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You need some way to make fuel and propellant, though. Phobos would be a great choice for a launchpad, but in such a scenario you would do ISRU on Mars and lift

You need some way to make fuel and propellant, though. Phobos would be a great choice for a launchpad, but in such a scenario you would do ISRU on Mars and lift fuel and propellant there - which will be much more efficient than on Earth, since there's less gravity and less atmosphere.

ncmncm 5y ago
Any fuel you could generate on Mars would be overwhelmingly easier and cheaper to ship in from Earth; and you wouldn't need to land a million tons of freight on Mars first. A million tons of fuel delivered to LEO would take you quite a long way, and you could start immediately. If you want to go somewhere beyond Mars, stopping there and then starting again just sets you back. (Same goes for the moon, or lunar orbit.) "Stepping stones" have strongly negative value in space transport.
- mannerheim 5y ago
  A million tons of fuel doesn't cut the delta v requirements down. You'd have to ship the required fuel to Mars orbit (or wherever you plan on doing refuelling) still.
  - deleted 5y ago
    [deleted]
  - ncmncm 5y ago
    If you need to refuel, send the fuel where it would be useful to get home with, i.e. where you are really going. Dumping it at Mars does no good. You would then have to stop at Mars to collect it.
    - mannerheim 5y ago
      That's assuming you have enough fuel to reach those destinations from Earth, let alone make it from Earth to there with enough payload for a return voyage.
      - ncmncm 5y ago
        I see you are finding this very hard. Try to think it through: If you can't get there without a stop at Mars, then you really, really can't get there with a stop at Mars. Stopping at Mars costs extra. If you will need extra fuel to get home with, sending it to Mars is completely useless, because where you need it to be is not at Mars, but at the place where you will be at the time when you need it. That place is not Mars. Is this really so difficult? Stop, breathe, and think.
        mannerheim 5y ago
        > If you can't get there without a stop at Mars, then you really, really can't get there with a stop at Mars. Stopping at Mars costs extra. This simply isn't true. From Mars to Jupiter is a little over 6 km/s of delta-v. From Earth to Jupiter is almost 9. The latter is just barely possible with SpaceX's Starship. The former allows for not only some breathing room, but more payload.
        ncmncm 5y ago
        If you will need more delta-V than you have on-board tankage for, sending another ship at the same time and acceleration, and refueling from it on the way, is overwhelmingly better than launching literally dozens of ships to get even more fuel parked at Mars, and then spending extra fuel stopping there to pick it up, and more again to get moving again. If your true goal is to have crap on and in orbit around Mars, do that without pretending it has any other value. You don't fool anybody, but you make people wonder about you.
        mannerheim 5y ago
        Or, hear me out, you get the available infrastructure set up on the surface of Mars to manufacture fuel and propellant, and then you can send a single ship from Mars to Jupiter. And, if you can bring payload, you can set up the infrastructure to do ISRU from one of the moons of Jupiter, and eventually bring your ships back with samples. Versus, cannibalising several extremely expensive ships in order to get one ship to a destination it's never coming back from. And this is just one example. The lower delta-v from Mars would allow extra payload to the belt, so if anyone ever intend to exploit those resources, starting from Mars will allow them to get heavy equipment there in less time and fewer trips (provided, of course, that they can manufacture that equipment on Mars).
- Tepix 5y ago
  > Any fuel you could generate on Mars would be overwhelmingly easier and cheaper to ship in from Earth Source?

ncmncm 5y ago

Any fuel you could generate on Mars would be overwhelmingly easier and cheaper to ship in from Earth; and you wouldn't need to land a million tons of freight on Mars first. A million tons of fuel delivered to LEO would take you quite a long way, and you could start immediately. If you want to go somewhere beyond Mars, stopping there and then starting again just sets you back. (Same goes for the moon, or lunar orbit.) "Stepping stones" have strongly negative value in space transport.

mannerheim 5y ago
A million tons of fuel doesn't cut the delta v requirements down. You'd have to ship the required fuel to Mars orbit (or wherever you plan on doing refuelling) still.
- deleted 5y ago
  [deleted]
- ncmncm 5y ago
  If you need to refuel, send the fuel where it would be useful to get home with, i.e. where you are really going. Dumping it at Mars does no good. You would then have to stop at Mars to collect it.
  - mannerheim 5y ago
    That's assuming you have enough fuel to reach those destinations from Earth, let alone make it from Earth to there with enough payload for a return voyage.
    - ncmncm 5y ago
      I see you are finding this very hard. Try to think it through: If you can't get there without a stop at Mars, then you really, really can't get there with a stop at Mars. Stopping at Mars costs extra. If you will need extra fuel to get home with, sending it to Mars is completely useless, because where you need it to be is not at Mars, but at the place where you will be at the time when you need it. That place is not Mars. Is this really so difficult? Stop, breathe, and think.
      - mannerheim 5y ago
        > If you can't get there without a stop at Mars, then you really, really can't get there with a stop at Mars. Stopping at Mars costs extra. This simply isn't true. From Mars to Jupiter is a little over 6 km/s of delta-v. From Earth to Jupiter is almost 9. The latter is just barely possible with SpaceX's Starship. The former allows for not only some breathing room, but more payload.
        ncmncm 5y ago
        If you will need more delta-V than you have on-board tankage for, sending another ship at the same time and acceleration, and refueling from it on the way, is overwhelmingly better than launching literally dozens of ships to get even more fuel parked at Mars, and then spending extra fuel stopping there to pick it up, and more again to get moving again. If your true goal is to have crap on and in orbit around Mars, do that without pretending it has any other value. You don't fool anybody, but you make people wonder about you.
        mannerheim 5y ago
        Or, hear me out, you get the available infrastructure set up on the surface of Mars to manufacture fuel and propellant, and then you can send a single ship from Mars to Jupiter. And, if you can bring payload, you can set up the infrastructure to do ISRU from one of the moons of Jupiter, and eventually bring your ships back with samples. Versus, cannibalising several extremely expensive ships in order to get one ship to a destination it's never coming back from. And this is just one example. The lower delta-v from Mars would allow extra payload to the belt, so if anyone ever intend to exploit those resources, starting from Mars will allow them to get heavy equipment there in less time and fewer trips (provided, of course, that they can manufacture that equipment on Mars).
Tepix 5y ago
> Any fuel you could generate on Mars would be overwhelmingly easier and cheaper to ship in from Earth Source?