"Earth is the cradle of humanity, but one cannot live in a cradle forever."
- Translated from Konstantin E. Tsiolkovsky, Father of Russian Astronautics, 1896
"The meek shall inherit the Earth. The rest of us are going into space."
"All civilizations become either spacefaring or extinct."
-- Carl Sagan
"Single-planet species do not last."
-- John Young
While the following projects below are not part of the initial effort,
they give some flavor of possible future directions after the initial LEO
and GEO tethers are in operation. The LEO and GEO tethers will
drastically reduce the cost to get anywhere in space. A famous saying by
Robert Henlin is that, "If you reach LEO you are halfway to anywhere in
the solar system." In our case the saying should be that, "A good toss
from GEO and you can get to anyplace in the solar system."
the demand that will justify a Space Tether, which in turn will
drastically reduce the cost to LEO. But what happens after this?
Reduced cost to LEO makes many things affordable that were not reasonable at high costs.
For example, mining the asteroids or sending people to Mars might soon
follow. Tourism to the Moon, or even colonizing the Moon, is not too hard
once you have cheap LEO transportation.
Lunar Flyby (LF) Hotel
A small hotel that was tossed from GEO on a trajectory that went out past
the moon and back (Lunar Safe Return Orbit) would be a natural first
follow-on project. The LF (Lunar Flyby) hotel would take customers on an 8 day trip
that goes around the moon and then back to get caught again by a GEO
hotel. The LF hotel is not limited by the size of the SSTT, as any amount
of people and cargo can be collected at the GEO hotel. Since it can only
go twice a month we would want it to be much larger than the SSTT. Maybe
big enough for 20 to 50 customers or more.
The LF hotel can only be tossed every 14 days because the Moon only
crosses through the plane of the orbit that the GEO hotels are in twice
every 28 days. So the LF hotel would travel for 8 days and then spend
about 6 days in port. The waste from LF hotel would be transfered to the
GEO hotel where it would be recycled. Food grown at the GEO hotel would
supply the LF hotel.
A tether in orbit around the Moon can land payload on the Moon or pick up payload
from the Moon. As long as it picks up as many pounds of lunar regolith as
it drops of payload, the tether transport will not require any additional
energy to operate. The regolith can provide radiation shielding for the
orbital hotels. Tethers also make it easy to build a hotel on the moon.
If the tether is in a polar orbit it can service landing/pickup sites
all over the moon, including the poles.
The Lunar Flyby Hotel could take people to the Lunar Tether. So a Lunar
Tether would follow the Lunar Flyby project.
The moon is about 2160 miles in diameter and only rotates once every 28
days. So if you wanted to drive along the Moon's equator and keep the Sun
directly overhead you would only have to average about 10 miles per hour.
Having sunlight all the time lets you avoid the problem of storing energy
for people and plants. Moving along the moon could also make an
interesting scenic trip for tourists.
The first step would be to build a dirt road (say 2
meters wide) around the moon staying near the equator.
To reduce engineering, this road would detour around major craters and
look for gentle grades.
After this was
done we could have a convoy of Lunar RVs that always had sunlight for
solar power and growing plants. So these RVs can make a sort of mobile
Hermann Oberth [Oberth 1957] designed a Moon Car that
balanced with a gyro and could jump. The body of the vehicle was held up
by one leg that acted like a big gas shock absorber for a smooth ride.
We now know the jumping is not really needed. Today we could do the
balancing with a computer as is done in the Segway instead of a gyro. Oberth had two
tank racks instead of wheels because he was not sure how soft the Lunar
dust would be. Today we know that two big soft tires side by side should
work fine. As gravity on the Moon is only 1/6th that of Earth, and there
is no wind, the vehicle could be 10 meters square with solar panels even
wider than that.
If the Lunar RV rotates forward by a certain amount, say 20%, then 2 front tires
come onto the ground for a total of 4 tires on the ground. To get
back on 2 tires the vehicle just accelerates hard to "pop a wheelie".
In the 4 tire mode a bulldozer blade can be used to clear a road when necessary.
Could design it so it could operate on either the back 2 wheels,
the front 2 wheels, or either side pair. On the back or front it
is like a segway. On a side pair it is like a motorcycle. This
way a failure of a tire or motor does not require repair right away.
Could also have tow rope so that another vehicle could tow a broken
We would want bumpers so that if the vehicle ever did fall over it did not
hurt anything. The Segway style leaning into the hills would mean that as
the RV went up or down a hill that people, or glasses of water, inside did
not tip over.
The solar panels could be spaced such so that some sunlight went between
them and to the plants growing under them. On the Moon there is no
atmosphere to reduce the intensity of the Sun and the Moon Car will
move so that the Sun is always directly overhead, so
unfiltered sunlight would be too strong for the plants.
With a single big spring and leaning into hills, the RV could provide a
very comfortable ride for tourists even over a dirt road at the required
10 MPH. The ride should be smooth enough to move around inside, eat, and
sleep while the RV keeps moving all the time.
