NASA Says Webb’s Excess Fuel Likely to Extend Its Lifetime Expectations

If the optical path was enclosed the JWST would probably be too big to fit on any existing rocket.

Factors I can think of:

1. Bigger mirror = better. Enclosing a mirror requires mass and volume, limiting mirror size.

2. The L2 orbit is unstable. Far less risk of being hit by debris than low Earth orbit.

3. Webb's sun shield blocks the primary light pollution angle. Hubble would need more protection from all angles due to the Sun, Earth, and Moon.

Hubble needed to hide mirror because it is passing from sunlight into shadow every 47 minutes and mirror has to be protected from thermal stress. Also Earth emits some light even on night side that would interfere with observations.

JWST's mirror is always in shadow and stray light from sides will not be a problem at L2.

Main reason I heard was that enclosing it would be preferable, but then it wouldn't fit in any currently in use fairing.

I've been glued to that page since the launch. The temperature delta just came online so you can now see the 'top' and 'bottom' temperature.

In the end it will be several hundred degrees difference, which given the distances involved is extremely impressive.

Fascinating that it's already covered 40% of the distance, but it's only on day 4 out of 30. That makes sense once you realize that its radial velocity needs to slow to zero when it reaches L2. I'd love to see the shape of how the velocity curve slows.

i've been checking for the past few days and it looks like JWST is available now in NASA's little 3D space model. you can literally it in the solar system model now too!

https://solarsystem.nasa.gov/solar-system/our-solar-system/o...

Agreed. This whole operation has been a superb advert for Ariane 5.

It's career ending to not do that.

That's just a natural consequence of designing with safety margins.

In other words, it should be the norm and not the exception. But of course the vast majority of us work in fields where overpromising is the norm.

It's so consistently done by NASA that I'm no longer impressed when they reach past EOL. It just shows that they were covering their asses.

"though many factors could ultimately affect Webb’s duration of operation." JWST also needs helium coolant with no possibility to recharge therefore limiting its lifespan to ~10 years, I believe. Interesting about Herschel and L2.

Wait if Hershel was the largest optical telescope in orbit, how come it didn't catch the public imagination like Hubble did?

I don't believe Hershel was optical at all - pretty certain it was far infra-red

Just to enumerate some recent missions:

  * NASA Curiosity: "2 years" -> 9.5 years, and counting.
  * NASA Spirit: "90 days" -> Just over 6 years, ending in 2010.
  * NASA Opportunity: "90 days" -> Over 14 years, ending in 2018.

NASA has had some failures too, of course. These stats are cherry-picked but still impressive.

> Underpromise, overdeliver.

Also called sandbagging. :)

For some things like the rovers it seems like the "design life" was just the minimum required to justify the mission. It would be silly to call a mission a failure if it died after a year when the mission would have been justified with just 90 days of operation simply because we had expected it to last two years.

A lot of the core research wouldn't have to be repeated, but the build and verification costs would not go away, and to do proper verification takes many many years.

A lot of those people hang out in the comments on Eric Berger's posts on Ars. Here's one example: https://arstechnica.com/science/2021/11/james-webb-space-tel...

He estimates that a second would cost about 90% of the first.

From my experience the cost breakdown of a typical [0] satellite is on the order of 60% recurring engineering, 40% non-recurring engineering. I don't have a good sense of the breakdown for JWST but the assembly and verification campaign is huge compared to most satellites and they would have to do that again so I would expect the recurring engineering to be higher. Coupled with the fact that it wouldn't be directly build-to-print due to parts obsolescence and technology upgrades they would want to make the cost would probably be higher still. So its not going to be a huge cost savings but you could maybe do it for something like 70-80% of the original cost.

As for the timeline, that's going to be a hard one to change. Consider that all of the mirror segments and optics were delivered by the end of 2013. So the integration and test campaign of the spacecraft took 8 years. There would definitely be some optimization and lessons learned from that and you could likely shave off a couple years. However, if we are also looking at building it "now" the supply chain issues also hit the aerospace industry. There are typical things that you would expect like chip shortages, but also random things like its difficult to buy the epoxy we normally use to glue solar cells on to panels.

[0] "Typical" varies wildly here. So for typical I am assuming something like a large NASA earth science mission with building one spacecraft of a relatively unique design.

Remember that no matter how far from the earth you get, you're always being pulled by it, decreasing velocity. The Webb left earth moving at 7km/s, but now is going less than 1km/s.

It's going to let Earth's gravity slow it down so that it reaches (effectively) zero at exactly the right spot.

It's literally rocket science to do the equations to make it work, but by God we've gotten pretty good at it.

Take a look at the dashboard and note the current speed: https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html

Right now it's traveling at about 0.55 miles per second. When I checked the other day that was over 0.7, and a bit after launch it was over 1.

Putting JWST into L2 is essentially the world's biggest curling toss ( https://en.m.wikipedia.org/wiki/Curling ).

As the OP alludes to, JWST's operational life is hard-limited by its fuel capacity. L2 (like L1 and L3, but unlike L4 and L5) is an unstable orbit, and without regular corrections it will drift out of position. This means that you want to save ALL your fuel for making those corrections, and thus spend as little of it as possible on getting there in the first place. So over the next month it's going to slowly crawl into place, cruising on no power other than what the Ariane initially gave it, getting continually slower and slower via the effect of the earth and sun's gravity until it stops perfectly in position.

There is a very good and detailed answer to your question here: https://space.stackexchange.com/questions/38389/is-it-possib...

They are planning one!

Physics doesn’t make this impossible, but it’s _enormously_ expensive to get payload to L2.