WO2015057268A1

WO2015057268A1 - Non-hazardous coated rocket starter

Info

Publication number: WO2015057268A1
Application number: PCT/US2014/038422
Authority: WO
Inventors: Edwin Brown; Peter Ian VON MALTITZ; Kathleen Denise LIMBERIS
Original assignee: Estes-Cox Corp.
Priority date: 2013-05-16
Filing date: 2014-05-16
Publication date: 2015-04-23

Abstract

A starter for a solid fuel model rocket engine comprising: a pair of low resistance lead wires; a high resistance bridge wire attached to the low resistance lead wires at attachment points; a coating entirely surrounding the bridge wire and the attachment points designed to heat a solid rocket fuel to its combustion point, wherein the coating comprises only non-hazardous materials. Various embodiments incorporate more specific compositions of the coating, including compliance with various regulations related to non-hazardous materials, lead-free materials, and phthalate-free materials.

Description

NON-HAZARDOUS COATED ROCKET STARTER

BACKGROUND

[0001] Model rocket engines typically contain a solid propellant that must be ignited. The simplest form of a starter is a fuse containing gunpowder. However, the fuse gives little control over the precise ignition time, and can be unreliable.

[0002] A more advanced form of a starter is one that can be triggered using a switch. A power source, such as a battery, is used to deliver energy to a part of the starter that is proximate the solid rocket propellant. This proximate part heats to a temperature sufficient to cause the propellant to burn. In this design, the part of the starter proximate the propellant is typically a high-resistance wire made of a material such as nichrome, which is welded to lower resistance wires that are run out to the switch and battery. Although this simple design is sufficient to ignite the engine propellant, significant care must be employed when using it to ensure that the high-resistance portion is in contact with the engine propellant, while at the same time not using too much force so that this portion of the wire is damaged, the welds come undone, or electrical shorting of the lower resistance wires occurs.

[0003] In an advancement over this design, a coating has been applied to cover the high- resistance portion as well as the welds and end portions of the low-resistance wires. This coating provides additional strength to the high-resistance portion of the starter and the associated welds, and prevents accidental electrical shorting. With this coating, however, the heat from the high-resistance wire is at a further distance from the engine propellant.

[0004] Therefore, historically, it was thought that such coatings would need to contain pyrotechnic components themselves so that the coating would in essence act as an extension of the propellant and thereby ensure that the engine propellant would ignite, even though the engine propellant was not in direct contact with the high-resistance wire. Designs for such coatings thus contain materials that could be classified as explosives or hazardous (pyrotechnic materials). In one formulation, the coating contains potassium nitrate (an oxidizer) combined with carbon and cornstarch, and then mixed in a binder of hide glue. However, it is not always desirable to utilize components designated as explosives or hazardous. SUMMARY

[0005] It was inventively recognized that the pyrotechnic component of the coating is not essential to the coating, provided that the coating has the following desirable

properties/characteristics as defined in the numbered paragraphs below; as used herein, the term "starter" will be used to define a device having a coating described below— the desirable characteristics of the coating are:

1) Sufficient mechanical force strength to protect (by remaining intact) the high- resistance portion and the associated welds during transport and handling. A compressive force as low as 40 gf (grams-force) is sufficient to cause damage. Ideally the compressive force should bend the low-resistance portion before damaging the high-resistance portion. This protection is achievable with the described coating where the coating protects the high-resistance portion to compressive forces less than or equal to 300 gf. As defined herein, sufficient mechanical force strength means remaining intact when a force of 300 gf is applied.

2) Sufficient mechanical stability strength to allow the starter high-resistance portion to remain mechanically stable when electric current is passed through it. The coating provides this property of stability when a current at 150% of that required for adequate initiating combustion is applied for 150% of the time required to adequately initiate combustion. These requirements are met when 2 amperes (A) of current is passed through the starter bridge wire of approximately the dimensions defined below for a maximum period of 1 second. As defined herein, sufficient mechanical stability strength means remaining mechanically stable when a current of 3 A is passed through a starter bridge wire as specified herein for a period of 1.5 seconds.

3) Minimal heat insulation and absorption to allow the most efficient transfer of heat from the high-resistance portion to the rocket propellant. This requirement is met when the outer surface of the high-resistance portion plus coating reaches a temperature greater than 450 degrees Celsius fast enough to cause the rocket propellant to begin combustion in a time of less than or equal to one second.

Although such a material will typically burn or melt during this process, such burning or melting is of no consequence for the coating to work effectively. As defined herein, minimal heat insulation and absorption means allowing an outer surface of the coating having dimensions as described herein, when heated with a bridge wire as described herein by passing 2 A of current through it, creates an outer surface temperature of at least 450 degrees Celsius within one second.

