High Density Hybrid Rocket Motor

Abstract

A high density, generally recognized as safe hybrid rocket motor is described which has a density-specific impulse similar to a solid rocket motor, with good performance approaching or equal to a liquid rocket motor. These high density hybrid motors resolve the packaging efficiency/effectiveness problems limiting the application of safe, low cost hybrid motor technology.

Claims

1. A high density hybrid rocket motor utilizing a storable, non-toxic oxidizer and high density, high regression fuel grain including: a. a oxidizer storage tank containing a high density, atmospheric pressure storable oxidizer containing >10% water and an AN, HAN, or HAP ionic liquid and having a density of at least about 1.4 g/cc; b. a fuel grain fabricated from a polymeric material with a density not including metal additions of at least 1.25 g/cc, and a mass regression rate at least about 25% greater than HTPB, and typically at least about 50% greater than HTPB; c. an injector sized to control atomization and flowrate at a design pressure; d. a pressurization system wherein said motor exhibits stable burning and near constant ISP within the O/F range of at least about 1.5-3, and typically within the O/F range of about 1-4, with an ISP of at least 260 seconds.

2. The motor as defined in claim 1, wherein a high density polymeric fuel is used, said fuel contains oxygen and has a density greater than about 1.25, and typically at least about 1.35 g/cc.

3. The motor as defined in claim 2, wherein said fuel contains about 10-50% metal fuel additions, and typically about 25-35% metal fuel additions.

4. The motor as defined in claim 3, wherein said metal fuel additions includes one or more metals selected from the group consisting of Al, AlMg, Mg, TiH.sub.2, AlMgB14, CaB6, AlB2, MgB2, SiB6, or B, where the metal fuel may be coated with a fluoropolymer such as PVDF, THV, PTFE, ETFE, VDF, or other flourpolymer, at 1-5% by weight of the metal.

5. The motor as defined in claim 2, wherein said fuel includes one or more compounds selected from the group consisting of polyacytal, sorbitol, PETA, polysaccharide, high molecular weight carboxylic acid, and other high density oxygen-containing polymer.

6. The motor as defined in claim 4, wherein said fuel includes one or more compounds selected from the group consisting of polyacytal, sorbitol, PETA, polysaccharide, high molecular weight carboxylic acid, and other high density oxygen-containing polymer.

7. The motor as defined in claim 1, where the fuel grain contains an accelerater or modifier at 0.05-5%, and preferably 0.05-1%, said accelerate or modifier includes one or more compounds selected from the group consisting of PETA (pentaerythrital), iron acetylacetonate, zero valent iron, iron oxide, oxalic or other carboxylic acid, iron sulfide, ammonium dichromate, potassium dichromate, ferrocene, lewis acid, and other decomposition accelerant.

8. The motor as defined in claim 6, where the fuel grain contains an accelerater or modifier at 0.05-5%, and preferably 0.05-1%, said accelerate or modifier includes one or more compounds selected from the group consisting of PETA (pentaerythrital), iron acetylacetonate, zero valent iron, iron oxide, oxalic or other carboxylic acid, iron sulfide, ammonium dichromate, potassium dichromate, ferrocene, lewis acid, and other decomposition accelerant.

9. The motor as defined in claim 1 wherein the fuel grain contains between 1 and 10%, and preferably 1-5% of an energetic compound or compounds.

10. The motor as defined in claim 8, wherein the fuel grain contains between 1 and 10%, and preferably 1-5% of an energetic compound or compounds.

11. The motor as defined in claim 9, wherein the energetic compound is selected from GAP, polyGlyN, or polyNIMMO, PETN, RDX, HMX, CL-20, FOX-7, furazan-based molecules such as diaminoazoxyfurazan, nitrocellulose, BAMO, and other nitramines.

12. The motor as defined in claim 10, wherein the energetic compound is selected from GAP, polyGlyN, or polyNIMMO, PETN, RDX, HMX, CL-20, FOX-7, furazan-based molecules such as diaminoazoxyfurazan, nitrocellulose, BAMO, and other nitramines.

