The Space Catapult, anAlternative to the SpaceElevator?

In his novel "From the earth
to the moon" (1865) Jules
Verne, maybe the first SF
author described a giant
cannon with a vertical barrel
of 274m length which sent a manned projectile with
16.5km/s to the moon. Mr.
Verne ignored maybe
knowingly two problems of
this endeavor: 1) The acceleration in the
barrel would be 50 000g. A
person of 80kg mass would
be pressed down with a force
of ca. 4000t. You may
imagine the consequences yourself. 2) After leaving the cannon
the projectile would move
with 16.5km/s through the
air and would behave like a
meteorite. To build a modern and well
behaving space cannon, you
have to overcome these 2
obstacles. 1) You have to reduce the
acceleration by prolonging
the barrel. E.g. to attain the
necessary 8km/s for LEO
(low orbits) with moderate
2.6g, it must be 1250km. 2) The barrel should end
well outside the atmosphere,
about 120km (70miles) high,
so that the projectile
wouldn't lose much of its
precious kinetic energy and be incinerated. To prevent
this to happen already in the
barrel, you must evacuate it. Point 2) implies the good
news that the barrel can be
laid nearly horizontally and
relatively near to the surface
most of its way instead of
vertically, which makes its construction tremendously
cheaper and easier. If the
barrel starts horizontally and
goes on in a straight line for
1250km, its muzzle will be
123km above the surface because of its curvature. The
angle to the surface at that
point is about 11 degrees and
in that direction the
projectile will start rising to
an orbit or farther. Running on the surface for too long
and bending upwards only at
the end would cause
centrifugal forces too high
for passengers. Another
advantage of accelerating horizontally is, that
acceleration of 2.6g and
gravity of 1g don't add up to
3.6g as with vertical starts but
only to ca. 2.8g (Pythagoras).
It is not important to put a lid on the muzzle of the
evacuated barrel constantly,
because there is very little air
up there to fall into it. In realizing this Space
Catapult ("Space cat"), you
have to meet 2 great
challenges: 1) To develop an
electromagnetic drive, linear
motor rail gun, mass driver...
that can accelerate cargo of
maybe up to 10t or more to
desirably far more than 11.2km/s (escape velocity) in
a vacuum tube gliding by
magnetic suspension
(maglev). 2) A construction of several
1000km length going up
from zero to 120km height at
the end to carry the tube.
From the thorough research
on space elevator topics we know, that this is possible
with existing materials and
methods. It could consist for
instance of a long row of
towers, looking like the
highest radio towers: slim masts with guys that are
anchored about as far
sideways as the height of the
tower. The dangers of masts
and guys for aircraft-traffic
must be taken care of. Some advantages of the space
catapult: 1) You can send spacecraft to
any orbit from LEO, MEO to
GEO(stationary orbit) by
varying the firing speed. 2) You can build the space cat
on nearly every place on
land where there is some
1000 km room. It can be
built in your own country; it
need not be placed at the equator and on the water.
The start station can be
situated in a region where
many people live and can get
there easily. E.g. Vandenberg
Air Force Base near Los Angeles and the tube going
to the New Orleans region
(aiming in eastern direction
is advantageous). 3) You can use the space cat
for return traffic from space
to earth too. The projectiles
have to hit exactly the
muzzle of the tube and in the
exact direction (with a little help from laser beacons,
radar and computers). Then
the linear motor acting as a
generator would softly slow
them down and win the
kinetic energy back as electricity. 4) The travel time is
relatively short: about 6
minutes accelerating in the
tube and e.g. 10 min in the ballistic curve going
up to the orbit, where some
steering jets do the exact
positioning. 5) The transport capacity is
unbelievably high. The
container capsules could start
in intervals of seconds or
less, their distance when
leaving the tube would be several km's nevertheless. 6) The building material
need not be brought up to
space first by rockets (ca. 10M
$/t) 7) The vulnerability against
assault is relatively little.
Destroying one mast or one
guy should not crash the
whole structure. To hit a guy
of several cm diameter from the distance is difficult. The
masts are relatively thin too
and guarded by cameras,
radar and trained personnel.
The tube could be hit in the
first several 100 km's before it vanishes in the sky. Then air would flush into
the tube, and stop the nearest
vehicles. To hit a vehicle
itself, going that fast and not
to be seen from the outside is
very improbable. 8) Maybe a much greater
blessing than for space travel
would be the "spin-off" for
terrestrial transportation.
Imagine maglev railways in
vacuum tubes with speeds of thousands of km/h traveling
in hours through whole
continents. When the long
planned bridge over the
Bering Street is built, you
could ride from London to New York on the ground
faster than with an airplane.
Maybe it will be the other
way round: The development
of maglev railgun vacuum
tube transportation technology for terrestrial
uses will make the space
catapult possible. One shortcoming of the
space cat against rockets
shall not be withheld: It can
shoot only at one fixed angle
with the equator. Maybe
other countries will build space cats too, and if they
choose other angles, they can
use their space cats mutually
by international cooperation.
But there is a way to change
the emitting angle of a space cat up to 90 degrees without
additional energy: A tether is
spanned from the muzzle of
the tube to an anchor point
on the surface in 1250km
distance and in a direction at right angles to the tube.
When the projectile leaves
the tube, the tether is
fastened to it, so that it
swings in a huge circular arc.
When the desired direction is attained, the tether is clicked
off. A cord is fastened to the
loose end of the tether to
pull it back fast enough, that
it won't touch ground. You
can install 2 of these tethers on both sides of the tube. The space catapult has been
known for a long time for
use on the moon (and maybe
other planets) and there was
never any doubt about its
feasibility. But on the moon it would be much easier to
build: You don't need a
vacuum tube, the escape
velocity is lower (only
2.4km/s) and the rail could
be laid on the surface on the whole length. At the end the
rail has to hold the projectile
down against the centrifugal
force. Maybe the great
spaceships for future
interplanetary or even interstellar travels will be
produced or put together on
the moon and in moon
orbits, transportation up and
down done by the rail gun.
Even hydrogen and oxygen as rocket fuel can be
produced on the moon, if we
find water there. The energy
stems from solar panels
during the half-month-day
of the moon. A space elevator on the
moon is only suboptimal:
The moon stationary orbit
(MSO) is very high up
because of the slow rotation
of the moon. One could use the Lagrange point/libration
point L1 between earth and
moon instead, which is
"selenosynchronous" too.
But being 58 000km (58Mm)
above it is even higher than the GEO. A nice future vision as a
farewell: With costs reduced
drastically an ordinary
family can do a trip to the
orbit by space cat on its free
day. They reside for some hours in the LEO satellite
hotel, turning slowly around
its axis to give the substitute
of gravity and after going 1
or 2 times around our planet
return home contentedly. Steffen Kummerow studied
physics at the Universities of
Hamburg and Karlsruhe, got
his diploma at the Nuclear
Research Center of
Karlsruhe KFZK and worked in future research
and in teaching. He has been
a dedicated follower of
serious and hard core Science
Fiction all his life. Article Source: http:// EzineArticles.com/?
expert=Steffen_Kummerow