European Space Research and Technology Centre 1 article published in JoVE Chemistry Experimental Methods for Efficient Solar Hydrogen Production in Microgravity Environment Katharina Brinkert1,2, Ömer Akay3, Matthias H. Richter1,4, Janine Liedtke2, Katherine T. Fountaine5,6, Hans-Joachim Lewerenz7, Michael Giersig3,8 1Division of Chemistry and Chemical Engineering, California Institute of Technology, 2European Space Agency/ ESTEC, 3Department of Physics, Freie Universitat Berlin, 4Applied Physics and Sensors, Brandenburg University of Technology Cottbus, 5Resnick Sustainability Institute, California Institute of Technology, 6NG Next, Northrop Grumman Corporation, 7Division of Engineering and Applied Science and Joint Center for Artificial Photosynthesis, California Institute of Technology, 8International Academy of Optoelectronics at Zhaoqing, South China Normal University Efficient solar-hydrogen production has recently been realized on functionalized semiconductor-electrocatalyst systems in a photoelectrochemical half-cell in microgravity environment at the Bremen Drop Tower. Here, we report the experimental procedures for manufacturing the semiconductor-electrocatalyst device, details of the experimental set-up in the drop capsule and the experimental sequence during free fall.