2. Praxis Business School
The Space Elevator
A report submitted to Prof. Prithwis Mukherjee
In partial fulfilment of the requirements of the course
Business Information System
On 7th November 2010
By Nahid Anjum
2
3. Index
No. Topic Page No.
1 Abstract 4
2 Introduction 4
3 Space Elevator 4
4 Structure 5
5 How the space elevator will work 7
6 Space Elevator ribbon 8
7 Riding a space elevator to the top 9
8 Transport system for the space elevator 10
9 Delivery capabilities 11
Cost of suggested space transport
10 12
installation
11 Cost of delivery 13
12 Space Elevator maintenance 13
13 Space Elevator impact 14
14 Conclusion 15
15 Reference 16
3
4. Abstract:
At present, rockets are used for launches and flights into space and to carry people and payloads
into space. It is only the source to connect us from space. This method is very expensive, and requires a well
developed industry, high technology, expensive fuel and complex devices. Their major drawbacks are very
high cost of space launching $20,000 – 50,000/kg, large fuel consumption and fuel storage problems because
the oxidizer and fuel require cryogenic temperatures, or they are poisonous
substances. In recent years scientists have investigated a series of new
methods for non-rocket space launch, which promise to revolutionize space
launches and flight. Especially in this area new, cheaper and more fuel
efficient methods are being investigated. Such new methods include the gas
tube method, cable accelerators, tether launch systems, space elevators,
solar and magnetic sails, circle launcher space keepers and more.
Introduction:
Non-rocket space launch is an idea to reach outer space specifically from the Earth‘s surface
without the use of traditional rockets, which today is the only method in use. In the past years the scientists
have published a series of new methods which promise to revolutionize space launching and flight. These
include the gas tube method, cable accelerator, tether launch systems, space elevators, solar and magnetic
sails, circle launcher and space keeper, space elevator transport system, etc. Some of these have the
potential to decrease launch costs thousands of times, other allow the speed and direction of space apparatus
to be changed without the spending of fuel. The idea is very unique to go to space without rockets and without
fuel consumption.
Space Elevator:
The space elevator is a cable-like tool which could connect the earth with
a fixed structure in outer space. It is a proposal structure designed to
transport material from a celestial body‘s surface into space. It would
provide a permanent link between earth and outer space which could be
able to send material or person to space. The concept most often refers
to a structure that reaches from the surface of the earth on near the
Equator to geostationary orbit (GSO) and a counter-mass outside of the
atmosphere. A space elevator for earth would consist of a cable
anchored to the earth‘s surface, reaching into space. By attaching a
counterweight at the end or by further extending the cable for the same
purpose, inertia ensures that the cable remains stretched out, countering
the gravitational pull on the lower sections, thus allowing the elevator to
remain in geostationary orbit. Once beyond the gravitational midpoint, carriages would be accelerated further
by the planet‘s rotation. The space elevator is a theoretical concept which will provide a permanent link
between earth and space.
4
5. Structure: The centrifugal force of earth‘s rotation is the main principle behind the elevator. As the earth
rotates, the centrifugal force tends to align the nanotubes in a stretched manner. There are a variety of tether
designs. Almost every design includes a base station, a cable, climbers, and a counterweight.
Base station- The base station can be categorized into two categories—mobile and stationary.
Mobile stations are large oceangoing vessels. Mobile platforms have the advantage of being able to avoid
high winds, storms, and space debris. Whereas stationary platforms would generally be located in high-
altitude locations, such as on top of the mountains, or even potentially on high towers. They have access to
cheaper and more reliable power sources, and require a shorter cable.
Cable- The cable in a space elevator must be strong enough to
carry its own weight as well as the weight of the climbers. The required
strength of the cable will vary along its length, since at various points it
has to carry the weight of the cable below, or provide a centripetal force
to retain to retain the cable and counterweight above. The cable in a
space elevator could only be constructed from an extremely strong,
flexible and light weight material such as carbon nanotubes. There are
some properties of carbon nanotubes due to which it can be used in
the cable of space elevator. They are 200 times stronger than steel. It is the first synthetic material to have
greater strength than spider silk. It is heat resistant as it resists burning like a metal. Its molecular structure
is carbons atoms in regular, tabular structure. Its properties are strong, light metal-like. Its properties make it
possible to be used in cable of space elevator.
