<story><title>SpaceX just landed a rocket on a drone ship for the first time</title><url>http://techcrunch.com/2016/04/08/spacex-just-landed-a-rocket-on-a-drone-ship-for-the-first-time/</url></story><parent_chain><item><author>crispyambulance</author><text>Here&amp;#x27;s one thing I don&amp;#x27;t understand... The rocket lands upon a floating platform in the ocean. Presumably the platform rocks along with the waves. How do they keep the rocket from tipping over after the landing? If it were as huge as an aircraft carrier I can imagine that it might be possible but the platform is relatively small.</text></item></parent_chain><comment><author>JshWright</author><text>A rocket is basically a giant fuel tank with some very heavy engines at the bottom. By the time it lands, the tanks are almost empty, so the center of mass is _extremely_ low.&lt;p&gt;There are two main tanks in the stage, the top ~half is liquid oxygen, and the bottom ~half is kerosene. The liquid oxygen is lighter, and boils off pretty quickly once they open up the vents. So what little fuel is left (the kerosene in the bottom tank) also settles to the bottom, which helps push the CoM even lower.</text></comment>
<story><title>SpaceX just landed a rocket on a drone ship for the first time</title><url>http://techcrunch.com/2016/04/08/spacex-just-landed-a-rocket-on-a-drone-ship-for-the-first-time/</url></story><parent_chain><item><author>crispyambulance</author><text>Here&amp;#x27;s one thing I don&amp;#x27;t understand... The rocket lands upon a floating platform in the ocean. Presumably the platform rocks along with the waves. How do they keep the rocket from tipping over after the landing? If it were as huge as an aircraft carrier I can imagine that it might be possible but the platform is relatively small.</text></item></parent_chain><comment><author>pilsetnieks</author><text>The center of gravity for the rocket is actually very low. The engines are on the bottom, and the rest is just a light aluminum tube (with other smaller tubing and tanks inside but still.)&lt;p&gt;Also, after the landing they vent the remaining oxygen, and afterwards people come aboard to weld the rocket legs to the surface so it wouldn&amp;#x27;t slide off.&lt;p&gt;Maybe very strong winds would be an issue, or very rough seas immediately after landing but they wouldn&amp;#x27;t launch in rough weather anyway.</text></comment>