5 ms·

I am way out of my comfort zone discussing this, but I really like the idea of building oribiting infrastructure. Not sure why they are not using an earth-moon

by syoc 5y ago

I am way out of my comfort zone discussing this, but I really like the idea of building oribiting infrastructure. Not sure why they are not using an earth-moon Lagrange point. I agree that it would probably be cheaper and more practical to go directly to the moon with a simpler refuling scheme. I do however also believe that some infrastructure is needed for further space travel and a larger more permanent off-earth presence. Starting new missions from outside a strong gravity field seems like such a huge advantage. I guess most people want a destination and not just a more long term established presence.

sneak 5y ago
I imagine that we'd need hundreds or thousands of people in space to make such a base/fuel depot worth it - IIRC it's less fuel to use a transfer orbit than to go to L4 or L1 and stop on the way. Such a thing might make sense once there are, say, 50 or 100 starships. For the foreseeable future, all missions will "start" in Earth's gravity well due to the fact that the o2 and ch4 are all down here. It will be some years until we have significant fuel stores in space.
Armisael16 5y ago
> Starting new missions from outside a strong gravity field seems like such a huge advantage. You don’t get to do this, period. All your crew and all your materials are ultimately coming from Earth (or, in some plans, are mined in-situ). You use considerably more resources getting to your waypoint than you save by leaving from there. Being farther out of the gravity well isn’t entirely positive either; you’re losing out on significant savings from the Oberth effect. Earth-Moon Lagrange points are well past the minimum-cost orbit.
- avmich 5y ago
  > All your crew and all your materials are ultimately coming from Earth Wait till we start making LOX (and later, I think, metals) on the Moon from regolith. The process is old and tested on Earth, the missing part is actually experimenting with this on the Moon. And as soon as we have more or less robust Earth-Moon transportation, this will become important, as it will significantly simplify near Moon operations. Do you know NASA runs, right now, competitions for e.g. lunar ice extraction and purifying?
- ethbr0 5y ago
  > All your crew and all your materials are ultimately coming from Earth This is the key state differentiator. If you bring everything from Earth, it doesn't make sense. (So why are we doing it now?) But once you start procuring resources from outside gravity well, things look different.
  - Yizahi 5y ago
    Exactly what do you plan to acquire/create outside of Earth, and from where to where do you plan to transfer it realistically? Except for fully autonomous human colonies which will mine stuff nearby and use, almost no transfer of resources in space makes sense, it is way too costly and there is no demand (even imaginary). Since there is no need for that, there is also no need for transfer stations (warehouses) anywhere, be it a planet orbit or Lagrange points.
    - m4rtink 5y ago
      Propelant depots, those make all the difference.
      - zardo 5y ago
        They make sense for an individual mission. Bring up fuel and leave it in the parking orbit. But the optimal parking orbits are going to be different for different destinations, vehicles, and times.
  - jandrese 5y ago
    It makes sense if you want to use the rockets you already have instead of building the absolutely titanic rockets you would need to carry everything in one trip. There are metallurgical limits to just how big you can make the rockets as well. But this isn't necessarily advocating for a full time in-orbit refuelling station either. The plan might be to instead launch 2 or 3 rockets, 1 with the stuff and the others with fuel. They meet up in orbit and the fuel rockets refill the stuff rocket so it can go on to Mars or wherever, then they return to Earth for the next mission.
Yizahi 5y ago
Only some orbits would intersect with L1 point, others will require immense fuel waste to get there and then change orbit to original target. Also there are no gas stations in space, for multiple reasons - there is no steady demand to fuel in space, it is at best sporadic and spiky, and in the mean time you'll need to keep up cryo fuel from boiling off; then it is hard to operate anything remotely, so Gateway gas station would be harder to operate than ISS in LEO; there is no need to place gas station farther than LEO because in space we don't need to bother with actual distances, but with gravity. Earth to Mars is 62 million kilometers, so speaking in analogies it would make sense to refuel at half of the distance, similar to the traveling by car from New York to San Francisco. But in reality it is not. Getting 300 kilometers from Earth to LEO takes 9 km/s of delta V, getting the rest 62000000 kilometers from LEO to Mars takes 5-6 km/s of delta V. LEO is much more than half way to Mars already and there is literally zero point is refuelling anywhere else (excluding fuel generation in space possibility).

