Heavy Ion Composition and Flux Measurements as a New, Sustainable Window on Space Weather: Observations From the GOES-16 Energetic Heavy Ion Sensor (EHIS)

Energetic heavy ions measurement are a new window on Space Weather. Energetic heavy ions are a particular concern for single event effects (SSE's) in electronics, and for radiation exposure for humans in space because energy deposition increases with the nuclear charge (Z) squared. Thus an iron (Fe) ion deposits energy at 676 times the rate of a proton with the same energy/nucleon. The high quality factor (relative biological effectiveness) of heavy ions further increases their import for human radiation exposure. An Energetic Heavy Ion Sensor (EHIS) was launched on the GOES-16 satellite (formerly, GOES-R) on 10 November, 2016 and is now operational in geostationary orbit. The second EHIS was launched on GOES-17 (formerly, GOES-S) on 1 March 2018. These are two of four EHIS instruments built by the University of New Hampshire, subcontracted to Assurance Technology Corporation, as part of the Space Environmental In-Situ Suite (SEISS) for GOES-R, -S, -T and -U with mission lives of 15 years and a project life of 30 years. EHIS is the first heavy ion instrument to fly on a GOES satellite. EHIS measures energetic ions over the range 10-200 MeV for protons, and energy ranges for heavy ions corresponding to the same stopping ranges (e.g., 18-335 MeV/u for carbon and 38-825 MeV/u for iron). EHIS uses the Angle Detecting Inclined Sensors (ADIS) technique to provide single-element charge resolution. On an operational mission for Space Weather monitoring, EHIS offers a new source of high quality Solar Particle Event (SPE) data for both space weather and scientific studies. With a high rate of on-board processing ( 2000 events/s), EHIS provides exceptional statistics for ion composition measurements in large SPEs. For the GOES Level 1-B and Level 2 data products, heavy ions are distinguished in EHIS using pulse-height analysis with on-board processing producing charge histograms for five energy bands. Fits to these data are normalized to priority rate data on the ground. We discuss the EHIS heavy ion data which show elemental peaks from H to Fe.

The EHIS instrument development project was funded by NASA under contract NNG06HX01C.