6 ms·

So that's purely for a chemical rocket, right? Is there any combination of tricks that can realistically push the envelope there? For example can we use a spac

So that's purely for a chemical rocket, right? Is there any combination of tricks that can realistically push the envelope there? For example can we use a space elevator to start higher/faster (or, I don't know, balloons? a catapult or railgun or something?), laser power delivery from the ground, so we don't have to carry all the fuel, and an orbiting way-station for refueling, etc.?

Miner49er 7y ago
Solar sails might be able to beat it. https://en.wikipedia.org/wiki/Solar_sail https://en.wikipedia.org/wiki/Solar_sail
- AgentME 7y ago
  Aren't solar sails just for propelling yourself once you're in space? I can't imagine how you could launch off the surface of a planet with a solar sail.
  - 0xffff2 7y ago
    Yes, and even then they're incredibly low thrust devices. A light sail (whether solar or laser powered) may well be viable for sending a tiny unmanned probe to another star system (see [0]). It's really unlikely that it will ever scale up enough to take an average communication satellite the same distance, much less a manned craft. [0] https://en.wikipedia.org/wiki/Breakthrough_Starshot https://en.wikipedia.org/wiki/Breakthrough_Starshot
- hinkley 7y ago
  M2P2 was going to test out magnetic sails, but Wikipedia is telling me they generate less thrust per kilowatt hour than ion thrusters. Explains why I haven't heard anything further about it. https://en.wikipedia.org/wiki/Magnetic_sail https://en.wikipedia.org/wiki/Magnetic_sail
- civilian 7y ago
  Solar sails are good for inter-planetary travel, but they aren't going to move the needle for launching off of a planet with 2g gravity! You need something that is compact and would give you a big impulse. As a KSP engineer would say, it "needs more boosters" https://i.redd.it/zuymxc5bb7s21.jpg https://i.redd.it/zuymxc5bb7s21.jpg
ta1234567890 7y ago
Exactly From the reference article: > Travelling from the surface of Earth to Earth orbit is one of the most energy intensive steps of going anywhere else. This first step, about 400 kilometers away from Earth, requires half of the total energy needed to go to the surface of Mars. Which means that if we use something like a balloon/blimp in the first stage, it would be a lot more energy efficient. Anyone knows why it's not done that way already? Also, whatever happened with the plane+rocket Virgin Galactic project?
- yourbandsucks 7y ago
  Orbit isn't a height, it's a speed. 7 km/sec for low earth orbit. A balloon floating you higher while not making mach 20 isn't much of a shortcut.
  - kadoban 7y ago
    How poor of a shortcut is it? I'm not really clear on what the math would look like. Would it just be better by approximately the ratio of gravity's strength at the surface vs the height of the balloon?
    - yourbandsucks 7y ago
      Basically just saves what you would've lost to wind resistance and gravity while getting to that height, while adding the complication of accelerating from 0 to orbital before falling back into the atmo. Space elevator ideas usually have the hop-off point all the way out at geosynchronous orbit to solve the velocity problem. Which is.. a really tall elevator.
    - usrusr 7y ago
      Better than the miniscule gain in potential energy (height x mass x gravity) because you also save a lot of aerodynamic drag not punching through the lower atmosphere at high speed and some "hovering losses" (rise time x mass x gravity, I'm sure there is a better term for that). But still not worthwhile due to the difficulty of floating a full size rocket. If you had a very very high mountain or tower, moving that full size rocket to the peak could be worthwhile. Theoretically, a civilisation trapped in a gravity well too deep for a solution to the rocket equation could dig themselves out by reshaping their planet from a roughly spherical geoid into a disc or rod (or into a torus for the really adventurous)
buboard 7y ago
Launching from a mountain is a possibility ( I think China does it) Realistically, but not plausibly unless its an emergency, Thermonuclear bombs: https://www.youtube.com/watch?v=EzZGPCyrpSU https://www.youtube.com/watch?v=EzZGPCyrpSU
lopmotr 7y ago
Nuclear bomb rockets would probably do https://en.wikipedia.org/wiki/Nuclear_pulse_propulsion https://en.wikipedia.org/wiki/Nuclear_pulse_propulsion
deleted 7y ago
[deleted]
mabbo 7y ago
> For example can we use a space elevator to start higher/faster (or, I don't know, balloons? a catapult or railgun or something?), laser power delivery from the ground, so we don't have to carry all the fuel, and an orbiting way-station for refueling, etc.? These methods will all help with the first 1% of your problem, getting off of the earth. But you need so many orders of magnitude more energy to reach the kinds of velocity needed to get to another star in less than a million years. It's just an unfathomable amount of energy per kg. Put simply: if you can get to another star, getting off the planet is nothing.

