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A cursory examination of rocket engineering rapidly identifies LH2/LOX rocket engines as the gold standard for efficiency. It's hard to beat 450+ seconds of vacuum specific impulse, even though hydrolox rockets don't always have the greatest T/W ratios and require very large fuel tanks which eat into mass fraction rapidly. I think I can beat that, though. Hydrogen peroxide is not a very good monopropellant. It has only 161 s of impulse. Hydrazine is a bit better, as far as monopropellants go; it boasts upwards of 220 s. And together, they're not much improved; a hydrazine/peroxide bipropellant rocket can't even break 300 s in a vacuum. Put them together in the right way, though, and I think I might be on to something. This is a fairly basic, no-nonsense linear aerospike engine. There's just a single difference: instead of using small bipropellant combustion chambers, it uses staggered monopropellant combustion chambers, alternating between hydrazine and high-test peroxide. The peroxide thrusters and hydrazine thrusters produce flows which, after beginning to expand against the aerospike, are already moving very fast. High-test peroxide's 161 seconds of specific impulse corresponds to an exhaust velocity of around 1.58 km/s while hydrazine's 220 seconds corresponds to an exhaust velocity of around 2.16 km/s. At a molar mass ratio of 3:2 (peroxide:hydrazine), the mutual flow is traveling down the aerospike at an average velocity of 1.83 km/s. But it doesn't stay that way. As the two compressed supersonic flows mix, they ignite with each other: Decomposed hydrazine contains 4 grams of diatomic hydrogen per mole; decomposed peroxide contains 16 grams of diatomic oxygen per mole. At the previously-mentioned 3:2 molar ratio, the oxygen and hydrogen will burn with a vacuum specific impulse of 430-450 seconds. Of course, the reactants compose only one third of the mass of the flow, so the net increase in propellant flow speed will be about 2.49 km/s. However, because that increase takes place in a flow which is already moving at 1.83 km/s, the speeds stack. This staged combustion results in a total exhaust velocity of 4.32 km/s, for a specific impulse of 441 seconds. Because monopropellant thrusters are being used, the thrust-to-weight ratio will be fantastic, a major advantage over other linear aerospike designs. Moreover, both fuels are dense and liquid at room temperature, allowing small tank volume and a smaller launch vehicle.