Advanced Space Mission Concerns & Solutions

1. Mission concerns we are watching • Mass – Mission was exceeding mass allocations. Potential solutions could have had operational impacts. Solutions now appear benign (incl. new Arianne lift capability). • Pointing Transients – Variety of pointing issues had potential science impacts (e.g., coronagraphic and NIRSpec/MSA programs). Mitigations (slew control laws, fuel tank baffles, star tracker redesign) underway. • FGS FSW – Major issues with fundamental functions when first delivered. Our staff played major role in discovery & characterization. Updates have resolved fundamental problems. Pursuing tests of more complex observing situations. • Stray light – Increases in temperatures of primary mirror and observatory core are causing mid-infrared stray light levels to exceed requirements. Some mitigations (e.g., changing the OTE bib) will help, but the outcome and impacts remain unclear. • NIR Detectors – Degradation of the original near-IR detectors. Development of replacement flight parts with a new design. Yield higher than expected. New parts appear superior with the exception of intermittent “snow balls.” • MIRI Sensitivity – Acceptance review went well. Several concerns, including MRS Channel 4 throughput and decreased sensitivity at all wavelengths. FRB concluded that required MIRI sensitivity could be reached through appropriate data reduction and operational approaches. Several potential paths forward. Looking for most operationally efficient approach.

2. Mission concerns we are watching • Mass – Mission was exceeding mass allocations. Potential solutions could have had operational impacts. Solutions now appear benign (incl. new Arianne lift capability). • Pointing Transients – Variety of pointing issues had potential science impacts (e.g., coronagraphic and NIRSpec/MSA programs). Mitigations (slew control laws, fuel tank baffles, star tracker redesign) underway. • FGS FSW – Major issues with fundamental functions when first delivered. Our staff played major role in discovery & characterization. Updates have resolved fundamental problems. Pursuing tests of more complex observing situations. • Stray light – Increases in temperatures of primary mirror and observatory core are causing mid-infrared stray light levels to exceed requirements. Some mitigations (e.g., changing the OTE bib) will help, but the outcome and impacts remain unclear. • NIR Detectors – Degradation of the original near-IR detectors. Development of replacement flight parts with a new design. Yield higher than expected. New parts appear superior with the exception of intermittent “snow balls.” • MIRI Sensitivity – Acceptance review went well. Several concerns, including MRS Channel 4 throughput and decreased sensitivity at all wavelengths. FRB concluded that required MIRI sensitivity could be reached through appropriate data reduction and operational approaches. Several potential paths forward. Looking for most operationally efficient approach.

3. Mission concerns we are watching • Mass – Mission was exceeding mass allocations. Potential solutions could have had operational impacts. Solutions now appear benign (incl. new Arianne lift capability). • Pointing Transients – Variety of pointing issues had potential science impacts (e.g., coronagraphic and NIRSpec/MSA programs). Mitigations (slew control laws, fuel tank baffles, star tracker redesign) underway. • FGS FSW – Major issues with fundamental functions when first delivered. Our staff played major role in discovery & characterization. Updates have resolved fundamental problems. Pursuing tests of more complex observing situations. • Stray light – Increases in temperatures of primary mirror and observatory core were causing mid-infrared stray light levels to exceed requirements. However, current analysis has stray light at both 10 and 20 microns within requirements, due to: • NIR Detectors – Degradation of the original near-IR detectors. Development of replacement flight parts with a new design. Yield higher than expected. New parts appear superior with the exception of intermittent “snow balls.” • MIRI Sensitivity – Acceptance review went well. Several concerns, including MRS Channel 4 throughput and decreased sensitivity at all wavelengths. FRB concluded that required MIRI sensitivity could be reached through appropriate data reduction and operational approaches. Several potential paths forward. Looking for most operationally efficient approach. • Realistic assumptions regarding dust distribution & emissivity on mirror • Extending the frill to block warmer portions of the bib • Deployable tower assembly now completely blocked by bib & sunshield