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Two methods can be used to achieve the Vulcan hypersonic engine

DARPA held an industry day where it outlined some of its plans for hypersonic aircraft of the future. The program being shown off at the industry day was the DARPA Vulcan project. The project centers around developing an aircraft that uses a constant volume combustion (CVC) engine capable of flight at speeds from a standstill to Mach 4 and over.

Aviation Week’s Ares blog reports that the first part of the program was an introduction to the problem the program faces -- how exactly to accelerate an aircraft from a stop to speeds fast enough to activate a supersonic-combustion ramjet.

The program has some interesting slides and information (PDF) from the famed Lockheed Skunk Works HTV-3X flight demonstration vehicle that was conceived as part of the DARPA Falcon program. One of the slides gives an idea of the size of the HTV-3X vehicle by comparing it to the Have Blue aircraft that ended up being about 60% of the F-117 stealth fighter.

The Lockheed HTV-3X vehicle itself has been superseded by the DARPA Blackswift hypersonic program DailyTech has covered before. The engine that DARPA envisions for the Vulcan project is a CVC and turbojet combination.

According to Ares two methods can be used to achieve this type of engine. In one method a common air inlet would be used for both the turbojet engine that is to carry the aircraft from a stop to Mach 4 and higher speeds and the CVC that would take over at propel the aircraft to Mach 6 and over. This method is called turbine-based combined cycle.

The second method to achieve the engine needed is called an annular approach and would embed a turbojet inside a CVC ramjet engine. The big challenge here is that the turbojet would have to be cocooned when the CVC is active to protect it from the high heat produced inside the Vulcan engine over Mach 2.

Because a turbojet capable of propelling a aircraft over Mach 4 would be large and expensive to develop, DARPA instead wants to take a conventional Mach 2 turbojet and combine it with a CVC to get an engine capable of high Mach speeds, but at much cheaper development costs.



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RE: Is that fast enough to reach orbit?
By Mojo the Monkey on 6/26/2008 2:45:59 PM , Rating: 2
No, but it might be the most effective delivery system to take you to the place where air doesnt exist. Once there, like and initial thrust engine, a space propulsion thruster could do the job with MUCH less fuel than it would need if it were air/space dual purpose.


RE: Is that fast enough to reach orbit?
By phazers on 6/27/2008 1:01:20 PM , Rating: 2
Exactly so. IIRC, it was Arthur C. Clarke, the recently-deceased SF author, who first published the idea of a hybrid space-plane (he also first published the idea of telecomm satellites). As I recall, his idea was to mount a rocket-powered plane on the back of an air-breathing lift vehicle which would get above the troposphere where 90% of the atmosphere lies. The end speed of the air-breathing lift vehicle doesn't really matter - it's the air resistance encounted during conventional rocket launch that requires the bulk of the fuel. And by launching west-to-east near the equator, you already gain ~1000 mph due to Earth's rotation. Also, you save the weight of the oxidizer and added propulsion system components such as tanks, plumbing and pumps, needed for a rocket engine.

Unfortunately Werner Von Braun, who favored giant rockets, left his legacy at NASA which is likely why the space shuttle is launched using a huge external fuel tank and SRBs. The entire system has to be strong (& heavy) enough to stand up to the acceleration and pressure encountered at the 'max Q' or transition to supersonic flight.

In contrast, the Bell X1 and later X15 rocketplanes were launched from underneath the wings of bomber aircraft. So what I would imagine for the next-gen shuttle Orion lift vehicle would be something like an upscaled B1 with additional (sc)ramjet engines to kick the final launch velocity up to mach 4 or beyond.


By US56 on 6/30/2008 3:03:18 AM , Rating: 2
In fact, Von Braun was in favor of using a "flyback booster" for the Shuttle. One favored proposal was to use the flight controls, wings, engines, nacelles, and other key components of the Lockheed C-5 and build what would have effectively been a huge flat-bed flying truck. The use of the 747 to launch the Shuttle Enterprise for flight testing evolved from the concept. The design of the tail modification to the 747 Shuttle carrier was borrowed from the twin vertical stabilizer configuration of the proposed flyback booster. The original design of the Shuttle itself was about the same overall size and weight and had the same general apearance as the current Shuttle but the main engine liquid propellant tanks were internal. No throwaway external tank. The SRB's were to have been much smaller so a segmented design would not have been necessary. The SRB's would have been mounted something like the launch configuration of the X-15 for the last series of high-speed tests. The SRB's could have been made recoverable so the entire system would have been reusable. The Shuttle payload bay would have been less than half the size of the current Shuttle, only large enough for one typical communications satellite of the day. The name Shuttle came from the main purpose of the system which would have been to shuttle space station crews or deep space manned mission crews to and from orbit. It also would have performed on orbit maintenance and repair such as has been done for Hubble as well as missions such as refueling KH series satellites which was the original mission of the X-20, conceptually the forerunner to the Shuttle system for which the USAF did not receive funding. The payback from that activity in itself might have paid for the whole Shuttle program since the KH's even then cost $1B or so to build and get into orbit and have a relatively short service life if heavily used without refueling. A separate heavy launch system, most likely the Saturn IB would have been funded. The reason that Shuttle system was not built was Congress did not want to fund the flyback boosters projected to cost $100M for two examples nor the separate heavy launcher at a time before Project Apollo had met its goal and during one of the costliest years of the Vietnam War. Von Braun was so upset about the decision he set his retirement date as a result and never had the same degree of influence within NASA. When I first saw the artist's conception of the current Shuttle launch configuration I thought it was about the most awkward looking vehicle imaginable. The current idiom is, "What were they thinking?" The large, segmented SRB's and foam insulated external tank turned out to be the Achille's Heel of the Shuttle program. Had the original Shuttle system been built, it could have undergone a more evolutionaary development since the major components would not have been so interdependent. Conceivably, we could now be flying a second or third generation Shuttle using the original flyback boosters which should have had an indefinite service life like a B-52H or KC-135R.


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