Are Space elevators a feasible solution for sending
people and goods into space more cheaply?
Abstract
Transporting materials into space has become a regular practice
with inventions like satellite Internet and television. With the everincreasing demand for materials to be sent into space, a cheaper more
economic way of sending things into space has become a necessity. This
paper answers the questions: Are space elevators a feasible solution for
transporting people and goods into space? And, What will it take to
make space elevators a viable option. Through articles and research the
safety issues, technological/ logistical problems and the overall cost
efficiency of space elevators will be analyzed and discussed. The paper
will conclude by stating that space elevators are not an economic
solution for taking people and materials into space and by describing
what needs to happen if they were to be an economic solution.
Introduction
Sending things into space from the earth’s surface is
extremely expensive. Chemical rockets are complicated and dangerous
as well as expensive to build and launch. Space elevators have shown
the possibility of a simpler, safer and cheaper alternative. This is the
main argument for developing an elevator that will take things from the
earth’s surface into orbit. So far technological and logistical roadblocks
have been holding the concept of a space elevator from becoming a
reality. The technology of carbon nanotubes is a ways away from
becoming the 60,000 km tether for the elevator. Finding the funding and
manpower for building such a massive structure in itself will prove to
be a logistical marvel in itself. If the understanding and utilization of
carbon nanotube technology does not improve, and the needs for
massive funding, manpower, and engineering genius are not met, there
will be no space elevator.
The designs and function for a space elevator are discussed in the
next section followed by the pros and cons of using such a space
elevator. Then a conclusion is stated which includes what needs to
happen for space elevators to become a real life solution for bringing
cargo into space.
Space Elevator Design and Function
The main components of a space elevator are: an anchor, a tether,
a climber, and a counterweight (Swan 2006). The anchor of the elevator
should be placed on the equator to maximize the centrifugal force on the
counter weight (Swan 2006)(Wikipedia Contributors H, 2011). The
anchor could be in one fixed position on the equator most likely at a
high altitude position to decrease the size of the elevator, which would
reduce the cost (Wikipedia Contributors H, 2011). It could also be a
heavy seagoing base that could move around to avoid high winds, bad
weather, and space debris (Swan 2006)(Wikipedia Contributors H,
2011).
The tether for the space elevator needs to be incredibly strong
and light at the same time. It would also need to be around 60,000 km
long. A rocket would have to launch into space while the tether was
unspooling to keep the center of mass (Chang 2011). By the time the
tether was done unspooling the rocket needs to be at the final altitude of
the counterweight. Then the tether would need to be connected to the
counter weight and to the anchor.
The climber needs to be able to reach the top of the elevator safely
and within a reasonable amount of time. One was the climber could
ascend the tether would be to crawl up it with tank-like track on either
side (Chang 2011). Another would be a magnetic levitation system,
which would propel the climber up using electromagnetic fields
(Wikipedia Contributors H, 2011). The energy would be sent to the
climber by beaming it from the ground or anchor and collected by the
climber on receptor panels (Swan 2006).
The counter weight would be at the end of the tether and would
keep it taut with the centrifugal force it would generate while orbiting
around the earth. The counter weight would need to be something quite
massive to balance out the weight of the elevator. One idea is to collect
an asteroid and attach it to the end of the tether (Chang 2011). Another
was to build a space station at the end of the tether, which would act as
a dock for incoming climbers and outgoing spacecraft (Swan 2006).
(Wikipedia Contributors H, 2011)
Pros
A space elevator would be cheaper than using chemical rockets.
To build the first space elevator it is projected to cost around 6- 12
billion dollars (Chang 2011). The cost of building any additional
elevators is said to cost around 2 billion dollars each because the
materials to build them could be sent up on the first elevator (Chang
2011). In comparison the Saturn V rocket alone cost 6.5 billion dollars
during its operation between 1964 and 1973 (Wikipedia Contributors E,
2011). Also space elevators would be completely reusable. Once the
elevator was built it would go until a part was broken or worn out.
