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Someone use drones already. Whoever is using drones to launch many air-breathing components that return on their own and launch stages that glide in after re-e

Someone use drones already. Whoever is using drones to launch many air-breathing components that return on their own and launch stages that glide in after re-entry wins. The rest of this stuff has obvious gigantic weight disadvantages. Current gas turbines are not optimized for pure thrust-to-weight or else why are military engines outperforming civilian in thrust-to-weight? Turbofan-to-turbo-jet for high Isp in atmospheric flight and then fly everything back on its own. Firefly's rocket has a max thrust of 90klb on the main while a big gas turbine pulls 100klb easy. While we're talking about Isp and re-usability, the entire first stage of a rocket could be gas-turbine powered and the engines just peel away and fly home after they're done. The engine needs gas. The gas takes space. Put the gas in a wing. Wing glides the engine home after launch. Easy as 1,2,3-a-bunch-of-engineering. Go!

ceejayoz 12y ago
You're advocating for air launch, not drones - the Falcon 9 / Dragon is already an unmanned drone craft. It has been successfully tried - http://en.wikipedia.org/wiki/Pegasus_%28rocket%29 http://en.wikipedia.org/wiki/Pegasus_%28rocket%29 - but my understanding is payloads are pretty severely limited. You can see the size of the Pegasus launcher is much, much smaller than a Falcon 9 - it's certainly not going to work for SLS/Falcon Heavy/MCT-sized payloads. edit: For ground-launch with jets as the first stage, I really don't think that's going to work. http://en.wikipedia.org/wiki/Thrust-to-weight_ratio#Jet_and_rocket_engines http://en.wikipedia.org/wiki/Thrust-to-weight_ratio#Jet_and_... indicates the SR-71's engine had a thrust-to-weight ratio of 5.2. SpaceX's Merlin has a thrust-to-weight of 150. There might be room for improvement, but 30-fold? I doubt it.
- knappador 12y ago
  Haha, right. I am not sure that a typical rocket body can handle the moment loads of being slung under a wing, even a delta, so I don't know about trying to fly an entire rocket, but certainly I'm advocating an even more modular approach to first stages where you have drone booster gas turbines that separate when they are no longer aerodynamically favorable (Mach 0.8 for turbofan, Mach ~2 for turbojet?) enough to keep building around them. Throw a big delta wing on there and land it at high speed using vortex lift. Low drag, no high-lift, and plenty of space for some gas.
- knappador 12y ago
  T:W for rockets vs air-breathing are really skewed by fuel consumption. Falcon 9's Merlins will burn ~25-30k lb fuel (70% launch mass is 1st stage gas?) per minute (180s total 1st stage time) vs ~1k lb fuel per F119. The jet engine will scorch the rocket in effective T:W for it's short atmospheric burn. More modern F119 has a T:W of about 8. With ceramics and pure focus on re-heat and specific thrust, you can get over T:W of 10 likely. There may be other tricks on fuels besides jet fuel that might even allow more focus on re-heat, making the T:W even higher without necessarily affecting fuel consumption. Going COTS with F119 is interesting, but ceramics might make some game-changers. Ceramic turbine blades and afterburner pipes will drastically lower the weight vs Nickel superalloy parts while lower cost and manufacturing complexity. Turbine blades are really impressive, but it's all cost.
- knappador 12y ago
  Now that I'm back interested in the topic =D.. F404 is just not quite at 10:1 T:W, which just goes to show that even COTS parts these days can make a very high Isp 0.5 stage.
jccooper 12y ago
A high thrust-to-weight air-breathing flyback first stage is certainly attractive. Load up a bunch of fighter jet engines on it, and go: no need for engine development or carrying a bunch of oxidizer. Main obstacle there is that optimum staging altitude and speed are very high by aircraft standards. 100km and Mach 10. Not much air up there. So you couldn't replace an F9-1 like that. You could perhaps use it as a 0.5-stage to get an otherwise SSTO rocket over the hump, but it may not be worth it compared to a standard architecture: still requires a separate giant lower-stage airframe, and one with much different technology from the rest of the system.
- knappador 12y ago
  Yeah, definitely you would look for either a very short-lived (2min) 1st stage or 0.5 stage. Max q is what makes it seem right. An STS flight profile can't even use max thrust again until 50k ft and Mach 2. Turbojets peeling away and glide back from around 60k ft and Mach 2.5 seems right. This is easier than a sea recovery, and because the burn duration is so short, it almost doesn't make sense to do anything but go full reheat and target the highest thrust in the lightest package. As more ceramic matrix composites replace Nickel, I would expect the T:W to get over 10, so it's really about what the smallest airframe is that you can wrap around a gas turbine and still land it on its own. The airframe size of the 0.5 stage (1st stage?) is the biggest departure from normal. You can get ten F119's around the base of an F9 without thinking too hard, but that's only ~400k lb thrust for 40k lb of engine and almost doubling the diameter at the base. Could get weird. Ceramic composites will be pretty critical. If you can replace Nickel parts with ceramic, you can get rid of bleed air and raise the temperature, which is what you need when you're sacrificing a little extra NOx for vastly higher T:W.
  - Gravityloss 12y ago
    Why air breathing? Rockets work very well. The propellant cost is not much.
    - knappador 12y ago
      It's one more tool for achieving reuseability without sacrificing performance. The size and weight of an air-breathing system will be lower due to greatly increased Isp of the 1st stage, the largest stage by mass. A smaller 1st stage fuel tank might mean that heat-shielding or higher temp materials is more of an option, which means you can raise the 1st stage separation velocity closer to what is "optimum" in the rocket sense and still recover the 1st stage. This puts the 2nd stage closer to its natural optimum design point. Overall size might not be a show-stopping problem now, but for building space colonies or Mars missions, overall vehicle size does eventually become concerning. Think of trying to build a jig to friction-stir weld a 180m long, 14m wide fuel tank. It's cool but also a bit of a distraction to have to build and handle everything at unusual scale. It would be super cool to see big packs of ten F414's at the base separate off, curve back towards the launch site, flip out some wings, and then cobra into a vertical landing. GE should step in right now to have the perfect platform to develop ceramic parts without the same service life requirements as aviation gas turbines.

