Fifty years of hypersonics: where we've been, where we're going

Hypersonic flight has been with us since 22 September 1963, when Robert M. White flew the North American X-15 at 4520 mph at an altitude of 354,200 ft-a Mach number of 6.7! This remarkable achievement was accomplished over six decades due to intensive research and development by a large number of scientists and engineers. In spite of that momentous achievement, designers have found the hypersonic environment to be harsh and non-forgiving. New programs since the 1960s have often uncovered the unknown unknowns, usually the hard way-early flights of new systems have often revealed problems of which the designers were unaware. Such problems include: the ineffectiveness of the body flap for the Space Shuttle Orbiter, the viscous/inviscid interactions produced by the umbilical fairings that damaged the conical section tile protection system of the Gemini Capsule, and the shock/shock interaction that damaged the X-15A-2 when it carried the hypersonic ramjet experiment. In order to continue to make advances in hypersonic flight a sustained and visionary effort is essential to generate required knowledge and technology. In order to better prepare for future developments in hypersonic flight, this article reviews the advances made within the past 50 years and then looks into the future, not just for new technological developments, but for new ways of thinking about the unknown challenges that lie ahead. (C) 2003 Elsevier Ltd. All rights reserved.