There is some coverage by the veteran's group of the SES booster being inspected and handled. Of those grid fins on view there is no loss of structural integrity that I can see. On the re-entry video I guess we may have been seeing very hot burning paint doing what it is designed to do ( taking the thermal hit to spare the device ). Once that layer goes we then see the underlying metal which is rather cooler because of that protection ! Again I am reminded of the scale of the gadget by the small humans running around underneath it.
@AgentB : it would be interesting to see what is happening at say 1000ft. They might punch the major part of the task with 3 engines and then shut the outer two off. That's plausible. But with such a relatively light vehicle at that stage the efficiency gain may not be worth it.
Cheers, Mike.
NB the sparing of the burn pattern about half way up is due to a slight surface lip created at a circumferential join. What has happened is that very high up at hypersonic speed a coherent surface layer of air formed above that join - in the 'lee' of the lip - and has excluded mixing with layers just further out from the surface. So it escaped much of the carbonisation. Further up that relatively cleaner segment the hotter layers have managed to arc back and penetrate to directly contact the paint.
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
Again I am reminded of the scale of the gadget by the small humans running around underneath it.
Yes see here for an older flight inspecting the grid fins.
Quote:
@AgentB : it would be interesting to see what is happening at say 1000ft. They might punch the major part of the task with 3 engines and then shut the outer two off. That's plausible. But with such a relatively light vehicle at that stage the efficiency gain may not be worth it.
I think this could be determined from the telemetry, the deceleration can be worked out - the fuel and weights are roughly known, the burn durations are known and the maximum thrust for one engine is known.
If you will bear my digression about the fuel efficiency issue with respect to number of engines :
- imagine at the moment of launch only one or a few engines fired up but at just a sufficient thrust level to equal the weight of the entire craft at that time. It would just sit there, going neither up nor down but with no support from any structures including what it sits on. In other words it would hover. Eventually the fuel would expend, the engines would cease to provide thrust and it would then continue to be in the same initial position and return to being supported by the pad structures. Admittedly during this time one would progressively lower the engine(s) power as the total weight diminishes, that happening because you are throwing fuel away. Thus you'd need less total engine power at the end of this process than at the beginning. However nothing terrible happens*, no laws of physics are breached, merely no useful result for the intended task ie. getting something to orbit. The total distance traveled during this 'flight' would be zero ( close to ). This is the equivalent of forcefully spinning the driving wheels of a car, you get no interesting traction to proceed anywhere fast ( assuming that matters ) ! :-)
- Hence providing thrust at only 1g for that mass is considered wasteful for purpose in rocketry of this type. Generally it may be happily suffered though eg. helicopters where the hovering capability is a virtue. The aim in rocket ascent is to spend as much of the total fraction of engine operating time producing the highest acceleration level practicable. Specifically it is the excess thrust to accelerate above 1g nett upwards that is useful.
- Do beware the language here though. You need to distinguish b/w thrust available and any nett acceleration upwards. The math is simple : if unsupported we accelerate at 1g down whatever the mass, then punching from below at 1g up ( by whatever means ) gives us a hover with nett acceleration zero and velocity vertical zero ( if we started that way ). Alas we tend to use the use the 'gee' word ( acceleration ) when we mean thrust ( force ), in detail that relies on an assumption about gravitational field strength at a location of interest**.
- available thrust is by no means the only constraint. The material of the rocket has to not fail during launch, the pressure of onrushing air must be kept likewise below some threshold. You don't want to melt the rocket substance while operating. The turbo pumps can only spin so fast. Etc. Etc.
- the same set of concerns on the way up also govern the trip back down. Particularly for fuel efficiency it is still true during descent that : spend as much of the total fraction of engine operating time producing the highest acceleration level practicable. But here there are added concerns like targeting, room for error in all important dynamical constraints. Compare that to a moment before launch where you are already dynamically situated where you want to be, at zero thrust, with zero acceleration, and zero velocity. Frequently the key constraint is a short launch window/instant ie. time alone.
- now to engine count. Three identical engines each working well at the same thrust setting will provide three times the total thrust than one engine at said thrust setting. However a one percent decrease per engine in a triplet is the same as 3 percent decrease for a singlet ( at least over most of the Merlin's operating range ). To match the finesse ( how small is the smallest thrust change for the vehicle overall at some time ) using a singlet, one has to adjust a triplet by 1/3 as much on engine settings. While Merlin's have a deep throttle capability - down to about 40% - that's not the same as finesse or how gradual you can do that.
