JWST Built with ‘Unobtainium’


The James Webb Space Telescope (JWST) is the much anticipated, long awaited “next generation” telescope, which we hope will look further back in time, and deeper within dusty star forming regions, using longer wavelengths and more sensitivity than any previous space telescope. In order to take us to this next level, you’d kinda figure that new technologies would have to be developed in order for this ground-breaking, super-huge telescope to be built. You’d be right.

In fact, engineers had to use a little unobtainium to build the one-of-a-kind chassis, the backbone that will hold the spacecraft together.

Unobtainium isn’t just the name of the material mined in James Cameron’s movie “Avatar.” It is a word used in engineering — and sometimes fiction – to describe any extremely rare, costly, or physically impossible material or device needed to fulfill a given design for a given application.

The chassis for JWST – called the the Integrated Science Instrument Module ISIM – is made of a never-before-manufactured composite material which had to withstand the super-cold temperatures it will encounter when the observatory reaches its orbit 1.5-million kilometers (930,000 miles) from Earth.

The ISIM just passed an extremely important test, surviving temperatures that plunged as low as 27 Kelvin (-411 degrees Fahrenheit), colder than the surface of Pluto during a cycle of testing in Goddard’s Space Environment Simulator — a three-story thermal-vacuum chamber that simulates the temperature and vacuum conditions found in space.

The team at Goddard Space Flight Center who were charged with building the chassis needed a material that would assure the various instruments on JWST would maintain a precise cryogenic alignment and stability, yet survive the extreme gravitational forces experienced during launch.

The test was done to find out whether the car-sized structure contracted and distorted as predicted when it cooled from room temperature to the frigid — very important since the science instruments must maintain a specific location on the structure to receive light gathered by the telescope’s 6.5-meter (21.3-feet) primary mirror. If the structure shrunk or distorted in an unpredictable way due to the cold, the instruments no longer would be in position to gather data about everything from the first luminous glows following the Big Bang to the formation of star systems capable of supporting life.

When they first began, there was nothing out there that remotely fit the description of what was needed. So, that left one alternative: developing their own as-yet-to-be manufactured material, which team members jokingly referred to as “unobtainium.” Through mathematical modeling, the team discovered that by combining two composite materials, it could create a carbon fiber/cyanate-ester resin system that would be ideal for fabricating the structure’s square tubes that measure 75-mm (3-inch) in diameter.

During the recent 26-day test, and with repeated cycles of testing, the truss-like assembly designed by Goddard engineers did not crack. The structure shrunk as predicted by only 170 microns — the width of a needle —when it reached 27 Kelvin (-411 degrees Fahrenheit), far exceeding the design requirement of about 500 microns. “We certainly wouldn’t have been able to realign the instruments on orbit if the structure moved too much,” said ISIM Structure Project Manager Eric Johnson. “That’s why we needed to make sure we had designed the right structure.”

This type of structure could serve NASA in the future for the next-generation beyond JWST, and could also be a “spinoff” that manufacturers could find useful in designing structures that demand a high tolerance in conditions.

Source: NASA Goddard

15 Replies to “JWST Built with ‘Unobtainium’”

  1. MISTER T:

    How does a square tube have a diameter???

    According to the Oxford English Dictionary:

    diameter — noun 1. a. a straight line passing from side to side through the centre of a body or figure, especially a circle or sphere.
    b. a transverse measurement of something; width or thickness.

  2. I am little surprised to learn that the main spacecraft structure to operate at 27 Kelvin. I suppose that can help to prolong the coolant life. But typically primary structure is internal to satellite you know. It will be fun to know how to keep hot power system and electronic system from interfering with structure cooling uniformly! Temperature gradient can warp structure like pretzels.

  3. The first link in this article takes you to the James Webb Telescope main page. There’s a ton of info. in there to browse through…. What’s going to be ‘trick’ with this scope is always keeping the sunshade between Sol and the Integrated Instrument Module (The IIM structure is shown above) which must be kept extremely cold for the instrument suite to perform correctly. On the other side of the shade/screen is the spacecraft bus, which will hold the
    # Electrical Power Subsystem
    # Attitude Control Subsystem
    # Communication Subsystem
    # Command and Data Handling Subsystem
    # Propulsion Subsystem
    # Thermal Control Subsystem

    This You Tube animation sequence shows how the spacecraft becomes a telescope. It kind of reminds me of a ‘Transformer’? Everything seems to keep unfolding and unfolding and… is WAY trick!


