5 ms·

There is always some extra fuel and oxidizer, as it is used to slow the vehicle, and is needed until touchdown. If the vehicle were to run out of propellant be

• melling 12y ago
  Complete destruction is obviously expensive. Finding a way to prevent an explosion if it falls over after landing seems worthwhile. If it hovered for 5 seconds at .5 meters, for example, could it burn off enough extra fuel?
  • cryptoz 12y ago
    > If it hovered for 5 seconds at .5 meters, for example, could it burn off enough extra fuel? The Falcon 9 cannot hover. The thrust of the single landing engine, even when throttled down to minimum, will provide significant lift to the empty rocket. That's part of what makes this maneuver so difficult and so awesome: it's called the hoverslam, where you achieve 0m altitude and 0m/s velocity at time = 0. For reference, though, the Grasshopper/F9R-dev1, could hover due to it only having 3 engines, not 9, and because they could ballast it with additional fuel.
    • TeMPOraL 12y ago
      > it's called the hoverslam, where you achieve 0m altitude and 0m/s velocity at time = 0 Also known as making a "suicide burn", at least in the KSP world.
  • CHY872 12y ago
    Their eventual goal is for every rocket to land and not have problems. Providing enough fuel for five seconds of hovering is a waste of valuable fuel (see how they're already so low that they run out in the process). Also, falling over almost certainly also leads to a writeoff, as otherwise they'd just fly the rocket into a big pit of fire retardant foam blocks. I'd imagine that the lateral stresses involved in a crash landing are more than enough to write off the rest of the rocket, and so the explosion would just make the barge slightly harder to clean up.
    • melling 12y ago
      Of course, their plan is to not have problems. That's everyone's plan. It's planning for when things don't go right that makes the difference.
      • TeMPOraL 12y ago
        I imagine making the rocket sturdy enough to withstand falling over would be prohibitive in terms of both costs and reduced capacity, so it makes sense to them to ignore this problem completely and work on perfecting the landing so that the rocket does not fall over.
      • mikeash 12y ago
        They are planning for when things go wrong, which is why the landing ship is unmanned and in the middle of a big exclusion zone in the ocean.
        • melling 12y ago
          I'm talking about the economics of failures. Insurance prices will go down, the cost to orbit will be cheaper. Could probably land at the Cape, decreasing turn around time. We'll have flights everyday!
          • mikeash 12y ago
            The explosion isn't going to cause significant damage to the landing ship or the landing pad. There isn't much fuel left onboard at that point anyway, so it's fairly superficial. The rocket is scrap if it falls over regardless of whether or not it explodes, and the explosion won't hurt much, so there's not much reason to put effort into reducing the risk of an explosion in a crash. The plan is to eventually land at the Cape once the technique is proven, but there's no need to make a rocket that can tip over without blowing up to achieve that.
            • melling 12y ago
  • vonklaus 12y ago
    > Finding a way to prevent an explosion if it falls over after landing seems worthwhile. They probably are spending more effort into not letting it fall over.
• trothamel 12y ago
  It probably would explode before crashing. The various machinery in the engine expects fuel to be there, providing resistance. From what I understand, if gas was to be sucked into the engine, the end result would be a rapid disassembly.
• erobbins 12y ago
  In addition, the tanks are slightly pressurized which adds to the effect.. probably 30-50psi begging to be released :)