AUSROC III The Development of Australian Launch Vehicle Capability M. A. Blair B.E.(Mech.), Grad. I.E.Aust. ASRI Director Ausroc Program Coordinator 1. INTRODUCTION Ausroc III is the third of the Ausroc series of liquid fuelled rockets aimed at the promotion of research, development and education of the field of launch vehicle technologies within Australia. Ausroc III is being designed as a sounding rocket capable of lifting 100kg of useful scientific payload to an altitude of 500km and then recovering it intact. The vehicle is also being developed as a test bed for a number of technologies that have direct application in satellite launchers. These technologies include: regenerative liquid propulsion, composite structures, inertial navigation, vehicle guidance and control, telemetry and flight termination systems, ground support, tracking and range safety. The Australian Space Research Institute (ASRI) supports and promotes the Ausroc program through cooperation with Australian Universities and a team of dedicated ASRI members. This paper describes the past present and future development of the Ausroc III program as well as its educational benefits. 2. AUSTRALIAN SPACE RESEARCH INSTITUTE The Australian Space Research Institute Ltd. (ASRI) was formed on the 17th May 1993 as a result of the merger between the Australian Space Engineering Research Association Ltd. (ASERA), and the Ausroc Projects Group. ASRI will be undertaking space related research, development and education programs in the launch vehicle and satellite technology areas. The Institute has been formed to fill a void in these research and development disciplines within Australia. The objects with which the company (ASRI) has been established are to, on a non-profit basis : a. Develop and advance space science and technology. b. Conduct, encourage and promote research in the field of space science and technology. c. Educate and extend knowledge in the field of space science and technology and to make available education opportunities in the field of space science and technology to supplement and further those opportunities made available by established educational institutions. d. Conduct, co-ordinate and support projects for the advancement of the above objects. The Ausroc program is now one of 3 major program areas within ASRI. The other 2 being the AUSTRALIS Micro-satellite program and the SCRAMJET Development program. 3. AUSROC PROGRAM BACKGROUND The Ausroc Projects Group was established in 1988 to fill an educational void in launch vehicle engineering disciplines within Australia. Ausroc I was a 2.6m bi-propellant liquid fuelled rocket using nitric acid and furfuryl alcohol as propellants. It was launched from the Graytown Proof Range in Victoria on the 9th of February, 1989. The vehicle velocity and altitude were approximately 600km/hr and 3.5km respectively. Although the recovery system failed to operate as planned during this flight, the propulsion system worked very well, as did the electronics and telemetry system. The Ausroc I project was undertaken as a private project, although assistance was given by several members of the Monash Uni. Mechanical Engineering staff. The success of Ausroc I paved the way for a much more ambitious project, Ausroc II. In 1989, Monash Uni. Engineering students commenced an official project to design, build and test launch a bi-propellant Lox/Kero rocket system. The Ausroc II regeneratively cooled, rocket motor was constructed and static test fired at the Ravenhall Test Facility in Deer Park, Melbourne, on three separate occasions during 1991-92. These trials were performed to validate the system performance and familiarise the launch crew with operating and safety procedures associated with liquid fuel rocketry. The launch trial, conducted during October 1992 at the Woomera Rocket Range in S.A., resulted in the destruction of the vehicle on its' launcher. The failure was caused by the liquid oxygen supply valve failing to operate successfully. Ausroc II was the largest liquid fuelled rocket designed and manufactured in Australia and was one of the worlds' largest amateur rocket systems. A second improved vehicle, Ausroc II-2, is currently under construction for launch in 1994. 