H2/O2/A1 based engine that burns fuel on a H:O:A1 = 1:3:4 mix will give a specific impulse (Isp) over 400 seconds (18). This Isp is somewhat less than proposed advanced H2/O2 engines (480 - 490 sec) and less than state of the art H2/O2 engines (460 - 490 sec) proposed for OTV applications. However, a comparison of the economics of using powdered aluminium as a primary component of the fuel burned in a rocket versus the economics of burning only liquid fuels suggests that this is a capability well worth the time and effort to study. The energy advantage of the Aluminium fueled rocket is that the Aluminium - Oxygen reaction delivers 22% more energy per unit mass than the Hydrogen - Oxygen reaction does (18, 19). The economic advantage is that the aluminium burning engine utilizes already orbiting ETs as a primary source of fuel. In two studies of advanced propulsion for OTV applications by Dr. A. H. Cutler of the California Space Institute, the Aluminium fueled engine is compared with an advanced technology engine and the Centaur RL-10 (a proposed OTV candidate) (18, 19). The comparison was made through models of future OTV traffic levels and mass requirements. The assumption was made to use scavenged ET cryogenic residuals as the primary OTV fuel for all three rockets. Analysis of costs showed that if the fuel demand for OTV traffic models remains below the available scavenged cryogenics, it is more economical to use the RL-10 for primary OTV propulsion. However, if there are not enough scavenged cryogenics available, then it becomes far more advantageous to develop and use the Aluminium fueled rocket. This engine is a better choice for two reasons. First, it reduces the mass required in LEO for both fuel and tankage by about 30% over the RL-10 and about 15% over the advanced engine. Second, it is about 40 - 50% cheaper to fuel because ET aluminium is used for reaction mass and does not need to be launched. The problem with the Aluuminium engine is a very expensive development cost - on the order of $1 - 2 billion (18). This cost, the processing facility cost, and the engine production cost all were added into the analysis. Even with these high costs, the Aluminium engine is far more economical to develop and operate in a scenario which includes a shortfall of scavenged cryogenics. The cost savings is entirely due to the availability of Aluminium at a low cost in LEO.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==