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The James Webb Space Telescope and stuff


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1 hour ago, RCgothic said:

The article is wrong in one respect - there is a crewed spaceship under design that could make it.out to L2 for a servicing mission. Starship could theoretically be made to have enough endurance and capability.

However, it's true that Webb has no grapple fixture and no serviceable parts. There's no way to refuel it as far as I can tell.

Well never say never, remember there is now satellite services in which a symbiotic satellites docks to a rocket nozzle of the host satellite and then the symbiotic sat takes over the propulsion functions of the host.

 

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The James Webb Telescope can't be turned around, so it depends on the injection from the Ariane 5 2nd stage to be under the value to propel it to the L2 position, with its on-board thrusters to make the fine corrections.  If it was over, it couldn't stop and would drift out into a heliocentric orbit at greater ranges (and thus lower data rates) from Earth.

More info in this video.

 

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8 hours ago, RuBisCO said:

Well never say never, remember there is now satellite services in which a symbiotic satellites docks to a rocket nozzle of the host satellite and then the symbiotic sat takes over the propulsion functions of the host.

 

That was the one I was talking about, and yes that should be an option. An obvious benefit is that here you can go all inn on bells ans whistles.

And that is the future, you plan your carrier for space and ended up as an fuel station attendant refueling satellites. 
Kind of like Fry in Futurama, still an delivery boy. 

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so where we at in terms of deployments? distance to its lagrange point is pretty much the least of its problems right now.  its got to make it through a long and intentionally drawn out series of deployments before we know if the thing they are sending is actually a telescope and not a half assembled ball of junk. nasa can get pretty creative when major systems on an interplanetary probe stop working. wonder what they would come up with if they encountered a mission breaking glitch or permanent damage to any of the mirror elements or their deployment systems.

Edited by Nuke
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19 minutes ago, Nuke said:

deployments?

Comms was the second deployment after power - which we saw deployed shortly after separation. 

Next will be the long, multistage sun shade deployment and tensioning.  Apparently if this does not work, neither will Webb as the instruments will never be cold enough. 

There is a video on this and a graphic. 

I think they start to deploy the mirrors and major parts of the telescope after the sun shade and then the insertion burn(s) followed by waking up the major systems of the observatory, testing and initial science - reveal sometime in June followed by the work scheduled 

... 

Anyone know the research schedule?  I know many want deep scans and origin work, but I really hope there are some surveys of sunlike stars vis 18 scorpii in the first year. 

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2 hours ago, JoeSchmuckatelli said:

 

Anyone know the research schedule?  I know many want deep scans and origin work, but I really hope there are some surveys of sunlike stars vis 18 scorpii in the first year. 

I have no sources, but I’d guess there’d be some calibration shots, and then a few hi res PR shots for the NASA press office to show off.     And then it’s probably booked solid for the next 3-4 years after that.  

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On 12/26/2021 at 6:40 PM, RCgothic said:

Estimate of MC-1 is about 16/17 m/s based on burn time, against 22m/s expected.

 

Unclear as yet how this affects fuel reserves and life.

Webb did it's second MCC burn (MCC-1B), of 9 minutes 27 seconds.  (567s)

https://blogs.nasa.gov/webb/2021/12/27/webbs-second-mid-course-correction-burn/

next steps should be the sunshield's pallets opening :) 

Edited by sgt_flyer
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7 hours ago, sgt_flyer said:

Webb did it's second MCC burn (MCC-1B), of 9 minutes 27 seconds.  (567s)

https://blogs.nasa.gov/webb/2021/12/27/webbs-second-mid-course-correction-burn/

next steps should be the sunshield's pallets opening :) 

567s is more than the nominal duration for that burn.

It's on about 4440s total compared to about 5400s expected, so still good for beyond-nominal life.

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On 12/26/2021 at 11:48 AM, RCgothic said:

not currently being designed to take advantage of increased size and capacity.

