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On Friday May 6, A SpaceX Dragon capsule successfully completed a pad abort test at Kennedy Space Center. The abort test was performed by the same propulsion system that is envisioned to land Dragon 2 with precision in the near future. Dragon 2's capsule propulsion system differs from the experimental, reusable Falcon 9 booster, and the possibility to experience similar flight instability problems is minor.

However, there is a lesson learned as a result the F9R experimental flights - the fact that the first stage failed to reduce significantly the range uncertainty solely by adjusting supersonic retro-burns. In science and technology, the negative results are sometime more significant than positive results, but this finding was obscured by advertising the "invention" of the ‘X-wings’. The grid fins, by using the lifting body properties of slender rocket body, have made the real breakthrough: reducing the landing point uncertainty from 10 miles to 10 meters. On the other side, experimental rocket landers like Morpheus and Xombe demonstrate less than a half mile lateral maneuvers at very high Delta V loss ( > 500 m/s) even after hard optimization.

As Dragon 2 does not appear to have any aerodynamic controls or significant lifting body abilities at transonic and subsonic speeds, how will it perform a pinpoint landing?

SpaceX animation do not shows the flight phase between hypersonic deceleration and retroburn. SpaceX animation

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    $\begingroup$ The Dragon 2 capsule is not going to do a pinpoint landing as far as I know, it's going to come down anywhere in a large area and use the thrusters to cushion the final contact with land/water. $\endgroup$ – GdD May 28 '15 at 12:23
  • $\begingroup$ Thanks for spieling and grammar editing. The meaning of one sentence was altered meanwhile. @GdD, if you are right that will be a conceptual turn from largely promoted pinpoint landing. $\endgroup$ – Val May 29 '15 at 3:03
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Dragon 2 does have aerodynamic controls. It contains a movable ballast sled (written statement by Garrett Reisman for a congressional-hearing), which can be used to change the craft's attitude:

a movable ballast sled allows the angle of attack to be actively controlled during entry to further provide precision landing control.

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Apollo capsules were designed with the center of gravity off center from the descent center of pressure. That causes the capsule to have more lift on one side than the other. The capsule was then slowly spun on descent to null out the lift to get a normal descent. They could also stop the spin at a certain point, thus allowing the capsule lift to alter the trajectory. I'm guessing the ballast will also allow the capsule to have it's c/g altered.

The Dragon2 also has its 8 super-draco motors to further control the descent, something that is not on the F9R. The F9R engines are not quite as adjustable. To get the F9R to land, they originally added cold propellent thrusters to help stabilize the rocket. These proved to be inadequate to fully adjust the descent so they also added the grid fins.

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A capsule can actually fly and control its path somewhat using just the aerodynamic lift while flying tilted.

SpaceX has already demonstrated reasonably accurate landings under parachutes with the cargo Dragon.

Landing under parachute (3 round ones, vs a more parawing form) is less accurate as the wind will blow you around during the fairly long parachute descent.

Using the movable ballast sled in the capsule will allow control of the angle of attack on the heat shield to adjust the path.

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  • $\begingroup$ Have we some numbers published about currently achieved landing accuracy? $\endgroup$ – Val May 28 '15 at 15:33

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