The tensile strength of several materials and their comparison with carbon nanotubes—
Material Young‘s modulus Tensile strength Density
(GPa) (GPa) (g/cm3)
Single wall nanotube 1054 150 1.4
Multi wall nanotube 1200 150 2.6
Diamond 600 130 3.5
Kevlar 186 3.6 7.8
Steel 208 1.0 7.8
Wood 16 0.008 0.6
Climbers- The elevator cable anchored to the ground is counter-balanced by an equal length of
cable beyond the geosynchronous point, built up by photocell-pushed ―climbers‖. These climbers would also
be used to launch payloads up the elevator. Climbers cover a wide range of designs. On elevator designs
whose cables are planar ribbons, most propose to use pairs of rollers to hold the cable with friction. Other
5
6. climber designs involve magnetic levitation. Climbers must be placed at optimal timings so as to minimize
cable stress and oscillations and to maximize throughput. Lighter climbers can be sent up more often, with
several going up at the same time. This increases throughput somewhat, but lowers the mass of each
individual payload. Both power and energy are significant issues for climbers – the climbers need to gain a
large amount of potential energy as quickly as possible to clear the cable for the next payload.
All proposals to get that energy to the climber fall into three categories—
1. Transfer the energy to the climber through wireless energy transfer while it is climbing
2. Transfer the energy to the climber through some material structure while it is climbing
3. Store the energy in the climber before it starts—this requires an extremely high specific energy
Nuclear energy and solar power has been proposed, but generating enough energy to reach the
top of the elevator in any reasonable time without weighing too much is not feasible. The horizontal speed of
each part of the cable increases with altitude, proportional to distance from the center of the earth, reaching
orbital velocity at geostationary orbit. Therefore as a payload is lifted up a space elevator, it needs to gain not
only altitude but angular momentum as well. This angular momentum is taken from the earth‘s own rotation.
As the climber ascends it is initially moving slightly more slowly than the cable that it moves onto and thus the
climber drags on the cable.
6
7. Counter weight—several solutions have been proposed to act as a counterweight:
1. A heavy, captured asteroid
2. A space dock, space station or spaceport positioned past geostationary orbit
3. An extension of the cable itself far beyond geostationary orbit.
The concept of counterweight is like a small asteroid is diverted from deep space and locked into high orbit
above earth. The end of the elevator cable beyond geosynchronous orbit is anchored to it as a counterweight.
The mass of the asteroid moving in a higher orbit keeps the cable under tension and the cable straight. This
way, the overall length of the cable can be greatly shortened.
A shorter cable may be desirable for economic reasons; today, carbon nanotubes cost about $500
per gram of mass, or roughly $500 million dollars per ton. A space elevator cable will, of course, weigh many
thousands of tons. If this price does not significantly building an equal length of cable beyond
geosynchronous orbit. The asteroid could also have the added advantage of being used as a source of raw
materials to build space facilities for the elevator, such as the geosynchronous station, or complete
additional cables for more tracks along the elevator. The third idea has gained more support in recent years
due to the relative simplicity of the task and the fact that a payload that went to the end of the counterweight-
cable would acquire considerable velocity related to the earth, allowing it to be launched into interplanetary
space.
How the space elevator will work—
The basic principle of a space elevator is fairly simple to envision. Tie a
string to a baseball and twirl the string above your head. The string will remain
taut and straight as long as the twirling motion is in effect. The earth is spinning
far faster than your hand could ever manage, about 1000 miles per hour. If you
anchored an incredibly strong wire to earth‘s surface at the equator, then
attached the other end to a large enough mass to keep it taut, you end up with a
perfectly straight railroad track right into space. The space elevator‘s center of
mass would be at geosynchronous orbit, approximately 22,300 miles above the
equator, helping to keep the entire construct fixed over a stable position on earth.
The geosynchronous point is also where the cable would be under the most
stress, so it would have to be thickest there and taper down exponentially as one
move away from it in either direction.
Once the cable is set up, elevators can ride it up and down via magnetic rails, delivering cargo
straight into orbit. The earth-end of the elevator cable is usually envisioned as being attached to the top of a
7
8. mountain or a super-high artificial tower. However, though both of these options could imply setting up the
elevator, they are not strictly necessary. One scheme, primarily involving the photocell climber elevator,
details anchoring the cable to a specially-built but standard-height off-shore platform.
