A Discussion Paper on the ASRI /UQ Scramjet Program By W.R. Williams ASRI Director Scramjet Program Co-ordinator 1. Introduction Scramjet powered vehicles theoretically provide a low cost alternative to conventional rocket technology for placing payloads into low earth orbit, and to propel hypersonic flight vehicles such as America's National Aero-space Plane. Consequently, world attention has focused for many years on development of a scramjet to a functioning prototype stage. The scramjet, otherwise known as the supersonic combustion ramjet differs from the traditional ramjet in that fuel injection and combustion takes place at supersonic speeds. The main advantage of this propulsion system is that the oxygen required for combustion is obtained from the atmosphere, thereby eliminating the need for oxidiser carriage. This feature has benefits in that the vehicle fuelled mass and structural mass can be reduced, resulting in considerable performance improvements and cost savings. Research on scramjet propulsion has been undertaken at the University of Queensland (UQ) over many years. It is only recently that the AUSROC Projects Group, now ASRI, expressed interest in developing a free-flight prototype vehicle in collaboration with the University of Queensland. The primary objective of the ASRI/ UQ collaborative program is listed below. * To develop, manufacture and test a free-flight scramjet prototype with the purpose of gaining and extending the knowledge of supersonic combustion ramjet technology. The ASRI/ UQ concept involves the development of an ablatively cooled scramjet prototype to be mounted on top of a suitable solid rocket booster. The scramjet is accelerated to a velocity of approximately Mach 4 to allow supersonic combustion, thereby allowing measurement of performance parameters. 2. Summary of 1992 Undergraduate Projects The first series of ASRI/ UQ scramjet projects were initiated in 1992 as a request to further develop the extensive research undertaken by the University of Queensland. This developmental work took the form of six undergraduate projects investigating various aspects of a proposed rocket boosted amateur scramjet. The six undergraduate projects are listed below. 1. The Design of Intakes and Leading Edges for an Amateur Scramjet. 2. Structural Design of a Scramjet. 3. Fuels for an Amateur Scramjet. 4. Flight Dynamics and Trajectory Analysis of an Amateur Scramjet. 5. Ablation of Scramjet Surfaces. 6. The Design of the Combustion Chamber and Thrust Nozzle of an Amateur Scramjet. These projects are based on an ablatively cooled scramjet configuration, which is separated from the rocket after booster burnout. Details of this configuration and others are discussed in the following sections. 3. Scramjet Program Strategic Plan 3.1 Funding Funding is probably one of the major barriers impeding program progress. The financial aspects requires effort in two areas. These two areas are listed below. (i) Procurement of boosters. (ii) Manufacture of scramjet prototype. It is proposed that the manufacture of a scramjet prototype, and the publicity it would attract, would drive the cost effective acquisition of suitable boosters. Therefore, the initial goal of ASRI is to identify and secure a manufacturer of the scramjet prototype. However, it is well known that ASRI cannot depend on large financial support that would make this task very much easier. 3.2 Configuration Design One of the technical problems associated with the scramjet prototype as proposed by ASRI/ UQ, is scramjet flight stabilisation after booster separation. It is proposed that the concept be altered to 'fix' the scramjet to the booster for the duration of powered flight. Thrust and drag measurements can be affected using a conventional load cell arrangement mounted between the booster and scramjet. It is expected that scramjet burn times will be decreased as a consequence. However this design compromise may be compensated by use of high sampling rate data acquisition systems. The scramjet can then be separated after the programmed burn is complete to assist in the recovery of the prototype for post-flight inspection. In order to pursue this flight profile, additional research is required to establish scramjet/ booster performance characteristics based on the selected booster configuration. 3.2.1 Flight Dynamics Further work is required to establish a suitable scramjet flight path based on the proposed performance characteristics of the selected booster configuration. Reference [1] describes the use of the ARE type rocket booster. However, it is unlikely that this booster will available, and therefore it will be necessary to evaluate flight dynamics based on the new booster selection. It is hoped to acquire 'Honest John' type boosters that have become available with the recent disarmament programs taking place in Europe. Detailed information regarding booster performance is difficult to obtain due to the current classified nature of the hardware. Some information has been supplied for flight dynamic modelling [Ref. 1]. However, ASRI will attempt to obtain additional performance specifications and geometrical information for detail design. 3.2.2 Identification of Suitable Boosters Considerable effort has been spent identifying a suitable local source of boosters. All locally available boosters have been found lacking the required performance characteristics, even with the reduction of maximum scramjet payload weight. Many of the configurations evaluated required staging to fulfil the Mach number requirement at burnout. This factor, and the required reduction in scramjet payload weight have deemed the locally acquired booster concept unacceptable for this particular program. As stated in 3.2.1 it has proposed that the 'Honest John' type booster be used, as it appears that this booster may be the easiest to acquire given ASRI's resource constraints. 3.2.3 Recovery System It is proposed that a recovery system be installed to enable post-flight investigation and analysis of scramjet ablation. This recovery system is yet to be defined. However, several undergraduate projects have been undertaken at various Universities to develop payload recovery systems for Ausroc III. It is hoped that the scramjet recovery system will draw on this design knowledge to facilitate low risk development of a scramjet based system. 