The results and status of engine technology efforts to date and related company funded activities are presented. Advanced concepts in combustors and injectors, high speed turbomachinery, controls, and high-area-ratio nozzles that package within a short length result is engines with specific impulse values 35 to 46 seconds higher than those now realized by operational systems. The improvement in life, reliability, and maintainability of OTV engines are important

Zachary, A. T.

English

NASA Technical Reports Server

ADVANCED OTV ENGINE CONCEPTS 
A. T. Zachary 
Rockwell International/Rocketdyne Division 
Orbital transfer vehicles (OTVs) of the 1990 to 2000 period will deliver payloads 
for the more energetic of the NASA missions currently defined: large structure de- 
ployment, satellite servicing, and manned sorties to geosynchronous orbit. Along with 
advances in vehicle design, advances in engine technologies are required to improve 
overall engine capabilities, and thus vehicle performance, reliability, cycle fatigue 
life, maintainability, and cost. This paper briefly presents the results and status 
of NASA-LeRC-funded engine technology effort to date and related company-funded 
activities. 
Advanced concepts in combustors and injectors, high-speed turbomachinery, con- 
trols, and high-area-ratio nozzles that package within a short length result in engines 
with specific impulse values 35 to 46 seconds higher than those now realized by opera- 
tional systems. Equally, if not more important, will be the improvement in life, re- 
liability, and maintainability. 
INTRODUCTION 
Studies conducted under NASA contracts have identified near-term, intermediate-,. 
term, and longer term technologies to meet the needs of a broad-based program of space 
utilization. As shown in figure 1, the evolution of the development process for the 
OTV leads to manrated service near the end of the century. The technology drivers in 
meeting the goals of a viable, space-based system are space basing, aeroassist, manned 
operation, and low-g transfers. As presented in figure 2, approaches have been iden- 
tified; however, with specific challenges that must be met. These challenges of on- 
orbit servicing, increased life, reliability, maintainability, reduced length, and 
increased performance will be achieved through an evolutionary process as indicated in 
figure 3. 
The NASA plan for technology acquisition for the orbit transfer rocket engines of 
the period 1990 to 2000 is a three-phase approach encompassing conceptual- definition, 
preliminary experimental evaluation, and critical component technology verification 
stages. This approach is as follows, with the principal goals of the studies 
identified. 
PHASE I Conceptual Designs and Technology Definition 
e Identify, screen, evaluate, and select advanced technology 
concepts 
Provide engine conceptual designs and technology acquisition 
plans 
https://ntrs.nasa.gov/search.jsp?R=19850008692 2020-03-20T20:37:31+00:00Z

TECHNOLOGY PROPULSION 
DRIVERS SYSTEM CHALLENGES *PPRo*CH 
SPACE BASING 
AERO ASSIST 
MAINTENANCE 
a INCREASED 
PERFORMANCE 
a REDUCED LENGTH 
e REDUCED WEIGHT 
a WIDE THROTTLE 
TRANSFERS 
PERFORMANCE e CONTINUOUS vs 
E 
HIGH 6 NOZZLES 
- - 
*IMPROVED ANALYTICAL TE 
OMATERIAL IMPROVEMENTS 
.LONG LIFE BEARINGS 
.COMPOSITE MATERIALS FOR NOZZLES 
ADVANCED CONTROLS AND DlAGNOSTl 
E N H A N C E D  HEAT TRANSFER CONCEPTS 
-TURBOPUMP PERFORMANCE ENHANCEMENTS 
TIME ------d 
Figure 3. Cryogenic OTV Propulsion 
PHASE I1 Exploratory Research and Technology 
Unique and generic advanced technology concepts 
@ Simulation testing in test rigs 
PHASE IIT Critical Component Design and Fabrication 
Critical component design and fabrication readiness 
An Lmport~ant first step in these plans has been taken with the completion of the 
coneeptuaP design and technology definition studies entitled, "Orbit Transfer Rocket 
Engine Technology," with the primary objective of identification, and selection of 
adganced teehriology concepts and technology acquisition plans that will benefit the 
OTV engines of the 1990s. 
ULTIMATE OTV ENGINE EVOLUTION 
A phased approach has been selected for experimental development and verification 
of the technologies that will be featured in the ultimate OTV engine (fig. 4). The 
technologies bill be evaluated in an integrated components evaluator upon which thrust 
chamber, turbcmachinery, control system, and auxiliary system technologies will be 
verified in an engine system environment. The integrated components evaluator will 
iacllitate the verification of advanced component concepts in three technology group- 
r n g s :  near-term, intermediate-term, and long-range categories, and their successive 
-11tegration into advanced engine cores. At the completion of each technology period, 
an engine candidate and its technologies will have been defined that can be developed 
according to NASA needs. Each of these engines would provide large performance and 
operational benefits over the reference engine used in the studies (RL10A-3-3) and, 
because of the technology approach taken, could be developed as a growth version of 
t \ e  Advanced Gore Engine. The near-term engine schematic and mockup are shown in 
flgvres 5 and 6, respectively. 
The devel3pment of the ultimate engine would occur in the mid-1990s. The engine 
is planned as an expander cycle engine with a chamber pressure of 2000 psia, A nozzle 
eupansion area ratio near 1300:1, and a specific impulse greater than 480 seconds. 
O>erat.ionally, the engine will be capable of 20 hours of service-free life, deep 30:l 
~hrottling, and, with its health-monitoring and control system, capable of full space 
based maintenance and operation. For vehicles based in the Space Transportation Sys- 
t d n i  (STS) and Eor medium lift-to-drag aeromaneuvering OTVs, the engine will be fitted 
w ~ t h  a retractable nozzle to reduce stowed length to 40 inches. 
The engine thrust level and number of engines will undergo final selection when 
the vehicle crew safety and reliability approach are definitized. Since a large degree 
of technology commality exists in the range of thrusts of 3000 to 15,000 pounds, 
Roc~etdynek interim selection of 15,000 pounds engine rhrust is appropriate for tech- 
nc)log-y development. 
KEY ENGINE DESIGN ISSUES 
Key issues of the engine system and component design reside in the combustor/ 
injector, nozzle, turbomachinery, control system, and the auxiliary heat exchangers 
as outlined in figure 7. High heat extraction in the combustor, injector, and nozzle, 
wtth simul~:aneous efficient combustion and gas expansion, are required to provide high 
cilsrnber pressure and high specific impulse. A combustor and injector with extended 


