Oxidizer Compound for Rocket Propulsion

Abstract

A rocket propulsion oxidizer compound that is a mixture that is a homogenous and stable liquid at room temperature that includes nitrous oxide and nitrogen tetroxide.

Description

ORIGIN OF THE INVENTION

The invention described herein was made in part by an employee of the United States Government and may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefore.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to rocket propellants. More specifically, the invention is an oxidizer compound for use in a rocket propulsion system.

2. Description of the Related Art

The need for high performance propulsion systems for space access and satellites has existed for decades. Small and large propulsion systems are needed for a variety of tasks or systems including rocket boost, orbit insertion and maintenance, attitude control systems (ACS), reaction control systems (RCS), station keeping, orbital maneuvering systems (OMS), and auxiliary power units (APU). However, the drawbacks and consequences associated with systems utilizing current propellants are still daunting, and research and development efforts over the years have not greatly improved the technology during this period. Present systems are either liquid propellants that use hypergolic or cryogenic oxidizers, or solid propellants that are single use only, cannot be throttled, and can detonate.

The current challenge is to attain the high energy and density goals for these propulsion systems while maintaining acceptable physical properties for the propellants. In general, the research goal is to identify propellants for a chemical propulsion system that are readily available, are easier to handle, non-toxic, produce high performance, and provide significant reductions in the cost of operations. While the problem is well understood, practical solutions which meet the objectives have been elusive and research has not been very fruitful to date.

In terms of liquid and hybrid propulsion systems that use oxidizers, the problems and tradeoffs associated with current oxidizers are varied and well known. For example, high operating costs result from occupational safety requirements associated with the handling of toxic, hypergolic propellants using inherently dangerous materials such as fluorine, nitrogen tetroxide (N₂O₄), inhibited red fuming nitric acid, etc. If the propellant requires cryogenic storage (e.g., propellants using liquid oxygen, nitrogen fluoride, etc.), other or additional operating complications include the storage of the materials in a way that prevents “boil off” prior to usage. Cryogenic storage systems also require the use of insulation which adds dry weight to both launch and space vehicles thereby reducing the vehicle's payload weight fraction. While less toxic and easily stored propellant oxidizers are known (e.g., nitrous oxide (N₂O)), their energy (i.e., heat of formation or ΔH_f) is generally too low to provide the required performance.

Other drawbacks and limitations of current technologies include the added weight and complexity of pressurants and feed systems for the propellants, state change of the propellants during prolonged storage, and the general problems of hot gas impingement and contamination to cold receiving surfaces from undesirable exhaust gas constituents. Unfortunately, current solutions available to address the storage and handling issues severely impact performance. Research to identify new liquid propellants (i.e., both fuels and oxidizers) is needed to enhance performance and minimize or eliminate the above-described undesirable properties without added complexity and cost. Finally, one of the most significant future needs is operational responsiveness enabled by on-demand propulsion systems for manned and unmanned missions that can be operational with short notice. This requirement places a premium on development of storable, non-cryogenic and non-toxic propellants that also meet reasonably high performance requirements.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide an oxidizer for use in a rocket propulsion system.

Another object of the present invention is to provide a rocket propulsion oxidizer that is not toxic in its exhaust products, and has reduced toxicity in its stored state.

Still another object of the present invention is to provide a rocket propulsion oxidizer that is easily stored at ambient conditions.

Yet another object of the present invention is to provide a rocket propulsion oxidizer that provides good performance.

Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings.

In accordance with the present invention, an oxidizer compound for use in a rocket propulsion system is provided. The compound is a mixture that is a homogenous and stable liquid at room temperature that includes nitrous oxide and nitrogen tetroxide.

