New Mars Forums

I think it is basically undeniable that the moon is and always will be in most important respects, an undesirable place to live.  In terms of its inventory of things that we need in order to survive, it is one of the least desirable pieces of real estate in the solar system.  In some respects, it would be easier to live on the surfcae of Pluto than on the surface of the Earth's moon.  The need to import such basic things as water, carbon and nitrogen, places some firm limitations on the habitability of the place.  The need to import extends to all but the most basic metals and ores.

The moon may eventually end up holding a significant population simply by virtue of the growing demand for the basic ores that it holds, as a Near Earth free-space population expands progressively.

Ultimately, the location where most of the off-world population will reside will be Earth-orbit in artificial habitats.  Given the unlimited space, unlimited solar energy and relatively low delta-v to volatile rich asteroids, the population of near-earth space will likely grow far more rapidly than that of either the moon or Mars.

This idea has been around for quite some time.  It is commonly called a 'mass driver'.  Other names include 'linear electric motor' or 'rail gun'.

A mass driver could be used to accelerate a space craft (as a projectile) to extremely high velocities.  It would not need to be attached to a planet in order to work.  However, given that momentum is always conserved, it would experience recoil and would need to expend energy and propellant to maintain its position in space each time it discharged.

Alternatively, by attaching a mass driver to a space craft, it can be used as an 'electric' rocket engine, using virtually any material as propellant, including ground up lunar/asteroid rocks, or waste produced on the spacecraft.  The electricity required to power the device could come from solar cells or a nuclear reactor.

What terraformer was proposing was a nuclear thermal rocket engine.  This produces thrust by passing hydrogen (or some other propellant) through a high temperature nuclear reactor and venting it out the rear as reaction mass.  The reactor DOES NOT explode, merely gets very hot (~2000degC) and and heats the hydrogen, which acts as a propellant.  Note that the fuel in this case is the uranium embedded within the reactor, not the hydrogen, which does play any part in the energy production, but just gets heated and dumped out the back.

What you are describing are two variants of bomb-propelled space craft, which were developed under the US Orion programme in the 1950s and 60s.  Orion propulsion concepts greatly exceed the specific impulse that could ever be provided by a nuclear thermal rocket because the reactor is allowed to reach its maximum posible temperature and power density by allowing it to explode at the rear of the ship.  The downside is that in a nuclear thermal rocket the fission products and the unspent fuel are neatly contained within the ship, whereas Orion atmomises them and vents them into the environment.  This is a problem if the propulsion system is intended to be used in the vicinity of a planet (especially Earth).  This, and the atmoic test ban treaty, pretty much put the lid on the Orion project and all further development of nuclear propulsion focuses on nuclear thermal rockets, in spite of their significantly lower performance.

Although large, your cyclinder would be quite easy to build.  You simply produce a thin-foil 'substrate' which you inflate with a non-oxidising gas, and then build up the required wall thickness using vacuum plating.

Terraforming is a multi-lifetime human project that is likley to challenge the budgets of major human institutions for centuries to come.  The idea that we would de-terraform a planet that has been terraformed is ridiculous.  It would be rather like building a skyscraper and then demolishing it afterwards, it isn't a practical proposition.  The sort of training that people would need is basic atmospheric physics and chemistry, not something that you would need to de-terraform a planet to learn.

I know that these forums are spectulatory at best, but it would help if you thought your suggestions before you posted them.

Building habitats from cometary material certainly appears far more efficient (in terms of total material needed) than attempting to terraform a comet.

In one respect a comet would be a much more useful starting material than an asteroid or lunar rock: it is rich with water, carbon and nitrogen.  Having made some back of the envelope calculation for o'Neill type habitats, it very quickly became obvious to me that the bulk of the mass of the habitat was in the radiation shielding, the interior furnishings and the atmosphere.  Only about 3% of the total mass was accounted for by actual structure.  Water and cometary carbon provide much more of what we need for large Earth-like habitats.

Generally, smaller habitats provide a much more efficient utilisation of materials than very large ones.

One other thing: if the habitat is constructed within the Oort cloud or even the Kuiper belt, sunlight is likely to be far too weak to be useful as an energy source.  Under this circumstance, an artificial energy source would be needed: probably fission/fusion.  Given that we would no longer need to worry about how sunlight would permiate the internal geometry of the habitat, it would make more sense to create volumetric habitats, which do not waste large amounts of internal volume with 'empty' atmosphere.  This dramatically reduces the size of a habitat needed to house a given number of people.