The concept is that a very long cable will be laid around 35 degree to -35 degree longitude i.e.
highest lifting efficiency at equator, up into space, with the center of mass at the geosynchronous orbit that will
be a counterweight either in form of space station or asteroids will be in higher latitude. From the ground
station, the climber will climb up the cable, powered by, with current idea of ground based laser that will strike
the photovoltaic cells abroad the climber. Its estimated speed is around 190 km/h, so it would take around a
week to get up. Climbers ascend a ribbon, 100,000 km long, strung between an anchor on earth and space in
a way never before possible, the space elevator will enable us to inexpensively and completely expand our
society into space.
Space elevator ribbon—
The space elevator ribbon is the carbon nanotubes composite ribbon.
The counterweight spins around the earth, keeping the cable straight and
allowing the robotic lifters to ride up and down the ribbon. Under the design
proposed, the space elevator would be approximately 62,000 miles (100,00 km)
high. The centrepiece of the elevator will be the carbon nanotubes composite
ribbon that is just a few centimetres wide and nearly as thin as a piece of paper.
Carbon nanotubes, discovered in 1991, are what make scientists believe that the
space elevator could be built. Carbon nanotubes have the potential to be 100
times stronger than steel and are as flexible as plastic. The strength of carbon
nanotubes comes from their unique structure. Once scientists are able to make
fibres from carbon nanotubes, it will be possible to creates threads that will form
the ribbon for the space elevator. Previously available materials were either too
weak or inflexible to form the ribbon and would have been easily broken. They
have very high elastic modulus and their tensile strength is really high, and that all points to a material that
should make a space elevator relatively easy to build. A ribbon could be built in two ways:
1. Long carbon nanotubes—several meters long or longer—would be braided into a structure resembling a
rope. As of 2005, the longest nanotubes are still only a few centimetres long.
2. Shorter nanotubes could be placed in a polymer matrix. Current polymers do not bind well to carbon
nanotubes, which results in the matrix being pulled away from the nanotubes when placed under tension.
Once a long ribbon of nanotubes is created, it would be wound into a spool that would be launched into
orbit. When the spacecraft carrying the spool reaches a certain altitude, perhaps Low Orbit it would being
unspooling, lowering the ribbon back to earth. At the same time, the spool would continue moving to a
higher altitude. When the ribbon is lowered into earth‘s atmosphere, it would be caught and then lowered
and anchored to a mobile platform in the ocean. The ribbon would serve as the tracks of a sort of railroad
into space. Mechanical lifters would then be used to climb the ribbon to space.
8
9. Riding a space elevator to the top—
While the ribbon is still a conceptual component, all of the
other pieces of the space elevator can be constructed using known
technology, including the robotic lifter, anchor station and power-
beaming system. By the time the ribbon is constructed, the other
components will be nearly ready for a launch sometime around 2018.
Lifter—The robotic lifter will use the ribbon to guide its ascent into
space. Traction tread rollers on the lifter would clamp on to then ribbon
and pull the ribbon through, enabling the lifter to climb up the elevator.
Anchor Station—The space elevator will originate from a mobile
platform in the equatorial Pacific, which will anchor the ribbon to earth.
Counterweight—At the top of the ribbon, there will be a heavy counterweight. Early plans for the space
elevator involved capturing an asteroid and using it as a counterweight. However, more recent plans include
the use of a man-made counterweight. In fact, the counterweight might be assembled from equipment used to
build the ribbon including the spacecraft that is used to launch it.
Power Beam—The lifter will be powered by a free-electron laser system located on or near the anchor
station. The laser will beam 2.4 megawatts of energy to photovoltaic cells, perhaps made of Gallium Arsenide
(GaAs) attached to the lifter, which will then convert that energy to electricity to be used by conventional,
niobium-magnet DC electric motors.
Once operational, lifters could be climbing the space elevator nearly every day. The lifters will vary in
size from five tons, at first, to 20 tons. The 20-ton lifter will be able to carry as much as 13 tons of payloads
and have 900 cubic meters of space. Lifters would carry cargo ranging from satellites to solar-powered panels
and eventually humans up the ribbon at a speed of about 118 miles per hour.