[0006] Accordingly, described herein is a starter for a solid fuel model rocket engine comprising: a pair of low resistance lead wires; a high resistance bridge wire attached to the low resistance lead wires at attachment points; a coating entirely surrounding the bridge wire and the attachment points designed to heat a solid rocket fuel to its combustion point, wherein the coating comprises only non-hazardous materials.

DESCRIPTION OF THE DRAWINGS

[0007] The drawings illustrate various embodiments of the invention, in which:

Figure 1 is a pictorial side view diagram of an embodiment of the inventive starter;

Figure 2 is a pictorial perspective view illustration showing the starter of Figure 1 and a rocket engine;

Figure 3 is a pictorial perspective cut-away view illustrating the insertion of the starter into the engine; and

Figure 4 is a pictorial perspective view of the engine with the starter inserted and a plug added.

DETAILED DESCRIPTION

[0008] Figure 1 illustrates a starter 10 according to an embodiment of the invention. A thin bridge wire 12 having a high resistance (e.g., made of nichrome or similar alloy) is joined with low resistance lead wires 14 and welded together at a weld location 16. The coating 18 is provided to cover the bridge wire 12, the end portions of the lead wires 14, and the welds 16. A piece of tape 20 may also be provided to lessen independent movement of a portion of the lead wires 14 that might result in shorts and stress at a part where the lead wires 14 meet the coating 18.

[0009] Figure 2 illustrates a rocket engine-starter combination 5, where the starter 10 is shown immediately before insertion into the rocket engine 30. The engine 30 has an end piece 32 with a hole 34 in it that accommodates the tip of the starter 10. As can be seen in Figure 3, when the starter 10 is inserted into the hole 34 of the rocket engine 30, a properly placed starter 10 will allow the coating 18 to contact the solid fuel 36 by entering a hole 38 in the fuel 36. Figure 4 illustrates use of a plug 40 that can be placed in the hole 34 to keep the starter 10 in place.

[0010] When the starter 10 is activated, a current is run through the lead wires and the bridge wire 12 such that the bridge wire 12 heats to a temperature that causes the coating 18 to heat to a high enough temperature to begin combustion of the rocket propellant 36, i.e., the heated coating 18 causes the solid fuel 36 to combust and allows the rocket to launch.

[0011] As noted above, the inventive coating 18 is made of a non-pyrotechnic / non- hazardous material, in order to provide a safe, yet reliable, mechanism for causing the solid fuel 36 to combust. As such, the coating 18 must be made of a material that is not considered to be explosive or hazardous.

[0012] In an embodiment, the coating 18 is approximately 4.78 mm in length and 2.29 mm in width (but can range from 4 to 5.5 mm in length and 1.5 to 3 mm in width) to accommodate a lead wire having a diameter of approximately 0.40 mm (but can range from 0.25 mm to 0.6 mm in diameter), and a bridge wire having a diameter of approximately 0.16 mm (but can range from approximately 0.07 mm to 0.25 mm). An exemplary mass of the coating is approximately 10 to 20 mg. The chemical composition, in an embodiment is approximately 83% hide glue and approximately 17% corn starch by weight. Such a composition provides a sturdy and robust coating 18 that provides the necessary strength and protection to the end portion of the starter 10, while at the same time comprising no

pyrotechnic/explosive/hazardous material components. In a related embodiment, the ratios of these components can be adjusted.

[0013] Although this formulation provides an advantageous composition, it is one of many possible compositions contemplated for the coating. It is not essential to include the corn starch, although the use of corn starch can improve the mechanical properties of the starter coating. However, a formulation that is 100% hide glue could be utilized. As defined herein, hide glue means a composition comprised of a protein generally derived from collagen, a principal protein constituent of animal hides. An embodiment of the hide glue is a typical formulation of: carbon 51-52%, hydrogen 6-7%, oxygen 24-25%), and nitrogen 18-19%) , and having a molecular weight ranging from approximately 20,000 to 250,000.

[0014] Various embodiments of the invention vary the formulation further to include chemical compositions that are compatible with the three characteristics identified in the Summary section, but are not explosive or hazardous. The coating formulation is not limited to the hide glue and corn starch ingredients described. A number of other binders (organic or nonorganic) could be used in place of the hide glue with or without the addition of corn starch. Other thickeners or fillers (organic or non-organic) could be used in place of the corn starch. In one embodiment, the coating formulation includes the addition of additives that improve its thermal conductivity, such as the addition of (but not limited to) metal powders.