BRIEF DESCRIPTION OF THE DRAWING(S)

Other objects, features and advantages of the present invention will become apparent upon reference to the following description of the preferred embodiments and to the drawings, wherein corresponding reference characters indicate corresponding parts throughout the several views of the drawings and wherein:

FIG. 1 is a schematic view of a rocket propulsion system using an oxidizer compound in accordance with the present invention; and

FIG. 2 illustrates graphs of oxidizer-to-fuel ratio versus specific impulse for a variety of fuel-oxidizer combinations to include several examples of oxidizer compounds in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The novel oxidizer compound of the present invention can be used in a variety of rocket propulsion systems to include, for example, those used in launch vehicle propulsion systems, multi-mode spacecraft propulsion systems, upper stage spacecraft propulsion systems, and missile propulsion systems. Furthermore, the oxidizer compound of the present invention can be matched with a variety of propellant fuels in these propulsion systems. Accordingly, it is to be understood that the type of propulsion system and/or propellant fuel used therein are not limitations of the present invention.

In general, the oxidizer compound of the present invention is a mixture of nitrous oxide and nitrogen tetroxide that is homogenous and a stable liquid (i.e., will not boil off) at room temperature. As used herein, the term “room temperature” is defined as temperatures that are generally close to approximately 20° C. or 72° F. as would be well understood in the art.

The new oxidizer compound of the present invention strikes a balance over a variety of oxidizer attributes that have traditionally been at odds with one another. More specifically, exemplary attributes balanced by the oxidizer compound of the present invention can be described as follows:

• • reduces storage problems by providing for room temperature storage thereof;
  • reduces propulsion system weight since room temperature storage reduces need for storage tank insulation;
  • provides for long-term storage since cryogenic boil-off is not a problem;
  • has a relatively high specific impulse when compared to traditional energetic but inherently problematic oxidizers;
  • has a relatively high energy density when compared to traditional energetic but inherently problematic oxidizers;
  • has reduced toxicity over pure nitrogen tetroxide in its stored state; and
  • produces environmentally benign exhaust products when burned in a propulsion system.

As mentioned above, the oxidizer compound is a homogenous, stable-liquid room temperature mixture that includes nitrous oxide and nitrogen tetroxide. While the particular mixture should strike an attribute balance for the particular propulsion system, it has been found that this balance is generally achieved for many of today's propulsion systems when the mixture includes at least approximately 35% (molar ratio) nitrogen tetroxide in the mixture and can range up to approximately 65% (molar ratio) nitrogen tetroxide. In terms of weight percent, this translates to a mixture having at least approximately 28 weight percent nitrogen tetroxide ranging up to approximately 52 weight percent nitrogen tetroxide. However, it is to be understood that other applications and propulsion systems may be able to create and utilize oxidizer compounds having as little as 5 weight percent nitrogen tetroxide (i.e., 95 weight percent nitrous oxide) or as much as 95 weight percent nitrogen tetroxide (i.e., 5 weight percent nitrous oxide), without departing from the scope of the present invention. These percentages were arrived at using the Trans 72 Chemical Equilibrium Combination (CEC) Prediction Code disclosed by S. Gordon et al. in “Computer Program for Calculation of Complex Chemical Equilibrium Compositions, Rocket Performance, Incident and Reflected Strikes, and Chapman-Jouquet Denotations,” NASA Report No. NASA-SP-273, 1971.

The oxidizer compound of the present invention could also include small or trace amounts of one or more additives that enhance performance, improve chemical stability, adjust exhaust by-products, etc., without departing from the scope of the present invention. For example, the oxidizer compound might have its performance enhanced by including a trace amount of an earth-storable oxidizer that has a “theoretical” specific energy (i.e., BTU's/lb) greater than that of nitrous oxide, but that would be too dangerous/toxic to use in any appreciable quantity. “Earth-storable” oxidizers are those that are liquids at room temperature such as “inhibited red fuming nitric acid” (IRFNA), nitrogen tetroxide or hydrogen peroxide. The term “theoretical” is used because the oxidizer's elements do not attain specific energy until mixed with a fuel that can be oxidized thereby.

Referring now to FIG. 1, a top level schematic of a rocket propulsion system using the oxidizer compound of the present invention is shown and is referenced generally by numeral 10. One storage container 12 stores (at room temperature) the homogenous and stable-liquid, nitrous oxide/nitrogen tetroxide compound of the present invention. A second storage container 14 stores a rocket fuel such as methane or RP-1. A combustion chamber 16 coupled to containers 12 and 14 through control valves (not shown) that control the mixing/burning of the oxidizer compound/rocket fuel with the combustion by-products being exhausted via a nozzle 18 to generate thrust. A variety of well-known mixing and exhausting systems can be used. Accordingly, combustion chamber 16 and nozzle 18 are not limitations of the present invention.

