Hybrid Rocket Propulsion  Explained

SPG is involved in all aspects of hybrid propulsion system design, modeling, testing, fabrication and qualification. Our engineering team can take a propulsion system from the mission requirements stage to flight production.

The significant technological advances made by Space Propulsion Group (SPG) have resulted in the development of high performance hybrid rockets without compromising their simplicity, cost and safety advantages over the solid and liquid propulsion systems. These advanced hybrid rocket systems rely on three key SPG technologies: 1) fast burning paraffin-based fuels which allow for the use of single circular fuel port geometry leading to excellent fuel utilization, 2) unique internal ballistic design which results in stable and efficient combustion without resorting to complex fixes that has been employed in the earlier development programs (such as injection of pyrophoric fluids to vaporize the incoming oxidizer) and 3) advanced carbon composite technology for the fabrication of the motor case which leads to light weight, cost effective propulsion systems. Based on the measured efficiencies, SPG's LOX/paraffin-based hybrid motor would deliver a vacuum Isp performance of 340 seconds (for an nozzle expansion ratio of 70:1), which is approximately 30 seconds higher than modern solid rockets and better than most liquid LOX/RP systems.

Some of the key virtues of SPGs hybrid rocket technology can be listed as (see Table for a summary):

  • Development of a portfolio of fast burning liquefying fuels (mostly paraffin-based) has enabled the use of a single circular port design approach which significantly simplifies the grain design/processing and improves the fuel utilization to 98-99% level.

  • Use of cost effective propellants and motor fabrication technologies.

  • Controlling the regression rate by adjusting the concentration of additives. This feature allows for the use of a single motor for a wide range of missions.

  • Elimination of the low frequency instabilities in the LOX/paraffin-based hybrids by the use of a novel injector/fore-end configuration as opposed to the conventional methods of addition of heat or injection of a pyrophoric substance (such as TEA) at the fore of the motor. The conception of this passive method used to mitigate the low frequency instabilities substantially simplifies the propulsion system and eliminates the use of additional subsystems that increases the weight, complexity and the cost of the vehicle.

  • Development and implementation of methods to attenuate the acoustic instabilities.

  • Realization of high combustion efficiencies, in the 95-97% range, in the LOX/paraffin-based motors. Similar efficiencies have been measured in nitrous oxide and Nytrox systems which are somewhat easier to achieve due to the noncryogenic nature of the oxidizer.

  • Use of gaseous oxygen as the pressurant eliminates the need for the expensive helium gas. Efficient combustion of the oxygen gas, which has been demonstrated in motor testing, results in substantial improvement in the structural coefficient.

  • Use of environmentally friendly propellants and materials in the propulsion system.

  • No exotic materials are used in the construction of the motors.

  • Use of carbon composite case material along with the high fuel utilization lead to low burn out weight for the hybrid motors.

  • A pintle throttling valve has been developed and tested. Throttling ratios of 3:1 has been successfully demonstrated.

  • SPG hybrids are inherently safe and suitable for manned missions.

  • SPG has developed a comprehensive set of analytical tools that can be used to design a new hybrid rocket system for a given mission. This capability is essential for the rapid and cost effective development of new propulsion systems. Some of the specific areas of expertise that SPG has developed over the years include:

  • Fuel formulation/optimization

  • Hybrid injector and pre-combustion chamber design

  • Grain structural design and integration

  • Internal ballistic design

  • Instability modeling

  • Nozzle design

  • Oxidizer tank, valving and feed system development

  • Mission optimization