- hence you trade total available grunt ( how many engines do I use ) for degrees of control within the range of operation. It would seem, my impression here, is that SpaceX prefers to err on the hard landing side of things eg. the hops caused by rebound on the legs. If it stops above the deck and then accelerates back up then one can only cut thrust to then have it drop. That is less controlled because engine gimbal doesn't assist steering at low/no thrust.
So as you say with regard to telemetry : you have to look at actual demonstrated craft performance to decide. Clearly one engine alone seems capable of doing that on total grunt grounds. Bear in mind that a lighter craft ( inertial mass I mean ) will give a greater dynamical response for a given Merlin engine setting change than a more massive one. I guess that's a convenient regime to be in for landing on ships in the ocean. But I'd like to know what part of the thrust range it is in during the last 500 meters, say. Is there ability to exceed rated maxima here ? For short times ? After all, in a few seconds time it can cool down for an extended period when thrust is cut.
Cheers, Mike.
* At least not within the deliberate simplicity of the scenario I am describing. There is an old saw from the early 1960s Atlas development program ( as ICBMs plus adaption for human flight ) that the first few inches upwards were the most interesting ones. There are some pretty epic videos of it rising just slightly, the thrust failing, all falls back down and then the enormous explosion.
** And so we, inadvertently by common usage, confound the inertial mass of an object by the force of deflection upon say, a bathroom scales indicator. It just so happens that the display is calibrated to give 'the mass that would give said deflection in an assumed gravitational field of 9.8 m/s2 '. That phrase doesn't sell kitchen appliances or lounge suites either .... :-)))
Noteworthy is that as the rocket ascends it's increasing distance from Earth affords a mild decrease in gravitational attraction via inverse square ( measured from the centre of mass of the Earth/rocket system which is at Earth's core ).
( edit ) For that matter : what does determine the practical upper power limit for a Merlin ? Temperature ? Turbo spin ? LOX/RP-1 density ? ....
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
When you see the guys in a cherry picker you can see how massive the leg dampers are and thus why a 'bounce' speaks of significant forces. They protect the relatively fine line b/w a nice landing and a huge loss. Been there, done that.
IMHO I don't think any other enterprise is going to replicate SpaceX's capability any time soon. Some of the key stuff is not only physically invisible but always will be so ie. decisions, choices, processes, procedures, algorithms etc. Just a glance at a blueprint would not help too much. No substitute for experience. Which is always the advantage that first time discoverers have. Still Elon made an early wise choice to not apply for patents : it just hands the blueprints and your logic to parties that disrespect claims without recourse.
For some reason I can never get the true scale right when I view the landing videos from barge mounted cameras. Maybe it's because they have fish-eye characteristics or something. The booster just seems rather smaller than it actually is. Does anyone else get that too ?
Cheers, Mike.
( edit ) I think there was a much smaller second hop after the first, possibly even a third. So we have the legs acting very well to progressively soak up energy ( & in turn heating up within ) in the fashion of rally car or dirt bike shockers.
( edit ) FWIW : this is the best version ( audio especially ) I have found for the SES-10 post launch press conference. For the grid fins in particular Elon makes some interesting points from 29:30 onwards eg. the newer titanium type to come has higher angle of attack on re-entry and better control authority. This is tech-code for fuel saving ( grid fins save fuel burns ) and better mission payload benefit etc. Peak heating goes like the cube of velocity !
( edit ) Well that answers one question : the block 5 Falcons will operate at another 7 - 8 %, that being at the intended design figure ie. to date they have been operating in the low 90's % of maximum specified rating. Plus the phrase now is not 're-used' but 'flight-proven' ;-))
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
There is some coverage by the
)
There is some coverage by the veteran's group of the SES booster being inspected and handled. Of those grid fins on view there is no loss of structural integrity that I can see. On the re-entry video I guess we may have been seeing very hot burning paint doing what it is designed to do ( taking the thermal hit to spare the device ). Once that layer goes we then see the underlying metal which is rather cooler because of that protection ! Again I am reminded of the scale of the gadget by the small humans running around underneath it.
