The return flight of the first stage booster starts at the moment of separation from the Falcon 9 second stage that is delivered to a trajectory from where it can boost the payload into its desired orbit. First stage burn duration in missions that include a propulsive return is on the order of 160 seconds.
Separating the second stage at about 80km in altitude at a speed of Mach 10, the first stage heads on to an apogee altitude of around 140 Kilometers. Initially, the first stage uses its cold gas thrusters for attitude control – starting with a maneuver to depart the engine plume of the second stage before re-orienting to an engines-first position that is maintained past the point of apogee.
Around T+4.5 minutes into the mission, the first stage re-lights a subset of its engines for a boost-back maneuver that slows the vehicle down and controls the downrange travel distance of the stage, beginning to target the planned landing site – either on land or in the ocean. The duration of the boost-back burn depends on the target landing site and is also driven by propellant availability for the return which varies depending on payload mass and insertion orbit.
Heading back into the dense layers of the atmosphere, the first stage completes its supersonic retro propulsion burn using three engines that are fired for about 20 seconds starting at an altitude of 70 Kilometers. This burn in combination with drag in the atmosphere slows the first stage down from 1,300m/s to about 250m/s.
The first stage aft section has been outfitted with shielding material to be able to withstand the re-entry environment and during atmospheric flight, the stage can maintain an engine-forward position by its low center of gravity caused by the heavy engine compartment in the aft.
Beginning at re-entry, the first stage starts using its four grid fins for roll, pitch and yaw control, especially during periods of flight when the engines are not running. Covering the final 40 Kilometers to landing, the booster uses its grid fins to maintain a pitch-trim to continue refining the course towards the landing platform while maintaining stable yaw and roll rates.
Homing in on its landing spot, the first stage ignites its center engine to begin slowing down to a landing speed of just about two meters per second and make the final cross-track and range adjustments to land on the platform. Ten seconds into the landing burn, the four landing legs are deployed to put the stage into its final landing configuration with touchdown just a few seconds later.
It seems the author has used FAA documents to source much of this info, and recently too. It appears the final burn is thus under about 15 seconds duration. Desired contact speed is 2 m/s ..... no dawdling ! :-)
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 did that one time with a full length school bus we all had to drive to 'certify' we could drive the thing. They said we had to drive as fast as we could around a course and then stop within 24 inches of a cone to 'certify', after a bunch of other guys went first I hoped in drove it around and slid to a stop 8 inches from the cone. They were NOT impressed and made me do it again slower, so I did just to get out of there. The first time I got lucky as both sets of dual tires in the back and both front tires were locked up and sliding to a perfect stop! Of course I told them it was skill as I hopped out. But the guy in charge was hoping up and down VERY angry that I had worn some tread off his precious tires. They were cheap school bus tires and I didn't leave any black marks as I was sliding on gravel. The guy loved to hop up and down though when he got angry, all the guys behind him were laughing their butts off at him, but of course I had to keep a straight face as he yelled at me to do it again. The guy was about 5 foot 3 inches tall and actually hopped up and down as he screamed at you, it was hilarious unless you were the one being yelled at!
Just as a rocket on the pad just barely lifts and then accelerates, so on return the 1st stage will severely decelerate ( upward marked as positive axis here ) and then vertically stop just barely above the pad.
Yes like a helicopter in auto-rotation. A "real" E-ticket ride.
Space.com has just posted a story stating that this is a new image taken from the barge a moment before the April 14, 2015 crash landing.
Could this be just a frame grab from the barge-top video we have seen before?
If so it is a high-resolution one, and I spotted something I don't recall being discussed. There appears to be a water stream directed at the deck surface from a nozzle atop one of the containers on the far side, and there appears to be water on the deck. Perhaps this is a low-rent version of the water protection employed at launch pads?
Space.com has just posted a story stating that this is a new image taken from the barge a moment before the April 14, 2015 crash landing.
Could this be just a frame grab from the barge-top video we have seen before?
If so it is a high-resolution one, and I spotted something I don't recall being discussed. There appears to be a water stream directed at the deck surface from a nozzle atop one of the containers on the far side, and there appears to be water on the deck. Perhaps this is a low-rent version of the water protection employed at launch pads?
