MESSENGER stares at a supernova

MESSENGER's X-Ray Spectrometer (XRS) instrument underwent calibrations last week, spending five days "looking" at one of the stronger x-ray sources in the sky, the supernova remnant Cassiopeia A. The test gives the XRS team its best look yet at the instrument's detectors, allowing them to measure how well its anti-coincidence and pulse shape discrimination circuits eliminate background signals from x-ray measurements.
"Background rejection is important because it improves the signal-to-background ratio, thereby increasing the sensitivity of the XRS measurements," says Richard Starr, XRS instrument lead scientist, from NASA Goddard Space Flight Center. "We expect this observation of Cas-A to provide more reliable data than ground measurements on how well the background rejection is working."

The team will spend the next several weeks analyzing the test data and hopes to observe Cassiopeia A again during the cruise to Mercury to track the X-Ray Spectrometer's performance.

XRS wasn't the only part of the science payload to get a workout last week; the team also turned on the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) Feb. 7 for two days of maintenance operations.

 

Smooth Steering

On Feb. 4 the spacecraft team performed a successful steering test on the back phased-array antenna. MESSENGER is the first deep space mission to use an electronically steered phased-array antenna. Two phased arrays, mounted on opposite sides of the spacecraft, provide MESSENGER's high-gain downlink coverage.

MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is a scientific investigation of the planet Mercury, and the first NASA mission designed to orbit the planet closest to the Sun. Dr. Sean C. Solomon, of the Carnegie Institution of Washington, leads the mission as principal investigator. The Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, built and operates the MESSENGER spacecraft and manages the Discovery-class mission for NASA.