate for that, you end up not going to L₂ today.

Well who the hell was suggesting just thrusting without any GNC? I'm pretty sure the regulars here understand the concept that you can't just apply a force to a craft through a rigid connection and walk away. I'm pretty sure we wouldn't want to spin stabilize the telescope, but gimbaled engines are a thing. Thrusters are a thing and reaction wheels are a thing.

But yes, if your vision of an ion engine lifting the telescope to space was an uncontrolled thrust added to the structure, then I'll spot you that's a really good way to destroy the telescope. Fortunately, controlled thrust in space has been solved for 5+ decades now.

 

[jaminb]

The question related to sending the telescope from LEO to the LaGrange point with an ion engine. So the concern about needing more fuel is a non-starter.

Is it your understanding that ion engines don't use fuel? Because I can assure you that they do.

But it’s an ion thruster. The ~7.5km/s needed to spiral out to SEL-2 only takes around 1.5t of extra propellant. The problem is going to be time, not all the extra propellant mass.

And the current mass balance is such that they don't have an extra 1.5t to spare.

I asked about risks and your answer is basically that it's riskier without explanation. What's shifting once the sunshade is deployed and the mirror is open and locked? Nothing is.

The fuel for the ion thruster (it is a gas, but still vulnerable to sloshing). The liquid helium onboard the JWST. Both of which can create dangerous oscillations.

Then there are the much smaller but non-neglible effects of light pressure on the opened canopy.

At the extremely low acceleration of an ion thruster, why would any of that matter?

Because it is simpler and safer not to take those risks in the first place. At this point any risk that can be avoided must be avoided, lest we lose the ten billion dollar investment.

You forgot to subtract the 7.5 km/s from the propellant needed to reach L2 using chemical rockets. If it's a hypergolic insertion stage is going to have < half the Isp of an ion engine (and yes, I am aware reaction mass is necessary). If it's not an insertion stage and you're using the Ariane second stage, you're also lifting all the mass of the second stage while doing the insertion. In either case, not inserting directly isn't a performance cost.

The "it's more dangerous to do it staged" is classic Old Space groupthink. Actually, it's not even groupthink. It was Boeing's mantra to maintain existence in the launch market. It is simply a political slogan - something that sounds great and means nothing.

You do understand that liquids sloshing at 0.05 g is a really minor concern, right? If that's a problem, good luck station keeping when the helium tank is at 15% liquid volume.

Would the helium get too warm if the thing pauses in LEO, waiting for astronaut repair, and/or the slow outward spiral departure?

 

[Wickwick]

The question related to sending the telescope from LEO to the LaGrange point with an ion engine. So the concern about needing more fuel is a non-starter.

Is it your understanding that ion engines don't use fuel? Because I can assure you that they do.

But it’s an ion thruster. The ~7.5km/s needed to spiral out to SEL-2 only takes around 1.5t of extra propellant. The problem is going to be time, not all the extra propellant mass.

And the current mass balance is such that they don't have an extra 1.5t to spare.

I asked about risks and your answer is basically that it's riskier without explanation. What's shifting once the sunshade is deployed and the mirror is open and locked? Nothing is.

The fuel for the ion thruster (it is a gas, but still vulnerable to sloshing). The liquid helium onboard the JWST. Both of which can create dangerous oscillations.

Then there are the much smaller but non-neglible effects of light pressure on the opened canopy.

At the extremely low acceleration of an ion thruster, why would any of that matter?

Because it is simpler and safer not to take those risks in the first place. At this point any risk that can be avoided must be avoided, lest we lose the ten billion dollar investment.

You forgot to subtract the 7.5 km/s from the propellant needed to reach L2 using chemical rockets. If it's a hypergolic insertion stage is going to have < half the Isp of an ion engine (and yes, I am aware reaction mass is necessary). If it's not an insertion stage and you're using the Ariane second stage, you're also lifting all the mass of the second stage while doing the insertion. In either case, not inserting directly isn't a performance cost.

The "it's more dangerous to do it staged" is classic Old Space groupthink. Actually, it's not even groupthink. It was Boeing's mantra to maintain existence in the launch market. It is simply a political slogan - something that sounds great and means nothing.

You do understand that liquids sloshing at 0.05 g is a really minor concern, right? If that's a problem, good luck station keeping when the helium tank is at 15% liquid volume.

Would the helium get too warm if the thing pauses in LEO, waiting for astronaut repair, and/or the slow outward spiral departure?

The heat load in LEO is a bit higher than way the hell out at L2. When you're on the sunny side of earth you're not able to efficiently radiate to space. However, I don't know that you'd bother to bring all the instruments down to their near-zero operating points until you were on-station if you were designing a mission with this profile. So then it's just a matter of what's the boil-off of the helium Dewar. I don't know the answer to that. Certainly it's non-zero. So it would certainly shorten the otherwise maximum mission duration. However, had the telescope been designed with an ion engine as the insertion engine, it's possible the mass saved could have allowed a sufficiently larger helium supply. Or perhaps the added mass might have been allocated to the sun shade and the instrument would have been taking data for the last three years already.