Fuel substances as follows: a. Hydrazine (CAS 302-01 - 2) with a concentration of more than 70%; b. Hydrazine derivatives as follows: 1. Monomethylhydrazine (MMH) (CAS 60-34 - 4); 2. Unsymmetrical dimethylhydrazine (UDMH) (CAS 57-14-7); 3. Hydrazine mononitrate; 4. Trimethylhydrazine (CAS 1741-01-1); 5. Tetramethylhydrazine (CAS 6415-12-9); 6. N,N diallylhydrazine; 7. Allylhydrazine (CAS 7422-78-8); 8. Ethylene dihydrazine; 9. Monomethylhydrazine dinitrate; 10. Unsymmetrical dimethylhydrazine nitrate; 11. Hydrazinium azide (CAS 14546-44-2); 12. Dimethylhydrazinium azide; 13. Hydrazinium dinitrate; 14. Diimido oxalic acid dihydrazine (CAS 3457-37-2); 15. 2-hydroxyethylhydrazine nitrate (HEHN); 16. Hydrazinium perchlorate (CAS 27978-54-7); 17. Hydrazinium diperchlorate (CAS 13812-39-0); 18. Methylhydrazine nitrate (MHN); 19. Diethylhydrazine nitrate (DEHN); 20. 3,6-dihydrazino tetrazine nitrate (DHTN); c. Spherical or spheroidal aluminium powder (CAS 7429-90-5) in particle size of less than 200 x 10 -6 m (200 μm) and an aluminium content of 97% by weight or more, if at least 10% of the total weight is made up of particles of less than 63 μm, according to ISO 2591:1988 or national equivalents; d. Metal powders of any of the following: zirconium (CAS 7440-67-7), beryllium (CAS 7440-41-7), magnesium (CAS 7439-95-4) or alloys of these, if at least 90% of the total particles by particle volume or weight are made up of particles of less than 60 μm (determined by measurement techniques such as using a sieve, laser diffraction or optical scanning), whether spherical, atomised, spheroidal, flaked or ground, consisting of 97% by weight or more of any of the above mentioned metals; Note: In a multimodal particle distribution (e.g. mixtures of different grain sizes) in which one or more modes are controlled, the entire powder mixture is controlled. e. Metal powders of either boron (CAS 7740-42-8) or boron alloys with a boron content of 85% or more by weight, if at least 90% of the total particles by particle volume or weight are made up of particles of less than 60 μm (determined by measurement techniques such as using a sieve, laser diffraction or optical scanning), whether spherical, atomised, spheroidal, flaked or ground; Note: In a multimodal particle distribution (e.g. mixtures of different grain sizes) in which one or more modes are controlled, the entire powder mixture is controlled. f. High energy density materials, usable in the systems specified in 1.A. or 19.A., as follows: 1. Mixed fuels that incorporate both solid and liquid fuels, such as boron slurry, having a mass- based energy density of 40 x 10 6 J/kg or greater; 2. Other high energy density fuels and fuel additives (e.g., cubane, ionic solutions, JP-10) having a volume-based energy density of 37.5 x 10 9 J/m 3 or greater, measured at 20 o C and one atmosphere (101.325 kPa) pressure.