Monday, August 3, 2015

Where to?

To get into deeper detail requires settling on one or more locations.

 I think we can rule out any free-space colonies just on the basis of radiation shielding. The required mass is just so enormous that there does not seem to be any cost-effective way to collect it. A habitat for 10,000 people could take up to a few hundred thousand tons of shielding. NASA's asteroid retrieval mission was set to retrieve about one thousand tons for one to two billion dollars. Granted if one wanted to capture a hundred asteroids the economies of scale would drive down the cost, but we would still be talking about tens of billions of dollars.

 Bodies with gravity are a decent idea. The Moon is close, fairly easy to leave (re-usable shuttles could be used) and a habitat there would have a useful level of gravity for plant, people and industry. The trouble is that the Moon has very little carbon, basically no nitrogen and an unknown amount of hydrogen in the form of water ice. Oxygen is abundant, as are lighter metals and silicon. As it goes, this might make a good stepping stone for proving hydroponic systems and resource extraction with less risk than some other places. Solar power on the Moon is hard because of the two-week night period; activity here will tend to run in cycles of two weeks busy, two weeks slow. A polar base could avoid that power difficulty in exchange for higher shipping costs. Because of the proximity to Earth, a Lunar surface base working with an L1 or L2 station could build or service satellites for use in Earth orbit; this is a near-term service with significant potential value. In the long run a Lunar colony would always require supplies from Earth or another colony, but will probably do enough business in trade to be viable.

 Mars is another good idea. The gravity is higher than the Moon. There's carbon and buffer gases right there in the atmosphere, plus proven reserves of water ice and enormous amounts of iron oxides. All the elements necessary for plant life are available. Downsides are the harsh weather (nasty dust storms, sometimes for months at a time), long travel time (several months trip only once every 2.2 years) and high cost to launch from the surface to get anywhere else. As long as there is political will, some Earth governments might be willing to support a very basic Mars outpost. If this also includes the equipment necessary to produce PE plastic then that outpost could eventually produce the materials for the first large colony. Shipping costs are high and the travel time is long, so Earth-based launchers would probably be stiff competition.

 Bodies without significant gravity are also possible. The Martian moons Phobos and Deimos are basically large asteroids in orbit around Mars. Solar power is more reliable than on the surface. There is no gravity to speak of, so shipping is cheaper. It makes the habitats more complex because they will need spin gravity, but there is still plenty of material to bury them under for shielding. As with the Moon there are no buffer gases, but carbon is available as is water ice. Ceres is another possibility out in the asteroid belt, with huge amounts of water but otherwise many of the same limitations as the Martian moons and the added difficulty of even less solar power available.

 A Phobos base paired with a Mars surface base could be a very good team, particularly with the use of tethers. This provides reduced shipping costs, access to the full spectrum of necessary elements, a broader range of things for trade (including science data and samples in the early phases) and a nearby backup facility in case something goes wrong. That long gap between launch windows is still really annoying, but for bulk materials it could be managed. Martian surface exports would include structural plastic, argon for use in atmospheres and as electric engine fuel, nitrogen for atmospheres and as fertilizer, CO2 as a carbon source and methane as a fuel, carbon source and/or hydrogen source. Phobos exports would include water ice, metals, food, bulk shielding and valuable elements (platinum-group metals, rare earth elements, gold, etc.)

 For now I will assume the Moon serves as a technical demonstration environment. Before technologies are incorporated into the final colony they will first be tested on the Moon or in Lunar orbit. That also means Lunar products will be available to accelerate the program compared to an all-Earth-launch baseline, and a market for goods and services in Earth orbit will exist. The baseline colony will be split between Phobos and Mars. My target is an estimated cost of $150 billion or less, roughly the cost of the international space station. As a permanent colony, the program can take a long time to complete if necessary but should result in habitable structures within 30 years.


  1. Delta V to reach the lunar poles isn't much more than for the lower lunar altitudes. But launch windows are more restricted and a polar orbit doesn't enjoy the any time return we'd like to have if the space craft carry live passengers. But still I believe the poles are accessible.

