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What could SpaceX have learned about landing a rocket on a boat resting on waves? It seems like the craziest idea. I would have said "No chance. Land it on lan

What could SpaceX have learned about landing a rocket on a boat resting on waves? It seems like the craziest idea. I would have said "No chance. Land it on land, like the word says." but they've managed the risks down to where it's not surprising that they've landed yet another one. Some special magic has gone into that and I can't even imagine what issues they've had to solve.

ygra 10y ago
They mentioned on the live stream that the landing point doesn't really change the difficulty. It doesn't matter whether they land on water or on land, for the most part. What makes the landings difficult is how much propellant is left in the first stage. There's more of it left after a LEO launch, so they can do a longer landing burn and during that have more opportunity to correct, e.g. for winds. With the GTO launches there's only very little left, so the landing burn is shorter, which also stresses the vehicle more. This time they were happy to actually do a one-engine landing burn as opposed to three engines like they did with the drone ship landings so far (I think it has always been three engines at first and then one engine for the very last bit for drone ship landings until now). They've also noted numerous times that waves don't really matter much to the landing.
- brianwawok 10y ago
  So can they add 5% more propellant to the rocket, or perhaps lower the weight of the rocket a bit so for the same propellant - more is left when it lands?
  - ygra 10y ago
    Propellant tanks are full at liftoff, so no, there's no way of adding more. And there's also no room to save weight either, considering that every bit of saved mass is more payload capacity to orbit. Two features of the Falcon 9 Full-Thrust upgrade increased propellant limits, though: One was bigger tanks, but I think they said they're now at a height limit for various reasons (structural integrity of an empty rocket stage is usually abysmal, for example, and you want to land it upright and empty). The other was superchilling the propellants, which made them a bit denser, thereby fitting more.
  - whamlastxmas 10y ago
    5% more fuel = ~5% more weight, which means you need another 3% to accommodate for that, but wait, that's more weight, etc etc etc. You get diminishing returns adding size/fuel to a rocket. Play Kerbal for a while and you'll see this in action.

ygra 10y ago

They mentioned on the live stream that the landing point doesn't really change the difficulty. It doesn't matter whether they land on water or on land, for the most part. What makes the landings difficult is how much propellant is left in the first stage. There's more of it left after a LEO launch, so they can do a longer landing burn and during that have more opportunity to correct, e.g. for winds. With the GTO launches there's only very little left, so the landing burn is shorter, which also stresses the vehicle more. This time they were happy to actually do a one-engine landing burn as opposed to three engines like they did with the drone ship landings so far (I think it has always been three engines at first and then one engine for the very last bit for drone ship landings until now). They've also noted numerous times that waves don't really matter much to the landing.

brianwawok 10y ago
So can they add 5% more propellant to the rocket, or perhaps lower the weight of the rocket a bit so for the same propellant - more is left when it lands?
- ygra 10y ago
  Propellant tanks are full at liftoff, so no, there's no way of adding more. And there's also no room to save weight either, considering that every bit of saved mass is more payload capacity to orbit. Two features of the Falcon 9 Full-Thrust upgrade increased propellant limits, though: One was bigger tanks, but I think they said they're now at a height limit for various reasons (structural integrity of an empty rocket stage is usually abysmal, for example, and you want to land it upright and empty). The other was superchilling the propellants, which made them a bit denser, thereby fitting more.
- whamlastxmas 10y ago
  5% more fuel = ~5% more weight, which means you need another 3% to accommodate for that, but wait, that's more weight, etc etc etc. You get diminishing returns adding size/fuel to a rocket. Play Kerbal for a while and you'll see this in action.