  4. @Mister T – My thought and question EXACTLY! : )

    Aren’t ya glad the Shuttle went and fixed up the Hubble so that the Webb Telescope scientists could have the luxury of this kind of development?

    The Shuttle program took the hobbled Hubble and made it wonder Hubble and then, again, it took a hobbling Hubble and made it into wunder Hubble!

    Can’t wait to watch Webb “Transformer” live…

  5. Well I suppose you do need to test the Instrument Structure at its operational temperature to see if some component was not made to spec. You do realize that this structure houses number of instrument, which will be hot. And from the images online, it will be enclosed and not out their in the breeze. Which makes passive uniform cooling difficult.

    Scariest part is the number of mechanisms needed to deploy every thing. One glitch, one hung up, and you got dead telescope!

  6. I stand corrected. Covering up the structure will ensure that heating environment is more uniform. It keeps inside nice and toasty warm. And you don’t get this spike of heat source from separate boxes.

  7. The expansion goes roughly as the fourth power of temperature, unless you have something wacky like a phase change unlikely for a solid at these temperatures. You will probably get most of the contrastions by the time you have gone to liquid nitrogen temperatures. Of course, you might as well take it all the way down to the operating temperature while it’s on the ground.

    I used to made stuff that was supposed to run in liquid helium. Circuits worked under helium, though some things olike the Allan-Bradley carbon resistors changed so much they could be used as a helium depth gauge. I held metal parts together with pastic bolts because those would contrast more and so stay tight. Blu-tack is really tough at these temperatures. If you can’t get enough unobtanium, try filling it out with Blu-tack.

  8. “and could also be a “spinoff” that manufacturers could find useful in designing structures that demand a high tolerance in conditions”

    Maybe yet another material that will save lives that those who poo poo the money spent on space and astronomy conveniently ignore.


  9. Hello Astronary.

    Try wearing a business analyst’s hat for a second.

    It has been pointed out by others in previous posts that the Hubble (HST) owes its basic design to the NRO’s obsolete fleet of Keyhole surveillance satellites, hence the similarity in size and shape etc., the differences being that Keyholes were pointed toward Earth and launched on Titan III rockets. At the price point of the HST, (much, much less than the Shuttle system used to service it), it would have been far cheaper to launch a brand new HST each time on a Titan III or similar than use the Shuttles to extend the life of a single HST!

    If you are still wearing the hat, you might also consider that if the savings from NOT using Shuttles to service a single HST where turned into launching a formation of HSTs, we could have had a space based optical interferometer for imaging exoplanets by now. In this manner the Shuttle way of servicing the HST has held back astronomy by many many decades (ref: SIM-lite and TPF mission delays and cancellations).

    In regards to the JWST program, some are becoming alarmed at the cost overruns and as with the Shuttle/HST topic in your post, whether or not the JWST is a good science investment may depend on how better the same money could have been spent and $5,000 million USD so far makes for a hole lot of alternative spending.

  10. Meanwhile Herschel is already out there at L2 doing all of this. Perhaps they used previously unobtanium.

  11. I like the economic sanity espoused here. Mega-projects being late or difficult means mega-waste.

    @ Mister T:

    While not so much used, sensibly diameter has been generalized since the greek idiosyncratic definition.

    Actually already Wikipedia has a good definition:

    For a convex shape in the plane, the diameter is defined to be the largest distance that can be formed between two opposite parallel lines tangent to its boundary,

    So the diameter of a square shape is its diagonal. Inside info is that next HP movie will show Potter doing a Diame Trick to get to the magic market (Diagon Alley).

  12. TerryG, you are exactly right. And since NASA seems to be more of a “works project,” more interested in providing jobs than science, think of how many more people could have been employed building a fleet of HSTs.

    A fleet of HSTs could also be used the way many earth-based telescopes combine their abilities, across vast distances, to create huge “virtual apperatures.”

    I’m sure the could have imaged exoplanets.

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