If they could recover on land we might see an entirely different result of a positive nature. Landing on a floating platform only further complicates a complicated recovery. Years ago Kennedy Space center was a quiet little community. Not a lot of density. Now it, like everywhere else, is wall to wall 3/4 bedroom houses with little margin for error.
I remember my time in Karratha, Western Australia. I could stand on a road, rotate 360 and see nothing but open space occasionally interrupted by 3 mile long ore train. The outback or a wide open location like the outback would be ideal for launch and recovery of an effort like what SpaceX is attempting. Don't have to worry about putting down in someone's living room should guidance be off.
They're very close. The control inputs in those last few seconds before touchdown were too large, they appear to just need fine tuning of the approach. To hit the target (literally) twice in a row now bodes well for success though.
I wonder if they are using the two concentric circles on the barge for computing location over the barge. If that is true then any movement in that barge would/could certainly account for last minute inputs which would be excessive, especially the closer you got.
An interesting question. Here was I thinking that targeting would be the main issue and thus be a doddle because we've been placing missiles through windows and down chimneys etc for several decades now. We want to not destroy either the craft or the target in this instance, so therein lies the key challenge. I wonder what the crucial delta-v is ie. the tolerance below which one can touch the surface of the barge with the stage-1 legs and not come to grief ? That would likely have different magnitude components along the usual axes.
Probably a bit late to implement but one solution is hook and line trapping like the recovery of planes onto a carrier. Only in this case have the netting draped vertically, with the stage drifting gently sideways into it under power. The stage would have hooks protruding along the side of it's barrel and hopefully snag on one or more parts of the net. Make the netting hang with plenty of play/slop and thus it would buffer any residuals nicely.
There is some precedent for this. The original Corona satellite series payloads ( film canisters ) were recovered by flying a plane with a long Y-shaped prong attached to the nose. With a bit of finesse the pilot would catch the shrouding of the parachute in the maw of the Y, and the canister itself recovered via the aft of the plane. There was a very early VTOL jet that hooked itself onto a latch also, while hovering tail down, I forget it's name.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
I've just viewed the ( crash ) landing footage. It's a driven pendulum. My money is on fuel sloshing around at the bottom of the tank and being over-corrected for. If so they need to put a feed-forward in to stop that escalating. Or put baffles inside. Something like that.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
Aviation Week has posted an article which asserts that there may have been a physical problem in the vehicle contributing to the unfavorable dynamics at the end.
I'm a subscriber, and get sent email to updates. I don't know whether this link will work for you. It does for me.
The key point is that apparently Elon posted a tweet and later withdrew it which said “the issue was stiction in the biprop throttle valve, resulting in control system phase lag.†I think the rest of the article is reasoned commentary from an AvWeek writer, not unattributed inside information.
I wonder what the crucial delta-v is ie. the tolerance below which one can touch the surface of the barge with the stage-1 legs and not come to grief ? That would likely have different magnitude components along the usual axes.
From a quick calc assuming parameters similar to an aircraft carrier landing, the vertical speed probably needs to be around 3-5m/s @ initial touchdown. It depends on how much travel their landing gear has on impact and what level of decel their parts can survive. In terms of lateral speed that's basically an automotive rollover threshold calculation - it depends mostly on CG height and track width of the landing gear. I wouldn't have a guess at what the actual CG height of the vehicle is with most of the fuel gone.
Maybe they need to rethink the whole concept of the landing. Instead of a precise, slow landing on a hard surface, how about a less precise, faster landing on a soft surface. I'm thinking either some sort of net, or giant air bags like Hollywood stunts. Either would have to be made to withstand the weight and heat of the rocket, of course. Or it could even drop into the water with a net stretched out underneath to keep it from sinking to the bottom.
This would probably also reduce the fuel consumed by the landing at least a little bit because the craft itself wouldn't need to do all the decelerating itself -- the landing surface would be responsible for the final deceleration to a stop.
David
Miserable old git
Patiently waiting for the asteroid with my name on it.
That's contrary to the operational model they're trying to establish though - their end goal is to land boosters back at the launch complex from which they left, with no 'help' from airbags, nets etc.
Dropping into the water also immediately bathes everything in saltwater, which leads to obvious corrosion issues that makes reusing components difficult.
Aviation Week has posted an article which asserts that there may have been a physical problem in the vehicle contributing to the unfavorable dynamics at the end.
I'm a subscriber, and get sent email to updates. I don't know whether this link will work for you. It does for me.