Its difficult to say from this picture/perspective but how much vertical deflection/movement is there in the "legs"? It does not appear to me to be enough to absorb a 6m/sec set down rate. The legs are spread wide and while this will ensure a more stable vertical orientation after engine shutdown the vertical movement on the legs does not appear to provide sufficient displacement to protect the engines from barge contact. I think if this landing had been successful at the 6m set down rate that the engines would have been driven up into the first stage causing significant damage to both components - engine and 1st stage. Again this is my opinion based solely on visual observation provided by the picture.
[EDIT]
here is a diagram of the engine configuration:
Is it the engine at 4 o'clock in this diagram that is firing? It does not look like the center engine. Or does it?
The water stream is probably as you state: used to provide cooling during the short time the flame is in contact with the deck.
This barge landing scenario makes this effort more complicated, but until they can demonstrate reasonable success at recovery on a barge they won't dare try a land based landing in a congested area.
Its difficult to say from this picture/perspective but how much vertical deflection/movement is there in the "legs"? It does not appear to me to be enough to absorb a 6m/sec set down rate. The legs are spread wide and while this will ensure a more stable vertical orientation after engine shutdown the vertical movement on the legs does not appear to provide sufficient displacement to protect the engines from barge contact. .
The barge-perspective photos have pretty serious point-of-view and wide-angle lens disadvantages for judging that. This capture I made from the distant hi-res landing video is perhaps better for judging the leg positions.
Quote:
Is it the engine at 4 o'clock in this diagram that is firing? It does not look like the center engine. Or does it?
I think it is the center engine. If you watch the hi resolution version (be sure to set your viewer to enable 1080p) of the distant landing video, it appears to me that the engine is both gimballing and throttling on the way down, but generally looks likely to be the center one, which would make the most sense to me.
Its difficult to say from this picture/perspective but how much vertical deflection/movement is there in the "legs"? It does not appear to me to be enough to absorb a 6m/sec set down rate. The legs are spread wide and while this will ensure a more stable vertical orientation after engine shutdown the vertical movement on the legs does not appear to provide sufficient displacement to protect the engines from barge contact. .
The barge-perspective photos have pretty serious point-of-view and wide-angle lens disadvantages for judging that. This capture I made from the distant hi-res landing video is perhaps better for judging the leg positions.
Quote:
Is it the engine at 4 o'clock in this diagram that is firing? It does not look like the center engine. Or does it?
I think it is the center engine. If you watch the hi resolution version (be sure to set your viewer to enable 1080p) of the distant landing video, it appears to me that the engine is both gimballing and throttling on the way down, but generally looks likely to be the center one, which would make the most sense to me.
This pic does give a better perspective and the engine that firing does seem like the center one and it is gimballing to keep the tail under the nose. The 4 legs also seem to have more vertical deflection/travel then in the other picture. Looking at that video the descent speed is fast though. Definitely hover/slam. There does not seem to be any margin for error.
In an earlier post I was wrong about no land landings until barge landings were successful. I just saw a news article stating that the July launch would be a return to a land based recovery.
I think it will be fine for a land landing. The trouble so far has been with lateral adjustment in the terminal phase. On land they will have a much bigger barn door to hit, so no need for last moment desperate corrections. SpaceX is writing the textbook for the future here.
@robl : helicopter auto-rotation is indeed a good analogy here.
@archae86 : now there is a picture worthy of jigsaw puzzle ! :-)
As for the legs, they remind me of spiders. That is : the splay is broad and flat. That gives a more stable base, the vertical travel is less but a relatively longer travel for the actual dampers.
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
Current weather here is looking less than sterling - rain and a relatively low ceiling. The window seems to be fairly large so it might still be a go should the weather clear up.
