Chair Force Engineer

Saturday, March 11, 2006

Somewhere, John Andrews is smiling

Clark Lindsay at HobbySpace has a series of posts (here, here, and here) discussing "Blackstar," a two-stage orbital spaceplane that has been championed by Aviation Week for the past 16 years. The story sounds like "Aurora" under another name. The reaction of several co-workers has been one of amusement; it would certainly solve a lot of our space launch problems if such a system did exist. For me, most of the amusement stems from the fact that Aviation Week's best source appears to be a plastic model kit from 13 years ago.

Back in 1993, the Testors plastic model company unveiled its own "Project Aurora" model kit, based on the eyewitness sightings that contributed to Aviation Week's stories. John Andrews, who designed the kit at Testors, certainly had a keen mind for the design of aircraft. Bearing in mind Lockheed's attempts to launch a Mach 4 drone (D-21, Project Tagboard) from the back of a modified A-12 Blackbird, Andrews created an even bigger, Mach 7 version of the concept. Andrews's "Aurora" consisted of two massive airplanes: the 80' long XR-7 Thunder Dart, and the 160' SR-75 Penetrator mothership. Until the "Blackstar" story was reported, Aviation Week had never made this mothership-daughtercraft connection.

In the speculative model, the SR-75 would carry the XR-7 on its back to high altitudes. From there, the XR-7 would light its "pulse detonation wave engines" and conduct recon missions at Mach 7. After all, reasoned Andrews and other Aurora believers, the Air Force has to have something better than the SR-71 Blackbird. They can't possibly be retiring the SR-71 without something that goes faster!

Of course, there were problems with Andrews's logic.

--The XR-7 would not be carried on the SR-75's back, as this style of carriage wasn't very successful during Project Tagboard (and one of the aircrew involved paid the ultimate price in the ensuing crash.) The daughter craft would almost certainly be carried underneath the mothership, just like X-15+B-52, Pegasus+L-1011, and SpaceShipOne+White Knight.

--Pulse Detonation Wave Engines, to the best of my knowledge, have never gone beyond the developmental stage. Popular Science did a story about Pulse Detonation Engines back in 2003 or 2004, but viewed them as a performance enhancement for existing turbofan engines.

--The SR-71 need not be replaced by a faster plane. In the case of the SR-71, high speed and high altitude were the "survivability conops." In the U-2 and Global Hawk, high altitude is the survivability conops. In the Predator, stealth (being small and flying at low altitudes where radar isn't effective) is part of the survivability conops, although most people aren't very worried about a Predator getting killed in the first place. From where I sit, the Air Force's recon needs look like they are being well-met by existing U-2, Global Hawk, and Predator assets.

--Operational hypersonic systems are very difficult to maintain. The space shuttle is proof of this, although a Mach 7 system might not have the same difficulties that the orbital Shuttle does.

--Andrews proposed an active cooling system using the vehicle's methane fuel. The problem with methane or any hydrocarbon as a coolant is that heat breaks the molecules down, creating the sooty effect known as "coking."

--According to popular lore, Aurora's contrail looks like a string of donuts or sausages. Pictures of this contrail are available on the internet. I must also confess to seeing strange contrails in the sky--coming from behind normal passenger planes. I asked a professor (whose background was in propulsion and computational fluid dynamics) about these contrails, and he asserts that they are produced by traditional engines under certain conditions (a conclusion I fully agree with.)

--Andrews's SR-75 would likely be limited to Mach 2 speeds, if it was powered by four F100 engines like Andrews claimed. It would only have roughly two-thirds the thrust of the XB-70's six J93 engines. It would also lack the optimized design of the XB-70, which relied on downswept wingtips and other features to ride on its shockwave and reduce drag at supersonic speeds. The B-1A, which is smaller than Andrews's SR-75 and had more thrust, was only a Mach 2 airplane (and a freaking awesome one at that.)

Having already scored a commercial success with 1986's "F-19 Stealth Fighter," Testors once again had a model kit that was being mentioned on nightly news broadcasts due to its controversial subject matter. While the SR-75 and XR-7 did not surpass the F-19 model in terms of sales (the F-19 is the best-selling model kit in history,) they are quite large in 1/72 scale and make for interesting conversation pieces.

Today, few people remember the Testors "Aurora" models. The kits aren't in production anymore. John Andrews passed away in April 1999. The name "Aurora" is rarely mentioned, except by people who love conspiracies and spend all day watching the Nevada skies. All of a sudden, Aviation Week is trying to bring it to the forefront again. I can't help but think that John Andrews, from his position in the afterlife, is taking great humor in Aviation Week and the Blackstar believers.