3 ms·

It is not wrong, you can reduce the cost but it will never be economical simply due to the gravity well. > the minimum cost imposed by gravity (the energy need

It is not wrong, you can reduce the cost but it will never be economical simply due to the gravity well. > the minimum cost imposed by gravity (the energy needed to get into space) is incredibly low. This is straight up false.

pfdietz 4y ago
Nope, you're completely wrong. Do the math. Propellant cost is a tiny fraction of the cost of a launch, even on the partially reusable Falcons.
- Aperocky 4y ago
  That fraction is still larger than the economical utilization of space. Think about how little propellant it takes to move products on Earth. And that's not even counting for the fact that transport vehicles on Earth runs a heavy percentage of its life time while a rocket does not do that. Even Falcons spend most of their time getting ready or recycled and not on an ascend or descend trajectory. Any real trade will not happen at these gravity tax rates.
  - epicureanideal 4y ago
    But a 747 needs continued fuel to keep going whereas once on target a spacecraft can use its initial velocity to travel much much further.
  - pfdietz 4y ago
    > That fraction is still larger than the economical utilization of space. What does this sentence even MEAN? There are economical uses of space at today's launch costs. There would be even more such uses if launch costs were a few times the cost of propellant, as the cost of air travel is. I get the feeling you are not thinking clearly on this subject.
    - Aperocky 4y ago
      If launch cost were few times the cost of propellant, what economic activities become feasible in space? Sending tourists? Sure, tourists are already up there and it costs even less propellant to drop to the ocean floor but not many people/business seemed to be doing that. Maybe with the exception of oil platforms. Speaking of which, what oil platform will be of space? Even a floating city in space that is purely afforded by the tourist spending generates no true economic value up there - all of it is being essentially propped up by the ground. What economic incentive are there? The only way out is to manufacture IN SITU, sourcing from locally or gravitationally less burdensome locations, like the asteroid belt. It takes less deltaV to go to the asteroid belt from LEO than it takes to get to LEO from the ground. Trust me I've been thinking about this plenty - though probably not to any use.
      - pfdietz 4y ago
        A tourism analogue could be Antarctica rather than the sea floor. Antarctica is also an analogue for manned science. Reduce costs enough and it makes sense to put people in space rather than do things remotely. There's a base at the South Pole. The cost to get there would be similar to the cost of getting to LEO, in this few-times-propellant cost scenario. Yet no one talks about automating that base, it just doesn't pencil out. Lower launch costs will enable much larger satellites to be built, with much larger apertures of antennas and optics, and with higher bandwidth, or with much less focus on expensive mass optimization. We could see satellites in high earth orbit being maintained manually. At a few tens of dollars per kilogram, space disposal of nuclear waste starts to make sense.
      - m4rtink 4y ago
        I can recommend Terra Invicta as a very realistic grand strategy game demonstrating it nicely - you will never lift the thousands of tons needed for just a single ship in your fleet to protect the Mother Earth from aggressive extraterrestrial invasion. But plop a few mining complexes (each couple dozen tons IIRC) on the Moon or near Earth asteroid and the tables turn quite quickly. As now you can build more station from extraterrestrial resources, which mine said resources and it goes from there. :-)
iso1631 4y ago
Well it's technically correct. To get a 100kg object from the surface to a 100km Karman line needs about 30kWh of power. That's the same order of magnitude as travelling 100km sideways in an electric vehicle. At 20c/kWh it would cost $100 to lift a 2 ton car and 4 occupants into space, or $100 each to get to the c. 400km altitude of the ISS. Of course to stay in space requires far more energy as you also have to go sideways, fast. Very Fast. But it's still pretty low. Sticking 1kg into Geostationary Orbit and keeping it there would take about 15kWh. A 2 ton vehicle with 4 passengers at 20c/kWh would be $1500 each. Of course we lack a practical way of doing this other than with rockets, and thus enter the tyranny of the rocket equation. But the fuel cost is still far lower than the cost of the entire shuttle or apollo system, as shown by the efficiency of SpaceX -- fuel costs of $20/kg to LEO, or $1500 for a typical adult.
- Aperocky 4y ago
  kWH of power and its cost does not translate here, your kWh of power does not have any specific impulse.
  - randallsquared 4y ago
    Space elevators and Lofstrom loops also do not have Isp (or have very, very poor Isp, if you're treating the Earth as reaction mass...).
  - iso1631 4y ago
    kWh is a measure of energy, not power. And specific impulse is only of relevance to rockets, not to the amount of energy required to lift. The problem in space access isn't an energy problem, it's a method problem.
- matheusmoreira 4y ago
  You're comparing rocket engines designed to operate in a vacuum to electric vehicles designed to operate on the ground. Rocket engines need a lot more fuel to generate that amount of power.
  - 4y ago

pfdietz 4y ago

Nope, you're completely wrong. Do the math. Propellant cost is a tiny fraction of the cost of a launch, even on the partially reusable Falcons.

