THE NEAR MAGNETIC-FIELD INVESTIGATION - SCIENCE OBJECTIVES AT ASTEROID EROS-433 AND EXPERIMENTAL APPROACH

The NEAR magnetic held investigation is an integrated technical, scien tific, and management undertaking that was selected by NASA to achieve the following goals: to coordinate and support the development, calib ration, and integration aboard the NEAR spacecraft of the magnetometer facility instrument (MAG), to provide technical assistance to the NEA R project in the area of magnetic cleanliness, and to ensure maximum s cience data quality. The prime objective of the MAG investigation is t o establish the nature of the magnetic field of 433 Eros and any detec table effects of its interaction with the solar wind. The detection of an intrinsic magnetic field would place a strong constraint on the co mposition and structure of the asteroid's interior and thermal evoluti on. NEAR magnetometer data will be primarily available through the Joh ns Hopkins University Applied Physics Laboratory (APL) Science Data Ce nter, http://sd-www.jhuapl.edu/NEAR. The basic building block of the M AG investigation is the facility-class magnetometer instrument flown a board the NEAR spacecraft [Lohr et at, 1997]. The NEAR MAG was built a s a cooperative undertaking between the Laboratory for Extraterrestria l Physics of the Goddard Space Flight Center (GSFC) and APL. GSFC prov ided the sensors and analog systems, and APL provided the digital proc essing unit and power converter as well as oversight for test and inte gration activities on the spacecraft. No booms or appendages were used to place the MAG sensor away from the spacecraft; instead and in anal ogous fashion to ESA's Giotto spacecraft, the sensor assembly was moun ted on the high-gain antenna feed structure. This arrangement results in a minimum detectable magnetic signature of 2-5 nT.