rjnoe@ihlts.UUCP (Roger Noe) (10/23/84)
The oceanfront dock at the new $2.5 billion space shuttle launch complex at Vandenberg AFB was damaged slightly when a barge delivering a shuttle fuel tank broke loose, the Air Force said Monday. No one was injured, and the $21 million external fuel tank was not damaged. The accident did cause a six-hour delay in unloading the 154-foot-tall, 70-ton tank. The fuel tank is to be used in ground tests prior to first shuttle launch at Vandenberg, scheduled for October 1985. The new complex is for high- security military shuttle flights. The apparent cause of the mishap was a failure by the barge to dump its ballast water quickly enough to keep the vessel level as the tide receded in brisk winds. -- Roger Noe ihnp4!ihlts!rjnoe
stevel@haddock.UUCP (10/26/84)
Vandenburg is built for Polar launches. Now it just happens that
most military flights use polar orbits and the military is paying
for the Vandenburg facility, but a good number of civilian
flights use polar orbits also. Landsat, weather satilites,
anything that wants to cover the whole surface of the earth.
Correct me if I am wrong but I think the sun syncronous orbit is
approximatly polar also.
Steve Ludlum, decvax!yale-co!ima!stevel, {amd70|ihnp4!cbosgd}!ima!stevelkarn@mouton.UUCP (10/27/84)
The "sun synchronous" orbit is a special case of a polar orbit, but it is by far the most popular one. "Sun synchronous" means that the angle between the orbital plane and the earth-sun line stays essentially constant over time. This cannot happen in simple two-body motion, of course, because the orbital plane would remain fixed in inertial space while the sun appeared to move around it once per year. However, the equatorial bulge of the earth can be exploited. It turns out that the angle between the orbital plane and the "fixed" stars measured in the equatorial plane (and known as the Right Ascension of the Ascending Node) changes on each orbit due to the tugging of the earth's equatorial bulge. The rate of change of RAAN depends on the orbital period (and hence on altitude), and also on the orbital inclination. It turns out that for a given altitude, there is a "magic" inclination (always greater than 90 degrees) in which the RAAN increases exactly 360 degrees per year. This means that the orbital plane will precess eastward, exactly matching the apparent motion of the sun around the earth during the year. This orbit is very useful for earth observation satellites (of all types) as they can monitor the earth at the same local time and sun angle each day. You select the local time you want by launching at a particular time. Typical launch windows for sun-synchronous missions are 5 MINUTES long, once per day, and should prove to be an interesting challenge for the shuttle. Because sun synchronous orbits always have inclinations near 90 degrees (e.g., Oscar-11: 700 km altitude, 98.2 degree inclination; Oscar-7, 1450 km altitude, 101.4 deg inclination), they must be launched on either a northwest or southwest trajectory. This is impossible from Cape Canaveral without passing over land early in the flight. From Vandenburg AFB, however, there is nothing but thousands of kilometers of empty ocean to the southwest. This also presents quite a challenge to an emergency landing, of course. Phil
broehl@wateng.UUCP (Bernie Roehl) (10/29/84)
The other nice thing about a sun-synchronous orbit (in addition to passing
over points on the earth's surface at the same local time each cycle) is
that it can be set up so the plane of the orbit is roughly perpendicular to
the earth-sun vector, guaranteeing that the satellite is *always* facing the
sun. This means solar panels can provide all the power all the time, and
storage batteries for operation during the "night" portion of an orbit can
be eliminated (at a substantial saving in launch mass and hence in launch cost).
--
-Bernie Roehl (University of Waterloo)
...decvax!watmath!wateng!broehl