Space architecture of space and a space transportation infrastructure can be accelerated. Virgin Galactic has indicated plans for an orbital craft, SpaceShipThree. The demand for space tourism is one without bound. It is not difficult to imagine lunar parks or cruises by Venus. Another impetus to become a spacefaring species is planetary defense. The classic space mission is the Earth-colliding asteroid interception mission. Using nuclear detonations to split or deflect the asteroid is risky at best. Such a tactic could actually make the problem worse by increasing the amount of asteroid fragments that do end up hitting the Earth. Robert Zubrin writes:
Space tourism subtropics, whereas the temperature at the poles would increase by between . The ozone layer would also be affected, with the tropics losing up to 1.7% of ozone cover, and the polar regions gaining 5–6%. The researchers stressed that these results should not be taken as "a precise forecast of the climate response to a specific launch rate of a specific rocket type", but as a demonstration of the sensitivity of the atmosphere to the large-scale disruption that commercial space tourism could bring. Several organizations have been formed to promote the space tourism industry, including the Space Tourism Society, Space