NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) passed its Post-Launch Assessment Review at JPL this week, clearing the way for the mission to enter into its science operations phase in the next month.

NuSTAR is currently in the final stages of "Phase C/D," or the design and development phase, which included building and testing the flight hardware, launch and early operations (e.g., spacecraft checkout, mast deployment, instrument commissioning and calibrations).

In August, NuSTAR will enter "Phase E," or the operations phase, meaning that it will primarily gather science data.

Since obtaining its first-light images of the galactic black hole Cygnus X-1 on June 28, NuSTAR has been observing bright X-ray sources across the sky as part of the instrument commissioning.

Last week, the mission participated in a major international cross-calibration campaign where NuSTAR and NASA's Chandra and Swift telescopes, together with INTEGRAL, Suzaku, and XMM-Newton, observed the quasar 3C 273 in concert.

Quasar 3C 273, an extremely bright high-energy source at a distance of 2.4 billion light years, is the first quasar ever to be identified and is the optically brightest quasar in the sky. The coordinated observations of this bright, variable source will allow X-ray satellites to accurately measure their relative sensitivities and to conduct science investigations with joint data sets.

One example of a joint science observation took place between July 21 and 24. NuSTAR observed the supermassive black hole that resides at the center of our own Milky Way galaxy as part of a large, multi-wavelength campaign. This supermassive black hole, our closest example, is known as Sagittarius A* and weighs approximately 4 million times as much as the sun.

NuSTAR obtained high-energy X-ray data on Sagittarius A*, complementing coordinated infrared images obtained with the Keck telescopes, low-energy X-ray data obtained with Chandra, and very high-energy gamma-ray data obtained with the High-Energy Stereoscopic System (HESS).

These data will monitor the flickering of Sagittarius A* as it grows by accreting matter, thereby teaching astronomers about the extreme environments around black holes and the physics of black hole growth.