This study summarizes the available information on slush hydrogen and answer pending engineering questions that arise in the design of slush hydrogen propellant systems The four methods for the production of slush are discussed For storage slush hydrogen must be pressurized free from impurities and continuously upgraded Slush flowing at low flow rates has a higher viscosity than the liquid however at higher velocities it approaches the viscosity of neat liquid For the entire range of natural convection and nucleate boiling the heat transfer at the triple point temperature and pressure is nearly the same for the liquid and slush The natural convection from smooth surfaces for slush can be predicted using available correlations However for engineering analysis and design of a system involving a slush cryogenic propellant reliable information is required on production flow heat transfer, and instrumentation of these fluids Some relevant and important aspects of slush hydrogen which have not yet been fully answered are presented (C) 2010 Professor T Nejat Veziroglu Published by Elsevier Ltd All rights reserved