Correction: ISS Attitude

From: Jeff (jayteepee@worldnet.att.net)
Date: Fri Dec 15 2000 - 18:24:40 PST

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     From my earlier post, I incorrectly stated:
    
     >I believe the X-axis stays perpendicular to the ground. Soyuz leading.
    
    Actually, the X-axis is =parallel= to the ground with the Soyuz =trailing=.
    
    (I should have known better than replying before the first cup of coffee in 
    the morning.  Sorry for the confusion...)
    
    
    Transcribed from the Expedition One Mission Status Briefing (via NASA TV 
    on  2000.12.15)
    
    Reporter: Phil Chein - "Earth News"
    Official: Jeff Hanley - Expedition One Lead Flight Director
    
    Q. The P6 Array - Is it rotating now to face the Sun throughout the orbit 
    or are you just leaving it in one position and just accepting the fact that 
    you are not getting all the watts - which you don't really need anyway?
    
    A. We're leaving it in one position - wings flat and level - and we won't 
    start rotating them until the beta angle, relative to the orbit plane - the 
    angle of the Sun relative to the orbit plane - gets high enough for us to 
    see a drop off in the performance of the wings.  But we're very satisfied 
    with the performance of the solar arrays to date.
    
    Q. So are you in an "X-POP" attitude still or are you in "LVLH" to minimize 
    the drag because of the big arrays?
    
    A. We're in "LVLH". We plan to stay there throughout the beta regime.  As 
    the beta grows and then decreases we plan to stay in LVLH to save 
    propellant.  The propellant costs in flying "X-POP" is very high.  We'd 
    really like to avoid that till we get the CMG system on the US segment 
    active and can use momentum management to hold attitude.
    
    (later in the briefing - from Phil)
    
    Q. One more question about the attitude with the "LVLH".  I assume it's PMA 
    forward - Z1 going to nadir - PMA-3 going to zenith, straight into the 
    flight direction?
    
    A. No.  PMA-3 is facing Earth.  P6 is sticking up, facing the zenith and 
    wings flat.  It's in the attitude you saw in the fly-around video when the 
    (STS)97 crew undocked from the station.  It's in exactly the same attitude.
    
    Here is a good picture of the arrangement.  POV is behind the station's 
    line of travel.
    http://spaceflightnow.com/ops/stage4a/001209snapshots/withearth.html
    
    Here is a tech paper on ISS attitudes. (with illustrations)
    http://idb.exst.nasda.go.jp/edata/02110/199810K02110020/199810K02110020.html
    
    Figure 1.1.1-1 is a good example of "LVLH".
    
    "LVLH" = Local Vertical, Local Horizontal
    
    Jeff
    
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