Posted: 12/12/2012 6:02:32 AM EDT
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Why is it we use multistage rockets to lift spacecraft from the ground? Seems like it'd be a lot cheaper to build a flippin huge heavy lift jet to get em up and moving, and then use fewer stages of rockets. Hell, you could use a gargantuan hot air balloon for that matter. Gravity is stronger at low altitude, so the higher you get prior to lighting the fire, the less tons of rocket fuel you have to lift. Seems like that first hundred thousand feet or so is the cost driver.
Any aero engineer types wanna school me on why we do it the way we do? |
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Why is it we use multistage rockets to lift spacecraft from the ground? Seems like it'd be a lot cheaper to build a flippin huge heavy lift jet to get em up and moving, and then use fewer stages of rockets. Hell, you could use a gargantuan hot air balloon for that matter. Gravity is stronger at low altitude, so the higher you get prior to lighting the fire, the less tons of rocket fuel you have to lift. Seems like that first hundred thousand feet or so is the cost driver. Any aero engineer types wanna school me on why we do it the way we do? It pays to reduce vehicle and fuel weight simultaneously. Once the fuel that section contained is burned, it would be far less efficient to try and keep pushing that sections weight into orbit. ETA: velocity is the key not altitude. |
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First, the difference in gravity anywhere you could fly in the atmosphere is so close to the sea level value that the difference is mostly trivial.
Multi stage rockets are used in order to shed mass during the launch. Small rockets could be launched from air vehicles flying at high altitude, but most of these payloads are simply too large. Some satellites we've put up are the size of a large RV and heavy, the assembly is tightly packed in order to hold the external dimensions down. I don't have time right now, but you could compute the volume (and cost to fill) of helium filled balloons large enough to launch the payload weight you have in mind. A dirigible I sized several years ago to lift 1 million pounds was over 1000 feet long and I recall about 150 or 160 feet in diameter; your payload won't be that heavy, but the vehicle will still be enormous. |
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Quoted: Quoted: Physics fail. It's not about getting it away from gravity, it's about gettting it spinning to use centripetal force to keep it up there. I thought Scaled Composites launched SS1 that way. That barely touched space for minutes then fell right back down. IT was no where near getting into an orbit. |
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Physics fail. It's not about getting it away from gravity, it's about gettting it spinning to use centripetal force to keep it up there. I thought Scaled Composites launched SS1 that way. That barely touched space for minutes then fell right back down. IT was no where near getting into an orbit. This. SS1 had only 2% of the power required to achieve orbital velocity. It's one thing to go up to 65 miles and drop back down. It's quite another to go up hundreds of miles and stay there. |
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First, the difference in gravity anywhere you could fly in the atmosphere is so close to the sea level value that the difference is mostly trivial. Multi stage rockets are used in order to shed mass during the launch. Small rockets could be launched from air vehicles flying at high altitude, but most of these payloads are simply too large. Some satellites we've put up are the size of a large RV and heavy, the assembly is tightly packed in order to hold the external dimensions down. I don't have time right now, but you could compute the volume (and cost to fill) of helium filled balloons large enough to launch the payload weight you have in mind. A dirigible I sized several years ago to lift 1 million pounds was over 1000 feet long and I recall about 150 or 160 feet in diameter; your payload won't be that heavy, but the vehicle will still be enormous. True, but the sky is big and you could use hot air in stead of helium. I bet it would be way cheaper to lift into the stratosphere and then generate velocity with a tiny fraction of the atmospheric drag. It seems like the first stage is the biggest. Wonder how high it goes before it burns out and is jettisoned. |
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First, the difference in gravity anywhere you could fly in the atmosphere is so close to the sea level value that the difference is mostly trivial. Multi stage rockets are used in order to shed mass during the launch. Small rockets could be launched from air vehicles flying at high altitude, but most of these payloads are simply too large. Some satellites we've put up are the size of a large RV and heavy, the assembly is tightly packed in order to hold the external dimensions down. I don't have time right now, but you could compute the volume (and cost to fill) of helium filled balloons large enough to launch the payload weight you have in mind. A dirigible I sized several years ago to lift 1 million pounds was over 1000 feet long and I recall about 150 or 160 feet in diameter; your payload won't be that heavy, but the vehicle will still be enormous. True, but the sky is big and you could use hot air in stead of helium. I bet it would be way cheaper to lift into the stratosphere and then generate velocity with a tiny fraction of the atmospheric drag. It seems like the first stage is the biggest. Wonder how high it goes before it burns out and is jettisoned. It's not. NASA has considered this method, and is actually trying it out for launching very small satellites. |
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Get your calculator out then.
If you're trying to save money, a hot air balloon is probably not a great choice. Here's a summary of the standard atmosphere I put together just for GD. The first four bold entries highlight sea level pressure, then 75%, 50%, and 25% the sea level values. 
