"Henry Spencer" wrote in message
...
In article ,
David Findlay wrote:
...Many spacecraft do a bbq
roll which is basically keeping the vehicle rolling so that no side of the
vehicle gets too hot.

A "barbecue roll" in fact isn't *that* common; most spacecraft are
designed to handle being constantly one side to the Sun. Apollo did it
not to keep things from getting too hot, but to keep one specific thing
from getting too cold: it proved impossible to qualify the CM heatshield
material for prolonged "cold soak" conditions, so a slow rotation with the
spacecraft axis roughly perpendicular to the sunlight was needed to keep
it within its temperature limits.

Positioning the spacecraft axis roughly north-south -- which did indeed
imply traveling sideways -- and rolling around it was a simple way of
doing this, independent of the exact trajectory being followed and
satisfying some other arcane constraints.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |


On April 14th, 1970 the moon was in quarter phase, so the sun would
have been at some angle less than 90 degrees from a north/south axis.

RT