Why the launch of James Webb Space Telescope postponed?

There are possible reasons why James Webb Space Telescope postponed. The main reason for the delay of James Webb Space Telescope is that the technology needed took longer to develop than expected.

Let me try to explain why. You see, the Webb telescope is put together from segments. The reason for that is that rockets are only so big, and telescopes larger than about 2.5 meters just won’t fit inside the faring. Here is the James Webb telescope primary mirror compared to the Hubble primary mirror:

The Hubble is about as large as you can launch intact, so the segments have to be stacked up for launch and then connected together in orbit. Except that they have to be oriented and positioned to an accuracy of about 1/50 wavelength of light. That is about 20 nm, or roughly the 50 times the diameter of an atom.* Not only do they need to be aligned in 6 degrees of freedom, but they have to remain undeformed.

There were ideas on how to measure the segments and move them with micro-positioners. However, nothing really worked as planned. You see, when you are talking about such small changes in position, the mirrors twist and bend and deform when you try to hold them or move them. We have a saying that most people probably won’t understand. “When you need a precision of nanometers, everything is made of rubber.” There are many ideas you have that you think would have to work and you would swear it’s going to work this time. You test it, and right before your eyes, it bends out of shape instead of moving to a new position. Imagine it like this: suppose I measure a bridge to be very slightly tilted.

Suppose I put a jack under the low corner and jack up that corner an inch. I measure the tilt of the bridge: unchanged! I look at the corner I jacked up and realize I just bent the corner of the bridge by an inch.

NASA is not the only government organization to try to build a telescope as a smart structure. We designed a segmented telescope for the space based laser. We had some of the same people involved who were working on the NGST (that’s what it was called before it was called the JWST).

However, NASA is the only organization to stick with it. When costs escalated for other government agencies, they shut it down, rather than subject themselves to the Nunn-McCurdy Act of 1982. NASA is not covered by this act. But more importantly, NASA does not want the stigma of a failed space telescope. They also view this as a trail blazer for other large telescopes. Recently, Congress put the JWST on special notice: no more cost growth!

So yes, the costs escalated on the JWST by even more than the shuttle program, which is an unenviable accomplishment. The schedule delay is legendary. The issue is that NASA was led to believe that the technology was at TRL5 to 6 when it was actually more like TRL 4. Many people do not understand the TRL scale very well and they consistently overestimate the TRL of their technology. As soon as someone says his technology is TRL 7, I know that he doesn’t really understand TRLs.
This means that NASA for once is developing a technology that the Air Force, MDA, the Navy, the astronomy community, and everyone else who uses large optics will benefit from.

Segmented primary mirror built for the DARPA space based laser program (later part of the Air Force/MDA space based laser program) This was named the Neil Griff telescope.

Segmented primary mirror telescope at the Naval post graduate school.

NASA Technology Readiness Levels (TRLs)

*Based on a van der waals atomic diameter of uranium of 400 pm.

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