Given the recent advances in genetic engineering and the use of algaes and bacteria in the production of synthetic fuels, the idea of terraforming may eventually be obsolete, long before we become capable of putting it into practice.  Human beings will be capable of efficiently producing sufficient amounts of food from algae and bacteria, using artifical energy drawn from atomic sources.  In addition, some proteins, sugars and vitamins could be manufactured entirely chemically.  With enough skill, these methods could eventually produce food that is physically indistinguishable from that which we enjoy today.

This has huge implications for future human colonisation of space.  Instead of requiring large fields dependant upon sunlight, food production would take place within relatively tiny and compact chemical plants.  Land vegetation such as trees and plants would then be maintained purely for aesthetic purposes and the small amounts required, could easily be illuminated using synthetic energy.

What this effectively means for space colonisation is that humna beings can effectively colonise any world with sufficient raw materials.  Limitations such as sunlight and low surface temperature, would no longer have any bearing upon the habitability of a world, given that all energy is derived from artificial sources, fission and fusion.  Under these conditions, Pluto would be no less habitable than Mars.  The moons of Jupiter become hot property because they combine an abundance of raw material with relatively high surfcae gravity.

Stellar physics is reasonably well understood and observed results fit theoretical models quite well.  I submit that there may still be surprises that could challenge existing models, but they are much more than just 'educated guesses'.

All stars are prone to solar flaring, including our own sun.  We survive these flaring events because the Earth's magnetic field and atmosphere protects us.  The same is likley to be true for other planets.

We simply do not have enough examples of interstellar intelligent life to be able to determine whether our own main sequence star represents ideal conditions.

(1) Alpha Centauri isn't a planet, but a triple starsystem.  But I guess you were refering to some hypothetical planet orbiting one of the stars?
(2) It is 4.3 lightyears away, not 8.5.
(3) Why would you assume that Alpha Centauri is the star system most likely to have intelligent life?  Presumably you mean most likely within our immiediate stellar neighbourhood, but what leads you to this conclusion?
(4) Proxima Centauri is a red dwarf and red dwarfs do indeed tend to be prone to massive solar flaring, which would make space travel in their vicinity quite hazardous.  Actually, all main sequence stars experience this early in their lives and red dwarfs have lifetimes ~1trillion years long, so every red dwarf in the universe can be assumed to be only a small percentage of the way through its life.  In a few tens of billions of years, most of them will settle down a bit.  But not all red dwarfs are unstable in this way.  Gliese for example, is relatively stable.  Also, it should be remembered that red dwarfs represent 70% of the stars in the galaxy.  Even if a large percentage of them are still within their hyperactive stages, that still leaves plenty of stable stars to choose from.
For a planet bound species, solar flaring wont neccesarily be disasterous.  Planetary magnetic fields will shield the planets from the worst of the flare and the planet's atmosphere would attenuate the radiation, even if the magnetic field were compressed.

Of course, all red dwarf planets within the habitable zone can be expected to be tidally locked.  that might produce some interesting climating effects.

Some sort of magma electrolysis may turn out to be easier.  At the sort of impact speeds neccesary for mass driver derived oxygen production, much of the gas would have a free-path speed that exceeded escape velocity.  As soon as a significant atmosphere began to accumulate, the operation of the mass driver would be impeded.

Magma electrolysis would occur on a large scale anyway, as soon as large scale manufcature of metals were carried out by lunar colonists on the surfcae of the moon.  Because the molten magma contains metals and is itself conductive, there is potential to avoid the need for expensive electrodes.

Not quite what I meant.  The moon is potted with asteroid/cometary impact craters.  Most of those bodies contained water and other volatiles.  Is it not therefore possible, that whilst the surface of the moon is bone dry, water could be trapped 100s of metres beneath craters (all over the moon)?

The average surface temperature of the moon is -20C, so any water that was trapped beneath the surface would be frozen.  Could water not exist in sub-surface pockets all over the moon?

Is it not possible that pockets of water and other volatiles are trapped beneath lunar craters?  After all, the moon has been subject to a huge number of impacts from comest and carbonaceous asteroids throughout its history.