NASA will revisit an engineering technique which could solve many of the problems associated with hypersonic flight, according to reports. The research might offer genuinely re-usable space launch vehicles, among other benefits.
At present, the only method humanity has to accelerate things up to the Mach 25+ speeds required to reach orbit is the use of multiple rocket stages. As a result, launch costs are high and only a few things are thought worth putting into space: satellites, space probes, and nuclear warheads, mostly.
More: http://www.theregister.co.uk/2007/12/03/mhd_turbo_jet_nasa_ajax_research/