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

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  •  Salt-water Landing Makes It Virtually Impossible (4+ / 0-)

    Salt water is one of the most corrosive elements on the planet.  It tends to consume almost any metal which it can find access to.  Worse, it has a voracious appetite for copper and copper alloys, which must be specially formulated to avoid corrosion.  I won't speak much about iron and iron alloys and sea water, because the the latter loves to munch on the former.  

    To make that first stage reusable after a salt-water landing, SpaceX would have needed a way to seal any and all openings in the structure before it hits the water.  That can be done, but the weight penalty could be pretty substantial.  It's a wonderful concept, but actually pulling it off requires more than just a first-stage engine restart.  The latter might have been done mostly to determine if it could be accomplished before going down the much more rigorous path of materials and structure redesign.  Such a vehicle would no longer be the Falcon but some other bird.

    "Love the Truth, defend the Truth, speak the Truth, and hear the Truth" - Jan Hus, d.1415 CE

    by PrahaPartizan on Sun Sep 29, 2013 at 05:42:24 PM PDT

    [ Parent ]

    •  Isn't (2+ / 0-)
      Recommended by:
      Kevskos, FarWestGirl

      Isn't the ultimate goal to land it on land though?  

    •  Just put it down in a lake! (0+ / 0-) ~ @MatthewBorgard

      by zegota on Sun Sep 29, 2013 at 06:46:30 PM PDT

      [ Parent ]

    •  I believe the current plan (3+ / 0-)
      Recommended by:
      eOz, Kevskos, FarWestGirl

      is to move towards a land VTVL, like the DC-X or the Lunar Lander Challenge vehicles.  

      I think the primary purpose is to fishing one out of the sea is to see what sort of damage that results in re-light and the like

    •  The plan is for the 1st stage to fly back... (3+ / 0-)
      Recommended by:
      eOz, Kevskos, FarWestGirl the launch site.

      That's part of the point of Falcon 9 1.1 - the extra fuel from the stretched fuel tanks can be used to flip the 1st stage to point back home, do enough of a burn using 3 engines to take her back to Cape Canaveral or Vandenberg, and then do a landing with the one center engine on a landing pad there.

      If everything goes right, the Falcon 9 would not touch the ocean.

      •  ??? (2+ / 0-)
        Recommended by:
        buddabelly, FarWestGirl

        Wow. Not saying it isn't so, but the energetics have got to be crazy. The SpaceX web-site says "return to the launch pad for a vertical landing", so you're almost certainly right.

        Still, by the time the first stage burns out, it's a hundred miles or so downrange and moving very fast. Even though it's substantially lighter than the original stage and payload, the energetics of turning it around and getting it back are unreasonable. And then it would need to be slowed down (again!) and landed.

        It would be hugely easier to launch with downrange recovery targets, using the atmosphere to slow and orient the rocket, using minimal rocket thrust at higher altitudes to put the stage through altitude-velocity-distance windows, and more thrust at lower altitudes to drop it on the target.

        That would constrain the launch and recovery sites considerably, however, as the nation's traditional launch sites have been specifically chosen so that descending hardware can fall safely onto unpopulated areas.

        •  True enough, but (2+ / 0-)
          Recommended by:
          jrooth, Wino

          by that time the stage is almost entirely defueled, so it's very light, especially compared to the amount of thrust the engines can generate. Lack of weight can make up for a lot.

          We are all in the same boat on a stormy sea, and we owe each other a terrible loyalty. -- G.K. Chesterton

          by Keith Pickering on Sun Sep 29, 2013 at 11:53:19 PM PDT

          [ Parent ]

          •  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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