A NASA Discovery mission to conduct the first orbital study
of the innermost planet
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Thermal Design

thermal image
Inspection of MESSENGER's sunshade prior to thermal vaccum testing

While orbiting Mercury, MESSENGER will “feel” significantly hotter than spacecraft that orbit Earth. This is because Mercury’s elongated orbit swings the planet to within 46 million kilometers (29 million miles) of the Sun, or about two-thirds closer to the Sun than Earth. As a result, the Sun shines up to 11 times brighter at Mercury than we see from our own planet.

MESSENGER’s first line of thermal defense is a heat-resistant and highly reflective sunshade, fixed on a titanium frame to the front of the spacecraft. Measuring about 2.5 meters (8 feet) tall and 2 meters (6 feet) across, the thin shade has front and back layers of Nextel ceramic cloth – the same material that protects sections of the Space Shuttle – surrounding several inner layers of Kapton plastic insulation. While temperatures on the front of the shade could reach 370° C (about 700° F) when Mercury is closest to the Sun, behind it the spacecraft will operate at room temperature, around 20° C (about 70° F). Multilayered insulation covers most of the spacecraft.

Radiators and diode (“one-way”) heat pipes are installed to carry heat away from the spacecraft body, and the science orbit is designed to limit MESSENGER’s exposure to heat re-radiating from the surface of Mercury. (MESSENGER will only spend about 25 minutes of each 12-hour orbit crossing Mercury’s broiling surface at low altitude.) The combination of the sunshade, thermal blanketing, and heat-radiation system allows the spacecraft to operate without special high-temperature electronics.

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