This paper illustrates experiments that were conducted on the formation of solid hydrogen particles in liquid helium. Solid particles of hydrogen were frozen in liquid helium, and observed with a video camera. The solid hydrogen particle sizes, their molecular structure transitions, and their agglomeration times were estimated. article sizes of 1.8 to 4.6 mm (0.07 to 0. 18 in.) were measured. The particle agglomeration times were 0.5 to 11 min, depending on the loading of particles in the dewar. These experiments are the first step toward visually characterizing these particles, and allow designers to understand what issues must be addressed in atomic propellant feed system designs for future aerospace vehicles.Palaszewski, BryanGlenn Research CenterGELLED ROCKET PROPELLANTS; CRYOGENIC ROCKET PROPELLANTS; SOLID CRYOGENS; LIQUID HELIUM; AGGLOMERATION; FEED SYSTEMS; AEROSPACE VEHICLES; CRYOGENIC EQUIPMENT; VIDEO DATA...