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The James Webb Space Telescope and stuff


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4 hours ago, tater said:

As @sevenperforce said, Progress has been doing this for decades, so it was clearly a possibility.

My guess is that refueling MIR and later ISS is much easier than an fragile and exposed space telescope out at L2. Is lifetime limit because of fuel limits very relevant as it is it likely to break for other reasons first. 

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If we're being properly optimistic, we could hope that by the time JWST reaches the end of its lifespan, it will be a matter of a routine Starship flight to go out there and refurbish it. Popping in a new tank of hydrazine, inserting some new sensors, improving comms, all that jazz. Or maybe just installing a new telescope entirely and taking JWST down to be exhibited in a museum.

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4 minutes ago, Codraroll said:

If we're being properly optimistic, we could hope that by the time JWST reaches the end of its lifespan, it will be a matter of a routine Starship flight to go out there and refurbish it. Popping in a new tank of hydrazine, inserting some new sensors, improving comms, all that jazz. Or maybe just installing a new telescope entirely and taking JWST down to be exhibited in a museum.

Docking itself may be a problem, JWST with the sunshield deployed is extremely fragile. The vibrations during docking would be a problem

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1 hour ago, magnemoe said:

My guess is that refueling MIR and later ISS is much easier than an fragile and exposed space telescope out at L2. Is lifetime limit because of fuel limits very relevant as it is it likely to break for other reasons first. 

Still, it was not an impossible notion. I think minus the cost overruns maybe it mattered less—that's really the problem with these incredibly expensive flagship projects, throwing in the kitchen sink makes more and more sense because it's so ^%R&ing expensive.

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I wish I remembered enough from my undergraduate optics class to calculate the size of the largest possible telescope that could fit inside a custom Starship.

Hubble's primary mirror is 2.4 meters with a gross area of 4.52 m2. Webb's primary mirror is 6.5 meters with a gross area of 26.8 m2.

A 9-meter telescope would have a gross area of 63.6 m2, more than double that of JWST, but if you tilted it sideways inside the Starship payload bay it could be oval-shaped and thus even larger. This would result in some aberration but nothing that couldn't be corrected.

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21 minutes ago, sevenperforce said:

I wish I remembered enough from my undergraduate optics class to calculate the size of the largest possible telescope that could fit inside a custom Starship.

Hubble's primary mirror is 2.4 meters with a gross area of 4.52 m2. Webb's primary mirror is 6.5 meters with a gross area of 26.8 m2.

A 9-meter telescope would have a gross area of 63.6 m2, more than double that of JWST, but if you tilted it sideways inside the Starship payload bay it could be oval-shaped and thus even larger. This would result in some aberration but nothing that couldn't be corrected.

Say 8 meter diameter or a bit larger as inside diameter is smaller and you will want an margin. Don't think I would keep it inside the spaceship however unless it was for testing. 
Having it free flying would let you target much more easy and without using fuel. Would obviously make it easy to service. probably have the rear part an as an large torus who let you access the rear of the telescope trough an hatch or gateway then you put it in maintenance mode. You would not be so concerned saving some hundred kg after all. 

3 hours ago, Beccab said:

Docking itself may be a problem, JWST with the sunshield deployed is extremely fragile. The vibrations during docking would be a problem

One idea who some is working on for communication satellites as contract is signed is to have an control satellite grabbing it and then take over station keeping and perhaps even reaction wheels. For web this would probably be more to have the secondary wheels doing the grunt works of pointing and saturated the web wheels who is probably needed for fine control. 

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They have a nice press kit:

https://www.arianespace.com/wp-content/uploads/2021/12/VA256-launchkit-EN.pdf

From it

Quote

The journey of the telescope in detail: 
On the third day, the heat shield will begin to deploy.
On the eleventh day, the secondary mirror will begin positioning.
Between the 13th and 14th day, the primary mirror, comprising 18 hexagonal segments and measuring 6.5 meters in diameter, will be assembled.
The telescope is slated to arrive at its final destination, 1.5 million kilometers from Earth, approximately 29 days after launch.

Am I reading this correctly? Does this mean they'll start to unfold the mirrors before it gets to L2?

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1 hour ago, JoeSchmuckatelli said:

My 11 y.o. daughter tells me I'm not allowed to interrupt XMass to watch. 

"They'll have it on video, Daaaaad."

You tell Her that watching Webb launch is your Christmas gift.

Also rollout is complete:

Arianespace's Ariane 5 rocket, with NASA's James Webb Space Telescope onboard, was rolled out to the launchpad in French Guiana on Thursday.

It feels almost like a dream seeing this finally happen, and on Christmas day, the timing is amazing...or horrible depending on what happens.

If this thing fails NASA is going on the governments naughty list for a good decade or two at least.

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