The moon is only tiled about 1.5 degrees relative to the sun. So the
artic circle is about 26 miles from the pole. So you could make a
"Path Of Eternal Light" along mountain ridges around the pole such
that you would only need to average under 1 MPH to stay in the sunlight.
Going along the ridges also makes for nice views for lunar tourists.
There can of course be an infinite number of different paths of eternal light.
This makes issues of light for solar, heat control, and light for algea much
easier than on a base that is dark for 14 days every month. Oxygen recycling
and energy become almost easy problems for a vehicle on the "Path Of Eternal Light".
A similar idea for autonomous robot explorers has been called
There are mountain tops near the Lunar poles that always or
nearly always in sunlight. A tower of solar panels that rotated ones
every 28 days could always be in sunlight. This would be a nice place to
locate a Moon base.
Also at the poles are be craters that are always dark.
These craters have radiated heat, and become very cold.
of this there seems to be ice available there. It should be relatively
easy to collect this and warm it to get water.
Movies or TV shows could be made in space or on the moon. Because of the
novilty they could get more viewers. This could be travel shows, reality TV shows,
sports shows, the next James Bond movie, etc. The possibilities are
endless. There have already been talks where someone making a TV show
would pay part of the cost of sending someone up on a Soyuz.
As mentioned in the discussion of investment opportunities, asteroids
are an attractive source of precious metals.
With SSTT, getting to our GEO hotel is very inexpensive. If we wanted a
mining vehicle vehicle bigger than one load of the SSTT we could assemble
it at the GEO hotel. Then the mining vehicle could be tossed toward an
asteroid. When material is coming back from the asteroid it could use
aerobreaking to slow down. This is would make mining the asteroids so
much cheaper than it is today that it should be profitable.
In this picture of Eros you can see house sized boulders. If a
tether were attached to these and they were pushed out a bit the
spin of Eros could be used to give them a good velocity. You
could then release at the right time and send them toward Earth.
Mining Asteroids on Moon
Many asteroids have impacted on the moon. These impacts brought
precious metals to the surface of the moon. The metals could be
mined and brought to Earth.
Mars-Earth Rapid Interplanetary Tether Transport - MERITT
MERITT - Mars-Earth Rapid Interplanetary Tether Transport system [Forward 1999].
Robert Forward and Gerald Nordley did an analysis of a tether transport between Earth
and Mars. From their abstract; "Routine travel to and from Mars demands
an efficient, rapid, low cost means of two-way transportation. To answer
this need we have invented a system of two rotating tethers in highly
elliptical orbits about each planet. Tethers with tip velocities of 2.5
km/s can send payloads to Mars in as little as 90 days. Tether systems
using commercially available tether materials at reasonable safety factors
can be as little as 15 times the mass of the payload being handled."
In a detailed example, the initial Earth tether orbit has an eight hour
period, an apogee of 33,588 km, and the tether and control system have a
mass 15 times the payload. After toss, the Earth tether orbit apogee is
only 24,170 km, and the period is 5.37 hours. This sample takes 150 days
to get to Mars. A tether in orbit around Mars, with an apoapsis of 21,707
km catches the payload, soaks up 4 km/s of payload velocity, drops it for
entry at Mars with a 2.4 km/s velocity. The Mars tether finishes with an
apoapsis of 115,036 km. Aerobrake could reduce the load on the Mars
Pioneers to Asteroids
Some people may decide to live and raise families on asteroids.
This would be the ultimate in freedom from oppression.
As John Lewis puts it in [O'Neill, 2000, page 137],
"Keep your laws off my asteroid". Asteroids have some real advantages,
on top of being so far away from everyone else that nobody
will bother you. Shielding from radiation is easy, as there
is plenty of mass available. You can mine the asteroid for
many of the things you need, like oxygen, metal, water, carbon, etc.
You can make a small asteroid keep one side facing the Sun so
you always have solar power. Winching out some mass from
a rotating asteroid on a long tether absorbes a large amount of
angular momentum per Kg.
Phobos Deimos Tether Ladder
Paul Penzo in [Penzo 1986] discusses the use of Mars Satellites for
transfer between Low Martian Orbit (LMO) and escape. Phobos and Deimos
are small, less than 20 km in diameter, but that is huge by tether
standards. They are low, and in equatorial orbits.
A 375 km tether in LMO, can toss a payload to a 1160 km tether hanging from
Phobos. An elevator lifts the payload to Phobos, then another elevator
lifts the payload up a 940 km tether above Phobos. This allows a toss to
a 2960 km tether hanging below Deimos. Here a pair of elevators lifts the
payload to 6100 km above Deimos, where the payload will have escape
This process saves 1.6 km/s that would be supplied by propellant. It can
work in both directions. Penzo's analysis was done with Kevlar; Spectra
2000 would use less mass. The elevator is a slight problem, one that
rotating tethers avoid by turning to release the payload. Since the down
and up lengths are different, an elevator or winch of some kind is
required for this system.
Penzo also has numbers for a Lunar Station to assist transport between the
surface of the Moon and trans-Earth orbit.