Aperocky 4y ago
That fraction is still larger than the economical utilization of space. Think about how little propellant it takes to move products on Earth. And that's not even counting for the fact that transport vehicles on Earth runs a heavy percentage of its life time while a rocket does not do that. Even Falcons spend most of their time getting ready or recycled and not on an ascend or descend trajectory. Any real trade will not happen at these gravity tax rates.
- epicureanideal 4y ago
  But a 747 needs continued fuel to keep going whereas once on target a spacecraft can use its initial velocity to travel much much further.
- pfdietz 4y ago
  > That fraction is still larger than the economical utilization of space. What does this sentence even MEAN? There are economical uses of space at today's launch costs. There would be even more such uses if launch costs were a few times the cost of propellant, as the cost of air travel is. I get the feeling you are not thinking clearly on this subject.
  - Aperocky 4y ago
    If launch cost were few times the cost of propellant, what economic activities become feasible in space? Sending tourists? Sure, tourists are already up there and it costs even less propellant to drop to the ocean floor but not many people/business seemed to be doing that. Maybe with the exception of oil platforms. Speaking of which, what oil platform will be of space? Even a floating city in space that is purely afforded by the tourist spending generates no true economic value up there - all of it is being essentially propped up by the ground. What economic incentive are there? The only way out is to manufacture IN SITU, sourcing from locally or gravitationally less burdensome locations, like the asteroid belt. It takes less deltaV to go to the asteroid belt from LEO than it takes to get to LEO from the ground. Trust me I've been thinking about this plenty - though probably not to any use.
    - pfdietz 4y ago
      A tourism analogue could be Antarctica rather than the sea floor. Antarctica is also an analogue for manned science. Reduce costs enough and it makes sense to put people in space rather than do things remotely. There's a base at the South Pole. The cost to get there would be similar to the cost of getting to LEO, in this few-times-propellant cost scenario. Yet no one talks about automating that base, it just doesn't pencil out. Lower launch costs will enable much larger satellites to be built, with much larger apertures of antennas and optics, and with higher bandwidth, or with much less focus on expensive mass optimization. We could see satellites in high earth orbit being maintained manually. At a few tens of dollars per kilogram, space disposal of nuclear waste starts to make sense.
    - m4rtink 4y ago
      I can recommend Terra Invicta as a very realistic grand strategy game demonstrating it nicely - you will never lift the thousands of tons needed for just a single ship in your fleet to protect the Mother Earth from aggressive extraterrestrial invasion. But plop a few mining complexes (each couple dozen tons IIRC) on the Moon or near Earth asteroid and the tables turn quite quickly. As now you can build more station from extraterrestrial resources, which mine said resources and it goes from there. :-)

iso1631 4y ago

Well it's technically correct. To get a 100kg object from the surface to a 100km Karman line needs about 30kWh of power. That's the same order of magnitude as travelling 100km sideways in an electric vehicle. At 20c/kWh it would cost $100 to lift a 2 ton car and 4 occupants into space, or $100 each to get to the c. 400km altitude of the ISS. Of course to stay in space requires far more energy as you also have to go sideways, fast. Very Fast. But it's still pretty low. Sticking 1kg into Geostationary Orbit and keeping it there would take about 15kWh. A 2 ton vehicle with 4 passengers at 20c/kWh would be $1500 each. Of course we lack a practical way of doing this other than with rockets, and thus enter the tyranny of the rocket equation. But the fuel cost is still far lower than the cost of the entire shuttle or apollo system, as shown by the efficiency of SpaceX -- fuel costs of $20/kg to LEO, or $1500 for a typical adult.

Aperocky 4y ago
kWH of power and its cost does not translate here, your kWh of power does not have any specific impulse.
- randallsquared 4y ago
  Space elevators and Lofstrom loops also do not have Isp (or have very, very poor Isp, if you're treating the Earth as reaction mass...).
- iso1631 4y ago
  kWh is a measure of energy, not power. And specific impulse is only of relevance to rockets, not to the amount of energy required to lift. The problem in space access isn't an energy problem, it's a method problem.
matheusmoreira 4y ago
You're comparing rocket engines designed to operate in a vacuum to electric vehicles designed to operate on the ground. Rocket engines need a lot more fuel to generate that amount of power.
- 4y ago