Disposal Of Surplus Injectant

Injection system design shall provide for disposal of surplus injectant to reduce flight weight and to obtain additional thrust. The injectant flow rate should be measured and integrated over time, so that at any instant of flight time the total amount of liquid actually used will be known. A computer or control device should continuously compare the amount of liquid used with the maximum that could be used up to that time without jeopardizing the completion of the mission. Flight control...

Pressurization System

High-pressure gas required to pressurize the fluid is provided either by a tank of compressed gas such as nitrogen or helium or by a solid-propellant gas generator (table XII). In some systems, the same gas generator is used as a source of gas for roll-control jets. The compressed gas system, if independent of the liquid tank, consists of a metal gas tank or bottle of any convenient shape, a squib valve, and a pressure regulator valve. The initial pressure of the gas is from two to seven times...

Amount Of Pressurization Gas Required

The liquid injectant in the system is kept under high pressures by gas that acts on the liquid in the tank either through a bladder (fig. 23) or piston or directly (fig. 27). The supply of compressed gas is made large enough so that when the liquid is expelled from the tank at the largest expected flowrate, its displaced volume is filled by fresh gas at a flowrate and pressure sufficient to ensure that the system pressure does not fall below its required level. The amount of gas that must be...

Injector Location And Discharge Angle

The injector is positioned on the nozzle wall (fig. 23) at a location and a discharge angle that is optimum for the expected schedule of vectoring for a typical flight. The optimum location for injection is a compromise of two opposing tendencies that add to or subtract from the side force. If the injection point is as far upstream in the nozzle exit cone as possible, the nozzle wall area over which the pressures are augmented by injection is increased. However, as the injection point is moved...

System Optimization

To optimize an LITVC system for a particular design, the usual procedure is to compile weight, bulk, and performance data from known LITVC components and from selected designs provided by manufacturers. These data then are generalized in empirical equations or curves. Schematic designs representing the design alternates (e.g., type of fluid, number of injectors, and injection location) then are prepared to serve as a basis for optimization calculations. These alternates are evaluated for...

Foreword

NASA experience has indicated a need for uniform criteria for the design of space vehicles. Accordingly, criteria are being developed in the following areas of technology Guidance and Control Chemical Propulsion Individual components of this work will be issued as separate monographs as soon as they are completed. This document, part of the series on Chemical Propulsion, is one such monograph. A list of all monographs issued prior to this one can be found on the final pages of this document....

Adaptation Of The Motor For Litvc

The motor design shall provide injector mounts and ports and external brackets for system support. The nozzle design should make provision for holes and mounts for the injectors. The metal orifice ends of the injectors should be recessed sufficiently inside the injection port (fig. 29) that they will not be damaged by heat flux. The heat flux at the inside end of the injection port should be estimated (refs. 134 and 135). The port hole should be made conical to fit the shape of the liquid jet...

Configuration

Thrust Vectoring For Model Rockets

The flexible joint consists of rings of an elastomeric material alternating with rings of metallic or composite material. These rings are usually spherical sections with a common center of radius referred to as the geometric pivot point. A joint wherein the rings were identically shaped conical sections has been designed and successfully tested (ref. 22). This design had the advantage of requiring a single set of tooling for all the rings rather than tooling for each ring as is necessary with...

Nozzle Misalignment

Thrust Vectoring For Model Rockets

Axial deflection causes a vectoring misalignment of the nozzle. When the actuator attachment points are a fixed distance apart, as in the case just after booster launch before the guidance system begins to control the vehicle, the nozzle is not free to translate aft as the motor pressure increases. An actuator length that holds the movable components aligned to the fixed components at zero motor pressure would be too short at operating pressure. The nozzle at pressure would vector as though the...

Storage Tank And Bladder

The liquid injectant tank shall preserve the liquid without degradation or loss during vehicle storage and provide positive expulsion of the liquid during motor operation. The shape of the tank should be selected to result in minimum weight. The required amount of injectant to be carried should be determined as described in section 3.2.1.5. It is recommended that, if the amount of liquid required is relatively small, one or more spherical tanks be used, because the sphere is the most efficient...

Inspection Processes

The inspection processes shall have the capability of detecting all critical defects. For the reinforcements, the following minimum inspection is recommended Spherical radius at sufficient positions to establish expected thicknesses of elastomer rings in a joint. Thickness at various positions. For the elastomer, the minimum inspection should cover thickness and porosity. Mold a joint without adhesive on the reinforcement surfaces, then disassemble it. Measure elastomer thicknesses and evaluate...

