Metallized gelled rocket propellants have been considered for many different applications. While operational usage has not yet come to fruition, there are many technology programs that are underway to eliminate the unknowns with gelled propellants and the propulsion systems that will use them. Numerous studies have shown the potential benefits of gelled fuels and oxidizers. Technology programs to prove the combustion performance of gelled propellants have been conducted most recently by the U.S. Army Missile Command, with their industry and university partners, for tactical missile applications. The NASA Lewis Research Center and its partners have investigated O₂ / H ₂ / Al and O₂ / RP-1 / Al for NASA missions and conducted experimental programs to validate elements of the combustion and fuel technology. Gelled and metallized gelled hydrogen and RP-1 have been emphasized because hydrogen and RP-1 are typical propellants for NASA launch vehicles and upper stages. Derivatives of these propellants are therefore preferred to minimize the incremental risk for a newly introduced propulsion concept. Gelled hydrogen technology is emphasized in this paper. It's likely applications would be for rocket powered launch vehicles and upper stages, rocket based combined cycle airbreathing vehicles, and combination (rocket and airbreathing) propulsion options.

High Energy Density Propellants and Solid Hydrogen

New technologies in atom formulation and physics of material manipulation has led to the discovery and synthesis of materials that can be used in rocket propellants. sing these propellants is more complex than traditional propellants because of their unique chemistry. While the abovementioned monopropellants are often simpler fuels with additives that are traditional molecules which are stable in storage, the high energy species must be formulated very meticulously because they are not occurring in nature. These formulations offer increased energy density, but they must be manufactured and stored in a stabilizing medium. This medium may be solid hydrogen particles that surround the newly created atoms or molecules and isolate them. Next generation RLV propulsion systems can use these frozen hydrogen particles in a cryogenic liquid carrier, such as helium.

These fuels are the penultimate step in the development of higher performance, higher density propellants. These more advanced propellants will require longer development times, so they would not be the first propellants to be commercialized. Near term aspects related to these high energy species might be the production methods of the atoms or species, the cryogenic feed system components, such as superinsulation, valves and other flow control components, feed lines, cryogenic storage, and leak detection systems.

In-situ resources for planetary exploration

The future exploration of the Solar System will require innovations in transportation and use of the in-situ resources at many planetary landing sites. The cost of space missions has always been prohibitive, and using the natural resources that are available at the sites of exploration can reduce the cost, mass, and complexity of these missions. This paper will describe some of the resources available at the sites, and survey the overall technologies for propulsion that may be attractive for future Solar System missions.

The Moon

With advanced chemical propulsion, there are several alternatives for using in-situ resources. The most likely option considered in past studies has been lunar oxygen. The composition of lunar materials from samples returned to Earth shows that oxygen is approximately 42 percent of the lunar regolith, trapped in oxides of silicon aluminum, titanium, and iron. Using these resources, planned lunar bases and industries would become self sufficient or at least less reliant upon Earth based materials. Several lunar ascent-descent vehicles and related architectures were assessed. Many studies show the importance of a precise architecture selection to make the scenario supportable, maintainable, and cost effective.

Another more volatile fuel possibility is hydrogen trapped in the lunar soil. This hydrogen is there as a result of billions of years of bombardment by the solar wind. Mining concepts conceptual designs of large extraction machinery have been assessed. Possible uses in spacecraft will be addressed. Fusion fuels such as Helium 3 (3He) have also been identified in the lunar samples. While chemical propulsion may not use 3He, there are potential fusion propulsion systems that may benefit from this fuel.

Mars

A simple method of using in-situ resources would be to transport fuel to Mars, and only produce O₂. With an O₂/CH₄ propulsion option, the mass of a Mars Sample Return Vehicle would be reduced by 50 percent. Other more ambitious propulsion options focus on producing both fuel and oxidizer on Mars.
These concepts use CO - O₂. . Subsurface water is another potential propellant option, and a Mars exploration vehicle with a melting probe is envisioned.

Additional research has been more recently conducted on carbon dioxide with metal particles. Using CO₂ ? Metal propellants, the CO₂ and metal would both be extracted from Mars, or the metal would be brought from Earth.

Asteroids

Using asteroidal materials has been an attractive option for propellants, as well as other resources that may be used for the entire Earth. Carbonaceous chondrite materials predicted to be on many asteroids may contain water and other volatiles. Production of O₂ and H₂ and other energetic materials has been assessed, and there are many potential propellants.

The Outer Solar System

Our Outer Solar System is composed of gas giant planets, moons, and many smaller bodies than may contain significant resources for propellants. The Galilean moons of Jupiter have been studied intensively by the Galileo spacecraft, and the implications of these studies imply that oceans of water may exist below these moons? icy surfaces.

If there are sufficiently power intensive systems for these outer moon missions, options exist for melting or penetrating the ice, and creating hydrogen and oxygen. Other volatiles and mineral such as salts, and more typical metal oxides are also available for fuel and oxidizer production.

Preliminary designs from past studies will be described and summarized to focus on what technologies are most attractive for use of in-situ materials for chemical propulsion propellants. Other options for atmospheric flight will also be reviewed, including flight in planetary atmospheres with advanced fuels.

Main Project Website

For more information please visit the main project website.

Researchers

Bryan A. Palaszewski