Patent Grant
6837464
The inventions described herein were made in the performance of work under one or more of the following: Lockheed Martin Michoud Space Systems IRAD M-21D, IRAD M-24D, IRAD M-28D, Cooperative Agreement No. NCC8-115 dated 1 Jul. 1996, General Dynamics RD-1 No. 611-5588-453 and reported in GDSS-ERR-90-600.
Not applicable
1. Field of the Invention
The present invention relates to tanks for liquid oxygen. More particularly, the present invention relates to composite tanks for liquid oxygen.
2. General Background of the Invention
The following U.S. Patents are incorporated herein by reference: U.S. Pat. No. 5,056,367; 5,251,487; 5,380,768; 5,403,537; 5,419,139; and all references cited in those patents.
The following international applications published under the PCT are incorporated herein by reference: International Publication Nos. WO 97/18081 and WO 97/28401 and all references cited in those publications.
A fiber-reinforced composite is defined as a material consisting of fibers of high strength and modulus embedded in or bonded to a matrix with distinct interfaces or boundaries between them. In this form, both fibers and matrix retain their physical and chemical identities, yet they produce a combination of properties that cannot be produced by either constituent alone. In general, fibers are the principal load carrying members, while the surrounding matrix keeps them in desired location and orientation, transfers loads between fibers, and protects the fibers. The matrix material may be a polymer, a metal, or a ceramic. This disclosure focuses on polymer matrix composites.
The fibers can be made from a variety of materials. These materials include glass, graphite or carbon, polymers, boron, ceramics, or metals. Glass fibers include E-glass (electrical) and S-glass (structural) types. Carbon fibers include those made from different precursors, such as polyacrylonitrile (PAN) or pitch. Polymer fibers include, but are not limited to, aramid (Kevlar®), polyethylene (Spectra®), or PBO (Zylon®). Ceramic fibers may include silicon carbide (SiC) or aluminum oxide (Al2O3).
For cryogenic tanks, the preferred matrix material is a polymer. The preferred fiber is carbon fiber, more preferably PAN-based fibers, more preferably high strength (over 500 ksi) and high modulus (over 30 Msi) fibers. The most preferred fibers are ultra high modulus fibers (over 60 Msi), specifically M55J fiber by Toray.
The development of polymer matrix composite liquid oxygen tanks is a critical step in creating the next generation of launch vehicles. Future reusable launch vehicles need to minimize the gross liftoff weight (GLOW) by reducing the dry mass fraction. The (dry) mass fraction is the weight of the launch vehicle without fuel divided by the weight of the vehicle with fuel.
The required mass fraction is possible due to the reduction of weight that composite materials can provide. Traditional oxygen tanks are usually made from metals. The space shuttle external tank (ET) has historically been made from 2219 aluminum and more recently 2195 aluminum/lithium alloy.
In addition to meeting the required mass fraction, a liquid oxygen tank must be compatible with oxygen. The ASTM definition for oxygen compatibility is the “ability of a substance to coexist with both oxygen and a potential source(s) of ignition within the acceptable risk parameter of the user.” It is imperative that materials are selected that will resist any type of detrimental, combustible reaction when exposed to usage environments. Typically, non-metallic materials are not used in these applications because most are easily ignited in the presence of oxygen. However, there are some polymeric materials with inert chemistries that may be used for this application and resist ignition. These chemistries were evaluated by fabricating coupons and testing them with various ignition mechanisms in the presence of liquid and gaseous oxygen. The testing performed reflected situations in launch vehicles that could be potential sources of ignition in composite. These tests included pressurized mechanical impact, particle impact, puncture, puncture of damaged, oxygen-soaked samples, electrostatic discharge, friction, and pyrotechnic shock.
Applications include liquid oxygen for future launch vehicles, such as the Lockheed Martin Reusable Launch Vehicle (RLV). They could also potentially be used in other aerospace applications, including but not limited to, RFP (rocket fuel propellant) tanks and crew vehicle cabins. Other industries that may be interested in composite oxygen tanks include the air handling and medical industries. The ability to resist ignition may also be useful in chemical storage tanks and NGV (natural gas vehicle) tanks.
The apparatus of the present invention solves the problems confionted in the art in a simple and straightforward manner. What is provided are composite tanks for liquid oxygen.
The composite tanks can be made in accordance with any of the methods disclosed in any reference incorporated herein by reference. The invention could be made, for example, using the method of U.S. Pat. No. 5,403,537.
