Off San Diego? I think there was some swell, maybe 3-foot seas. But
nothing a ship that size can't handle with good stability.
On 2016-03-06 18:48, Henry Vanderbilt wrote:
IIRC, it was near dead-calm that day, not so?
On 3/6/2016 7:38 PM, George Herbert wrote:
The last barge landing before this one was dynamically a success - touched down low vel, nearly level, settled.
The leg lock mechanism failure means there was subsequent tipover and destruction, so the recovery failed. But not the landing.
The last two normal regime landings both were successes (land, sea).
I don't have as much concern as some of the rest of us. ...
George William Herbert
Sent from my iPhone
On Mar 6, 2016, at 3:22 PM, Henry Vanderbilt <hvanderbilt@xxxxxxxxxxxxxx> wrote:
On 3/6/2016 3:11 PM, Chris Jones wrote:
On 03/06/16 4:52 PM, John Dom wrote:
I did not see video of the landing yet. My point was I assumed the
unstable geometry of the long stick & lander legs were again the
culprit of collapse. The distance between the LM legs was almost as
big as it's hight. Something a blind horse would notice. I was never
pointing at guidance or propulsion.
OK, but I still believe that the factors SpaceX had pointed to before
the launch (namely a higher speed, lower propellant reentry by the
returning first stage, resulting in tight or non-existent margins) are
probably the main factors. SpaceX has demonstrated (not with comforting
or even acceptable success rates) the ability for the stage as designed
to land successfully (albeit on land, not on a barge), so I'm not sure I
understand what your objection is to the landing leg geometry. I think
a wider base (i.e. greater perimeter) of the landing legs would result
in greater stability (or are you objecting to 4 being too few legs?).
I think lack of deep throttling in the Merlin engine is the main factor in barge-landing difficulties. This means all landings are done at T:W >1, which in turn means the final deceleration burn must be precalculated before burn start to end up with velocity close enough to zero for the legs to absorb on deck-arrival.
Given the position and velocity of the barge deck varying in a partially chaotic manner in any kind of swell, the difficulty seems obvious, and inherent.
I've been assuming for a while they'll have to either go to some sort of semi-submersible barge that's less subject to wave movement, or develop deep(ish) throttling, or impose really strict wave-height limits, to make barge landings routinely reliable.
Henry
