Maintaining Access to ACE Real-Time Solar Wind Data

The Advanced CCD Imaging Spectrometer (ACIS) instrument on NASA’s Chandra X-Ray Observatory uses a set of front-illuminated CCDs that have been shown to be susceptible to radiation degradation by “soft” (100–500 keV)... [ view full abstract ]

The Advanced CCD Imaging Spectrometer (ACIS) instrument on NASA’s Chandra X-Ray Observatory uses a set of front-illuminated CCDs that have been shown to be susceptible to radiation degradation by “soft” (100–500 keV) protons. The protons scatter off the grazing incidence x-ray mirrors and onto the CCDs when ACIS is located in the focal plane position required for science observations.  Chandra’s orbit is approximately 10,000 km x 140,000 km, exposing the spacecraft to soft proton threat environments once every 64 hours as it passes through the radiation populations trapped in the Earth’s magnetic field and episodically during solar particle events when the spacecraft is in interplanetary space.  Chandra’s operations teams have successfully mitigated soft-proton damage to the ACIS instrument through a combination of (1) scheduled observations which avoid exposure during radiation-belt transits, (2) autonomous intervention based upon onboard hard-proton detectors, and (3) manual intervention based upon real-time monitoring of the soft-proton environment.  Records from the Advanced Composition Explorer (ACE) Electron, Proton, and Alpha Monitor (EPAM) instrument distributed by NOAA’s Space Weather Prediction Center (SWPC) as a component of the Real-Time Solar Wind (RTSW) data provides the only real-time monitor of the soft-proton environment relevant to Chandra operations outside of the Earth’s magnetosphere.  The recent changeover from ACE to the Deep Space Climate Observatory (DSCOVR) spacecraft as the primary L1 space weather monitor has put Chandra’s access to the real-time soft proton data at risk since DSCOVR lacked a comparable energetic-particle instrument to EPAM.  NASA and NOAA SWPC are collaborating to maintain access to the ACE RTSW data required to support the Chandra radiation mitigation program.  This presentation will first describe the Chandra time resolution and data latency requirements to support the radiation mitigation program.  We then provide a status of the work to identify additional ground tracking stations to maintain access to ACE RTSW and forward the data to NOAA SWPC for processing and distribution.  The intent of this paper is to bridge the gap between pure scientific research, data gathering in support of this research, and the real-world applications of having the situational awareness of the space weather environment to support on-orbit operations.