While working for different NASA contractors during the 1960s, he helped design, develop and test the rocket engines for the Apollo/Saturn launch vehicles and the Apollo Lunar Module that enabled humans to walk on the Moon.
French is a long-time advocate of a mission architecture for a Mars probe, known as Mars Sample Return with In-Situ Propellant Production, that would manufacture propellant from resources at the target planet to power a return trip, to dramatically reduce the size of the outbound vessel and the cost of the mission.
He also published an article in the Journal of the British Interplanetary Society in 1989, recommending in-situ propellant production for a crewed Mars mission, though he recommended that the technique would not be feasible until a Mars base was already well-established, due to the risks of relying on fueling a spacecraft with in-situ produced propellant.
[1] French now works as a private space systems engineering consultant, and is a Fellow of the American Institute of Aeronautics and Astronautics (AIAA).
[citation needed] French is currently a director and engineering chief for the Golden Spike Company, which is planning commercial missions to the moon.