The form of the homogenous mixture of nitrous oxide and nitrogen tetroxide can be a non-viscous liquid or a viscous liquid (i.e., a gel) without departing from the scope of the present invention. Non-viscous liquid forms of the present invention would typically be used in launch vehicle propulsion systems and multi-mode propulsion systems. The gel form of the present invention might be used in some missile applications.

Applying a predictive testing routine using the above-referenced Trans 72 CEC Prediction Code, the oxidizer compound of the present invention was compared to liquid oxygen (LOX) and nitrogen tetroxide (N₂O₄) oxidizers in a propulsion system using methane (CH₄) as the rocket fuel. Comparisons of specific impulse (ISP) at a particular oxidizer-to-fuel (O/F) ratio and typical exhaust products are presented in Table 1 below. Also shown in Table 1 is a predictive test of the present invention's oxidizer compound (i.e., N₂O—N₂O₄ mixture) used in a propulsion system operating using the well-known RP-1 rocket fuel.

	TABLE 1
	Rocket Fuel:
	CH4	CH4	CH4	RP-1	RP-1
Oxidizer:	LOX	N2O4	65% N2O,	LOX	65% N2O,
			35% N2O4		35% N2O4
ISP:	407.4	382.5	351.9	405.8	333.6
O/F:	4.0	5.8	7.4	3.3	6.4
CO:	0.00005	0.0000	0.000000	0.03405	0.00000
CO2:	0.33265	0.2479	0.20189	0.47224	0.28881
H:	0.00000	0.0000	0.00000	0.00005	0.00000
HCO:	0.00000	0.0000	0.00000	0.00000	0.00000
HNO:	0.00000	0.0000	0.00000	0.00000	0.00000
HO2:	0.00000	0.0000	0.00000	0.00000	0.00000
H2:	0.00006	0.0000	0.00000	0.0127	0.00000
H2O:	0.66532	0.4958	0.40378	0.48088	0.28044
H2O2:	0.00000	0.0000	0.00000	0.00000	0.00000
N:	0.00000	0.0000	0.00000	0.00000	0.00000
N2:	0.00000	0.2507	0.39413	0.00000	0.42458
O:	0.00000	0.0000	0.00000	0.00000	0.00000
OH:	0.00006	0.0000	0.00000	0.00007	0.00000
O2:	0.00185	0.0056	0.00021	0.00000	0.00616

As is readily apparent from the data in Table 1, the oxidizer compound of the present invention provides comparable specific impulse performance at statistically greater oxidizer-to-fuel ratios. That is, the high-density oxidizer compound of the present invention means that less storage tank volume is required as compared to liquid oxygen or nitrogen tetroxide oxidizers. Accordingly, vehicle performance will be improved owing to smaller storage tank requirements. Further, since the present invention oxidizer can be stored at room temperature, the problems associated with the cryogenic storage of liquid oxygen are eliminated. The nitrous oxide-nitrogen tetroxide compound of the present invention is safe to handle and produces benign exhaust products as is evidenced by the data in Table 1.

To further illustrate the advantages of the present invention, FIG. 2 shows graphs of oxidizer-to-fuel ratio versus specific impulse for methane fuel and the following oxidizers:

Oxidizers (in weight percents) Curve No.
100% N2O4                      20
48% N2O, 52% N2O4              22
68% N2O, 32% N2O4              24
72% N2O, 28% N2O4              26
100% N2O                       28

As is clearly evident from these curves, having at least approximately 28 weight percent nitrogen tetroxide in the nitrous oxide-nitrogen tetroxide oxidizer compound, with the resulting benign exhaust products, yields comparable specific impulse performance to the highly dangerous nitrogen tetroxide oxidizer while yielding greatly superior specific impulse performance when compared to an oxidizer that is 100 weight percent nitrous oxide. Thus, the new oxidizer compound of the present invention solves at least some of the problems associated with the use of cryogenic liquid oxygen and provides better performance than liquid oxygen, while simultaneously providing performance comparable to the more highly energetic oxidizers without any of the handling/storage problems associated therewith.