There would be no need to have expensive booster stages that would be
dropped back down to earth and destroyed once used up (Wikipedia E,
2011). Once the space elevator was built it would be much cheaper to
use continually without much maintenance.
The most expensive part of any space mission using chemical
rockets is getting to Low Earth Orbit. This is because of the earth gravity
and atmosphere. Because the fuel for chemical rockets weighs so much
itself they have to carry a tremendous amount of fuel to be able to lift a
relatively small payload into Low Earth Orbit (Wikipedia Contributors
E, 2011). Also the whole time the rocket is also fighting air resistance
until it leaves the atmosphere, which takes more fuel, which reduces
payload and increases cost per kilogram of the payload. The Saturn V
rocket, one of the most powerful rockets ever launched carried a
payload of around 119,00kg into Low Earth Orbit and cost 1.1 billion
dollars per launch, which comes out to around 8403 dollars per
kilogram (Wikipedia Contributors E, 2011). The cost of sending a
kilogram of payload into Low Earth orbit on a space elevator would be
around $220 per kilogram (Wikipedia Contributors F, 2011). It is said
that a space elevator could carry payloads of 11,193kg per climber and
that up to eight climbers could be sent up the tether at once (Chang
2011).
Many times payloads need to be sent into what is called a
geosynchronous orbit or a geostationary orbit (Wikipedia Contributors
F, 2011). A geostationary orbit allows a satellite to follow a single point
of the earth surface for its entire orbit (Wikipedia Contributors D,
2011). A geosynchronous orbit allows a satellite to oscillate from north
south in a figure eight pattern over a specific area of the earth’s surface
(Wikipedia Contributors D, 2011). For instance satellites used for
satellite TV need to have an orbit that allows them to send information
to its consumers where they live. To achieve a Geosynchronous a
transfer orbit is required to gain the additional altitude needed
(Wikipedia Contributors F, 2011). This in turn takes much more fuel
that reduces the overall payload by a third, and makes the cost per
kilogram much higher (Wikipedia Contributors F, 2011). A space
elevator would eliminate the fuel costs for getting a payload for this
type of mission into Low Earth Orbit. Since there is no gravity and no air
resistance in space cheaper more efficient types of rockets could be
used to bring satellites into geostationary or geosynchronous orbits.
Electrical and nuclear rockets that have extremely high specific
impulses that do not weigh very much could be sent up on the elevator
and used to put satellites into these orbits (Wikipedia Contributors D,
2011).
A space elevator could be much safer in some ways than using
chemical rockets. The climbers would use power beamed from the
ground instead of highly volatile chemicals (Chang 2011). There would
be none of the dangers that you have when you are using chemical
rocket fuel There would be no fuel that needed to be kept in a liquid
state (Wikipedia Contributors E, 2011). You would not have to build a
massive flame trench or have people standing three miles away to
watch it lift off (Wikipedia Contributors E, 2011). There could be safety
mechanisms that would grab onto the tether if something went wrong
with the elevators propulsion system. When something goes wrong with
a chemical rocket during lift off the payload is usually ejected or
destroyed.
There could be less tragic accidents on because an
atmospheric reentry at extremely high velocities would not be
necessary. With a space elevator you would not need to worry about the
intense heat during reentry (Wikipedia Contributors A, 2011). You
would not have to worry about keeping super hot plasma out of the
climber because on the way up and down the elevator it would not go
fast enough to generate that much friction with the air molecules in the
atmosphere (Wikipedia Contributors A, 2011). You would not need to
replace plates from the protective heat shield on a regular basis
(Wikipedia Contributors A, 2011). Another thing that space missions
have chronic issues with is a parachute. A space elevator would need no
parachutes. Instead of hurtling down towards the earth’s surface like a
reentry module it would simply climb back down the tether and avoid
all of the complications of a ballistic reentry (Swan 2011).
