Guys, those pics are great. I stand in awe of SpaceX's accomplishments. Looking at those pics - blue skies, calm seas, and a slightly singed rocket. A perfect day!!!
The end of the first stage is really pushing +3.5G still against gravity.
The Burn 2 interval (which if we are to believe the commentary is no burn at all) must be the atmosphere decelerating, and i have just picked some points arbitrarily for that "stage". Some heat generated i expect - i wonder if they change the orientation to to side-on to bleed off speed higher up.
18 seconds before landing it is still doing approximately Mach1 downwards!
Forgot to mention, i liked the time lapse photo, showing launch - the stars give you the direction to North as well here
That profile is basically that of an artillery shell. In fact with the application of drag to steer and slow it is not unlike the targeting mode of the hyper-accurate Excalibur shell, which also delivers to an absolute GPS position.
I think just enough fuel was spent on the re-entry burn to limit the peak heating for the drag components, leaving just enough fuel for the landing burn. They must have extreme confidence in their timing finesse of the re-lights, remembering that the onrushing air is going up into the rocket bells at approx 2 km/sec. I still reckon an ablative drogue chute, later let go, would be nice to place at the interstage end and chew some joules.
Three in a row now ! :-)
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
Thanks Mike for posting that up, still can't google to give me a working inline.
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I think just enough fuel was spent on the re-entry burn to limit the peak heating for the drag components, leaving just enough fuel for the landing burn.
They must have extreme confidence in their timing finesse of the re-lights, remembering that the onrushing air is going up into the rocket bells at approx 2 km/sec.
aka Mach 7! Pass the matches Eton, it's a little windy outside but we do need to get this lit...
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I still reckon an ablative drogue chute, later let go, would be nice to place at the interstage end and chew some joules.
I was thinking if the legs were extended a little the drag would increase a lot. I guess the counter to drag, is the need for stability and accuracy.
I was thinking if the legs were extended a little the drag would increase a lot. I guess the counter to drag, is the need for stability and accuracy.
I believe that the paddles near the top provide two functions: they provide steering and drag. The drag they provide helps stabilize the rocket such that the top remains the top and the bottom with the legs remains the bottom. By extending the legs, even slightly during free fall, if they were to induce more drag then the paddles the vertical orientation of the rocket might change drastically, i.e, you might be relaying on the paddles for landing struts. But then again ...
Interesting and thanks for pointing that out. I'd seen those frames but didn't twig to the significance. It must have been the boost stage in-tank view ( ? LOX, because if it is true color then it's not kero ), and not the second stage which had much more to do later on, and so wouldn't have had that little left. The relevant number for a single Merlin 1D is 68 kg/sec of propellant ( RP1 plus LOX ) at full throttle. With the ( oxygen rich ) ratio as used that's approx 42 kg LOX to 26 kg RP1. 42kg of LOX is ~ 38 litres ..... so that sloshing amount at the tank's bottom was how many seconds worth ? :-)
.... for example, if you think that picture indicates say 400 litres then that is ~ 10 seconds at full mojo for a single engine .... but with the corollary that a three engine burn for just over three seconds longer uses that 'reserve' up !!! :-)
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Quote:
They must have extreme confidence in their timing finesse of the re-lights, remembering that the onrushing air is going up into the rocket bells at approx 2 km/sec.
aka Mach 7! Pass the matches Eton, it's a little windy outside but we do need to get this lit...
LOL ! The exhaust gas speed for a full throttle Merlin 1D is about 2.5 km/sec !! That doesn't matter in a ( near ) vacuum but is very relevant at the lower altitudes ie. blowback onto the shell !
Cheers, Mike.
( edit ) I know this is BOTE ( Back Of The Envelope ) but the ballpark is quite right. Take home message : SpaceX has exhibited much finesse in handling this gadget.
( edit ) BTW SpaceX-Stats puts the next launch on May 27 for Thaicom-8, another GSTO punt but lighter at 3100 kg than the 4700 kg of the JCSAT-14. On the face of it then more margin for booster recovery.
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
A couple of things struck me, what happens to the LOX (and RP1) during the transition periods of engine on to off to on. How much does it slosh about? Does it turn into raindrops etc?
What is the pressure inside the tanks and how does that affect things? After all if you take out all the liquid the atmosphere would crush it at sea level.
How many cameras (and lights) do they have on each stage? Is it sponsored by GoPro? (*)
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so that sloshing amount at the tank's bottom was how many seconds worth
If it was any average sized aircraft they would have been said "mayday" on approach as there would be no go around on this landing..
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The exhaust gas speed for a full throttle Merlin 1D is about 2.5 km/sec
There is probably something in this - namely they have to get the re-entry speed into the atmosphere under a certain speed or good things won't happen.
(*) I recall hearing SpaceX make their own cameras.
A couple of things struck me, what happens to the LOX (and RP1) during the transition periods of engine on to off to on. How much does it slosh about? Does it turn into raindrops etc?
