NASA 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.