Yet famously Blue Origin is planning to use liquefied natural gas as the fuel for their primary engine family. Practically speaking this means almost entirely methane.
LNG has a lot going for it, requiring a far lower tank size and posing less of an insulation problem than liquid hydrogen, while still having appreciably higher energy content per unit weight than kerosene. Dirt cheap, also.
I was not even aware that Blue Origin had built a liquid hydrogen engine until I started preparing a post to contradict Mike, and did some checking first.
In my checking I stumbled across this technology page on Blue Origin's website. I thought they had a reputation of extreme secrecy, so was surprised to see this much detail on this page. Perhaps it is only recently public? Well worth a look if you have not seen it yet.
Many years ago while on assignment to Western Power in Australia some friends took me out the the LNG plant at Port Hedland (I believe this is the location of the LNG plant). It was pitch black except for the lights that lit up the LNG facility. Huge LNG tankers sat ready for refueling. LNG as a fuel source for rocketry - go figure. Almost forgot, to look up at a sky without much ambient light revealed a star system unlike any I had ever viewed before. Yes it is a different hemisphere but the clarity was incredible except for the ignition stacks which would light off occasionally from the LNG plant.
The Vertical Landing Booster on the page Archae86 provided really is intriguing. Clean looking. Wow, it just seems that with private companies entering the race they are making advances at a more rapid rate then did government funded efforts.
Yes it is and very easy to fall in love with. As a newly minted medico I did a range of outback/rural jobs and never minded the night shifts too much for that reason. I mean if you're up you may as well make the most of it. My best recollection was in 1987 when walking across a large lawn ( Mildura ) : I looked up and saw an extremely bright but unfamiliar star. I tried to work out which one it was, but failed. I figured I was just a bit too tired to sort that out properly. Later on I saw the morning's news ....
As for propellant mixes I think the best method is for one tank to be full of the densest fluid that you can lay your hands on. You will get terrific thrust and performance. Provided the other tank is the anti-matter counterpart that is. :-0 :-)
As for Blue Origin's change of secrecy : they've probably twigged that if they want paying customers ( and astronauts to boot ) then close to crystal transparency is mandatory. In that regard SpaceX is way ahead of the pack in terms of public engagement. Rich and clever people will want to kick the tyres. Precedents for mistrust abound here.
Cheers, Mike.
( edit ) Aha. The LNG will pressurise the tank sufficiently on it's own. Nice touch. It'll be the BE-4 which goes for orbit.
( edit ) I've noticed what I think is a key point for SpaceX's Falcon 9 first stage re-usability : the Merlin 1D can only throttle down to 70%. It shuts off below that. So nothing in the range from 0 thru 70%. That is why they come in hot and try to do a 'hover-slam' on the barges. It doesn't behave like the Grasshopper series at all. In general this is an old rocket design problem. If you want big grunt then you discard subtlety and vice versa. Probably it is a rule that if you try to optimise both you will only really trade.
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 noticed what I think is a key point for SpaceX's Falcon 9 first stage re-usability : the Merlin 1D can only throttle down to 70%. It shuts off below that. So nothing in the range from 0 thru 70%. That is why they come in hot and try to do a 'hover-slam' on the barges. It doesn't behave like the Grasshopper series at all. In general this is an old rocket design problem. If you want big grunt then you discard subtlety and vice versa. Probably it is a rule that if you try to optimise both you will only really trade.
So you are saying they need a second setup for the landing, still using the same fuel but different 'landing' hardware. Maybe a jettisonable, I know not a real word but you get what I mean, tail cover that then reveals the actual landing hardware with the 0% to 70%, or more, control they need.
I know too heavy for some missions, but it can't be too heavy for all of them, making the landing on the barge an option without 'hover-slamming' into it.
The problem is that at 70% throttle with lightest weight the acceleration is too much for any subtle hovering, positioning and calm landing. Zero throttle gives free fall and you can't relight them in a timely fashion to flick b/w 0% and 70% as you please ( ie. effectively averaging the thrust to something midway ). Try parallel parking a dragster with either zero or hero on the revs.