4. AUSROC III CONCEPT DEFINITION The interest and support shown for Ausroc II and the enthusiasm of those involved, led the Ausroc team to prepare a plan for the future of the Ausroc launch vehicle series. In late 1990 it was decided that the ultimate goal of the Ausroc projects group would be to develop a satellite launch vehicle capable of placing a microsatellite into a low earth orbit. This goal encompasses many technical aspects which have not yet been addressed in the previous 2 rocket programs. Therefore, it was decided to develop an intermediate launch vehicle system that could be used as a technology demonstrator for the satellite launcher. This intermediate launch vehicle concept forms the basis of the Ausroc III program. The primary objective of this third generation Ausroc system is: S To carry a useful scientific payload of 100 kg mass to an altitude of 500 km on a predetermined and controlled, suborbital trajectory and recover it intact. Ausroc III, would, if completed, be the largest amateur rocket ever built and would be a useful instrument for performing research in fields such as; atmospheric physics, microgravity materials processing, high altitude observations, hypersonics research and evaluation of satellite launch vehicle hardware. This new project represents a challenge that encompasses a diverse range of science and engineering disciplines. The Ausroc III system has been sub-divided into a number of sub-systems that are described in more detail below. Each of these sub-systems represent a project that can be undertaken by groups of science and engineering students at Universities and Institutes around Australia or by groups of amateurs, outside the tertiary education system, who would like to see the fruition of the Ausroc launch vehicle program and its associated benefits. The Ausroc III program is broken down into the following work areas: Propulsion Structures Navigation, Guidance & Control Flight Electronics Ground Infrastructure Payload 5. AUSROC III PROPULSION SYSTEM In meeting our primary objective of lofting a 100 kg payload to 500 km, we started by determining the type of rocket propulsion that would be used as this would, undoubtedly, determine the size of the vehicle and the required subsystems. Our preliminary calculations, using a trajectory simulation program (ref.1) indicated that approximately 1200 kg of propellant, assuming an average specific impulse of 250 sec, will be required to meet the objective. Solid, liquid and hybrid rocket propulsion systems were considered for use on Ausroc III. Australia does not yet have the capacity to cast the required 1200kg of solid propellant from one mix and the mixing, storing and transportation of solid propellant is a hazardous operation that requires strict process control and safety supervision. A hybrid rocket has a solid fuel grain and a liquid oxidiser. The fuel is, generally, no more dangerous than a block of rubber and the oxidiser can be loaded at the launch site. With this system there are no storage or transportation problems and in the case of a malfunction there is no opportunity for the 2 propellants to intimately mix and explode. Hybrids, however, have not had the same extensive development history as solid and liquid rockets and for this reason there is only a limited amount of published data available on hybrid rocket propulsion. Liquid fuelled rockets offer a safety advantage over solid propellant rockets in that the propellants are only loaded into the vehicle at the launch site. This way, the rocket is safe and easy to store and transport. The Ausroc team has chosen to develop a bi-propellant liquid propulsion system, utilising liquid oxygen and kerosene for use in Ausroc III for the following reasons: a. High Specific Impulse b. Lowest Propellant Cost c. Large technical data base exists d. Motors are controllable and reusable e. Vehicle is inert and safe until fuelled on launcher 5.1 Motor Design Due to the complexities involved with turbo-pump propellant delivery systems, Ausroc III will utilise a pressure feed system to deliver the propellants to the combustion chamber. Thus the propellant tanks must operate at pressures in excess of the chamber pressure. A combustion pressure of 2 MPa was chosen as a good compromise between overall tank weight and specific impulse. The propulsion system will be operational for the first 80 seconds of flight in a pressure environment that extends from 1 atm at launch to a near vacuum at shut-down. The Ausroc III motor nozzle will be designed to expand the 2 MPa combustion gases to 0.55 x ambient pressure at sea-level to avoid nozzle flow separation. This corresponds to a nozzle expansion ratio of 6. Given these values, the optimal propellant mixture ratio (Mox/Mf) of 2.4 was determined using the Nasa/Lewis thermodynamics code (ref.2). The continual decrease in ambient pressure, as the rocket gains altitude, causes a proportional increase in motor thrust. This increase in thrust corresponds to an increase in specific impulse (Isp) and the thrust coefficient (Cf). In order to avoid any possible interaction between the rocket and the launcher stand at lift-off, a net launch acceleration of approximately 1g was specified. This implies a lift-off thrust of 35 kN. With this information the motor geometry can be determined using a set of standard motor equations as can be found in refs.3-4. Table I summarises the key motor parameters and dimensions. Four cooling techniques were considered for the Ausroc III motor. These were regenerative, ablative, radiation and