This guest post by Geeked on Goddard friend, Andy Ptak, is about an exciting new X-ray astronomy mission that’s about to be launched.
What is NuSTAR?
This week NASA plans to launch its next X-ray astrophysics satellite, NuSTAR. X-rays are where really exotic stuff in the Universe shines, like black holes, supernovae explosions (massive stars blowing themselves up) and really, really hot gas (millions of degrees or hotter).
But it is very hard to focus X-rays. As any card-carrying astronomer would tell you, you focus X-rays in the same way you skip a rock on a lake (we risk getting our X-ray astronomer card taken away if we don’t use that analogy). Normally an X-ray photon would go right through a mirror just like tossing a rock would splash into water. But if it hits at a slight angle, the X-ray will bounce off.
NuSTAR will be the first satellite to focus astrophysical X-rays at highest X-ray energies, some roughly at the same energy as those used in medical X-rays. Scientists and technicians at Goddard helped make the glass used for the NuSTAR mirrors, and several of us went up to Nevis Labs (part of Columbia University in New York) to help with the testing of the mirrors once they were completed last year.
A problem with focusing X-rays is that it means you need to keep the mirror and detector far apart, especially if you want to focus very energetic X-rays. NuSTAR is also designed to be very inexpensive (by satellite standards) so it needs to be able to fit in a small launcher. The solution to this is that it has a nifty extendible mast, as shown in this video.
Normally NASA engineers don’t like moving parts on satellites, because they might get stuck (the moving parts, not the engineers). But even they would probably admit it looks cool when NuSTAR is extending its mirrors (the shiny metal-plated thingees) away from the detectors (on the main body of the spacecraft).
A technical challenge is that once extended, that mast will “flap around like a wet noodle”, as one senior NASA scientist put it. This isn’t directly because the satellite will be moving from target to target (called slewing). It’s because as NuSTAR moves in and out of the Earth’s shadow, the change in temperature of the mast will induce some motion. This motion is very slight, but enough to mess with the images that NuSTAR is taking. To get around this a laser system is installed on NuSTAR. The laser is attached to the mirror module and shines down near the X-ray detectors. By tracking how the spot made by the laser moves we can track how the optics and detectors are moving relative to each other. This might sound like a band-aid fix (because it is) but it is a lot cheaper than moving up to a larger launcher.
Waiting for Launch
Since building something like NuSTAR literally is rocket science, it is not surprising that there are occasionally launch delays. All systems have recently passed flight readiness reviews and NuSTAR is planned for launch on June 13. NuSTAR is going to launch from a rocket called Pegasus that is first dropped from an airplane. You can watch the launch coverage online.
Right now one of the main roles of GSFC scientists is to help test the software that will be used to analyze NuSTAR observations. A slight silver lining to the launch delay is that it gives us more time to do this and to get more practice with simulated data. This will put is in a better position to analyze the real data when it comes. And with NASA satellites, once the data starts coming it really does quickly feel like drinking from a fire hose, so the more practice we have the better.
— Andy Ptak
OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.