From: mll@aio.jsc.nasa.gov (Mark Littlefield)
Subject: Re: EVA troubles (Was Re: ground vs. flight
Reply-To: mll@aio.jesnet.jsc.nasa.gov
Organization: Lockheed ESC/NASA JSC
Date: Thu, 24 Dec 1992 19:42:18 GMT

In article <j6v2=m#@rpi.edu>, strider@clotho.acm.rpi.edu (Greg Moore) writes:
|> In article <Bzr29K.5GB@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes:
|> >In article <=hv29vp@rpi.edu> strider@clotho.acm.rpi.edu (Greg Moore) writes:
|> 
|> >>	Also, given that the bottom of the shuttle is covered with
|> >>tile, can the orbiter exert a Y+ (i.e. vertically up) translation?
|> >
|> >There aren't any RCS nozzles on the orbiter's belly, but both the forward
|> >and aft RCS systems have nozzles angled down so that they can (somewhat
|> >inefficiently) thrust upward.
|> >
|> 	Ok, taht's what I thought.  So I'd assume you'd want to do as
|> little Y+ translations as possible.  Anyone know the approach path 
|> for the orbiter?  Will it approach cargo bay first, or will it attempt
|> to do a partial "flyby" where it approaches nose first (i.e X+ translation).
|> I'd assume the latter, to safe fuel, and to allow it to "float by' if 
|> something goes wrong.  With a Y+ translation if an 'up" thruster
|> (to stop the Y+ movement) fails, you risk running the shuttle into the
|> orbiter.  With the X+, if something fails, you just float on by.  If
|> it works, you simply stop 15'-20' away and let the arm pull oyu in the
|> rest of the way.

First off, as a data point, "Y+" is not "vertical up".  There are two
coordinate systems that both the shuttle and SSF use:  LVLH and
vehicle body.  LVLH, or Local Vertical, Local Horizontal is a
coordinate system has X in the direction of flight, Y to the right of
the direction of flight, and Z toward the center of the earth.  This
is different from the orbiter or SSF body coordinate systems.  For the
orbiter the body coordinate system is X along the nose, Y out the
right wing, and Z out of the bottom.  For SSF it's X out of the US
lab/hab side, Y to the right solar panels, and Z to form the right
hand coordinate system  Also note that the SSF body coordinate system
is nominally oriented with LVLH. 

The orbiter can, in fact, thrust in the -Z "body vertical" direction.
Not working in orbiter systems I don't have the details handy.
However, there are a set of RCS jets on the orbiters nose that point
at about Z+-30 degrees.  When these jets are fired, it pitches the
orbiter (positive Y rotation).  If I am not mistaken there are also Z
pointing thrusters near the tail.

As far as docking/berthing the orbiter to SSF.  As of ~March 1992
(when I took a set of SSF orientation classes), the decision to dock
or berth the orbiter had not been made.  At the time things seemed to
be leaning to berthing (that is, moving the orbiter close to SSF and
letting the RMS move the orbiter to attach to SSF, rather than just
letting the orbiter slide up and mate like Apollo).  My guess is now
that with the studies of the Russian androgynous docking adapter, that
may change.  If anyone has heard anything new, let me know.

-- 
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Mark L. Littlefield              Intelligent Systems Department
internet: mll@aio.jsc.nasa.gov 
USsnail:  Lockheed Engineering and Sciences 
          2400 Nasa Rd 1 / MC C-19            
          Houston, TX 77058-3711
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