film. Regenerative cooling involves the circulation of one of the propellants through passages along the motor wall to absorb the heat transfered from the chamber. Ablative motors are one shot devices used, primarily, in short burn liquid motors or solid propellant motors. They use endothermic materials which decompose and absorb large quantities of heat in the process. Radiation cooling relies on the motor wall reaching thermal equilibrium with its surroundings.This requires the use of rare and expensive high temperature refractory metals and ceramics. Film cooling can be incorporated into any of the previous 3 types of motors and involves injecting a coolant fluid along the motor wall to generate a 'cool' gas boundary layer to slow the rate of heat transfer. TABLE I: AUSROC III Motor Specifications Fuel: Kerosene Oxidiser: Liquid Oxygen Burn Duration: 80 sec. Combustion Pressure: 2 MPa Mixture Ratio (Ox/F): 2.4 Thrust Correction Factor: 0.94 Thrust Coefficient: 1.394 s.l. - 1.698 vac. Specific Impulse (corrected): 241 sec (s.l.) - 293 sec. (vac.) Thrust (N): 35 kN (s.l.) - 42.6 kN (vac.) Nozzle Throat Diameter: 130 mm Nozzle Expansion Ratio: 6 Nozzle Exit Diameter: 320 mm Expansion Cone Half Angle: 15 degrees Chamber Contraction Ratio: 3 Chamber Diameter: 230 mm Characteristic Length (L*): 1.0 m Chamber Length: 340 mm Contraction Cone Half Angle: 30 degrees Throat Radius: 65 mm Contraction. Rad: 65 mm The Ausroc III program will require numerous static firings to fine tune the motor performance and control system before a launch can be approved. Ablative motor construction was eliminated on the grounds that multiple firings would require multiple motors to be manufactured and this would increase the costs of development. To meet the multiple firing criterion for the motor, a regenerative cooling system has been selected. Of the 2 propellants onboard Ausroc III, the kerosene fuel was selected as being the more suitable regenerative coolant. A program of work is currently being undertaken to develop a 'Tube Wall' rocket motor for Ausroc III. This motor is fabricated by brazing together and reinforcing a bundle of pre-contoured nickel alloy coolant tubes and attaching inlet and outlet manifolds. The tubes form the geometric wall of the motor. Once the tooling has been established to fabricate the first motor, it would be a relatively straightforward process to produce subsequent motors for further development or future vehicles. The propellant requirements and tank volumes can be calculated with a knowledge of the specific impulse, thrust level, mixture ratio, ullage requirements and burn time. The propellant requirements are as follows: Propellant Mass Flow = F / Isp g = 14.8 kg/s Mass of Propellant = 80 x 14.8 = 1184 kg Mass Lox = 836 kg Mass Kerosene = 348 kg Density of Lox = 1142 kg/m3 Density of Kerosene = 800 kg/m3 Volume of Lox = 732 lt Volume of Kerosene = 435 lt Lox Tank Volume = 800 lt Kerosene Tank Volume = 500 lt The rocket, as mentioned previously, is to be pressure fed. There are 2 gases that have been identified as being applicable to this application; nitrogen and helium. Nitrogen was eliminated as the flight pressurant gas on the grounds of its 7 fold increase in weight over helium and also because of the close proximity of its boiling point to that of the lox which causes density and solubility problems. Nitrogen, however, is very cheap and readily available in large quantities. For the static firings and ground tests, nitrogen can be used as the pressurant since weight and storage volume is not of concern in these instances. The flight pressurant tank will store the helium gas at high pressure (30MPa). This high pressure gas will then be regulated down to the liquid oxygen and kerosene tank pressures of 3 and 4MPa respectively. Thus, a pressure tank volume of 200 lt, which includes an extra 20 lt for the cold gas roll control thrusters, is required. 5.2 Injector Design The injector attaches to the forward end of the motor and its purpose is to introduce and meter the propellants into the combustion chamber. It also atomises and mixes the propellants to enhance combustion efficiency. The Ausroc III injector design is being modelled on the Ausroc II injector configuration. A set of 200 triplet injectors are to be used whereby 2 15 degree half angle fuel injection streams impinge with each axial oxidiser stream. The injector elements are to be 2.1mm diameter for the liquid oxygen and 1.05mm diameter for the kerosene (ref. 6). To assist in chamber wall cooling, it is planned to bias the mixture ratio of the injectors which are closest to the wall in favour of the fuel. This generates a cooler fuel rich zone along the inside wall of the motor. The injector configuration also has a substantial effect on combustion stability and this issue will receive further attention in the near future. The injector will be manufactured from aluminium alloy due to its machinability and high heat transfer coefficient. 