So the idea is to finesse it by large accelerations more or less at the last few moments. Do-able but you run the risk, as demonstrated, by controls lagging if something sticks. And those little thrusters are too powerless to catch and adjust the vertical displacements*. Hence 'close but no cigar'. On the way down the kinetic energy gained by descent needs to be bled away by drag and rocket thrust. Now the drag goes like speed squared, which is great for the fin usage up at Mach 2 & whatnot, but the other side of that coin is less effect at low speeds.
Cheers, Mike.
* You could view the entire problem as one of 'sensitive dependence upon initial conditions'. That is the exact moment to moment thrust level ( including especially which moment you start ) will greatly affect the velocity on touchdown say. But a relatively wee change in throttle timing & level causes a large change in the desired result.
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
You sure about that?
I think it is landing burning just one of the nine engines, so the minimum thrust would be just 6.3% of maximum. Not so far from what I'd guess to be the mass fraction. I really don't think Elon's gang would try to do a vertical landing without being able to provide the thrust for 1G at the end.
Of course, of you have sources, I'll bow. After all, I doubted her LH2/LO2 claim. On that one I found I was wrong before finishing my post.
My reference for the Merlin 1D performance is a tweet from Mr Musk, but as discussed in that link the question/answer has ambiguity. So my interpretation is 70% being : down 40% from 110%, where 100% is the 'rated' thrust with 110% being actual full throttle setting. Confusing : yes indeedy ! :-)
As for the rest I have interrogated the various spec sheets at SpaceX's website. The relevant ones are :
mass fully loaded Falcon ~ 500,000kg at liftoff
mass at landing 1st stage ~ 23,000kg - 26,000kg ( upper limit according to legs etc )
thrust at takeoff = 100% ( was 85 in earlier launches )
thus the reasoning is :
upward thrust at landing = (11.8/9.8) * (1/9) * (500/26) * 0.7 ~ 1.8 g
Nett upward acceleration at thrust minimum on landing = 1.8 - 1 = 0.8g
But the other crucial point that I didn't mention is fuel remaining ( @ 70% rated ) when nearly empty to hover for the period of time to do a finesse at that nett ?
However this analysis falls over if Elon actually meant lower throttle limit = 40% of rated. In which case :
Nett upward acceleration at thrust minimum on landing = 1.03 - 1 ~ 0.0g ( 'pure' hover )
Personally I reckon if he had achieved that ( 40% rated on deep throttle ) we'd definitely know more about it because that would an unprecedented/outstanding result for such a high specific impulse engine ( in that total power category ). But your feeling is good. While the thrust is 6.3% of maximum, the mass is 5% of takeoff .... :-)
Cheers, Mike.
( edit) FWIW the H2/LOX of Blue Origin solves that potential future problem by being able to throttle down to 20% of rated.
( edit ) To be clear : I am not claiming error by Elon/SpaceX. Not at all. I'm just pointing out the design choice and implications thereof with my 101st Rocket Science Chairborne Corps hat on .... :-)
( edit ) To be more precise that 2 m/s^2 ( ie. about 0.2g ) at the moment of takeoff rapidly rises because of the massive fuel expenditure rate and thus quick mass loss from the total fuel remaining to be burnt ( which determines the momentary nett at constant throttle ).
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
Actually ( for those that can bear my excruciating detail ) this brings up a key core point of Newtonian dynamics which is often misquoted/misunderstood. Isaac Newton did NOT say F = ma ! Seriously he didn't. He used F = rate of change of momentum. With his wording ( considering the idioms of the time ) momentum = 'quantity of motion', with that in turn being the product of mass and velocity. F = ma is only true either (a) as instantaneous comment and even then only if (b) mass is constant. The full horror is :
F = dp/dt = d/dt[mv] = m * dv/dt + v * dm/dt
using the product rule for differentiation .... that is, both mass and velocity considered to vary with time. So m * dv/dt = ma for sure. The second term ( in the context of rocketry ) devolves to the velocity of the exhaust gases multiplied by the time rate of how much fuel you are throwing away.
