Live data from Hacker News

The James Webb Space Telescope has passed the final mission analysis review

asc-csa.gc.ca

181–190 of 301 posts

Re: The James Webb Space Telescope has passed the final mission analysis review

#181
post #176
post #170

Earlier quoted context omitted.

> I don’t think it’s a great example of using existential threat for sales, when the whole thing was sold as a cost saving. Again, if there is no threat (perceived or real), there is no need for a weapons system, period. Think of it this way, if there was a proposal for a cost savings for an anti-spacecraft/anti-asteroid system mounted to the JWST? I'm saying no, because there is no credible threat that would prevent…

Threat mitigation is largely nuclear shield; but if you’re taking about maintaining air superiority then the F-22 is where it is at. The Navy carrier fleets and Marines are force projection. The JSF were sold around cost savings; half the price so you could buy twice as many.

I think you're taking a very narrow definition of what a threat means to make your point. To a Marine in Afghanistan, the threat was not mitigated by a nuclear arsenal. To them, close air support from a technologically inferior aircraft like the A10 did a better job of eliminating a threat than the F22 in many instances. To the original point, this is why it became difficult to retire the old plane despite the JSF and F22. It could be tied to a specific threat, and that meant it was politically much easier to defend keeping it around even if the business case was that it costs too much money. At the end of the day, politically defending a budget is much easier if it can be concretely tied to a credible risk.

Re: The James Webb Space Telescope has passed the final mission analysis review

#182
post #179

Earlier quoted context omitted.

> Pretty much everyone at the time just wanted more F-22s The Navy and Marine Corps didn't, especially after development of the Naval variant of the F-22 was cancelled in 1991.

I’m sure the Navy wished it wasn’t canceled, and the Marines probably would have been happy with Harriers. The stealth window of usefulness is closing anyway with improved radar.

> I’m sure the Navy wished it wasn’t canceled

It was canceled because the Navy said it wouldn't work, both because of cost and take-off weight of the proposed Naval variant relative to the capacity of then-current and in-development carriers.

Re: The James Webb Space Telescope has passed the final mission analysis review

#183
post #131
post #127

Earlier quoted context omitted.

That argument only holds because it was purported to replace different weapons systems that were needed for mitigating a threat. The threat is the primary motivation and cost reduction is secondary. I.e., if not but for the existential threat there's no need for the JSF or any system it would replace.

The F-22 was sufficient for threat mitigation. The F-35 raison d'être was cost reduction, after that was exportability which again was supposed to help with cost reduction. Edit; comparing the logic of a 'but for' vs a 'necessary' condition. Was the F-35 necessary for threat mitigation. No. Was it framed as the necessary for cost savings, yes.

Your oversimplifying and missing a lot. The F-35 is not a replacement or substitute for the F-22.

The F-22 is an air superiority fighter. The F-35 is a multi role strike aircraft. The F-22 would never be allowed for export, because it has features we don't want to share even with allies. The F-35 was designed for export to allies from day one.

There's no scenario where just buying more F-22's made more sense than building the F-35. The F-35's project problems, primarily driven from the joint acquisition strategy are their own thing, completely independent of the F-22.

Re: The James Webb Space Telescope has passed the final mission analysis review

#184

Earlier quoted context omitted.

Thanks for this comment; that's a fascinating bit of information.

But that was just like saying what F-35's mission is to fly high in the skies , sorry. This sort of proves my point, no one knows which exactly research JWST will do upon deployment, because original mission goals mainly became obsolete.

There is a long list of scientists that know exactly what research they are doing on JWST down to the minute [0]

For example, Dr Christine Chen et al will be using JWST for at least 34.9 hours to study the Icy Kuiper Belts in Exoplanetary Systems using near infrared spectroscopy [1]

[0] https://www.stsci.edu/jwst/science-execution/approved-progra...

[1] https://www.stsci.edu/jwst/phase2-public/1563.pdf

Re: The James Webb Space Telescope has passed the final mission analysis review

#185
post #12
post #8

Earlier quoted context omitted.

Same feelings here! Ever since it was announced I have been anxious about it all going to plan. Sometimes I put myself in the shoes of the engineers and controllers, and I can’t imagine how nerve wracking it must be, waiting and waiting! The thing could simply blow up on the launch pad, for goodness sake!