5.3 Propellant Utilisation System The propellant utilisation system consists of the following items; ball valves, valve actuators, flow meters, tank level sensors and fill/drain facilities.This system controls the flow of propellant during startup, burn and shutdown and also has provision for interfacing to the launcher fuelling equipment. For the majority of the burn time the propellant utilisation system will ensure that the mixture ratio of the propellants is maintained at 2.4. Towards the end of burn, the system will continually sense the tank levels and adjust the mixture ratio to ensure that both propellants are exhausted simultaneously. Failure to do this can lead to considerable performance losses. 6. AUSROC III STRUCTURE The performance of a rocket structure is usually determined by its mass ratio. The mass ratio is the ratio of propellant weight to total weight excluding payload. The Ausroc team has set a target mass ratio of 0.85 for the Ausroc III system. This means that for a propellant mass of 1200 kg, the total dry weight of all non-payload items will be approximately 220 kg. This target mass ratio is quite high for a pressure-fed liquid fuelled rocket and extensive use of strong, lightweight materials will be essential to achieve it. For this reason it was decided to develop the system around the use of high strength and lightweight filament wound tanks and composite layup fairings. Where possible, 7075 aluminium alloy will be used for machined components. 6.1 Structure Components It was determined (ref.5) that the optimal length to diameter (L/D) ratio of the launch vehicle, to minimise drag, was approximately 12. Given this value and the tank and payload volume requirements, the body dimensions were set at: Nominal Body Diameter: 0.7 m Total Body Length: 8.4 m (includes payload) Ausroc III consists of 12 major structural items which are listed in Table II and shown in figure 1. The 3 pressure vessel tanks are to be manufactured by filament winding epoxy resin impregnated carbon fibre rovings over thin walled stainless steel or aluminium mandrels. The mandrels also serve as impervious tank liners. The performance rating of pressure vessels is usually given in units of meters and determined by the following relationship: Performance Rating = Pressure x Volume / Mass x g Modern high performance aerospace pressure vessels have been fabricated, via filament winding techniques, with performance values exceeding 25000m. The minimum performance for the Ausroc III filament wound tanks has been specified as 12000m since no tanks of this type have been manufactured in Australia to date and much has to be learnt regarding the processes involved. In March 1993 a filament winding machine, of sufficient size to manufacture the Ausroc III tanks and being surplus to DSTO requirements, was transfered on permanent loan to the Mechanical Engineering Dept. of the University of Adelaide. This machine is currently being commissioned by the department for student projects. TABLE II: Ausroc III Major Structural Items Item Structure Fabrication Method 1 Nose Cone Composite Lay-up 2 Payload Fairing Composite Lay-up 3 Payload Support Structure Machined 7075 Al. 4 Helium Tank (30 MPa) Filament Winding 5 Upper Intertank Fairing Composite Lay-up 6 He/Lox Tank Interface Machined 7075 Al. 7 Lox Tank (3 MPa) Filament Winding 8 Lower Intertank Fairing Composite Lay-up 9 Lox/Kero Tank Interface Machined 7075 Al. 10 Kerosene Tank (3.5 MPa) Filament Winding 11 Boattail Fairing Composite Lay-up 12 Thrust Mount / Gimbal Unit Machined 7075 Al. The fairings are to be manufactured as single piece units using composite lay-up construction techniques which use pre-preg carbon fibre mat materials and autoclave curing processes. Honeycomb sandwich cores will be used where enhanced strength and stiffness properties are required. The all composite fairings will bolt directly to aluminium mounting rings which are filament wound into each end of the 3 flight tanks. Each fairing will contain 2 flush mounting hatches, 250 x 250mm square, for access and assembly purposes. All the cylindrical fairings are to be manufactured with common tooling and both intertank fairings are to be identical items. The junction between the base of the payload fairing and the helium tank will contain a separation device that will be initiated immediately after engine cut-off. This device will disconnect the payload module and provide a positive separation force. The nose cone is a tangent-ogive with an L/D of 2.14 and will incorporate ablative materials to protect it from the high aerodynamic temperatures experienced during the flight. A number of air pressure ports will be incorporated into the nose cone to provide air speed and angle of attack data to the flight computer. The boattail fairing has a 6 degree taper