SpaceX (Vol. 2)
Discussion
Beati Dogu said:
Boeing were forced into a shotgun wedding with Lockheed to form ULA. Now they’re only really surviving as a second source launch provider. Their lunch having very much been eaten along with Roscosmos and Arianespace’s by SpaceX.
ULA are doing pretty well, Boeing much less so.The Vulcan rocket has 74 flights contracted to it equating to more than $10 billion of revenue. Company is up for sale so precisely how that is leveraged into long term success will be the choice of the new owners.
They have stated that they will implement smart reuse from the first few flights in. Assuming that those 74 launches have been contacted on the basis of a non reusable booster they could also become quite profitable.
You could leverage that into making Vulcan more reusable, potentially making it into a 5 engine core stage with retro propulsive landing, SpaceX perfected that in less than 20 launches.
For space probes you don't actually want a reusable second stage so there is still a market for the existing upper stage. If you want to reuse the second stage you could either look at bringing it back with an inflatable heat shield or by putting some wings on it and landing it on a runway. The latter is actually more manageable rateable than retro propulsive landing and no disadvantage if you don't want to land on Mars.
Talksteer said:
For space probes you don't actually want a reusable second stage so there is still a market for the existing upper stage. If you want to reuse the second stage you could either look at bringing it back with an inflatable heat shield or by putting some wings on it and landing it on a runway. The latter is actually more manageable rateable than retro propulsive landing and no disadvantage if you don't want to land on Mars.
However you land it, you still need a heat shield. If you want to put wings and landing gear on it, you've got to re-engineer it (and potentially lose a lot of payload) because now your rocket is coping with bending loads, not primarily axial loads - as Virgin Orbit discovered, resulting in far lower payload capacity.Starship works because it is a much larger diameter: 9m vs 5.4m for Centaur V. That allows for a different distribution of loads, and a much greater specific bending stiffness (recalling that, all other things being equal, the bending stiffness of a cylinder will be proportional to the cube of the radius - Starship's specific bending stiffness can easily be 5 times times that of Centaur V for a given construction). That's one of the reasons Starship is so large.
skwdenyer said:
However you land it, you still need a heat shield. If you want to put wings and landing gear on it, you've got to re-engineer it (and potentially lose a lot of payload) because now your rocket is coping with bending loads, not primarily axial loads - as Virgin Orbit discovered, resulting in far lower payload capacity.
Starship works because it is a much larger diameter: 9m vs 5.4m for Centaur V. That allows for a different distribution of loads, and a much greater specific bending stiffness (recalling that, all other things being equal, the bending stiffness of a cylinder will be proportional to the cube of the radius - Starship's specific bending stiffness can easily be 5 times times that of Centaur V for a given construction). That's one of the reasons Starship is so large.
I now want to see a design for a carrier plane you could hang Super Heavy off.......Starship works because it is a much larger diameter: 9m vs 5.4m for Centaur V. That allows for a different distribution of loads, and a much greater specific bending stiffness (recalling that, all other things being equal, the bending stiffness of a cylinder will be proportional to the cube of the radius - Starship's specific bending stiffness can easily be 5 times times that of Centaur V for a given construction). That's one of the reasons Starship is so large.
Edited by xeny on Tuesday 14th May 13:46
xeny said:
I know want to see a design for a carrier plane you could hang Super Heavy off.......
The costs outweigh the benefits.Timm Dodd (Everyday Astronaut) has a video on this.
But succinctly,
1. Plane and rocket need to be designed for the job.
2. 2 vehicles = more expensive.
3. Rocket needs to be able to handle differing thrust loads when operating on a rocket, making it heavier.
4. You only get around 600mph of delta v from the process of the roughly 20,000 you need to reach orbit.
Basically, you can either build the heaviest lift plane ever constructed+ the rocket, with modifications.
Or make the rocket slightly bigger...
Oh, certainly the engineering logic is terrible.
BTW, I'm guessing everyone here is aware of this proposal for the reverse of the process? https://www.youtube.com/watch?v=ARqBJxsXUfk
BTW, I'm guessing everyone here is aware of this proposal for the reverse of the process? https://www.youtube.com/watch?v=ARqBJxsXUfk
xeny said:
Oh, certainly the engineering logic is terrible.
BTW, I'm guessing everyone here is aware of this proposal for the reverse of the process? https://www.youtube.com/watch?v=ARqBJxsXUfk
That’s gloriously nuts, in a Thunderbirds style. It would have perhaps made slightly more sense if it used a variant of the Fairey Rotadyne (rotors driven by tip jets, rather than a monstrous gearbox).BTW, I'm guessing everyone here is aware of this proposal for the reverse of the process? https://www.youtube.com/watch?v=ARqBJxsXUfk
skwdenyer said:
That’s gloriously nuts, in a Thunderbirds style. It would have perhaps made slightly more sense if it used a variant of the Fairey Rotadyne (rotors driven by tip jets, rather than a monstrous gearbox).