What is the pressure inside the tanks and how does that affect things? After all if you take out all the liquid the atmosphere would crush it at sea level
I think Elon said sometime that they had to add more baffle materials to keep the slosh acceptable. I'd guess the exact configuration may be rather proprietary.
As I recall the in-flight explosion last year involved a helium tank, which I believe served the function of pressurizing the ullage for the LOX and/or Fuel tanks. I don't know whether this has a structural purpose (as in the original Atlas design) or is just for fuel management.
Until your question it never occurred to me, but perhaps part of the reason they do re-entry engine end first is so that in all major modes of flight with significant acceleration the direction is the same--so they don't have to manage fuel for both cases of longitudinal acceleration.
I agree that there will be much proprietary happening with the tank feeds. The general problem has been solved long before this eg. high performance military jets maintaining fuel flow in various attitudes and loads. Those cope with up to about 9 gee though not for long ( pilot not airframe factors ). Bear in mind that when the boost stage barrel gets hot some of that may penetrate to the tank interior and passively pressurise. But there are many tricks available to keep the fuel flow up to the very thirsty engines and also reducing the dynamic wobbles from slosh.
Quote:
If it was any average sized aircraft they would have been said "mayday" on approach as there would be no go around on this landing..
SpaceX has always been testing. That includes the cases where they found out : the fuel limit by running out; the correct amount of hydraulic fluid for the open circuit ( ie. just discard ) to the vanes by running out; the ice load issue for proper leg extension; the correct ( in house ) manufacture route for the He tank strut; .......
Now in case you're not aware ( I wasn't ) there is footage of a Falcon 9 engine loss in flight from 2012. This answers a previous query of mine about the resilience of the Octaweb cluster to exactly that :
.... this frame clearly shows lots of enginey bits & bobs leaving the scene and a space left behind, like a gap tooth. As luck would have it this was the first ISS re-supply ie. CRS-1, which was a complete success. They just ran the remaining eight engines for longer. :-)
Payload design limits ie. make your payload to tolerate this envelope and we won't exceed that. This doesn't quite say what a returning first stage will do ( the payload has separated by then ) but is a good guideline to how much rock'n'roll to expect :
I can't find much of detailed interest for the stuff we're chatting about eg. if I had a schematic of the LOX tank base then I could estimate the fuel left from that internal tank view. I'd need some scale hints/landmarks.
Quote:
There is probably something in this - namely they have to get the re-entry speed into the atmosphere under a certain speed or good things won't happen.
I reckon this is part of the speed cubed dependency for peak heating. You'd get a quadratic/square from basic dynamic friction. But the length of time you spend being licked by your own flames would be proportional to top speed ( more to retard thus faster is longer ). These would multiply for the peak value, but not say the total, while keeping this in mind :
.... here the boost stage is travelling toward the left of frame, grunty end first. It's obvious there is no standard plume as seen with launch. And yep, that still leaves you a fully functioning vehicle afterwards ! ;-)
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
JCSAT-14 | 2016-05-06 Flight
)
JCSAT-14 | 2016-05-06 Flight profile
Quite a different profile from the previous one. I'll post an update to that table later.
Guys, those pics are great.
)
Guys, those pics are great. I stand in awe of SpaceX's accomplishments. Looking at those pics - blue skies, calm seas, and a slightly singed rocket. A perfect day!!!
Table showing flight
)
Table showing flight profile
Some interesting points.
The total flight time is almost the same.
The end of the first stage is really pushing +3.5G still against gravity.
The Burn 2 interval (which if we are to believe the commentary is no burn at all) must be the atmosphere decelerating, and i have just picked some points arbitrarily for that "stage". Some heat generated i expect - i wonder if they change the orientation to to side-on to bleed off speed higher up.
18 seconds before landing it is still doing approximately Mach1 downwards!
Forgot to mention, i liked the time lapse photo, showing launch - the stars give you the direction to North as well here
That profile is basically
)
That profile is basically that of an artillery shell. In fact with the application of drag to steer and slow it is not unlike the targeting mode of the hyper-accurate Excalibur shell, which also delivers to an absolute GPS position.
I think just enough fuel was spent on the re-entry burn to limit the peak heating for the drag components, leaving just enough fuel for the landing burn. They must have extreme confidence in their timing finesse of the re-lights, remembering that the onrushing air is going up into the rocket bells at approx 2 km/sec. I still reckon an ablative drogue chute, later let go, would be nice to place at the interstage end and chew some joules.
Three in a row now ! :-)
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
Thanks Mike for posting that
)
Thanks Mike for posting that up, still can't google to give me a working inline.
there was just a little left...
aka Mach 7! Pass the matches Eton, it's a little windy outside but we do need to get this lit...
I was thinking if the legs were extended a little the drag would increase a lot. I guess the counter to drag, is the need for stability and accuracy.
RE: I was thinking if the
)
I believe that the paddles near the top provide two functions: they provide steering and drag. The drag they provide helps stabilize the rocket such that the top remains the top and the bottom with the legs remains the bottom. By extending the legs, even slightly during free fall, if they were to induce more drag then the paddles the vertical orientation of the rocket might change drastically, i.e, you might be relaying on the paddles for landing struts. But then again ...
