From: russell@sweetpea.jsc.nasa.gov (thomas russell 283-4007)
Newsgroups: sci.space.shuttle
Subject: Re: SSF
Date: 21 Aug 92 18:13:03 GMT
Organization: McDonnell Douglas Space Systems Company

In Article <1992Aug20.000610.2462@aio.jsc.nasa.gov> kjenks@gothamcity.jsc.nasa.gov
says:

>SSF will be in a circular orbit, about 250 nautical miles up, at a 28.5
>degree inclination to the equator.  (I'm unsure about the exact
>altitude, but that's close.)

>The spacecraft will be in one of the less stable "gravity gradient"
>positions, with one end of the long structure always pointed in the
>direction of travel, and the modules always pointed at the Earth
>below.  I'll try another ASCII sketch.  Think of this as a sequence
>of pictures, with "0" being the Earth:
>
>                        _             
>            /                       \
> |  0         0         0         0         0 |       0         0         0
>                                                        /       _       \
>
>   1         2         3         4          5        6         7         8
>
>
>Picture a stick (SSF) running clock-wise around a ball (Earth).
> ... <deleted>


After the Station Builds reach the Permanently Manned Configuration (PMC),
it will spend most of its time in an attitude such that the truss is
purpendicular to the direction of travel. Thus the station rotates about
its long axis at approx. 6 degrees/min to keep the module pattern oriented
towards earth.  This general attitude is refered to as the Local Vertical
Local Horizontal (LVLH) orientation. This is only a general attitude because
the station flys with its principle axes more or less aligned
with the LVLH frame. Deviations from the principle axis alignment are
used to generate gravity gradient torque to oppose the small aerodynamic
torques which are experienced in LEO. This attitude is normally called the
Torque Equilibrium Attitude (TEA) and must be maintaned to prevent
momentum saturation of the Control Moment Gyros (CMGs).

To borrow Ken's picture:


                      Velocity into page

                               O-------> Out of Orbit Plane Direction
                               |
                               |
                               |
                              \|/ 

                             Earth


     SSSS                                               SSSS   SSSS
     SSSS      T                                    T   SSSS   SSSS /|\   |
     SSSS      T                                    T   SSSS   SSSS   \ _ /
    tSSSStttttttttttttttttttttttttttttttttttttttttttttttSSSStttSSSSt
    tSSSStttttttttttttttttttttttttttttttttttttttttttttttSSSStttSSSSt 6 deg/min
     SSSS      T            nMMMMMMMn               T   SSSS   SSSS   rotation
     SSSS      T            cMMMMMMM                T   SSSS   SSSS
     SSSS                                               SSSS   SSSS

    Legend:  t = truss, S = solar panel, T = thermal radiator, 
             n = node, M = module, c = Cupola


Clear as Mud right? Hope this helps a little.

The Attitude which Ken refers to is used for orbit reboost prior to PMC.
The SSF attitude control community refers to it as the Arrow Orientation.

As for the rest of Ken's response, I'll go along with his simple answers...

   - Tom Russell / MDSSC-Houston
Newsgroups: sci.space.shuttle