James Webb Space Telescope
It is hard to believe that there was a time when the James Webb Space Telescope was supposed to launch in the first decade of the new century. The new launch date, which has slipped several times, is now 2018. It does appear that real progress is being made though. As can be seen in the live clean room camera at Goddard Space Flight Center where the instrument sections of the satellite are being constructed. Recently the telescope also had its cameras installed. Being one of the most expensive projects NASA is undertaking this important mission is finally making real strides towards launch after delays, not so much due to technical issues, but due to financial issues. The head of NASA issued a statement about how important this mission is and the dedication of NASA to it.The funding for the mission was spread over several extra years in order to keep the mission going. These delays ultimately wind up costing the taxpayers more money in the long run as opposed to just building the satellite as planned but that is a topic for another post.
For now it is good news that there is actually hardware in clean rooms being put together to create this mighty telescope. With the recent addition of the backplane support frame, a fixture that will be used to connect all the pieces of the telescope together.
The backplane support frame will bring together Webb’s center section and wings, secondary mirror support structure, aft optics system and integrated science instrument module. ATK of Magna, Utah, finished fabrication under the direction of the observatory’s builder, Northrop Grumman Corp.
The backplane support frame also will keep the light path aligned inside the telescope during science observations. Measuring 11.5 feet by 9.1 feet by 23.6 feet and weighing 1,102 pounds, it is the final segment needed to complete the primary mirror backplane support structure. This structure will support the observatory’s weight during its launch from Earth and hold its18-piece, 21-foot-diameter primary mirror nearly motionless while Webb peers into deep space.
“Fabricating and assembling the backplane support frame of this size and stability is a significant technological step as it is one of the largest cryogenic composite structures ever built,” said Lee Feinberg, James Webb Space Telescope optical telescope element manager at NASA’s Goddard Space Flight Center in Greenbelt, Md.
The frame, which was built at room temperature but must operate at temperatures ranging from minus 406 degrees to minus 343 degrees Fahrenheit, will undergo extremely cold, or cryogenic, thermal testing at NASA’s Marshall Space Flight Center in Huntsville, Ala. The backplane support frame and primary mirror backplane support structure will shrink as they cool down in space. The tests, exceeding the low temperatures the telescope’s backbone will experience in space, are to verify the components will be the right size and operate correctly in space.
The primary mirror backplane support structure consists of more than 10,000 parts, all designed, engineered and built by ATK. The support structure will measure about 24 feet tall, 19.5 feet wide and more than 11 feet deep when fully deployed, but weigh only 2,138 pounds with the wing assemblies, center section and backplane support frame attached. When the mission payload and instruments are installed, the fully populated support structure will support more than 7,300 pounds, more than three times its own weight.
The primary mirror backplane support structure also will meet unprecedented thermal stability requirements to minimize heat distortion. While the telescope is operating at a range of extremely cold temperatures, from minus 406 degrees to minus 343 degrees Fahrenheit, the backplane must not vary more than 38 nanometers (approximately 1 one-thousandth the diameter of a human hair).
The primary backplane support structure is made of lightweight graphite materials using and advanced fabrication techniques. The composite parts are connected with precision metallic fittings made of invar and titanium.
“The ATK team is providing program hardware that is arguably the largest and most advanced cryogenic structure ever built,” said Bob Hellekson, ATK’s Webb telescope program manager.
The assembled primary backplane support structure and backplane support frame are scheduled for delivery to Marshall later this year for the extreme cryogenic thermal testing. They will undergo structural static testing at Northrop Grumman’s facilities in Redondo Beach, Calif. in early 2014, and then be combined with the wing assemblies.
The James Webb Space Telescope, the successor to NASA’s Hubble Space Telescope, will be the most powerful space telescope ever built. It will observe the most distant objects in the universe, provide images of the first galaxies formed and see unexplored planets around distant stars. The Webb telescope is a joint project of NASA, the European Space Agency and the Canadian Space Agency.
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I can only go back to my basic theme that everything that we do in space needs to be oriented towards our long term presence there. Every satellite needs to have provisions for repair or de-orbiting and there need to be standards that allow such to be built so that a standard robotic/telerobotic unit of reasonable capability can work on them. It will never be energetically efficient to approach every piece of equipment in all orbits, but with proper design, all will be able to be de-orbited if they cannot be repaired. Once we have a permanent presence in GSO and possibly lower, we can use laser deceleration to move almost all small debris and satellites out of LEO and MEO. Above that, we will probably have to use highly efficient tugs or tethers to manage, though at those orbits, there is much less to do.
And, to be more specific, it is criminal to wait until after boost out of Earth orbit to do such essential functions on such an expensive piece of equipment. The loss of that mission would be a death blow to the overall NASA science mission, considering the number of missions that have been and will be forgone because of it.
This fantastic expense to build a supposedly invariant structure is a total wast of time and money. As I worked on one of the early laser disc projects, we ran into this same problem, trying to manufacture dependably accurate and stable platforms for the lasers. We could not do it, but we could build dynamic alignment capabilities into the drives. Haven't we learned enough from the Keck telescopes to be able to do adaptive optics. If a platform is fully and accurately characterized, then absolute rigidity is less important. If we had modular, on-orbit assembly with a tug to transport and possibly maintain, the need to create something of that size at that extreme low mass with that level of rigidity would go away.
On your first point about the structure. I do not work on JWST any more but I do know that the mirrors are adaptive. They flex as needed to maintain the shape of the overall mirror. I suppose that the structure also has to be as stable as possible so that the amount of work the adaptive optics has to do is minimized. As for your second point I agree. I was at a speech at Goddard Space Flight Center a few years ago at which the NASA Administrator Michael D. Griffin was speaking. When an engineer in the audience asked the question about JWST and servicing it he answered that by the time we launch JWST we will be a solar system fairing nation. We would be back on the moon and able to send astronauts to service JWST. Of course back then we were back on the moon by 2015...(yea right I believed that). There was also discussion about putting hand holds on JWST. (Why if it was not serviceable). In any case the fact that it does not deploy the mirror, heat shields etc. until it is out of Earth orbit means it cannot be fixed if something goes wrong...It would be like the partially deployed antenna on Galileo. There would just be nothing we could do about it. I always thought it was smarter to get it deployed while it was still in earth orbit, test it, and then send it out to it's final position. At least that way we could go up and fix it if something was wrong.
For a mission as expensive and important as this we really do need to get it right. If course if something does fail we would then find a way to send something, most likely a robot, to hopefully fix it. But that would take years to develop and cost a significant amount of money as well.