I believe the proposal was for two jet engines at each blade tip, with a 7th driving the tail rotor, I was presuming via a gearbox, but as Hiller specialised in tip jets, I suspect now actually with the exhaust ducted down the tail rotor blades to drive tip jets.Yes, gloriously nuts. Mentioning Thunderbirds, and drifting slightly - https://www.youtube.com/watch?v=zx1iluQsJdE
skwdenyer said:
xeny said:
Oh, certainly the engineering logic is terrible.
BTW, I'm guessing everyone here is aware of this proposal for the reverse of the process? https://www.youtube.com/watch?v=ARqBJxsXUfk
That’s gloriously nuts, in a Thunderbirds style. It would have perhaps made slightly more sense if it used a variant of the Fairey Rotadyne (rotors driven by tip jets, rather than a monstrous gearbox).BTW, I'm guessing everyone here is aware of this proposal for the reverse of the process? https://www.youtube.com/watch?v=ARqBJxsXUfk
They're hugely loud, make a euro fighter seem quiet
They aren't any more intrinsically loud than any other jet engine. The prototype was loud as the tip jets used were originally designed for a rotodyne with an MTOW of approximately half the weight of the aircraft built; to compensate the fuel and air flow were increased greatly, which reduced efficiency and increased noise. Modern materials technology and CFD software would likely make tip jets and gyrodynes socially acceptable, or at least as much as the average gas turbine powered helicopter.
skwdenyer said:
Talksteer said:
For space probes you don't actually want a reusable second stage so there is still a market for the existing upper stage. If you want to reuse the second stage you could either look at bringing it back with an inflatable heat shield or by putting some wings on it and landing it on a runway. The latter is actually more manageable rateable than retro propulsive landing and no disadvantage if you don't want to land on Mars.
However you land it, you still need a heat shield. If you want to put wings and landing gear on it, you've got to re-engineer it (and potentially lose a lot of payload) because now your rocket is coping with bending loads, not primarily axial loads - as Virgin Orbit discovered, resulting in far lower payload capacity.Starship works because it is a much larger diameter: 9m vs 5.4m for Centaur V. That allows for a different distribution of loads, and a much greater specific bending stiffness (recalling that, all other things being equal, the bending stiffness of a cylinder will be proportional to the cube of the radius - Starship's specific bending stiffness can easily be 5 times times that of Centaur V for a given construction). That's one of the reasons Starship is so large.
A horizontal landing upper stage is essentially a space plane however there is no reason to make it as complex as the shuttle. Firstly if you stick with hydrogen as the fuel your upper stage becomes particularly "fluffy" once you also incorporate the payload bay. The net result is that your surface area to volume is much less than something like starship (see also square cube). This means that the heat shield for a hydrogen fueled space plane is pretty negligible it ends up being acceptable to use metallic foil type structures which also serve a dual duty as insulation for the propellant. If you want a detailed look at this the late 70's NASA space plane studies, the 80's "Frequent flyer" study and the Skylon use this property of a hydrogen fuel vehicle to re-enter high and gently to allow a reusable and light heat shield.
The other notable thing about this "upper stage" is that unlike the Virgin rocket it never operates fueled or under thrust using aero-dynamic control. It flies the same profile on ascent as a regular upper stage with similar bending loads. When it's returning it only needs to support its empty structure, for something like a Vulcan upper stage this means it will barely be into double figures of tonnes, which means that the wings and under carriage could be exceeding light. The other thing you could do as it isn't the shuttle is the under carriage could be on the cold side with the craft just rolling to orientate it after re-entry.
annodomini2 said:
xeny said:
I know want to see a design for a carrier plane you could hang Super Heavy off.......
The costs outweigh the benefits.Timm Dodd (Everyday Astronaut) has a video on this.
But succinctly,
1. Plane and rocket need to be designed for the job.
2. 2 vehicles = more expensive.
3. Rocket needs to be able to handle differing thrust loads when operating on a rocket, making it heavier.
4. You only get around 600mph of delta v from the process of the roughly 20,000 you need to reach orbit.
Basically, you can either build the heaviest lift plane ever constructed+ the rocket, with modifications.
Or make the rocket slightly bigger...
1: If you are air launching a re-usable single stage to orbit space plane your "stage one" is likely to be a used A380, this is widely available at knock down values and will fly thousands of missions without heavy maintenance with incredibly high reliability.
