http://messenger.jhuapl.edu/webcam/annotatedimages/annotated-20031230.html

MESSENGER Mission News
December 30, 2003

Keeping MESSENGER Cool

While orbiting Mercury, MESSENGER will "feel" significantly hotter than spacecraft that orbit Earth. This is because Mercury's orbit swings the planet to within 0.31 astronomical units (AU) of the Sun- about 46 million kilometers (29 million miles), or about one-third of the distance between the Sun and Earth. The Sun also appears 11 times brighter at Mercury than we see from our own planet.

Without extra protection in such an extreme environment the spacecraft and its instruments would overheat and cease to function- but MESSENGER engineers answered this challenge by designing a heat- resistant and highly reflective sunshade. The team installed the 254- by-180 centimeter (8-by-6 foot) shade on Dec. 12, shortly before moving the spacecraft to NASA Goddard Space Flight Center for prelaunch tests.

The thin sunshade is a high-tech parasol constructed from Nextel ceramic cloth, with several inner layers of Kapton plastic insulation. While MESSENGER's Sun-facing side could heat to above 310? Celsius (590? Fahrenheit) during the orbit, preliminary tests and thermal analyses show the sunshade will keep the spacecraft operating near room temperature, around 20? C (or 68? F).

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, Md., is building and will operate the MESSENGER spacecraft and manages the Discovery- class mission for NASA.