JWST Launches



The James Webb Space Telescope (JWST) launched on Christmas Day, 25 December 2021. And, what a Christmas present it was — thirty years in design, fifteen years in construction, thousands of engineers employed, and ten billion dollars spent.

The JWST has been well described in numerous publications. (I always start with (and donate to) Wikipedia.) My purpose here, as always, is just to share some of my favorite write-ups, YouTubes, and personal stories involving the JWST.

The Webb is an international collaboration among NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA). So, the best website describing the JWST is NASA's.

JWST people

The JWST team assembled at NASA's Goddard Lab in Maryland

My next door neighbor, Mike, a senior Lockheed engineer has been vibration testing the JWST for several years. He places various components on a shake table to make sure they can withstand all the thermal and launch stresses. This has involved successive trips to Goddard Space Flight Center in Maryland, to Northrup in LA, and to JPL in Pasadena. He and I have been awaiting the launch for over a decade.

I initially started following the JWST's progress at its inception 15 years ago. It was regularly discussed in lectures at the SETI Institute in Mountain View, California.

Several of my favorite space bloggers deserve your attention. In random order — Astrum is a consistenly excellent YouTube site. For example, here is Astrum's Alex McColgan showing the Webb's Fascinating Deployment from Start to Finish. The intricacies of these events have had the science world on edge since the Chistmas Day launch. (As I write this on 2 Jan 2022 tensioning of the sunshield has just begun following the successful unfolding of the shield's five Kapton layers.) The shield must keep the infrared-sensitive instrument pack at a cool 40 degrees Kelvin (that's minus 233 degrees Celsius.)

I regularly listen to physicist Prof. Brian Greene's World Science Festival. Here this superb panel of scientists discuss the Webb's science goals. I've despaired at the improbability of successful deployment. Now it seems that success is just around the corner.

Webb is Fully Deployed!

On 8 January 2022 NASA held a press conference to make this major announcement. After launching on Christmas Day exactly two weeks ago the JWST has deployed all its major subsystems. The latest milestone was the locking into place of the two side wings of the primary mirror. Now all eighteen hexagons of the primary mirror are in place. Where is Webb? (Here's the fast answer in one image.)

Over the past two weeks the JWST has had to accomplish depolyments involving 344 single-point failure devices (the failure of any one of which would have doomed the entire mission.) This was an outstanding achievement. How do you achieve that kind of reliability? The brief answer is by using shape-memory alloys as explained here at Northrup Grumman's JWST website.

Stay tuned. This article is under development. More soon.

Published: January, 2022


Correspondence


I welcome substantive comments on all my articles. With your permission I may include excerpts. You can post here anonymously, but to do so you should have a verifiable identity, eg a website, Linked-in ID, or Facebook page, etc. Mail comments to bob AT bobblum DOT com (with the usual syntax.)


9 Jan 2022: Electro-optics engineer Dennis Hancock writes:

Bob: yes, lots of amazing technology on the JWST. For example, of the many, many specifications we had to deal with during the design competition was the one related to the cryo-actuators being used to control the surface shape of the mirror. (Not the tip-tilt actuators for each hexagon.) The specs were: zero power on hold, operation at 10 K, 1 mm total stroke length with 1 nm resolution, no hysteresis, and something like 25 newtons of force output. (incidentally the original NASA request was to have something like 12 actuators pushing on each hexapod to adjust the shape, or figure, which was imagined to change due to thermal warpage. Now I see they only have one cryo-actuator to be used for radius of curvature control.)

And yes, my understanding is the primary mirror segments will be phased up now while enroute to L2. I’m not current with the rms spec but the mirrors are to be positioned to be on the imaginary parent surface , which I ‘ve read is an ellipse of some unknown to me eccentricity . The rms surface figure used to be something like 10 nm. This is a good trick to accomplish wherein the 18 surfaces need to be controlled as to tip and tilt as well as in-and-out along the optical axis. (That last part is referred to ‘piston’ in the adaptive optics world.)

So yea. You can get an idea of what the image of a star will look like when this alignment is completed by looking at my video at http://www.DennisHancock.com about Ultra High Precision Optical Distortion Measurement. The left panel when the sensor’s image plane is at 0 distance away from the optical design spec, gives you the point spread function for a circular primary, the famous Airy disk pattern. (The Webb’s point spread function will be a bit different due to the gaps between hexagons as well as the over-all primary shape not being a circle. But the wave physics is the same.)


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