4 ms·

Travel on Airless Worlds (2014)

38 points by edward 5y ago

xwdv 5y ago
This seems more complicated than just traveling in an off-road vehicle, and for not much gain.
- nawgz 5y ago
  I will be impressed by whatever vehicle exists that can travel thru space, climb rocks of uncontrolled steepness or terrain, traverse fluids, and do it all with a human survivable cockpit with safety guarantees. Much more impressed than with a rocket like spaceX already has today, say
  - m4rtink 5y ago
    Airless off-road vehicles will have unique challenges - terrain with very sharp edges due to no wind or fluid erosion, all shadows being almost perfectly dark due to no atmospheric diffusion, only radiative cooling of all components or even long lasting plumes of dust (especially on low g airless worlds) obscuring vision.
  - bserge 5y ago
    So, the M35 Mako from Mass Effect. Elon should get on it.
- abecedarius 5y ago
  The net energy cost of ballistic travel in vacuum can be arbitrarily low. The post talks about rockets, but that's not the only way.
  - keyle 5y ago
    I don't know much about this but I'd be keen to hear what alternatives to rockets there would be on the moon to get off the rock? Are you implying one-off ballistic shots?
    - abecedarius 5y ago
      Throwing and catching are reversible operations, like a regenerative brake in an electric car. Even if your tech is too crude for a regenerative catcher, at the throwing end you could still finesse the rocket equation with a https://en.wikipedia.org/wiki/Mass_driver https://en.wikipedia.org/wiki/Mass_driver See also https://en.wikipedia.org/wiki/Skyhook_(structure) https://en.wikipedia.org/wiki/Skyhook_(structure)
erklik 5y ago
It's kind of crazy how KSP has introduced so many to such complicated topics about space travel.
- Aperocky 5y ago
  Space travel in itself is fairly straightforward. It's getting there and keeping the meat bag alive that's the hard part.
  - dragonwriter 5y ago
    “Keeping the meatbag alive” is what makes it travel. Unmanned flight isn't travel.
    - s1artibartfast 5y ago
      Anything can travel. The voyager probes have traveled to the edge of the solar system. Rovers travel a cross the Martian sand. Photons travel out from the sun through the galaxy. There is noting inherently biological about the word travel.
cletus 5y ago
This is interesting for sure but I have several issues with the premise. 1. The issue of using rockets to transport goods and people rapidly on Earth has already been discussed at length. The only real benefit is speed. The risks involved in a rocket launch are significant and will probably remain so for some time; 2. With Earth's gravity and atmosphere a chemical rocket is currently the only realistic option as nothing else has the necessary specific impulse. Railguns have been proposed but these remain impractical; 3. Certainly for traveling to other stars and even within the solar system, the energy costs and required engineering of moving sufficient people and supplies to colonize another world are so massive that the costs of building a planetary rail network on an airless network are likely to be a rounding error; 4. It's unlikely we'd want to settle more than a few places. We just don't have the same pressures that led us to colonize almost every corner of the Earth. And if we do cover such a world, it's likely that the population and industry are so large that a complex land-based transportation network will likely evolve anyway; and 5. Here's the big one: I'm increasingly convinced humanity's future won't be at the bottom of large gravity wells. It'll be in orbitals and small rocky bodies that essentially become orbitals. Entering and particularly leaving a gravity well is expensive (in energy terms). Orbitals through spin gravity can provide a much more Earthlike experience (other than, you know, the negative curvature). And most importantly: large bodies are incredibly inefficient ways to create living space in terms of area per unit volume. IIRC I saw a rough estimate that 1% of Mercury's mass could build a billion orbitals with enough living area for >10^15 people comfortably. Additionally, such orbitals would have access to virtually unlimited cheap energy through solar power. Many of us (including Elon Musk it seems) have an irrational romantic notion of living on other worlds, particularly Mars. The truth is, Mars isn't even remotely habitable. It does have an atmosphere but it's barely above a vacuum and certainly not high enough pressure to breathe even if it was the right gas mix (which, of course, it is not). In some ways, Mars' atmosphere is worse than no atmosphere because all it does is allow dust to blow around and cover everything you have on the surface. Dirt and sand on Earth have been eroded over billions of years. This isn't the case on Mars. The particle are jagged, will stick to things and likely tear things apart. Mars has no protection from radiation, is cold and has Moon-like gravity, which wouldn't be particularly comfortable.
- patrickwalton 5y ago
edward 5y ago
Part 2: https://news.ycombinator.com/item?id=28904048 https://news.ycombinator.com/item?id=28904048

