Gaseous Oxygen Propulsion System With Chemical Oxygen Generation

Abstract

The present invention relates generally in gaseous oxygen propulsion systems with solid-phase chemical oxygen generation for in-space propulsion systems. Chemical oxygen generation is provided by alkali metal chlorates, alkali metal perchlorates or metal peroxides.

Claims

1. A method for storing oxygen in a solid phase material for a rocket propulsion system comprising: providing a solid-phase compound selected from the group consisting of alkali metal chlorates, alkali metal perchlorates or alkali metal peroxides and mixtures thereof; heating said solid phase compound and generating gaseous oxygen at a pressure of greater than or equal to 250 psia over a time period of 2.0 minutes or greater; introducing said gaseous oxygen to said rocket propulsion system.

2. The method of claim 1 wherein said pressure of said oxygen gas in said accumulator is greater than or equal to 250 psia to 4000 psia.

3. The method of claim 1 wherein said time period for generation of said oxygen gas is 2.0 minutes to 60.0 minutes.

4. The method of claim 1 wherein said rocket propulsion system generates heat and heating said solid phase compound utilizing said heat from said rocket propulsion system.

5. The method of claim 1 wherein said alkali metal chlorate comprises M.sup.+(ClO.sub.3).sup. wherein M.sup.+ is selected from Li.sup.+, Na.sup.+ or K.sup.+.

6. The method of claim 1 wherein said alkali metal perchlorate comprises M.sup.+(ClO.sub.4).sup. wherein M.sup.+ is selected from Li.sup.+, Na.sup.+ or K.sup.+.

7. The method of claim 1 wherein said alkali metal peroxide comprises Li.sub.2O.sub.2, Na.sub.2O.sub.2, or K.sub.2O.sub.2.

8. The method of claim 1 further providing to said solid-phase compound a metal oxide compound.

9. The method of claim 8 wherein said metal oxide compound comprises manganese oxide or chromium oxide.

10. The method of claim 9 wherein said solid phase compound comprises an alkali metal perchlorate and the mole ratio of said alkali metal perchlorate to said metal oxide is in the range of 3:1 to 7:1.

11. The method of claim 9 wherein said mole ratio is 4:1 to 6:1.

12. The method of claim 9 wherein said alkali metal perchlorate comprises LiClO.sub.4 and said metal oxide comprises MnO.sub.2.

13. The method of claim 1 wherein said solid phase compound is present as particles with a size in the range of 10 m to 100 m.

14. A method for storing oxygen in a solid phase material for a rocket propulsion system comprising: providing a solid-phase compound comprising an alkali metal perchlorate in combination with a metal oxide wherein at a mole ratio of 3:1 to 7:1; heating said solid phase compound and generating gaseous oxygen at a pressure of greater than or equal to 250 psia over a time period of 2.0 minutes or greater; introducing said gaseous oxygen to said rocket propulsion system.

15. The method of claim 14 wherein said alkali metal perchlorate comprises LiClO.sub.4 and said metal oxide comprises MnO.sub.2.

16. The method of claim 15 wherein said LiClO.sub.4 and said MnO.sub.2 are present at a mole ratio of 4:1 to 6:1.

17. The method of claim 14 wherein said alkali metal perchlorate is present as particles with a size in the range of 10 m to 100 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1 illustrates the use of an alkali metal perchlorate in a gaseous oxygen hybrid propulsion system.

[0006] FIG. 2 identifies the pressure and oxygen yield versus time for the thermal decomposition of LiClO.sub.4 in the presence of MnO.sub.2 at a 5:1 mole ratio.

[0007] FIG. 3 illustrates the pressure and oxygen yield versus time profiles measured for the thermal decomposition of LiClO.sub.4.

[0008] FIG. 4 illustrates the pressure and oxygen yield versus time profiles measured for the thermal decomposition of Li.sub.2O.sub.2.

[0009] FIG. 5 illustrates the pressure and oxygen yield versus time profiles measured for the thermal decomposition of LiClO.sub.4 in the presence of Li.sub.2O.sub.2 at a 2:1 mole ratio.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention is directed at solid state oxygen storage for in-space propulsion systems. The solid state oxygen storage refers to solid-phase chemical compounds that are stable at standard temperature and pressure but which decompose to release oxygen at elevated temperatures. The released oxygen can then be combined with a separate fuel source for space-propulsion applications.

