In the book The First Space Race, Erika Vadnais and I discussed the discovery by Jame Van Allen and his team of the lower Van Allen belt in early 1958 by a particle detector placed on the Explorer 1 satellite. There are now known to be two belts, varying in thickness and intensity based on natural events (the Sun pouring out an increased volume of energetic particles) or human-made events ("pumping the Van Allen belts"), an effect most famously seen in the Starfish Prime nuclear test of 1962, which degraded or destroyed several satellites. In 2013, NASA announced the discovery of a third belt. The this belt was outside the other two, appeared only when a solar prominence had unleashed a very large flow of particles, and lasted up to four weeks. It was once feared astronauts could be launched only through the polar regions, where the belt effects were weak or absent, but limiting astronauts' time in orbit and restricting them to an orbital altitude above or below the inner belt works, too. Only the Apollo astronauts transited the outer belt, and they punched through it rapidly on their way to and from the Moon, limiting the exposure time and thus the exposure in rads to to a level that was survivable.
Van Allen belts (in yellow) in 2013 illustration released by NASA's Goddard Space Flight Center
See:
Wiley J. Larson and James R. Wertz (Editors), Space Mission Analysis and Design, 3rd
Edition, Section 8.2, "Hardness
and Survivability Requirements," 1 October 1999.
Fox, Karen. “NASA's Van Allen Probes Discover a
Surprise Circling Earth,"
NASA press release, 28 February 2013.
Bille and Lishock, The First Space Race (Texas A&M), 2004.
5 comments:
I have heard that the Apollo Astronauts do have cataracts more then usual.
You're right, although there is still some question about the mechanism involved. https://science.nasa.gov/science-news/science-at-nasa/2004/22oct_cataracts
How can it really be known what the earths periods of eccentricity, perihelion and obliquity are when the observational data only cover at most 3,000 years? What I mean is that these parameters involve cyclical change so we have no direct observational evidence that would give the turning points of these cycles or the lengths of them. Considering that they are supposed to be controlled by the tiny masses of the planets I wonder how they can possibly know. For example, the obliquity cycle is supposed to be 41,000 years but since we are in the middle of that...
I particularly wonder how they could vary from the periodicity of precession. How could the physics be such as to have the precessional wobble vary at a different rate than the obliquity?
I think that common sense would suggest that the periodicities would be the same.
Laurence, excellent point about how complex all this is. I've no expertise in the questions you ask, though. Anyone?
Thanks Matt. You are just the first person I thought of when wondering who would know. I bet the mathematicians are mistaken. A man named Shackleton made the calculations used by Pilgrim and then by Milankovitch... I am sure I can find a site specializing in this...
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