It's unusual for me to write two pieces on SpaceX in a week, but they nailed another landing at sea this morning, this time pretty much centering the Falcon 9 booster in the middle of the landing bulls eye on their drone barge, "Of Course I Still Love You". Having the luxury of being retired, we decided to get up a little after 1 this morning. Went outside to watch the launch; night launches are always pretty, and we were able to follow it until it was well into the second stage burn. Then we came in to see the coverage of the attempted booster landing on the
SpaceX website.
For their part, SpaceX tried to downplay expectations. Landing rockets autonomously on unpiloted drone barges at sea isn't exactly something that has been done enough times to be boring routine. The mission was to put a satellite into a geosynchronous transfer orbit, which they said made recovering the booster harder.
"Given this mission's GTO destination, the first stage will be subject
to extreme velocities and re-entry heating, making a successful landing
unlikely," SpaceX representatives wrote in a description of the JCSAT-14 mission.
When the booster made it to the barge, the video cameras couldn't handle the brightness of the rocket flames and the screen went white for a second or two. The crowd apparently thought the brightness meant the booster had crashed into the ship and you could hear cries and moans of disappointment. Moments later, the video recovered and the booster could be clearly seen sitting right where it was supposed to be, residual fuel still burning. The crowd erupted in cheers, transitioning to chanting, "USA! USA! USA!".
Video here.
A few hours later, once the sun had risen, SpaceX released this photo. In the
past, SpaceX has said that to ensure the booster isn't toppled by weather or sea conditions, that once the vehicle is safe (and I don't know all that means), they will weld steel "shoes" over the booster's feet to help ensure it stays put.
Congratulations to them once again!
ReplyDeleteIt's good to see they were better aligned this time.
It has made me wonder how they do that navigation. Especially the landing. I would bet they do some sort of closed loop system; they project where they're going to land and correct the path. But they come in pretty darned fast with no fuel to hang in the air and decide what they need to do, so it's a fast loop.
DeleteWell, the two may communicate with each other (details are perhaps purposefully vague), but given the relative speeds one could treat the ship as stationary. I do not know what technologies (radar, video, differential GPS, laser ranging, etc.) are employed to register the relative positions.
DeleteIf it were me, I'd hang all the sensors I could manage on the drone ship, and just transmit the relative state vector to the oncoming first stage. The stage could then incorporate that data into its Kalman filter (or whatever modern equivalent it uses) to improve its aimpoint.
It's largely a ballistic trajectory, and they can do the maths for that. I expect they're using GPS for position and velocity information, and probably attitude as well. And Bargey McBargeface is also undoubtedly doing the same calcs and reporting to the rocket. Most likley delta info which the rocket can easily use to adjust its previous thrust level and thrust vector calculation.
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