Design refinements packaged into ambitious Australian hypersonic demonstrator
At just over 6 ft. in length, Australia's Scramspace hypersonic demonstrator may seem an unlikely first step toward space, but its diminutive size is inversely proportional to its potential importance as a national research vehicle.
Currently taking shape at the University of Queensland, the Scramspace I (Scramjet-based Access-to-Space Systems) is the Australian Space Research Program's flagship effort. The concept aims to harness the country's growing inertia and expertise in hypersonics and forms an initial experiment on a planned 20-year road to scramjet-based access to space systems.
“We have started working on the assembly,” says Russell Boyce, project director and scientific lead at the University of Queensland. “We have received the main single-piece aluminum inlet/combustor module, as well as almost all of the off-the-shelf components. We are still waiting on some of the machined items,” he adds.
Assembly comes after some refinements to the final tail design to improve vehicle stability during its Mach 8 flight test, which is now on track for 2013. The changes, and more critically the availability of a launch window at Australia's expansive Woomera test range, pushed the flight into next year from the original target date of October this year. That was an ambitious plan, acknowledges Boyce, who says the new schedule gives a little extra margin. “We are still on a tight timetable, but we are on track to fly within three years of the start of the program and we are within budget.”
Six deployable fins in the original design have been replaced with four fixed—but smaller—fins. The overall length of the vehicle has also grown after the decision was taken to elongate the thrust nozzle and stretch the distance between the vehicle's center of gravity and center of pressure. “We did a lot of analysis on what we'd lose and gain with aerodynamics and thrust measurement, but at end of the day we had to get into the window for stability,” says Boyce.
Part of the issue relates to maintaining the stability of the overall rocket-powered stack during ascent as well as the payload on the way down. “We needed pretty chunky fins, but if you do that forward of the stack it could destabilize the whole thing,” says Boyce. Detailed analysis using computational fluid dynamics led to the design of a set of fins “that we could get into the stability window. The DLR (German aerospace research agency) independently checked and they found the same, so we will be stable on the way down.” The fins are provided by DLR's Stuttgart-based Institute of Structures and Design, and will be made of the same carbon and silicon carbide based high- temperature resistant material used on the Shefex II Mach 11 sharp-edge flight experiment.
Changes to the thrust nozzle also partly reflect lessons learned from the U.S. Air Force-led X-51 program. “Eighteen month ago we didn't have a carbon-fiber thrust nozzle, we had a small carbon-carbon unit at the end of the thrust chamber. But we needed to properly seal that to stop any chance of it leaking heat into the vehicle like the X-51,” adds Boyce. The unit, which is made by Teakle Composites, is built using a wound-carbon phenolic resin with data-collecting thermocouples embedded within the structure during manufacture.
Scramspace I's primary role is to test the design and operation of the scramjet engine which operates on the principle of radical farming. In this design, hydrogen fuel is injected from holes in the inlet, rather than in the combustion chamber. Leading-edge shocks are deliberately ingested into the inlet where they interact with other shock waves and expansion fans in the constant-area combustor. The combination produces an area of localized higher pressure and temperatures where “radicals” are formed.
This process not only helps accelerate the ignition process but combustion is achieved at lower mean static temperatures and pressures than would be created in a larger combustion chamber. As radical farming injects fuel in the intake, this reduces the mixing length needed in the combustor, therefore enabling the use of a smaller chamber which also reduces skin friction drag.
Secondary experiments will include a tunable-diode laser flight instrument to measure flow, temperature and possibly angle-of-attack data, as well as the thrust nozzle. Tertiary experiments include ultra-high-temperature ceramic materials made by the Italian aerospace research agency CIRA, as well as temperature-sensitive paints from the University of New South Wales on the inside of the vehicle to provide thermal loads and distribution data post-flight.
Additional materials and propulsion-related flowpath testing continues with international partners. Other Scramspace members include the Universities of Adelaide and Southern Queensland, while government and industry members include the Australian Defense Science and Technology Organization (DSTO);, Aimtek and Teakle. International partners also include the Japanese Aerospace Exploration Agency (supporting optics for the laser experiment), and the University of Minnesota.
To make testing affordable, the project is “piggybacking” off the joint Australian-U.S. HIFiRE fundamental hypersonic research program (see page 42) which is around the halfway point in a multi-year effort involving nine flights between 2009 and 2014. The first opportunity for launch was originally expected to be the seventh HIFiRE experiment in May/June 2013. However, DSTO is now thought to be reviewing the possibility of launching instead on the repeat run of HIFiRE 5 around March-April 2014.
Scramspace will be launched on an S30-Improved Orion two-stage sounding rocket to around 100 km (62.5 mi.) when the deployment sequence will start with a de-spin maneuver and payload separation. The nose cone and starting door covers will then eject, and the vehicle reaction control system activated to position it for reentry and starting the scramjet as it hurtles down at Mach 8 through a test window between 32 km and 27 km altitude.
Testing and assembly is expected to be completed by March 2013, after which the vehicle qualification will take place. Pending a successful effort, the payload will be finalized by the end of May.