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Geo 4

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To make sure that the spacecraft components are not damaged by the intense solar radiation, a variety of solutions will be employed by the MESSENGER design team. For example, heat-resistant materials are used to build the components of the spacecraft, and a sunshade is constructed to protect the sensitive instruments from the Sun. The spacecraft's orbit around Mercury has been designed so that its closest approach to the planet is away from the most sun- baked region of the surface and so that it flies quickly over the sunlit areas. This is achieved by an orbit where the periapsis (the closest point to the surface of Mercury and also the part of the orbit where the spacecraft's speed is at its highest; the distance from the surface is 200 km, or 124 miles) is at a high latitude, and the apoapsis (the farthest point of the orbit and also the part of the orbit where the spacecraft's speed is at its lowest; the distance from the surface is 15,193 km, or 9443 miles) is far away from the surface of Mercury. This orbital design keeps the amount of infrared radiation received from the planet's extremely hot surface at safe levels. The solar panels are constructed from materials that can withstand high temperatures, and the system is designed so that the panels do not face the Sun directly. Using these precautions, the operating temperature at the solar panels is expected to be less than 135 ̊C, and the instruments are in a thermal environment comparable to room temperature: during Mercury's orbit around the Sun, the temperature on the instrument deck of MESSENGER is expected to vary from a few degrees below 0 ̊C (32 ̊F) to 33 ̊C (91 ̊F).