NASA's Mars Science Laboratory will set down on Mars, via a revolutionary landing system dubbed the "sky crane". The idea is to lower the rover from the delivery spacecraft, as the latter hovers above the surface of Mars. Once the rover has landed, the delivery vehicle will touch down at a safe distance.
The idea is cool — but not quite as revolutionary as NASA thinks. In fact, the idea's been around for decades.
More than fifty years ago (about 1959 to be exact), Convair aerospace engineer Krafft Ehricke came up with his remarkable HELIOS lunar spacecraft concept — which anticipated the sky crane in almost every detail.
"HELIOS" stood for "Heteropowered Earth-Launched Inter-Orbital Spacecraft. It was designed to be lofted into space by a first stage consisting of a shuttle-like "rocket-glider". Powered by two conventional chemical rocket engines providing 2,700,000 lbs of thrust, it had a 90-foot wingspan. The pilot of the booster rode in a special capsule that could be jettisoned in case of emergency. The second stage was powered by a nuclear engine. (It was based on an actual nuclear rocket engine, NERVA, that had been tested at Jackass Flats, Nevada. The NERVA program was eventually scrapped in the early '60s.) The complete rocket would stand 200 feet tall, be 20 feet in diameter and weigh 1,800,00 lbs.
The first stage carries the spacecraft to an altitude of 170,000 feet, at which point the nuclear-powered stage separates. The crewed booster then glides back to Earth. After the stages separate, cables attached to the manned section unreel, until the cabin is 1000 feet behind the nuclear rocket. At this point the nuclear engine ignites.
When the HELIOS spacecraft reaches the Moon, the nuclear rocket hovers while the 15,000-lb cylindrical habitat is lowered to the surface. Afterward, the nuclear rocket will travel a safe distance away. The landing procedure is reversed for the return to Earth.
Back in the day when plastic spaceship models were all the rage, Revell put out a nifty kit of the HELIOS (which I'm glad to say I still have!). The model stood nearly 18 inches tall and in addition to a manned cabin loaded with spectacular detail, it could even be lowered by threads unwound (by twirling the nose cone!) from the tips of the nuclear stage's landing legs. This was what God meant space toys to be.