9
10. Transport system for the space elevator –
This section proposes a new method and transportation system to fly into space, to the Moon, Mars,
and other planets. This transportation system uses a mechanical energy transfer and requires only minimal
energy so that it provides a ‗Free Trip‘ into space. It uses the rotary and kinetic energy of planets, asteroids,
meteorites, comet heads, moons, satellites, and other natural space bodies. The main difference in the
offered method is the transport system for the space elevator and the use of the planet rotational energy for
a free trip to another planet, for example, Mars. The objective of these innovations is to provide an
inexpensive means to travel to outer space and other planets, simplify space transportation technology and
eliminate complex hardware. This goal is obtained by new space energy transfer for long distance, by using
engines located on a planet, the rotational energy of a planet, or the kinetic and rotational energy of the
natural space bodies.
Free trip to moon—
A proposed centrifugal space launcher with a cable transport system which includes an equalizer
located in geosynchronous orbit, an engine located on earth, and the cable transport system having three
cables—a main central cable of equal stress and two transport cables, which include a set of mobile cable
chains, connected sequentially one to another by the rollers. One end of this set is connected to the equalizer,
the other end is connected to the planet. Such a separation is necessary to decrease the weight of the
transport cables, since the stress is variable along the cable. This transport system design requires a
minimum weight because at every local distance the required amount of cable is only that of the diameter for
the local force. The load containers also connected to the chain. When containers come up to the rollers and
continue their motion up to the cable. The entire transport system is driven by any conventional motor located
on the planet. When payloads are not being delivered into space, the system may be used to transfer
mechanical energy to the equalizer. This mechanical energy may also be converted to any other sort of
energy. The space satellites released below geosynchronous orbit will have elliptic orbits and may be
connected back to the transport system after some revolutions when the space ship and cable are in the same
position. If low earth orbit satellites use a brake parachute, they can have their orbit closed to a circle. The
space probes released higher than geosynchronous orbit will have a hyperbolic orbit, fly to other planets, and
then can connect back to the transport system when the ship returns. Most space payloads, like tourists, must
be returned to earth. When one container is moved up, then another container is moved down. The work of
lifting equals the work of descent, except for a small loss in the upper and lower rollers. The suggested
transport system lets us fly into space without expending enormous energy. This is the reason why the
method and system are named a ―Free Trip‖.
Assume a maximum equalizer lift force of 9 ton at the
earth’s surface and divide this force between three
cables—one main and two transport cables. The mass of
the equalizer creates a lift force of 9 ton at the earth‘s
surface, which equals 518 ton for K=4. The equalizer is
located over a geosynchronous orbit at an altitude of
10
11. 100,000 km. Full centrifugal lift force of the equalizer is 34.6 ton, but 24.6 ton of the equalizer are used in
support of the cables. The transport system has three cables—one main and two in the transport system.
Each cable can support a force of 3000 kgf. The main cable has a cross section area of equal stress. Then
the cable cross section area is A=0.42mm^ at the earth‘s surface, maximum 1.4 mm^ in the middle section,
and A=0.82 mm^ at the equalizer. The mass of main cable is 205 ton. The chains of two transport cable loops
have cross-section areas to equal the tensile stress of the main cable at given altitude, and the capabilities are
the same as the main cable. Each of them can carry 3 ton force. The total mass of the cable is about 620 ton.
The three cables increase the safety of the passengers. If any one of the cables breaks down, then the other
two will allow a safe return of the space vehicle to the earth and the repair of the transport system.
If the container cable is broken, the pilot uses the main cable for delivering people back to earth. If
the main cable is broken, then the load container cable will be used for delivering a new main cable to the
equalizer. For lifting non-balance loads for example, satellites or parts of new space stations, transport
installations, interplanetary ships, and the energy must be spent in any delivery method. When the transport
system is used, the engine is located on the earth and does not have an energy limitation. Moreover, the
transport system can transfer a power of up to 90,000 kW to the space station for a cable speed of 3 km/s.
At the present time, the International Space Station has only 60 kW of power.