The interior of the tanks disclosed herein typically have a volume of at least 1 liter, more often at least one gallon, and usually have a volume sufficient to allow their use to contain liquid oxygen for typical aerospace applications.
A mechanical impact of at least 10+ft-lbs at around −300 degrees F. (at around −350 degrees F. when densified oxygen (slush oxygen) is contained in the lank) is preferred, but is not a requirement. Historically materials have been required to pass the Lox mechanical impact test at 72 ft-lbs or otherwise be shown to be safe for use in application. Lox compatible composite materials have demonstrated the ability to resist combustion when subjected to any potential ignition source. For a composite tank, realistic potential ignition sources were determined to include, but are not limited to mechanisms such as pyrotechnic shock, friction, puncture, electrostatic discharge, and particle impact. These tests are taken to extreme levels. For example, in the puncture test, a sharpened serrated spike pierced a composite material while submerged in Lox without igniting the composite. This same puncture test has ignited Titanium, a material that is not oxygen compatible, and does not ignite aluminum. The pyrotechnic shock test was also an extreme test in that composites were placed in Lox and subjected to shock loads equivalent to existing metallic Lox tanks such as that on the External Tank. The friction test was extreme in that the composites were abraded to dust with a drill bit in pure oxygen without ignition. In the electrostatic discharge test, composites were subjected to energies that could far exceed any instrumentation or static build up; specifically, these composites do not ignite when subjected to 112.5 Joules from 5000 Volts.
The apparatus of the present invention includes composite tanks for liquid oxygen. The unique, nontraditional concept explored in one embodiment herein is to use fiber-reinforced PEAR composites to create liquid oxygen tanks. A PEAR material is one that is characterized by multiple ether and amide groups or linkages. An amide group is an organic group of atoms that is derived from a carboxylic acid and an amine. Ether is defined as any of a class of organic compounds structurally related to water in which hydrogen atoms have been replaced by organic groups. See
Generally, there are two types of PEAR resins: hot melt and solution.
Several types of resins and composites have been subjected to an extensive battery of tests for their sensitivity to reaction in the presence of oxygen. Historically, the approach was to test the material in the standard mechanical impact test in liquid oxygen (LOX). If the material had an impact threshold of 72 foot-pounds, it was acceptable for use in oxygen environments, such as launch vehicle LOX tanks. If the material's threshold was less than 72 foot-pounds, it typically was not used. Due to limitations in the testing as well as differences in the material structures between metals and composites, standard high strength composite materials have not been able to pass at this level at typical RLV tank wall thicknesses. The approach taken here, which was developed in conjunction with NASA, was to use the standard mechanical impact test to rank composites with respect to each other. Furthermore, an evaluation of the compatibility of composites in oxygen environments would only be determined after testing composite materials with respect to specific ignition mechanisms while in the presence of oxygen. The ignition mechanisms tested included pressurized mechanical impact, particle impact, puncture, puncture of damaged, oxygen-soaked samples, electrostatic discharge, friction, and pyrotechnic shock. If the material could withstand ignition in these environments, it could possibly be considered oxygen compatible.
Several PEAR materials are undergoing evaluation in the standard mechanical impact test. It is expected to do well in liquid oxygen testing due to its high flammability resistance. See
Another critical parameter for a composite tank is the ability to withstand repeated temperature changes (thermal cycles) without microcracking. One factor that contributes to microcrack resistance is toughness. PEAR resin is tougher than most standard epoxies. See FIG. 5. One effect of thermal cycling is a loss of mechanical properties.
The composite feedline of the present invention preferably has an inner diameter of around 1″ to 36″.
As used herein, “form of fiber” means unidirectional tape, slit tape, tow, fabric, woven fabric, chopped fiber, or felt.
For a further understanding of the nature, objects, and advantages of the present invention, reference should be had to the following detailed description, read in conjunction with the drawings, wherein time is in seconds and mechanical impact is in foot-pounds:
A spherical tank 24 is simply a sphere as shown in FIG. 10. Tank 24 can have a diameter of between about 1-150 feet.
An ogived tank 25 is a tank with an ogive shape along its sides. The sides can measure between about 1 and 150 feet wide or about 3 and 150 feet high. An example of an ogive tank 25 is the external Tank LO2 tank.
