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The SpaceX Mars architecture: it is the answer to an unknown question, an artifact from the future time traveling back to the present. The objectives and const

by marze 10y ago

The SpaceX Mars architecture: it is the answer to an unknown question, an artifact from the future time traveling back to the present. The objectives and constraints that were used in the design process are not revealed. It is like Phouchg and Loonquawl getting the answer 42 from Deep Thought. People generally have no clue what to make of it. I'd guess that if the objectives and constraints used in the design process were revealed, it would all make complete sense. Elon has a track record of making technical and business decisions that turn out to be 100% correct in retrospect. The epic size of the vehicles are a feature, not a bug, for instance.

fizixer 10y ago
Ok I'll mention the elephant in the room. Musk has been surprisingly silent (or has seriously downplayed) on the radiation question, which is a pretty big deal for travel beyond earth's magnetosphere. But here's the thing, IMO: Musk is offering ITS as a transport facility, nothing more, nothing less. If you have payload (a living human) that is fragile (sensitive to radiation) you bring your own extra styrofoam (you include weight of shielding water or lead or what have you as part of the payload). But if he says that out loud, it'll hurt the momentum of the movement. So there you have it.
- mrfusion 10y ago
  Why would it hurt the momentum?
  - blackguardx 10y ago
    Because it wouldn't be as sensational if he said it cost $10 million to go vs $200k.
    - snrplfth 10y ago
      The idea of the $200K ticket price is only once the system is mature and well-tested. The early trips will have to cost a lot more. Probably a lot more than $10 million a seat.
      - blackguardx 10y ago
        Where is that price structure and timeline laid out?
        snrplfth 10y ago
        In the presentation: https://youtu.be/IFA6DLT1jBA?t=42m29s https://youtu.be/IFA6DLT1jBA?t=42m29s Early trips would of course not have a large crew, since they'd be mostly focused on setting up a base, and be more about cargo and equipment. Saying "several tens of millions" is because that's generally what it costs right now to get someone to low Earth orbit. If we can get early trips to Mars down to what it would cost for a current orbital mission, that would be very impressive.
        djokkataja 10y ago
        The graph he's showing at the point you linked to shows the max cost around $550k to Mars, which fits with some extremely simplified ballpark math for making the trip efficient: Start with ~$30 million (based on "several tens of millions") to get a person to orbit using current tech. Current tech doesn't use reusable rockets, and the cost of building a rocket greatly exceeds the cost of the fuel for the launch, so we'll assume fuel costs are 0. If you make a rocket that you can reuse for 10 launches, your price tag is down to $3 million to get a person to orbit. The next step is to make a bigger rocket: currently the Soyuz rocket is the only rocket taking people to the ISS (assuming this is roughly what you mean by getting someone to low Earth orbit), and it can only take 3 people at a time[0]. If you make your reusable rocket big enough to take 100 people at a time, your price tag goes down ~33x to $100k to get a person to orbit. Of course, a bigger rocket will probably cost more to make than current "small" rockets -- but a big reusable rocket would have to cost 330x more to build than a modern small rocket for future seats to cost ~$30 million per ticket. So even the first trip to Mars should be well under $1 million per person as long as they make the rockets big and reusable. [0] http://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-is-the-soyuz-spacecraft-k-4 http://www.nasa.gov/audience/forstudents/k-4/stories/nasa-kn...
        10y ago
- mden 10y ago
  If I remember correctly from the presentation, Must claimed radiation was not a significant concern with the exception of things like solar flares. Can anyone comment on the accuracy of that?
  - snrplfth 10y ago
    Well, it's not nice out there, but hardly crippling. Cosmic radiation on the ISS is about 150 milliSieverts a year. Interplanetary space could get up to about 800 mSv a year. Not good, but if you can get there in, say, three months, then you've cut your exposure down to what an ISS crewmember would get in a year. The actual danger is solar flares, and for that you'll need some kind of shielding compartment onboard. The ISS is reasonably well-protected from those, but they'll really roast you if you're caught in interplanetary space.
    - djokkataja 10y ago
      I think Musk mentioned it somewhere in the presentation, but the initial plan for shielding if you're aware that there's going to be a solar flare is to angle the spaceship so that the engines are between the Sun and the crew compartment, and then have everyone packed near the water tank... or something along those lines (it might have been in response to a question in the Q&A time afterwards; I don't remember). I don't know that they'll have this on the first trips there, but I'd guess that magnetic shields might eventually be a standard component: http://space.stackexchange.com/questions/3772/how-much-power-would-a-spacecrafts-magnetic-shield-require http://space.stackexchange.com/questions/3772/how-much-power...
      - snrplfth 10y ago
        Yes, I expect that more advanced active shielding will eventually be developed - particularly since you can detect solar flare events before the radiation arrives. The challenge with flares is that the radiation can come in from multiple directions, so a cylindrical water container that people can pack into is probably a better defense than just the bulk of the engines.
      - 10y ago
- elihu 10y ago
  Perhaps that's one of the advantages of using a really big ship; you can put more shielding / water tanks between the sun and the passengers. If it's a major problem, they might just orient the ship in a direction that gives the best radiation protection to the passengers and just leave it like that for most of the trip.