[0011] Preferably, the solid-phase chemical compounds are alkali metal perchlorates having the formula M.sup.+(ClO.sub.4).sup. or alkali metal chlorates having the formula M.sup.+(ClO.sub.3).sup., where M is selected from Li.sup.+, Na.sup.+, K.sup.+, or mixtures thereof. Upon decomposition, the following occurs:

MClO.sub.4.fwdarw.MCl+2O.sub.2

2MClO.sub.3.fwdarw.2MCl+3O.sub.2

[0012] Table 1 below identifies the oxygen storage characteristics of the identified perchlorate compounds in comparison to gaseous and liquid oxygen:

TABLE-US-00001 TABLE 1 Oxygen Mass Oxygen Density Decomposition Compound Fraction kg/m.sup.3 Temperature, C. Lithium Perchlorate 60% 1,461 400 (LiClO.sub.4) Sodium Perchlorate 52% 1317 480 (NaClO.sub.4) Potassium Perchlorate 46% 1,164 500 (KClO.sub.4) Liquid Oxygen @ 100% 1,141 N/A 14.7 psi Gaseous Oxygen @ 100% 668 N/A 10,000 psi Gaseous Oxygen @ 100% 92 N/A 1,000 psi

[0013] As can be seen from the above, lithium, sodium and potassium perchlorate all provide excellent oxygen density. Lithium perchlorate provides the highest oxygen mass fraction, highest oxygen density and lowest decomposition temperature. Accordingly, lithium perchlorate is particularly well-suited herein for storing oxygen for a space propulsion application. In addition, it is worth noting that the decomposition of the alkali perchlorates, which is preceded by endothermic melting, is weakly exothermic, which is reference to an exothermic heat generation in the range of 7 kJ/mol to 28 kJ/mole. Accordingly, the alkali chlorates herein are such that they indicate an exothermic decomposition of 28 kJ/mole. The alkali perchlorates herein are therefore relatively safe to detonation making them particular suitable for the in-space propulsion applications described herein.

[0014] In addition to the alkali metal chlorates and alkali metal perchlorates that can be used for oxygen gas generation herein, one may also utilize an alkali metal peroxide (Li.sub.2O.sub.2; Na.sub.2O.sub.2, K.sub.2O.sub.2). Of these, preferably, one can utilize lithium peroxide. Upon heating and decomposition, oxygen gas generation proceeds according to the following general equation:

2Li.sub.2O.sub.2.fwdarw.2Li.sub.2O+O.sub.2

[0015] It should also be noted that the alkali metal peroxide may be used on its own or in combination with the alkali metal chlorates and/or alkali metal perchlorates noted above. More specifically, one may utilize the alkali metal chlorate and/or alkali metal perchlorate at a molar ratio to the alkali metal peroxide of 1:1 to 3:1, More preferably, the molar ratio of alkali metal chlorate to alkali metal perchlorate to the alkali metal peroxide is 2:1.

[0016] FIG. 1 identifies the use of an alkali metal perchlorate in a gaseous oxygen hybrid propulsion system. As can be seen, the alkali metal perchlorate at 10 is configured to decompose at elevated temperature to produce gaseous oxygen. The alkali metal perchlorates, as well as the alkali metal chlorates or the alkali metal peroxides, are preferably present as particles with a particle size (longest linear diameter) in the range from 10 m to 100 m, more preferably 50 m to 70 m. The gaseous oxygen is introduced to a gaseous oxygen accumulator 12, which as shown, includes a vessel to store the oxygen gas under pressure for subsequent release to a rocket propulsion system 14. However, the oxygen accumulator herein may also include a supply line for direct feeding of gaseous oxygen into the rocket propulsion system. Moreover, the rocket propulsion system is understood herein as an engine that provides propulsion by expelling a reaction mass in accordance with Newton's third law of motion.

[0017] Preferably, the decomposition is such that oxygen pressures of greater than or equal to 250 psia are achieved (250 psia). More preferably, the oxygen pressures that are achieved are contemplated to fall in the range of 250 psia to 4000 psia. For example, the oxygen pressures that are achieved may also preferably be 500 psia, or 750 psia, or 1000 psia. Such pressures are also preferably achieved over a time period of 2.0 minutes or greater. Preferably such pressures are achieved in the range of 2.0 minutes to 60.0 minutes. More preferably, the time period is in the range of 2.0 minutes to 20 minutes or in the range of 2.0 minutes to 10.0 minutes. In addition, the alkali metal chlorate storage is such that, in discrete event fashion, it can replenish the accumulator volume several times over a given period of time at the required pressures of 250 psia, depending upon the requirements of the rocket propulsion system 14. In other words, the alkali metal storage is such that it can repeatedly recharge the accumulator to pressures of 250 psia to supply requisite levels of oxygen gas to the rocket propulsion system for in-space travel requirements. Alternatively, the alkali metal perchlorate decomposition may directly feed the rocket propulsion system 14 if prolonged burns are necessary in the rocket propulsion system.

[0018] As therefore noted, the gaseous oxygen is introduced into a rocket propulsion system 14 and combined with a fuel source. The rocket propulsion system is preferably a gaseous oxygen-hybrid system that relies upon the gaseous oxygen and a solid fuel. The solid fuel may include a polyethylene such as high-density polyethylene (HDPE), rubber (e.g polybutadiene such as hydroxyl terminated polybutadiene). One may also utilize a paraffin containing 20-40 carbon atoms.

[0019] As noted above, the decomposition of the alkali metal perchlorate to promote oxygen gas formation occurs with heat. Such heat may be provided from electric resources, such as solar panels or batteries. Solar radiation may also be relied upon to directly heat the alkali metal perchlorate. It may also rely upon the separate reaction of pyrotechnic materials. In addition such heating may conveniently rely upon heat from the rocket propulsion system. For example, it is contemplated that heat from the rocket chamber or even heat generated from the output plume of the rocket may be utilized to provide the requisite heating for alkali metal perchlorate decomposition and oxygen gas generation.

