IN 1993, Sotheby鈥檚 of New York auctioned off dozens of artefacts from the
Soviet space program. Among them were a long machete and a fishing kit,
complete with hooks, lines and artificial flies 鈥� the emergency equipment
carried by the two-man crew of Soyuz 22, a space capsule launched in 1976. The
idea was that if the vehicle had to make an emergency landing in unknown
territory the crew could fend off attackers with the machete and survive on
fish until they were found.
At about the time of the auction, the Russian and American space agencies
were putting the finishing touches to an agreement to build the International
Space Station Alpha. The deal included a new role for Soyuz as an emergency
escape module for astronauts while the station is being built. During the four
years that the station will take to build from 1998, a Soyuz re-entry vehicle
will be permanently docked at the station, ready at a moment鈥檚 notice to bring
the astronauts back to Earth in an emergency. But Soyuz capsules can only
survive in space for a short period so Russia will have to provide a steady
supply of replacements.
Three years on, NASA is starting to worry that the Russians will not be
able to meet the demand. Last year, it allocated $3 million to develop
an alternative means of escape called the Experimental Crew Return Vehicle or
X-CRV. But in December, the project ran into trouble when a mock-up crashed
during tests. Since then NASA has found another $8 million to build
another prototype but nobody knows if there will be enough money to build the
real thing.
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Designing an escape module is no easy task. The trouble with Soyuz is that
there is no telling where the bell-shaped descent module will land, since it
cannot be steered once it is inside the atmosphere. Russian cosmonauts have
flown in Soyuz vehicles for almost 30 years, but even today they never know
where they will land if forced to return in an emergency. When the vehicle re-
enters the atmosphere it falls ballistically, like a rock, decelerating only
as a result of friction with the air. At a preprogrammed altitude the vehicle
deploys a parachute and fires retro rockets just before touch-down that soften
the landing.
But even when all goes according to plan, the landing site cannot be
pinpointed exactly. On one occasion, a returning Soyuz vehicle landed on a
hillside and rolled to the bottom. On another, it plunged through the frozen
surface of a lake, leaving rescuers working frantically to free the cosmonauts
from beneath the ice.
Cramped conditions
But the most serious problem is that a Soyuz capsule can survive in space
for only six months. Its attitude control system, which positions the module
for re-entry, uses hydrogen peroxide as fuel and this gradually decomposes
into water and oxygen. Nor are the vehicle鈥檚 battery and cooling system
designed to be reliable over long periods. To cap it all, the capsule is so
cramped that almost half of the American astronaut corps would not fit
inside.
Overcoming these problems for the X-CRV is a task that has fallen to John
Muratore and a small team of engineers at the Johnson Space Center. Their
answer is a vehicle based on an experimental plane called the X-24 which was
built and tested by the US Air Force in the 1960s. The X-24 was designed to
find out whether pilots could safely fly and manoeuvre unpowered vehicles
returning from space. Although it lacked wings, its carefully shaped body
produced aerodynamic lift at high speed. The test pilots of so-called lifting
bodies such as the X-24 pioneered many of the flying techniques now used by
shuttle pilots as they come in to land.
A lifting body is the ideal re-entry vehicle. 鈥淲ith a ballistic re-entry,
you鈥檙e like a cannon ball. Once a cannon ball is launched you have very little
ability to affect its trajectory,鈥� explains Muratore. 鈥淏ut the X-CRV generates
lift and so you can steer it.鈥� Although it has no wings, the pilot manoeuvres
the vehicle using aerodynamic control surfaces around the craft. Two vertical
tail fins turn the vehicle from side to side while flaps on the bottom of the
fuselage move the nose up and down, controlling its angle of descent.
Since it is based on an established design, the craft鈥檚 aerodynamics are
already known. And because the space shuttle was designed using data from
these early lifting body experiments, the flight control system will be very
similar to the shuttle鈥檚. 鈥淲e鈥檙e taking all the equations out of the shuttle
and reprogramming them for the X-CRV,鈥� says Muratore. The flight control
system will be able to determine the craft鈥檚 location using the global
positioning system and automatically approach any one of a number of
preprogrammed landing sites.
Although lifting bodies are ideal for re-entry they make far from perfect
flyers. They are stable at speeds of around Mach 25 but can become unstable at
slower speeds. During a landing, says Muratore, the major worry is that if the
craft is hit by a gust of wind it will start spinning like a top.
In the 1960s and 70s, test pilots managed to land lifting bodies at
subsonic speeds, but it was a risky business and some crashed. When American
TV producers needed an opening sequence for the 1970s series The Six Million
Dollar Man they chose a clip of a US Air Force lifting body tumbling down a
runway. Following these tests, the designers of the space shuttle added wings
to combat the instabilities at slow speed.
