James Webb Space Telescope

[masser]

Originally Posted by xilman

No planned service missions.

Who knows what young Mr Musk may be able to do by 2035?

NASA is reporting that the launch and first midcourse correction were precise enough that JWST will have enough fuel to last more than 10 years.

Will it be more expensive to build a new JWST+ OR to perform a mission continuance service mission?

I'm guessing JWST wasn't designed to be serviceable in space, so all we can hope for is a little more than 10 years of results from the mission.

[Uncwilly]

Originally Posted by masser

I'm guessing JWST wasn't designed to be serviceable in space, so all we can hope for is a little more than 10 years of results from the mission.

It wasn't built with the intent of being serviced. But the ring that was used to hold it to the launch vehicle is in a great place for a Mission Extension Vehicle (MEV) to attach. Similar to what is going on in geostationary, a MEV for NGST (the original name), would dock and take over the thrusty bit of the work. In 10 years this should be a well developed field.

[Dr Sardonicus]

Originally Posted by masser

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Will it be more expensive to build a new JWST+ OR to perform a mission continuance service mission?
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I'm assuming a service mission would have to have a human crew. Cheerfully ignoring that we don't AFAIK even have a plan for such a mission, let alone a system in place to carry it out, the requirements for a service mission to the Earth-Sun L2 point might make it cost more than replacing the telescope.

But I don't know enough about the requirements for such a mission to be sure.

Of course, simply replacing science mission spacecraft near L2 as they crap out could lead to the region becoming so cluttered with "space junk" as to render it unusable for further space missions. I don't know what provisions may have already been made to remove spacecraft from the vicinity as they become incapable of furthering their missions. If present ability to deal with defunct missions at L2 is insufficient, it would become necessary at some point to develop a plan for missions to deal with them. It might not be necessary for such missions to have human crews. That would probably reduce their cost significantly.

In any case, continuing to use L2 for scientific space missions would seem to require a long term commitment to doing the science.

[kriesel]

Originally Posted by Uncwilly

It wasn't built with the intent of being serviced. But the ring that was used to hold it to the launch vehicle is in a great place for a Mission Extension Vehicle (MEV) to attach. ... a MEV for NGST (the original name), would dock and take over the thrusty bit of the work. In 10 years this should be a well developed field.

For the same total payload mass, an MEV for only the orbit maintenance thrust may be able to add more than another 10 years station-keeping. Robot docking with locking clamps by an autonomous vehicle with a big fuel tank, since it would need to maneuver more mass once docked. JWST ~6200kg alone. The addon could also conceivably carry a software update for JWST for very short range transmission. Even have another ring on its back if it makes sense to consider a second refuel-by-attach. Should not cost nearly as much as JWST did.

https://jwst.nasa.gov/content/about/faqs/facts.html says 5-10 years for JWST as launched.

Conceivably such robot tugs could be used to declutter L2 someday.

This is a useful explanation/visualization for L1-L5.

[Uncwilly]

Originally Posted by Dr Sardonicus

I'm assuming a service mission would have to have a human crew.

False assumption. There is a current MEV in operation at GEO. No crew on board. Changing out instruments is a different thing. But the main issue with the telescope should be fuel.

the requirements for a service mission to the Earth-Sun L2 point might make it cost more than replacing the telescope.

A super MEV delivered with a Falcon Heavy would likely run less than $0.5 billion.

Of course, simply replacing science mission spacecraft near L2 as they crap out could lead to the region becoming so cluttered with "space junk" as to render it unusable for further space missions.

JWST and other missions "at" L2 and L1 are in orbits around the L point. And as such, there is a huge amount of space in the area. IIRC the orbit JWST around S-E L2 will be larger than the orbit of the moon around earth.

[retina]

Originally Posted by Uncwilly

JWST and other missions "at" L2 and L1 are in orbits around the L point. And as such, there is a huge amount of space in the area. IIRC the orbit JWST around S-E L2 will be larger than the orbit of the moon around earth.

L2 is fine. L2 orbits are unstable and require fuel to maintain an object there.

So after the fuel runs out the craft will gradually drift away and fall behind into a heliocentric orbit, clearing the area. Other craft have already done this.

