Oleg Zabluda's blog
Tuesday, May 22, 2012
 
First attempt to launch Falcon 9 was made and aborted at 1:45:18 am PDT Sun May 20, 2012.
First attempt to launch Falcon 9 was made and aborted at 1:45:18 am PDT Sun May 20, 2012. Second attempt, was successful 2 days later, Tue May 22, at 12:44:38 am PDT.

Why was it 10 min 40 sec earlier in the day?

ISS orbit precesses by ~5 degrees per day (making complete circle in ~70 days), due to gravitational attraction of Earth's equatorial bulge, taking the launch side (24*60*5)/360=20 min less time to get under the orbit.

Also, on Earth, we keep time relative to Sun, not stars, making sidereal day (24*60)/365 ~= 4 min shorter then solar day. So, it takes the launch side 4 min less time to get under the orbit

Net result is 20+4=24 min per day of time advance.

That's exactly how Shuttle launches used to be scheduled. It would accumulate 48 min in 2 days.

Why Falcon 9/Dragon accumulated only 10:40 min in 2 days, I can't easily calculate. Must have something to do with Dragon's orbit precessing faster then ISS (because it has a 50km lower orbit), before the docking on Friday.

It is clearer why it was launched 2 days later. ISS orbit is 92.5 min. So in 24 hours it makes (24*60)/92.5=15.56 orbits, i.e. almost exactly out-of-phase on the opposite side of the orbit. So they had to wait another day to get it back in phase.

http://www.spaceflight101.com/dragon-c2-mission-updates.html
http://forum.nasaspaceflight.com/index.php?topic=4392.425
http://www.spaceflight101.com/dragon-c2-mission-updates.html

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