F i g u r e  6 .  RS-44 llockup 
e MlGH HEAT-LOAD 
COMBUSTQR/INJECTOR @HIGH AREA RATIO NOZZLE 
e HIGH a EXP-RA~TIGN 
r LONG LlFE 
e LIGHT WEIGHT 
e LONG LlFE 
e S1MPLICITVIRELlAr)ILIM 
@HIGHSPEED, MULTISTAGE 
TURBOMACHINERY 
@a LIGHT WEIGHT 
e ROTORDVNAMlCS 
€4 LONG LlFE 
e HIGH STRENGTH M A T L S  
--- I, ADVANCED CONTROL AND DIAGNOSTICS 
@ TURBINE-GAS 
REGENERATOR 
o RELIABILITV/SIMPLICITV 
COMPACTNESS 
L I G H T  WEIGHT 
0 LONG LlFE 
9 COST 
HEAT TRANSFER EFF. 
COMPACTNESS 
€4 LIGHT WEIGHT 
F i g u r e  7 .  Ul t imate  Engine Design - Key I s s u e s  
heat transfer surfaces, providing high heat extraction, efficient wall cooling, and 
wall strain management to maintain desired component life, are the techriology chal- 
lenges in the combustor and injector. A large nozzle expansion area ratio with a re- 
tractable nozzle is necessary for high specific impulse and envelope compactness, Ad- 
vanced material technologies and retraction mechanisms that reduce weight and yet pro- 
vide adequate reliability are key technology issues of the nozzle assembly. 
High speed, multiple staging, small size, and high turbine and pump efficiency 
are requirements of the OTV engine turbomachinery. The technologies and technology 
issues to be addressed in achieving the high levels of performance required in each of 
these areas are: bearing life; rotordynamic characteristics of multiple-staged impel- 
lers; materials for increased turbine and impeller strength, life, and reduced weight; 
and reduction of parasitic performance losses of small turbomachinery through use of 
soft seals and efficient diffuser design of impeller-to-impeller crossover n(>tworks, 
Low-torque, light-weight, electrically driven valves, and driver motors are tech- 
nology issues to be developed for the advanced control system, as well as adxianced 
sensor technology and advanced multivariable controller systems. 
A turbine gas regenerator will provide increased power cycle performance through 
heat recuperation. For maximum benefits, the recuperator and the idle-mode heat ex- 
changer will require high heat transfer efficiency in a compact envelope. 
CONTROL SYSTEM TECHNOLOGY EVOLUTLON 
The near-term OTV engine shown in figure 4 uses a control and diagnostic system 
based on the current state of the art (SSME program) with one notable exemption: con- 
trol valves are low-torque devices with an electric motor providing the 3rimary means 
of actuation. Electrical power is desirable for upper-stage engines; however, law 
power requirements are necessary to keep the power supply small. The near-term 0TV 
engine control system provides functions similar to the SSME system: control of engine 
operating modes, checkout and status monitoring, input/output data processing, and 
protection of engine and manrated capability. The controller is a full-range system 
providing closed-loop control of thrust and mixture ratio during mainstage, start, 
and shutdown transients. Control during transients is required to maintain component 
operating limits at levels compatible with the long life required in the near tern 
(300 cycles, 10 hours). Redundancy in the controller, valves, and valve actuators is 
used to enhance the manrating capability of the system. 
The longer range technology development of this system aims to improve control 
accurac.y during transients, improve control system weight and simplicity:, and improve 
control and diagnostic system reliability through improvements of the weakest link rn 
the system: the sensors. Control accuracy improvement procedures will address modern 
multivariable control methodology and take advantage of modern miniaturin:ation tech- 
niques for controller components. Emphasis of the long-range technology will be to 
provide a highly reliable control and diagnostics system specially suited for space- 
based OTV engine maintainability. The system will do continuous wear monitoring and 
fault prediction, and ideally be capable of fault compensation or avoidance. The diag- 
nostic system is summarized in figure 8. 

