> Is JWST as brittle as the news want to make us think? Or are there technical reasons or acceptable failure modes that gives confidence that those steps are not as critical as the news let us people know?
There is no room for redundancy in many aspects of the design, unlike, say a Boeing 777 or Airbus A350.
How can you have a redundant heat shield, or primary mirror (two parts of which swing)? I'm sure some computer systems have redundancy and perhaps comms.
But like with a helicopter: how can you have redundancy in the tail rotor?
So with the JWST: there's no way around many SPOFs.
The answer to your redundancy question is: Assembly line.
Instead of ramping up a project, and building 1 of something, you would plan to do more than one, and you could iterate over time as you learn. SpaceX is doing a good job of this.
If 1 Webb telescope is valuable then wouldn't 3 or 5 also be valuable?
We have a number of proven space designs at this point: Soyuz, Spirit/Opportunity rovers.
It's really not - just by having more hardware available (at higher total expenses) doesn't make the pool of money available (public research funding) to book time on these things more. These things are one-off, you build a new one if you expect 10x improvement over the old one.
We don't need a fleet of X1 to break the sound barrier for the first time. We do need many Airbus/Boeings to fly people and stuff from A to B.
Note that that is the case with the unique research hardware you cite as well - we're not sending another Spirit/Opportunity, but have graduated to something else.
Soyuz is a different use case, as there is an economic demand to be filled - that's why a private company like SpaceX is in that sector with its Dragon. On the other hand, you don't see SpaceX cranking out Spirits or JWSTs or Washington Monuments.
The JWST only has a planned mission duration of 10 years. If it’s as epic as everyone claims it could be, there must be a follow up mission planned. So even if it fails, we’ll still see a successor at some point.
There are quite a few more telescopes planned, I think the next major one is the Nancy Grace Roman telescope, which is another infrared scope, made from an old NRO telescope. The decade survey called for another massive space telescope to look at the optical and UV spectrums, so Id expect that to be the next truly big flagship telescope.
Intermeshing rotors are interesting as an alternative to having a tail rotor. They are pretty slow & stable, should feather relatively safely as a failure mode.
Not the kind of heat shield you would use to re-enter.
The telescope is designed to image very faint sources of infrared light. The problem is that everything (including the telescope itself) glows in infrared. The hotter things are the more infrared they emit. Because of this you want to keep the instrument as cold as possible. (You do this because you don’t want to drown the faint sources by the glow of the telescope itself.)
Now of course there are parts which has to be “hot”. At least relatively to the very cold instruments. The solar panels are heated by the sun, the transmission electronics and the processing turns electricity into heat. The positioning thrusters burn chemicals which makes them hot.
Because of this they designed the spacecraft with two sides, a cold one for the instrument and a hot one for everything else. They even choose the orbit cleverly so they can keep the sun and the earth and the moon always on the hot side of the vehicle.
And then you have this problem that you have to make sure that the hot side won’t warm up your cold side. This is where the heat shield comes into play. Sometimes it is also called a sun shield since the sun is the main source of heat for it to shield against of course, but it also shields the instrument from the heat of the hot side equipments.
Structurally it is a 5 layer lassagne. They just replaced the pasta with metalized kapton tape and the sauce with the vacuum of space. It is about the size of a tennis court, launches folded up and will un-fold in space. Hopefully. :)
Thanks for the detailed answer! I forgot it was mainly for infrared but I didn't think of this implication anyway. Very interesting! I hope we'll see this in the coming days.
There is no room for redundancy in many aspects of the design, unlike, say a Boeing 777 or Airbus A350.
How can you have a redundant heat shield, or primary mirror (two parts of which swing)? I'm sure some computer systems have redundancy and perhaps comms.
But like with a helicopter: how can you have redundancy in the tail rotor?
So with the JWST: there's no way around many SPOFs.