How hypervelocity impacts can affect the LISA mission - The MIRAD study: Paper presented at 70th International Astronautical Congress 2019, 21-25 October 2019, Washington, D.C., USA

ESA has initiated the MIRAD (microparticle impact related attitude disturbances) study to quantify the threat posed by microparticle (i.e. micrometeoroid) impacts to the LISA (laser interferometer space antenna) mission. This manuscript gives an overview on the study, presenting the experimental testing and momentum enhancement modelling approach, the framework which will be used to implement the momentum enhancement or transfer model, and the planned system-level analyses for the LISA mission based on this model. The size and momentum of relevant particles impacting the spacecraft are determined based on the mission parameters (orbit and expected duration). Relevant test articles based on the preliminary LISA spacecraft design are identified. The experimental campaign to derive the momentum transmitted onto the spacecraft following a microparticle impact is described. When considering the most severe attitude disturbances to be expected during the LISA mission, a particle having a momentum of 15 mN∙s (not including momentum enhancement) is expected to impact one of the three spacecraft once during the ten-year mission duration, which corresponds to a 0.8 mm micrometeoroid particle (density 2.5 g/cm³) at 22 km/s. Every day, in yearly average, the LISA constellation has to cope with a 9 μN∙s particle (not including momentum enhancement), which corresponds to a 70 μm particle impacting at 20 km/s.