Re: What is the radiation level at the Van Allen belts

vince_at_offshore.ai
Date: 01/09/05 

To: sci-space-tech@moderators.isc.org
Date: 9 Jan 2005 01:45:54 -0800

>>From an ealier post I did:
http://spacetethers.com/posts/20031117

In "The Space Environment" by N. H. Langton (1969) they say the
Apollo plan was to avoid most of the van Allen belt radiation by
going through near the edge. Cape Canaveral is 28.5 degrees North,
which is about right for going toward the Moon. The radiation
belts are inclined about 11 degrees (as is the Earth's magnetic
field) and are about +- 40 degrees wide. If you time your
departure for the Moon so you are at the Northern part of your
orbit while over the longitude where the radiation belts are South,
you can miss most of the radiation. From pages 134-136 I quote:

>The problem of making a suitable exit through the trapped radiation
>is not in fact particularly difficult. The lunar missions at
>present proposed will leave from a parking orbit below the van Allen
>region and the most opportune instant to leave this orbit will of
>course be chosen. The radiation intensity is quite low at and above
>magnetic latitude 40 degrees North or 40 degrees South and the
>geomagnetic dipole is at an angle of 11 degrees to the Earth's
>rotational axis. The rotational axis is at an angle of 66.5 degrees
>to the plane of the ecliptic at the equinoxes and the plane of the
>lunar orbit is inclined at 5 degrees to that of the ecliptic,
>around which it rotates with a period of just over 18 years.
>Accordingly, once every 18 years, at the equinox, there is an
>instant each day when a straight line from Earth to the Moon is the
>normal at magnetic latitude 39.5 degrees. The situation is shown
>in Fig. 4.10. While this ideal path may not be followed (it imposes
>considerable restrictions on dates and times of lunar missions, and
>takes no account of solar flare incidence) the general principles
>involved are clear, and a lunar mission is unlikely to incur
>a high dose burden from the van Allen belts on its way from and
>to the Earth.

  -- Vince

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