The Mass-Separating Ion Spectrometer on the AMPTE ion-release module

The Mass Separating Ion Spectrometer (MSIS) on an ion release module of the AMPTE spacecraft is a modified version of an instrument originally intended for the U.S. portion of the Solar Polar Mission. SPIS is configured to employ electric and magnetic fields to separate particles and perform energy and mass per unit charge analyses. Two quadrispherical lenses form a hemispherical analyzer. A radially directed magnetic field between the entrance slit and exit provides high resolution unit charge measurements. Details of all other major system components are given, along with a block diagram of the system electronics. The MSIS was underfunded in development and rushed to meet launch deadline. Consequently, some organic materials were used instead of longer-lived alloys. The solar wind program must be transmitted since it was not stored in PROM, and error analysis is necessary for the measurements because time to launch considerations did not leave leeway for proper calibrations.