[Dr Sardonicus]

Let's see if I have this right:

1) As long as extending the mission of JWST (or other craft near L2) only requires additional propulsion, that could be accomplished with types of spacecraft already being used to extend missions, though requiring more lift capacity to get them to where they're needed.

2) If propulsion to maintain orbit around L2 runs out, the craft will drift clear of the region on its own.

3) If servicing of the vehicle is needed (repair or replace instruments, mechanical components, etc.), a human crew would be required.

[Uncwilly]

Originally Posted by Dr Sardonicus

1) As long as extending the mission of JWST (or other craft near L2) only requires additional propulsion, that could be accomplished with types of spacecraft already being used to extend missions, though requiring more lift capacity to get them to where they're needed.

More or less, yes. MEV's are new. A Falcon9 could fling one to L2. A FalconHeavy would be able to send a much bigger and complex one out to L2.

2) If propulsion to maintain orbit around L2 runs out, the craft will drift clear of the region on its own.

Yes, slowly. L1, L2, and L3 don't hold on to objects the way L4 and L5 do.

3) If servicing of the vehicle is needed (repair or replace instruments, mechanical components, etc.), a human crew would be required.

Even if people went there, it wasn't built like Hubble. Hubble was designed to be refurbished (the plan was initially for it to be returned to earth and serviced and sent back up.) The instruments could be pulled out and replaced. The Wide Field Planetary Camera was changed out in the first servicing mission (it was not able to use the CoSTAR system that 'fixed' the other instruments). And now there is yet a newer version of it on board. And without a very long robot arm, getting from the hot side (where the ring is) to the cold side would be difficult to do while not causing problems for the sunshield.

[xilman]

Originally Posted by kriesel

For the same total payload mass, an MEV for only the orbit maintenance thrust may be able to add more than another 10 years station-keeping. Robot docking with locking clamps by an autonomous vehicle with a big fuel tank, since it would need to maneuver more mass once docked. JWST ~6200kg alone. The addon could also conceivably carry a software update for JWST for very short range transmission. Even have another ring on its back if it makes sense to consider a second refuel-by-attach.

If designed appropriately, The MEV could undock and get out of the way of its replacement, exactly how the Ariane did.

[kriesel]

Originally Posted by xilman

If designed appropriately, The MEV could undock and get out of the way of its replacement, exactly how the Ariane did.

Yes. It depends on design details whether the grippers reliably unlatch again, power remains to run them, whether economics and component life expectancies favor replacing thrusters and control systems or refueling the first MEV. In critical components it's usual to have nose to nose redundancy. On WUPPE there were nose to nose gearmotors for opening the telescope to view space or closing the main aperture to protect the optics from gases from shuttle attitude control thrusters etc. One could seize solid and if the other worked the telescope still worked. Stacked MEV grippers might be the way to go to ensure release from JWST. Since there are probably at least 3 grippers onto the ring, that ~triples ring grip release failure probability, so some redundancy for release would be valuable; if the gripper won't release the ring, release the gripper from the MEV, sever any electrical connection, the replacement MEV grips on the ring at a different clock angle to avoid the stuck gripper(s). It's less reliable to require release of the first MEV, but reducing the controlled mass by removing the first MEV is an advantage. One can imagine having a grip ring on the first MEV in case of release failure or refuel manuever failure. Second MEV then has more than one way to fulfill its mission. Man years would get spent analyzing different scenarios and probabilities and tradeoffs.

[Dr Sardonicus]

NASA's new space telescope 'hunky-dory' after problems fixed

CAPE CANAVERAL, Fla. (AP) - NASA's new space telescope is on the verge of completing the riskiest part of its mission - unfolding and tightening a huge sunshade - after ground controllers fixed a pair of problems, officials said Monday.
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Flight controllers in Maryland had to reset Webb's solar panel to draw more power. The observatory - considered the successor to the aging Hubble Space Telescope - was never in any danger, with a constant power flow, said Amy Lo, a lead engineer for the telescope's prime contractor, Northrop Grumman.

They also repointed the telescope to limit sunlight on six overheating motors. The motors cooled enough to begin securing the sunshield, a three-day process that can be halted if the problem crops up again, officials said.
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