Adam Hadhazy’s article on artificial gravity [“Artificial gravity’s attraction,” April] was right on target: We have learned that long-term habitation in microgravity has health effects that are not easily avoided, and using centrifugal gravity may be required for human missions to the planets. However, while the article discussed centrifuges and “wheel” type solutions, it failed to mention an even better, and far simpler, solution: the use of tethers. By attaching the human habitat to a counterweight (perhaps an empty fuel tank) using a kilometer or more length of high-strength cable, the assembly can be rotated around the common center of mass, providing the required centrifugal force to give the effect of gravity. The advantage is that such cables can easily be kilometers long, thus avoiding the high rotation rates required for a centrifuge or a wheel.
Tethers were investigated by NASA back in the 1990s, but have been out of fashion at NASA in the last 20 years. But the history of spaceflight shows that the simplest solutions are often the best, and it’s time we gave the idea of tether-based artificial gravity a second look.
Geoffrey A. Landis
AIAA associate fellow
Argon arc plasma testing
The “Blackout busters” article [April] is very interesting to me as it involves an electric arc argon gas plasma for testing of manned space vehicle re-entry problems. The described test concept and facility are very sophisticated and should help solve the current re-entry communications blackout problem.
Why is this of special interest to me, retired from a rather long Lockheed “aviation” career? Before aviation (while at the U.S. Army’s Redstone Arsenal in Huntsville, Alabama, in 1957, just before Sputnik, Explorer, NASA Marshall, ICBMs, etc.), I was materially involved in the design, construction and test of a similar, smaller, but less sophisticated argon arc-jet plasma test facility for unmanned space vehicle re-entry heating problems. “Arc-Jet” was our descriptive word for the test concept. Our main purpose was to help develop heat resistant materials for ballistic missile nose cones. We got the argon arc-jet plasma prototype operational before my two years of Army duty were up. In those days, I was a research project officer (with a recent physics/math degree and an ROTC second lieutenant’s commission), working with civilian and military scientists and engineers at the Army Rocket and Guided Missile Agency Research Laboratory at Redstone.
John S. “Jack” Gibson