Military-Grade Awesome, Prototypes and Experiments, Technostalgia

Cool Nights and Hot (Lifting) Bodies

Every pixel in this image is cooler than you.

You know, because the edge of space is cold, and the friction of reentering the atmosphere causes a lot of heat. Get your minds out of the gutter, folks, and harken to the tale of the HL-10, a fantastic design from the best toyshop in all of America: the Northrop Corporation.

Yes, that Jack Northrop, the AtomicToasters posterchild of manic aircraft. Northrop’s hangers were an island of misfit toys to rival only Lockheed’s subsequent Skunkworks for industrial-grade airborne excitement. Not familiar with Northrop’s creations? By all means, read up on them on your own, but also watch this space for more nutso planes. But back to the issue at hand – you want a plane to go into space. Simple enough, right? Pop a Bell X-1 on a big enough missile and you can go anywhere you want. The problem is coming back down. As I mentioned earlier, atmospheric reentry can make a vehicle hot and bothered – so much so that a relatively small hole can destroy an entire spacecraft by allowing superheated gases to melt structural components. The heat and stresses involved are hell on a wing, and trying to design a normal airplane wing (think of a typical jetliner’s swept wing) to survive, let alone properly maneuver, in such extreme circumstances is enough to make an engineer cry. So who needs wings? Ditch ’em. Enter the lifting body.

The HL-10 wasn’t the first lifting body ever designed, but it was the most successful. The idea had also been around since the ’20s, so it wasn’t a new principle. However, it’s a hell of a lot harder to get a lifting body airframe to fly straight and not cartwheel into the ground than a traditional winged aircraft. So with little compelling need for terrestrial craft to adopt the full lifting body configuration, it took until the era of spaceflight for it to, erhm, take to the wing. The strength inherent in concentrating the aerodynamic lift in a stout lift-body rather than spindly wings should be obvious, and that’s why NASA looked to the lifting body as a possible reusable spacecraft.

The HL-10 was designed by NASA and built by Northrop, and flew from 1966 to 1975 to evaluate the concept. Packing 4 throttle-able rockets providing 400 lbs of thrust, the HL-10 eventually acheived the ultimate speed (Mach 1.86) and altitude (90,030 feet, or about 17 miles) in the program. However, that was far short of the 50 miles (264,000 feet) required to be certified as an astronaut by NASA, and even further under their specified reentry height of 76 miles (401,280 feet). Then again, that was with the onboard rockets, after being dropped from a B-52 at about 45,000 feet, and the HL-10 was never intended to evaluate the single-stage-to-orbit concept. It did almost fly in space though, with the support of Wernher von Braun and some of the engineers on the project. The idea was to fit the HL-10 with an ablative heat shield and orbital maneuvering apparatus, strap it to a Saturn V, and rocket the thing into space. Von Braun loved the idea, NASA did not, what with the Apollo program winding down and Saturn Vs being rather expensive. So it never happened. But the data gained from the HL-10 proved useful in designing the Space Shuttle, although that aircraft reverted to a delta-wing design, reputedly because it was too tough to bolt a cylindrical tank to the lifting body’s curved underbelly.

I’m not sure that’s the only reason. It’s more likely (and suggested by some sources) that the delta wing gave the Shuttle a greater ability to reroute to alternate landing sites. Whatever the reason, the lifting body hasn’t left the mind of aerospace engineers, cropping up again and again in reusable space vehicle designs. Maybe, at some point in the distant future, lemurs will decipher our primitive scribblings and revive the concept.