Internal Aerodynamic Torque

' The internal aerodynamic torque acting on a submerged nozzle is the result of unsymmetric flow between the propellant grain and the movable nozzle. Pressure variations that occur around the vectored nozzle cause side forces and a resultant torque. If the pivot point is forward of the nozzle throat, the aerodynamic torque is a restoring torque and hence is an increment to the actuation torque and needs to be calculated. If the pivot point is aft of the nozzle throat, the aerodynamic torque is...

Glossary

Symbol Definition Appears In A reinforcement material constant affecting eq. (3) value of elastomer shear modulus with superimposed pressure C conversion factor, 144 in.2 ft2 eq. (13) d distance from point of liquid injection to fig. 43 dQ diameter of the discharge orifice of the figs. 39 and 42 dt nozzle throat diameter, in. (cm) fig. 36 E hoop modulus of elasticity of reinforce- fig. 19 Fa axial component of the rocket motor thrust, figs. 35, 36, 37, Fs side force due to liquid injectant,...

Flexible Joint

The joint fabrication process shall be consistent with the needs and characteristics The molding process selected must depend primarily upon the dimensions of the joint, the number of elastomer layers, and the thickness of the elastomer layers and reinforcements rather than on the scope of the joint program. Joints with thin elastomer layers (layers that cannot be fabricated by injection molding) should be fabricated by compression molding in order to improve the bond to the reinforcements....

Adhesive Bond System

For test joints with either steel or composite reinforcement and a natural-rubber formulation intended for operation between 65 F (291 K) and 85 F (303 K), fabricated by injection molding or compression molding, the adhesive system has consisted of Chemlok 205 primer and Chemlok 220 adhesive. The bond failed at low strength levels in steel test specimens even though the surfaces of the steel were carefully prepared. This problem was overcome by ensuring that the material lots were of sufficient...

Insulating Boot Torque

A flexible joint often is protected against hot motor gases by use of an insulating boot (fig. 7). Either this insulating boot is wrapped directly around the joint, or a dead air space separates the joint and the boot. The wrap-around boot adds significantly to the nozzle vectoring torque. For example, use of a wrap-around boot fabricated of silica-filled butadiene acrylonitrile rubber (GTR V-45) on a 13-in. (33 cm)-diameter joint increased the actuation torque from 1000 in.-lbf deg (113 m-N...

Staticfiring Program

The static-firing program shall demonstrate that the joint design fulfills the motor requirements and shall provide the data needed to design other components that Measurements should be made during the static firing program to determine nozzle misalignment requirements, friction characteristics, natural frequency, and damping coefficient of the nozzle, axial deflection, and vectoring capability. Sufficient data to develop a statistical variation should be obtained. Compare measured results and...

Thermal Protection

In most cases, the flexible joint is protected against exposure to warm or cold atmospheres by controlling the atmosphere surrounding the joint prior to firing. Most joint testing is conducted with the joint at temperatures from 65 F (291 K) to 85 F (302 K). Limited bench testing has been conducted on joints at conditions from -40 F (233 K) to 165 F (347 K) (ref. 85). The joint is protected from hot motor gases either by use of an insulating boot (fig. 7(a)), or by use of sacrificial ablative...

Reinforcements

Joints have been fabricated with steel reinforcements and with composite reinforcements. The composite reinforcements have been formed with S-glass filaments and epoxy resin (refs. 27, 28, and 29) and S-glass filaments and phenolic resin (refs. 24 and 25). The important properties in the selection of the reinforcement material are compressive yield stress, ultimate and yield tensile stress, modulus of elasticity, ease of fabrication, ease with which elastomers can be bonded to the material, and...

Amount Of Liquid Injectant Required

In the system optimization calculations, the amount of liquid required is the parameter that usually indicates the relative efficiency of each design concept considered. Not only is the amount of liquid the largest item of weight that must be carried, but it determines, through its equvalent volume, the size and weight of the tubing, injectors, and tankagfe. The latter is usually the heaviest item of inert weight. Thus, the system design concept that requires the smallest amount of injectant...

