To get a basic experimental understanding of hybrid propulsion we used the XLR-2 test setup. This engine was originally build as a throttleble rocket engine for propelling a manned rocket boat. The basic design had been extensively tested for use in a TV show.
Therefore XLR-2 was a very convenient beginning for the design of a large hybrid fueled booster.
In the original form XLR-2 had a thrust of 1 kN, but as it was refined during the series of tests this was increased to 4.5 kN.
During all test we explored a combination of an epoxy resin and nitrous oxide.
Nitrous oxide essentially an energetic mono propellant oxidizer and, as a result, it gives excellent performance over a wide range of oxidizer to fuel rations.
This makes nitrous oxide a very favorable hybrid oxidizer.
Also at its high vapor pressure it can act as essentially a self pressurizing propellant.
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