RADFET dosimeters in the belt: The Van Allen Probes on day 365

Van Allen Probes spacecraft VAP-A and -B, launched over a year ago [August 2012], carried 16 pMOS RADFETs into an orbit designed by NASA to probe the heart of the trapped-radiation belts. Nearly 350 days of in situ measurements from the Engineering Radiation Monitor (ERM) (a) demonstrated strong variations of dose rates with time, (b) found a critical correlation between its RADFET dosimeter and Faraday cup data on charged particles, and (c) mapped the belts by measuring variation with orbit altitude. This paper provides update on early results given in [1] along with details and discussion of the RADFET dosimetry analysed.