DARPA demonstrators among developments discussed at Canberra conference
Details of thermal protection system (TPS) technologies for the US Defense Advanced Research Projects Agency's Falcon hypersonic technology demonstrators have emerged as a Lockheed Martin-led team prepares to fabricate the first aeroshell for its test vehicle.
The Falcon programme is developing technology for a prompt global strike system using hypersonic unmanned vehicles capable of reaching anywhere in the world in 2h. It requires reusable TPS materials that can withstand the heat of extended hypersonic cruise.
Lockheed's team is taking existing high-temperature materials - mostly silicon carbide and carbon-carbon composites - and improving them with coatings. "The contractors are tweaking current systems," said NASA Langley Research Center-based TPS and hot structures expert David Glass at this month's Canberra conference organised by the American Institute of Aeronautics and Astronautics and the Australian Hypersonics Initiative.
One way to improve the oxidation resistance of silicon carbide, for example, is to vacuum-impregnate its surface with a pre-ceramic polymer. With this type of coating and combinations of substrates, the Falcon TPS is expected to operate from 10min to 1h in temperatures exceeding 1,650°C (3,000°F) and be reused up to 10 times.
Glass said cutting-edge TPS candidates such as carbon nano-tubes were rejected because of low maturity. Mature systems are being enhanced for the first unpowered demonstrator, Hypersonic Test Vehicle (HTV)-2. HTV-1 was cancelled this year.
HTV-2 will have a carbon-carbon aeroshell with sharp leading edges and a warm insulating structure that can withstand 1,090°C for 1h, compared with 980°C for today's materials. HTV-2 is due for launch by Orbital Sciences Minotaur booster in late 2008, and will end its flight by crashing into the sea. A reusable HTV-3 will be designed to return to a runway landing.
The Skunk Works-led team, meanwhile, has ground tested an inward-turning, or axisymmetric, scramjet inlet under the Falcon combined-cycle engine technology programme.
Source: Flight International