ENGINE PACKAGING FOR SPACE-BASED MAINTAINABILITY 
Several engine packaging concepts are shown in figure 9. Components in rhe ncar-  
term OTV engine are packaged to conserve space in a volurne-limited shuttle orbiter, 
Power package components arranged around the combustor allow retraction of tke excend- 
ible nozzle for stowage in the shuttle, and still provides required mainitenarce volunlcs 
for ground-based maintenance operations. The component interfaces of the near-"term 
engine are designed with ground-based, line-replaceable unit philosophy. 
For space-based operations, the overall maintenance, system and/or subsystem 
changeout philosophy will determine the engine component packaging arrangement and 
component interface design. Space-based maintenance costs and component changeout ease 
will determine the final maintenance philosophy. If, after economic analysis, engine 
changeout is the smallest maintenance module operation defined, then the near-term 
conventional engine packaging design with advanced enginelvehicle interface connections 
will be capable of space-based operation and maintenance. 
The open-pack engine design will allow changeout of key engine compon.ents in a 
space environment. Increased maintenance volume will be defined for those components 
and a packaging design selected to facilitate component maintenance and $changeout. An 
advanced control and diagnostics system will facilitate component changeout for cause 
rather than mandatory scheduled replacement. 
In a space-based maintenance scenario where any or all components are subject to 
in-place maintenance and changeout, en advanced engine packaging configuration for 
efficient and speedy checkout removal and replacement will be desired. The components 
will be placed to facilitate access and their interface joints designed for minirnunr 
checkout and uncoupling time. A diagnostics system to facilitate judgement of cam- 
ponents due for replacement and checkout of new components would then be required. 
CONTRACT AND COMPANY-FUNDED ACTIVITIES 
The current status of the NASA LeRC contract activities and Rocketdyne-funded 
parallel effort is outlined in Table I. With the completion of the system study to 
identify specific technology tasks to be studied, several of the tasks are rzow being 
funded or are in the process of approval and will be initiated shortly. The specific 
tasks in process are listed in Table I1 and encompass a number of critical technology 
areas in support of providing the technology base for a full capability engirze in Lhe 
1990s. 
In conjunction with the NASA funded effort, key technologies have been under 
study at Rocketdyne and are now entering the hardware stage for demonstrarior~. T h r  
key elements are shown in figure 10, and represent an important learning process En 
design and fabrication of high performance engine components. It is planned to con- 
tinue the evaluation of these components and thus develop a realistic perspective In 
the problems of developing a high performance, reliable, maintainable engine system, 
ADVANCED PACKAGING CONCEPTS 
-- 
CONVENTIONAL PACICAGINC; OPEN PACKAGING FOR 
EASE OF MArNTENANCE 
MODULAR PACKAGING 
PULL OUTIPLUG IN MAINTENANCE 
F i g u r e  9 .  Engine Packaging f o r  Space-Based M a i n t a i n a b i l i t y  

Table I. Contract and In-House OTV Engine Activities 
@ NASA OTV ROCKET ENGINE TECHNOLOGY PROGRAM PLANNED TO 
CONTINUE THROUGH 1990 
o CONTRACT NAS3-23172 COMPLETED 
e SYSTEM STUDY - DEFINITION OF NEEDED TECHNOLOGY 
o CONTRACT NAS3-23733 STARTED 
e COMPONENT TECHNOLOGY AND SYSTEM STUDIES 
@ ROCKETDYNE IN-HOUSE COMF'ONENT ANALYSIS, DESIGN, AND 
FABRICATION PROCEEDING ON SCHEDULE 
Table 11. OTV Engine Technology Contract NAS3-23773 
Task Status 
@ ENHANCED HEAT LOAD THRUST CHAMBER 
@ INTEGRATED CONTROL AND HEALTH-MONITORING SYSTEM 
e INTEGRATED COMPONENTS EVALUATOR 
HIGH VELOCITY DIFFUSING CROSSOVER 
SOFTWARE RING SEALS 
CONCLUDING REMARKS 
There are many potential problems in producing a high-performance, space-viable 
rocket engine system for the OTV. The process will be evolutionary and will require 
the support of NASA and Industry. The process has been initiated with a well-ordered 
plan for establishing the required technology base and continued future effort should 
he strongly supported. 


Advanced OTV engine concepts

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