13. The motor as defined in claim 1, wherein said oxidizer includes one or more compounds selected from the group consisting HNO3, HAN, HAP, HP, ADN, AN, and AP, including mixtures of AN-HAN-water, AN-HAP-water, HAP-AP-water, HAN-AN-HP-water, and HAN-ADN-AN-water containing less than 25%, and preferably 15% or less of water.

14. The motor as defined in claim 12, wherein said oxidizer includes one or more compounds selected from the group consisting HNO3, HAN, HAP, HP, ADN, AN, and AP, including mixtures of AN-HAN-water, AN-HAP-water, HAP-AP-water, HAN-AN-HP-water, and HAN-ADN-AN-water containing less than 25%, and preferably 15% or less of water.

15. The motor as defined in claim 12, wherein said mixture includes a decomposition control agent.

16. The motor as defined in claim 13, wherein said mixture includes a decomposition control agent.

17. The motor as defined in claim 15, wherein said decomposition control agent is formulated to reduce ignition temperature, said decomposition control agent is a hydrocarbon soluble in said AN-HAN solution.

18. The motor as defined in claim 16, wherein said decomposition control agent is formulated to reduce ignition temperature, said decomposition control agent is a hydrocarbon soluble in said AN-HAN solution.

19. The motor as defined in claim 15, wherein said decomposition control agent includes buffers and/or sequestering agents to increase long-term stability.

20. The motor as defined in claim 18, wherein said decomposition control agent includes buffers and/or sequestering agents to increase long-term stability.

21. The motor as defined in claim 19, wherein said buffering agent includes one or more compounds selected from the group consisting of ammonium or organic amine dihydrogen phosphates such as NH.sub.4 H.sub.2 PO.sub.4, or diammonium or di-organic amine monohydrogen phosphates such as (NH.sub.4).sub.2 HPO.sub.4.

22. The motor as defined in claim 20, wherein said buffering agent includes one or more compounds selected from the group consisting of ammonium or organic amine dihydrogen phosphates such as NH.sub.4 H.sub.2 PO.sub.4, or diammonium or di-organic amine monohydrogen phosphates such as (NH.sub.4).sub.2 HPO.sub.4.

23. The motor as defined in claim 19, wherein said sequestering agent includes one or more compounds selected from the group consisting of phenanthroline or dipyridyl and their ring-substituted derivatives.

24. The motor as defined in claim 22, wherein said sequestering agent includes one or more compounds selected from the group consisting of phenanthroline or dipyridyl and their ring-substituted derivatives.

25. The motor as defined in claim 1, wherein said oxidizer is gelled.

26. The motor as defined in claim 24, wherein said oxidizer is gelled.

27. The motor as defined in claim 25, wherein said gel includes PVA.

28. The motor as defined in claim 26, wherein said gel includes PVA.

29. The motor as defined in claim 1, including a pressurization system, said pressurization system selected from the group consisting of an inert gas system, a self-pressurizing gas such as N.sub.2O, GO.sub.x, a mechanical diaphragm or other mechanical pressurization system, a gas or electrically operated turbopump, or a chemical pressurization system capable of supplying at least 500 psig, and preferably at least 1500 psig.

30. The motor as defined in claim 28, including a pressurization system, said pressurization system selected from the group consisting of an inert gas system, a self-pressurizing gas such as N.sub.2O, GO.sub.x, a mechanical diaphragm or other mechanical pressurization system, a gas or electrically operated turbopump, or a chemical pressurization system capable of supplying at least 500 psig, and preferably at least 1500 psig.

31. The motor as defined in claim 1, including a thermally-insulated precombustion chamber.

32. The motor as defined in claim 30, including a thermally-insulated precombustion chamber.

33. The motor as defined in claim 31, wherein said precombustion chamber includes an arrangement for heating/preheating.

34. The motor as defined in claim 32, wherein said precombustion chamber includes an arrangement for heating/preheating.

35. The motor as defined in claim 33, wherein, said an arrangement for heating/preheating includes resistance wires, foams, mesh, or wool.

36. The motor as defined in claim 34, wherein, said an arrangement for heating/preheating includes resistance wires, foams, mesh, or wool.

