Ride the Fireball
By Ben lannotta, New Scientist, 31 July 1999
You’ll need nerves of steel, a giant surfboard and $50 million – but you’re guaranteed the thrill of a lifetime, says Ben lannotta
It’s the ultimate adrenaline rush – a sky dive from space. The challenge is to re-enter the Earth’s atmosphere without burning up, to decelerate from an orbital velocity of 27,000 kilometres per hour to the few metres per second needed for a safe landing and to carry out the whole task without spinning out of control. Simple!
It may sound unlikely but a surprising number of engineers, space enthusiasts and would-be daredevils suspect that jumping from a spacecraft and returning to Earth will one day become the ultimate adventure sport. Many say that the challenges can be solved with today’s technology and that it’s only a matter of time before the first space divers return from orbit – minus their spacecraft. There is even a name for this new pastime. “Orbital surfing is what I call it,” says Rick Tumlinson, chairman of the Space Frontier Foundation, a California-based group that promotes space exploration.
Daredevil dive
The record for the highest skydive was set in 1960 by Joseph Kittinger, a captain in the US Air Force. Kittinger jumped out of a balloon at an altitude of more than 31 kilometres to test the equipment and techniques needed to save pilots who might have to bail out of high-altitude aircraft such as the U2 spyplane.
Although 30 kilometres isn’t technically high enough to be considered space, Kittinger was up against many of the problems that face astronauts working in space. He needed a pressure suit, an oxygen supply and protection from solar radiation. All his equipment was automated in case he lost consciousness. After he jumped, there was no whistling wind or flapping clothing – the air is too thin at that altitude. After more than 4 minutes of free fall, having reached a top speed of almost 1000 kilometres per hour, close to the speed of sound at that altitude, Kittinger’s canopy opened, bearing him safely to the ground. The entire dive took 13 minutes and 45 seconds.
Jumping from space is even more ambitious. Soon after Kittinger made his record breaking jump, NASA began to worry about bringing back astronauts from crippled space capsules. If something went wrong with a Gemini or Apollo capsule, how would the astronauts return to Earth? “It’s a very tough problem without a vehicle around you,” says John Muratore, programme manager for the X-38, NASA’s prototype crew rescue ship for the International Space Station. That didn’t stop them trying.
In 1966, the American engineering company General Electric proposed a scheme called MOOSE, which stands for manned orbital operations safety equipment. The MOOSE unit was little more than a Mylar bag with two pockets. The idea was that an astronaut would climb into the front pocket and push away from the disabled spacecraft. A couple of canisters would fill the other pocket with foam. The result was a kind of giant bean bag that enveloped the astronaut’s back and sides but left their front exposed. General Electric’s literature from the time reads: “Although engulfed by flames, no heat reaches the astronaut’s body – protected by the insulating plastic foam and his spacesuit.”
NASA wasn’t so easily convinced. The re-entry angle had to be calculated by eye but if the angle was wrong the astronaut might enter the atmosphere side on and roast in a 1300°C fireball. And even if re-entry was successful, the astronaut could end up almost anywhere on Earth with little chance of being rescued.
MOOSE looked like an accident waiting to happen and NASA soon abandoned the idea of a bale-out system for the Apollo Moon missions. Even if someone did try it, a ballistic trajectory a la MOOSE would not draw many sponsors. Falling through the atmosphere like a glorified meteorite is not very dignified and there would be nothing to paint the sponsors’ logos on. But in a convenient twist for advertisers, engineers say they could reduce heating by spreading the jumper’s mass over a larger area. Ideas range from using a space parachute to strapping the jumper inside an upturned cone.
Bevin McKinney, a rocket designer at the Rotary Rocket Company, favours the parachute idea. The jumper would climb out of the capsule, look at the Earth’s horizon and figure out when to fire the retro rockets to begin the descent. “Eyeballing direction is kind of hard. You’d probably look for a landmass. When Abu Dhabi is straight down, you would fire your motors,” he says.
Surfers would be attached to a mattress-like shield to protect them from the heat of re-entry, and the parachute would be erected in space using inflatable struts. The combination of the large chute and the retro rockets would slow surfers enough for gravity to drag them into the atmosphere.
Navigation would be tricky. “The skill would be how well you could aim the thing without some radio gyroscope,” McKinney says. The person who landed nearest a target would win a cash prize. He compares the sport to a yacht race: “You can’t put it on autopilot. The skill is in deciding how to steer the boat,” he says.
But hitting a target is the least of an orbital surfer’s worries. The shuttle heats up to 1700°C as it enters the atmosphere, and ballistic space capsules, such as Apollo, get even hotter. Those temperatures would easily destroy a parachute. The only way to prevent that would be to re-enter gradually.
“The trick is to come down very slowly from high altitude,” McKinney says. “You can glide along the top and radiate the heat so that it never gets too hot.” However, the surfer would have to survive temperatures up to 1000°C, as well as forces of up to 8 g – eight times the Earth’s gravity – for about two minutes, according to a 1974 paper by two scientists who looked at such an escape system for the Skylab crew.
Even at these relatively low temperatures, the chute would have to be made from heat-resistant ceramic fibres, perhaps similar to those that protect the upper surfaces of the space shuttle, McKinney says. Keeping the “cords” connecting the flyer to the chute cool might be the biggest technical challenge. Sharp edges are more prone to heating, which is why the leading edges of the space shuttle are curved.
Human torch
Of course, if something went wrong, the outcome would make an Evel Knievel crash look tame. The flyer would not know anything was wrong until they reached an altitude of about 90 kilometres, when he or she would start to sweat as the heat mounted. “You’re screaming back in. You can’t feel how fast you’re going until you start hitting the atmosphere. You’re going to torch soon after,” says Jeff Bull, a materials engineer at NASA’s Ames Research Center near Mountain View.
If anything, Bull thinks a dish-shaped heat shield without any parachute might be better. “A guy just sits behind it in a harness,” he says. The dish enters with the surfer protected by their space suit and perhaps some heat-resistant foam similar to that used to retard fire in airliners.
Engineers at the American aviation company Douglas Aircraft came up with just such a concept in 1967 and dubbed it Paracone. It was supposed to land within 800 kilometres of a planned impact point with a peak stress on the astronaut of 24 g. No parachute would be required because the dish included a crumple zone that would absorb the impact when it hit at 42 kilometres per hour.
It might be feasible, but don’t expect orbital surfing to hit your 24-hour sports channel soon. Perhaps the biggest barrier preventing people throwing themselves out of spacecraft is the cost of getting up there in the first place. A return ticket to space costs at least $50 million – and a one-way ticket is not likely to be any cheaper.
Ben lannotta is a space journalist who is based in Florida
Linked from 27/1/2006 Journal