Miner49er 7y ago

Solar sails might be able to beat it. https://en.wikipedia.org/wiki/Solar_sail https://en.wikipedia.org/wiki/Solar_sail

AgentME 7y ago
Aren't solar sails just for propelling yourself once you're in space? I can't imagine how you could launch off the surface of a planet with a solar sail.
- 0xffff2 7y ago
  Yes, and even then they're incredibly low thrust devices. A light sail (whether solar or laser powered) may well be viable for sending a tiny unmanned probe to another star system (see [0]). It's really unlikely that it will ever scale up enough to take an average communication satellite the same distance, much less a manned craft. [0] https://en.wikipedia.org/wiki/Breakthrough_Starshot https://en.wikipedia.org/wiki/Breakthrough_Starshot
hinkley 7y ago
M2P2 was going to test out magnetic sails, but Wikipedia is telling me they generate less thrust per kilowatt hour than ion thrusters. Explains why I haven't heard anything further about it. https://en.wikipedia.org/wiki/Magnetic_sail https://en.wikipedia.org/wiki/Magnetic_sail
civilian 7y ago
Solar sails are good for inter-planetary travel, but they aren't going to move the needle for launching off of a planet with 2g gravity! You need something that is compact and would give you a big impulse. As a KSP engineer would say, it "needs more boosters" https://i.redd.it/zuymxc5bb7s21.jpg https://i.redd.it/zuymxc5bb7s21.jpg

ta1234567890 7y ago

Exactly From the reference article: > Travelling from the surface of Earth to Earth orbit is one of the most energy intensive steps of going anywhere else. This first step, about 400 kilometers away from Earth, requires half of the total energy needed to go to the surface of Mars. Which means that if we use something like a balloon/blimp in the first stage, it would be a lot more energy efficient. Anyone knows why it's not done that way already? Also, whatever happened with the plane+rocket Virgin Galactic project?

yourbandsucks 7y ago
Orbit isn't a height, it's a speed. 7 km/sec for low earth orbit. A balloon floating you higher while not making mach 20 isn't much of a shortcut.
- kadoban 7y ago
  How poor of a shortcut is it? I'm not really clear on what the math would look like. Would it just be better by approximately the ratio of gravity's strength at the surface vs the height of the balloon?
  - yourbandsucks 7y ago
    Basically just saves what you would've lost to wind resistance and gravity while getting to that height, while adding the complication of accelerating from 0 to orbital before falling back into the atmo. Space elevator ideas usually have the hop-off point all the way out at geosynchronous orbit to solve the velocity problem. Which is.. a really tall elevator.
  - usrusr 7y ago
    Better than the miniscule gain in potential energy (height x mass x gravity) because you also save a lot of aerodynamic drag not punching through the lower atmosphere at high speed and some "hovering losses" (rise time x mass x gravity, I'm sure there is a better term for that). But still not worthwhile due to the difficulty of floating a full size rocket. If you had a very very high mountain or tower, moving that full size rocket to the peak could be worthwhile. Theoretically, a civilisation trapped in a gravity well too deep for a solution to the rocket equation could dig themselves out by reshaping their planet from a roughly spherical geoid into a disc or rod (or into a torus for the really adventurous)

buboard 7y ago

Launching from a mountain is a possibility ( I think China does it) Realistically, but not plausibly unless its an emergency, Thermonuclear bombs: https://www.youtube.com/watch?v=EzZGPCyrpSU https://www.youtube.com/watch?v=EzZGPCyrpSU

lopmotr 7y ago

Nuclear bomb rockets would probably do https://en.wikipedia.org/wiki/Nuclear_pulse_propulsion https://en.wikipedia.org/wiki/Nuclear_pulse_propulsion

deleted 7y ago

[deleted]

mabbo 7y ago

> For example can we use a space elevator to start higher/faster (or, I don't know, balloons? a catapult or railgun or something?), laser power delivery from the ground, so we don't have to carry all the fuel, and an orbiting way-station for refueling, etc.? These methods will all help with the first 1% of your problem, getting off of the earth. But you need so many orders of magnitude more energy to reach the kinds of velocity needed to get to another star in less than a million years. It's just an unfathomable amount of energy per kg. Put simply: if you can get to another star, getting off the planet is nothing.