Lasso the Moon

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I have been a personal fan of the concept of the Space Elevator (SE) since attending a talk by Bradley Edwards describing his work developing the concept. From that time I have always thought it was self-evident that this was the method that eventually most of the mass traveling between Earth and the rest of space would use. The problem to this point is that currently there is no material in commercial production that could be used to build the elevator. I have faith that material sciences will eventually resolve this issue but this could be decades away. There is a variation on the concept that is currently feasible, a Moon SE.

The Slow Boat to Luna

Currently the LiftPort Group is promoting the concept of and SE stretching from the surface of the Moon through the first Lagrange point (L1). Unlike the Earth based elevator this would not require a yet undeveloped material but would be possible with various existing materials such as Kevlar. Several modern synthetic fibers could be used because of the lower lunar gravity even though L1 is about 30% further from the surface of the Moon than GEO is from the surface of Earth.

Another difference is that while a SE from the surface of Earth is able to “self-counterweight”. A cable/ribbon of consistent cross section would need to extend almost 240,000 km beyond L1 to just counterweight the cable/ribbon to the Moon. For every 1 kg of payload to be lifted from the Moon you would need 33 kg in counterweight. A cable/ribbon of this length would possibly conflict with an Earth based elevator when one is built.

One advantage of a cable/ribbon this long is that a payload released from the end would come within 15,000 km of Earth. This could make returning to Earth from the Moon fairly cheap. If some way could be developed to capture payloads from the Earth any rocket able to deliver a payload to GEO would be able to deliver it to the Moon.

Like all space elevators the one to the Moon would be ideal for moving cargo. What it will not be very good for is moving people. Even if the climber moved at an average 1,000 km/h it would take over 2 days to make the trip between L1 and the Moon’s surface. The reality is the top speed will likely be less than half of that making the trip more like a week. A climber would be an extremely cramped space to live in for a week. It is unlikely that until space elevators are built for loads of at least 50 tons of mass that it will be used to transport people except in dire emergency.

What Good is It

A lunar space elevator would enable much more extensive exploration of the Moon’s surface. Exploration vehicles could be much more complex because their landing would be very soft and because potentially they can be returned from the surface for repairs and maintenance. It would be far cheaper to supply a permanent human habitation on the Moon. It would provide an ideal opportunity to develop a permanent habitation at L1. It would greatly simplify returning payloads from the Moon to the Earth; first scientific samples and later products of commercial value.

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The Next Frontier in Real Estate

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Where will we live beyond Earth?

The most common assumption about an interplanetary race is that a majority of the race will live on planetary surfaces. There are actually many disadvantages to living on a planetary surface. The gravity of most planets is far from ideal. The gravity wells of planets require huge amounts of energy to move people and goods up and down them. Most atmospheres are far from ideal. The most convenient source of power is solar energy and half of the time any surface colony will be in darkness. There are a wealth of contaminants such as dust that are either a hazard to human health or to the operation of our machinery.

Orbital habitats avoid most of these issues. We know how to create artificial gravity that will avoid known health problems simply by rotating the habitat; the same solution is impractical on the ground. The energy to get to and from them is much lower than the energy to get between orbit and surface location. In space there is no atmosphere so it makes it equal to the most favorable atmospheric conditions we have encountered off Earth and you do not get the weather problems that come with an atmosphere. Even in LEO a station would have sunlight at least 60% of the time in an equatorial orbit and this can be increased by sitting at the higher end of LEO and using an inclined orbit. Once you are above the inner Van Allen belt the station would have at least 90% sunlight. The orbital environment is considered equal to the best clean room.

There are disadvantages. Any raw materials are a long way away. A colony on a planetary surface will have some raw materials very available to it. The value of the raw materials will be limited and at the start most of the supplies for any colony will need to come from Earth and it will be more expensive to get the supplies to any planetary surface. The cost of transporting resources from locations like the Moon or asteroids will be fairly low and easily offset by other advantages. Radiation could be a more significant issue but even colonies on planetary surfaces will need to deal with this issue.

The Shape of Things to Come

A large part of the design of orbital colonies will strongly influenced by the fact that a zero G environment is not health for humans over the long term. This means artificial gravity is required and the only current feasible way to do this is to spin the colony. Some assume that for humans to be health they must have near full Earth gravity. This is likely far from true, especially for individuals who intend on never returning to Earth but some gravity will likely be needed. The first colony will likely be a “dumbbell” design with 2 modals connected by a narrow passage way. As colonies expand in size a torrid design will eventually become common. Only the primary habitations will require the maximum artificial gravity so eventually the inside of the torus will be filled with spaces for food production, storage, machinery for operating the colony and industries employing the colonist.

What we will not see is a recreation of the terrestrial environment so often seen in suggested designs for orbital colonies. The colony designs from the 1970’s come from the myth that the human mind will break if it is not able to see vast expanses of open space on a regular basis. The fact is that about half of the world’s population lives in areas that do not provide such vast vistas. Most of these design look like they are trying to sell the idea to suburbanites rather than come up with reasonable designs for habitats. Every one of the designs are a massive waste of resources and are very impractical.

The amount of atmosphere needed for these designs will be at best be only 10 times what a more efficient design would be but will more likely be far more than that. This much atmosphere also has the disadvantage of creating weather that could damage the station in much the same way as weather damages structures on Earth. As only a fraction of the volume is used there is far more surface area for a given population requiring more shielding from impacts and radiation. Most of these designs assume that as much as half of the outer surface of the colony will be transparent. That means that section has no function but to collect sunlight wasting more space. The transparent surfaces will also need to be able to sustain impacts from micro meteors without shattering and provide the same amount of radiation shielding as the rest of the outer surface. In the end the designs reflect 2 dimensional thinking in a 3 dimensional environment.

I am not saying that there will not be any open spaces but those that exist will be similar to parks, a public space designed to look terrestrial. Once a colony exceeds 1,000 people it will likely be practical to create such spaces. However by this time most inhabitants will likely have technology to simulate outdoor environments in their own quarters. Recreating the sights, sound and even smells of any location they wish.

What’s for Dinner

Some things will be shipped to an extraterrestrial colony from Earth but food will not be among them. An extraterrestrial colony will need to produce all its own food. The designs for colonies for the 1970’s imagined that along with living much the way we do on Earth we would farm much the same way too. Using anything like conventional tilled farming methods will be completely impractical for any extraterrestrial colony. At the time of these designs little was known of any other method of growing crops but new techniques have been developed.

A concept known as vertical farming will be key in efficiently growing crops in and orbital colony. Vertical farming on Earth refers to any indoor farming method that uses more than a single story. Some commercial vertical farm projects produce 150 times per acre of floor space as a conventional farm. That would translate into a 10 story building on a 1 acre lot would produce 1,500 acres of conventional farm land. Not all crops could achieve this level of production but vertical farming could far surpass conventional farming for most.

Another big advantage of vertical farms is they use fewer resource than conventional farming. Some vertical farming projects report a 95% reduction in the water used. As most techniques depend on hydroponic the amount of fertilizer used is reduced. As the crops will be in near clean room environments that can have physically isolated from each other almost no fungicide will be needed.

Another point is that natural sunlight in orbit has not been filtered by the Earth’s atmosphere. This means it is 150% as strong as the sunlight at the equator and much higher in the UV spectrum and comes with higher levels of radiation. Solar thermal power generation will likely be able to achieve at least 40% efficiency converting sunlight to electricity. Plants only make use of 10% of the spectrum of sunlight and new LED grow lights that produce only this spectrum are now available. If the LED are only 50% efficient at converting electricity to light the useable light will be double what you would get by shining the sunlight directly on the plants.