"Jorge R. Frank" wrote in message
...
Sure. How detailed an explanation you want? :-)

The temperature restrictions are expressed with respect to a parameter
called "solar beta angle". That's the angle between the ISS orbit plane
and the line-of-sight to the sun. This varies throughout the year due to
the Earth's axial tilt with respect to its orbit around the sun (called
the "obliquity of the ecliptic", about 23.4 degrees), and the Earth's
equatorial bulge, which causes the ISS orbit plane to shift westward
about five degrees per day.

Beta angle affects both solar power generation and thermal control. At
higher beta angles, ISS spends less time in the Earth's shadow, and must
fly different attitudes to keep its solar arrays facing the sun and its
radiators edge-on away from the sun. At beta angles above 70 degrees,
there is no orbital night at all. The maximum beta angle is 75 degrees,
the sum of the ISS orbit inclination (51.6 degrees) and the obliquity of
the ecliptic.

Throw a docked orbiter into the mix and you have a third constraint,
shuttle thermal control. The attitude of the orbiter/ISS stack must be
chosen to satisfy ISS power/thermal constraints and shuttle thermal
constraints. It turns out that at beta angles larger than 60 degrees,
there is no attitude that satisfies all three. So the shuttle program has
a launch window cutout when the beta angle will exceed 60 degrees at any
time during docked ops.

These cutouts occur around the solstices, because that's the time of year
when the sun's declination is farthest north (summer) or south (winter)
and so the odds are greatest that the sum of the sun's declination and
the orbit inclination will exceed 60 degrees. The summer cutout affects
night launches and the winter cutout affects day launches. The shuttle
return-to-flight restriction on night launches has effectively mooted the
summer beta cutout, but the combination of the night launch restriction
and the winter beta cutout makes winter launch opportunities few and far-
between.

The 60 degree limit on beta angle during docked ops is a certification
limit. The station program is looking at expanding certification to relax
the limit. This will not be complete any time soon.


O.K Jorge, I am humbled by your knowledge. I have to ask one thing. Did you
type that all out on the fly? or copy and paste it from somewhere. I didn't
understand any of it, although, oddly enough. It made sense.