Penzo has two pages on the use of EDT to maneuver in Jupiter's magnetic
field. The magnetic field at Jupiter is much stronger than around the
This is a fun vision of some of the capabilities of tethers.
Space Solar Power
As they say in [Glaser1998, page 184], "The primary
economic problem now preventing an SPS system from
being built is the lack of cheap access to space.".
Land for a microwave power receiver would be like 30 times
smaller than land for a ground based solar power system.
A solar power station in GEO can collect solar power nearly 100%
of the time, so unlike a ground based solar power system you
don't have an energy storage problem.
On the ground you average only like 25% of direct sunlight
(with nighttime, angle of the sun,
and clouds). Even full sunlight on the ground is less
than full sunlight in space, since the atmosphere blocks some.
A ground based solar power system would need to have
a energy storage system which also looses some power.
In space you don't need to buy the land to put your
solar collectors on. Beaming power by microwaves seems possible.
If the energy density on the microwave beam is the same as
sunlight, it would take something like 30 times less land
for the same net power. The microwave conversion is around
90% efficient, where solar is more like 20%. With nighttime,
clouds, and storage losses, you need a lot more land if
it is covered with solar collectors than with microwave
receivers. The microwave receiver is a bunch of wires
which would let most of the sunlight through. So the land
underneath could be used for agriculture in the microwave
case, and probably not for anything else in the solar case.
With affordable launch prices, space solar power would make
economic sense. In [Glaser, 1998, page 541] they estimate
that space solar power becomes competitive at $320/Kg.
In fact, some of the space solar power enthusiasts have
recognized that tethers might be the way to get low costs
to GEO. For example in [Glaser1998, page 551] they
say, "A large tether system could be used to place payloads
on a geosynchronous transfer orbit. A second tether system
could be used to 'catch' the payloads at apogee and
complete the transfer. The low Earth orbit tether system
could be a rotating tether or an oscillating tether.
The high-altitude system would very likely be a rotating
Fusion power gets about $1 billion a year in federal funding.
Space based solar power seems easier to achieve than
fusion and would solve our future energy needs just as well.
However, it does not get anything near the funding fusion
O'Neil Style Colony
The O'Neill plans in 1975 [O'Neill, 2000] were based on an expected
$100/lb to orbit on the
coming space shuttle and an electromagnetic catapult on the Moon.
Prototype electromagnetic catapults were built and the ideas for these
were verified. However, when
the shuttle turned out to be like 50 times more expensive than advertised,
the O'Neill plans suddenly became too costly.
With affordable launch prices, we could see the O'Neill vision realized.
Mercury is orbiting the Sun fast enough that 3 times a year
you could conveniently ship things between Mercury and the Earth.
This transfer orbit needs a high DV, so tethers would make the
difference between very expensive and economical. There is
no atmosphere so tethers could go down to the surface.
There seems to be ice in craters at the poles that are always
in shadow. This is the best hypothesis explaining the data
from Earth based radar. The Sunlight is 7 times as strong,
so a solar sail reboost for a tether would be even more
attractive, as well as collecting it on the surface.
In these same shadowed craters you could build a base
Mercury has a thin crust; precious metals or just heavy elements should be
more accessible than on the Earth [Gillett1996].
Search for Extra Terrestrial Intelligence - SETI
3 largest movable radio teliscopes
on earth are 64 meter Parkes Radio Telescope, the 75 meter
Lovell Telescope at Jodrell Bank,
and the 100 meter
Effelsberg near Bonn.
Allen Telescope Array is made of 350 dishes each 6.1 meters
in diameter to get around the problems of building a single large dish.
The total area is 10,229 sq meters which is the same area as a 114
meter diameter dish. There are advantages and disadvantages to
having lots of small dishes so it is not the same as one large
dish, but that discussion is beyond our scope here.
The 305 meter
in Puerto Rico was built in a crater and can not move.
Building a large dish and keeping the shape exactly right
even when it moves to different positions is hard when
you have gravity. But in orbit there is no gravity problem,
so you could build very large movable dishes and hold the shape.
A small 8 meter diameter radio telescope called Halca was launched in 1997.
While gravity does not limit the size, the launch costs currently does.
However, with greatly reduced launch costs it would be practical to
make a really large dish in space.
A bigger dish collects more signal and so can detect signals that
a smaller dish can not. The signal collected goes up with the
radius of the dish squared. The strength of a signal goes down
with the distance squared.
So with twice the diameter dish you
can hear the same power transmitter from twice the distance.
The volume of space you can search
goes up with the cube of the distance you can listen at.
So if you can listen to things twice a far away you can search 8 times
the volume of space. If you can listen to things 10 times as far
away then you can search 1,000 times the volume of space.
So a bigger
dish increases our chances of receiving a signal from
extra terrestrials. While this is a high risk venture,
the value of the information found could justify
Mining He3 on Moon
He3 from the sun has been deposited in the surface on the Moon.
It could be mined and brought back to Earth. If He3 becomes
is used in fusion power, as some people anticipate,
it could be valuable fuel.
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