to reduce the base area of the rocket by approximately 50%. This significantly reduces the base drag of the vehicle. The thrust mount / gimbal assembly, to be manufactured from 7075-T6 aluminium stock, is a multi-purpose item which transfers the vectored thrust load of the motor into the vehicle structure. It also provides interfacing and mounting provisions for the following: -Propellant utilisation system components -Hydraulic system components -Launcher release system 6.2 Structure Analysis The Ausroc III vehicle will be exposed to a multitude of loads including ground winds, wind shear, motor thrust, aerodynamic drag and lift, propellant slosh and TVC. The structure is being designed to withstand a flight angle of attack of 5 degrees at maximum dynamic pressure (69kPa). The calculated normal force distribution imposed on the vehicle during these conditions is shown in figure 2. Wind tunnel testing of a scale model will be undertaken to verify the calculated aerodynamic coefficients A theoretical analysis of the static and dynamic characteristics of individual structural components and the integrated assembly will be undertaken using finite element analysis techniques to ensure that the structure will maintain its integrity for the entire flight profile. It is essential to ensure that the natural frequency of the vehicle does not coincide with the control system frequency of 10 Hz. Therefore a target first natural frequency for the structure has been set at 30 Hz. This analysis is to be followed up by a test and evaluation program utilising flight hardware. Figure 2: Ausroc III Normal Force Distribution 7. AUSROC III GUIDANCE, NAVIGATION & CONTROL (GN&C) Information in this section was obtained from ref 8. 7.1 Navigation Navigation involves the determination of the position, velocity and attitude of the vehicle with respect to a convenient reference frame. The inertial measurement unit (IMU) consists of sensors that are attached to the vehicle body. Gyroscopes sense the angular velocity of the vehicle and accelerometers sense the specific force. Navigation will be done by a dedicated computer which will communicate with the IMU, GPS and the computer responsible for guidance and control. 7.2 Guidance Guidance involves using navigation data and guidance algorithms to generate commands for the control system in order to achieve the desired trajectory. The commands consist of attitude or attitude rate commands. The current trajectory profile consists of: 1. Vertical Ascent to 200m. 2. Pitch over, decreasing the flight angle from 90 to 88 degrees. 3. Gravity turn, to minimise aerodynamic loads. 4. Coast, until initial recovery system deployment. 5. Final recovery system deployment using steerable parachute. Wind loads during the period of high dynamic pressure will be reduced by 'steering into the wind'. This is done by using the lateral acceleration measurements to null side forces. When the dynamic pressure becomes low enough, a closed loop guidance algorithm can be used to reduce the effects of disturbances such as wind and non-ideal vehicle behaviour. The guidance algorithms will be implemented as part of the software of the flight management computer. 7.3 Control Control refers to the control of the vehicle, implemented as a closed loop control system. This accepts attitude or attitude rate commands and generates commands for the thrust vector control system (TVC). It uses IMU data to provide feedback for its control loops. The control algorithms will also be implemented as part of the software of the flight management computer. Given the nature of the Ausroc III system, it was decided to implement an electro-hydraulic, gimballed motor TVC system to provide control in the pitch and yaw planes and a cold gas thruster system for roll control. 8. AUSROC III ELECTRONICS For Ausroc III to achieve its stated program objectives, a comprehensive flight management system is required. This system will consist of the following major items: 1. Flight management controller (FMC) 2. Inertial Navigation Unit (INU) 3. Attitude Control System (ACS) 4. Power Supply and Control (PSC) 5. Data Acquisition and Telemetry 6. Electro / Hydraulic / Pyrotechnic Drivers 7. Flight Termination System (FTS) 8. Radar Transponder Figure 3 and reference 7 provide the general arrangement of the electronics systems. It is proposed to use commercial 32 bit 80386 motherboards for the FMC, ACS and INU due to low cost and easy access to peripherals, documentation and software development tools. The 'C' programming language has been selected as the basis for all flight software development. The communications interface bus between all the system units has not yet been determined but the current options include RS-422, Ethernet and Mil-1553B. The complete data acquisition and telemetry system will consists of up to 128 sensors, 16 data formatters, a multiplexer and a transmitter. The telemetry transmitter is to have a bandwidth of 500 kHz, a minimum power output of 5W and operate on either L-band or S-band. A similar video transmitter is to be included to relay optical data from the flight and payload cameras. Two C-band radar transponders will be incorporated into the vehicle to assist the Woomera range radars in providing accurate range safety tracking. A Flight Termination System (FTS) utilising 2 WREBUS receivers will provide command destruct capability. WREBUS was the system used extensively at Woomera in the past. It is planned to develop an omnidirectional strip antenna unit for each of the flight transmitters and receivers to provide complete coverage irrespective of vehicle attitude. 