168 P H V SIC S OF THE IMPOSSIBLE
ize the way we view space travel. With a simple push of an elevator
button, one could in principle take an elevator ride into outer space for
the price of a plane ticket.
But formidable practical hurdles have to be solved before we build
a space elevator on which we can levitate our way into heaven. At present pure carbon nanotube fibers created in the lab are no more than
15 millimeters long. To create a space elevator, one would have to create cables of carbon nanotubes that are thousands of miles long. Although from a scientific point of view this is just a technical problem,
it is a stubborn and difficult problem that must be solved if we are to
create a space elevator. Yet, within a few decades, many scientists believe that we should be able to master the technology of creating long
cables of carbon nanotubes.
Second, microscopic impurities in the carbon nanotubes could
make a long cable problematic. Nicola Pugno of the Polytechnic of
Turin, Italy, estimates that if a carbon nanotube has even one atom
misaligned, its strength could be reduced by 30 percent. Overall,
atomic-scale defects could reduce the strength of the nanotube cable
by as much as 70 percent, taking it below the minimum gigapascals of
strength necessary to support a space elevator.
To spur entrepreneurial interest in the space elevator, NASA is
funding two separate prizes. (The prizes are modeled on the $10 million Ansari X-prize, which successfully spurred enterprising inventors
to create commercial rockets capable of taking passengers to the very
edge of space. The X-prize was won by Spaceship One in 2004.) The
prizes NASA is offering are called the Beam Power Challenge and the
Tether Challenge. In the Beam Power Challenge, teams have to send a
mechanical device weighing at least 25 kilograms up a tether (suspended from a crane) at the speed of 1 meter per second for a distance
of 50 meters. This may sound easy, but the catch is that the device cannot use fuel, batteries, or an electrical cord. Instead, the robot device
must be powered by solar arrays, solar reflectors, lasers, or microwaves-energy sources that are more suitable for use in outer space.
In the Tether Challenge, teams must produce 2-meter-long tethers
ize the way we view space travel. With a simple push of an elevator
button, one could in principle take an elevator ride into outer space for
the price of a plane ticket.
But formidable practical hurdles have to be solved before we build
a space elevator on which we can levitate our way into heaven. At present pure carbon nanotube fibers created in the lab are no more than
15 millimeters long. To create a space elevator, one would have to create cables of carbon nanotubes that are thousands of miles long. Although from a scientific point of view this is just a technical problem,
it is a stubborn and difficult problem that must be solved if we are to
create a space elevator. Yet, within a few decades, many scientists believe that we should be able to master the technology of creating long
cables of carbon nanotubes.
Second, microscopic impurities in the carbon nanotubes could
make a long cable problematic. Nicola Pugno of the Polytechnic of
Turin, Italy, estimates that if a carbon nanotube has even one atom
misaligned, its strength could be reduced by 30 percent. Overall,
atomic-scale defects could reduce the strength of the nanotube cable
by as much as 70 percent, taking it below the minimum gigapascals of
strength necessary to support a space elevator.
To spur entrepreneurial interest in the space elevator, NASA is
funding two separate prizes. (The prizes are modeled on the $10 million Ansari X-prize, which successfully spurred enterprising inventors
to create commercial rockets capable of taking passengers to the very
edge of space. The X-prize was won by Spaceship One in 2004.) The
prizes NASA is offering are called the Beam Power Challenge and the
Tether Challenge. In the Beam Power Challenge, teams have to send a
mechanical device weighing at least 25 kilograms up a tether (suspended from a crane) at the speed of 1 meter per second for a distance
of 50 meters. This may sound easy, but the catch is that the device cannot use fuel, batteries, or an electrical cord. Instead, the robot device
must be powered by solar arrays, solar reflectors, lasers, or microwaves-energy sources that are more suitable for use in outer space.
In the Tether Challenge, teams must produce 2-meter-long tethers