[0020] It has also been identified herein that oxygen gas formation from the solid alkali metal perchlorate can be generated at different rates through the effect of catalysis. Specifically, one may use, in combination with the alkali metal perchlorate, a metal oxide. Such metal oxides can preferably include manganese oxide (MnO.sub.2) or chromium oxide (Cr.sub.2O.sub.3). The mole ratio of the solid alkali perchlorate to the metal oxide is preferable in the range of 3:1 to 7:1, more preferably 4:1 to 6:1. In a most preferred embodiment, the mole ratio of the solid alkali perchlorate to the metal oxide is 5:1.

[0021] FIG. 2 identifies the pressure and oxygen yield versus time for the thermal decomposition of LiClO.sub.4 in the presence of MnO.sub.2 at a 5:1 mole ratio. This plot is overlaid with the profiles for the vessel temperature and the integrated Joule heating (right ordinate), which corresponds to the measured energy input supplied to the heating element of the test vessel to attain the thermal profile. In this case, the pressure rise from the catalytic evolution of oxygen occurred at such a relatively high rate that the monitoring system for the volumetric analyzer employed automatically increased the volume of the calibrated reservoir volume (4.61.fwdarw.11.47 cm.sup.3) to avoid over-pressurizing of the system. This event was reflected by the spike in the pressure profile at 0.4 hours. The computed oxygen yields beyond this time point were corrected for the larger reservoir volume. As can also be seen, the first steady-state plateau was attained within about 26 minutes from the start of the heating curve and within only a few minutes after attaining isothermal conditions at around 460 C. By contrast to pure LiClO.sub.4, the decomposition reaction nearly achieved the theoretical yield for oxygen within the first aliquot (99%). Additionally, a marked decrease (75 C.) in the temperature range of which significant oxygen generation occurs was realized with MnO.sub.2 as a catalyst in combination with LiClO.sub.4, as opposed to the use of LiClO.sub.4 on its own. Reference is therefore made to FIG. 3 which provides the pressure and oxygen yield versus time profiles measured for the thermal decomposition of LiClO.sub.4. Steady-state conditions were achieved after approximately on hour, or within 30 minutes after attaining isothermal conditions at 460 C.

[0022] Attention is next directed to FIG. 4 which provides the pressure and oxygen yield versus time profiles measured for the thermal decomposition of Li.sub.2O.sub.2. As can be seen in FIG. 4, the first steady-state plateau was attained in about 30 minutes from the start of the heating curve and within a few minutes after obtaining isothermal conditions at 450 C. The oxygen yield at the first plateau was 84% at 50 bar. Complete decomposition and oxygen yield was then achieved. FIG. 5 provides the pressure and oxygen yield versus time profiles measured for the thermal decomposition of LiClO.sub.4 in the presence of Li.sub.2O.sub.2 at a 2:1 mole ratio.

[0023] Table 2 below provides a summary of the preferred solid-phase chemical oxygen generating compounds and exemplary formulations. The mole ratios for the formulations recite the catalysts MnO.sub.2 and Cr.sub.2O.sub.3 and are based on the number of cations in each oxide. The theoretical yields for these formulations assume the metal oxide is reduced to yield 0.5 moles of oxygen:

TABLE-US-00002 TABLE 2 Total Content Bulk Analysis Theoretical Compound/ MW (wt. % Density Tm Decomposition Weight Yield (mol Formulation (g/mol) Oxygen) (g/cm.sup.3) ( C.) Temp. ( C.) (g) O.sub.2) LiClO.sub.4 106.39 60.15 2.420 236 400 2.5543 0.0480 Li.sub.2O.sub.2 45.88 34.87 2.310 195 330 3.5235 0.0384 LiClO.sub.4 + 55.67 5.0242 0.0825 Li.sub.2O.sub.2* (2:1 mol) LiClO.sub.4 + 86.94 54.29 5.030 535 483 5.9969 0.1018 MnO.sub.2* (5:1 mol) LiClO4 + 151.99 49.12 5.220 2,435 1,200 6.0290 0.1014 Cr.sub.2O.sub.3* (5:1 mol) [0024] For mixtures, the molecular weight, bulk density, melting point and decomposition temperatures are given for the component not previously listed in the table, if applicable. Thus, these fields are blank for LiClO.sub.4+Li.sub.2O.sub.2 entry and give the values for MnO.sub.2 in the LiClO.sub.4+MnO.sub.2 entry.

[0025] As can now be appreciated, the invention herein is particular beneficial to hybrid rockets systems where the fuel is already stored in the solid phase. Storing the oxygen in the solid phase and generating gaseous oxygen on-demand facilitates a liquid-free propulsion system that is contemplated to be relatively safe, compact and capable of a plurality of restarts, all with throttling. The system herein is therefore further contemplated to be denser and more environmentally friendly than existing hydrazine monopropellant thrusters while achieving a similar mass.