Rocket Exhaust Plume Phenomenology Frederick S. Simmons The Aerospace Press El Segundo, California American Institute of Aeronautics and Astronautics, Inc. Reston, Virginia The Aerospace Press 2350 E. El Segundo Boulevard El Segundo, California 90245-469 1 American Institute of Aeronautics and Astronautics, Inc. 1801 Alexander Bell Drive Reston, Virginia 20 19 1-4344 Library of Congress Catalog Card Number 98-074945 ISBN 1-884989-08-X Copyright 0 2000 by The Aerospace Corporation All rights reserved Printed in the United States of America. No part of this publication may be repro- duced, distributed, or transmitted in any form or by any means, or stored in a data- base or retrieval system, without the prior written permission of the publishers. Data and information appearing in this book are for informational purposes only. The publishers and the authors are not responsible for any injury or damage result- ing from use or reliance, nor do the publishers or the authors warrant that use or reliance will be free from privately owned rights. The material in this book was reviewed by the Air Force Space and Missile Sys- tems Center, Air Force Materiel Command, and approved for public release. Launch of a captured German V-2 rocket at the White Sands Proving Ground in New Mexico shortly after World War 11. In effect, those activities at White Sands were the start of the U.S. ballistic missile development program. The first opera- tional U.S. medium-range missile, the Redstone, exhibited some of the features of the V-2, and many of the missiles currently proliferating into the developing nations are derivatives of the Russian Scud, a direct descendent of the V-2.( Photo from J. B. Edson, “Optical Studies of the V-2 Missile in Flight,” Ballistic Research Laboratories Report No. 708, Aberdeen Proving Ground, Maryland, October 1949.) Preface This book is concerned with the physical and chemical processes in rocket engines and their exhaust plumes, It is intended as a basic tutorial treatise on the flow properties, gas dynamics, and radiative mechanisms responsible for generat- ing emission in rocket exhaust plumes at various wavelengths. Such emissions, particularly at infrared wavelengths, provide the basis for detection and tracking of rocket-powered vehicles by sensors aboard spacecraft deployed for missile defense. More specifically, this work is primarily concerned with the phenomenol- ogy of rocket exhaust plumes as the targets of space-based surveillance systems; however, the spectral, temporal, and spatial distributions of the infrared emission from rocket-powered vehicles are also required for the design and optimization of sensors for various other defense-related missions. In many cases, rocket plumes as targets must be viewed against the highly structured radiance fields of the Earth and atmosphere; in those cases, motion of the sensor line of sight can generate clutter that can limit system performance. In the design and optimization of sen- sors for such purposes, knowledge of the atmospheric background phenomenol- ogy is as important as knowledge of the target characteristics. However, the sub- ject of background phenomenology is necessarily beyond the scope of this work. The information presented here was accumulated throughout my professional career, which included relevant activities at NASA Lewis Flight Propulsion Labo- ratory (1948-1955), Rocketdyne Field Laboratory (1955-1962), Willow Run Laboratories of the University of Michigan (1962-1 97 l), and The Aerospace Cor- poration (19 7 l-present). The text itself in good part was extracted from two of my previous works. The first was a discourse on the subject, originally written in 1979 (reissued with revisions in 1982) for the Department of Defense Advanced Research Projects Agency. That work was Carrie? out by commission of Dr. Stephen Zakanycz of the Space Technology Office. The second work was one of 10 volumes on the subject of missile launch phenomenology, written in 1994 for the Ballistic Missile Defense Organization, commissioned by Dr. William G. D. Frederick of the Technology Office.? That material has been augmented and updated with some recent developments. *“Handbook for Infrared Emission from Missile Plumes,” The Aerospace Corporation Report No. TOR-0083(3753-06)-1, Vols. I and 11, 1982. t“The SDIO Handbook of Missile Launch Phenomenology; Infrared Characteristics of Rocket Plumes,” The Aerospace Corporation Report No. TOR-92(2069)-3, Vol. 11, 1994. ix Contents ....................................................... Preface., ix ................................................ Acknowledgments xi ........................................ Chapter 1 Rocket Engines 1 1.1. Introduction. .............................................. 1 1.2. Ideal Engines ............................................... 1 1.3. Real Engines ............................................. 12 1.4. References ............................................... 19 ....................... Chapter 2 Characteristics of Exhaust Plumes 21 2.1. Inviscid Core ............................................ 21 2.2. Mixing Layer ............................................ 23 2.3. Flight Regimes ........................................... 26 2.4. Two-Phase Flow ......................................... $29 2.5. Multiple Nozzle Effects .................................... 31 2.6. Effects of Recirculation .................................... 33 2.7. Plume-Trail Transition .................................... 36 2.8. References ............................................... 36 ................................... Chapter 3 Radiation Processes 39 3.1. Origin of Emission ........................................ 