Also the space elevator could climb the tether at a much slower
speed so that people would not have to endure such intense G-forces
wile ascending (Wikipedia Contributors G, 2011). During a rocket
launch the G-forces are tremendous. During takeoff on the space shuttle
the astronauts endure G-forces around 3 G’s, and in the Apollo 16 on
reentry the astronauts endured G’s of around 7.19 (Wikipedia
Contributors C, 2011). The speed of the space elevator climbers has not
yet been determined clearly but they would be able to control the rate
of acceleration and deceleration so that the G-forces would be less
extreme. This would allow the less physically fit such as the very young
or elderly etc. to go into space, not just astronauts who are highly
trained and world-class athletes.
Cons
Advancements in many types of technologies must be made
before a space elevator can be constructed. The anchor for the elevator
would most likely have to be a giant ship out at sea (Swan 2006). This
giant ship would encounter tropical storms, which include severe winds
and high waves. The material for the tether of the elevator would needs
to be much stronger than any steel cable and lighter at the same time
(Wikipedia Contributors G, 2011). The best candidate for this material is
carbon nanotubes. Carbon nanotubes are highly conductive and have
incredible tensile strength (Wikipedia Contributors B, 2011). Carbon
nanotubes are pure carbon joined together to make a tube structure
with the atoms in a hexagonal pattern.
When the nanotubes are made they start out extremely short.
Aligning them end-to-end is difficult and not practical for making
nanotubes longer than a few centimeters (NOVA 2007). The longest
nanotube ever made was created by stretching out a bunch of nanotube
fragments in a solvent until it made a long strand, it was still only a
couple of meters long (Bourzac 2011). However the alignment was not
good enough for the strength needed from this material for a space
elevator tether. A method for the mass production of carbon nanotubes
has not yet been discovered (Bourzac 2011). The nanotubes for the
space elevator need to be 22,000 km long and have to be perfectly
linked to maximize the amount of tensile strength (NOVA 2007).
Even if a means of creating nanotubes that are 60,000 miles
long there are still going to be defects within the nanotube material
(Wikipedia Contributrors G, 2011). The strength of the material will be
greatly decreaced if any flaws occur in the nanotube structure
(Wikipedia Contributors G, 2011). The strength of the nanotubes has
been speculated to be less than that of steel cables because of all of the
flaws that are bound be made over 60,000 km of tether (Wikipedia
Contributors G, 2011). By increasing the size of the tether you would
increase the weight and total cost of the structure. A means of creating
nanotubes on a massive scale and with atomic precision must be found
for it to be used on a space elevator.
Although space elevators could be safer than chemical rockets in
some ways they still pose many hazards to their potential users. You run
the risk of planes, satellites, meteoroids, and micrometeoroids colliding
with the elevator (Wikipedia Contributors G, 2011). The tether itself
would be hard to see and would be swaying with the wind. Any aircraft
would have to know where the paper-thin tether was going to be. The
counter weight and the 30,000 plus KM of tether outside of the earth
atmosphere would have to avoid all of the satellites orbiting around
earth (Wikipedia Contributors G, 2011). Because the space elevator
would be constantly orbiting the earth and would always be in space
there is a high chance that a meteoroid would collide with it. Protection
from meteoroids would require more weight and would reduce the cost
efficiency of the elevator. Micrometeorites would constantly bombard
the tether and could potentially weaken it enough over time so that it
would break (Wikipedia Contributors G, 2011). Once again protection
from these micrometeorites would add weight and increase the cost of
construction (Wikipedia Contributors G, 2011).
When the tether is enduring the extreme cold of the upper
atmosphere and when it encounters severe weather systems large
amounts of ice may form on the tether (Wikipedia Contributors G,
2011). Climbers would need to have special systems for clearing the ice
off of the tether in order to climb the tether (Wikipedia Contributors G,
2011). Also vibration harmonics come into play with the tether with the
earth’s winds, magnetosphere and the climbers moving up and down
the tether (Wikipedia Contributors G, 2011). If the vibrations match the
tethers natural harmonic frequency the vibrations may prove to be too
strong and could exceed the tethers tensile strength limits (Wikipedia
Contributors G, 2011). Some vibration dampening systems would have
to be employed to avoid such a problem (Wikipedia Contributors G,
2011).
