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It turned out that parachutes are great for soft uncontrolled landings, but if you want a soft controlled landing you need some form of propulsion. So if you wa

It turned out that parachutes are great for soft uncontrolled landings, but if you want a soft controlled landing you need some form of propulsion. So if you want propulsion why not use the main engines, and since you are going to use those formthe soft controlled landing why not use them for the descent too. At this point you have traded several tons of parachutes and many more points of failure which could cause loss of mission (parachutes are complex mechanisms) for a smaller weight of fuel and exactly the same points of failure as a rocket always has. Then SpaceX added grid fins, since purely propulsive landing was not going to be anywhere near accurate enough. Classic example of working to your strengths, where the greatest strength of a rocket is acceleration along its primary axis :D

gozur88 10y ago
>It turned out that parachutes are great for soft uncontrolled landings, but if you want a soft controlled landing you need some form of propulsion. They could do something like the Russians do with Soyuz - small solid rocket boosters that fire right at landing. But yeah, that's a lot more things that have to go right.
- simonh 10y ago
  Also solid rocket motors are a lot less weight efficient than liquid fuelled rockets and are not throttleable and are awkward to gimble. Also where would you put them without increasing air resistance on the way up? Also even with the rocket motors Soyuz hits the ground pretty hard.
  - gozur88 10y ago
    You could put them around the rocket nozzles. They wouldn't have to be very big. And yes, Soyuz hits pretty hard. But Soyuz was developed over fifty years ago. I'll bet we could do better today.
    - simonh 10y ago
      Isn't that what SpaceX have already done? I'm not sure what advantage additional solid landing rockets would provide over just slightly bigger fuel tanks for the main engines.
      - gozur88 10y ago
        As I understand it, the F9 first stage can't actually hover because a single engine at the lowest setting gives the overall stage a TWR > 1. Thus the "hoverslam" - they calculate the landing burn such that the stage reaches 0 velocity and 0 altitude (from the pad) at the same instant. But this means the only margin for error is in the landing legs, and they've had some hard landings. I was originally thinking about solid rockets in context of a parachute system, but the more I think about the more I believe truly gentle landings aren't really a feature of the current design. I'm not sure how much weight it would add, but it seems like having the ability to fine-tune the thrust at the very end would allow them to land much more gently and feel better about not introducing metal fatigue or other damage. Of course the addition of a smaller LF engine probably makes the most sense.
willvarfar 10y ago
The ULA are now planning a reusable rocket to counter SpaceX, and they plan heat-shield then deploy parachute and finally capture by helicopter. This seems much simpler than SpaceX's landing approach as helicopters and large aircraft have been snagging things parachuting back from space since the beginning.

gozur88 10y ago

>It turned out that parachutes are great for soft uncontrolled landings, but if you want a soft controlled landing you need some form of propulsion. They could do something like the Russians do with Soyuz - small solid rocket boosters that fire right at landing. But yeah, that's a lot more things that have to go right.

simonh 10y ago
Also solid rocket motors are a lot less weight efficient than liquid fuelled rockets and are not throttleable and are awkward to gimble. Also where would you put them without increasing air resistance on the way up? Also even with the rocket motors Soyuz hits the ground pretty hard.
- gozur88 10y ago
  You could put them around the rocket nozzles. They wouldn't have to be very big. And yes, Soyuz hits pretty hard. But Soyuz was developed over fifty years ago. I'll bet we could do better today.
  - simonh 10y ago
    Isn't that what SpaceX have already done? I'm not sure what advantage additional solid landing rockets would provide over just slightly bigger fuel tanks for the main engines.
    - gozur88 10y ago
      As I understand it, the F9 first stage can't actually hover because a single engine at the lowest setting gives the overall stage a TWR > 1. Thus the "hoverslam" - they calculate the landing burn such that the stage reaches 0 velocity and 0 altitude (from the pad) at the same instant. But this means the only margin for error is in the landing legs, and they've had some hard landings. I was originally thinking about solid rockets in context of a parachute system, but the more I think about the more I believe truly gentle landings aren't really a feature of the current design. I'm not sure how much weight it would add, but it seems like having the ability to fine-tune the thrust at the very end would allow them to land much more gently and feel better about not introducing metal fatigue or other damage. Of course the addition of a smaller LF engine probably makes the most sense.

willvarfar 10y ago

The ULA are now planning a reusable rocket to counter SpaceX, and they plan heat-shield then deploy parachute and finally capture by helicopter. This seems much simpler than SpaceX's landing approach as helicopters and large aircraft have been snagging things parachuting back from space since the beginning.