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NASA Still Trying to Verify Anti-Gravity Claims
uncoda writes "The L.A. Times has an article about NASA research into a phenomenon in which the effect of gravity is supposedly reduced. It sounds like cold fusion or polywater to me, but who knows?" We've posted two previous stories about Podkletnov's research: one from a couple of years ago and another more recently.
This has been going on for a while. See the most recent note on this subject from Bob Park's "What's New." He refers to an earlier $2M that got dropped on this crackpottery.
Evgeny Podkletnov and Giovanni Modanese have posted one of their papers on the arXiv: http://xxx.lanl.gov/abs/physics/0108005
Sustained rotation in a given plane (as when in a rotating craft) causes the inner-ear fluid to flow with the same angular velocity. If the head is moved out of the plane of rotation (as by turning your head), the continuing fluid movement in the old plane gives a sense of rotation in the new plane, even though no such movement is occurring. This disorienting and nauseating sensation, called Coriolis cross-coupling, is made worse by high rotation rates and short radial arms. Any movement not parallel to the axis of rotation will provoke Coriolis forces. An astronaut climbing towards the axis of rotation decelerates as he/she moves into an area of lower velocity, and experiences a force in the direction of rotation. An astronaut climbing down the same ladder feels a force pushing him/her against the direction of rotation. An astronaut running in the direction of rotation gains angular velocity and thus feels heavier, and one running against rotation feels lighter. Research at NASA Langley Rotating Space Station Simulator indicates that ambulation in the direction of rotation at rotation rates corresponding to greater than 0.3 g produces a disturbing heaviness in the legs, while ambulation against the direction of rotation is not possible below 0.05g. Finally, Coriolis forces act on any moving object; even fluid poured in a rotating field deviates in its course.
Then there's the problem of gravity gradients. Centripetal acceleration (the 'gravity') is a linear function of radius; thus, there is a 100% gravity gradient running from the axis of rotation to the outer rim. An object weighing 10 kg on the 'floor' (rim) would weigh 5 kg if moved half-way up towards the 'ceiling' (axis). The percentage weight change an object moving from a point Ra to a point Rb experienced is given by:
W1/W2 = (Ra - Rb)/Rb
Thus, an object raised to a 1 meter shelf in a 4-meter rotating station (from Ra = 4 m to Rb = 3 m) would lose 25% of its weight. It is unknown how this sudden weight loss would affect materials handling; e.g., would a suddenly lightened box tend to fly out of one's hands?
In addition, a 2-meter tall astronaut standing in a 4-meter rotating station would feel literally 'light-headed'; the head (nearer the axis of rotation) weighs 50% less than the feet!
Despite these concerns, the gravity gradient appears to be the problem of least concern in designing a rotating habitat, and was considered a 'non-problem' in NASA's recent Artificial Gravity Working Group.
How we know is more important than what we know.