G Warwick, Tech Take, Aviation Week & Space Technology, 10-23 February 2025, p62

In US, a hybrid propulsion system using liquid hydrogen comprising a gas turbine with the compressor powered by a fuel cell is to be studied by the University of Illinois Urbana-Champaign. In the Hy2PASS system, hydrogen is also combusted to drive the fan, allowing the compressor to operate indepently at variable speeds, improving energy efficiency and emissions.