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First, the difference in gravity anywhere you could fly in the atmosphere is so close to the sea level value that the difference is mostly trivial. Multi stage rockets are used in order to shed mass during the launch. Small rockets could be launched from air vehicles flying at high altitude, but most of these payloads are simply too large. Some satellites we've put up are the size of a large RV and heavy, the assembly is tightly packed in order to hold the external dimensions down. I don't have time right now, but you could compute the volume (and cost to fill) of helium filled balloons large enough to launch the payload weight you have in mind. A dirigible I sized several years ago to lift 1 million pounds was over 1000 feet long and I recall about 150 or 160 feet in diameter; your payload won't be that heavy, but the vehicle will still be enormous. True, but the sky is big and you could use hot air in stead of helium. I bet it would be way cheaper to lift into the stratosphere and then generate velocity with a tiny fraction of the atmospheric drag. It seems like the first stage is the biggest. Wonder how high it goes before it burns out and is jettisoned. It's not. NASA has considered this method, and is actually trying it out for launching very small satellites. Somehow, I have little trust in NASA's dedication to cost control. 
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Get your calculator out then. If you're trying to save money, a hot air balloon is probably not a great choice. Here's a summary of the standard atmosphere I put together just for GD - http://www.ar15.com/media/viewFile.html?i=43559 OK, so temperature pressure and density drop as you go up higher. Got it. Should be easier to accelerate to orbital speeds from up there. How do you figure the cost would be higher? I mean, half of the equation is what it would cost to get it up there with a balloon, and the other is the cost of using the existing systems. |
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Why is it we use multistage rockets to lift spacecraft from the ground? Seems like it'd be a lot cheaper to build a flippin huge heavy lift jet to get em up and moving, and then use fewer stages of rockets. Hell, you could use a gargantuan hot air balloon for that matter. Gravity is stronger at low altitude, so the higher you get prior to lighting the fire, the less tons of rocket fuel you have to lift. Seems like that first hundred thousand feet or so is the cost driver. Any aero engineer types wanna school me on why we do it the way we do? I'm sitting in the class that just explained this, lets see if I can upload a picture.... |
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... Somehow, I have little trust in NASA's dedication to cost control. You can send your proposal to use firewood and coal to heat the air. I have no doubt that nuttier ideas have crossed the threshold at NASA, we're a country of inventors. Use labor from the welfare roles to cut the wood, that will heat them up twice. |
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Quoted: It pays to reduce vehicle and fuel weight simultaneously. Once the fuel that section contained is burned, it would be far less efficient to try and keep pushing that sections weight into orbit. ETA: velocity is the key not altitude. This is the answer. I've used programs that will help determine total weight, lift needed, etc. |
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You can send your proposal to use firewood and coal to heat the air. I have no doubt that nuttier ideas have crossed the threshold at NASA, we're a country of inventors. Use labor from the welfare roles to cut the wood, that will heat them up twice. We'd be better off just rendering them into ScreechjetBioDiesel™ |
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You can send your proposal to use firewood and coal to heat the air. I have no doubt that nuttier ideas have crossed the threshold at NASA, we're a country of inventors. Use labor from the welfare roles to cut the wood, that will heat them up twice. We'd be better off just rendering them into ScreechjetBioDiesel™ Your Newsletter, I wish to subscribe! |
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First, the difference in gravity anywhere you could fly in the atmosphere is so close to the sea level value that the difference is mostly trivial. Multi stage rockets are used in order to shed mass during the launch. Small rockets could be launched from air vehicles flying at high altitude, but most of these payloads are simply too large. Some satellites we've put up are the size of a large RV and heavy, the assembly is tightly packed in order to hold the external dimensions down. I don't have time right now, but you could compute the volume (and cost to fill) of helium filled balloons large enough to launch the payload weight you have in mind. A dirigible I sized several years ago to lift 1 million pounds was over 1000 feet long and I recall about 150 or 160 feet in diameter; your payload won't be that heavy, but the vehicle will still be enormous. True, but the sky is big and you could use hot air in stead of helium. I bet it would be way cheaper to lift into the stratosphere and then generate velocity with a tiny fraction of the atmospheric drag. It seems like the first stage is the biggest. Wonder how high it goes before it burns out and is jettisoned. It's not. NASA has considered this method, and is actually trying it out for launching very small satellites. what percent of the fuel burned by say the Saturn V was lost to atmospheric drag? compare that fuel cost to the cost of building a rocket launch pad supported by balloons in the upper atmosphere |
