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On 2015-12-22 09:12, Anders Sandberg wrote:<br>
<blockquote cite="mid:567905E2.9040401@aleph.se" type="cite">
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In the pictures it looks like the vehicle came in from the sea
side, which makes sense from a safety perspective, but I can't
figure out the orbital mechanics. <br>
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Ah, here Elon explains it:<br>
<a class="moz-txt-link-freetext" href="http://www.spacex.com/news/2015/12/21/background-tonights-launch">http://www.spacex.com/news/2015/12/21/background-tonights-launch</a><br>
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<blockquote type="cite">In the case of the Falcon 9 rocket, the
boost stage is able to accelerate a payload mass of 125 metric
tons to 8000 km/h and land on an ocean platform or to 5000 km/h
and land back at the launch site. The second one is lower
because the rocket is moving super fast away from the launch site,
so it has to do a screetching U-turn with nitrogen
attitude thrusters, then fire the engines to create a reversed
ballistic arc, then reorient again for atmospheric entry and have
the engines pointed in the right direction for the landing burn.
Since the propellant is liquid, it wants to centrifuge out during
these maneuvers, so there has to be a system of baffles and
internal holding tanks to keep it in place. It also needs three
axis control surfaces that don't melt easily and work well from
hypersonic through subsonic speeds.</blockquote>
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<pre class="moz-signature" cols="72">--
Anders Sandberg
Future of Humanity Institute
Oxford Martin School
Oxford University</pre>
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