by syoc 5y ago

sneak 5y ago

I imagine that we'd need hundreds or thousands of people in space to make such a base/fuel depot worth it - IIRC it's less fuel to use a transfer orbit than to go to L4 or L1 and stop on the way. Such a thing might make sense once there are, say, 50 or 100 starships. For the foreseeable future, all missions will "start" in Earth's gravity well due to the fact that the o2 and ch4 are all down here. It will be some years until we have significant fuel stores in space.

Armisael16 5y ago

> Starting new missions from outside a strong gravity field seems like such a huge advantage. You don’t get to do this, period. All your crew and all your materials are ultimately coming from Earth (or, in some plans, are mined in-situ). You use considerably more resources getting to your waypoint than you save by leaving from there. Being farther out of the gravity well isn’t entirely positive either; you’re losing out on significant savings from the Oberth effect. Earth-Moon Lagrange points are well past the minimum-cost orbit.

avmich 5y ago
> All your crew and all your materials are ultimately coming from Earth Wait till we start making LOX (and later, I think, metals) on the Moon from regolith. The process is old and tested on Earth, the missing part is actually experimenting with this on the Moon. And as soon as we have more or less robust Earth-Moon transportation, this will become important, as it will significantly simplify near Moon operations. Do you know NASA runs, right now, competitions for e.g. lunar ice extraction and purifying?
ethbr0 5y ago
> All your crew and all your materials are ultimately coming from Earth This is the key state differentiator. If you bring everything from Earth, it doesn't make sense. (So why are we doing it now?) But once you start procuring resources from outside gravity well, things look different.
- Yizahi 5y ago
  Exactly what do you plan to acquire/create outside of Earth, and from where to where do you plan to transfer it realistically? Except for fully autonomous human colonies which will mine stuff nearby and use, almost no transfer of resources in space makes sense, it is way too costly and there is no demand (even imaginary). Since there is no need for that, there is also no need for transfer stations (warehouses) anywhere, be it a planet orbit or Lagrange points.
  - m4rtink 5y ago
    Propelant depots, those make all the difference.
    - zardo 5y ago
      They make sense for an individual mission. Bring up fuel and leave it in the parking orbit. But the optimal parking orbits are going to be different for different destinations, vehicles, and times.
- jandrese 5y ago
  It makes sense if you want to use the rockets you already have instead of building the absolutely titanic rockets you would need to carry everything in one trip. There are metallurgical limits to just how big you can make the rockets as well. But this isn't necessarily advocating for a full time in-orbit refuelling station either. The plan might be to instead launch 2 or 3 rockets, 1 with the stuff and the others with fuel. They meet up in orbit and the fuel rockets refill the stuff rocket so it can go on to Mars or wherever, then they return to Earth for the next mission.

Yizahi 5y ago

Only some orbits would intersect with L1 point, others will require immense fuel waste to get there and then change orbit to original target. Also there are no gas stations in space, for multiple reasons - there is no steady demand to fuel in space, it is at best sporadic and spiky, and in the mean time you'll need to keep up cryo fuel from boiling off; then it is hard to operate anything remotely, so Gateway gas station would be harder to operate than ISS in LEO; there is no need to place gas station farther than LEO because in space we don't need to bother with actual distances, but with gravity. Earth to Mars is 62 million kilometers, so speaking in analogies it would make sense to refuel at half of the distance, similar to the traveling by car from New York to San Francisco. But in reality it is not. Getting 300 kilometers from Earth to LEO takes 9 km/s of delta V, getting the rest 62000000 kilometers from LEO to Mars takes 5-6 km/s of delta V. LEO is much more than half way to Mars already and there is literally zero point is refuelling anywhere else (excluding fuel generation in space possibility).