3.2.4 Data Acquisition, Flight Management and Telemetry Systems A data acquisition system will be required to measure various scramjet performance parameters such as thrust and drag, fuel flowrates, combustion pressures and temperatures at various points in the scramjet cycle, and possibly ablation rates. In addition to the recording of performance parameters, there will be a requirement for an onboard flight processor to monitor and control the scramjet burn program, to initiate the recovery system process and carry out general flight management functions. It is possible that the flight based telemetry transmitter and management system will be manufactured separately, therefore it is proposed to include these units as a stand-alone packages. Obviously ground based telemetry receivers and associated software are required. It is proposed to draw on Ausroc III developed telemetry technology to satisfy both flight and ground based requirements in this area. 3.2.5 Structural Design As stated earlier, his prototype scramjet concept involves a fixed scramjet/ booster configuration for the duration of the scramjet burn. This particular configuration introduces problems with scramjet/ booster interface structural integrity. Further research is required to evaluate the effect of scramjet exhaust impinging on the booster attachments and the influence on any contained instrumentation or systems. 3.3 Procurement of Boosters As discussed in section 3.1, the procurement of suitable boosters is one the more difficult aspects of this program. Not only does ASRI have to source suitable boosters for this program, provisions are required for transport, storage and preparation for launch. Further details of booster procurement are outlined in the following section, Instrumented Range Requirements. 3.4 Instrumented Range Requirements ASRI is presently negotiating with the RAAF to use the Woomera Instrumented Range (WIR) for the Ausroc II-2 launch. It is hoped that the outcome of these negotiations will be known later this year. Even though ASRI is reasonably confident of a positive outcome, this decision will ultimately set a precedent for future range usage. Nethertheless, ASRI will pursue a program of work under the presumption that the WIR will be available. There are many range issues that require addressing. One of the more important issues include transportation and storage of boosters. Arrangements will be required to transport the boosters from their present location, via Adelaide to Woomera for storage and eventual use. Preliminary discussions indicate that a person, or persons representing the supplier of the boosters will be required to accompany the boosters during transit until use, to satisfy international arms control treaties. This will pose major problems both logistically, as well as financially. ASRI is still addressing this issue. The 'Range Safety Trace' and the 'Trials Instruction' are two mandatory documents required to undertake trials at the WIR. The range safety trace is usually prepared by some recognised authority (usually DSTO) and includes an assessment of wind effects, vehicle fin and thrust misalignments and dynamic instabilities. The trials instruction is prepared by an authority approved by the RAAF (usually DSTO), and is generated from an outline submitted by the range user. One of the major impediments to the preparation of these documents is the loss of expertise in the relevant areas of the DSTO due to retirement, rationalisation and restructuring. One solution, that Ausroc has implemented in the past, is to secure the voluntary skills of retired DSTO experts in the relevant areas. Another problem that faces ASRI is the lack of suitably qualified personnel to prepare the boosters for launch. Again it may be possible to convince qualified staff from DSTO to volunteer time for this cause. However, this raises some serious legal concerns due to the hazardous nature of these operations. ASRI will address this issue as the situation arises. The remainder of tasks required to conduct a rocket based flight trial from Woomera can be satisfactorily handled by ASRI. 3.5 Prototype Manufacture ASRI is presently compiling a list of potential scramjet manufacturers. The best option at this stage is the manufacture of the scramjet prototype as a developmental project within an Australian University or Institute of Technology. A preliminary survey of autoclave facilities in tertiary Institutions has revealed that this capability exists in at least one Australian University. ASRI will continue such investigations in the hope that arrangements can be made to manufacture the scramjet prototype as the practical component of an undergraduate project. 4. Future Undergraduate Projects The list of proposed future projects for the 1994 calender year are as follows. This list is by no means complete, nor fully defined at this stage. It is hoped that this project list will provide a starting point for further discussion. a. Scramjet/ Booster Flight Dynamics, Trajectory Modelling and Sensitivity Analysis. b. Scramjet/ Booster Structural Interface Design. c. Thrust Nozzle Design Review. d. Heat Transfer Analysis for Scramjet Interfaces. e. A Proposal for an Integrated Scramjet Recovery System. f. Flight data acquisition, flight management and telemetry systems 5. Conclusions The first series of undergraduate projects associated with the ASRI/ UQ collaborative scramjet program were completed in 1992. These projects have involved the efforts of 6 undergraduate students undertaking research in varied disciplines, culminating in the initial configuration design of a amateur scramjet. It is quite apparent that attempting a scramjet test program of this nature is not only very ambitious technically, but also logistically and financially. The ASRI organisation have undertaken several ambitious rocket programs, with varying degrees of success. However, success depends very much on program objectives. To that extent ASRI has been successful in developing flight hardware to the prototype test stage, giving many students the unique opportunity to develop practical skills and knowledge in various space engineering disciplines. Therefore, as long as ASRI assumes an optimistic approach and continues to promote and encourage space based projects in the Universities, then there will be a strong possibility that successful free- flight scramjet tests will take place. This will require dedicated effort not only from the ASRI team but also support from participating Australian Universities, Government and Industry.