3,171,249 United States Patent Office Patented Mar. 2, 1965 i 2 fuel rocket engine. The above and other objects of this 3,171,249 PROPELLANT AND Rick |PROPULSSON METH invention will become apparent from the discussion OXD EMPLOYANG EYERAZINE WITH AMSNO which follows. TETRAZOLES The objects of this invention are accomplished by the Ronald E. Be, Canoga Park, Calif., assigner to use of compounds having the general formula: North American Aviatiosa, Bac. No Drawing. Fied Nov. 29, 1961, Ser. No. 155,803 NH2. (R) 8 Clains. (C. 60-35.4) N This invention relates to a novel rocket propellant. YS More particularly, this invention relates to a novel in 10 N--H proved rocket propellant and a method of operating a wherein x varies from 0 to 1 and R is selected from the rocket engine. class consisting of HCl, H2O, HNO3, and HCIO, as addi The criterion by which rocket propellants are classi tives to a hydrazine-based rocket fuel in an amount suffi fied is specific impulse, Is, defined as thrust in pounds 5 cient to depress the freezing point at least 40° C. while divided by the total mass flow of fuel and oxidizer in retaining about the same density impulse and specific pounds per second. Specific impulse is thus given in impulse. Hence, an embodiment of this invention com units of "seconds.” Oxidizer-fuel propulsion system prises a method of operating a rocket engine comprising compositions with a relatively high specific impulse are ejecting from the reaction chamber of the engine a gaseous known in the art. Such systems, however, quite often 20 product produced by a spontaneous combustion of an employ a non-storable oxidizer such as liquid oxygen, oxidizer and hydrazine-based fuel having therein a salt for example. The non-storability of certain rocket pro of 5-amino tetrazole, said fuel and oxidizer being injected pellant components results in a tactical disadvantage pro in separate streams into the combustion or Teaction viding rockets which can not be held in a full state of in chamber. stantaneous readiness. Consequently, a search has cen 25 More particularly, the invention concerns a rocket tered on development of a high energy, storable, liquid fuel comprising from about 65 to about 80 weight percent system which is invariably hypergolic (spontaneously hydrazine and from about 20 to about 35 weight percent combustible on fuel-oxidizer contact), and that remains so of a 5-amino tetrazole or Salt thereof. A more preferred even at very low pressures and temperatures. For ex composition having particularly high density impulse is ample, hydrazine, N2H4, is a well-known rocket fuel. 30 one having from about 68 to about 72 weight percent Chlorine trifluoride, ClF3 is a storable oxidizer. In order hydrazine and from about 28 to about 32 weight percent to derive the greatest possible benefit from using an oxi of 5-amino tetrazole or salt thereof. In order to improve dizer with an extremely wide liquid range such as chlo the low temperature viscosity behavior of the hydrazine rine trifluoride, the fuel itself should have a correspond based fuel containing the sait of 5-amino tetrazole, a small ingly large liquid range. In this case, hydrazine must be 35 amount of monomethyl hydrazine, MMH, may be added eliminated due to its relatively high freezing point. to the fuel composition. It is found to be particularly Therefore, a need exists for a fuel having a low freez advantageous to add from about 2 to 25 weight percent ing point and a high specific impulse when used with a of the Inonomethyl hydrazine to the fuel composition of storable oxidizer. this invention. Thus, a typical fuel of this invention con Previously, in order to obtain a fuel with a wide liquid 40 tains 50-70 weight percent hydrazine, 20-35 weight per range, a sacrifice has been made in the density impulse cent of a salt of 5-amino tetrazole and 0–25 weight per of the fuel, I, which is defined by the formula: cent monomethyl hydrazine. Various liquid oxidizers may be used in combination I =I.x. At with the hydrazine fuel containing the additives of this MR ) 45 invention. Non-limiting examples of the various oxidizers do ti, which may be used include: fluorides which may be bromine pentafluoride, chlorine trifluoride, perchloryl wherein MR (mixture ratio)=ratio of the oxidizer con fluoride, bromine monofluoride, bromine trifluoride, sumption Tate to the fuel consumption rate. chlorine monofluoride, iodine pentafluoride, nitrogen do=density, oxidizer, g./cc. fluoride, nitrosyl fluoride, nitryl fluoride, nitrogen tri d=density, fuel, g/cc. fluoride, oxygen difluoride; oxides including hydrogen. peroxide, tetroxide, nitric oxide, nitrogen dioxide, chlo The density impulse of a fuel is an important factor in rine dioxide, chlorine heptoxide, chlorine hexoxide, chlo