From: kjenks@gothamcity.jsc.nasa.gov
Newsgroups: sci.space.shuttle
Subject: Re: SSF
Keywords: space station Freedom
Date: 20 Aug 92 00:06:10 GMT
Organization: NASA/JSC/GM2, Space Shuttle Program Office
Originator: kjenks@gothamcity

In article <1872.2A928EDB@catpe.alt.za> Grant.Smith@f5.n7103.z5.fidonet.org (Grant Smith) asks some reasonable questions:
>I have [heard] a lot about space station Freedom, but still don't know
>quite a few things.....
>.
>1) What will it look like (circular, conical etc.)
>.
>2) Above where will it orbit? Will it's orbit be fixed?
>.
>3) Will it be put into a spin for gravity purposes?


Before I begin, I'll warn you: I'm a Shuttle guy, not a Freedom guy.
I'll give you the best beginner-level answers I can, but there are some
real SSF folks on the Net who may be able to shed more light.

>1) What will it look like (circular, conical etc.)

The current plan, under review yet again, is to have pressurized
modules hanging in the middle of a 90-meter long truss.  The four
white, cylindrical modules are to be about 10 meters long, and five
meters in outside diameter.  Toward each end of the truss are to be
solar panels for electrical power generation.  Between the modules and
the solar panels are to be some thermal radiators to rid the spacecraft
of excess heat.  (One recent re-design concept calls for half-length
modules.  They're less efficient, by almost all measures, but they're
cheaper up-front.)

The four modules are to be connected end-to-end to form a "race track,"
with "nodes" in between the modules.  Atop one of the nodes is a
"cupola" to allow external observation and visual navigation to assist
rendezvous operations.  (The modules have no windows, so the cupola is
the only place to look out through glass.  There will be several
externally-mounted TV cameras.)  Space Shuttles (and maybe other
spacecraft) will be able to dock with one of the nodes.  (There's a
big fracas in the SSFP about docking vs. berthing.  Don't ask.)

Those are the major features.  Now, for my next trick, I'll try an
ASCII picture:

     SSSS                                               SSSS   SSSS
     SSSS      T                                    T   SSSS   SSSS
     SSSS      T                                    T   SSSS   SSSS
    tSSSStttttttttttttttttttttttttttttttttttttttttttttttSSSStttSSSSt
    tSSSStttttttttttttttttttttttttttttttttttttttttttttttSSSStttSSSSt
     SSSS      T            nMMMMMMMn               T   SSSS   SSSS
     SSSS      T            cMMMMMMM                T   SSSS   SSSS
     SSSS                                               SSSS   SSSS

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

I've "drawn" the solar panels facing perpendicular to your line of
sight, and the thermal radiators parallel to your line of sight, but
they will gimbal to maintain this geometry with respect to the Sun, so
the panels get as much incident solar radiation as possible, and the
radiators get as little as possible.  Think about it.


>2) Above where will it orbit?  Will it's [sic] orbit be fixed?

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).  This
is certainly not to scale.  Earth's diameter is around 7,900 miles.  A
250 nm orbit is just skimming the surface, barely outside most of
the atmosphere.

(For the orbital mechanics on the Net, this is an incredible
simplification, and even blatantly wrong, because the orbit is
counter-clockwise if Earth is viewed down the North Pole axis.  
For everybody else, it's probably just gibberish.)

Just as with the Space Shuttle and every other large spacecraft, you'll
be able to see it from Earth as a bright, moving spot at sunset and
sunrise if the light is right.


>3) Will it be put into a spin for gravity purposes?

No.  The structure isn't strong enough to do this.  Strong structures
tend to be heavy, and minimizing launch mass is one consideration.  If
we wanted spin "gravity," we'd put at least one module at the end of
the truss, instead of clustered in the middle.  Or, more likely, we'd
use a tether that we could reel in and out for variable gravity.

Spinning spacecraft make for a treacherous rendezvous.

I'll try to get some introductory SSF briefing material scanned in and
posted to ames.arc.nasa.gov.  No promises.

-- Ken Jenks, NASA/JSC/GM2, Space Shuttle Program Office
      kjenks@gothamcity.jsc.nasa.gov  (713) 483-4368

     "The earth is the cradle of humanity, but mankind will not stay in
     the cradle forever." -- Konstantin Tsiolkvosky