We normally talk of F = ma in everyday usage with objects having ~ constant mass so dm/dt = zero.
Cheers, Mike.
( edit ) Recall that Isaac was one of the inventors of calculus so he definitely knew about the product rule etc.
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 problem is that at 70% throttle with lightest weight the acceleration is too much for any subtle hovering, positioning and calm landing. Zero throttle gives free fall and you can't relight them in a timely fashion to flick b/w 0% and 70% as you please ( ie. effectively averaging the thrust to something midway ). Try parallel parking a dragster with either zero or hero on the revs.
So the idea is to finesse it by large accelerations more or less at the last few moments. Do-able but you run the risk, as demonstrated, by controls lagging if something sticks. And those little thrusters are too powerless to catch and adjust the vertical displacements*. Hence 'close but no cigar'. On the way down the kinetic energy gained by descent needs to be bled away by drag and rocket thrust. Now the drag goes like speed squared, which is great for the fin usage up at Mach 2 & whatnot, but the other side of that coin is less effect at low speeds.
Cheers, Mike.
* You could view the entire problem as one of 'sensitive dependence upon initial conditions'. That is the exact moment to moment thrust level ( including especially which moment you start ) will greatly affect the velocity on touchdown say. But a relatively wee change in throttle timing & level causes a large change in the desired result.
To clarify my suggestion was to have a 2nd set of controls that could give finer control during landing. I understood the 70% on or off problem and was just thinking of a possible alternative to it.
( edit ) I've noticed what I think is a key point for SpaceX's Falcon 9 first stage re-usability : the Merlin 1D can only throttle down to 70%. It shuts off below that. So nothing in the range from 0 thru 70%. That is why they come in hot and try to do a 'hover-slam' on the barges. It doesn't behave like the Grasshopper series at all. In general this is an old rocket design problem. If you want big grunt then you discard subtlety and vice versa. Probably it is a rule that if you try to optimise both you will only really trade.
Mike, if by "Grasshoper series" you are referring to the prototype launches referenced throughout this thread, I would think that landing scenario (nice and gentle) is exactly what SpaceX must achieve from space. The whole point of recovery is re-usability and if the "hover-slam" approach is the best SpaceX has to offer in ground based landings (the 70% you reference) then you can almost guarantee a low percentage of reusable stages as a result of heavy impact. I wish that Blue Origin's launch had been successful in that they could have recovered their first stage. It would have provided a glimpse into how this is supposed to work.
RE: Interesting engine.
)
Yet famously Blue Origin is planning to use liquefied natural gas as the fuel for their primary engine family. Practically speaking this means almost entirely methane.
LNG has a lot going for it, requiring a far lower tank size and posing less of an insulation problem than liquid hydrogen, while still having appreciably higher energy content per unit weight than kerosene. Dirt cheap, also.
I was not even aware that Blue Origin had built a liquid hydrogen engine until I started preparing a post to contradict Mike, and did some checking first.
In my checking I stumbled across this technology page on Blue Origin's website. I thought they had a reputation of extreme secrecy, so was surprised to see this much detail on this page. Perhaps it is only recently public? Well worth a look if you have not seen it yet.
Many years ago while on
)
Many years ago while on assignment to Western Power in Australia some friends took me out the the LNG plant at Port Hedland (I believe this is the location of the LNG plant). It was pitch black except for the lights that lit up the LNG facility. Huge LNG tankers sat ready for refueling. LNG as a fuel source for rocketry - go figure. Almost forgot, to look up at a sky without much ambient light revealed a star system unlike any I had ever viewed before. Yes it is a different hemisphere but the clarity was incredible except for the ignition stacks which would light off occasionally from the LNG plant.