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what percent of the fuel burned by say the Saturn V was lost to atmospheric drag? compare that fuel cost to the cost of building a rocket launch pad supported by balloons in the upper atmosphere An incredibly small percentage of fuel was used to overcome drag, the Saturn V was very aerodynamic, steering losses were greater. The major obstacle was gravity, and a rockoon would still have to overcome gravity. Even if you did that, you still need to accelerate the rocket to 6,000 mph to equal the first stage, so you would need to lift a rocket damn near the same size as the Saturn V to be able to get the payload into orbit and reach escape velocity (if we are performing the same mission as the Saturn V.) You don't save anything by making a Rockoon/Saturn V. For small stuff, airplane launched can make sense. You have the advantage of being able to fly above the weather and launch whenever you want, something a rockoon or normal launch can't do. |
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First, the difference in gravity anywhere you could fly in the atmosphere is so close to the sea level value that the difference is mostly trivial. Multi stage rockets are used in order to shed mass during the launch. Small rockets could be launched from air vehicles flying at high altitude, but most of these payloads are simply too large. Some satellites we've put up are the size of a large RV and heavy, the assembly is tightly packed in order to hold the external dimensions down. I don't have time right now, but you could compute the volume (and cost to fill) of helium filled balloons large enough to launch the payload weight you have in mind. A dirigible I sized several years ago to lift 1 million pounds was over 1000 feet long and I recall about 150 or 160 feet in diameter; your payload won't be that heavy, but the vehicle will still be enormous. also, think of the operation size and safety issues involved in casting in the solid propellant to a single-stage tube the size of a Saturn V. |
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First, the difference in gravity anywhere you could fly in the atmosphere is so close to the sea level value that the difference is mostly trivial. Multi stage rockets are used in order to shed mass during the launch. Small rockets could be launched from air vehicles flying at high altitude, but most of these payloads are simply too large. Some satellites we've put up are the size of a large RV and heavy, the assembly is tightly packed in order to hold the external dimensions down. I don't have time right now, but you could compute the volume (and cost to fill) of helium filled balloons large enough to launch the payload weight you have in mind. A dirigible I sized several years ago to lift 1 million pounds was over 1000 feet long and I recall about 150 or 160 feet in diameter; your payload won't be that heavy, but the vehicle will still be enormous. also, think of the operation size and safety issues involved in casting in the solid propellant to a single-stage tube the size of a Saturn V. Was it solid fuel? I don't think it was because its not efficient enough |
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Lockheed tried to build a single-stage-to-orbit (SSTO) vehicle in the '90s called the X-33 VentureStar, but they couldn't get it to work. The light weight composite fuel tanks never worked properly, so NASA cancelled the program.
In 2004, Northrop said they made a successful carbon fiber fuel tank that could be used on a SSTO vehicle, so who knows what may be developed? |
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First, the difference in gravity anywhere you could fly in the atmosphere is so close to the sea level value that the difference is mostly trivial. Multi stage rockets are used in order to shed mass during the launch. Small rockets could be launched from air vehicles flying at high altitude, but most of these payloads are simply too large. Some satellites we've put up are the size of a large RV and heavy, the assembly is tightly packed in order to hold the external dimensions down. I don't have time right now, but you could compute the volume (and cost to fill) of helium filled balloons large enough to launch the payload weight you have in mind. A dirigible I sized several years ago to lift 1 million pounds was over 1000 feet long and I recall about 150 or 160 feet in diameter; your payload won't be that heavy, but the vehicle will still be enormous. also, think of the operation size and safety issues involved in casting in the solid propellant to a single-stage tube the size of a Saturn V. Was it solid fuel? I don't think it was because its not efficient enough The only solid fuel engines on the Saturn V was the escape tower on the Apollo capsul. All the other engines were liquid fueld. |
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First, the difference in gravity anywhere you could fly in the atmosphere is so close to the sea level value that the difference is mostly trivial. Multi stage rockets are used in order to shed mass during the launch. Small rockets could be launched from air vehicles flying at high altitude, but most of these payloads are simply too large. Some satellites we've put up are the size of a large RV and heavy, the assembly is tightly packed in order to hold the external dimensions down. I don't have time right now, but you could compute the volume (and cost to fill) of helium filled balloons large enough to launch the payload weight you have in mind. A dirigible I sized several years ago to lift 1 million pounds was over 1000 feet long and I recall about 150 or 160 feet in diameter; your payload won't be that heavy, but the vehicle will still be enormous. also, think of the operation size and safety issues involved in casting in the solid propellant to a single-stage tube the size of a Saturn V. Was it solid fuel? I don't think it was because its not efficient enough The only solid fuel engines on the Saturn V was the escape tower on the Apollo capsul. All the other engines were liquid fueld. I've been looking for the quote on the internet ascribed to Von Braun that said, "Humans shouldn't ride solids." Obviously, launch escape towers are an exception for the speed of ignition and separation required, but still... |