ceejayoz 12y ago

You're advocating for air launch, not drones - the Falcon 9 / Dragon is already an unmanned drone craft. It has been successfully tried - http://en.wikipedia.org/wiki/Pegasus_%28rocket%29 http://en.wikipedia.org/wiki/Pegasus_%28rocket%29 - but my understanding is payloads are pretty severely limited. You can see the size of the Pegasus launcher is much, much smaller than a Falcon 9 - it's certainly not going to work for SLS/Falcon Heavy/MCT-sized payloads. edit: For ground-launch with jets as the first stage, I really don't think that's going to work. http://en.wikipedia.org/wiki/Thrust-to-weight_ratio#Jet_and_rocket_engines http://en.wikipedia.org/wiki/Thrust-to-weight_ratio#Jet_and_... indicates the SR-71's engine had a thrust-to-weight ratio of 5.2. SpaceX's Merlin has a thrust-to-weight of 150. There might be room for improvement, but 30-fold? I doubt it.

knappador 12y ago
Haha, right. I am not sure that a typical rocket body can handle the moment loads of being slung under a wing, even a delta, so I don't know about trying to fly an entire rocket, but certainly I'm advocating an even more modular approach to first stages where you have drone booster gas turbines that separate when they are no longer aerodynamically favorable (Mach 0.8 for turbofan, Mach ~2 for turbojet?) enough to keep building around them. Throw a big delta wing on there and land it at high speed using vortex lift. Low drag, no high-lift, and plenty of space for some gas.
knappador 12y ago
T:W for rockets vs air-breathing are really skewed by fuel consumption. Falcon 9's Merlins will burn ~25-30k lb fuel (70% launch mass is 1st stage gas?) per minute (180s total 1st stage time) vs ~1k lb fuel per F119. The jet engine will scorch the rocket in effective T:W for it's short atmospheric burn. More modern F119 has a T:W of about 8. With ceramics and pure focus on re-heat and specific thrust, you can get over T:W of 10 likely. There may be other tricks on fuels besides jet fuel that might even allow more focus on re-heat, making the T:W even higher without necessarily affecting fuel consumption. Going COTS with F119 is interesting, but ceramics might make some game-changers. Ceramic turbine blades and afterburner pipes will drastically lower the weight vs Nickel superalloy parts while lower cost and manufacturing complexity. Turbine blades are really impressive, but it's all cost.
knappador 12y ago
Now that I'm back interested in the topic =D.. F404 is just not quite at 10:1 T:W, which just goes to show that even COTS parts these days can make a very high Isp 0.5 stage.

jccooper 12y ago

A high thrust-to-weight air-breathing flyback first stage is certainly attractive. Load up a bunch of fighter jet engines on it, and go: no need for engine development or carrying a bunch of oxidizer. Main obstacle there is that optimum staging altitude and speed are very high by aircraft standards. 100km and Mach 10. Not much air up there. So you couldn't replace an F9-1 like that. You could perhaps use it as a 0.5-stage to get an otherwise SSTO rocket over the hump, but it may not be worth it compared to a standard architecture: still requires a separate giant lower-stage airframe, and one with much different technology from the rest of the system.

knappador 12y ago
Yeah, definitely you would look for either a very short-lived (2min) 1st stage or 0.5 stage. Max q is what makes it seem right. An STS flight profile can't even use max thrust again until 50k ft and Mach 2. Turbojets peeling away and glide back from around 60k ft and Mach 2.5 seems right. This is easier than a sea recovery, and because the burn duration is so short, it almost doesn't make sense to do anything but go full reheat and target the highest thrust in the lightest package. As more ceramic matrix composites replace Nickel, I would expect the T:W to get over 10, so it's really about what the smallest airframe is that you can wrap around a gas turbine and still land it on its own. The airframe size of the 0.5 stage (1st stage?) is the biggest departure from normal. You can get ten F119's around the base of an F9 without thinking too hard, but that's only ~400k lb thrust for 40k lb of engine and almost doubling the diameter at the base. Could get weird. Ceramic composites will be pretty critical. If you can replace Nickel parts with ceramic, you can get rid of bleed air and raise the temperature, which is what you need when you're sacrificing a little extra NOx for vastly higher T:W.
- Gravityloss 12y ago
  Why air breathing? Rockets work very well. The propellant cost is not much.
  - knappador 12y ago
    It's one more tool for achieving reuseability without sacrificing performance. The size and weight of an air-breathing system will be lower due to greatly increased Isp of the 1st stage, the largest stage by mass. A smaller 1st stage fuel tank might mean that heat-shielding or higher temp materials is more of an option, which means you can raise the 1st stage separation velocity closer to what is "optimum" in the rocket sense and still recover the 1st stage. This puts the 2nd stage closer to its natural optimum design point. Overall size might not be a show-stopping problem now, but for building space colonies or Mars missions, overall vehicle size does eventually become concerning. Think of trying to build a jig to friction-stir weld a 180m long, 14m wide fuel tank. It's cool but also a bit of a distraction to have to build and handle everything at unusual scale. It would be super cool to see big packs of ten F414's at the base separate off, curve back towards the launch site, flip out some wings, and then cobra into a vertical landing. GE should step in right now to have the perfect platform to develop ceramic parts without the same service life requirements as aviation gas turbines.