@AgentB : it would be interesting to see what is happening at say 1000ft. They might punch the major part of the task with 3 engines and then shut the outer two off. That's plausible. But with such a relatively light vehicle at that stage the efficiency gain may not be worth it.
Cheers, Mike.
NB the sparing of the burn pattern about half way up is due to a slight surface lip created at a circumferential join. What has happened is that very high up at hypersonic speed a coherent surface layer of air formed above that join - in the 'lee' of the lip - and has excluded mixing with layers just further out from the surface. So it escaped much of the carbonisation. Further up that relatively cleaner segment the hotter layers have managed to arc back and penetrate to directly contact the paint.
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
Quote:Mike Hewson wrote:
)
Yes see here for an older flight inspecting the grid fins.
I think this could be determined from the telemetry, the deceleration can be worked out - the fuel and weights are roughly known, the burn durations are known and the maximum thrust for one engine is known.
It's just rocket science!
If you will bear my
)
If you will bear my digression about the fuel efficiency issue with respect to number of engines :
- imagine at the moment of launch only one or a few engines fired up but at just a sufficient thrust level to equal the weight of the entire craft at that time. It would just sit there, going neither up nor down but with no support from any structures including what it sits on. In other words it would hover. Eventually the fuel would expend, the engines would cease to provide thrust and it would then continue to be in the same initial position and return to being supported by the pad structures. Admittedly during this time one would progressively lower the engine(s) power as the total weight diminishes, that happening because you are throwing fuel away. Thus you'd need less total engine power at the end of this process than at the beginning. However nothing terrible happens*, no laws of physics are breached, merely no useful result for the intended task ie. getting something to orbit. The total distance traveled during this 'flight' would be zero ( close to ). This is the equivalent of forcefully spinning the driving wheels of a car, you get no interesting traction to proceed anywhere fast ( assuming that matters ) ! :-)
- Hence providing thrust at only 1g for that mass is considered wasteful for purpose in rocketry of this type. Generally it may be happily suffered though eg. helicopters where the hovering capability is a virtue. The aim in rocket ascent is to spend as much of the total fraction of engine operating time producing the highest acceleration level practicable. Specifically it is the excess thrust to accelerate above 1g nett upwards that is useful.
- Do beware the language here though. You need to distinguish b/w thrust available and any nett acceleration upwards. The math is simple : if unsupported we accelerate at 1g down whatever the mass, then punching from below at 1g up ( by whatever means ) gives us a hover with nett acceleration zero and velocity vertical zero ( if we started that way ). Alas we tend to use the use the 'gee' word ( acceleration ) when we mean thrust ( force ), in detail that relies on an assumption about gravitational field strength at a location of interest**.
- available thrust is by no means the only constraint. The material of the rocket has to not fail during launch, the pressure of onrushing air must be kept likewise below some threshold. You don't want to melt the rocket substance while operating. The turbo pumps can only spin so fast. Etc. Etc.
- the same set of concerns on the way up also govern the trip back down. Particularly for fuel efficiency it is still true during descent that : spend as much of the total fraction of engine operating time producing the highest acceleration level practicable. But here there are added concerns like targeting, room for error in all important dynamical constraints. Compare that to a moment before launch where you are already dynamically situated where you want to be, at zero thrust, with zero acceleration, and zero velocity. Frequently the key constraint is a short launch window/instant ie. time alone.
- now to engine count. Three identical engines each working well at the same thrust setting will provide three times the total thrust than one engine at said thrust setting. However a one percent decrease per engine in a triplet is the same as 3 percent decrease for a singlet ( at least over most of the Merlin's operating range ). To match the finesse ( how small is the smallest thrust change for the vehicle overall at some time ) using a singlet, one has to adjust a triplet by 1/3 as much on engine settings. While Merlin's have a deep throttle capability - down to about 40% - that's not the same as finesse or how gradual you can do that.
- hence you trade total available grunt ( how many engines do I use ) for degrees of control within the range of operation. It would seem, my impression here, is that SpaceX prefers to err on the hard landing side of things eg. the hops caused by rebound on the legs. If it stops above the deck and then accelerates back up then one can only cut thrust to then have it drop. That is less controlled because engine gimbal doesn't assist steering at low/no thrust.
