My suggestion in that thread was that if SpaceX is concerned about this, they might address it by, for future windy landings, positioning the ASDS so it's centered a yard or two upwind of the coordinates for touchdown.
Quote from: CJ on 04/10/2016 10:02 pmMy suggestion in that thread was that if SpaceX is concerned about this, they might address it by, for future windy landings, positioning the ASDS so it's centered a yard or two upwind of the coordinates for touchdown. I assume you mean downwind? Being upwind of the GPS location would make the stage's final stopping point even further from the center of the deck.
Over in the CRS-8 discussion thread, there's quite a bit of concern regarding the off-center location where the stage ended up after some downwind sideways motion on landing. My suggestion in that thread was that if SpaceX is concerned about this, they might address it by, for future windy landings, positioning the ASDS so it's centered a yard or two updownwind of the coordinates for touchdown. So my question here is, is there anything known about the ASDS control system that would preclude making such a simple adjustment in case of need? My guess as to how they could do it is simply change the ASDS's target coordinates by a yard ot two in the appropriate direction. Doing the above just seems, to me, vastly simpler and cheaper than some of the proposed (in that thread and others) changes to the ASDS and the F9, to fix a problem that we don't, yet, know is actually a problem or not.
Also: some of the bounce might be velocity overshoot---getting to positive a few fractions of a meter per second up, instead of precisely to zero. Engine shutdown transient might do that, it's notoriously difficult to predict the amount of thrust from the shutdown transient.
To me, it seems like if this "skidding off the deck" thing were a real problem, then it would be easiest to get a bigger boat. Unless they are currently at some particular width limit etc...
Quote from: cscott on 04/10/2016 07:49 amAlso: some of the bounce might be velocity overshoot---getting to positive a few fractions of a meter per second up, instead of precisely to zero. Engine shutdown transient might do that, it's notoriously difficult to predict the amount of thrust from the shutdown transient. I can't see them eliminating the bounce entirely in anything other than calm seas - because it's impossible for anyone to predict the exact vertical position of the barge deck at the exact moment of touchdown whenever you have waves striking the hull. It's a far easier engineering ask to put design constraints on the amount of bounce..
Quote from: CJ on 04/10/2016 10:02 pmOver in the CRS-8 discussion thread, there's quite a bit of concern regarding the off-center location where the stage ended up after some downwind sideways motion on landing. My suggestion in that thread was that if SpaceX is concerned about this, they might address it by, for future windy landings, positioning the ASDS so it's centered a yard or two updownwind of the coordinates for touchdown. So my question here is, is there anything known about the ASDS control system that would preclude making such a simple adjustment in case of need? My guess as to how they could do it is simply change the ASDS's target coordinates by a yard ot two in the appropriate direction. Doing the above just seems, to me, vastly simpler and cheaper than some of the proposed (in that thread and others) changes to the ASDS and the F9, to fix a problem that we don't, yet, know is actually a problem or not.It would be really very easy to tweak the location reference in the Thustmaster's position system to do this, but I, for one, don't think they would do it for the following reasons:1. A barge moving in any direction has significant momentum - it can't stop instantly - and presumably they want it stationary at the moment of impact (jumping onto a moving platform is more hazardous than jumping onto a stationary one - try it at home!).2. If something went screwy with the comms link at the last second, the barge could start driving off underneath the landing stage, which would be a bad day all around. 3. The landing deck is big enough - it's simply not worth the risk.
Quote from: CameronD on 04/10/2016 11:55 pmQuote from: CJ on 04/10/2016 10:02 pmOver in the CRS-8 discussion thread, there's quite a bit of concern regarding the off-center location where the stage ended up after some downwind sideways motion on landing. My suggestion in that thread was that if SpaceX is concerned about this, they might address it by, for future windy landings, positioning the ASDS so it's centered a yard or two updownwind of the coordinates for touchdown. So my question here is, is there anything known about the ASDS control system that would preclude making such a simple adjustment in case of need? My guess as to how they could do it is simply change the ASDS's target coordinates by a yard ot two in the appropriate direction. Doing the above just seems, to me, vastly simpler and cheaper than some of the proposed (in that thread and others) changes to the ASDS and the F9, to fix a problem that we don't, yet, know is actually a problem or not.It would be really very easy to tweak the location reference in the Thustmaster's position system to do this, but I, for one, don't think they would do it for the following reasons:1. A barge moving in any direction has significant momentum - it can't stop instantly - and presumably they want it stationary at the moment of impact (jumping onto a moving platform is more hazardous than jumping onto a stationary one - try it at home!).2. If something went screwy with the comms link at the last second, the barge could start driving off underneath the landing stage, which would be a bad day all around. 3. The landing deck is big enough - it's simply not worth the risk.Regarding point #1, I didn't mean to imply any momentum. I was thinking something like this; ten minutes or so before launch, check wind speed an direction (I'm assuming the ASDS has an anemometer). If needed, command the ASDS to move a yard or two downwind. That (a movement of 6 feet or less) wouldn't take long, and it should be at a relative standstill again by launch.
Points 2 and 3 are very valid IMHO. Of course, the only reason to try something like this is if there's a problem that needs fixing. My guess is that for the conditions we saw, there isn't one, but stronger winds might change the equation on that and thus might make trying something along these lines worthwhile. At least, that's my guess as to what they might have in their high winds contingency folder.
Regarding point #1, I didn't mean to imply any momentum. I was thinking something like this; ten minutes or so before launch, check wind speed an direction (I'm assuming the ASDS has an anemometer). If needed, command the ASDS to move a yard or two downwind. That (a movement of 6 feet or less) wouldn't take long, and it should be at a relative standstill again by launch.
Hmmmm, maybe they could just make some sort of retractable or unfold- able deck extension to give the stage just a few more yards to land on. Maybe with an inflatable floatation device of sorts to give it a tiny bit of extra stability underneath. Not sure if that would make sense.
What, exactly do they need to change? Accuracy? Why?
seems simpler to send the same wind data to the landing stage