Ion mass spectrometer on Ionosphere Sounding Satellite (ISS-b)

An ion mass spectrometer was flown on the Ionosphere Sounding Satellite (ISS-b), which was put into a nearly circular orbit with an inclination of 70 deg and an altitude of about 1100 km. The observations of global distribution of the positive ions are assured by two identical Bennett spectrometer tubes which are mounted at the top and bottom covers of the spacecraft. The Bennett tube is constructed from fifteen planar grids and works as a RF linear accelerator. The mass scan range is 1 to 20 AMU and major positive ions such as H(+), O(+), and He(+) can be observed. The absolute densities of the positive ions are deduced by in-flight calibration method. In addition to detailed description of the instrument, brief accounts of the observational results are also given.