the design of a missile system because it indicates the im rine monoxide, nitrous oxide, sulfur dioxide, nitrogen pulse obtainable from a given volume of fuel. Since the 55 trioxide; chlorides which may be bromine chloride, iodine volume capacity of a missile is limited, it is thus obviously chloride, nitrogen trichloride, nitrosyl chloride, phos desirable to obtain the highest impulse from a given phorous oxychloride, selenium oxychloride, pyrosulfury volume of the fuel. Hydrazine has a relatively high den chloride; halogens including fluorine, chlorine, bromine; sity impulse. As a result, it is desirable to maintain or carboxylic acids which may be caproic acid, acetic acid, approximate this high density impulse of hydrazine in 60 formic acid, butyric acid, lactic acid, acrylic acid; addi addition to lowering its freezing point while keeping the tional oxidizers are oxygen difiuoride, nitric acid, oxygen, specific impulse high. ozone, tetranitramethane, tetrafluorohydrazine, hydrogen It is an object of this invention to provide a new hy sulfide, bromoazide, perchloric acid, chlorine azide, chlo drazine-based fuel. Another object of this invention is rosulfonic acid, difluorophosphoric acid, hexafluorophos to provide a storable rocket fuel or composition possess 65 phoric acid, fluorosulfonic acid, hydrogen bromide, nitro ing a high specific impulse. It is also an object of this syl bromide, phosphoric acid, pyrophosphoric acid, invention to provide a storable rocket fuel. A further selenic acid. object of this invention is to provide a rocket fuel com position having a low freezing point. One other ob EXAMPLE ject of this invention is to provide a novel rocket fuel A hydrazine fuel composition of this invention was having a high density impulse. A still further object of 70 made by preparing a mixture of 65 percent hydrazine, the invention is to provide a method of operating a liquid 6 percent by weight monomethyl hydrazine and 29 per 3,171,249 3. 4. cent by weight 5-amino tetrazole hydrate. The three tetrazole such as 5-amino tetrazole nitrate, 5-amino tetra components were simply stirred together at ambient con zole hydrochloride and 5-amino tetrazole perchlorate. ditions. It makes no difference as to what order the EXAMPLE IV compounds are added to each other in preparing the mix Various compositions containing 5-amino tetrazole and tures of the invention. The density of the foregoing fuel salts thereof were prepared in accordance with this in coin position at 68° F. was 1.1261 g/cc. The freezing vention. The following Table III illustrates some of point was -53 C. these compositions that were prepared. EXAMPLE I Table III Various hydrazine-based fuel compositions were pre O Composition compounds: Weight percent pared adding thereto monomethyl hydrazine and 5-amino tetrazole hydrate. In addition, other hydrazine fuel com (1) 5-amino tetrazole-hydrate --------------- 20 positions containing compounds similar to the 5-amino Hydrazine ---------------------------- 80 tetrazole hydrate were prepared. Surprisingly, it was dis (2) 5-amino tetrazole-nitrate ---------------- 30 covered that the aforementioned closely related corn 5 Hydrazine ---------------------------- 70 pounds did not significantly lower the freezing point. The (3) 5-amino tetrazole-perchlorate ------------ 35 results are shown in the following Table I. Hydrazine ---------------------------- 65 8.-- (4) 5-amino tetrazole ---------------------- 20 Table I Hydrazine ---------------------------- 55 20 Monomethyl hydrazine ----------------- 25 Composition Weight Freezing Percent Point, C. (5) 5-amino tetrazole hydrochloride ---------- 25 Hydrazine ---------------------------- 65 1. N2H4---------------------------------- 100.00 --2.0 Mononethyl hydrazine ----------------- O 2. NH4------------ 65.76 -5.6 Nitroguanidine- 34.24 25 (6) 5-amino tetrazole hydrate --------------- 25 3. N2H4------------ 63.72 -25.5 5-Amino 1, 3, 4, Triazole 36.28 Hydrazine ---------------------------- 73 4. NH4--------------------- 77.4 -5.8 Monomethyl hydrazine ----------------- 2 Carbohydrazide----------------------- 22.86 5. NH4---------------------------------- 62. 70 -79.0 EXAMPLE V 5-Amino Tetrazole Hydrate----------- 3.30 6. N2H4------------------------ 65.00 -53.0 Monomethyl Hydrazine----- 6.00 30 The novel fuel compositions of this invention may be 5-Amino Tetrazole Hydrate-------- 29.00 utilized in conventional liquid propulsion rocket engines. Thus, an embodiment of this invention involves a method of operating a conventional liquid rocket engine utilizing EXAMPLE I as a fuel, therefore, the herein compositions. A conven Two mixtures of hydrazine, monomethylhydrazine and tional liquid engine system as described on page 9 of the 5-amino tetrazole hydrate were prepared.