38 points by edward 5y ago

xwdv 5y ago

This seems more complicated than just traveling in an off-road vehicle, and for not much gain.

nawgz 5y ago
I will be impressed by whatever vehicle exists that can travel thru space, climb rocks of uncontrolled steepness or terrain, traverse fluids, and do it all with a human survivable cockpit with safety guarantees. Much more impressed than with a rocket like spaceX already has today, say
- m4rtink 5y ago
  Airless off-road vehicles will have unique challenges - terrain with very sharp edges due to no wind or fluid erosion, all shadows being almost perfectly dark due to no atmospheric diffusion, only radiative cooling of all components or even long lasting plumes of dust (especially on low g airless worlds) obscuring vision.
- bserge 5y ago
  So, the M35 Mako from Mass Effect. Elon should get on it.
abecedarius 5y ago
The net energy cost of ballistic travel in vacuum can be arbitrarily low. The post talks about rockets, but that's not the only way.
- keyle 5y ago
  I don't know much about this but I'd be keen to hear what alternatives to rockets there would be on the moon to get off the rock? Are you implying one-off ballistic shots?
  - abecedarius 5y ago
    Throwing and catching are reversible operations, like a regenerative brake in an electric car. Even if your tech is too crude for a regenerative catcher, at the throwing end you could still finesse the rocket equation with a https://en.wikipedia.org/wiki/Mass_driver https://en.wikipedia.org/wiki/Mass_driver See also https://en.wikipedia.org/wiki/Skyhook_(structure) https://en.wikipedia.org/wiki/Skyhook_(structure)

erklik 5y ago

It's kind of crazy how KSP has introduced so many to such complicated topics about space travel.

Aperocky 5y ago
Space travel in itself is fairly straightforward. It's getting there and keeping the meat bag alive that's the hard part.
- dragonwriter 5y ago
  “Keeping the meatbag alive” is what makes it travel. Unmanned flight isn't travel.
  - s1artibartfast 5y ago
    Anything can travel. The voyager probes have traveled to the edge of the solar system. Rovers travel a cross the Martian sand. Photons travel out from the sun through the galaxy. There is noting inherently biological about the word travel.

cletus 5y ago

This is interesting for sure but I have several issues with the premise. 1. The issue of using rockets to transport goods and people rapidly on Earth has already been discussed at length. The only real benefit is speed. The risks involved in a rocket launch are significant and will probably remain so for some time; 2. With Earth's gravity and atmosphere a chemical rocket is currently the only realistic option as nothing else has the necessary specific impulse. Railguns have been proposed but these remain impractical; 3. Certainly for traveling to other stars and even within the solar system, the energy costs and required engineering of moving sufficient people and supplies to colonize another world are so massive that the costs of building a planetary rail network on an airless network are likely to be a rounding error; 4. It's unlikely we'd want to settle more than a few places. We just don't have the same pressures that led us to colonize almost every corner of the Earth. And if we do cover such a world, it's likely that the population and industry are so large that a complex land-based transportation network will likely evolve anyway; and 5. Here's the big one: I'm increasingly convinced humanity's future won't be at the bottom of large gravity wells. It'll be in orbitals and small rocky bodies that essentially become orbitals. Entering and particularly leaving a gravity well is expensive (in energy terms). Orbitals through spin gravity can provide a much more Earthlike experience (other than, you know, the negative curvature). And most importantly: large bodies are incredibly inefficient ways to create living space in terms of area per unit volume. IIRC I saw a rough estimate that 1% of Mercury's mass could build a billion orbitals with enough living area for >10^15 people comfortably. Additionally, such orbitals would have access to virtually unlimited cheap energy through solar power. Many of us (including Elon Musk it seems) have an irrational romantic notion of living on other worlds, particularly Mars. The truth is, Mars isn't even remotely habitable. It does have an atmosphere but it's barely above a vacuum and certainly not high enough pressure to breathe even if it was the right gas mix (which, of course, it is not). In some ways, Mars' atmosphere is worse than no atmosphere because all it does is allow dust to blow around and cover everything you have on the surface. Dirt and sand on Earth have been eroded over billions of years. This isn't the case on Mars. The particle are jagged, will stick to things and likely tear things apart. Mars has no protection from radiation, is cold and has Moon-like gravity, which wouldn't be particularly comfortable.

patrickwalton 5y ago

edward 5y ago

Part 2: https://news.ycombinator.com/item?id=28904048 https://news.ycombinator.com/item?id=28904048