This 1963 photograph shows vent flowing cryogenic fuel and T/C Rake mounted on a 1/10 scale model Centaur rocket in the Supersonic Wind Tunnel at the Glen Rsearch Center. The fuel being tested is liquid hydrogen. Such tests were conducted to determine how far to expel venting fuel from the rocket body to prevent explosion at the base of the vehicle. The vent is used as a safety valve for the fumes created when loading the fuel tanks during launch preparation. Liquid hydrogen has to be kept at a very low temperature. As it heats it turns to gas and increases pressure in the tank, and, therefore, has to be vented overboard while the rocket sits on the pad.