During the 15-day ride up the elevator passengers and cargo
would be exposed to pockets of radiation in the atmosphere and when
out of the atmosphere it they would be exposed to radiation from the
Van Allen Belts (Wikipedia Contributors G, 2011). If there was not
adequate protection from the radiation the passengers would likely get
sick and the cargo could be contaminated or destroyed (Wikipedia
Contributors G, 2011). The tether for the elevator itself could also be
severely damaged by the radiation, become weak and break (Wikipedia
Contributors G, 2011).
If the tether were to be broken near the anchor it would send the
entire elevator into an unstable orbit and would be extremely difficult to
recover (Wikipedia Contributors G, 2011). If the tether were to be
broken up to around 23,000km then the lower portion would fall back
down to the earths surface and the rest would continue on in an
unstable orbit (Wikipedia Contributors G, 2011). “It is almost inevitable
that some objects --- climbers, structural members, repair crews, etc. --will accidentally fall off the elevator at some point” (Wikipedia
Contributors G, 2011) .If a climber was to fall off under 23,000km then
it would fall off and return to the earth’s atmosphere where it would
burn up and turn to ash (Wikipedia Contributors G, 2011). If the climber
were to detach above 23,000km it would escape into a high elliptical
orbit and would be hurtling aimlessly thousands of miles away from the
earth (Wikipedia Contributors G, 2011).
The climbers would need large amounts of power. Beaming
energy up to the climber from the ground using wireless energy transfer
is the most practical solution so far. Wireless energy transfer only has
an energy efficiency of .5% as of now (Wikipedia Contributors F, 2011).
With such a low efficiency the cost for the electricity of the elevator
alone would be 220 dollars per kg (Wikipedia Contributors F, 2011). IF
the climber cannot get enough energy from the power being beamed up
it may need additional energy that could be collected from solar panes.
This would increase the cost and weight of the climbers and would
make the climbers more dependant on the weather for the lower part
of the assent. If the efficiency of the wireless energy transfer is not
greatly improved the space elevator may need a power plant to be built
to meet its energy requirements (Swan 2006).
Conclusion
Space elevators are not a feasible solution for sending
people and goods into space. There are too many technological and
engineering roadblocks. The challenges of building such a thing are far
beyond anything that has been attempted before. The anchor for the
elevator would be one of the most massive structures ever built and it
would most likely has to be a ship that could move the entire elevator
from the sea. A way to collect a giant asteroid and a way to attach this
giant asteroid to the end of the tether needs to become a real life
possibility for the elevators counterweight. The technology for wireless
energy transfer needs to be greatly improved if the space elevator has
any hope of being a more efficient way of getting things to space. The
technology for the carbon nanotube tether is far from being ready.
Carbon nanotubes need to be made 66,000 km long and on a literally
astronomical scale. Once this is accomplished a way to make this
nanotube tether withstand the harsh weather and temperatures of the
earth atmosphere as well as intense vibrations, radiation, satellites,
meteoroids, and micrometeoroids would need to be found. The climber
must endure these challenges as well but it must also be able to keep
human passengers safe from them. The elevator must protect humans
from intense radiation and the vacuum of space along with the
challenges of the earth’s atmosphere for days on end. These challenges
are too much for the technology that we have at hand at this point in
time. As Dr. Bryan E. Laubscher said, “As soon as we can build it, we
should build it,” (ny times). But as of now a space elevator is not a
feasible solution for sending things into space because we just can’t
build one yet.
References:
Swan, Cathy W. / Swan, Peter A. , 2006
“Why we need a Space Elevator”
http://web.ebscohost.com/ehost/detail?sid=c2c5b5ed-a525-4986a14a99b6eec431dd%40sessionmgr15&vid=1&hid=10&bdata=JnNpdGU9ZW
hvc3QtbGl2ZQ%3d%3d#db=aph&AN=20822893
NOVA Science Now, 2007
“Space Elevator” (Video)
http://www.pbs.org/wgbh/nova/space/space-elevator.html
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