Flying into difficulty
In the X-CRV, the aerodynamic flaws of the earlier experimental lifting
bodies are compounded by the extra weight it will be carrying. 鈥淣ow we have
crew cabins, pressurised modules, docking collars and all the things you need
for a spacecraft,鈥� says Muratore. Any extra weight must be compensated for
with increased lift.
In the end, the team had to reject the idea of landing the X-CRV like an
aircraft. Instead, a parachute will open near to the ground. Even this will be
steerable, allowing the pilot to avoid hazards such as rocks and houses. The
X-CRV will touch down at about 3 metres per second. 鈥淓quivalent to jumping off
a desk,鈥� says Muratore.
Rapid return
Unlike Soyuz, the X-CRV will be able to glide for up to 1000 kilometres
after entering the atmosphere and this manoeuvrability greatly reduces the
time it would take to return to Earth in an emergency. 鈥淚f you鈥檙e over the
Pacific, for example, you can fly 700 miles in either direction so you can
land in Hawaii or Asia or Australia or the western US,鈥� says Muratore. At the
very most, the return journey would take 4.5 hours.
The team has also designed the X-CRV to survive in space for up to four
years. Its attitude control system relies on nitrogen, which will not degrade
in space. And whereas 45 per cent of American astronauts cannot fit in Soyuz,
all but the tallest 5 per cent of the population will fit inside the X-CRV.
The engineers have even set up a mock crew compartment at Johnson and
invited the astronauts who train there to check it out.
But not all the problems associated with Soyuz are so simple to solve. For
instance, engineers must develop a way of manipulating the flight control
surfaces that will work reliably even after several years sitting idle in
space. The type of hydraulic systems used in aircraft are out of the question.
鈥淵ou don鈥檛 want to use hydraulics because the fluid will freeze in space,鈥�
explains Muratore. Instead, his engineers are designing a system of wires and
electric motors that will move the vehicle鈥檚 flaps.
The X-CRV also needs a cooling system to dissipate heat during re-entry and
when it is in direct sunlight. Most cooling systems rely on chemicals such as
glycol, an alcohol also used in antifreeze. But these are corrosive so they
cannot be stored safely over long periods.
Muratore鈥檚 solution is to copy the design of the cooling system in the
Apollo lunar module, which is based on water. Apollo鈥檚 cooling system blew
cabin air over a network of pipes containing cool water. The heated water then
passed into a vacuum chamber where it froze and then sublimated into space.
The obvious disadvantage of this system is that the water supply will
eventually run out. However, the X-CRV will carry enough for 12 hours, which
should see the crew safely back to Earth.
Heat shields similar to those used on the space shuttle and the Apollo re-
entry vehicle will also protect the X-CRV from the huge temperatures generated
during re-entry. Engineers are unsure how the tiles will hold up under the
bombardment of tiny meteorites during its years in space. Muratore believes
the answer may be to wrap the vehicle in a protective cocoon made of thermal
blankets which could be removed before use.
The project is less than a year old but has already suffered a serious
setback. In December, a simple mock-up of the X-CRV crashed during a flight
test in Arizona. Engineers were assessing the vehicle鈥檚 basic aerodynamics and
parachute system by dropping it from the back of a cargo plane flying 2.4
kilometres above the desert. But one of the parachutes became entangled and
the vehicle plummeted to the ground.
鈥淵ou couldn鈥檛 see the impact because of the desert scrub. But you could
hear it. It made a big boom when it hit,鈥� Muratore says. 鈥淚t was very painful.
A lot of work went into this and it was all for naught. This was flight
迟别蝉迟颈苍驳.鈥�
Muratore and his team have decided move on to the next round of tests
without repeating the failed flight. They plan to spend $8 million this
year building a more advanced mockup that would include the computerised
navigation and flight control system. In November, they will drop it from a B-
52 bomber cruising at an altitude of 13 kilometres in a series of tests that
will run until spring 1997.
If these tests are successful, Muratore and his team plan to build two
operational emergency vehicles for $70 million. Such a sum will have to
be sanctioned by the US congress. Nobody knows whether it will agree.
In addition, some scoff at that estimate. 鈥淥f course this type of vehicle
will be created, but it will take ten years at least,鈥� says Valeri Ryumin, a
former cosmonaut who works at the Russian space company RSC Energia in
Kaliningrad. 鈥淔or this you will need time and a lot of research and
development. All this will cost a lot of money.鈥� Whether $70 million
will be enough remains to be seen.
In the meantime, the crew of the international space station will just have
to rely on Soyuz to bring them home to Earth in an emergency. After all, any
lifeboat is better than none at all.