And this isn't like hubble, where we could (and did) send up a space shuttle to fix an issue after launch. Really scary.
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.
"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...
"Send another robot!"
Could that happen?
The orbital mechanics around Lagrange points are weird.
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).
I'd watch this youtube red series
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.
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 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.
Ref: https://www.space.com/30302-lagrange-points.html "L1, L2 and L3 are all unstable points with precarious equilibrium."
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...