Around 1960 USAF development effort was funded to develop a Titan storable engine using a metallized fuel (for greater impulse density) and gelled propellants (to facilitate in-space starts after a period of coasting). Laboratory tests were sufficiently favorable for considerable hopes to be raised. However, the limited amount of funding was not sufficient to resolve the technical problems, The Aerozine 50 was slurried with aluminum powder (using Carbopol 904 gelling agent), and the engine was operated without any modifications, but could not attain stable, long duration operation in that configuration. This was the first time a liquid rocket booster engine had ever been run on aluminized propellant. Many years later Aerojet operated small thrusters on metallized storable propellants and achieved satisfactory results.

• Dorman, Bernie, et. al., Aerojet: The Creative Company, Stuart F Cooper Company, Los Angeles, 1995.. ISBN: 0-9659769-0-4. Out of print unauthorised history of Aerojet, as told by ex-employees. More such works are urgently needed to preserve the (non-governmental) history of the space race. More at amazon.com...