Complex sentence: ASTOS is being extensively used at ESA and aerospace industry community to calculate optimal launch and entry trajectories and was one of the tools used by ESA to assess the risk due to the ATV'Jules Verne' reentry.
Split into simpler sentences: Astos is being extensively used at ESA and aerospace industry community to calculate optimal launch and entry trajectories. ASTOS was one of the tools used by ESA to assess the risk due to the ATV'Jules Verne' reentry.