fusion powered starship plying it's way to Barnard's Star.
(Copyright Lee Krystek 1996)
Power and propellant are primary concerns when designing
a starship. Too little of either means the vessel will be incapable
of making the immense journey across the interstellar void. Too
much, if it increases the mass of the vessel, may render the ship
too heavy to accelerate to the necessary speeds.
Most spaceships we have today, or envision in the
near future, are designed around a basic principle of physics:
For every action there is an equal and opposite reaction. A jet
plane, by forcing the hot gases of combustion out of the rear
of it's engines, moves the aircraft forward through the air. A
rocket does the same thing, but since it carries both the fuel
and the oxygen to burn it, in internal tanks, the rocket can operate
in the vacuum of space.
In a chemical rocket the fuel provides both the
power and the propellant. As the fuel burns and expands it provides
the power that then thrusts the waste products of the burning
gases out the rear of the rocket. The problem with the chemical
rocket engines we use now is that they are relatively inefficient
and too much fuel is needed to take a ship great distances. New
designs attempt to give spaceships greater range by increasing
the power of the engine without increasing size or mass.
One possible power source for future deep spaceships
may be nuclear reactors. While nuclear fission reactors may produce
potentially hazardous by-products that are environmental problems
on Earth, they do produce a lot of power from a very small amount
of fuel. The amount of uranium used up by a nuclear submarine
traveling around the globe is about the size of a golf ball.
A nuclear fission reactor on board a spaceship
would produce lots of power, in the form of heat and electricity,
but no propellant. In order to make the ship go forward something
must be expelled out the back. Propellant tanks filled with something
inert like xenon would have to be carried on board. The electric
power from the reactor could then be used to force charged particles
(ions) of the propellant out the exhaust and this would move the
ship forward. NASA has a deep space probe in planning using this
design. It would leave our solar system and travel into space
1000 times more distant than the Earth is to the Sun, some 93,000,000,000
miles, to make astronomical observations.
Even with a fission reactor the amount of propellant
needed to push a ship at high speed between the stars is still
a problem. We can lessen the amount of propellant we need, though,
by increasing the speed at which it is expelled while keeping
the spaceship the same size. To increase the exhaust speed of
the propellant requires more power. To increase the power the
nuclear fission reactor can be replaced with a nuclear fusion
reactor. A fusion reactor can generate five times the energy from
the same amount of fuel. The extra power can be used to expel
the propellant faster giving the ship more range or more speed.
Unfortunately, we have yet to figure out how to make a fusion
reaction work on Earth, except in the heart of an H-bomb explosion.
Some fusion spaceship engine designs actually use
many "micro-explosions" to push the vessel forward. Tiny pellets
of helium-3 would be detonated, each a miniature H-bomb, by powerful
lasers 250 times a second. Using a design like this a velocity
of 12.2 percent of the speed of light
might be obtained during an interstellar voyage.
The ultimate power source for a spaceship is a
matter/anti-matter reaction. Often mentioned as the power source
in the popular Star Trek television series and movies,
it really exists. When a matter and anti-matter
particles meet their total mass is turned into energy. This means
that a matter/anti-matter engine would produce two hundred times
the power of a fusion engine for the same amount of fuel.
There may be ways, other than expelling propellant,
we can move spaceships through space. Scientists have speculated
that if we ever gain an understanding of exactly how gravity works,
and how to generate it artificially, we may be able to build "anti-gravity"
engines that would allow a ship to levitate or move away from
a gravity source like the Earth or Sun.
a Balloon Rocket
Different engine designs.
Copyright Lee Krystek 1996.
All Rights Reserved.