James Webb Space Telescope Deployment—“29 Days on the Edge”

Here are some statistics to ponder:

  • 50 major deployment events
  • 178 release mechanisms
  • 300 single-point failure items
  • Sun shield:
    • 140 release mechanisms
    • 70 hinge assemblies
    • 8 deployment motors
    • 400 pullies
    • 90 cables, totalling 400 metres in length

All of this has to work, or the James Webb Space Telescope, which has been under development for 25 years and cost US$10 billion, will be space junk. Positioned in an Earth-Sun L2 halo orbit, no repair mission will be possible.


Begs the question, why not setup in high earth orbit and then thrust to Lagrange position? Also, Plan B is always just one SpaceX Starship launch away (when ready) !!!


The film mentions that the telescope, and especially the sun shade, is very fragile once the deployment is complete. The amount of delta-v to get from any Earth orbit where an existing spacecraft could rendezvous with it to L2 would require a enough thrust that the acceleration would probably damage the deployed structure. Also, the deployment will dramatically change the centre of gravity of the structure, so the transfer stage would have to be positioned to compensate for this, which would make it difficult to fit into the payload fairing.


I wonder if 300 single-point failure items is in the usual range for complex satellites or an outlier? I also wonder what odds one could get in Vegas on the likelihood it becomes space junk? I can’t find what is the nature of Earth’s shadow at L2. I would think in & out of penumbra & not ever fully eclipsed, but that’s only a guess.

The mission plan is for Webb to be in a halo orbit around the L2 point, not exactly at L2. That will guarantee it constant sunlight and communications with Earth.


Thanks for providing this earlier link, Mr. W.

I can’t help but think of “A Bridge Too Far” – the incredibly complex (and ultimately unsuccessful) Operation Market Garden in World War II. NASA has done some amazing things with complex equipment that had to work right, such as the Mars landers. But this video invites the obvious question – Was there some other approach that would get us 80% of what the JWST could do with only 20% of the risk?

Separate issue – but maybe related. OK, this video is a product of NASA’s Public Relations rather than their science & engineering. Still, the absence of young white males in the video was painfully obvious. If the video accurately represents an organization in which gender & skin tone take precedence over technical competence, the Vegas odds on a successful mission would have to go down.

I am reminded of a photo in a Boeing Annual Report from a few years back, where the then-CEO was shown proudly surrounded by the recently-hired new engineering graduates – again with noticeable significant under-representation of individuals with one specific combination of gender & skin tone. Then the 737-Max started dropping out of the skies.

I am not suggesting that those diverse new hires had anything to do with the failures of the Max. I am suggesting that when an organization in a highly technical area starts to focus on individual’s external features rather than on technical competence, bad things will inevitably follow.


You succinctly state a simple, profound truth, which will need much courageous repetition - even though it is actually known by all but the most ideologically-blinded, emotionally incontinent bullies in control of Google, Twitter, Facebook and their accomplices.They will remain incapable of observing this truth until their very platforms collapse beneath their (low carbon) footprints due to the cumulative incompetence of those hired by means other than merit (due to inflation, 4 letter words may now include 5 letter words; I nominate ‘merit’ to head that bloated obscene roster).


We live in fascinating times. I found the following video to focus a bit more on the science, and less on the “rah-rah”.


Thanks for that link, ra. Definitely fascinating!

One has to wonder – when the detailed plans were being laid out with all their astonishing complexity and the 300 potential points of failure, someone must have suggested: Why not simply place the telescope on the far side of the Moon, and use it during the lunar night. Yes, it would need a lot more cooling, but for $10 Billion, it is probably possible to put quite a lot of mass on the lunar surface. And it would in principle be repairable.

Obviously, that guy was defenestrated. One wonders why?

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The far side of the Moon has a lot of disadvantages for an infrared telescope such as Webb. The cooling situation is many, many, times worse than in deep space. Even during the lunar night, the Moon’s surface is bright in the infrared, drowning out faint signals from distant objects. The only solution would be to use an active cryogenic cooler, which would be a mechanism likely to fail and probably requiring periodic servicing with helium to replenish leakage. In deep space, it is (barely) possible to achieve the required cooling entirely passively with a multi-layer sun shield. This extends mission duration and reduces the possibility of active component failure.

On the Moon’s surface, you only have sunlight half the time. That means a solar powered observatory will only be able to operate 50% of the time and, even worse, only when the Sun is in the sky, hampering observations near it in the sky. On the far side, you have no direct radio communications with the Earth, requiring a relay satellite in an Earth-Moon L2 halo orbit. That’s more expense, complexity, and another thing to fail. Finally, fixed on the lunar surface, even if you’re on the lunar equator you can only see half the sky at once, and which half depends upon where the Earth and Moon are in their orbits. The deep space observatory can observe most of the sky except close to the Sun. Finally, landing such a payload on the Moon and deploying it in 1/6 gravity would be much harder than delivering it to L2 in weightlessness.

The far side of the Moon is a superb location for a radio telescope—it is the only place in the solar system permanently shielded from the radio noise of the Earth. But it’s far from ideal for an infrared telescope.


Agreed that there would be many issues with a telescope on the far side of the Moon – just as there are 300 potential single points of failure with a sun-shielded telescope at L2.

The aim would be to operate the telescope only during the Lunar night, when temperature reportedly falls to about -300 deg F (-180 deg C). That limits the amount of further cooling necessary. The obvious source of power would be nuclear (as has been done for various satellites) since the telescope would be operating in the dark.

That is indeed the case – but it is completely feasible, as China is proving with its far side of the Moon lander.

It is back to the issue of how else could one deploy $10 Billion to achieve the mission objectives – preferably in a way that does not have the risk of so many potential points of failure.

Let’s wish NASA good luck!

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