DARPA: You didn't think we could make a Mach 6 spaceplane, so let us have this MACH TEN job
Cheap rockets? Bah! Give us a hyper-hydrocarbo-scramjet
Gutsy effort by DARPA ... but will it really be worth doing?
A Mach 10 plane capable of rapid turnaround between missions will need to be pretty tough to resist the heat generated as it bores through the atmosphere at hypersonic speed. In DARPA's view this will be pretty much as bad as the frying the space shuttle used to suffer and the X-37B still does. The XS-1 will need "low-maintenance thermal protection systems that provide protection from temperatures and heating rates ranging from orbital vacuum to atmospheric re-entry".
Should the XS-1 project, unlike most DARPA drawing-board outings, reach the stage of an actual flying testbed, the aim is to achieve ten flights in ten days. At least one of these flights should see the plane hit Mach 10, and at least one of them should see a payload of 3,000-5,000lbs placed into orbit.
And engines like this - but twice as fast
As far as space delivery goes, this effort is somewhat reminiscent of other winged-first-stage efforts like the Pegasus rocket and its airliner launch platform, or the planned Stratolaunch scheme, featuring a much bigger rocket carried by a colossal six-engined monster jet. However, DARPA's XS-1 would see much more of the job done by the hyperplane first stage, leaving much less work for the rocket second stage to do. The warboffins think that this might let the XS-1 put stuff into low orbit for as little as $1,000 per pound.
Oh, and a heatshield like this
By comparison, Elon Musk today offers lift to low orbit at about $2000/lb on his Falcon 9 rockets. He expects to get that down perhaps as far as $700 on the upcoming Falcon Heavy, which will be the most powerful rocket in service worldwide when it arrives - possibly as soon as next year. And this is without any re-usable Grasshopper tech as yet. The ambitious space kingpin has stated previously that he thinks $500/lb is "very achievable".
So it would seem that even if DARPA can make the huge technical leaps required for Mach-10 hydrocarb hyperjets and easily-reusable heatproof aeroshells, the agency may find itself left behind on cost by comparatively simple kerosene rockets.
However DARPA says this isn't just a space launch system, it's an attempt to build basic technologies:
The long-term intent is for XS-1 technologies to be transitioned to support not only next-generation launch for Government and commercial customers, but also global reach hypersonic and space access aircraft.
And in any case, as the XS-1 comes from DARPA, the odds are overwhelmingly against it being funded or succeeding if it does. The comparatively simple "Blackswift" plan, which would have produced a relatively modest Mach 6 hydrocarb hyperjet without any space-rocket launch capacity, was stifled by sceptical Washington politicians some years back. The limited success of various hypersonic projects since then wouldn't seem to have changed the landscape enough to mean a different fate for the much more ambitious XS-1.
Though the project will be classified as a military secret, like all advanced US aerospace projects, more information may be forthcoming in further public announcements. We'll keep you posted if so. ®