The Aurora is the new jet that people have been saying is the replacement for the SR-71- it is real but it isnt what youd think it is. First a little history.
The U-2 spy plane was essentially a jet powered glider. It had very long wings and a narrow body that could provide lift with relatively little power. It used the jet engine to take it very high into the air and then it would throttle back to near idle and stay aloft for hours. The large wings were able to get enough lift in the high thin air of the upper atmosphere partly because it was a very light weight plane for its size. Back in the early 60s, being high was enough protection but still allowed the relatively low resolution spy cameras to take good photos of the bad guys.
When Gary Powers U-2 got shot down, it was because the Soviets had improved their missile technology in both targeting and range and because, we gave the Russians details about the flight but that is another story. The US stopped the U-2 flights but immediately began working on a replacement. Since shear altitude was no longer a defense, they opted for speed and the SR-71 was born. Technically, the SR-71 (Blackbird) was not faster than the missiles but, because of its speed (about Mach 3.5) and its early attempt at stealth design, by the time they had spotted the spy plane and coordinated with a missile launch facility, it was out of range of the missiles.
The CIA and the Air Force used the Blackbird until the early 1980s when it was retired for spying and used only for research. At the time, the official word for why it was retired was that satellite and photographic technology had advanced to the point of not needing it any more. That is only partially correct. A much more important reason is that the Russians had new missiles that could shoot down the SR-71. By this time, Gorbachev was trying to mend relations with the west and trying to move Russia into a more internationally competitive position so he openly told Regan that he had the ability to shoot down the SR-71 before he actually tried to do it. Regan balked so Gorbachev conducted a “military exercise” in the Spring of 1981 in which the Russians made sure that the US was monitoring one of their old low orbit satellites and then during a phone call to Regan, the satellite was “disabled” explosively.
At the time it was not immediately clear how they had done it but it wasnt long before the full details were known. A modified A-60 aircraft code named “SOKOL-ESHELON,” which translates to “Falcon Echelon”, flying out of Beriev airfield at Taganrog, shot down the satellite with an airborne laser. When Regan found out the details, he ordered the Blackbird spy missions to stop but he demanded that Gorbachev give him some assurances that the A-60 would not be developed into an offensive weapon. Gorbachev arranged for an “accident” in which the only operational A-60 was destroyed by a fire and the prototype and test versions were mothballed and never flew again.
The spy community both the CIA and DoD did not want to be without a manned vehicle spy capability so they almost immediately began researching a replacement. In the meantime, the B-1, B-2 and B-117 stealth aircraft were refined and stealth technology was honed to near perfection. The ideal spy aircraft would be able to fly faster than the SR-71, higher than the U-2 and be more invisible than the B117 but it also had to have a much longer loiter time over the targets or it would not be any better than a satellite.
These three requirements were seen to be mutually exclusive for a long time. The introduction and popularity of unmanned autonomous vehicles also slowed progress but both the CIA and DoD wanted a manned spy plane. The CIA wanted it to be able to loft more sophisticated equipment into the complex monitoring of a dynamic spy situation. DoD wanted it to be able to reliably identify targets and then launch and guide a weapon for precision strikes. For the past 30 years, they have been working on a solution.
They did create the Aurora which uses the most advanced stealth technology along with the latest in propulsion. This, at least satisfied two of the ideal spy plane requirements. It started with a very stealthy delta-wing design using an improved design of the SR-71 engines, giving it a top speed of about Mach 4.5 and a ceiling of over 80,000 feet but that was seen as still too vulnerable. In 2004, following the successful test of NASAs X-43 scramjet reaching Mach 9.8 (about 7,000 MPH), DoD decided to put a scramjet on the Aurora. Boeing had heard that DoD was looking for a fast spy jet and they attempted to bust into the program with their X-51a but DoD wanted to keep the whole development secret so they dismissed Boeing and pretended there was no such interest in that kind of aircraft. Boeing has been an excluded outsider ever since.
