world, in which astronauts may perform simulated EVA tasks in preparation for space missions. The NBL contains full-sized mock-ups of the Space Shuttle cargo bay, flight payloads, and the International Space Station (ISS). The principle of neutral buoyancy is used to simulate the weightless environment of space. The suited astronauts are lowered into the pool using an overhead crane and their weight is adjusted by support divers so that they experience no buoyant force and no rotational moment about their center of mass. The suits worn in the NBL are down-rated from fully flight-rated EMU suits like those in use on the space shuttle and International Space Station. The NBL tank is in length, wide, and deep, and contains 6.2 million gallons (23.5 million liters) of water. Divers breathe nitrox while working in the tank. Neutral buoyancy in a pool is not weightlessness, since the balance organs in the inner ear still sense the up-down direction of gravity. Also, there is a significant amount of drag presented by water. Generally, drag effects are minimized by doing tasks slowly in the water. Another difference between neutral buoyancy simulation in a pool and actual EVA during spaceflight is that the temperature of the pool and the lighting conditions are maintained constant. Speculative or fictional mechanisms In science fiction, artificial gravity (or cancellation of gravity) or "paragravity" is sometimes present in spacecraft that are neither rotating nor accelerating. At present, there is no confirmed technique as such that can simulate gravity other than actual mass or acceleration. There have been many claims over the years of such a device. Eugene Podkletnov, a Russian engineer, has claimed since the early 1990s to have made such a device consisting of a spinning superconductor producing a powerful "gravitomagnetic field", but there has been no verification or even negative results from third parties. In 2006, a research group funded by ESA claimed to have created a similar device that demonstrated positive results for the production of gravitomagnetism, although it produced only 0.0001 g. This result has not been replicated. See also References External links List of peer review papers on artificial gravity TEDx talk about artificial gravity Revolving artificial gravity calculator Overview of artificial gravity in Sci-Fi and Space Science NASA's Java simulation of artificial gravity Variable Gravity Research Facility (xGRF), concept with tethered rotating satellites, perhaps a Bigelow expandable module and a spent upper stage as