37. The motor as defined in claim 1, including a chemically augmented ignition system, said chemically augmented ignition system including one or more components selected from the group consisting of catalysts, magnesium ribbon, and flammable or near-pyrophoric powders such as Al, Mg, Ti, Zr, Na, NaBH.sub.4, LiBH.sub.4, NaB.sub.2H.sub.6, LiB.sub.2H.sub.6, FeS, TiH.sub.2, ZrH.sub.2, LiAlH.sub.4, NaAlH.sub.4, Fe powders or filings.

38. The motor as defined in claim 36, including a chemically augmented ignition system, said chemically augmented ignition system including one or more components selected from the group consisting of catalysts, magnesium ribbon, and flammable or near-pyrophoric powders such as Al, Mg, Ti, Zr, Na, NaBH.sub.4, LiBH.sub.4, NaB.sub.2H.sub.6, LiB.sub.2H.sub.6, FeS, TiH.sub.2, ZrH.sub.2, LiAlH.sub.4, NaAlH.sub.4, Fe powders or filings.

39. The motor as defined in claim 1 is operated at a pressure above about 200 psig for burning stability, and typically above about 350 psig for burning stability.

40. The motor as defined in claim 38 is operated at a pressure above about 200 psig for burning stability, and typically above about 350 psig for burning stability.

41. The motor as defined in claim 1 that includes a non-pyrotechnic ignitions system, selected from an electrical or optical ignition system.

42. The motor as defined in claim 40 that includes a non-pyrotechnic ignitions system, selected from an electrical or optical ignition system.

43. The motor as defined in claim 1 which includes an electrothermal system located upstream of the fuel grain.

44. The motor as defined in claim 42 which includes an electrothermal system located upstream of the fuel grain.

45. The motor as defined in claim 1, wherein said motor is configured and used for upper stage propulsion.

46. The motor as defined in claim 44, wherein said motor is configured and used for upper stage propulsion.

47. The motor as defined in claim 1, wherein said motor is configured and used for tactical missile applications.

48. The motor as defined in claim 46, wherein said motor is configured and used for tactical missile applications.

49. The motor as defined in claim 1, wherein said motor is configured and used for use as boost stage propulsion systems.

50. The motor as defined in claim 48, wherein said motor is configured and used for use as boost stage propulsion systems.

51. A high density hybrid rocket motor which includes: a. A room temperature, atmospheric pressure storable, generally recognized as safe oxidizer solution having a density greater than 1.4 g/cc and containing at least 8% water, such as OXSOL, PERSOL, ANNA, with and without ADN additions. b. A high density, high regression rate fuel with an oxygen-containing polymer density above 1.3 g/cc containing one or more compounds selected from the group consisting of sorbitol, PETA, POM, polysaccharide, carboxylic acid. c. A powdered metal fuel additive dispersed in the fuel that includes one or more components selected from the group consisting of aluminum and aluminum-magnesium alloy; and, wherein said oxidizer solution is atomized into a fuel grain at pressures exceeding about 200 psig, and typically exceeding about 300 psig to obtain stable combustion with an ISP above 260 seconds, and preferably above 280 seconds.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] FIG. 1 illustrates two graphs directed to mass regression rates in a single port injector LGCP (long grain center perforate) hybrid test motor.

[0043] FIG. 2 illustrates two graphs directed to theoretical performance CEA (Chemical Equilibrium with Applications) specific impulse calculations for POM, Sorbitol, and HTPB fuels.

[0044] FIG. 3 is a graph directed to Delta-V performance versus O/F ratio for various high density oxidizer/fuel hybrid systems compared to state of the art upper stage bipropellant engine performance.

[0045] FIG. 4 illustrates a HTHB-145 stage preliminary design for functional equivalent to PSRM-120 reference design.

[0046] FIG. 5 illustrates a PID (piping and instrumentation diagram) and 4 HRTM (High resolution Test Motor) as modified with close-coupled liquid oxidizer blowdown system.

[0047] FIG. 6 illustrates a POM data plot showing stable combustion region with OXSOL and an image of firing.