In 2007, DARPA was testing a Mach10 prototype called the HyShot which actually was the test bed for the engine planned for the Aurora. It turns out that there are a lot technological problems to overcome that made it hard to resolve a working design in the post-2008 crashed economy and with the competition from the UAVs while also trying to keep the whole development secret. They needed to get more money and find somewhere to test that was not being watched by a bunch of space cadets with tin foil hats that have nothing better to do than hang around Area 51, Vandenberg and Nellis.
DoD solved some of these issues by bringing in some resources from the British and got NASA to foot some of the funding. This lead to the flight tests of the HiFire in 2009 and 2010 out of the Woomera Test Range in the outback of South Australia. The HiFire achieved just over 9,000 MPH but it also tested a new fuel control system that was essentially the last barrier to production in the Aurora. They used a pulsed laser to ignite the fuel while maintaining the hypersonic flow of the air-fuel mixture. They also tested the use of high velocity jets of compressed gas into the scramjet to get it started. These two innovations allowed the transition from the two conventional jet engines to the single scramjet engine to occur at a lower speed (below Mach5) while also making the combination more efficient at very high altitudes. By late 2010, the Aurora was testing the new engines in the Woomera Test Range and making flights in the 8,000 to 9,700 MPH range.
During this same period, the stealth technology was refined to the point that the Aurora has a RCS (radar cross-section) of much less than 1 square foot. This means that it has about the radar image of a can of soda and that is way below the threshold of detection and identification of most radars today. It can fly directly into a radar saturated airspace and not be detected. Because of its altitude and speed and the nature of the scramjet, it has an undetectable infrared signature also and it is too high to hear audibly. It is, for allintents and purposes, invisible.
This solved two of the three spy plane criteria but they still had not achieved a long loiter time. Although the scramjet is relatively fuel efficient, it really is only useful for getting to and from the surveillance site. Once over the spy area, the best strategy is to fly as slow as possible. Unfortunately, wings that can fly at Mach 10 to Mach 12 cannot support the aircraft at much slower speeds especially in the thin air at 80,000 feet.
Here is where the big surprise pops up. Thanks to the guys at NRL and a small contribution I made to a computer model, the extended loiter time problem was something that they began working on back in 2007. It started back when they retrofitted the HyShot engine into the Aurora, then NRL convinced the DARPA program manager to also retrofit the delta wings of the Aurora with a swing capability, similar to the F-14 TomCat. The result would be a wing that expands like a folding Japanese fan. In fast flight mode, the wing would be tucked into the fuselage making the aircraft look like the long tapered blade of a stiletto knife. In slow flight mode, the wings would fan out to wider than an equilateral triangle with a larger wing surface area.
As with any wing, it is a compromise design of flying fast and slow. The swing wing gave the Aurora a range increase from reduced drag while using the scramjet. It also allowed the wing loading to be expanded slightly giving it more lift at slower speeds and in thinner air. However, most of the engineers on the project agreed that these gains were relatively minor and it was not worth the added cost in building and maintenance. This was not a trivial decision as it also added weight and took up valuable space in the fuselage that was needed to put in the modified scramjet and added fuel storage. Outside of NRL, only two people were told why they needed to do this wing modification and how it could be done. Those two were enough to get the funding and NRL won the approval to do it.
What NRL had figured out was how to increase lift on the extended wing by a factor of 10 or more over a conventional wing. This was such a huge increase that the aircraft could shut off its scramjet and run one or both of its conventional jet engines at low idle speeds and still stay aloft even at extreme altitudes. Normally, this would require a major change in wing shape and size to radically change the airfoils coefficient of lift of the wing but then the wing would be nearly useless for flying fast. A wing made to fold from one type wing (fast) to another (slow) would also be too complex and heavy to use in a long-range recon role. The solution that NRL came up with was ingenious and it turns out it partly used a technology that I worked on earlier when I was at NRL.
