A New Perspective on Inner Zone Proton Data from 1971

The NASA Geospace Radiation Belt Storm Probes Mission will provide a new look at the inner magnetosphere, including the inner zone protons that originate from the decay of neutrons in interactions from galactic cosmic rays with the upper atmosphere. The G-RBSP mission is scheduled for launch in 2012. About forty years prior to the launch of G-RBSP, the US Air Force Orbiting Vehicle 20 (OV1-20) included instrumentation designed to capture a glimpse of the inner zone proton environment up to ~500 MeV. The Aerospace Corporation flew a Cherenkov counter on the OV1-20 propulsion module in a polar orbit of 130 km by ~1950 km; apogee was near the equator, and on-board hardware triggered the transmitter when the count rates were high. The data included singles rates, coincidence rates, and on-board magnetometer measurements. The Cherenkov counter used a fast coincidence between pairs of scintillator disk detectors to define the geometry, thus providing clean measurements in the penetrating, high-rate inner zone environment. The propulsion module re-entered about 10 days after launch in 1971. While the OV1-20 mission life was short, the data could offer an interesting look into the environment near the G-RBSP perigee. We will revisit the OV1-20 proton measurements with the perspective of the science and engineering requirements of G-RBSP as well as results from later missions that also sampled the inner zone protons from different orbits (CRRES; TSX-5; SAMPEX). This work was supported under The Aerospace Corporation's Independent Research and Development Program.