A University of Queensland lab has supersonic success.
- By Luba Vangelova
- Air & Space magazine, November 2002
(Page 2 of 7)
With wiry, sandy hair, and blue eyes, the six-foot-three Paull could pass as Christopher Lloyd’s chilled-out, antipodean cousin. Leaning back in his chair, the 42-year-old reflects on his groundbreaking work. Speaking in a broad Aussie accent, he liberally punctuates the tale with rightos and underscores his drier observations with a slightly mischievous smile.
In 1985, after earning a graduate degree in applied mathematics, Paull netted himself a job crunching numbers for Ray Stalker, a University of Queensland space engineer of global renown who had designed and built one of the world’s most sophisticated wind tunnels at the university and used it for pioneering scramjet research. When Stalker suffered a stroke in the 1990s, Paull found himself in charge of the program. Progress remained hampered by a central limitation: Even the university’s most cutting-edge shock wave tunnel allowed a test window of only two milliseconds.
Then opportunity came knocking, in the form of a Florida-based company called Astrotech Space Operations. The company had no interest in scramjets per se; it merely wanted to expand its sounding rocket business (selling cargo space for microgravity science experiments) into the Asia-Pacific region. What better way to make a public relations splash than by carrying “some sexy payload,” in Paull’s words, on the two demonstration flights the company had planned? An intermediary made the introductions, and in 1998 the two parties signed an agreement. Astrotech would provide the Terrier-Orion rockets for two launches; Paull would equip them with a cutting-edge scramjet experiment. The HyShot program was born.
Now the pressure was on: “We had to figure out how to make the engine fly and not fall apart” in a test time window hundreds of times longer than the one available in wind tunnels, Paull says.
Space programs from around the globe have tried to tackle the same perplexing dilemma for decades. The United States and Russia, in particular, have invested millions. What’s the carrot motivating their research? First and foremost, they hope one day to use scramjets as a cost-effective rocket replacement in space launch vehicles. Military planners want to add hypersonic missiles to their arsenals. On the commercial end of things, a scramjet-powered passenger airplane could, in theory, reduce travel time, allowing you to fly from, say, London to Sydney in two hours.
Indeed, eyeing such payoffs, the U.S. government began funding scramjet research in the 1960s; it now sponsors some half a dozen scramjet programs in the Department of Defense and NASA (see “A Matter of Seconds,” p. 76). Since 1994, NASA has worked with the much-lauded Russian program, which has launched some of the most successful tests to date. Today, half a dozen other countries have substantive programs as well.
Yet for half a century the scramjet has remained (excuse the pun) a pipe dream. Putting the simple theory into practice is fraught with engineering challenges. To begin with, there is the difficulty of igniting fuel with air that is traveling at supersonic speed. “It is like lighting a match in the middle of a blowing hurricane,” says Robert Mercier, head of HyTech, the U.S. Air Force’s scramjet program, located at Wright-Patterson Air Force Base in Ohio.
Then there is the heat issue: A vehicle traveling that fast can reach a temperature of 3,600 degrees Fahrenheit—similar to what the Apollo capsule experienced on reentry, and hot enough to warp, if not melt, most materials. (Some researchers are experimenting with heat-absorbing fuels that, prior to combustion, would circulate through channels in the engine walls to cool them down.) Also, to work effectively, scramjets must be integrated with the airframe; how best to do this remains a question.