State Of The

The vehicle flight-control system must perform two functions fly the vehicle along a commanded trajectory, and maintain vehicle flight stability in the atmosphere. Vehicles without aerodynamic stabilizing fins normally are unstable, and those with fins may be only marginally stable. Disturbances that effect vehicle attitude and stability include atmospheric winds motor thrust misalignments due to fabrication tolerances and thrust-vector-control-system offsets such as those that occur with...

Elastomer Thickness

The stresses in the elastomer are caused by vectoring and motor pressure. The shear stress due to vectoring is approximately constant in the elastomer and depends on the total thickness of elastomer i.e., number of elastomer rings x thickness of each layer and not the thickness of each ring. The induced stress due to vectoring is dependent on the joint spring torque, decreasing as the joint spring torque is reduced. The shear stress due to vectoring is given by the expression ref. 23 rv shear...

Injection Pressures And Injection Orifices

The injection pressure, the orifice size, and the number, spacing, and grouping of the orifices shall maximize the side thrust efficiency. The most efficient pattern for injection is obtained from many circular orifices located in a circumferential line on the nozzle wall figs. 29 and 31 and refs. 109, 121, 124, and 125 . For greatest efficiency, these orifices should have omniaxis control rather than pitch-yaw control ref. 142 . Minimum spacing to avoid overlap losses should be 7 to 14 times...

Selection Of Injectant

The chief factors considered in the selection of the liquid injectant are its side specific impulse, density, storability, and toxicity. Prime candidates for the injectant are nitrogen tetroxide and an aqueous solution of strontium perchlorate other candidates are hydrazine, Freon 114-B2, and hydrogen peroxide. The basic properties and characteristics of major operational injectants are presented in table IX and discussed below. Side specific impulse. Side specific impulse is a measure of the...

Aging Protection

The joint elastomeric material shall not be subject to adverse effects of aging and oxidation during pre-fabrication and post-fabrication storage. Polymerization of uncured elastomer should be minimized by storing the elastomer under conditions that maintain the elastomer within specifications. These conditions must be determined early in a program by the following steps 1 Fabricate and test quadruple-lap shear specimens sec. 2.1.7.1 from new elastomer stock to establish initial elastomer...

Subscale Test Program

The subscale specimen test program shall provide values for the elastomer mechanical properties used in design. The important mechanical properties for the elastomer are the shear modulus, shear stress at failure, and the strength of the bond between the elastomer and the reinforcement material. QLS specimens should be tested at the strain rate and over the temperature range expected in the joint. The bond between the elastomer and reinforcement should be cohesive, and the QLS specimen should...

Design Optimization

The flexible joint design shall be based on the movable-nozzle envelope constraints and joint, motor, vehicle, and mission design parameters that result in either maximum performance or maximum cost effectiveness, the choice depending on specific needs and characteristics of the program. The basic motor and vehicle joint design parameters motor pressure, vector angle, actuation rate, actuation acceleration, flight inertia loads, envelope constraints, mass properties, environmental conditions...

Joint Adhesive System

The joint adhesive system may be formed during the molding process for joints fabricated by compression or injection molding, or it may be obtained by secondary bonding, as in the 260-in. 6.6 m motor joint ref. 22 . Rubber-to-metal adhesive bonds are sensitive to small process changes. In a flexible joint, high stresses are imposed on these bonds, and the bulk of the fabrication problems involve the adhesive system. To ensure increased reliability, the adhesive system is required to develop a...

Bench Test Program

Thrust Vectoring For Model Rockets

Bench tests of joint characteristics shall establish acceptance criteria for production joints and shall verify that the effective pivot point is compatible with the nozzle clearance envelope. A joint bench test program must be set up during the motor development program to establish axial deflection characteristics, vectoring characteristics, and joint pressure sealing. The test for compressive axial deflection should be conducted in a test fixture with an unloading piston fig. 21 so that the...

Friction Torque

Friction torque in a conventional movable nozzle arises from sliding surfaces such as bearings and O-rings. Since there are no sliding surfaces in a flexible-joint nozzle, coulomb friction theoretically does not exist. Elimination of the joint friction eliminates problems from three major sources 1 Friction varies significantly from unit to unit and cannot be predicted with accuracy. 2 Friction is the major source of steady-state error in the servo actuator system. 3 The change from static to...

Frequency Response

The nozzle shall not be subject to excitation at its natural frequency of vibration. The stiffnesses of all parts of the nozzle should be designed so that their natural frequencies are higher than the natural frequency of the hydraulic actuator system. If the nozzle natural frequency is almost equal to the natural frequency of the actuator system, coupling of the nozzle and the actuator system will occur and will produce instability. If the nozzle natural frequency is less than the natural...