Any of the tanks of
A composite LO2 may be part of a single stage to orbit vehicle or a multiple stage to orbit vehicle where a multiple stage to orbit vehicle is composed of at least 2 stages.
A cylindrical tank is one that has a basic body as a cylinder 11 as shown in
In
In
A conformal tank 30 is any tank which aims to conform or shape itself to the vehicle inner mold line. Therefore, the shape of a conformal tank 30 will depend upon the vehicle body shape.
A PEAR tank can be fabricated using either of the uncured composite systems, any appropriate placement method, and any curing process. A listing of each of these systems, placement methods, and curing methods is found below. The best system to use depends on a variety of factors including, but not limited to, tank size and shape, composite material used, and available resources. Therefore, a decision on the best fabrication process must be made on a case-related basis.
Uncured Composite Systems:
A prepreg consists of reinforcement, such as graphite, glass, or Kevlar®, which is impregnated with a resin. A wet resin system is one where liquid resin is placed on the reinforcement at the time of manufacture.
Placement Methods for Prepreg Systems:
Placement Methods for Wet systems:
Fiber placement is an automated process where a robotic arm with a dispensing head is used to place several pieces of prepreg tow or slit tape, typically approximately 0.125 inches wide by 0.0055 inches thick, onto a mandrel in a desired orientation. Tape placement is a similar automated process, but the placement head is attached to a gantry rather than a robotic arm, and it places prepreg tape, typically 12 or 14 inches wide, onto the tool or mandrel. Filament winding is a process in which continuous prepreg tow or continuous fiber with wet resin is wound onto a rotating mandrel in a prescribed way. Hand lay-up is when prepreg, usually tape or fabric, or dry material and wet resin is manually applied to a tool or mandrel. Resin infusion or resin transfer molding is where resin is injected or otherwise forced into a dry reinforcement fabric or preform.
Curing Processes:
Curing of a composite material is the application of energy (heat or radiation) and possibly pressure to cause a chemical reaction and form a compact, solid part. The cure method may be any of the following: autoclave (elevated temperature and pressure), vacuum-bag oven cure (elevated temperature and vacuum pressure), oven cure (elevated temperature, ambient pressure), radiation cure (typically ambient temperature and pressure with radiation, such as electron beams or x-ray radiation), or in-situ curing in which the material is cured as it is placed (with for example, heat and mechanical pressure).
The foregoing detailed description is a description of Embodiment 7. Please see the patent applications incorporated herein by reference (and particularly the documents attached to the U.S. Provisional Patent Applications) for a detailed description of the other embodiments of the present invention.
One could combine features of the different embodiments to create a Lox compatible tank or feedline; e.g. one could line or coat the hybrid tank or feedline of embodiment 3.
The following is a list of parts and materials suitable for use in the present invention:
The following list describes the parts shown in FIG. 7:
All measurements disclosed herein are at standard temperature and pressure, at sea level on Earth, unless indicated otherwise. All materials used or intended to be used in a human being are biocompatible, unless indicated otherwise.
The foregoing embodiments are presented by way of example only; the scope of the present invention is to be limited only by the following claims.
This is a continuation of U.S. patent application Ser. No. 09/309,780 filed May 11, 1999, now U.S. Pat. No. 6,494,405 incorporated herein by reference. U.S. Provisional Patent Application Ser. Nos. 60/084,986; 60/084,987; 60/084,988; 60/084,989; 60/084,990; 60/084,991; 60/084,992; all filed 11 May 1998, are incorporated herein by reference; priority of these applications is hereby claimed. Also incorporated herein by reference are all U.S. patent applications filed on 11 May 1999 by the present inventors, namely U.S. patent application Ser. Nos. 09/309,780, 09/309,/781 (now U.S. Pat. No. 6,334,589), 09/309,804 (now U.S. Pat. No. 6,491,259), 09/309,805 (now U.S. Pat. No. 6,375,125), 09/309,806 (now abandoned), U.S. Pat. No. 09/309,807 (now abandoned), and U.S. Pat. No. 09/309,808 (now abandoned). All patents mentioned herein are incorporated herein by reference.
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| Number | Date | Country | |
|---|---|---|---|
| 60084986 | May 1998 | US | |
| 60084987 | May 1998 | US | |
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| Number | Date | Country | |
|---|---|---|---|
| Parent | 09309780 | May 1999 | US |
| Child | 10316131 | US |
