Hypersonic Developments

Alliant Techsystems (ATK) isworking on getting its Thermally Throated Ramjet (TTRJ) onto the X-51B hypersonic demonstrator (paid subscription required) that is due to succeed the X-51A demonstrator (2nd pic down) that will be conducting flights later this year.

The flight weight engine is now in test (see inlet diffuser and combustor combination, top pic), and as opposed to using the rather exotic, and difficult to ignite JP-7 that was used for the SR-71, it uses the more common JP-10 missile fuel, with the fuel cooling the combustor walls and being vaporized prior to ignition.

It's interesting in that the boundary between subsonic and supersonic flow inside the engine is controlled thermally, rather than through inlet geometry, with the heat of forward (subsonic) combustion taking the stream to supersonic speed.

In the meantime, the X-51A scramjet demonstrator appears ti be continuing on both budget and schedule, (paid subscription required) largely because the development team has limited requirement creep and "bleeding edge" technology wherever possible, with a first flight in October of this year.

There are a number of potential technical breakthroughs, a hydrocarbon fuel cooled scramjet, unstable aerodynamics, and long powered flight time (300s as vs NASA's 10s for its X-43-A), but structurally, it's simple, with a tungsten nose cone, aluminum structure, and an old fashioned ablative coating for much of its thermal protection.

Additionally, the 4 planned flight tests are designed to be identical, in order to provide redundancy.

While it's not an issue for the relatively slow (!) Mach 5-6 X-51A, future hypersonic vehicles, which can be expected to exceed Mach 10, will have issues with communication, as the speeds create an ionized sheath around the vehicle that will cause a communications blackout, which makes getting telemetry out of a vehicle problematic.

The potential solutions are interesting, ranging from using lasers or magnets to poke holes in the plasma, dropping capsules with the telemetry as the flight progresses, using the plasma to generate a signal, magnetic fields, etc.