[0015] Applicant, acting as their own lexicographer, herein defines the phrase "non- hazardous material" as being a material that, when the coating is in its final manufactured form, meets the three characteristics defined in the Summary Section, further exclude materials identified in the Hazardous Materials statutes 49 U.S.C. § 5101 et seq., and Hazardous Materials Regulations, specifically those contained within the Department of Transportation (DOT) Nine Classes of Hazardous Materials, particularly including Class 1 : Explosives addressed under 49 CFR 173.50, Class 2, compressed gasses; Class 3, flammable and combustible liquids; Class 4: Flammable Solids addressed under 49 CFR 173.124, Class 5: Oxidizers and Organic Peroxides addressed under 49 CFR 173.127 and 173.128, Class 6, Division 6.1 : Poisonous/Toxic Materials addressed under 49 CFR 173.132, Class 7:

Radioactive Materials, Class 8: Corrosive Materials addressed under 49 CFR 173.136, and Class 9: Miscellaneous Hazardous Materials addressed under 49 CFR 173.140, in effect at the time of this application being filed. This statute and the cited regulations effective at the time of filing are herein incorporated by reference.

[0016] In an embodiment, it is further desirable, but not essential, to adhere to the

Consumer Product Safety Improvement Act, enacted August 2008, sections 101 and 108, herein incorporated by reference. Section 101 defines upper limits of lead that can be in children's products. As defined herein, "lead-free" means containing lead at levels identified as acceptable according to the Consumer Product Safety Improvement Act, Section 101. Section 108 defines upper limits on the amounts of phthalates (certain chemical plasticizers) that can be in children's products. As defined herein, "phthalate-free" means containing phthalates at levels identified as acceptable according to the Consumer Product Safety Improvement Act, Section 108.

[0017] Phthalate levels are additionally regulated and defined according to the State of California Environmental Protection Agency, Office of Environmental Health Hazard

Assessment, Safe Drinking Water and Toxic Enforcement Action of 1986 Listing of

Chemicals Known to the State to Cause Cancer or Reproductive Toxicity (July 20, 2012). The term "phthalate-free" further means containing phthalates at levels identified as acceptable according to this document.

[0018] All references, including publications, laws, regulations, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0019] For the purposes of promoting an understanding of the principles of the invention, reference has been made to the preferred embodiments illustrated in the drawings, and specific language has been used to describe these embodiments. However, no limitation of the scope of the invention is intended by this specific language, and the invention should be construed to encompass all embodiments that would normally occur to one of ordinary skill in the art.

[0020] The present invention may be described in terms of functional block components and various processing steps. Such functional blocks may be realized by any number of components configured to perform the specified functions. The particular implementations shown and described herein are illustrative examples of the invention and are not intended to otherwise limit the scope of the invention in any way. For the sake of brevity, conventional electronics, control systems, software development and other functional aspects of the systems (and components of the individual operating components of the systems) may not be described in detail. Furthermore, the connecting lines, or connectors shown in the various figures presented are intended to represent exemplary functional relationships and/or physical or logical couplings between the various elements. It should be noted that many alternative or additional functional relationships, physical connections or logical connections may be present in a practical device. Moreover, no item or component is essential to the practice of the invention unless the element is specifically described as "essential" or "critical". [0021] The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural. Furthermore, recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. Finally, the steps of all methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. Numerous modifications and adaptations will be readily apparent to those skilled in this art without departing from the spirit and scope of the present invention.

Claims

What is Claimed Is:

1. A starter for a solid fuel model rocket engine comprising: a pair of low resistance lead wires; a high resistance bridge wire attached to the low resistance lead wires at attachment points; a coating entirely surrounding the bridge wire and the attachment points designed to heat a solid rocket fuel to its combustion point, wherein the coating comprises only non-hazardous materials.

2. The starter according to claim 1, wherein the coating composition consists of a binder and a thickener.

3. The starter according to claim 2, wherein the binder is hide glue.

4. The starter of claim 3, wherein the thickener is corn starch.

5. The starter according to claim 4, wherein the coating composition consists of 83% hide glue and 17% corn starch.

6. The starter according to claim 2, wherein the thickener is corn starch.

7. The starter according to claim 2, wherein the binder comprises a metal powder.

8. The starter according to claim 1, wherein the coating composition consists of hide glue.

9. The starter according to claim 1, wherein the coating composition meets all of the following characteristics: sufficient mechanical force strength, sufficient mechanical stability strength, and minimal heat insulation and absorption.

10. The starter according to claim 1, wherein the coating dimensions measure approximately 4 to 5.5 mm in length and 1.5 to 3 mm in width).

11. The starter according to claim 1, wherein the lead wire diameter ranges from 0.25 mm to 0.6 mm, and the bridge wire diameter ranges from 0.07 mm to 0.25 mm.

12. The starter according to claim 1, wherein the coating is lead-free.

13. The starter according to claim 1, wherein the coating is phthalate-free.