39 3.2. Spectral Line Growth ..................................... 42 3.3. Isothermal Emission ...................................... 45 3.4. Nonisothermal Emission ................................... 47 3.5. Line-by-Line Calculations .................................. 49 3.6. Molecular Band Models .................................... 53 3.7. Band Model Parameters ................................... 57 3.8. Band Strength Summary ................................... 58 3.9. Chemiluminescence ....................................... 59 3.10. Kinetic Excitation ......................................... 60 3.11. Emission and Scattering from Particles ....................... -61 3.12. Scattering of Sunlight from Particles ......................... 63 3.13. Infrared Resonance Scattering ............................... 69 3.14. References .............................................. 70 .................................... Chapter 4 Nozzle Flow Codes 73 4.1. General Considerations .................................... 73 4.2. Nozzle Performance Codes ................................. 74 4.3. The One-Dimensional and Two-Dimensional Kinetic Codes ....... 75 4.4. Empirical Adjustments to Code Inputs ........................ 91 Contents 4.5. Comparisons with Experiments ............................. 93 4.6. References .............................................. 96 ....................................... Chapter 5 Plume Models 99 5.1. ModelTypes ............................................ 99 5.2. SPF/SIRRM ............................................ 99 5.3. CHARM .............................................. 105 5.4. Other Detailed Plume Models .............................. 113 5.5. CFDCodes ............................................ 113 ............ 5.6. One-Dimensional Models for Low-Altitude Plumes. 113 5.7. Analytical Models for High-Altitude Plumes ..................1 18 5.8. References ............................................. 126 .................................... Chapter 6 Signature Scaling 129 6.1. Rationale for Scaling ..................................... 129 6.2. Empirical Scaling Laws .................................. 129 6.3. Derivation of Scaling Law for Low-Altitude Plumes ............ 130 ............ 6.4. Derivation of Scaling Law for High-Altitude Plumes 138 6.5. Scaling Law for Vacuum Plumes ........................... 139 6.6. Scaling through Detailed Modeling ......................... 140 6.7. References ............................................. 141 .................... Chapter 7 Time-Varying Properties of Plumes 143 7.1. Introduction ............................................ 143 7.2. Origin of Plume Modulations .............................. 143 7.3. Ignition and Cutoff Flashes ................................ 148 7.4. Staging Events .......................................... 150 7.5. RV Deployment ........................................ 154 ............................................. 7.6. References 155 .............. Chapter 8 Properties of Molecular Plume Constituents 157 8.1. Molecular Band Strengths ................................. 157 8.2. Representative Spectra ................................... 158 8.3. Rate Constants and Cross Sections .......................... 163 8.4. References ............................................. 170 .............................. Chapter 9 Carbon Soot Properties 173 ................................ 9.1. Mechanisms of Formation 173 9.2. Particle Sizes and Composition ............................ 178 9.3. Optical Properties ........................................ 180 9.4. Nonequilibrium Effects ................................... 182 9.5. Soot Oxidation in Plumes ................................. 183 Contents 9.6. Solar Heating of Soot Particles ............................. 188 9.7. References ............................................. 190 ....................... Chapter 10 Properties of Alumina Particles 193 10.1. Formation ............................................. 193 .................................. 10.2. Particle Sizes and Shapes 193 10.3. Particle Temperatures and Optical Properties ..................1 95 10.4. References ............................................. 198 Chapter 11 Diagnostic Techniques for Exit-Plane Exhaust ............................................... Characterization 201 11 .1, General Considerations ................................... 201 ...... 11.2. Emission-AbsorptionM easurements-Homogeneous Gases 202 11.3. Emission-AbsorptionM easurements-Inhomogeneous Gases .....2 13 ............. 11.4. Active Illumination and Crossed-Beam Techniques 223 ............................... 11 .5. Direct Sampling Techniques 231 ............................................. 11 .6. References 234 ...................... Chapter 12 Ultraviolet Properties of Plumes 239 12.1. Introduction ............................................ 239 12.2. Ultraviolet Emission from Exhaust Gases. .................... 239 12.3. Ultraviolet Emission from Particulates ....................... 248 12.4. References ............................................. 249 ............................... Chapter 13 Post-Boost Phenomena 251 13.1. Propellant Venting ....................................... 251 ......................................... 13.2. Persistent Trails 252 13.3. References ............................................. 255 .......................................... Chapter 14 Databases 257 14.1. Introduction ............................................ 257 14.2. MIDAS ................................................ 257 14.3. Defense Support Program ................................. 261 ................................. 14.4. The TRIM Data Collection 262 14.5. SDIOBMDO Databases from Airborne Sensors ............... 