2: One of your vehicles is already designed for you
3: There are some potential ways to handle the different loading cases, firstly you have you carrier aircraft pull up before landing. The launched SSTO craft then flies a semi-ballistic course for quite while which mean that the wings don't need to support the fueled weight of the craft. The different load cases make less of a difference to a SSTO which doesn't have the weak point of multi-stage rocket which separates at the interstages.. For a single stage the propellant tanks are pressurised in flight and proof against the full rocket thrust in the lateral direction, this makes them perfectly capable of holding their filled mass in the horizontal direction. The wings only have to support the craft at relatively high velocities so don't need to be massive.
4: The rocket equation is logarithmic, so an extra 5% of delta V makes a much bigger impact on payload. Launching from 35,000ft also means that you can run higher expansion ratio engines which gives you a better ISP and the aero-dynamic loads are much lower so you can trim weight from other parts of the structure.
The upshot of all this is that if you air launch you move an SSTO design from being a non starter to being completely plausible with a useful payload. This means that you now only have to design a single vehicle which doesn't split in flight. If you extrapolate from the 80's Teledyne Brown air launched space plane with modern technology and an A380 launch platform you are looking about15 tonnes LEO. You would achieve this with a single engine of the same thrust as a Raptor, which does indicate that in terms of equipment employed it may trade favorably with a two stage re-usable rocket.
The weight of a delta wing is likely a bit higher than a Starship style "Elonaron" but this is more than offset by the lack of need for landing propellant which you also don't need to maintain for the whole flight. The biggest advantage is however that a gliding landing is considerably safer than a propulsive landing, both from a statistical basis (thousands of landings per mishaps, the Shuttle obviously stuck every landing even with equipment failures) and and also from a a consequence of failure basis (if a glider landing fails an inert vehicle skids down the runway, if a propulsive landing fails fiery explosive death awaits)
The only real issues with a gliding landing is, you can't land anywhere other than earth and once you exceed the size of what can be carried by commercially available aircraft you stop being able to use COTS technology. It's probably best for putting up satellite constellations and moving people about in vast numbers.
Edited by Talksteer on Wednesday 15th May 20:53
hidetheelephants said:
They aren't any more intrinsically loud than any other jet engine. The prototype was loud as the tip jets used were originally designed for a rotodyne with an MTOW of approximately half the weight of the aircraft built; to compensate the fuel and air flow were increased greatly, which reduced efficiency and increased noise. Modern materials technology and CFD software would likely make tip jets and gyrodynes socially acceptable, or at least as much as the average gas turbine powered helicopter.
My Grandfather was a part of the Rotadyne design team. The noise was in part because the tip jets were going supersonic. At the time of cancellation, there was significant and productive work on noise reduction.What really annoyed the team was the Government, as the project’s funder, demanded that all work was completely destroyed. A pattern repeated elsewhere.
skwdenyer said:
Interesting projections that Starlink will be a $6bn revenue business this year. Which is pretty strong result. There are already 2.7m subscribers. Which will undoubtedly help with funding Starship.
It was pointed out that a decent proportion of that is from US subscribers who get partially funded by a federal grant to provide internet in remote places.The amount of funding was actually commensurate with the amount that SpaceX pledged to spend on the development of the starship lunar lander.
Talksteer said:
Tim's not an engineer, there have been numerous air launched studies by serious outfits which address all of this. Virgins approach of firing a multi-stage rocket was a little odd but if you look at air launching a re-usable single stage to orbit (SSTO, though arguably air launching is cheating in this regard) craft it starts to make sense.
1: If you are air launching a re-usable single stage to orbit space plane your "stage one" is likely to be a used A380, this is widely available at knock down values and will fly thousands of missions without heavy maintenance with incredibly high reliability.
2: One of your vehicles is already designed for you
3: There are some potential ways to handle the different loading cases, firstly you have you carrier aircraft pull up before landing. The launched SSTO craft then flies a semi-ballistic course for quite while which mean that the wings don't need to support the fueled weight of the craft. The different load cases make less of a difference to a SSTO which doesn't have the weak point of multi-stage rocket which separates at the interstages.. For a single stage the propellant tanks are pressurised in flight and proof against the full rocket thrust in the lateral direction, this makes them perfectly capable of holding their filled mass in the horizontal direction. The wings only have to support the craft at relatively high velocities so don't need to be massive.
4: The rocket equation is logarithmic, so an extra 5% of delta V makes a much bigger impact on payload. Launching from 35,000ft also means that you can run higher expansion ratio engines which gives you a better ISP and the aero-dynamic loads are much lower so you can trim weight from other parts of the structure.