Is that because (like Webb) the design originated before what we are seeing in development at present?  Or is there a requirement that you only design for currently proven tech in existence at the time? 

Surely (unless contracts are already signed) the designers could adjust part of the design to accommodate developing trends and increase the working life of a billion dollar project? 

4 hours ago, RCgothic said:

567s is more than the nominal duration for that burn.

It's on about 4440s total compared to about 5400s expected, so still good for beyond-nominal life

This is is interesting.  They always want Webb on Earth /Sun side of the 'flat' part of the gravity potential hilltop of L2:

 

Quote

the Ariane 5 launch insertion was intentionally designed to leave some velocity in the anti-Sun direction to be provided by the payload. MCC-1a similarly was executed to take out most, but not all, of the total required correction (to be sure that this burn also would not overshoot). In the same way, MCC-1b, scheduled for 2.5 days after launch, and MCC-2, scheduled for about 29 days after launch (but neither time-critical), and the station-keeping burns throughout the mission lifetime will always thrust just enough to leave us a little bit shy of the crest. We want Sisyphus to keep rolling this rock up the gentle slope near the top of the hill – we never want it to roll over the crest and get away from

https://blogs.nasa.gov/webb/2021/12/27/more-than-you-wanted-to-know-about-webbs-mid-course-corrections/

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10 minutes ago, JoeSchmuckatelli said:

Is that because (like Webb) the design originated before what we are seeing in development at present?  Or is there a requirement that you only design for currently proven tech in existence at the time? 

LUVOIR-A at 15.1m was baselined for a Starship/SLS B2 Cargo size fairing, so that would be contemporaneous with upcoming vehicles.

LUVIOR-B at 8m was baselined for current vehicles.

LUVOIR/HabEx as recommended by the decadal survey is smaller still at 6m.

 

So this is going backwards. IMO they should be counting on an 8m fairing minimum (SLS B1B Cargo/Starship) and up to 15m notional fairing.

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Sunshield deployment has started with the forward pallet, 

https://blogs.nasa.gov/webb/2021/12/28/forward-pallet-structure-lowered-beginning-multiple-day-sunshield-deployment/

so within the next few days, here comes some of the most complex deployement steps ever done in space,

outside of space station assemblies i guess :)

 

edit : aft sunshield pallet deployed :
https://blogs.nasa.gov/webb/2021/12/28/aft-sunshield-pallet-deployed/

From reading the blog, seems the actual motion is around 20 minutes - but they have a lot of intermediate steps to check before / after the motion (heaters, latches, attitude checks, etc) turning each step into a multi-hour process :)

Edited by sgt_flyer
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Seems nasa confirmed that the precision of the launch should allow for much more than 10 years of operation for james webb :)

https://blogs.nasa.gov/webb/2021/12/29/nasa-says-webbs-excess-fuel-likely-to-extend-its-lifetime-expectations/

 

In the blog, they give figures of 20m/s of delta-v change for the mcc-1a burn, and 2.8m/s for the mcc-1b burn.

they also started to extend the telescope tower, they indicate that it could take up to 6 hours, as it is controlled from the ground.

https://blogs.nasa.gov/webb/2021/12/29/webb-team-begins-process-of-extending-deployable-tower-assembly/

 

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37 minutes ago, sgt_flyer said:

Seems nasa confirmed that the precision of the launch should allow for much more than 10 years of operation for james webb :)

https://blogs.nasa.gov/webb/2021/12/29/nasa-says-webbs-excess-fuel-likely-to-extend-its-lifetime-expectations/

I think that's given for any long duration NASA mission and I suspect it has mainly to do with budgeting. “We can't approve running this mission for 10 years, but we can put 5 years in the budget." Once the mission is on the way: "Oh, look, we built our rover much better/didn't need as much fuel" and by magic the mission suddenly lasts 2×-3× as long (it would be stupid to abandon a successful mission because it runs longer than budgeted for, after all). I don't have hard proof but seeing the pattern over and over again makes me really wonder.

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