Thursday, July 29, 2010
The ultimate goal in exploring space in the short term (within our lifetimes or a bit beyond) is certainly this: the establishment of a self-sustaining colony somewhere, and if possible one with a breathable atmosphere on the outside. In other words, the establishment of a place that kind of feels like Earth. Gravity and length of day may be different, but the ability to wake up, go for a walk, explore places beyond the confines of a simple habitation or collection of buildings, achieving this will be of critical importance in that it will mark the first time we have been able to establish a place outside of Earth that actually feels like home to those living there. More places to explore than one can see in a single week, the ability to wander off the beaten path and find places you've never seen before even after years and years living there, this is what makes a place worth living for decades or more. Anything less than this and there will always be a yearning to return to Earth, the feeling that one can take a few months or even a few years, but no more.
So let's give some thought to how this can be achieved. Where in the Solar System can humans effectively create for themselves a second Earth? Mars is the clear long-term solution, but the surface area of the planet is equivalent to the total land surface on Earth, and terraforming Mars is well beyond our current abilities, estimated to take thousands of years. In addition, Mars itself is still very difficult (in fact, still impossible) for humans to land on, launch windows are less than favorable, weather and seasonal variation plus a relatively long day (26 hours) make electricity gathering difficult.
What we are capable of in the short to medium term, however, is paraterraforming (creating livable pockets and then expanding until the entire surface is inhabitable) smaller destinations. 24 Themis is a good example of an asteroid that is interesting but likely still too large for us to completely settle in the short to medium term. 24 Themis has a diameter of 200 km and thus a surface area of some 120,000 km2, similar to Pennsylvania or Greece. What makes it particularly interesting however is the presence of large amounts of water ice on the surface. It is very likely that the water on the surface is due to the same process that creates H2O in the Moon's soil (H+ in the solar wind combining with oxygen in the soil), and if so then it stands to reason that H20 should be present on other asteroids as well. This is still undetermined, but in the meantime let us assume that there are many other destinations out there with water ice.
The ideal destination would:
- have water ice on the surface,
- be large enough to provide a sense of adventure and the ability to regard it as a second home, as well as massive enough that one cannot simply fall off, breaking orbit through a simple misstep,
- be small enough that paraterraforming alone should eventually allow us to cover virtually the entire surface.
An ideal destination then would be an asteroid within the asteroid belt, with a diameter of some 30 to 50 km. This would give an escape velocity of some 80 - 130 kph, and a surface area of 2800 - 7800 km2, somewhere between Luxembourg and the Palestinian territories. This surface area would also be 18000 to 50000 times less than that of Mars, making it a monumentally easier task.
In other words, an asteroid of this size would be something akin to a Stanford torus in that it would be completely enclosed, but it would be much larger, would not have artificial gravity, and all the building materials would be right there instead of requiring them to be shipped in.
In the meantime the Moon is a much easier target than any of these, but we should keep our eyes open for the perfect candidate. One day we may find water ice on the surface of an asteroid of about this size at a fairly good distance and closely aligned to the orbits of the planets, and if so we may wish to begin thinking about the prospect of colonizing it once we have acquired the ability to send people to such destinations. As always, VASIMR is an absolute must before we can consider anything at this distance.
And before even this, the planned manned mission to a near-Earth asteroid in the 2020s if it goes through will provide us the first images of the surface of an asteroid as visited by humans, and this will also be a good time to discuss the subject.