Delivery capabilities—For tourist transportation the suggested
system works in the following manner. The passenger space vehicle
has the full mass of 3 ton to carry 25 passengers and 2 pilots. One
ship moves up, the other ship, which is returning, moves down; then
the lift and descent energies are approximately equal. If the average
speed is 3 km/s, then the first ship reaches the altitude of 21.5-23
thousand km in 2 h. At this altitude the ship is separated from the
cable to fly in an elliptical orbit with minimum altitude 200 km and
period approximately 6 h. After one day the ship makes four
revolutions around the earth while the cable system makes one revolution, and the ship and the cable will be
in the same place with the same speed. The ship is connected back to the transport system, moves down the
cable and lifts the next ship. The orbit may be also three revolutions or two revolutions. In one day the
transport system can accommodate 12 space ships in both directions. This means more than 100,000 tourists
annually into space. The system can launch payloads into space, and if the altitude of disconnection is
changed then the orbit is changed. If a satellite needs a low orbit, then it can use the brake parachute when it
flies through the top of the atmosphere and it will achieve a near circular orbit. The annual payload capability
of the suggested space transport system is about 12,600 ton into a geosynchronous orbit.
If instead of the equalizer the system has a space station of the same mass at an altitude of 100,00
km and the system can have space stations along cable and above geosynchronous orbit, then, these
stations decrease the mass of the equalizer and may serve as tourist hotels, scientific laboratories, or
industrial factories. If the space station is located at an altitude of 100,000 km, then the time of delivery will be
11
12. 9.36 h for an average delivery speed of 3 km/s. This means 60 passengers per day or 21,000 people annually
in space.
Let us assume that every person needs 400 kg of food for a 1-year-round trip to Mars, and Mars has the same
transport installation. This means we can send about 2000 people to Mars annually at suitable positions of
Earth relative to Mars.
Cost of suggested space transport installation—
The current International Space Station has cost many billions of dollars, but the suggested space
transport system can lost a lot less. Moreover, the suggested transport system allows us to create other
transport systems in a geometric progression. Let us examine an example of the transport system.
Initially we create the transport system to lift only 50 kg of load mass to an altitude of 100,000 km.
The equalizer mass is 8.5 ton, the cable mass is 10.25 ton, and the total mass is about 19 ton. Let us assume
that the delivery cost of 1 kg mass is $10,000. The construction of the system will then have a cost of $190
Million then the system costs $1.25 million. Let us put the research and development (R&D) cost of
installation at $29 million. Then the total cost of initial installation will be $220 million. About 90% of this sum is
the cost of initially rocket delivery. After construction, this initial installation begins to deliver the cable and
equalizer or parts of the space station into space. The cable and equalizer capability increase in a geom etric
progression. The installation can use part of the time for delivery of payload and self-financing of this project.
After 765 working days the total mass of equalizer and cables reaches the amount above 1133 ton and the
installation can work full time as a tourist launcher or continue to create new installations in only 30 months
with a total capacity of 10 million tourists/year. The new installations will be separated from the mother
installations and moved to other positions around the earth. The result of these installations allows the delivery
of passengers and payloads from one continent to another across space with low expenditure of energy.
Let us estimate the cost of the initial installation. The installation needs 620 ton of cable. Let us take
the cost of cable as $0.1 million/ton. The cable cost will be $62 million. Assume the space station cost $20
million. The construction time is 140 days. The cost of using the mother installation without profit is $5
million/year. In this case the new installation will cost $87 million. In reality soon after construction the new
installation can begin to launch payloads and become self-financing.
Cost of delivery—
The cost of delivery is the most important parameter in the space industry. Let us estimate it for the
full initial installation above. As we calculated earlier the cost of the initial installation is $220 million. Assume
that installation is used for 20 years, served by 100 officers with an average annual salary of $50,000 and
maintenance is $1 million in year. If we deliver 100,000 tourists annually, the production delivery cost will be
$160/person or $1.27/kg of payload. Some 70% of this sum is the cost of installation, but the delivery cost of
the new installations will be cheaper. If the price of a space trip is $1990, then the profit will be $183 million
annually. If the payload delivery price is $15/kg then the profit will be $189 million annually. The cable speed
for K=4 is 6.32 km/s. If average cable speed equals 6 km/s, then all performance factors are improved by a
12
13. factor of 2 times. In any case the delivery cost will be hundreds of times less than the current rocket powered
method.
Cost (in comparison to space shuttle)
Per kg: $100/kg vs $10,000-$40,000/kg
Construction: $6 billion vs $19 billion
Space elevator maintenance—
At a length of 62,000 miles (100,000 km), the space elevator will be vulnerable to many dangers,
including weather, space debris and terrorists. As plans move forward on the design of the space elevator, the
developers are considering these risks and ways to overcome them. In fact, to make sure there is always an
operational space elevator, developers plan to build multiple space elevators. Each one will be cheaper than
the previous one. The first space elevator will serve as a platform from which to build additional space
elevators. In doing so, developers are ensuring that even if one space elevator encounters problems, the
others can continue lifting payloads into space.
