Hi Gerhard I agree it certainly was not the Centaur engine burning as when I saw it it was still quite a long way to go before the Centaur burn. Whether it was the hydrazine thrusters I dont know. I had a good look at my images and I had what looks like three "puffs", seperated by several seconds and each one originally caused the satellite to brighten considerably and then this expanded into a concentric ring which expanded quite rapidly- I estimate there must have been at least 5 to 7 concentric rings before they became too faint. Towards the end of my pass the rocket stopped puffing and was entirely clear of concentric rings before going into the earths shadow as it headed northwards. It could well be that the rocket performed several thruster "burns" to maintain orientation etc and once it was correct the thrusters stopped. Anyway back to tracking - got 90085 which was my target for the evening! Cheers Greg ----- Original Message ----- From: "Gerhard HOLTKAMP" <grd.holtkamp@t-online.de> To: <SeeSat-L@satobs.org> Cc: "Greg Roberts" <grr@telkomsa.net> Sent: Tuesday, October 20, 2009 7:39 PM Subject: Re: Centaur-Clouds > After two days of deliberations I finally think I know exactly what it was > that I've seen with the fabulous Centaur pass on Sunday evening. > > The clouds (and also the concentric rings) must have been produced by the > hydrazine thrusters rather than the actual firing of the Centaur engine > because this engine burns liquid hydrogen and oxygen which would leave > pure > water vapor (and unless it condenses would not be seen). > > Just before the escape trajectory burn some attitude maneuvers would be > done > by the Centaur to get into the right attitude for the burn. This must have > caused the first bright cloud which remained near the position of the DMSP > F18 satellite. The actual firing did not produce a visible cloud but after > that firing some more attitude maneuvers were done to get into the right > venting attitude. This caused the fresh cloud which was now at the new > (escape trajectory) position. Having looked at it with 10x50 binoculars I > definitely saw a red dot (the engine was still hot from the firing) and > clouds did not emerge continuously but as *puffs of smoke*. > > There was a brief pause of cloud generation after the new attitude > maneuver > and the cloud just expanded and became weaker but then the venting started > and caused a continuous cloud generation and the cloud grew brighter > again. > > I wouldn't mind if they launch more Atlas Centaur rockets perfoming such > maneuvers! > > Gerhard HOLTKAMP > Darmstadt, Germany > > > ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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