karn@allegra.UUCP (Phil Karn) (04/15/84)
The orbit used by IRAS in which the orbital plane maintains the same angle to the sun throughout the year is a very common one, and is the reason for the existance of satellite launching facilities at Vandenburg. These are called "sun synchronous" orbits, and many satellites have used them including weather, scientific, amateur radio, spy, earth resources, etc. The basic idea is to utilize the equatorial "bulge" of the earth to precess the orbit plane so that it makes one complete revolution each year, following the apparent motion of the sun around the earth. The use of "nautical" miles is an anachronistic embarassment that should have been dropped years ago. My contact at JSC says that a lot of the software they're using in the shuttle program was taken directly from the Apollo program and they just never updated it. By the way, the kilometer has a nice geophysical significance to it - the meter was originally defined as 1/10000 the distance between the north pole and the equator. It has since been redefined (and the earth measured more accurately) but it is still a good approximation. Phil
karn@allegra.UUCP (Phil Karn) (04/15/84)
Er, make the "the KILOmeter was originally defined as 1/10000 of the distance..." Phil