DETAILED DESCRIPTION OF NON-LIMITING EMBODIMENTS

[0048] The present invention is related to a high density hybrid rocket motor having improved volumetric performance, and higher regression rates allows for efficient packaging and larger motors to be used. In particular, there is provided a high density hybrid rocket motor which has a density-specific impulse similar to a solid rocket motor, and with good performance.

[0049] In one non-limiting configuration, the high density hybrid motor design uses inert gas pressurized OXSOL oxidizer, and electric ignition system, and a POM (Polyoxymethylene)/40% Al fuel grain. To meet PSRM-120 (Printed solid rocket motor) delta V requirements, nominal motor volumetric requirements are 18.6 liters (4.9 gallons) of OXSOL.

[0050] For a 16 diameter tank size, the tank needs to have a 5.7 length to accommodate the required volume. For packaging, a good design is a cylindrical tank with an internally domed head on the aft end, and an outward elliptical domed head on the top. The required volume can also be met by use of a 13 diameter spherical tank. The walls of such tanks can be at least 0.20 thick and optionally formed of magnesium or aluminum.

[0051] Slightly more than wall thickness may be required for a magnesium cylindrical case with elliptical ends for 1200 psig pressure rating (20% margin), equating to roughly 7 lbs. for the oxidizer tank, with 0.4 elliptical ends. Total inert weight for the system is estimated at 32 lbs. when using magnesium tanks and cases, an aluminum gas bottle for the He pressurizing gas, steel valves and injectors, a 5.5 carbon-phenolic nozzle and closure assembly, and graphite throat and post-combustion chamber. As can be appreciated, different materials and material thickness of one or more of the components may result in different weights.

[0052] The fuel grains can require 763 in.sup.3 of volume. Such volume can translate into four 4 grains 17.5 long. These fuel grains are essentially the same volume and size of the 4 HRTM motor (3.75 grain diameter) tested with results shown in FIGS. 5 and 6. For a 500 psi rating, the wall thickness of a magnesium case is generally at least 0.045, plus insulation.

[0053] With 3/64 phenolic insulation thickness (the grain acts as insulator as well), four 3.5 motors can fit in a 10.5 scribed circle. The spacing is actually dictated by the nozzle size-within a 16 envelope, allowing for four 5.5 nozzle diameters, matching the 6 baseline design. Total mass of the four motor cases plus insulation is about 3.81 bs fabricated from Mg alloy ( 1/16 wall) extrusions with phenolic insulators. Mass estimates for the carbon-phenolic closures and nozzle assemblies is about 1.4 lbs/grain (5.6 lbs total). A 5000 psig He pressurization tank can be sized to run the 24 open motor length, requiring a 5.5 diameter to result in full system volume (oxidizer tank) end point pressure of 1100 psig. The center space with the 5.5 nozzles can be nearly 7 diameter, thus plenty of space for packaging. The wall thickness for a 6 aluminum tank required for 5000 psig is about 0.4, with a pressurization tank weight of 9 lbs. with elliptical ends, including He gas content. Adding about 7 lbs. for tubing, igniter, injector plates, battery, pressurization valve and structural supports, total inert mass for the hybrid motor is about 32 lbs., matching the initial estimates based on PSRM baseline designs (38 lbs. inert motor mass plus 50 lbs. payload).

[0054] HDHB145 Stage Design (High Density Hybrid, 145 lbs Propellant).

[0055] Motor configuration: pressurized cylindrical oxidizer tank, four 3.5 diameter15 cylindrical grains with pressurization tank centered between grains.

[0056] Motor total mass: 183 lbs.

[0057] Total motor inert mass: 32 lbs.

[0058] Motor diameter: 16.

[0059] Motor length: 38.

[0060] Total thrust: 36,685 lbf-sec.

[0061] This design fits within the 1742 volume constraint for the notional Nanolauncher design. Alternative designs, including a toroidal tank are not suitable for main thrust motor, but would be most desirable for a 30 orbital insertion motor, which would have one grain and roughly a 2 gallon tank. For a 30 design, oxidizer and pressurization tanks arranged around a central motor grain represent the (first analysis) optimal design.

