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I think the counter argument to the space elevator magic material was always that if you could make something that light and that strong... use it to make chea

by virtue3 12y ago

I think the counter argument to the space elevator magic material was always that if you could make something that light and that strong... use it to make cheaper/lighter rockets.

Florin_Andrei 12y ago
The energy per kilogram lifted to orbit is vastly different. It's order(s) of magnitude cheaper (in terms of energy) to lift stuff into orbit. Making the rocket from lighter materials won't matter, since the rocket is almost entirely fuel anyway.
- virtue3 12y ago
  The issue with rockets is that it takes x amount of fuel to get to your destination once in orbit and x amount of fuel to get the craft and the destination fuel to orbit. It's why rockets generally work best in stages (you just drop the extra support structure needed for the fuel). It's really an exponential problem. Every lb of infrastructure you remove from the rocket makes it _much_ more practical. See my comment above about having magic space elevator materials available anyway. Steam rockets and the like start to seem very practical at that point. And probably less insane than a cable all the way to space.
shalmanese 12y ago
The Space Shuttle is already 96% propellant to 4% structure (http://www.nasa.gov/mission_pages/station/expeditions/expedition30/tryanny.html http://www.nasa.gov/mission_pages/station/expeditions/expedi...). You're going to get much appreciable gains from lighter rockets.
- virtue3 12y ago
  I was being kind of sparse in details, sorry. Having a material that can self support itself into orbit can potentially unlock practical variations of: http://en.wikipedia.org/wiki/Steam_rocket http://en.wikipedia.org/wiki/Steam_rocket whose main problem is: The simplest design has a pressurised water tank where the water is heated before launch, however, this gives a very low exhaust velocity since the high latent heat of vapourisation means that very little actual steam is produced and the exhaust consists mostly of water, or if high temperatures and pressures are used, then the tank is very heavy. Although, that would also require the material to be very heat resistant as well. Which might be problematic. Compressed air might also work at that sort of level of material as well. At least for initial launch stages until you need to switch over to another type of propellant (or a more controllable engine).
  - derekp7 12y ago
    I thought the Space Shuttle was already primarily a steam rocket. It held liquid oxygen and hydrogen, which was combined, ignited, and the result is high temperature water (steam). Another way I wondered about, is to have a cold water tank with a nuclear reactor in it. As long as you ignore the safety part of the equation, do the physics work out? That is, would you get more thrust than from recombining hydrogen/oxygen?
- omikun 12y ago
  The 96% number refers to the orange fuel tank. Once you factor in the shuttle, the payload, and rocket engines, it's more like... 94% fuel. Some rockets are 88% fuel, but still only ~2-3% payload. A lighter rocket could mean 10% payload.

by virtue3 12y ago

I think the counter argument to the space elevator magic material was always that if you could make something that light and that strong... use it to make cheaper/lighter rockets.

Florin_Andrei 12y ago

The energy per kilogram lifted to orbit is vastly different. It's order(s) of magnitude cheaper (in terms of energy) to lift stuff into orbit. Making the rocket from lighter materials won't matter, since the rocket is almost entirely fuel anyway.

virtue3 12y ago
The issue with rockets is that it takes x amount of fuel to get to your destination once in orbit and x amount of fuel to get the craft and the destination fuel to orbit. It's why rockets generally work best in stages (you just drop the extra support structure needed for the fuel). It's really an exponential problem. Every lb of infrastructure you remove from the rocket makes it _much_ more practical. See my comment above about having magic space elevator materials available anyway. Steam rockets and the like start to seem very practical at that point. And probably less insane than a cable all the way to space.

shalmanese 12y ago

The Space Shuttle is already 96% propellant to 4% structure (http://www.nasa.gov/mission_pages/station/expeditions/expedition30/tryanny.html http://www.nasa.gov/mission_pages/station/expeditions/expedi...). You're going to get much appreciable gains from lighter rockets.

virtue3 12y ago
I was being kind of sparse in details, sorry. Having a material that can self support itself into orbit can potentially unlock practical variations of: http://en.wikipedia.org/wiki/Steam_rocket http://en.wikipedia.org/wiki/Steam_rocket whose main problem is: The simplest design has a pressurised water tank where the water is heated before launch, however, this gives a very low exhaust velocity since the high latent heat of vapourisation means that very little actual steam is produced and the exhaust consists mostly of water, or if high temperatures and pressures are used, then the tank is very heavy. Although, that would also require the material to be very heat resistant as well. Which might be problematic. Compressed air might also work at that sort of level of material as well. At least for initial launch stages until you need to switch over to another type of propellant (or a more controllable engine).
- derekp7 12y ago
  I thought the Space Shuttle was already primarily a steam rocket. It held liquid oxygen and hydrogen, which was combined, ignited, and the result is high temperature water (steam). Another way I wondered about, is to have a cold water tank with a nuclear reactor in it. As long as you ignore the safety part of the equation, do the physics work out? That is, would you get more thrust than from recombining hydrogen/oxygen?
omikun 12y ago
The 96% number refers to the orange fuel tank. Once you factor in the shuttle, the payload, and rocket engines, it's more like... 94% fuel. Some rockets are 88% fuel, but still only ~2-3% payload. A lighter rocket could mean 10% payload.