The advantages of the present invention are further evidenced by the data in Table 2 below. In particular, it is evident that the addition of nitrous oxide (N₂O) to nitrogen tetroxide (N₂O₄), even in modest amounts, results in a significant percentage of payload to orbit capability versus liquid oxygen (LOX) when a first order analysis of only Total Impulse for a given Gross Lift Off Weight (GLOW) is compared for two heritage launch systems (i.e., “Delta II” and “Atlas V”). When nitrous oxide is added in increasingly larger amounts (i.e., moving from right to left on Table 2), the “penalty” in terms of payload percentage is small while the decrease in toxicity of the exhaust products increases substantially.

TABLE 2
Total Impulse (propellant mass × Isp = lbm ·
sec) vs N2O/N2O4 Oxidizer (Numbers are N2O/N2O4 molar ratio)
(quantities in parentheses denote ratio referenced to LOX-based value)
	LOX-based	65/35	50/50	40/60
Atlas V
1st	211692442	192749659	193895227	194495850
Stage: RP-1	(1.000)	(0.911)	(0.916)	(0.919)
2nd	20709920	17314374	17605499	17762898
Stage: LH2	(1.000)	(0.836)	(0.850)	(0.858)
Total	232402362	210064033	211500727	212258748
(Payload to	(1.000)	(0.904)	(0.910)	(0.913)
Orbit Ratio)
Delta II
GEMs	63937554	63937554	63937554	63937554
(strap-on)	(1.000)	(1.000)	(1.000)	(1.000)
1st	63943535	58964553	59317742	59477505
Stage: RP-1	(1.000)	(0.922)	(0.928)	(0.930)
2nd Stage:	4244070	4244070	4244070	4244070
N2O4/	(1.000)	(1.000)	(1.000)	(1.000)
Aerozine 50
Total	132125159	127146177	127499366	127659129
(Payload to	(1.000)	(0.962)	(0.965)	(0.966)
Orbit Ratio)

Although the invention has been described relative to a specific embodiment thereof, there are numerous variations and modifications that will be readily apparent to those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described.

Claims

1. An oxidizer compound for use in a rocket propulsion system comprising a mixture that is a homogenous and stable liquid at room temperature wherein said mixture includes nitrous oxide and nitrogen tetroxide.

2. An oxidizer compound as in claim 1 wherein said mixture further includes at least one additive having a theoretical specific energy greater than that of said nitrous oxide.

3. An oxidizer compound as in claim 2 wherein said at least one additive is an earth-storable oxidizer.

4. An oxidizer compound as in claim 1 wherein said liquid is non-viscous at room temperature.

5. An oxidizer compound as in claim 1 wherein said liquid is a gel at room temperature.

6. An oxidizer compound for use in a rocket propulsion system comprising a homogenous mixture that includes nitrous oxide and approximately 28 to 52 weight percent nitrogen tetroxide.

7. An oxidizer compound as in claim 6 wherein said mixture is a non-viscous liquid at room temperature.

8. An oxidizer compound as in claim 6 wherein said mixture is a gel at room temperature.

9. A rocket propulsion system comprising:

a first container;

a rocket fuel stored in said first container;

a second container;

an oxidizer compound stored in said second container, said oxidizer compound comprising a homogeneous and stable liquid mixture at room temperature that includes nitrous oxide and nitrogen tetroxide; and

means coupled to said first container and said second container for controlling mixing of said rocket fuel with said oxidizer compound.

10. An oxidizer compound as in claim 9 wherein said mixture further includes at least one additive having a theoretical energy greater than that of said nitrous oxide.

11. An oxidizer compound as in claim 10 wherein said at least one additive is an earth-storable oxidizer.

12. An oxidizer compound as in claim 9 wherein said mixture is non-viscous at room temperature.

13. An oxidizer compound as in claim 9 wherein said mixture is viscous at room temperature.

14. An oxidizer compound as in claim 9 wherein said mixture comprises approximately 28 to 52 weight percent nitrogen tetroxide.