Multidisciplinary design and optimisation of a pitch trimmed hypersonic airbreathing accelerating vehicle

Abstract

The global economic environment combined with the rapid pace of technology advancement is placing importance on reducing the size and cost of access to space systems. Based on decades of practical experience with rocket-only launch vehicles, current technology is operated close to theoretical limits and only marginal further improvement is possible. A possible solution is to include an airbreathing stage into the launch system architecture. Performance wise, airbreathing hypersonic engines such as scramjets have an advantage over rocket propulsion in terms of a significantly higher specific impulse in the hypersonic flight regime. A reusable airbreathing stage could contribute to an increase in payload mass-fraction by using scramjet propulsion over a meaningful proportion of the launch trajectory and provides the flexibility of aircraft-like operations while being inherently reusable.Researchers at the University of Queensland investigated the use of a three stage to orbit rocket-scramjet-rocket system for transporting small payloads into LEO. The second stage scramjet powered accelerator of this system was the subject of a series of Multi-Disciplinary Optimisations (MDO) which involved flying complete trajectories. Promising results were achieved however this work did not include the requirement for the vehicle to be pitch trimmed, which is an important aspect which must be addressed.The purpose of the investigation described in this thesis was to gain a better understanding of the impact that the second stage vehicle's planform has on the pitch trim of the vehicle. This was addressed through a numerical study utilising and expanding on the capabilities of the MDO system developed by Jazra (2010) by: i) Defining a more realistic mission of delivering small satellites up to 500 kg into a Sun Synchronous Orbit of 566.89 km altitude suitable for several earth science missions.ii) Increasing the fidelity of the MDO system to enable an accurate estimate of the trim drag. This included refining the vehicle mass model and aerodynamic module updates such as introducing a 2-D aft body exhaust expansion model plus elevon force and pitching moment inclusions.

Adjoint-based aerodynamic design optimisation in hypersonic flow

“…In an effort to make MDO more practical, it is common to apply computationally inexpensive, low-fidelity methods to model the complex physics. For example, the use of panel methods based on shock-expansion theory to evaluate vehicle aerodynamic forces have been applied in several recent MDO of hypersonic vehicles [10,[15][16][17][18]. There is some concern that the reduced fidelity modelling does not adequately capture the complex flow phenomena that form around a hypersonic vehicle.…”

“…This inviscid result took approximately 5 hours to converge on 24 compute cores. If this vehicle was parameterised by 10 design variables, as done in the work by Jazra et al [16,17] and Preller et al [10,18], then one design iteration would take approximately 50 hours using finite differences. This is too prohibitive for vehicle design.…”

Trajectory Optimisation of a Partially-Reusable Rocket-Scramjet-Rocket Small Satellite Launch System

“…However, their development cost is likely to be very high, and they are generally suited for launching large amounts of payload-to-orbit [15][16][17][18][19][20][21][22], a market which is now extremely competitive thanks to the relatively recent advent of large, partially reusable, rocket-based launch systems. Alternatively, the launcher may be separated into multiple stages, similarly to typical, fully rocket-based launch systems [24][25][26][27][28][29][30][31][32][33]. Multi-stage airbreathing launch systems have the potential to bring cost-efficient reusability to small payload launchers [12], particularly if they are able to stage at high speeds [23].…”

“…There are as of yet no airbreathing launch systems that have progressed past the research and very early design stages [15][16][17][18][19][20][21][22][24][25][26][27][28][29][30][31][32][33]. The development and analysis of trajectories is a crucial part of this early design process, and it is a complex task to ensure that an airbreathing launch system is able to survive launch and fly with maximum efficacy.…”

“…Compared to single-stage airbreathing systems, multi-stage airbreathing launch system trajectories are far more complex, with even more complex trade-offs between the operational modes due to these modes being separated into mechanically distinct stages [34]. There is considerable disparity between studies of two-stage-to-orbit airbreathing launch system trajectories, with significant differences in the shape of the airbreathing flight [24][25][26][27][28][29][30][31][32][33]. The return trajectories of two-stage-to-orbit launch systems are generally performed under cruise power, utilising turbojet, or sometimes ramjet engines [24,26,30,31], or alternatively landing at a point downrange [27].…”