by marze 10y ago

fizixer 10y ago

Ok I'll mention the elephant in the room. Musk has been surprisingly silent (or has seriously downplayed) on the radiation question, which is a pretty big deal for travel beyond earth's magnetosphere. But here's the thing, IMO: Musk is offering ITS as a transport facility, nothing more, nothing less. If you have payload (a living human) that is fragile (sensitive to radiation) you bring your own extra styrofoam (you include weight of shielding water or lead or what have you as part of the payload). But if he says that out loud, it'll hurt the momentum of the movement. So there you have it.

mrfusion 10y ago
Why would it hurt the momentum?
- blackguardx 10y ago
  Because it wouldn't be as sensational if he said it cost $10 million to go vs $200k.
  - snrplfth 10y ago
    The idea of the $200K ticket price is only once the system is mature and well-tested. The early trips will have to cost a lot more. Probably a lot more than $10 million a seat.
    - blackguardx 10y ago
      Where is that price structure and timeline laid out?
      - snrplfth 10y ago
        In the presentation: https://youtu.be/IFA6DLT1jBA?t=42m29s https://youtu.be/IFA6DLT1jBA?t=42m29s Early trips would of course not have a large crew, since they'd be mostly focused on setting up a base, and be more about cargo and equipment. Saying "several tens of millions" is because that's generally what it costs right now to get someone to low Earth orbit. If we can get early trips to Mars down to what it would cost for a current orbital mission, that would be very impressive.
        djokkataja 10y ago
        The graph he's showing at the point you linked to shows the max cost around $550k to Mars, which fits with some extremely simplified ballpark math for making the trip efficient: Start with ~$30 million (based on "several tens of millions") to get a person to orbit using current tech. Current tech doesn't use reusable rockets, and the cost of building a rocket greatly exceeds the cost of the fuel for the launch, so we'll assume fuel costs are 0. If you make a rocket that you can reuse for 10 launches, your price tag is down to $3 million to get a person to orbit. The next step is to make a bigger rocket: currently the Soyuz rocket is the only rocket taking people to the ISS (assuming this is roughly what you mean by getting someone to low Earth orbit), and it can only take 3 people at a time[0]. If you make your reusable rocket big enough to take 100 people at a time, your price tag goes down ~33x to $100k to get a person to orbit. Of course, a bigger rocket will probably cost more to make than current "small" rockets -- but a big reusable rocket would have to cost 330x more to build than a modern small rocket for future seats to cost ~$30 million per ticket. So even the first trip to Mars should be well under $1 million per person as long as they make the rockets big and reusable. [0] http://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-is-the-soyuz-spacecraft-k-4 http://www.nasa.gov/audience/forstudents/k-4/stories/nasa-kn...
        10y ago
mden 10y ago
If I remember correctly from the presentation, Must claimed radiation was not a significant concern with the exception of things like solar flares. Can anyone comment on the accuracy of that?
- snrplfth 10y ago
  Well, it's not nice out there, but hardly crippling. Cosmic radiation on the ISS is about 150 milliSieverts a year. Interplanetary space could get up to about 800 mSv a year. Not good, but if you can get there in, say, three months, then you've cut your exposure down to what an ISS crewmember would get in a year. The actual danger is solar flares, and for that you'll need some kind of shielding compartment onboard. The ISS is reasonably well-protected from those, but they'll really roast you if you're caught in interplanetary space.
  - djokkataja 10y ago
    I think Musk mentioned it somewhere in the presentation, but the initial plan for shielding if you're aware that there's going to be a solar flare is to angle the spaceship so that the engines are between the Sun and the crew compartment, and then have everyone packed near the water tank... or something along those lines (it might have been in response to a question in the Q&A time afterwards; I don't remember). I don't know that they'll have this on the first trips there, but I'd guess that magnetic shields might eventually be a standard component: http://space.stackexchange.com/questions/3772/how-much-power-would-a-spacecrafts-magnetic-shield-require http://space.stackexchange.com/questions/3772/how-much-power...
    - snrplfth 10y ago
      Yes, I expect that more advanced active shielding will eventually be developed - particularly since you can detect solar flare events before the radiation arrives. The challenge with flares is that the radiation can come in from multiple directions, so a cylindrical water container that people can pack into is probably a better defense than just the bulk of the engines.
    - 10y ago
elihu 10y ago
Perhaps that's one of the advantages of using a really big ship; you can put more shielding / water tanks between the sun and the passengers. If it's a major problem, they might just orient the ship in a direction that gives the best radiation protection to the passengers and just leave it like that for most of the trip.