3 ms·

Remember the stage being retrieved to ground level weighs a lot less than the stage sitting on the launch pad, because it's empty. Grasshopper took off and land

by cstross 13y ago

Remember the stage being retrieved to ground level weighs a lot less than the stage sitting on the launch pad, because it's empty. Grasshopper took off and landed on the same (permanently extended) legs, so its legs, like the undercarriage of an aircraft, had to be able to support not only the engine and big hollow tank, but a fuel load. But the landing legs on the Falcon 9 first stage don't have to carry the weight of fuel fuel, never mind the weight of the second stage and payload and their fuel -- it launches from a pad and the legs only carry the dry stage at landing. The empty first stage is bulky, but relatively light. The real question in my mind is how much extra fuel it takes to re-light the first stage motor after separation and decelerate it to the point where it can land vertically. There's got to be quite a weight penalty in there. (Which AIUI is why the second-gen Falcon 9 first stage tankage is 30% bigger than the original. Fuel is cheap compared to precision engineering.)

Gravityloss 13y ago
On the other hand, if the system could land with all stages, it could mean that it was cabable of intact abort for a large portion of first stage flight. Just land back to landing pad. Hairy aerodynamics and balance issues. F9 has enough engines for very good engine out redundancy. I don't know if the "landlord" could accept flying towards ground with lots of propellant. For later portions of flight, abort is an abort to orbit. But eventually some such early abort capabilities will need to be incorporated when flight rates pick up. A robust system will not destruct in case of relatively minor problems. Twin jets have enough thrust for single engine ascent with full fuel. This necessitates a huge rudder. But the planes live with that.
- lutorm 13y ago
  I'm pretty sure you would never be able to abort during first stage flight. The aerodynamic loads associated with turning the stage around in the atmosphere are such that it breaks up, like Challenger. Jets may be able to engine-out climb with full fuel, btw, but they can't necessarily land with full fuel.

by cstross 13y ago

Gravityloss 13y ago

On the other hand, if the system could land with all stages, it could mean that it was cabable of intact abort for a large portion of first stage flight. Just land back to landing pad. Hairy aerodynamics and balance issues. F9 has enough engines for very good engine out redundancy. I don't know if the "landlord" could accept flying towards ground with lots of propellant. For later portions of flight, abort is an abort to orbit. But eventually some such early abort capabilities will need to be incorporated when flight rates pick up. A robust system will not destruct in case of relatively minor problems. Twin jets have enough thrust for single engine ascent with full fuel. This necessitates a huge rudder. But the planes live with that.

lutorm 13y ago
I'm pretty sure you would never be able to abort during first stage flight. The aerodynamic loads associated with turning the stage around in the atmosphere are such that it breaks up, like Challenger. Jets may be able to engine-out climb with full fuel, btw, but they can't necessarily land with full fuel.