Cryostabilized Propellant Additives

Abstract

There exists a set of normally unstable materials that can be cryogenically stabilized and used for the purposes of propulsion to provide revolutionary improvements in propulsive efficiency. The criteria for selection and formation of cryostabilized additives (CSAs) is described. Paths to the production of these CSAs may include 1) the formation of atmospheric pressure van der Waals compounds, 2) the capture and stabilization of radical species, and 3) techniques to concentrate or separate the CSAs. These routes to CSA production are described in general and for specific cases. The van der Waals compound H2Ne2 is described, together with its fabrication. The production and storage of HO2 is described. Specific techniques for separation and concentration of CSAs are described. The benefits and use of CSAs in combination with standard propellants are discussed. Cryostabilized Additives The hypothesis of this ongoing effort is that there exists a set of materials that are unstable at room temperature but which can be stabilized cryogenically to create high value, novel, propellant enhancers. These additives provide revolutionary improvements in propulsive efficiency. The characteristics of these cryostabilized additives (CSAs) can be defined and potential candidates identified. A critical element for the fabrication of CSAs is the path between its created state and its cryostabilized state. Specific paths to the scientific and engineering production of CSAs that are being investigated and described below include 1) the formation of room temperature van der Waals compounds, 2) production of cryostabilized radical species, and 3) techniques to concentrate or separate CSAs. This publication is not a review of previous relevant work, and focuses on experimental rather than theoretical or computational approaches. Analytical experimental techniques for determining material properties, while critical, will not be discussed. The overall objective of the effort is to establish experimental results that demonstrate or disprove the validity of each of the CSA production paths for a specific case as follows. For the CSA production path of forming a room temperature van der Waals compound, the specific objective will be to form H2Ne2. For the production path of choosing a radical species as a CSA, HO2 will be formed and stably stored. For the production path of CSA concentration, the technique of cryogenic sublimation concentration will be demonstrated. The most obvious host materials for CSA propellants are O2 and H2, but any propellant material can be cooled to cryogenic temperatures typically below 100 K to provide stabilization. The two primary classes of CSAs are those that are stable at cryogenic temperatures at 100% concentration, defined as CSA100s, and those that can only be stabilized at a lesser concentration. CSA100s are most easily formed and stabilized. An example of a CSA100 is an O2/H2 mixture at 10 K. Typical CSA densities for energetic fuel enhancement are on the order of 10 mole %; a catalytic CSA may be useful in significantly lower concentrations. CSA Stability A stable material at a specified temperature is defined as a material that will not spontaneously change state in response to its thermal environment. A metastable material (MM) is one that does not change state over some reasonably long period, but does eventually change state. For CSAs, a CAMM99, or Commercially Applicable MMs is defined as a material with 99% of its original CSA concentration over a period of 3 x 10 s (1 month); a usable propellant material. LAMM50s are stable to at least 50% concentration over 3 x 10 s (10 hrs) and useful for Laboratory Applications. LDMM are stable over 3 x 10 s for easy Laboratory Diagnosis. ADMM are stable over 3 x 10 s for easy Laboratory Diagnosis. A common misconception is that CSAs cannot exist in useful concentrations because the probability of two reactive atoms being adjacent approaches unity as the reactive atom fraction in the host material approaches 10%. When diffusion processes, particularly diffusion along grain boundaries, are taken into account, the estimated limiting concentration falls to 1-2%; work in radical trapping within solid matrices imply limiting concentrations of less than 1%. This only applies for species that have a zero potential barrier to reaction along the spatial coordinate between the molecules. There are a number of species (including radicals) of interest that have non-zero but small potential energy barriers to reaction. There are a smaller set of CSAs with potential barriers only in specific directions; these might be stabilized in an external field or a van der Waals compound. Detailed investigation of complex reaction potential energy surfaces is a modern science, although binary potential work is extensive (e.g. the H2 potential). Compilations exist for a variety of element pairs in their ground state (e.g. for alkali-inert pairs). The difficult problem in solid state compounds is to