DARPA is still considering scramjet propulsion, with particular emphasis of universal turbojet-scramjet type, as future for missiles and space vehicles.
It is not very hard to spot difference between technologies and general trends in USA civilian and military. It is result of different perspectives of NASA and US Air Force, different objectives and different methods for achieving different goals. But for the long years, general trends of development were rather close; both military and civilian space program were source of innovative ideas and conceptions which were flowed smoothly between NASA and military. Many projects were cooperation between NASA and military think-tank DARPA. Like one of most advanced in development project of Rockwell X-30 spaceplane, which was ultimately developed as launch vehicle, hypersonic plane and spaceplane. It was ambitious program developed and funded by NASA and the United States Department of Defense. Civilian and military financial engagement was equal and divided by following agencies and authorities: NASA, DARPA, the US Air Force, the Strategic Defense Initiative Office (SDIO) and the US Navy. Unfortunately it was one of the last cooperation between NASA and DARPA in large project. NASA left behind concept of the spaceplane and started to merely relying on conventional solutions like Space Shuttles and rockets; but DARPA did not resigned so easily and consequently developed conception of spaceplane. Eventually it gave results in successful X-37 unmanned spaceplane by Boeing, which have been utilized in various confidential missions since 2010.
New budget request of DARPA for 2017 is confirmation of own way of development and thinking about priorities in of the space program for Department of Defense. Big goals and deep space exploration were left for NASA definitely. There are no ideas like military space stations or new concepts of cooperation with NASA. Military space program is no-nonsense; is fully oriented on keeping dominating position of USAF in the world, any concepts which are not giving good chances for success will be abandoned to the favor of more promising projects. There is no place for “perhaps” in this budget. One of the first signs of big changes was canceling promising ALASA program. It was rocket which could be launched from conventional jet fighter and lift to orbit small satellites. Project was finally abandoned in the end of 2015 (You can read more here) after earlier statements about keeping ALASA in schedule. But economy won – there is not enough money to support programs which are generating costs without big chances for success (ALASA had continuous problems with fuel system). DARPA has now more ambitious and definitely clearer objectives: scramjet propulsion. Now it should be questioned not why, but why it was decided so late. After announcement of China about their first scramjet experimental plane success in October 2015 (read more here), about continuous development of British Skylon (appropriate post You can find here) and about Indian RLV project which will be starting tests this year (read more here) it seems that only Roscosmos, with shrinking budget and general economic problems, is not developing own scramjet program. Scramjet, which could be propulsion for launch vehicles, spaceplanes and missiles; revolutionary propulsion for using in atmosphere and in space. One engine, one fuel, one plane for both space and airborne missions.
Now it is time for facts about 2017 DARPA budget request and scramjet propulsion. First of all we have Advanced Full-Range Engine (AFRE) and turbine-base combined-cycle (TBCC) engine project. It is idea similar to British RB545 engine – one engine working in turbojet and scramjet mode with one fueling system. For preliminary phase of AFRE/TBCC DARPA will request for $9 million. Generally AFRE is continuing of halted in 2011 Mode Transition project. This propulsion will be part of the new strike vehicles with long range and ability for space strike. It could be vision of new strike fighter which could attack targets on Earth, in the air and in space by surprise with high speed without necessity of slowing during targeting and attacking. Such fighter would be integrated fighter and ASAT weapon, easy to use and remain under tactical command. Next project is Hypersonic Air-breathing Weapon Concept (HAWC) – long range strike cruise missile with hyperspeed ability. For this project DARPA would like to get $49.5 million to complete demonstrator for ground tests in 2017. For 2017 DARPA is also planning Tactical Boost Glide (TBG) – hypersonic missile launched from air which will accelerate to 5 Ma and next glide to the target (HAWC and TBG became more known in 2014). TBG would give possibility to create fully stealth hypersonic missile – one of biggest issues in stealth technology is working propulsion which is easily spotted by radars. TBG is planned as compatible with Air Force and Navy systems. Next project which is still developed is XS-1 spaceplane. Scheduled with request for $50.5 million project is alternative and cheaper launch vehicle for small satellites. Conception is developed by three contractors: Boeing, Northrop Grumman and Masten Space Systems. In August 2015 program entered in phase 1B and companies were awarded with $6.5 million each for further development. As we can see, DARPA is putting stress of scramjet propulsion but still it is only budget request. Congress could demand additional changes or even would like to choose different priorities. Still it seems that we clearly know what are general objectives in developing future vehicles for US Air Force – vehicles, because it seems that they would not be called “planes” anymore.