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View Diary: UPDATED: Quietly, SpaceX makes a revolutionary launch (67 comments)

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  •  Not to mention... (2+ / 0-)
    Recommended by:
    jrooth, FarWestGirl

    that at that point, it no longer has the weight a stack of stages sitting on top of it.   ;)

    Já þýðir já. Nei þýðir nei. Hvað er svona erfitt við það?

    by Rei on Mon Sep 30, 2013 at 07:16:45 AM PDT

    [ Parent ]

    •  Even so... (0+ / 0-)

      It's still going a goodly fraction of orbital velocity, and energy goes up w/ v^2.

      I did a little more looking, and it's both better and worse than I thought.

      To allow this, SpaceX had to make the second stage considerably more powerful, and have the first stage contribute somewhat less delta-v to the launch. That's not necessarily bad, as it means that more  propellant can be used more efficiently by the second stage. (Once you're out of the atmosphere, the larger, larger-expansion-nozzle engine is more efficient, and it doesn't matter nearly so much how quickly one burns it.)

      Secondly, one thing that SpaceX had to change to permit man-rating launches was to avoid the more-vertical, less-horizontal launches of Atlas and some other rockets. This, so that the ballistic trajectory at any point in the launch after a rocket failure can't plummet too quickly into dense atmosphere, where the g-forces would squash people flat. That makes the delta-v problems for the first stage worse, since it increases the downrange velocity, and it can't use the atmosphere for braking downrange motion.

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