> The thing could simply blow up on the launch pad, for goodness sake! exactly, I’ve wondered why they don’t build e.g. 2 or 3 of them in tandem since it’d likely be cheaper/easier to do up front vs after the fact if things went wrong. They would then have the additional telescopes if things went right, offering even greater access.

See my other comment: https://news.ycombinator.com/item?id=27767223

The timelines on this kind of project are so long spares don't make sense vs trying again with a new and updated design.

Re: The James Webb Space Telescope has passed the final mission analysis review

#186

While it‘s awesome to finally see the JWST finally come to close to launch after all those years, now it‘s a close race between it and SpaceX Starship that could have taken the 6.5 meter mirror up to space in one whole piece in its 9m diameter belly rather than having to do all the miraculous origami that took two decades to develop in the first place…

I wouldn't trust any payload on a SpaceX ship given their track record.

The Falcon 9 has had 126 missions so far and only 2 of those were failures. It's not a perfect record, but it's pretty decent. And presumably SpaceX has learned from those failures. Compare that to the Ariane 5 rockets (which will actually be launching the James Web Space Telescope) which has had 109 launches, and 5 of them ended in failure.

I'm just going to assume you're referring to Starship's various explosions. It's far too early in the Starship development cycle to draw any kind of conclusions about it's reliability.

Starship is a prototype. It's a completely new vehicle with completely new engines, and they're building it with the expectation that the early versions are going to blow up. It's like saying Falcon 9 is unreliable because their early "grasshopper" prototype (for testing landing) exploded and at times. Also probably a good idea to note that these explosions all happened during their landing attempt, so in theory any payload onboard would have already been deployed. It's just the vehicle that would be lost. Of course they're still so early in the development cycle that Starship hasn't even attempted an orbital flight yet.

I get that it's weird watching these very early prototypes blow up so spectacularly and publicly, but that's the development model SpaceX has chosen. And we're not used to watching rockets being built and tested so out in the open. Personally I think it's exciting watching the progress they're making.

Re: The James Webb Space Telescope has passed the final mission analysis review

#187
I really hope this isn't a "MAKE IT PASS, OR ELSE" situation.

this telescope doesn't deserve any functionality setbacks in exchange for more schedule setbacks.

a telescope made late because of fixes is a fully working telescope. a prematurely launched telescope is broken for its entire service life.

Re: The James Webb Space Telescope has passed the final mission analysis review

#188
post #100

Earlier quoted context omitted.

How long can it stay stable at that point? Does it have thrusters to keep a station there? If so, how long is the fuel for them provisioned for? Does use of the thrusters impact the sensors that the telescope uses?

The L2 point is unstable with a period of 23 days? I believe, so the JWT needs a course correct burn to stay positioned correctly (called station keeping). It does have thrusters - a ring of 16 hydrazine "burning" units that can produce thrust on 3 axis. The fact that the L2 point is unstable and that thrusters are required puts a lifetime on the telescope - I think NASA plans for a minimum of 5 1/2 years and are hop…

> The fact that the L2 point is unstable and that thrusters are required puts a lifetime on the telescope - I think NASA plans for a minimum of 5 1/2 years and are hoping to get up to 10. That's entirely reliant on the fuel supply.

So when the fuel is exhausted the orbit decays and the unshielded telescope disintegrates on re-entry into Earth's atmosphere?

Re: The James Webb Space Telescope has passed the final mission analysis review

#189

I really hope this isn't a "MAKE IT PASS, OR ELSE" situation. this telescope doesn't deserve any functionality setbacks in exchange for more schedule setbacks. a telescope made late because of fixes is a fully working telescope. a prematurely launched telescope is broken for its entire service life.

No, they know what's at stake. That's why it's been delayed... and delayed... and delayed...

The question we're all biting our nails for is - Will it work?

Re: The James Webb Space Telescope has passed the final mission analysis review

#190

I really hope this isn't a "MAKE IT PASS, OR ELSE" situation. this telescope doesn't deserve any functionality setbacks in exchange for more schedule setbacks. a telescope made late because of fixes is a fully working telescope. a prematurely launched telescope is broken for its entire service life.

The Hubble was launched broken. The mirror had a precision defect and produced blurry photos. A team had to go up and manually correct the focus.

https://www.nasa.gov/content/hubbles-mirror-flaw

Post reply on HN