They designed a series of bladders and chambers in the leading edge of the wing that could be selectively expanded by pumping in hydraulic fluid and expanding these bladders to alter the shape of the wing from a near symmetric chambered foil to that of a high lift foil. More importantly, it also allowed for a change in the angle of attack (AoA) and therefore, the coefficient of lift. They could achieve AoA change without altering the orientation of the entire aircraft this kept drag very low. This worked well and would be enough if they were at a lower altitude but in the thin air at 80,000+ feet, the partial vacuum created by the wing is weakened by the thin air. To solve that, they devised a way to create a much more powerful vacuum above the wing.
When they installed the swing-wing, there were also some additions to some plumbing between the engines and the wings suction surface (upper surface, at the point of greatest thickness). This plumbing consisted of very small and lightweight tubing that mixes methane and other gases from an on-board cylinder with super heated and pressurized jet fuel to create a very high volatile mix that is then fed to special diffusion nozzles that are strategically placed on the upper wing surface. The nozzles atomize the mixture into a fine mist and spray it under high pressure into the air above the wing. The nozzles and the pumped fuel mixture are timed to stagger in a checkerboard pattern over the surface of the wing. This design causes the gas to spread in an even layer across the length of the wing but only for about 2 or 3 inches above the surface.
A tiny spark igniter near each nozzle causes the fuel to burn in carefully timed bursts. The gas mixture is especially designed to rapidly consume the air in the burning creating a very high vacuum. While the vacuum peaks at one set of nozzles, another set of nozzles are fired. The effect is a little like a pulse jet in that it works in a rapid series of squirt-burn-squirt-burn repeated explosions but they occur so fast that they blend together creating an even distribution of enhanced vacuum across the wing.
You would think that traveling at high Mach speeds would simply blow the fuel off the wing before it could have any vacuum effect. Surprisingly, this is not the case. Due to something called the laminar air flow effect, the relative speed of the air moving above the wing gets slower and slower as you get closer to the wing. This is due to the friction of the wing-air interface and results in a remarkable slow relative air movement within 1 to 3 inches of the wing. This unique trick of physics was known as far back as WWII when crew members on B-29s, flying at 270 knots, would stick their heads out of a hatch and scan for enemy fighters with binoculars. If they kept within about 4 or 5 inches of the outer fuselage surface, the only effect was that they would get their hair blow around. The effect on the Aurora was to keep the high vacuum in close contact with the optimum lifting surface of the wing.
Normally, the combination of wing shape and angle of attack, creates a pressure differential above and below the wing of only 3 to 5 percent. The entire NRL design creates a pressure differential of more than 35% and a coefficient of lift that is controllable between .87 and 9.7. This means that with the delta wing fully extended; the wing shape bladders altering the angle of attack and the wing surface burn nozzles changing the lift coefficient, the Aurora can fly at speeds as low as 45 to 75 MPH without stalling even at very high altitudes.
At the same time, it is capable of reducing the angle of attack and reshaping the wing into a chambered wing (a very thin symmetric) shape and then sweeping the delta wing into a small fraction of its extended size so that it can achieve Mack 15 under scramjet power. For landing and takeoff and for subsonic flight, it can adjust the wing for optimum fuel or performance efficiency while using the conventional jet engines.
My cohorts at NRL tell me that the new version of the Aurora is now making flights from the Woomera Test Range in the outback of South Australia to Johnston Atoll (the newest test flight center for black ops aircraft and ships) a distance of 5,048 miles in just over 57 minutes which included the relatively slow speed climb to 65,000 feet. The Aurora then orbited over Johnson Atoll for 5 ½ hours before flying back to Woomera. In another test, the Aurora left Woomera loaded with fuel and a smart bomb. It flew to Johnson Atoll and orbited for 7 hours before a drone target ship was sent out from shore. It was spotted by the Aurora pilot and then bombed by the laser-guided bomb and then the pilot returned to Woomera.
I was also told that at least three of the precision strikes of Al Quida hideouts were, in fact, hit by the Aurora and then credited to a UAV in order to maintain the cover.
The Aurora is the fastest and the slowest highest altitude spy aircraft ever made and if the pilots dont make a mistake, you may never see it.