The key point is that apparently Elon posted a tweet and later withdrew it which said “the issue was stiction in the biprop throttle valve, resulting in control system phase lag.†I think the rest of the article is reasoned commentary from an AvWeek writer, not unattributed inside information.
If they could recover on land
)
If they could recover on land we might see an entirely different result of a positive nature. Landing on a floating platform only further complicates a complicated recovery. Years ago Kennedy Space center was a quiet little community. Not a lot of density. Now it, like everywhere else, is wall to wall 3/4 bedroom houses with little margin for error.
I remember my time in Karratha, Western Australia. I could stand on a road, rotate 360 and see nothing but open space occasionally interrupted by 3 mile long ore train. The outback or a wide open location like the outback would be ideal for launch and recovery of an effort like what SpaceX is attempting. Don't have to worry about putting down in someone's living room should guidance be off.
RE: They're very close. The
)
I wonder if they are using the two concentric circles on the barge for computing location over the barge. If that is true then any movement in that barge would/could certainly account for last minute inputs which would be excessive, especially the closer you got.
An interesting question. Here
)
An interesting question. Here was I thinking that targeting would be the main issue and thus be a doddle because we've been placing missiles through windows and down chimneys etc for several decades now. We want to not destroy either the craft or the target in this instance, so therein lies the key challenge. I wonder what the crucial delta-v is ie. the tolerance below which one can touch the surface of the barge with the stage-1 legs and not come to grief ? That would likely have different magnitude components along the usual axes.
Probably a bit late to implement but one solution is hook and line trapping like the recovery of planes onto a carrier. Only in this case have the netting draped vertically, with the stage drifting gently sideways into it under power. The stage would have hooks protruding along the side of it's barrel and hopefully snag on one or more parts of the net. Make the netting hang with plenty of play/slop and thus it would buffer any residuals nicely.
There is some precedent for this. The original Corona satellite series payloads ( film canisters ) were recovered by flying a plane with a long Y-shaped prong attached to the nose. With a bit of finesse the pilot would catch the shrouding of the parachute in the maw of the Y, and the canister itself recovered via the aft of the plane. There was a very early VTOL jet that hooked itself onto a latch also, while hovering tail down, I forget it's name.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
I've just viewed the ( crash
)
I've just viewed the ( crash ) landing footage. It's a driven pendulum. My money is on fuel sloshing around at the bottom of the tank and being over-corrected for. If so they need to put a feed-forward in to stop that escalating. Or put baffles inside. Something like that.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
Aviation Week has posted an
)
Aviation Week has posted an article which asserts that there may have been a physical problem in the vehicle contributing to the unfavorable dynamics at the end.
I'm a subscriber, and get sent email to updates. I don't know whether this link will work for you. It does for me.
The key point is that apparently Elon posted a tweet and later withdrew it which said “the issue was stiction in the biprop throttle valve, resulting in control system phase lag.†I think the rest of the article is reasoned commentary from an AvWeek writer, not unattributed inside information.
I was able to view your
)
I was able to view your aviationweek.com Link )
Thanks archae86 !
Bill
RE: I wonder what the
)
From a quick calc assuming parameters similar to an aircraft carrier landing, the vertical speed probably needs to be around 3-5m/s @ initial touchdown. It depends on how much travel their landing gear has on impact and what level of decel their parts can survive. In terms of lateral speed that's basically an automotive rollover threshold calculation - it depends mostly on CG height and track width of the landing gear. I wouldn't have a guess at what the actual CG height of the vehicle is with most of the fuel gone.
Maybe they need to rethink
)
Maybe they need to rethink the whole concept of the landing. Instead of a precise, slow landing on a hard surface, how about a less precise, faster landing on a soft surface. I'm thinking either some sort of net, or giant air bags like Hollywood stunts. Either would have to be made to withstand the weight and heat of the rocket, of course. Or it could even drop into the water with a net stretched out underneath to keep it from sinking to the bottom.
This would probably also reduce the fuel consumed by the landing at least a little bit because the craft itself wouldn't need to do all the decelerating itself -- the landing surface would be responsible for the final deceleration to a stop.
David
Miserable old git
Patiently waiting for the asteroid with my name on it.
That's contrary to the
)
That's contrary to the operational model they're trying to establish though - their end goal is to land boosters back at the launch complex from which they left, with no 'help' from airbags, nets etc.
Dropping into the water also immediately bathes everything in saltwater, which leads to obvious corrosion issues that makes reusing components difficult.
RE: Aviation Week has
)
Interesting read. Ok. Next time!!!!!