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The NuSTAR satellite will be the first space telescope capable of focusing high-energy x-rays into high-quality imagery--a feat that requires some incredibly intricate optics
January 26, 2011 | 8
One of NuSTAR's two mirrors, or optics, is assembled inside a clean room at Columbia University's Nevis Laboratories in Irvington, N.Y. Each optic will have 133 concentric shells of reflective glass separated by spacers that are held in place by epoxy....[More]
After completing each concentric layer of glass, engineers slide a bar into place, guided by the wheels at either end of the assembly machine, to put pressure on the glass while the epoxy is curing....[More]
This shot shows the front of a NuSTAR optic, with the spacers neatly stacked up between each layer of glass. The spacers create tiny gaps through which x-rays will pass once NuSTAR is launched and reaches its low Earth orbit destination next year....[More]
This is one of two hard-x-ray detector units developed at the California Institute of Technology. The detectors will sit on the opposite end of a long extending mast from the optics and will record the images that the optics capture, much like film in a camera records optical light captured by a lens....[More]
At launch, NuSTAR can be no larger than two meters long and one meter in diameter to fit on board a Pegasus rocket. Once it is in orbit, NuSTAR's extendable mast will deploy, folding out to about the length of a school bus with the optics at one end and the detector at the other....[More]
An engineer at the NASA Goddard Space Flight Center in Greenbelt, Md., examines a thin glass sheet destined for one of NuSTAR's optics. Each piece of glass, akin to the type used in laptop and cell phone screens, starts out flat....[More]
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8 Comments
Add CommentHow precisely does one go about 'focusing' X-rays? I was under the impression that they are difficult to refract. And where does NuSTAR's elaborate arrangement of mirrors come into the picture?
Reply | Report Abuse | Link to thisAnyone in the know out there, do enlighten me.
X-rays can be focused, but it's difficult. X-rays reflect (not refract) at what's called grazing incidence angles - i.e., *very* small angles. The higher the X-ray energy, the smaller the angle. That's why the mast of NuSTAR has to be so long, so that X-rays of very high energies (5-85 keV) have a long enough space to reflect and focus at the detector.
Reply | Report Abuse | Link to thisVery good question, rushil2u, and excellent explanation, starsandspice - thanks!
Reply | Report Abuse | Link to thisSo the x-rays focused in any single image must be within a very narrow window at a very specific distance - is that correct?
Just wondering why they picked glass for the "focusing" mechanism...If I remember correctly...previous x-ray telescopes used stainless steel.....
Reply | Report Abuse | Link to thisXMM had aluminum shells, if I recall, and Chandra had 2mm glass. But where Chandra had 4 layers, NuSTAR has 133 in each optic. Also, each NuSTAR shell is 1/10th the thickness of a Chandra shell. They chose glass because it was lightweight, cheap and the easiest to shape.
Reply | Report Abuse | Link to thisYou may find an in-depth explanation of NuSTAR's optics here: http://www.nustar.caltech.edu/about-nustar/instrumentation/optics
Reply | Report Abuse | Link to thisThe details of X-ray optics were given in the Sci Am article about the Uhuru satellite in the late 60s or early 70s. Sad to see that this article wasn't nearly as thorough, and also that the online archive doesn't go back nearly that far.
Reply | Report Abuse | Link to thisBut yes, it's very hard to refract X-rays, so the satellites use reflecting optics. The problem with that is that the fraction of X-rays reflected is small unless the angle of reflection is very small. It sounds like they use multiple, concentric mirrors, and each mirror has a layered reflective coating.
I'd have liked to see more detail on how they get all the mirrors to reflect coherently, the detector system, and how the deployable mast system achieves accurate enough alignment. For that matter, the sizes of the components aren't even discussed in the article!
I might be wrong above, the first X-ray focusing optics may have been on the Einstein satellite.
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