So as you say with regard to telemetry : you have to look at actual demonstrated craft performance to decide. Clearly one engine alone seems capable of doing that on total grunt grounds. Bear in mind that a lighter craft ( inertial mass I mean ) will give a greater dynamical response for a given Merlin engine setting change than a more massive one. I guess that's a convenient regime to be in for landing on ships in the ocean. But I'd like to know what part of the thrust range it is in during the last 500 meters, say. Is there ability to exceed rated maxima here ? For short times ? After all, in a few seconds time it can cool down for an extended period when thrust is cut.
Cheers, Mike.
* At least not within the deliberate simplicity of the scenario I am describing. There is an old saw from the early 1960s Atlas development program ( as ICBMs plus adaption for human flight ) that the first few inches upwards were the most interesting ones. There are some pretty epic videos of it rising just slightly, the thrust failing, all falls back down and then the enormous explosion.
** And so we, inadvertently by common usage, confound the inertial mass of an object by the force of deflection upon say, a bathroom scales indicator. It just so happens that the display is calibrated to give 'the mass that would give said deflection in an assumed gravitational field of 9.8 m/s2 '. That phrase doesn't sell kitchen appliances or lounge suites either .... :-)))
Noteworthy is that as the rocket ascends it's increasing distance from Earth affords a mild decrease in gravitational attraction via inverse square ( measured from the centre of mass of the Earth/rocket system which is at Earth's core ).
( edit ) For that matter : what does determine the practical upper power limit for a Merlin ? Temperature ? Turbo spin ? LOX/RP-1 density ? ....
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
The legs are off, plus a free
)
The legs are off, plus a free wash.
When you see the guys in a cherry picker you can see how massive the leg dampers are and thus why a 'bounce' speaks of significant forces. They protect the relatively fine line b/w a nice landing and a huge loss. Been there, done that.
IMHO I don't think any other enterprise is going to replicate SpaceX's capability any time soon. Some of the key stuff is not only physically invisible but always will be so ie. decisions, choices, processes, procedures, algorithms etc. Just a glance at a blueprint would not help too much. No substitute for experience. Which is always the advantage that first time discoverers have. Still Elon made an early wise choice to not apply for patents : it just hands the blueprints and your logic to parties that disrespect claims without recourse.
For some reason I can never get the true scale right when I view the landing videos from barge mounted cameras. Maybe it's because they have fish-eye characteristics or something. The booster just seems rather smaller than it actually is. Does anyone else get that too ?
Cheers, Mike.
( edit ) I think there was a much smaller second hop after the first, possibly even a third. So we have the legs acting very well to progressively soak up energy ( & in turn heating up within ) in the fashion of rally car or dirt bike shockers.
( edit ) FWIW : this is the best version ( audio especially ) I have found for the SES-10 post launch press conference. For the grid fins in particular Elon makes some interesting points from 29:30 onwards eg. the newer titanium type to come has higher angle of attack on re-entry and better control authority. This is tech-code for fuel saving ( grid fins save fuel burns ) and better mission payload benefit etc. Peak heating goes like the cube of velocity !
( edit ) Well that answers one question : the block 5 Falcons will operate at another 7 - 8 %, that being at the intended design figure ie. to date they have been operating in the low 90's % of maximum specified rating. Plus the phrase now is not 're-used' but 'flight-proven' ;-))
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
Move over Mr
)
Move over Mr Musk.
http://www.bbc.co.uk/news/science-environment-39512503
Waiting for Godot & salvation :-)
Why do doctors have to practice?
You'd think they'd have got it right by now
Mike Hewson wrote:( edit )
)
And also the lower limit. According to the documentation the main engines can throttle down to 70% and the secondary (in vacuum) down to 39%.
The first stage can land well with one, it would be quite impossible to hover with three.
AgentB wrote:Mike Hewson
)
Absolutely right. There's your answer. :-)
@Chris : Yes. LOL. Elon just be breaking his company to send people on a quarter-hour high altitude free fall ride. :-)
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
Mike Hewson wrote:AgentB
)
Ah yes, the Allen Shepard experience. Just enough time to fleece the customer.
Gary Charpentier wrote:Mike
)
And a mere 200GJ of energy short of doing anything else. :-)
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
Falcon Heavy performance
)
Falcon Heavy performance figures increased by ~20% source