IN 1964, MOST VIEWERS OF TELEVISED SPACE "SHOTS," AS THEY WERE CALLED THEN, knew what it took to protect a spacecraft from the fire of reentry. It took big, heavy shields bolted to pressurized metal vessels. One of the most nerve-racking moments of the early space program had been the final minutes of John Glenn’s 1962 Mercury flight, when Mission Control waited to learn whether his shield had remained attached to the Friendship 7 capsule during the violent return.
Two years later, on June 10, 1964, another, much lighter vehicle entered the atmosphere with no one on board. In engineering terms it was nearly as daring as the Mercury flights had been. Launched on a sounding rocket to an altitude of 96 miles over New Mexico, the craft dove back toward Earth at a speed of more than 5,000 mph. Being so light, it didn’t generate as much heat from atmospheric friction as Glenn’s capsule had, so it had only a thin coating of thermal protection—no shield. Odder still, it was inflated like a balloon in a Thanksgiving day parade.
The contraption was called IMP, for Inflatable Micrometeoroid Paraglider. It was developed by a team at NASA’s Langley Research Center in Virginia, led by a young project manager named Bill Kinard. Now 71, Kinard is still at Langley as a senior scientist. His paraglider, though, is all but forgotten.
Now engineers on both sides of the Atlantic hope to see a distant descendant of IMP fly. A European-Russian team has built and tested, not altogether successfully, an inflatable reentry vehicle, and has scheduled another test for next spring. So far, their cone-shaped spacecraft appears capable of protecting an instrument capsule on the return to Earth. Designers have big plans for the invention, which has been dubbed Inflatable Reentry and Descent Technology. First, it would return cargo from the International Space Station. Eventually—if formidable technical and even psychological hurdles can be overcome—it could serve as a personal escape pod for astronauts forced to bail out from orbit.
With IRDT, the idea of inflatable spacecraft is experiencing, if not a renaissance, at least a curious second look after decades of false starts and periodic bursts of hot air. “Technically, inflatables are feasible,” says retired NASA futurist Joe Loftus, who once headed the advanced planning office at the Johnson Space Center in Houston. “The question is: What is it that will make them desirable?”
Back in 1962, Bill Kinard thought he knew the answer. His goal was simple: Get something large, light, and cheap up above the atmosphere for just a few minutes, then return it to Earth safely. Scientists wanted to refine their models of meteoroid and micrometeoroid density in space so engineers would know how much protection to install on space vehicles. “We were interested in exposing large areas in space” to see how much bombardment they could withstand, Kinard says.
Rigid metal structures were too heavy and expensive, so Kinard’s team turned to unconventional approaches. Langley had already come up with the inflatable Echo balloon, which had an aluminum-coated Mylar surface that in 1960 was used to bounce radio signals back to the ground. Another group at the center was looking at using a modified Rogallo wing (the famous prototype of the hang glider) as an alternative to parachutes for gently landing a Gemini capsule. To reduce weight, the engineers replaced the wing’s metal struts with long cylinders made of tough fabric, which were inflated with gas until rigid.
Kinard’s team liked that idea, and started working on a paraglider that would be inflated with compressed nitrogen and would have a large surface area that could be covered with sensitive electronic meteoroid detectors. After launch, the paraglider would separate from its carrier rocket, inflate, spend about five minutes getting pelted by meteoroids, then fly back through the atmosphere for a desert landing at the Army’s White Sands missile range in New Mexico.
Early tests were encouraging. “I was amazed that a paraglider with a flexible canopy could fly so well at supersonic speeds,” Kinard recalls. “We did wind tunnel tests, and the [wing] fabric was like a piece of metal—no flutter, perfectly stable.” Flying at up to Mach 8 would generate heat from friction with air molecules, so the glider got a thin coating of silicone over its flexible Fiberglas fabric.
The actual flight of the IMP, on an Aerobee-150 sounding rocket in 1964, had mixed results. The paraglider inflated properly and collected meteoroid data. But the attached rocket nose cone failed to separate before reentry, so the glider began its descent through the atmosphere dragging an anchor. Amazingly, it righted itself and flew briefly, until the aerodynamic pressure got too high. At that point, one inflatable boom burst, probably from the stress of dragging the nose cone, and the IMP dropped to the desert like a wounded duck. It took days to find all the meteoroid collection panels that were torn off the wing as it fell.