The Vertical Landing Booster on the page Archae86 provided really is intriguing. Clean looking. Wow, it just seems that with private companies entering the race they are making advances at a more rapid rate then did government funded efforts.
RE: .... the clarity was
)
Yes it is and very easy to fall in love with. As a newly minted medico I did a range of outback/rural jobs and never minded the night shifts too much for that reason. I mean if you're up you may as well make the most of it. My best recollection was in 1987 when walking across a large lawn ( Mildura ) : I looked up and saw an extremely bright but unfamiliar star. I tried to work out which one it was, but failed. I figured I was just a bit too tired to sort that out properly. Later on I saw the morning's news ....
As for propellant mixes I think the best method is for one tank to be full of the densest fluid that you can lay your hands on. You will get terrific thrust and performance. Provided the other tank is the anti-matter counterpart that is. :-0 :-)
As for Blue Origin's change of secrecy : they've probably twigged that if they want paying customers ( and astronauts to boot ) then close to crystal transparency is mandatory. In that regard SpaceX is way ahead of the pack in terms of public engagement. Rich and clever people will want to kick the tyres. Precedents for mistrust abound here.
Cheers, Mike.
( edit ) Aha. The LNG will pressurise the tank sufficiently on it's own. Nice touch. It'll be the BE-4 which goes for orbit.
( edit ) I've noticed what I think is a key point for SpaceX's Falcon 9 first stage re-usability : the Merlin 1D can only throttle down to 70%. It shuts off below that. So nothing in the range from 0 thru 70%. That is why they come in hot and try to do a 'hover-slam' on the barges. It doesn't behave like the Grasshopper series at all. In general this is an old rocket design problem. If you want big grunt then you discard subtlety and vice versa. Probably it is a rule that if you try to optimise both you will only really trade.
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: I've noticed what I
)
So you are saying they need a second setup for the landing, still using the same fuel but different 'landing' hardware. Maybe a jettisonable, I know not a real word but you get what I mean, tail cover that then reveals the actual landing hardware with the 0% to 70%, or more, control they need.
I know too heavy for some missions, but it can't be too heavy for all of them, making the landing on the barge an option without 'hover-slamming' into it.
The problem is that at 70%
)
The problem is that at 70% throttle with lightest weight the acceleration is too much for any subtle hovering, positioning and calm landing. Zero throttle gives free fall and you can't relight them in a timely fashion to flick b/w 0% and 70% as you please ( ie. effectively averaging the thrust to something midway ). Try parallel parking a dragster with either zero or hero on the revs.
So the idea is to finesse it by large accelerations more or less at the last few moments. Do-able but you run the risk, as demonstrated, by controls lagging if something sticks. And those little thrusters are too powerless to catch and adjust the vertical displacements*. Hence 'close but no cigar'. On the way down the kinetic energy gained by descent needs to be bled away by drag and rocket thrust. Now the drag goes like speed squared, which is great for the fin usage up at Mach 2 & whatnot, but the other side of that coin is less effect at low speeds.
Cheers, Mike.
* You could view the entire problem as one of 'sensitive dependence upon initial conditions'. That is the exact moment to moment thrust level ( including especially which moment you start ) will greatly affect the velocity on touchdown say. But a relatively wee change in throttle timing & level causes a large change in the desired result.
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
Hmmm... Mike, You sure
)
Hmmm... Mike,
You sure about that?
I think it is landing burning just one of the nine engines, so the minimum thrust would be just 6.3% of maximum. Not so far from what I'd guess to be the mass fraction. I really don't think Elon's gang would try to do a vertical landing without being able to provide the thrust for 1G at the end.
Of course, of you have sources, I'll bow. After all, I doubted her LH2/LO2 claim. On that one I found I was wrong before finishing my post.