9. AUSROC III GROUND SUPPORT Ground support includes such things as: transportation, assembly, test, fuelling, launcher stand, launch control centre, tracking, flight termination, film and video systems and vehicle recovery. Woomera is the intended launch site for Ausroc III and, in particular, we are focussing on the use of Site 5 which is the old abandoned Black Knight launch site and is located approximately 5 km SW of the range instrumentation building. The block house still exists at site 5 and the exhaust deflection pit can be refurbished. As currently designed the launcher stand and access tower also doubles as the transport cradle and assembly jig. The range instrumentation building is more than adequate for use as the launch control centre. Pre-flight assembly and test will be performed in Test shop 1 as was done during the Ausroc II trial. There are currently 2 operational Adour radar units at the range, and with the use of transponders on the rocket, they would be capable of tracking the vehicle for its full 500km apogee trajectory. A high power flight termination system transmitter will need to be installed on the range and tested. Real time display and analysis of critical flight parameters will be available via an electrical umbilical prior to launch and by RF link after liftoff. A dedicated launch sequence controller will be developed to perform the critical preflight system checks, the launch sequence and abort routines. 10. CONCLUSION The Ausroc III program has now been in existence for 3 years and in that time approximately 50 students from 9 Universities around the country have undertaken engineering design exercises from the broad range of launch vehicle disciplines making up the Ausroc III system. The program represents a learning experience for all those involved since no launch vehicle of this type has ever been developed in Australia. Projects will continue to be forwarded to the Universities around the country in future years, culminating with the construction and test flight of the prototype vehicle. It is the belief of the ASRI directors and the Ausroc coordination team that the "hands-on" approach to launch vehicle education, as is currently being provided, will enhance the national technology base and provide a small stream of enthusiastic engineers and scientists capable of participating in future national or international programs. 11. ACKNOWLEDGMENTS As previously discussed, the Ausroc III program is dispersed throughout Australia. There are currently no fewer than 30 students and qualified engineers and technicians involved in the program. The author wishes to thank the lecturers and students from the following universities for their involvement in the Ausroc III Program: University of Adelaide University of South Australia Monash University RMIT University of NSW University of Sydney University of Queensland Queensland University of Technology University of Southern Queensland The author would also like to thank the many Ausroc core group members and industrial sponsors who have given much in the way of personal time and resources to the Ausroc activities over the past years. Their enthusiasm and commitment to an Australian Space Program is what has kept this program alive. REFERENCES No. Author Title 1. Cheers A. "A Spherical Earth Model Particle Trajectory Simulator Utilising a 4th Order Runge-Kutta Method" Computer Program (c) Ardebil 1991 2. Gordon S. and "Computer Program for Calculation of McBride B. Complex Chemical Equilibrium Compositions, Rocket Performance, Incident and Reflected Shocks and Chapman-Jouguet Detonations" NASA SP-273 1967 3. Huang D. and "Design of Liquid Propellant Rocket Engines" Huzel D. NASA SP-125 1971 4. Sutton G. "Rocket Propulsion Elements" John Wiley & Sons 1986 5. Clayton A. " Pressure Vessel and Fairing Design for the Heiland T. AUSROC III Amateur Rocket System" Reddon G. University of Adelaide, Project Thesis 1991 6. Williams W. "Propellant Injector Design Notes for Ausroc III Liquid Fuelled Rocket" Ausroc Conference 1991 7. Simmonds S. "Ausroc III - Flight Management System" Technical Note 1993 8. Cheers A. "Ausroc III - G N & C" Technical Note 1993