It鈥檚 the ultimate adrenaline rush鈥攁 sky dive from space. The challenge
is to re-enter the Earth鈥檚 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鈥檚 technology and that it鈥檚 only a matter of
time before the first space divers return from orbit鈥攎inus their
spacecraft. There is even a name for this new pastime. 鈥淥rbital surfing is what
I call it,鈥� 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.
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Although 30 kilometres isn鈥檛 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鈥攖he 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鈥檚 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? 鈥淚t鈥檚 a very tough problem
without a vehicle around you,鈥� says John Muratore, programme manager for the
X-38, NASA鈥檚 prototype crew rescue ship for the International Space Station.
That didn鈥檛 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鈥檚 back and
sides but left their front exposed. General Electric鈥檚 literature from the time
reads: 鈥淎lthough engulfed by flames, no heat reaches the astronaut鈥檚
body鈥攑rotected by the insulating plastic foam and his spacesuit.鈥�
NASA wasn鈥檛 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 掳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 脿 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鈥� logos on. But in a convenient
twist for advertisers, engineers say they could reduce heating by spreading the
jumper鈥檚 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鈥檚
horizon and figure out when to fire the retro rockets to begin the descent.
鈥淓yeballing direction is kind of hard. You鈥檇 probably look for a landmass. When
Abu Dhabi is straight down, you would fire your motors,鈥� 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. 鈥淭he skill would be how well you could aim the
thing without some radio gyroscope,鈥� McKinney says. The person who landed
nearest a target would win a cash prize. He compares the sport to a yacht race:
鈥淵ou can鈥檛 put it on autopilot. The skill is in deciding how to steer the boat,鈥�
he says.
But hitting a target is the least of an orbital surfer鈥檚 worries. The shuttle
heats up to 1700 掳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.
鈥淭he trick is to come down very slowly from high altitude,鈥� McKinney says.
鈥淵ou can glide along the top and radiate the heat so that it never gets too
hot.鈥� However, the surfer would have to survive temperatures up to 1000 掳C,
as well as forces of up to 8 g鈥攅ight times the Earth鈥檚
gravity鈥攆or 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 鈥渃ords鈥�
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. 鈥淵ou鈥檙e screaming back in. You can鈥檛 feel how fast you鈥檙e going
until you start hitting the atmosphere. You鈥檙e going to torch soon after,鈥� says
Jeff Bull, a materials engineer at NASA鈥檚 Ames Research Center near Mountain
View.
If anything, Bull thinks a dish-shaped heat shield without any parachute
might be better. 鈥淎 guy just sits behind it in a harness,鈥� 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鈥檛 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鈥攁nd a one-way
ticket is not likely to be any cheaper.