RE: there was just a little
)
Interesting and thanks for pointing that out. I'd seen those frames but didn't twig to the significance. It must have been the boost stage in-tank view ( ? LOX, because if it is true color then it's not kero ), and not the second stage which had much more to do later on, and so wouldn't have had that little left. The relevant number for a single Merlin 1D is 68 kg/sec of propellant ( RP1 plus LOX ) at full throttle. With the ( oxygen rich ) ratio as used that's approx 42 kg LOX to 26 kg RP1. 42kg of LOX is ~ 38 litres ..... so that sloshing amount at the tank's bottom was how many seconds worth ? :-)
.... for example, if you think that picture indicates say 400 litres then that is ~ 10 seconds at full mojo for a single engine .... but with the corollary that a three engine burn for just over three seconds longer uses that 'reserve' up !!! :-)
LOL ! The exhaust gas speed for a full throttle Merlin 1D is about 2.5 km/sec !! That doesn't matter in a ( near ) vacuum but is very relevant at the lower altitudes ie. blowback onto the shell !
Cheers, Mike.
( edit ) I know this is BOTE ( Back Of The Envelope ) but the ballpark is quite right. Take home message : SpaceX has exhibited much finesse in handling this gadget.
( edit ) BTW SpaceX-Stats puts the next launch on May 27 for Thaicom-8, another GSTO punt but lighter at 3100 kg than the 4700 kg of the JCSAT-14. On the face of it then more margin for booster recovery.
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: It must have been the
)
A couple of things struck me, what happens to the LOX (and RP1) during the transition periods of engine on to off to on. How much does it slosh about? Does it turn into raindrops etc?
What is the pressure inside the tanks and how does that affect things? After all if you take out all the liquid the atmosphere would crush it at sea level.
How many cameras (and lights) do they have on each stage? Is it sponsored by GoPro? (*)
If it was any average sized aircraft they would have been said "mayday" on approach as there would be no go around on this landing..
There is probably something in this - namely they have to get the re-entry speed into the atmosphere under a certain speed or good things won't happen.
(*) I recall hearing SpaceX make their own cameras.
RE: A couple of things
)
I think Elon said sometime that they had to add more baffle materials to keep the slosh acceptable. I'd guess the exact configuration may be rather proprietary.
As I recall the in-flight explosion last year involved a helium tank, which I believe served the function of pressurizing the ullage for the LOX and/or Fuel tanks. I don't know whether this has a structural purpose (as in the original Atlas design) or is just for fuel management.
Until your question it never occurred to me, but perhaps part of the reason they do re-entry engine end first is so that in all major modes of flight with significant acceleration the direction is the same--so they don't have to manage fuel for both cases of longitudinal acceleration.
I agree that there will be
)
I agree that there will be much proprietary happening with the tank feeds. The general problem has been solved long before this eg. high performance military jets maintaining fuel flow in various attitudes and loads. Those cope with up to about 9 gee though not for long ( pilot not airframe factors ). Bear in mind that when the boost stage barrel gets hot some of that may penetrate to the tank interior and passively pressurise. But there are many tricks available to keep the fuel flow up to the very thirsty engines and also reducing the dynamic wobbles from slosh.
SpaceX has always been testing. That includes the cases where they found out : the fuel limit by running out; the correct amount of hydraulic fluid for the open circuit ( ie. just discard ) to the vanes by running out; the ice load issue for proper leg extension; the correct ( in house ) manufacture route for the He tank strut; .......
Now in case you're not aware ( I wasn't ) there is footage of a Falcon 9 engine loss in flight from 2012. This answers a previous query of mine about the resilience of the Octaweb cluster to exactly that :
.... this frame clearly shows lots of enginey bits & bobs leaving the scene and a space left behind, like a gap tooth. As luck would have it this was the first ISS re-supply ie. CRS-1, which was a complete success. They just ran the remaining eight engines for longer. :-)
We should all RTFM, right ? :-)
From the latest Falcon Nine Users Guide. Typical orbital parameters :
Payload design limits ie. make your payload to tolerate this envelope and we won't exceed that. This doesn't quite say what a returning first stage will do ( the payload has separated by then ) but is a good guideline to how much rock'n'roll to expect :
I can't find much of detailed interest for the stuff we're chatting about eg. if I had a schematic of the LOX tank base then I could estimate the fuel left from that internal tank view. I'd need some scale hints/landmarks.
I reckon this is part of the speed cubed dependency for peak heating. You'd get a quadratic/square from basic dynamic friction. But the length of time you spend being licked by your own flames would be proportional to top speed ( more to retard thus faster is longer ). These would multiply for the peak value, but not say the total, while keeping this in mind :
.... here the boost stage is travelling toward the left of frame, grunty end first. It's obvious there is no standard plume as seen with launch. And yep, that still leaves you a fully functioning vehicle afterwards ! ;-)
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