[AR] Re: Say it ain't so Elon...
- From: Henry Vanderbilt <hvanderbilt@xxxxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Thu, 11 Jan 2018 16:50:18 -0700
On 1/10/2018 8:28 PM, John Schilling wrote:
On 1/10/2018 8:20 AM, Henry Spencer wrote:
And generally the upper stage considerably outweighs the payload, so
if the payload was still attached, an open-loop deorbit wouldn't
achieve quite the planned trajectory but would probably still get low
enough for air drag to take over.
A LEO payload will outweigh the upper stage by 5-10x. It won't be a
question of the open-loop deorbit achieving "quite" the planned
trajectory, but of it achieving anything even vaguely resembling the
planned trajectory. I'd bet at least even money that the stage+payload
would still be stuck in a stable orbit, and if it did come down it would
be far outside the planned impact area. Probably over land or in the
wrong ocean.
If we aren't getting an unexplained large new object in LEO, and we
aren't getting reports of a bolide on USA 280's track but far downrange,
it's likely that the payload separated and the upper stage alone
deorbited properly. But at this early a date, it's possible those
reports are slowly working their way through the system.
Some considerations here:
Per some quick googling, the standard F9 second stage dry mass is just
under 4 tonnes (plus who knows how much extra for N-G's one-off payload
adapter) while max LEO payload due east to 28 degrees with first stage
expended is listed as 22.8 tonnes.
Given that this launch's first stage was recovered, and orbital
inclination was likely around 50 degrees, the max payload mass was
likely more on the order of 12-15 tonnes. Given also that there would
have been some propellant reserve (possibly substantial) at the time of
deorbit burn, one might guesstimate the likely payload-to-upper-stage
mass ratio here as being in the very rough neighborhood of 3:1.
So even aside from the possibility they knew the sat was still
(hopelessly) attached at deorbit burn, and adjusted the burn to
compensate, I would place overshooting the planned (likely south Indian
Ocean) splash zone as much more likely than entirely failing to deorbit.
(If nothing else, it would have been spotted by now if the stage+sat
was still up there.)
FWIW, the estimated orbital track at
https://sattrackcam.blogspot.nl/2018/01/fuel-dump-of-zumas-falcon-9-upper-stage.html
seems to show most of the Pacific Ocean ahead for such an overshoot to
take place in largely unobserved.
Henry
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