RE: Verify your Atlantis predictions.

From: Erkenswick, Tom M. (JSC-DM3) (tom.m.erkenswick@nasa.gov)
Date: Fri Jun 22 2007 - 10:25:31 EDT

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    When writing about the node, I was actually referring to the geocentric LAN, not the inertial RAAN.  I should have specified.  The phasing and the LAN are interconnected, as you know.  The LAN (along with the overall groundtrack, as Sean described) has been shifted to the west to bring Edwards into the Shuttle's entry crossrange capability on the desired orbit.
    
    Tom
    
    
    The opinions expressed are my own and not those of NASA.
    
    
    -----Original Message-----
    From: Aaron Brown [mailto:asb110273@gmail.com] 
    Sent: Thursday, June 21, 2007 8:13 PM
    To: seesat-l@satobs.org
    Subject: Re: Verify your Atlantis predictions.
    
    It seems that increasing the semi-major axis would reduce the negative
    drift of the RAAN, putting the RAAN further east than it otherwise
    would be.  This would seem to have the opposite effect as desired.  As
    Sean mentions, I think it has more to do with the phasing of the
    orbit.  We don't really need the earth to turn for another 90 minutes
    to get the de-orbit opportunity.  Instead of waiting one extra full
    orbit to deorbit to EDW, we slow down the orbit rate just enough to
    allow the earth to turn under us just enough. See Sean's email for a
    good explanation of this.
    
    Aaron
    
    
    
    -----Original Message-----
    From: Sean Sullivan [mailto:seesat@golux.org] 
    Sent: Thursday, June 21, 2007 5:54 PM
    To: SeeSat-L@satobs.org
    Subject: Atlantis orbital adjustment
    
    
    This is just some casual speculation building on what I read in Bill 
    Harwood's article, and I haven't looked at the elements or thought this 
    through carefully.  But since there were a lot of messages about how this 
    adjustment might affect the position of the shuttle, I thought I'd try 
    giving an intuitive explanation.
    
    It sounds like NASA wants to create a landing opportunity at Edwards one 
    orbit before Atlantis would have (on its original orbit) had a shot there. 
    On this orbit, therefore, the Atlantis groundtrack would have been too far 
    east, and NASA wants to nudge the groundtrack west.  Since the earth is 
    turning west-to-east under the orbit, this is accomplished by giving the 
    earth more time to rotate before the shuttle crosses a given latitude. 
    To do this, the shuttle needs to run late relative to its original timing. 
    Thus, the orbital period needs to be increased, and that's done by raising 
    the orbit.  So I would expect to see Atlantis fall behind relative to its 
    original trajectory.
    
    Also, here's a wide-angle photo of Atlantis and ISS last night from 
    Boston, in a 10-second exposure:
    
    http://photo.ztn.net/static/satellites/sts117.jpg
    
    Sean Sullivan
    
    
    
    On 6/21/07, Erkenswick, Tom M. (JSC-DM3) <tom.m.erkenswick@nasa.gov> wrote:
    >
    > Chris,
    >
    > That is not what was meant by "earlier opportunity."  The purpose of the burn is to change the orbit's major axis, thus affecting the orbit's nodal regression, which brings Edwards into the crossrange limits one rev earlier than with the current orbit - in other words, it "buys" us an extra deorbit opportunity on an earlier rev, and based on the quote below it sounds like they're trying to land prior to the forecasted wind increase.  I believe the burn is posigrade, which means Atlantis will be later than current elements.
    >
    > Tom
    >
    >
    > The opinions expressed are my own and not those of NASA.
    >
    >
    >
    > -----Original Message-----
    > From: Chris Jones [mailto:clj@panix.com]
    > Sent: Thursday, June 21, 2007 2:39 PM
    > To: seesat-l@satobs.org; brad.young@domain-engineering.com
    > Subject: Re: Verify your Atlantis predictions.
    >
    > Brad Young wrote:
    > > Pardon my orbital ignorance, but wouldn't a scrub mean they would just
    > > continue their present orbit, slowly falling further behind ISS (since still
    > > higher) until de-orbit burn less than an hour before landing? So,
    > > practically speaking, look for ISS and wait, similar path a few minutes
    > > later?
    >
    > This is an excerpt from the "CBS Space News" mailing list sent out by William
    > Harwood:
    >
    >    astronaut Dominic "Tony" Antonelli radioed [Atlantis]... "At Edwards, the
    >    winds are going to pick up. So what we've come up with is in about three
    >    hours, we're going to do an 11-foot-per second (rocket firing) and what
    >    that's going to do for us is pull in an earlier Edwards opportunity"
    >
    > so it would seem that, after the rocket firing, Atlantis will be arriving
    > along its orbit earlier than the current elements would predict.
    >
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