The MESSENGER team is starting final closeout of the spacecraft in preparation for launch. In this week's annotated Webcam image, an engineer applies silver Teflon tape to the X-Ray Spectrometer's solar monitor. After the tape was applied, the thermal insulation blanket was tucked in around its edges in its flight configuration.
The X-Ray Spectrometer (XRS) solar monitor is a simple device that will play a critical role during the orbital phase of the mission. The main XRS instrument measures how solar X-rays interact with Mercury's surface, allowing scientists to estimate the abundances of elements such as magnesium, aluminum, silicon, sulfur, calcium, titanium and iron. Accurate measurements of these elements require knowledge of the intensity of X-rays hitting the surface - the solar monitor measures the X-ray intensity hitting the Sun-facing side of the spacecraft, "knowing" the planet will receive the same intensity. (Don't confuse the XRS solar monitor with the nearby Sun Sensor, which detects visible light.)
Combining the XRS surface measurements with the solar monitor's record of the flux from the Sun will help scientists accurately reconstruct the major element chemistry of Mercury's crust, thus allowing a peek into Mercury's past and providing information on how the planet evolved.
Other spacecraft activities last week included sealing up thermal insulation blankets and adding thermal mass to sensitive items - such as the Sun Sensors, battery, and Radio Frequency (RF) converter and amplifier - that will absorb heat during the short time the spacecraft is exposed to heat from Mercury. The extra mass keeps these items from getting too hot, too quickly.
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 will operate the MESSENGER spacecraft and manages the Discovery-class mission for NASA.
For more information, visit http://messenger.jhuapl.edu.