Fair query. Read on : My
)
Fair query. Read on :
My reference for the Merlin 1D performance is a tweet from Mr Musk, but as discussed in that link the question/answer has ambiguity. So my interpretation is 70% being : down 40% from 110%, where 100% is the 'rated' thrust with 110% being actual full throttle setting. Confusing : yes indeedy ! :-)
As for the rest I have interrogated the various spec sheets at SpaceX's website. The relevant ones are :
mass fully loaded Falcon ~ 500,000kg at liftoff
mass at landing 1st stage ~ 23,000kg - 26,000kg ( upper limit according to legs etc )
nett acceleration at takeoff ~ 2 m/2^2 ie. upward thrust achieves 9.8 + 2 = 11.8 m/s^2
engines used at takeoff = 9
engines used at landing = 1
thrust at takeoff = 100% ( was 85 in earlier launches )
thus the reasoning is :
upward thrust at landing = (11.8/9.8) * (1/9) * (500/26) * 0.7 ~ 1.8 g
Nett upward acceleration at thrust minimum on landing = 1.8 - 1 = 0.8g
But the other crucial point that I didn't mention is fuel remaining ( @ 70% rated ) when nearly empty to hover for the period of time to do a finesse at that nett ?
However this analysis falls over if Elon actually meant lower throttle limit = 40% of rated. In which case :
Nett upward acceleration at thrust minimum on landing = 1.03 - 1 ~ 0.0g ( 'pure' hover )
Personally I reckon if he had achieved that ( 40% rated on deep throttle ) we'd definitely know more about it because that would an unprecedented/outstanding result for such a high specific impulse engine ( in that total power category ). But your feeling is good. While the thrust is 6.3% of maximum, the mass is 5% of takeoff .... :-)
Cheers, Mike.
( edit) FWIW the H2/LOX of Blue Origin solves that potential future problem by being able to throttle down to 20% of rated.
( edit ) To be clear : I am not claiming error by Elon/SpaceX. Not at all. I'm just pointing out the design choice and implications thereof with my 101st Rocket Science Chairborne Corps hat on .... :-)
ASIDE : I have discovered the Falcon Nine User's Manual! :-0 :-)
( edit ) To be more precise that 2 m/s^2 ( ie. about 0.2g ) at the moment of takeoff rapidly rises because of the massive fuel expenditure rate and thus quick mass loss from the total fuel remaining to be burnt ( which determines the momentary nett at constant throttle ).
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
Actually ( for those that can
)
Actually ( for those that can bear my excruciating detail ) this brings up a key core point of Newtonian dynamics which is often misquoted/misunderstood. Isaac Newton did NOT say F = ma ! Seriously he didn't. He used F = rate of change of momentum. With his wording ( considering the idioms of the time ) momentum = 'quantity of motion', with that in turn being the product of mass and velocity. F = ma is only true either (a) as instantaneous comment and even then only if (b) mass is constant. The full horror is :
F = dp/dt = d/dt[mv] = m * dv/dt + v * dm/dt
using the product rule for differentiation .... that is, both mass and velocity considered to vary with time. So m * dv/dt = ma for sure. The second term ( in the context of rocketry ) devolves to the velocity of the exhaust gases multiplied by the time rate of how much fuel you are throwing away.
We normally talk of F = ma in everyday usage with objects having ~ constant mass so dm/dt = zero.
Cheers, Mike.
( edit ) Recall that Isaac was one of the inventors of calculus so he definitely knew about the product rule etc.
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: The problem is that at
)
To clarify my suggestion was to have a 2nd set of controls that could give finer control during landing. I understood the 70% on or off problem and was just thinking of a possible alternative to it.
The rest is way over my head.
RE: ( edit ) I've noticed
)
Mike, if by "Grasshoper series" you are referring to the prototype launches referenced throughout this thread, I would think that landing scenario (nice and gentle) is exactly what SpaceX must achieve from space. The whole point of recovery is re-usability and if the "hover-slam" approach is the best SpaceX has to offer in ground based landings (the 70% you reference) then you can almost guarantee a low percentage of reusable stages as a result of heavy impact. I wish that Blue Origin's launch had been successful in that they could have recovered their first stage. It would have provided a glimpse into how this is supposed to work.