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Quote:

Originally Posted by aeppel_cpm

I saw a report from the amateur sat trackers that the 2nd stage had been sighted over east Africa venting fuel (normal) at a time/place that implied a -higher- than initially guessed orbit.

And the 2nd stage is in-orbit when it's done. Other second stages have taken weeks to months to deorbit. If it came down in the Indian Ocean, it was because of a disposal burn - also common practice.

So, if the satellite didn't separate correctly, and a pre-programmed disposal burn brought it back down, I think the 2nd stage would have re-entered long - further SE of Australia than normal - because of the extra (unplanned) mass of the satellite making the disposal burn less effective.

I agree with your analysis. I think the witnessed propellant venting involved LOX (some of which would have to be vented, at least at intervals, to prevent over-pressurization and rupture of the LOX tank, and since they now use super-chilled, densified LOX, this would be an even more pressing--no pun intended!--need). They may even--although I'd have to check the Falcon 9 payload users' guide to be sure--vent a little LOX (or even just boiled-off gaseous oxygen) continuously during inter-burn coasting periods to provide "ullage thrust," to keep the LOX and RP-1 packed down on their respective inlets to the Vacuum Merlin engine. Also, pieces of a satellite (which would--usually--be denser and more massive [especially per unit of frontal area, giving a higher ballistic coefficient] than pieces of the hollow, lightweight second stage) would have a further tendency to land long, and:

The disposal burn of the Falcon 9 second stage is easily visible from the ground when skies are clear; *here* (see: www.youtube.com/watch?v=AlIQbmmxjus , www.youtube.com/watch?v=RiFBl1RQLbo , and www.youtube.com/watch?v=To9DXDzTCRU ) are ground views of the Stage 2 disposal burn that occurred during the CRS-10 Dragon flight to the ISS on 2/19/17 (the launch and Stage 1 landing can be seen here: www.youtube.com/watch?v=g2G8sUnvHak ). Because this event is visible from a pretty large area on the Earth's surface, even if there was bad weather (*some* patch of ground or ocean in the area should have clear skies), maybe one or more videos showing the disposal burn will turn up on YouTube (perhaps listed as UFO footage, as the above-linked CRS-10 second stage disposal burn videos were). Technically, they *were* UFOs to those witnesses, because they couldn't identify what they were seeing and videoing in the sky... :-)