6 ms·

What i don't understand is how are they going to solve the problem of landing precision. The stage is passive from the retroburn (just after the stage separatio

What i don't understand is how are they going to solve the problem of landing precision. The stage is passive from the retroburn (just after the stage separation) for the several hundreds seconds it is flying back, and large part of that trajectory is in atmosphere, and stage has a high sail factor: it is big and, being almost empty, lightweight. So it might be dragged by wind too far from the landing site to compensate in hover mode which is i assume only 100-200 meters or so, even if original entry trajectory is perfect. Ballistic missile warheads for example, accumulate about 100 meters or error due to this factor despite they are much smaller/have higher density and fly several times as fast. A an additional short mid-flight engine burn to compensate may be a solution but so far i haven't heard of that. Anyone has an idea?

ceejayoz 12y ago
Ballistic missile warheads aren't slowing down for a soft landing. Try landing a helicopter at Mach 1 and see how accurate it is compared to a normal landing.
Symmetry 12y ago
I believe that's what the new grid fins they've been testing out on the Grasshopper are for. Those are there to let the rocket steer even at the speeds it comes in at. http://en.wikipedia.org/wiki/Grid_fin http://en.wikipedia.org/wiki/Grid_fin
- toomuchtodo 12y ago
  They are! And they work well at both subsonic and supersonic speeds, just not transonic speeds.
  - anovikov 12y ago
    No, these things are just for improvement of stability when descending. But it seems that answer is aerodynamic control by partially (and differentially) extending the LEGS. Which appears brilliantly smart and should work. Same hardware, zero additional weight or cost, additional function.
    - toomuchtodo 12y ago
      "stability" = "steering"
TrainedMonkey 12y ago
"This test confirms that the Falcon 9 booster is able consistently to reenter from space at hypersonic velocity, restart main engines twice, deploy landing legs and touch down at near zero velocity." They are restarting main engine twice. First time is for trajectory correction I assume.

ceejayoz 12y ago

Ballistic missile warheads aren't slowing down for a soft landing. Try landing a helicopter at Mach 1 and see how accurate it is compared to a normal landing.

Symmetry 12y ago

I believe that's what the new grid fins they've been testing out on the Grasshopper are for. Those are there to let the rocket steer even at the speeds it comes in at. http://en.wikipedia.org/wiki/Grid_fin http://en.wikipedia.org/wiki/Grid_fin

toomuchtodo 12y ago
They are! And they work well at both subsonic and supersonic speeds, just not transonic speeds.
- anovikov 12y ago
  No, these things are just for improvement of stability when descending. But it seems that answer is aerodynamic control by partially (and differentially) extending the LEGS. Which appears brilliantly smart and should work. Same hardware, zero additional weight or cost, additional function.
  - toomuchtodo 12y ago
    "stability" = "steering"

TrainedMonkey 12y ago

"This test confirms that the Falcon 9 booster is able consistently to reenter from space at hypersonic velocity, restart main engines twice, deploy landing legs and touch down at near zero velocity." They are restarting main engine twice. First time is for trajectory correction I assume.