Green Propellant Rockets


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In recent years low toxicity (or “green”) liquid rocket propellants have become attractive as possible substitutes for hydrazines and nitrogen oxides in low or medium thrust engines because of the reduced environmental impact and, more so, the cost savings associated with the drastic simplification of the required health and safety precautions. High-energy green propellants (like ADN, HAN and HNF) are based on organic molecules and compensate the high molecular weight of their decomposition products with proportionally higher operational temperatures, which still pose significant challenges to the realization of durable catalytic reactors and radiatively cooled thrust chambers. Hydrogen peroxide (H2O2) does not suffer from these disadvantages and is now being reconsidered as a promising green monopropellant and bipropellant (in conjunction with hydrocarbons) for low and medium thrust applications.


A breadboard model of an hydrogen peroxide monopropellant rocket mounted on the thust balance in Alta’s GPRTF (left) and 0.6 mm diameter platinum-deposed alumina spheres before integration in the H2O2 catalytic reactor (right).

Alta’s chemical propulsion team focuses on the perfection of the capabilities of low and medium thrust green propellant rockets for spacecraft reaction control and orbital maneuver systems. Recent activities funded by ESA and the Italian Ministry of Industry include the development of monopropellant (H2O2) and bi-propellant (H2O2-ethane) thruster prototypes with thrust in the 1 to 5 N and 25 to 100 N ranges respectively, targeted to small LEO platforms.

SEM images of palladium on Al2O3 spheres, 40× (left) and ruthenium on
Syralox-30 pellets, 621× (right).

Testing of advanced catalyst/ceramic beds for rocket-grade hydrogen peroxide decomposition is underway in collaboration with the Chemistry and Industrial Chemistry Department of Università di Pisa as a cost-effective alternative to metal screen reactors with the aim of:

  • developing novel deposition techniques of different catalyst/substrate combinations (manganese oxides, palladium, platinum, ruthenium and silver on γ-Al2O3 and Si-doped Al2O3 spheres)
  • characterizing the deposed surface by means of Scanning Electron Microscope (SEM) analysis for the assessment of the surface properties and the measurement of the catalyst concentration and surface distribution
  • characterizing the catalyst/substrate combinations in atmospheric drop tests for the comparative evaluation of the chemical decomposition intensity and sensitivity to reactant temperature and concentration, the resistance to poisoning from common H2O2 contaminants and stabilizers, and the resistance to rupture and/or powdering due to thermal stresses during operation and its dependence on the intensity of the decomposition activity.

A breadboard model of an hydrogen peroxide monopropellant rocket firing in Alta’s GPRTF.

The most promising catalyst/substrate combinations are being assembled in the catalytic reactors of two rocket engine breadboard models for conducting firing demonstration tests in Alta’s Green Propellant Rocket Test Facility (GPRTF) under more realistic operational conditions. The tests are aimed at:
  • characterizing the catalytic reactor performance, integrity, lifetime and pressure losses in decomposing rocket grade hydrogen peroxide at realistic values of the flow pressure, bed load and residence time;
  • characterizing the engine’s propulsive performance, ignition, transient times and stability in H2O2 monopropellant and H2O2-ethane bipropellant operation.

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