Tuesday, 22 December 2015

Just watch the whole thing (Falcon 9)

Stayed awake to watch it, as I knew it was coming and couldn't have gone to sleep.

Summary: the Falcon 9 first stage rocket, which is 70m tall, delivers the second stage to 80km altitude (and, much more importantly for the purposes of spaceflight, a speed of approximately 6,000 kph). The first stage then detacheds from the second, relights 3 of its 9 engines, flips over, slows itself down from 6,000kph in a controlled manner, extends four enormous legs, and lands with a thump  upright on its legs on a concrete square a few thousand metres from the launch pad at Cape Canaveral. And then it just stands there while everyone finishes screaming.

The 2nd stage continues under its own power to orbital speed of about 26,000kph, delivers 11 relatively mundane truck-tracking satellites to their planned positions, then gracefully deorbits itself to burn up in the atmosphere (vaporisation of space junk comes for free with the atmosphere if you can slow it down just enough from 26,000 kph).

As famously explained by xkcd, space is not "up". Space is fast sideways. Go straight up to the altitude of the ISS and you'll just come straight down again. The astronauts in the ISS float not because they have escaped gravity, but because they are in freefall. The point is that they are going so fast sideways that every time they fall towards the earth, they miss. That's what orbit means; it means missing, in the same way that every half-year the earth falls towards the sun, misses, turns round, and falls again, still downwards, but in the other direction. Nice thought for a solstice.

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