NASA prepares NuSTAR, an X-ray telescope, for a February launch

Appears in Print As: Looking at the universe through X-ray specs

November 3, 2011

NASA will soon put the most-powerful space-based X-ray telescope in orbit

Authored by:
Stephen J. Mraz
Senior Editor
stephen.mraz@penton.com
Resources:
NuSTAR homepage

This February, NASA will launch NuSTAR (nuclear-spectroscopic telescope array) for a two-year mission exploring space using an advanced X-ray telescope. It will be the first orbiting telescope capable of focusing on and viewing this high-energy portion of the electromagnetic spectrum.

Previous X-ray telescopes, such as Chandra and the X-ray Multi-Mirror Mission (XMM), were limited in that they could not focus. Instead they used specially constructed apertures to image X-ray signals, and these structures had intrinsically high background noise and limited sensitivity. The two earlier X-ray telescopes were also limited to looking at low-energy X-rays (15 keV and lower). NuSTAR will be able to handle X-rays with up to 79 keV. According to NASA, NuSTAR will also have 10 to 100 times the sensitivity and spatial and spectral resolution of previous X-ray telescopes sent into space.

The spacecraft

SMEX: More bang for NASA’s bucks
NASA’s Small Explorer Program (SMEX) spreads NASA’s budget around to more-frequent and more-focused missions rather than multibillion, multidecade projects like Apollo and the International Space Station. To this end, spacecraft for SMEX missions generally weigh just 400 to 550 lb, and need 50 to 200 W of power, on average. Each mission is expected to cost approximately $35 million for design, development, and operations through the first 30 days in orbit.

Since the first SMEX mission in 1992, the missions have come to be called Explorer missions. Here are some of those past missions: 1992 – Sampex (Solar Anomalous and Magnetospheric Particle Explorer): detected solar energy particles, anomalous cosmic rays, and galactic cosmic rays throughout a solar cycle.

1997 – Trace (Transition Region and Coronal Explorer): explored the 3D magnetic structures on the visible surface of the Sun, as well as the geometry and dynamics of the sun’s upper atmosphere.

2003 – Galex (Galaxy Evolution Explorer): an orbiting space telescope that observes galaxies in UV light. Since its launch, it has surveyed tens of thousands of galaxies across 9 billion years of time.

To keep costs down on the NuSTAR mission, the spacecraft will be shot into space aboard a Pegasus launch vehicle, so it must fit in that rocket vehicle’s cargo bay. This limits NuSTAR to a 2-m-long, 1-m-diameter envelope. But this raises a problem: A focusing X-ray telescope needs focal lengths in the 10-m (33-ft) range. Both Chandra and XMM, for example, measure 10-m long and weigh about 9,000 lb. But it took the Space Shuttle to put Chandra in space and an Arianne 5 to take the XMM into orbit.

NASA engineers’ solution is an extendable mast, a scaled-down version of the 60-m mast used on a Shuttle-based radar topography mission. NuSTAR’s 10-m version, which collapses for storage, should provide a relatively stiff, stable, and reliable platform for the optics or focusing lenses, putting the necessary separation between the optics and detectors to focus the telescope and get clear images.

To ensure the optics and detectors are aligned, an adjustment mechanism is used when the mast is first deployed after the spacecraft is in orbit. Then to compensate for small, but inevitable, motions at the optics end of the mast, a pair of lasers will send light beams to three sensors mounted on the detector end of the telescope. Real-time measurements from the lasers will be used to correct X-ray images, which would otherwise be blurred.