Mach Diamond has successfully developed two generations of hypergolic bipropellant rocket engines (thrusters) with demonstrated thrust ranging from 450 to 600 lbf.
A significant accomplishment has been achieved by proving the thruster using the propellant combination of MON25/MMH. See "Hypergolic propellants and combustion stability" below.
The Missile Defense Agency (MDA) awarded three contracts (2006, 2008, and 2011) to Mach Diamond (doing business as Montcorp) to develop its high-performance/ low-cost technologies. The MDA uses this class of thrusters for rocket-propelled interceptors, which defend against incoming missiles. The thrusters have other space applications, in addition to missile defense.
The Mach Diamond design is capable of rapid on-off operation for maneuvering and attitude control. It is a bipropellant (liquid fuel, liquid oxidizer) thruster, capable of thrust durations ranging from a few milliseconds to several seconds. The thruster uses hypergolic (self-igniting) propellants, producing 6000°F combustion temperatures and full thrust within milliseconds.
Hypergolic propellants and combustion stability
These relatively simple devices are surprisingly challenging to design. Successful designs require expertise that can be characterized as a cross of rocket science and black art. Although Robert Goddard launched the first liquid-fueled rocket almost 90 years ago, designing rocket engines free of combustion instabilities remains a difficult task.
Combustion instability manifests itself as high-frequency pressure oscillations in the combustion chamber. These oscillations result in extreme heat fluxes that can quickly destroy a thruster, and most commonly occur in the 8000 to 40,000 hertz (cycles per second) range.
The liquid rocket engines in missile defense and other maneuvering applications use hypergolic (self-igniting) propellants. The hypergolic propellants most commonly used are a combination of the liquid oxidizer di-nitrogen tetroxide (also known as NTO) and the fuel monomethyl hydrazine (also known as MMH). Although stable NTO/MMH thrusters have been around for decades, every new thruster design requires expertise in design and analysis to derive a stable design. Designing for combustion stability became considerably more difficult with specifications of high-performance oxidizers, such as MON25.
MON is an acronym for “mixed oxides of nitrogen”. Di-nitrogen tetroxide is a mixed oxide of nitrogen (N2O4). Recent development programs have specified use of MON25 instead of NTO because of the lower freezing point, desirable for the cold-weather storage of the interceptors. MON25 is comprised of 75% N2O4 and 25% nitric oxide (NO) by weight. NTO freezes at 16 degrees F, whereas MON25 freezes at -67 degrees F. MON25 also provides slightly higher performance, but has a notorious propensity for combustion instability.