SOLAR PARTICLE-INDUCED UPSETS IN THE TDRS-1 ATTITUDE-CONTROL SYSTEM RAM DURING THE OCTOBER 1989 SOLAR PARTICLE EVENTS

The three large solar particle events, beginning on October 19, 1989 a nd lasting approximately six days, were characterized by high fiueuces of solar protons and heavy ions at 1 AU. During these events, an abno rmally large number of upsets (243) were observed in the random access memory of the attitude control system (ACS) control processing electr onics (CPE) on-board the geosynchronous TDRS-1 (Telemetry and Data Rel ay Satellite). The RAM unit affected was composed of eight Fairchild 9 3L422 memory chips, The Galileo spacecraft, launched on October 18, 19 89 (one day prior to the solar particle events) observed the fluxes of heavy ions experienced by TDRS-1., Two solid-state detector telescope s on-board Galileo, designed to measure heavy ion species and energy, were turned on during time periods within each of the three separate e vents, The heavy ion data have been modeled and the time history of th e events reconstructed to estimate heavy ion fluences. These fluences were converted to effective LET spectra after transport through the es timated shielding distribution around the TDRS-1 ACS system, The numbe r of single event upsets (SEU) expected was calculated by integrating the measured cross section for the Fairchild 93L422 memory chip with a verage effective LET spectrum, The expected number of heavy ion induce d SEU's calculated was 176. GOES-7 proton data, observed during the so lar particle events, were used to estimate the number of proton-induce d SEU's by integrating the proton fluence spectrum incident on the mem ory chips, with the two-parameter Bendel cross section for proton SEU' s, The proton fluence spectrum at the device level was gotten by trans porting the protons through the estimated shielding distribution, The number of calculated proton-induced SEU's was 72, yielding a total of 248 predicted SEU's, very close to the 243 observed SEV's. These calcu lations uniquely demonstrate the roles that solar heavy ions and proto ns played in the production of SEU's during the October 1989 solar par ticle events.