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From: (JamesOberg)
Date: 05 Dec 2000 15:42:01 GMT
Subject: Re: ISS- Orbit param's- ie, it's "Zodiac"

Not a bad question for a newbie! Any orbit has an 'ecliptic' and two poles.

The problem is, the orbital plane of ISS precesses rapidly due to Earth's
equator bulge, once every 60 days or so. So it's 'zodiac' is constantly

The axis bobs up and down with respect to Earth's orbital plane, and here's how
much. Earth is tilted up 67deg, and the orbital inclination is tilted 52deg to
Earth's axis. Every two months, the axis of ISS's plane varies between a
maximum of 75deg and a minimum of 29deg.

When the axis is closest to the Earth-sun line (it's minimal elevation from
Earth's ecliptic), and the Earth axis is angled most strongly toward the Sun
(winter and summer solstice) the ISS practically orbits continuously over
Earth's terminator, and is in continuous sunlight for several days. This plays
havoc with its thermal control system, as it did for Mir.

From: (JamesOberg)
Date: 06 Dec 2000 01:16:13 GMT
Subject: Re: ISS- Orbit param's- ie, it's "Zodiac"

<Am I missing something here? (Wouldn't be the first time) The Earths
axial tilt is 22 degrees.>

Depends on the reference frame. Since we're also talking about satellite orbits
whose inclinations are measured UP from the equator, I just converted the Earth
tilt to the same reference frame.

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