THE MESSENGER SCIENCE PAYLOAD

摘要

The MESSENGER spacecraft will orbit Mercury and gather data for one Earth year with a miniaturized scientific payload. The MESSENGER project is in the integration and test phase in mid 2003. Seven assembled and calibrated instruments are mounted on the spacecraft. The Gamma-Ray and Neutron Spectrometer has a Gamma-Ray Spectrometer to measure atomic composition with a high-purity germanium detector and a Neutron Spectrometer that uses lithium-glass and boron-loaded plastic scintillators for sensing thermal, epithermal, and fast neutrons. The X-Ray Spectrometer measures Mercury surface elemental abundances by examining solar-flare-induced X-ray fluorescence lines. Three gas-filled proportional counters detect the X-ray fluorescence lines from the planet's surface, and a solid-state solar monitor measures the X-ray input to the planet. The Mercury Dual Imaging System (MDIS) has both wide-field and narrow-field cameras to map the surface of the planet. MDIS is also multi-spectral, with a 12-position filter wheel for the wide-field camera. The Mercury Atmospheric and Surface Composition Spectrometer measures both surface spectral reflectance in the visible and near infrared and exospheric emission lines in the ultraviolet and visible. The Mercury Laser Altimeter (MLA) determines the range to the planet with a resolution of 0.3 m. MLA will be combined with the radio-science investigation to map the gravitational field of the planet and determine the obliquity and physical libration amplitude. A magnetometer, mounted on a 3.6-m boom, will map the internal and external magnetic field. The Energetic Particle and Plasma Spectrometer will measure particles accelerated in the magnetosphere and the interactions of the magnetosphere with the solar wind. MDIS has its own pivot platform. All of the other instruments are fixed to the spacecraft. Pointing is accomplished by steering the entire spacecraft. All of the instruments are designed to deal with the extreme thermal environment at Mercury, where the sunward face of the spacecraft will reach temperatures above 350°C. MESSENGER will launch in May 2004 and begin orbital observations of Mercury in October 2009.