Liquid Rocket Thrust Vector Control Methods

Most vehicles used for launching spacecraft require some guidance or steering to ensure that the required flight trajectory will be achieved. In addition, steering is needed to compensate for flight disturbances e.g., winds and for vehicle imperfections e.g., misalignment of thrust and center of gravity . To provide this steering, solid propellant rocket vehicles are equipped with a thrust vector control system. Both mechanical and aerodynamic techniques have been used to redirect the motor...

Contents

DESIGN CRITERIA and Recommended APPENDIX A - Conversion of U. S. Customary Units to SI Units 161 APPENDIX B- NASA Space Vehicle Design Criteria Monographs Issued to Date 185 SUBJECT STATE OF THE ART DESIGN CRITERIA SUBJECT STATE OF THE ART DESIGN CRITERIA Material Adhesive Bond Joint Thermal Mechanical General Design Definitions 2.1.4.1.1 46 Design Safety Flexible-Joint Structural Elastomer Reinforcement Advanced Joint Adhesive Flexible Subscale Test Bench Test...

Liquid Injection Thrust Vector Control

Liquid Thrust

Thrust vectoring by LITVC is accomplished by injecting a liquid into the supersonic exhaust of a rocket motor through holes in the wall of the nozzle exit cone. The injection produces side thrust by a combination of effects that include the thrust of the injectant jet itself, pressures on the nozzle wall from shock waves, and pressures on the nozzle wall resulting from addition of mass and energy to the exhaust flow. These effects are illustrated in figures 23, 24, and 25. Liquid injection TVC...

Joint Spring Torque

The flexible-joint spring torque resistance of the joint to movement usually is the maximum torque contributing to the actuation torque. It is dependent on a number of factors total thickness of elastomer, pivot radius, joint angles, and motor pressure it is also affected by environmental effects on the elastomer mechanical characteristics sec. 2.1.2.5.2 . The resistance of the joint to movement is overcome by the actuator for convenience of analysis, the necessary torque is calculated as the...

Ball And Socket Gimbal

Pintle Injector Rocket

Figure 1. - Classification of thrust vector control systems. Thrust vector control mechanisms have been undergoinging continual change. Concepts used in the past have been outmoded by increased severity of operational requirements and by development of lighter, more reliable systems. The general characteristics and technology status of the systems listed in figure 1 are presented in tables I through IV basic design features of major systems are shown in figures 2 through 11. The systems...

Envelope Limitations

The joint envelope is defined by the pivot radius Rp, the inner and outer joint angles j3j and j32, and the cone angle 0 fig. 12 . The pivot radius is determined primarily by the nozzle throat diameter, but the inner and outer joint angles and cone angle are selected by the designer. All joints that have been successfully tested to date have had angle 3 x ranging from 40 to 45 , angle j32 ranging from 45 to 55 , and angle 0 that was not greater than the joint angle 3 fig. 12 nor less than 0 ....

Nozzle Vector Angle And Pivot Point

Pivoting Rocket Nozzle

The amount of nozzle vector angle is determined by the vehicle control requirements. When the nozzle is vectored, the resultant side force acts approximately through the pivot point. The pivot point can be forward or aft of the nozzle throat fig. 15 . The position of the Figure 15. - Effect of pivot-point position on required envelope. Figure 15. - Effect of pivot-point position on required envelope. geometric pivot point is selected from a tradeoff study that considers the effect of position...

Elastomers

The important properties in the elastomer selection are the shear modulus, shear stress, reproducibility of these properties from lot to lot, and the ease of bonding the elastomer to the selected reinforcement material. Since it has been demonstrated that the joint spring torque could become zero because of axial compression, efforts are being made to determine shear properties with superimposed compression ref. 78 . The joint spring torque is directly proportional to the elastomer shear...

Performance Data For Design

In the early stages of the development period when optimization and tradeoff studies are being made to determine the general configuration of the motor system, the only LITVC performance data usually available are those generated in previous LITVC development programs. Data from at least ten LITVC development efforts are available refs. 46, 48, 50, 51, 107, 109, 121, 122, 124, through 127, 129, 133, and 137 through 142 . These data usually are reduced to standard plots and correlations sec....