The upshot of all this is that if you air launch you move an SSTO design from being a non starter to being completely plausible with a useful payload. This means that you now only have to design a single vehicle which doesn't split in flight. If you extrapolate from the 80's Teledyne Brown air launched space plane with modern technology and an A380 launch platform you are looking about15 tonnes LEO. You would achieve this with a single engine of the same thrust as a Raptor, which does indicate that in terms of equipment employed it may trade favorably with a two stage re-usable rocket.
The weight of a delta wing is likely a bit higher than a Starship style "Elonaron" but this is more than offset by the lack of need for landing propellant which you also don't need to maintain for the whole flight. The biggest advantage is however that a gliding landing is considerably safer than a propulsive landing, both from a statistical basis (thousands of landings per mishaps, the Shuttle obviously stuck every landing even with equipment failures) and and also from a a consequence of failure basis (if a glider landing fails an inert vehicle skids down the runway, if a propulsive landing fails fiery explosive death awaits)
The only real issues with a gliding landing is, you can't land anywhere other than earth and once you exceed the size of what can be carried by commercially available aircraft you stop being able to use COTS technology. It's probably best for putting up satellite constellations and moving people about in vast numbers.
1. Air launching makes it Two stage as the plane would be the first stage. It's not SSTO.1: If you are air launching a re-usable single stage to orbit space plane your "stage one" is likely to be a used A380, this is widely available at knock down values and will fly thousands of missions without heavy maintenance with incredibly high reliability.
2: One of your vehicles is already designed for you
3: There are some potential ways to handle the different loading cases, firstly you have you carrier aircraft pull up before landing. The launched SSTO craft then flies a semi-ballistic course for quite while which mean that the wings don't need to support the fueled weight of the craft. The different load cases make less of a difference to a SSTO which doesn't have the weak point of multi-stage rocket which separates at the interstages.. For a single stage the propellant tanks are pressurised in flight and proof against the full rocket thrust in the lateral direction, this makes them perfectly capable of holding their filled mass in the horizontal direction. The wings only have to support the craft at relatively high velocities so don't need to be massive.
4: The rocket equation is logarithmic, so an extra 5% of delta V makes a much bigger impact on payload. Launching from 35,000ft also means that you can run higher expansion ratio engines which gives you a better ISP and the aero-dynamic loads are much lower so you can trim weight from other parts of the structure.
The upshot of all this is that if you air launch you move an SSTO design from being a non starter to being completely plausible with a useful payload. This means that you now only have to design a single vehicle which doesn't split in flight. If you extrapolate from the 80's Teledyne Brown air launched space plane with modern technology and an A380 launch platform you are looking about15 tonnes LEO. You would achieve this with a single engine of the same thrust as a Raptor, which does indicate that in terms of equipment employed it may trade favorably with a two stage re-usable rocket.
The weight of a delta wing is likely a bit higher than a Starship style "Elonaron" but this is more than offset by the lack of need for landing propellant which you also don't need to maintain for the whole flight. The biggest advantage is however that a gliding landing is considerably safer than a propulsive landing, both from a statistical basis (thousands of landings per mishaps, the Shuttle obviously stuck every landing even with equipment failures) and and also from a a consequence of failure basis (if a glider landing fails an inert vehicle skids down the runway, if a propulsive landing fails fiery explosive death awaits)
The only real issues with a gliding landing is, you can't land anywhere other than earth and once you exceed the size of what can be carried by commercially available aircraft you stop being able to use COTS technology. It's probably best for putting up satellite constellations and moving people about in vast numbers.
Edited by Talksteer on Wednesday 15th May 20:53
2. You're not going to be able to launch much more than what Virgin Orbit did with Launcher one, 500kg-1000kg to orbit. Obviously non-reusable. Less to support reusability (probably nothing).
3. The benefits of initial speed and drag are limited by the lift capability of aircraft. You also cannot consume all the remaining take off mass of the aircraft as you're limited by how and where to mount the rocket such that it can be safely deployed. Without designing a dedicated aircraft you're very limited in what you can lift and deploy.
4. Single stage from the launch aircraft would be less mass efficient to orbit. As you have to get more mass to orbital velocity. If your inter-stage outweighs the rest of your rocket's 1st stage, then you haven't designed it correctly.
Prior to SpaceX landing the first stage of Falcon 9, air launch or SSTO were considered the future, and landing the first considered borderline impossible.
With that the game changed.
With a reusable 5 km/s dv first stage, air launch at 0.27km/s the benefit is insignificant for massively increased complexity.
SSTO may one day be practical, but not till we have a working solution for having 600+Secs of ISP and high thrust in the propulsion system, it's not going to happen any time soon.
I agree glider landing is more efficient on Earth, but Musk has stated directly that the goal of Starship is to land on other planets. Mars being the primary goal. Which doesn't have enough atmosphere or runways for that matter to support it.
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