active shielding). Inertia would necessitate powerful thrusters to start or stop rotation, or electric motors to spin two massive portions of a vessel in opposite senses. Shielding material can be stationary around a rotating interior. Psychological adjustment The monotony and loneliness that comes from a prolonged space mission can leave astronauts susceptible to cabin fever or having a psychotic break. Moreover, lack of sleep, fatigue, and work overload can affect an astronaut's ability to perform well in an environment such as space where every action is critical. Economics Space colonization can roughly be said to be possible when the necessary methods of space colonization become cheap enough (such as space access by cheaper launch systems) to meet the cumulative funds that have been gathered for the purpose, in addition to estimated profits from commercial use of space. Although there are no immediate prospects for the large amounts of money required for space colonization to be available given traditional launch costs, there is some prospect of a radical reduction to launch costs in the 2010s, which would consequently lessen the cost of any efforts in that direction. With a published price of per launch of up to payload to low Earth orbit, SpaceX Falcon 9 rockets are already the "cheapest in the industry". Advancements currently being developed as part of the SpaceX reusable launch system development program to enable reusable Falcon 9s "could drop the price by an order of magnitude, sparking more space-based enterprise, which in turn would drop the cost of access to space still further through economies of scale." If SpaceX is successful in developing the reusable technology, it would be expected to "have a major impact on the cost of access to space", and change the increasingly competitive market in space launch services. The President's Commission on Implementation of United States Space Exploration Policy suggested that an inducement prize should be established, perhaps by government, for the achievement of space colonization, for example by offering the prize to the first organization to place humans on the Moon and sustain them for a fixed period before they return to Earth. Money and currency Experts have debated on the possible usage of money and currencies in societies that will be established in space. The Quasi Universal Intergalactic Denomination, or QUID, is a physical currency made from a space-qualified polymer PTFE for inter-planetary travelers. QUID was designed for the foreign