Explanation: What's left after a star explodes? To help find out, NASA launched the Nuclear Spectroscopic Telescope Array (NuSTAR) satellite into Earth orbit last week. NuSTAR's ability to focus hard X-rays emitted from the nuclei of atoms will be used, among other things, to inspect the surroundings of supernova remnants so as to better understand why these supernovas occurred, what types of objects resulted, and what mechanisms make their surroundings glow so hot. NuSTAR will also give humanity unprecedented looks at the hot corona of our Sun, hot gasses in clusters of galaxies, and the supermassive black hole in the center of our Galaxy. Pictured above is an artist's illustration depicting how NuSTAR works. X-rays similar to those used in your dentist's office enter the telescope on the right and skip off two sets of parallel mirrors that focus them onto the detectors on the left. A long but low-weight mast separates the two, and the whole thing is powered by solar panels on the upper left. Part of the excitement involving NuSTAR is not only what things it is expected to see, but by looking at the universe in a new way, what things that are completely unknown that might be discovered. NuSTAR has a planned two year lifetime.
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk. — Garrison Keillor
I see NuSTAR has a planned 2-year service life. Via the 'skip-off' link, i hope they have enough rocks to last that long. Via the 'looking' link, i am finding that someone aboard the good ship Asterisk* has a big fondness for cats. Can't say anything against that. They do seem to position themselves for lots of purr-fect pictures.
<<Astronomical focusing of visible light by the use of mirrors and lenses is an old art, dating back 400 years to Galileo's first observations with his home-made telescope in 1609. However, scientists only recently discovered how to do the same with X-rays. With the intention of constructing an X-ray microscope, the German scientist Hans Wolter in 1952 designed a reflective optic for focusing and imaging X-rays. His invention, called the Wolter Type I or Wolter-I design, has since been widely used for astrophysical purposes, despite its original invention as a microscope.
The Wolter-I mirror reflects X-rays twice, once off of an upper mirror section shaped as a parabola and a second time off a lower mirror section shaped as a hyperbola. The surfaces of the mirrors are nearly parallel to the incoming X-ray, allowing the X-ray to become reflected instead of absorbed. The shallow angles, however, result in a very small collection area per surface and, to overcome this, consecutive shells of varying size are nested tightly together to fill out the aperture.
The first focusing X-ray telescope in space was the Einstein Observatory (also known as HEAO 2), launched in 1978. Since then, there has been a steady stream of missions to improve and expand upon the mirror design of the Wolter-I telescope in an effort to make images sharper and more sensitive.
NuSTAR will fly two Wolter-I optic units, each pointing at the same patch of sky. The co-aligned units increase collecting area, thus providing more sensitive images in a given amount of time. The images are co-added on the ground.
The reflection of X-rays not only requires very small incidence angles and precise construction of the reflecive surfaces. It also depends strongly on the material of the mirror and the surface smoothness of the mirror. Past missions, such as Chandra and XMM-Newton, used high density materials such as Platinum, Iridium and Gold as mirror coatings to achieve high reflectivity for low energy X-rays. However, the efficiency of those mirrors to reflect higher energy photons falls off rapidly. To overcome this threshold, the NuSTAR mirrors will be coated with structures called "depth-graded multilayers".
Multilayers are thin coatings of two alternating materials deposited one on top of the other. A typical multilayer has 200 pairs of coatings. To achieve enhanced reflectivity, a high density contrast between the two materials is needed, and common high density materials are Tungsten (W) and Platinum (Pt), while common materials for the low density layers are Silicon (Si), Carbon (C), and Siliconcarbite (SiC). In this manner, the multilayer stack acts as a crystal lattice and constructive interference creates enhanced reflectivity, superior to a single mirror reflection at the high energies probed by NuSTAR. NuSTAR will fly Pt/SiC and W/Si multilayers, allowing the mirrors to reflect energies all the way up to 79 keV. Above this energy, the Platinum starts absorbing rather than reflecting X-rays. Previous focusing X-ray missions were only sensitive out to approximately 15 keV. NuSTAR will therefore greatly expand the observational energy range for focusing telescopes to higher energies.
NuSTAR implements a conical approximation to the Wolter-I design and consists of 130 concentric mirror shells coated with Pt/SiC amd W/Si multilayers. The NuSTAR optics have an overall length of 450 mm (1.5 feet), a maximum radius of 191 mm (7.5 inches) and a focal length of 10 m (33 feet). The NuSTAR team has developed a novel approach to building these optics, focusing on a light-weight design. The mirror substrates are thin sheets of flexible glass, akin to laptop and cellular phone displays, which start out as flat sheets. At NASA's Goddard Space Flight Center in Greenbelt, Maryland, the glass is heated in an oven and slumped over precision polished cylindrical quartz mandrels to achieve the right curvature. The slumped mirror segments are then deposited with a multilayer coating at the DTU-Space at the Danish Technical University in Copenhagen.>>
I'm sure NuSTAR will allow people to do some marvelous science but we need to look beyond all that. The satellite has a projected two-year operational lifetime but what about after that? Will NuSTAR simply become another piece of stuff in the great junkyard in the sky or does it have the means for its own fiery demise? Science is great but we also need to look at these things from an ecological point of view.
zbvhs wrote:
I'm sure NuSTAR will allow people to do some marvelous science but we need to look beyond all that. The satellite has a projected two-year operational lifetime but what about after that? Will NuSTAR simply become another piece of stuff in the great junkyard in the sky or does it have the means for its own fiery demise? Science is great but we also need to look at these things from an ecological point of view.
The two-year operational lifetime is just what has already been planned & paid for and what was put into the original spec(ification)s.
If NuSTAR is still in good operating condition after the two-years they will request operating costs in order to run another year or two. (It might be assigned new tasks or even renamed OldSTAR.)
The primary surface mission for Opportunity, MER-B (Mars Exploration Rover – B) was planned to last 90 sols;
the mission has received several extensions and has been operating for 3068 days since landing.
zbvhs wrote:I'm sure NuSTAR will allow people to do some marvelous science but we need to look beyond all that. The satellite has a projected two-year operational lifetime but what about after that? Will NuSTAR simply become another piece of stuff in the great junkyard in the sky or does it have the means for its own fiery demise? Science is great but we also need to look at these things from an ecological point of view.
NASA's over two decades ahead of you on that one. In 1988 it became an official policy to take steps to minimize the creation of orbital debris. The policy was informal at first, but by 1997 had been boiled down to a set of standard methods of preventing the formation of orbital debris, including end-of-life disposal.
At the altitude NuSTAR is orbiting, it can be expected to fall back to earth within about 20 years.
"Any man whose errors take ten years to correct is quite a man." ~J. Robert Oppenheimer (speaking about Albert Einstein)
NuSTAR XRay Telescope Launched