    There are some plateaus at the lunar poles that enjoy nearly constant illumination. But when the sun is low in the sky, it is easy for one solar array to cast a shadow on his neighbor. So solar power is still difficult.

    At one time I was passionate about the moon. But there are conflicting data on richness of cold trap volatile deposits. If Spudis' imagined glaciers at least two meters thick turn out to be real, my passion will be rekindled.

    A Phobos base paired with a Mars surface base could be a very good team, particularly with the use of tethers.

    I'm in complete agreement. Where would you like to see a Mars base? On the equator on a high mountain? Marshall Eubanks suggests such a base would make for easier access to a Phobos tether.

    I've always thought Mars' atmospheric CO2 and argon were great resources should we expand our horizons to the main belt. After hearing your description how tether material might be manufactured from local carbon compounds, I'm even more enthusiastic.

  2. A lunar base seems to need captured C or D type asteroids for volatiles in the long run. Perhaps discoveries of large water supplies might change that and make a tramway from pole(s) to L1/L2 tether anchors reasonable.

    I think flywheel arrays could be the answer to energy storage on the moon; they can be built using local materials and do not degrade over time like chemical batteries. That might open up the territory a bit.

    As for Mars, I hadn't given much thought to a specific location. I assume it would be nearly equatorial for easy access to the Phobos tether, but those polar ices are such extremely rich sources of CO2 and water that it's hard to rule them out until we know more about subsurface ice near the equator. Perhaps suborbital transports could move cargo between the two sites.

    Making polyethylene from CO2 and water isn't simple, but it is a lot easier than trying to make aramids or PBO with all their benzene rings. Using ethanol as an intermediate step means easy conversion of biomass into a storable compound. It is volatile, toxic and flammable but compared to a lot of other chemical intermediaries it is quite safe.

    I was really into Phobos as a destination, but ongoing research seems to suggest that Mars will be much easier to colonize. I think there will be a place for Phobos as a research station demonstrating technologies to live on or in the minor bodies and as a manufacturing station for building and servicing ships, but it seems increasingly likely that we will inhabit either the Moon or Mars first.

  3. One thing we need to do before sending colonies to various moons or planets is work out the minimum gravity necessary for human reproduction. No point in a colony that can't create a new generation.

    1. It's an open question, one we will not be able to answer without a substantial laboratory presence in space. The ISS could run a series of small mammal experiments in microgravity (at the expense of a lot of other science), but this is something that requires access to a range of gravity values.

      I think the safe approach is to make a 1g area available from the beginning. We still don't know if there is any kind of health-risk cliff after some number of years in microgravity or what the effects (good or bad) of any particular value between 0 and 1 might be. A centrifugal habitat would give access to everything from 0 to 1 or more and allow for detailed experimentation on a number of species, with less risk for the occupants than the ISS approach. If they discover some harmful effect of microgravity the crew can spend most of their time in higher-gravity areas of the habitat. This is the kind of science we could bake into a rotating habitat in LEO or at EML-1 in parallel with other plans; NASA could include this as a research series in their 'dry-run' Mars transit habitat that is supposed to be placed in lunar orbit. Tackling the problem in stages would allow for automated test cycles checking for egg fertilization rates and preimplantation development for a variety of species and gravities, leaving the more complex work of evaluating end to end birth rates for a smaller number of species and gravities to on-site scientists. If we want a private option, a pair of Bigelow modules could be tethered and spun (or connected by a truss + tunnel and spun) for around $700 million (using F9H as launcher). Throw in another $300m for science equipment, supplies and staffing flights and you could run a 6 to 12 person variable gravity research station for a couple of years on a billion dollars or so. Such a station could be launched as early as 2017, and excess volume could be rented to other entities to help recoup costs.

      Aside from gravity, radiation is the other known problem affecting reproduction in space. Even if 0.16 g turns out to be just fine for humans a moon colony would still need dramatically better shielding than a short-term base.