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With the CRS-3 (SpaceX-3) launch of a Falcon 9 v1.1 with a Dragon capsule to the ISS the F-9 will launch with landing legs for the first time.

Elon Musk Tweeted an image of the legs mounted on the first stage.

enter image description here

You can see a bit better detail from an earlier tweet.

enter image description here

The bottoms look sculpted, and the question is, do they have an aerodynamic function for controlling the flight? We already know that like a figure skater, they are expected to help control the amount of spin so the ACS system can counteract the roll.

Will they allow the stage control to 'fly' to a more accurate landing? Do they have sufficient control in the legs to do that?

It has been noted that there are actually two versions of the legs built. The original image:

enter image description here

Then Steve Jurvetson posted one from the SpaceX lobby. enter image description here

These are supposed to be the model used since the CRS-3 flight. Note the arrow pointing out the major obvious difference.

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    $\begingroup$ I don't have a source for this, but I do have a degree in aerospace engineering: I think it's unlikely. The rocket has demonstrated an ability to fly uphill without any aero control surfaces, and the tests of the prototype in mcgregor also showed it could land without aero surfaces. Further, these legs are just supposed to deploy up and down, I could be missing it, but I don't see any hinge or mechanism to actuate them in any other direction $\endgroup$
    – Nickolai
    Mar 7, 2014 at 22:35
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    $\begingroup$ I couldn't find anything authoritative, so this is a comment rather than an answer. Those look like aerodynamic fairings whose intent is to keep the legs from interfering with aerodynamics as much as possible while the legs are not deployed. Deployment appears to be done with a simple hydraulic arm; once again it's not used for flight control. With regard to the spinning problem: That sounds a bit ominous. That's a sign of a vehicle with inadequate roll control authority. $\endgroup$
    – David Hammen
    Mar 8, 2014 at 19:36
  • $\begingroup$ What "major obvious difference"? $\endgroup$
    – Vikki
    May 16, 2019 at 0:24

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With the release of fairly detailed landing video for the CRS-6 landing attempt it is very clear that the legs do not deploy until 20 seconds at most before landing, so they are clearly not used as aero control surfaces.

In fact it can be seen in the video that the legs deploy half way, then only in the last few seconds deploy all the way down.

Elon Musk tweeted that by the 21st Falcon mission they will be using the legs more as aero surfaces, this means it will change the opening timeline.

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They are not used as aerodynamic surfaces during launch, but they are used to help balance the spacecraft and provide some control during the landing sequence. As to what level they will be used, only someone who works for SpaceX could tell you and they won't, but the Falcon 9 has full thrust vector control, not requiring external fins or other such items for control.

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    $\begingroup$ "but the Falcon 9 has full thrust vector control, not requiring external fins or other such items for control" Hehe, now they have grid fins. :) $\endgroup$
    – marked-down
    Mar 3, 2015 at 19:50
  • $\begingroup$ @ReactingToAngularVues: Yes, for landing. $\endgroup$
    – Vikki
    May 16, 2019 at 0:24

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