The NEAR magnetic field investigation: Science objectives at asteroid Eros 433 and experimental approach

The NEAR magnetic field investigation is an integrated technical, scientific, and management undertaking that was selected by NASA to achieve the following goals: to coordinate and support the development, calibration, and integration aboard the NEAR spacecraft of the magnetometer facility instrument (MAG), to provide technical assistance to the NEAR project in the area of magnetic cleanliness, and to ensure maximum science data quality. The prime objective of the MAG investigation is to establish the nature of the magnetic field of 433 Eros and any detectable effects of its interaction with the solar wind. The detection of an intrinsic magnetic field would place a strong constraint on the composition and structure of the asteroid's interior and thermal evolution. NEAR magnetometer data will be primarily available through the Johns Hopkins University Applied Physics Laboratory (APL) Science Data Center, http://sd-www.jhuapl.edu/NEAR. The basic building block of the MAG investigation is the facility-class magnetometer instrument flown aboard the NEAR spacecraft [Lohr et at, 1997]. The NEAR MAG was built as a cooperative undertaking between the Laboratory for Extraterrestrial Physics of the Goddard Space Flight Center (GSFC) and APL. GSFC provided the sensors and analog systems, and APL provided the digital processing unit and power converter as well as oversight for test and integration activities on the spacecraft. No booms or appendages were used to place the MAG sensor away from the spacecraft; instead and in analogous fashion to ESA's Giotto spacecraft, the sensor assembly was mounted on the high-gain antenna feed structure. This arrangement results in a minimum detectable magnetic signature of 2-5 nT.