265 14.6. The LBSS Experiments ................................... 275 14.7. References ............................................. 277 ............................ Glossary: Acronyms and Abbreviations 279 .......................................................... Index 283 1 Rocket Engines 1.1 Introduction Understanding plume phenomenology requires some knowledge of rocket engines, their fundamental principles of operation, and their basic configuration. This chapter by no means constitutes a comprehensive treatment of the subject nor even an in-depth introduction. For that, the reader should refer to the classic text by George Sutton'.' or a comparable source. Here the subject is reviewed to the extent necessary to provide missile defense system engineers and phenomenolo- gists the fundamental parameters characterizing engine performance, particularly their effect on the observable attributes of the plume. This chapter is divided into two parts. First, basic concepts and ideal engines are considered. Ideal in this context refers to the processes of operation characterized by one-dimensional isentropic fluid-mechanical relations. The content is restricted to those aspects of the flow that have a direct effect on the characterization 'of exhaust properties. The second part is devoted to the attributes of real engines that affect the reliability of plume properties based on the assumption of ideal combus- tion and flow processes. 1.2 Ideal Engines 1.2.1 Principles of Operation A chemical rocket engine is a device for generating thrust by high-pressure com- bustion of propellants, that is, reactants, carried aboard the vehicle. The propel- lants are contained either in separate tanks as liquid fuels and ozidizers or in the combustion chamber itself, combined as a solid-propellant grain. Thrust is conse- quent to the expansion of the combustion products through an exhaust nozzle. The gross thrust derives fiom the imbalance of pressure forces within the engine as shown schematically in Fig. 1.1. Within the combustion chamber, high pressure is produced by the reaction of the propellants. The pressure forces on the walls are balanced radially but not axially; the principal component of the thrust results from the force acting on the forward end of the chamber not balanced by an opposing force at the other end. That force acts on the gaseous combustion prod- ucts that are accelerated to supersonic velocities through a converging-diverging (De Lava0 nozzle. A second increment of thrust is generated by the imbalance of the longitudinal components of the pressure forces normal to the diverging section of the nozzle. The gross thrust is invariant with altitude provided the flow in the nozzle does not separate fiom the walls. The net thrust is slightly less; the difference is the integral of the atmospheric pressure over the external surface of the engine. Consequently, the net thrust increases with altitude to an asymptotic limit termed the vacuum *Engines powered by nuclear reactions, solar-generated electricity, laser or microwave energy transmitted from the ground, or other means are not relevant to the development of space-based defense systems. 1 2 Rocket Engines Fig. 1.1. Imbalance of forces in a rocket engine. thrust. (Aerodynamic drag on the engine is treated separately as part of the drag on the vehicle that also depends on the ambient atmospheric pressure.) The math- ematical basis for quantifying the various components of thrust is presented in a number of texts;’” the basic relations are discussed in Subsec. 1.2.3. 1.2.2 Engine ’Qpes All rocket engines generate their thrust consequent to high pressures generated by propellant combustion. The simplest engines, usually designated as motors, utilize solid fuels and oxidizers blended into a more or less homogeneous mixture, cast into the pressure-containing structure of the motor casing, as illustrated in Fig. 1.2. As the propellants are consumed, the chamber pressure and hence the thrust vary somewhat with time. Solid-propellant motors normally are not throttleable or restartable; the combustion once initiated continues until the propellant is depleted. A comparably simple engine uses pressure-fed liquid propellants, as indicated in Fig. 1.3. In this case, the tanks must be pressurized to a level higher than that in the combustion chamber; flow and combustion are initiated by the opening of valves in the propellant lines. (For hypergolic propellants, ignition is spontaneous; otherwise, an igniter of some sort is required. Frequently, initial injection of a small amount of a hypergolic combination is used as a starter.) Obviously, the walls of the tanks of a pressure-fed engine must be strong hence relatively heavy. Consequently, such liquid-propellant engines have found application only at very low thrust levels, for example, as required for space maneuvering where the weight of the tanks can be tolerated in the interest of simplicity and reliability. A hybrid engine, Fig. 1.4, uses a solid grain with a liquid oxidizer (or vice versa). This concept to some degree combines the simplicity of a solid propellant motor with the controlled combustion of a liquid propellant. There have been a number of such engines constructed and tested, but not used to date in any space or missile application. Large liquid propellant engines used in the older long-range missiles or space launch vehicles are configured as illustrated in Fig. 1.5. The propellants are car- ried in tanks at pressures only sufficient to control the flow into gas-turbine driven Ideal Engines 3 Fig. 1.2. Solid propellant motor. Fig. 1.3 Pressure-fed motor. Fig. 1.4. Hybrid motor. Fig. 1.5.Open-cycle engine.