[0062] FIG. 6 illustrates the overall HDHB-145 stage design.

EXAMPLE 1

[0063] A POM/Al hybrid rocket motor grain was prepared. Polyacetal motor grains were prepared by twin screw compounding followed by single screw extrusion into 3 diameter rods that were cut to 12 lengths. Polyacetal Twin screw extrusion compounding was completed on a W&P ZSK-30 with a processing profile consisting of 191 C. inlet temperature, 192-197 C. mixing zone temperature, 200 C. exit die, 103-105 rpm screw rate, and 50-60 torque. Single screw extrusion was completed at Apexco-ppsi to produce a solid fuel grain of 3 diameter directly. Grains were then adhesively bonded into the phenolic insulator tubes. Extruded rods were cut to length and epoxy cured into 0.25 thick phenolic paper tubes. diameter holes were bored into the bonded fuel grains using an extended twist drill mounted on a centerstock on a lathe. The fuel grain was centered using a 4-jaw chuck and the ID was bored by drilling.

[0064] The fuel grains were fired in a ground (non flight weight motor with a 4 configuration, noted as the high resolution test motor, at Penn State University. The 4 HRTM motor was modified to allow for liquid oxidizer feed, and close-coupling of the liquid oxidizer in the system to minimize O.sub.2/OXSOL overlap. To ensure reliable ignition, ignition was carried out with gaseous oxygen which was switched to liquid OXSOL feed during the first half-second of the burn. The modifications included adding a storable non-volatile liquid oxidizer feed system with appropriate safety and purge features, and fabricating and installing a significantly lengthened motor pressure vessel on the Hybrid Rocket Test Motor (HRTM) to provide for an appropriate fuel grain length with pre- and post-combustion mixing regions. A Process and Instrumentation Diagram (P&ID) for the upgraded test setup is shown in FIG. 5. Gas manifolds and the control area were separated from the motor and stand by 12 reinforced concrete test cell walls. All operations are remotely sequenced and monitored from the control area. All critical pressures were recorded. The control program monitored chamber and injector pressures for under- or over-pressure conditions and automatically aborted the test to a predetermined safe shutdown mode if any of the abort criteria were met. A manual abort button was also available on-screen, and the valves and connections revert to a failsafe condition (purges on, oxidizer flow off) if system power fails totally. To maximize system responsiveness and minimize oxidizer waste (and hazard), the OXSOL run tank was mounted on the motor stand, behind a blast plate. This run tank was only pressurized (with helium) seconds before the test starts, and was immediately depressurized and vented upon test completion or abort condition triggering. The data acquisition (DAQ) system was implemented on hardware independent of the LabVIEW-driven control system so that any potential failure or unexpected configuration in the control system could be monitored; commanded valve operations and igniter signals were recorded as digital signals in addition to analog pressure transducer readings at 1 KHZ.

[0065] The motor illustrated in FIG. 5 was tested with a single 0.039 port (-flow) design was used, combined with the diameter initial fuel port. A series of motor firings were conducted over a range of pressures and oxidizer flow rations, using OXSOL as the oxidizer to validate motor performance and design calculations. At 350 psig, a full length, highly stable burn was achieved. FIG. 6 illustrates the pressure trace and valve operation for the 350 psig OXSOL-40% Al/POM burn. A full 8 second burn, with 5-6 seconds of stable OXSOL-POM combustion were achieved, and repeated at oxidizer/fuel rations ranging from 1-4. Efficiencies comparable to state of the art formulations in ground test were observed, validating the design calculations and motor performance estimates.

[0066] It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made in the constructions set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. The invention has been described with reference to preferred and alternate embodiments. Modifications and alterations will become apparent to those skilled in the art upon reading and understanding the detailed discussion of the invention provided herein. This invention is intended to include all such modifications and alterations insofar as they come within the scope of the present invention. It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention, which, as a matter of language, might be said to fall there between. The invention has been described with reference to the preferred embodiments. These and other modifications of the preferred embodiments as well as other embodiments of the invention will be obvious from the disclosure herein, whereby the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims.