November 26, 2012
Credit: Credit: University of Queensland
Guy Norris Los Angeles
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.