Avoiding Space Debris—
Like the space station or space shuttle, the space elevator will need the ability to avoid orbital
objects like debris and satellites. The anchor platform will employ active avoidance to protect the space
elevator from such objects. Currently, the North American Aerospace Defence Command (NORAD) tracks
objects larger than 10 cm. protecting the space elevator would require an orbital debris tracking system that
could detect objects approximately 1 cm. This technology is currently in development for other space projects.
Repelling Attacks—
The isolated location of the space elevator will be the biggest factor in lowering the risk of terrorist
attack. For instance, the first anchor will be located in the equatorial Pacific, 404 miles (650 km) from any air
or shipping lanes. Only a small portion of the space elevator will be within reach of any attack, which is
13
14. anything 9.3 miles or below. Further, the space elevator will be a valuable global resource and will likely be
protected by the U.S. and other foreign military forces.
Space Elevator Impact—
The potential global
impact of the space elevator is
drawing comparisons to another
great transportation achievement—
the U.S. transcontinental railroad.
Completed in 1869at Promontory,
Utah, the transcontinental railroad
linked the country‘s east and west
coasts for the first time and sped
the settlement of the American
west. Cross-country travel was
reduced from months to days. It
also opened new markets and gave
rise to whole new industries. By 1893, the United States had five transcontinental railroads.
The idea of a space elevator shares many of the same elements as the transcontinental railroad. A
space elevator would create a permanent Earth-to-space connection that would never close. While it wouldn‘t
make the trip to space faster, it would make trips to space more frequent and would open up space to a new
era of development. Perhaps the biggest factor propelling the idea of a space elevator is that it would
significantly lower the cost of putting cargo into space. Although slower than the chemically propelled space
shuttle, the lifters reduce launch costs from $10,000 to $20,000 per round, to approximately $400 per round.
Current estimates put the cost of building a space elevator at $6 billion with legal and regulatory costs at $4
billion. Additionally, each space shuttle flight costs $500 million, which is more than 50 times more than
original estimates.
The space elevator could replace the space shuttle as the main space vehicle, and be used for
satellite deployment, defence, tourism and further exploration. To the latter point, a space craft would climb
the ribbon of the elevator and then would launch toward its main target once in space. This type of launch will
require less fuel than would normally be needed to break out of Earth‘s atmosphere. Some designers also
believe that space elevators could be built on other planets, including Mars.
Conclusion—
The Space Elevator is the most promising Space Transportation system on the drawing boards
today, combining scalability, low cost, qualify of ride, and safety to deliver truly commercial-grade space
access-practically comparable to a train ride to space. Rocket-based space launch systems are inherently
limited by the physics of rocket propulsion. More than 90% of the rocket‘s weight is propellant and the rest is
14
15. split between the weight of the fuel tank and the payload. It is very difficult to make such a vehicle safe or low
cost. A target cost of $1000 per kg is proving to be impossible to reach. In comparison, airlines charge us
about $1 per round, and train transportation is in cents per pound.
The Space Elevator is based on a thin vertical tether stretched from the ground to a mass far out in
space, and climbers that drive up and down the tether. The rotation of the earth and of the mass around it
keeps the tether taut and capable of supporting the climbers. The climbers travel at speeds comparable to a
fast train, and carry no fuel on board – they are powered by a combination of sunlight and laser light
projected from the ground. While the trip to space takes several days, climbers are launched once per day.
The Space Elevator is linearly scalable. The first ―baseline‖ design will use 20 ton climbers, but by making
the tether thicker we can grow the Space Elevator to lift 100, or even 1000 tons at a time. In addition to
launching payloads into orbit, the Space Elevator can also use its rotational motion to inject them into
planetary transfer orbits—thus able to launch payloads to Mars, for example, once per day. Imagine the kind
of infrastructure we can set up there, waiting for the first settlers to arrive...
Looking back from the year 2100, the construction of the Space Elevator will be considered to mark the true
beginning of the Space age; much like the advent of the airplane or steamboat heralded the true commercial
use of the air and sea.
15
