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Comment by Klathmon | Hacker News Reader

To be a bit more specific, we can't send something up to fix this because it's magnitudes further away from the earth than Hubble is.

JWT will be ~1.5 million km away from earth, in a special orbit around a spot called the "L2 Lagrange point". It's located there so that it can kind of hide in the earth's shadow at pretty much all times and keep all the nearby "bright" things behind the heat shield.

For comparison, the Hubble is ~600km away from the surface orbiting the Earth, and the Moon is a little under 400,000km away from the earth. JWT will be almost 4x further away than even the moon.

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I mean, the giddy idiot in me just gets excited about the urgent need for a human L2 mission to fix it.

Likewise. My train of thought goes like

"So what if it fails? There's a lot of money sunk into that! Well, maybe someone would actually decide it's worth going to the L2 to fix it, wouldn't that be cool!!"

So yeah, not the only idiot...

We would probably do this robotically.

"What do we do when the robotic satellite fails?"

"Send another robot!"

https://sspd.gsfc.nasa.gov/restore-L.html

also

https://www.darpa.mil/program/robotic-servicing-of-geosynchr...

Thank you. I was hoping to post these!

"What do we do when the L2 point is filled with broken robots?"

Could that happen?

Unclear. L2 is an unstable Lagrange point, so the robots wouldn't just stay put. But that doesn't mean they would leave, either, necessarily. They could end up in funky Lissajous orbits and go flying through L2 regularly.

The orbital mechanics around Lagrange points are weird.

If SpaceX’s Starship/Super Heavy (née BFR) actually pans out, it should be able to easily perform this mission.

With the irony being that if BFR pans out, this mission could have ended up being launched on it and eliminate a pile of complexity in the process. The mirrors wouldn't have to be hinged, for example.

Imagine going back to 1984, and telling the Hubble successor team "Just wait for a future heavy commercial space launch before planning any larger telescopes".

Or to 1997, and telling Goddard "Your specs will require technological development that we feel should be halted until a commercial spaceflight program develops. We're pretty sure next year someone will found a e-commerce business that will make him a billionaire, and he'll sort it all out."

Or to 2002, when tech internet tech was booming and paypal was going IPO, to tell TRW that the $824 million they just acquired should be put on a shelf until about 20 years later.

Or to 2005, 12 years before BFR was announced, when it appeared cost growth was a factor (not at all related to northrup aquisitions). Again, 2010 it passed review, 7 years before announcement. Is it really irony or somehow a waste? I don't think so.

(Full disclosure: I'm working on alternative tech to deoployables for large-aperture telescopes, but I greatly appreciate their efforts on JWST, given what we had over the last 20 years).

We also can't fix this, because it was designed to be unfixable. Making it fixable would counter productively make the design more complex.

With a $10 billion telescope dead in the water and the clock ticking, Louis Rossman leads a crack team of Apple repairmen -- specialists in fixing sytems designed to be unfixable -- through accelerated astronaut training for a last-chance human mission to L2! Will they save the day? Or will the inky clutches of space doom the mission and leave them stranded farther from civilization than any human in history?

Elon Musk spots them a SpaceX rocket. Joe Rogan puts them through basic training.

I'd watch this youtube red series

Can't wait for the theater version, starring Louis Rossman!

Starring Bill Nye and Neil deGrasse Tyson as Bill Nye and Neil deGrasse Tyson.

Minor nitpick, but the L2 point is selected so it doesn't need fuel to stay there. It's like a gravity well of the earth/sun system, any object getting a little further from it will get back to it.

I don't think that's true? At the exact L2 point, the forces are zero, anywhere off that point, they are non-zero, away from the point, from what I understand.

Ref: https://www.space.com/30302-lagrange-points.html "L1, L2 and L3 are all unstable points with precarious equilibrium."

That is incorrect, L2 is not a stable lagrange point, and will require station keeping adjustments to remain in position

They need to use fuel to station keep, there is a hard time limit to this.mission

Is it known how long it would last? Wikipedia doesn't say anything about this issue

The mission is minimum of 5 years with maximum 10 years based on the fuel.

https://jwst.nasa.gov/faq.html#howlong

What a shame. The mission won't be operational as long as its delays. After all that I'd at least hope there could be an option for re-fueling, but I bet there isn't.

After 10 years it will probably need more than just fuel. And doing maintenance in orbit, especially way out in the L2 point is easier said than done. Probably easier to build a new satellite with even more capability to replace it, except of course that the JWT is famously behind schedule and over budget and a more sophisticated replacement probably won't be any easier to build.

A replacement might actually easier to build. The detector is no small feat, but the major problems with JWST come from the foldable heat shield and the segmented mirror. Both of which are due to size constraints during launch. Basically it has to fit a 20 x 14 m heat shield and a 6.5 m mirror into the 6.4 by 4.6 m fairing of an Arianne 5.

Targeting a rocket with a larger fairing diameter (even at same payload mass) would make the design much simpler. An upper stage with 20 m length and 9 m diameter on a Falcon Super Heavy would allow to have a fixed mirror and heat shield that is only folded once, instead of the crazy origami that JWST is. But of course such an upper stage doesn't exist yet. SpaceX was only started 6 years after the work on JWST started...

L2 is unstable. There are stable Lagrange points that would be much better for this purpose if that was the reason.

The unique thing about L2 is that it's the only Lagrange point where the Sun is always blocked by the Earth. That's what they're going for here.

Not entirely true. Spacecrafts orbiting L2 do not stay still with respect to the Earth; rather, they follow a Lissajous orbit, which is quite efficient given the gravitational properties of the L2 point. Therefore, they will observe the Sun quite often. (The apparent size of the Sun from L2 is roughly the same as Earth's, so eclipsing the Sun would be too complicated.) And this is not bad, because otherwise solar panels could never produce the power necessary for the spacecraft to work!

The real reason why L2 is so interesting is that it violates Kepler's third law: despite being farther from the Sun than Earth, the orbital period is still the same as Earth, because of the gravitational attraction of Earth itself. This allows the spacecraft to keep the same distance from Earth during the year, which eases communications with ground stations.

(Disclaimer: I have been part of the Core Team of the ESA Planck mission, which flew around L2 like JWST will do.)

The spacecraft would also keep the same distance from the Earth during the year in Earth orbit, so there has to be another reason they picked L2.

The real reason for L2 is that the sun, moon, and Earth are all the same direction from the telescope when it is at L2, so the sunshield can block them all simultaneously. Yes, the spacecraft will receive insolation at L2 (yay solar power), but it will always be from the same direction and therefore the instrument can be persistently shielded.

EDIT: from the the horse's mouth:

> To have the sunshield be effective protection (it gives the telescope the equivalent of SPF one million sunscreen) against the light and heat of the Sun/Earth/Moon, these bodies all have to be located in the same direction.

> This is why the telescope will be out at the second Lagrange point.

https://jwst.nasa.gov/orbit.html

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