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    Re: LADEE Moon Probe Puzzle
    From: Derrick Young
    Date: 2013 Sep 16, 13:08 -0400

    First, To Fred and others, I apologize for this being a long post.  If not 
    relevant, please delete.
    
    Peter,
    
    You ask a good questions.  I don't know what NASA is doing now with the radar 
    tracking data.  I know what was done 40 years ago when we were launching 
    SCOUT missiles from Wallops Island, Vandenberg and San Marco Kenya as well as 
    the early shuttle launches from the Cape.
    
    There was always a projected gravity turn track that we wanted the launch to follow 
    to get payloads into orbit.  We had "dead bands" marked on either side of the 
    launch track that would serve as the boundary layers for the range safety 
    officers to consider separating the capsule and destroying the missile.  
    
    When SCOUT program was finally shutdown, it was the most successful launch vehicle 
    in the history of NASA.  Three solid propellant boosters and optional 2 
    liquid upper stages (5 total).  It had various add-ons to include the 
    strap-on booster rockets for the first and second stage to increase payload 
    capacity.  And there plans to use SCOUT as the Inertial Upper Stage (later 
    known as the IUS) for launches from the Space Shuttle, but that did not 
    materialize.  NASA and the Air Force opted for a new platform.
    
    Anyway, the SCOUT did launch a number of missions that very similar orbits to the 
    LADEE moon probe. Just not the hoopla, because that was normal business back then.
    
    Yes, the craft that was built as the IUS did perform automated cellnav.  It had to 
    because knew where it was when the Shuttle disconnected the data feed (that 
    included a time and position update), but there were no updates between the 
    disconnect from the shuttle and the time the IUS woke up to determine the 
    amount and direction of drift in the intervening 45 minutes between the 
    disconnect  and the wake up, when the Shuttle was moving away to a safe zone. 
     The IUS's "wake up" triggered the unshuttering a telescope on the horizontal 
    axis and begin a slow rotation around the horizontal axis looking for a 
    target star (actually a star of specific brightness with a specific star 
    field around it).  If found,  it would orient on that star (move it to center 
    field) and then begin a slow rotation to locate the next star in the 
    sequence.  If the IUS did not find a star that it recognized, it would stay 
    in the same plane and turn about 45 degrees to the right and rescan.  It 
    would repeat this process until found the set of stars needed to locate it's 
    starting position.    And it would continue until it had sufficient star sets 
    located so that it's position could be calculated.  Then based on knowing 
    where it is as well as the desired end point (final orbit desired or 
    interplanetary mission programmed in).  The IUS would calculate the best 
    method to get there using the least fuel.  It would send a radio signal that 
    it was ready to start, shortly thereafter initiate the assigned task.
    
    I know because I worked on the SCOUT program from 1974 to 1978, the Space 
    Shuttle and IUS programs from 1978 to 1980 (five on board computer systems, 
    each programmed differently, three of which had to agree for an action to be 
    taken) and the IUS (again multiple computers on board, had to agree for an 
    action to be taken).  Lots of fun very cutting edge for the time it was done.
    
    Unfortunately, it is very different from the programming that is done now.  Back then, we 
    were heavily constrained by memory, timing, processor speed and I/O.  Now my 
    tablet has more power than all of the computers in the Shuttle or the IUS 
    combined, and definitely more than any of the analogue computers in the 
    SCOUT.  But I would not trade that experience for anything in the world.  If 
    nothing else, I learned how to properly design and program,  making use of 
    every machine instruction and memory location out there.
    
    So be happy with the small position error you are seeing.  Practice will improve 
    your technique.  
     
    Derrick
    
    “We are not what we know but what we are willing to learn." Mary Catherine 
    Bateson, American writer and anthropologist
    
    
    -----Original Message-----
    From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Peter Monta
    Sent: Saturday, September 14, 2013 9:30 PM
    To: Young, Derrick CIV (US) DeCA HQ LEIP
    Subject: [NavList] Re: LADEE Moon Probe Puzzle
    
    ________________________________
    
    Nice result!  Is it likely that this 1.7 nmi disparity is estimation error from the 
    photos, or could it be actual deviation of the rocket from the published 
    track?  I'm not sure I'd entirely trust a table in a press kit; is 
    high-precision tracking data made available for these NASA launches after the fact?
    
    It brings to mind Jim Lovell's joke that the NASA mission controllers should 
    download his navigation state vector, generated autonomously on-board from 
    sextant observations, rather than use the one computed on the ground (which 
    was always used in practice).  The ground controllers replied "touch ".
    
    Cheers,
    Peter
    
    : http://fer3.com/arc/m2.aspx?i=125135
    
    

       
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