Ok, here's a long excerpt
)
Ok, here's a long excerpt from this page :
It seems the author has used FAA documents to source much of this info, and recently too. It appears the final burn is thus under about 15 seconds duration. Desired contact speed is 2 m/s ..... no dawdling ! :-)
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
RE: Imagine parking a car
)
I did that one time with a full length school bus we all had to drive to 'certify' we could drive the thing. They said we had to drive as fast as we could around a course and then stop within 24 inches of a cone to 'certify', after a bunch of other guys went first I hoped in drove it around and slid to a stop 8 inches from the cone. They were NOT impressed and made me do it again slower, so I did just to get out of there. The first time I got lucky as both sets of dual tires in the back and both front tires were locked up and sliding to a perfect stop! Of course I told them it was skill as I hopped out. But the guy in charge was hoping up and down VERY angry that I had worn some tread off his precious tires. They were cheap school bus tires and I didn't leave any black marks as I was sliding on gravel. The guy loved to hop up and down though when he got angry, all the guys behind him were laughing their butts off at him, but of course I had to keep a straight face as he yelled at me to do it again. The guy was about 5 foot 3 inches tall and actually hopped up and down as he screamed at you, it was hilarious unless you were the one being yelled at!
RE: Just as a rocket on
)
Yes like a helicopter in auto-rotation. A "real" E-ticket ride.
Space.com has just posted a
)
Space.com has just posted a story stating that this is a new image taken from the barge a moment before the April 14, 2015 crash landing.
Could this be just a frame grab from the barge-top video we have seen before?
If so it is a high-resolution one, and I spotted something I don't recall being discussed. There appears to be a water stream directed at the deck surface from a nozzle atop one of the containers on the far side, and there appears to be water on the deck. Perhaps this is a low-rent version of the water protection employed at launch pads?
RE: Space.com has just
)
Its difficult to say from this picture/perspective but how much vertical deflection/movement is there in the "legs"? It does not appear to me to be enough to absorb a 6m/sec set down rate. The legs are spread wide and while this will ensure a more stable vertical orientation after engine shutdown the vertical movement on the legs does not appear to provide sufficient displacement to protect the engines from barge contact. I think if this landing had been successful at the 6m set down rate that the engines would have been driven up into the first stage causing significant damage to both components - engine and 1st stage. Again this is my opinion based solely on visual observation provided by the picture.
[EDIT]
here is a diagram of the engine configuration:
Is it the engine at 4 o'clock in this diagram that is firing? It does not look like the center engine. Or does it?
The water stream is probably as you state: used to provide cooling during the short time the flame is in contact with the deck.
This barge landing scenario makes this effort more complicated, but until they can demonstrate reasonable success at recovery on a barge they won't dare try a land based landing in a congested area.
robl wrote:Its difficult to
)
The barge-perspective photos have pretty serious point-of-view and wide-angle lens disadvantages for judging that. This capture I made from the distant hi-res landing video is perhaps better for judging the leg positions.
I think it is the center engine. If you watch the hi resolution version (be sure to set your viewer to enable 1080p) of the distant landing video, it appears to me that the engine is both gimballing and throttling on the way down, but generally looks likely to be the center one, which would make the most sense to me.
RE: robl wrote:Its
)
This pic does give a better perspective and the engine that firing does seem like the center one and it is gimballing to keep the tail under the nose. The 4 legs also seem to have more vertical deflection/travel then in the other picture. Looking at that video the descent speed is fast though. Definitely hover/slam. There does not seem to be any margin for error.
In an earlier post I was wrong about no land landings until barge landings were successful. I just saw a news article stating that the July launch would be a return to a land based recovery.
I think it will be fine for a
)
I think it will be fine for a land landing. The trouble so far has been with lateral adjustment in the terminal phase. On land they will have a much bigger barn door to hit, so no need for last moment desperate corrections. SpaceX is writing the textbook for the future here.
@robl : helicopter auto-rotation is indeed a good analogy here.
@archae86 : now there is a picture worthy of jigsaw puzzle ! :-)
As for the legs, they remind me of spiders. That is : the splay is broad and flat. That gives a more stable base, the vertical travel is less but a relatively longer travel for the actual dampers.
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
FWIW : there is a pad abort
)
FWIW : there is a pad abort test tonite in about ~ 5 hours. There is also an overview.
Cheers, Mike.
( edit ) It will pull about 5.5g for about 5 seconds and by then will be 500m away. Not bad.
( edit ) That's nett upwards so a crew would feel well over 6g.
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
Current weather here is
)
Current weather here is looking less than sterling - rain and a relatively low ceiling. The window seems to be fairly large so it might still be a go should the weather clear up.