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B Would a manned flyby of Ceres be easier than a mars landing?

  1. Feb 19, 2017 #1
    I think it would be :confused:o_O
     
  2. jcsd
  3. Feb 19, 2017 #2

    mfb

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    Why do you think so, and what motivated that comparison?

    The requirements for the rocket would be lower: A Hohmann-like orbit to Ceres would need 2 km/s in addition to the Earth escape velocity (compared to 1 km/s for Mars). You can design it to go past Ceres and return to Earth without additional fuel, unlike a manned Mars landing, where you have to launch from Mars again.
    The requirements for the habitat would be higher: Total mission time would be 3 years, longer than a Mars mission. The astronauts would be in space all the time, which means they need more radiation protection, they will probably need artificial gravity, and they have to carry everything with them or produce it on board. On Mars you have free CO2 and ice close to the surface, you can use them for food and fuel production.
     
  4. Feb 19, 2017 #3

    Chronos

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    A landing is always more energy intensive than a flyby - assuming you intend to eventually depart. You are, of course, much deeper inside the gravity well than you need approach on a flyby.
     
  5. Feb 21, 2017 #4

    stefan r

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    Elon Musk was talking about making the Mars trip one way. Spacex had over 200,000 volunteers and more than 1000 are in round two of the selection.

    If you are including a return from Ceres it might cost a lot of fuel. The lack of gravity on Ceres limits orbital velocity. So a turn around means actually accelerating your spaceship in reverse.

    What would you do on a Ceres flyby? The robots take nice pictures without humans. How is flying by Ceres better than flying by Phobos?
     
  6. Feb 21, 2017 #5

    mfb

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    I guess you mean Mars One, not SpaceX.
    SpaceX wants to have return trips, it doesn't look for volunteers and does not have selection rounds. Its plan is to offer commercial trips in the same way you can buy airplane tickets today (just much more pricey).
    You don't need any fuel, Sun provides the necessary acceleration - you just go on an eccentric orbit with perihelion close to Earth orbit and aphelion close to Ceres.

    There are not many things you could do with a flyby. Control robots in real time for a while, but that would be a very odd mission.
     
  7. Feb 21, 2017 #6

    stefan r

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    http://www.newsmax.com/Newsfront/elon-musk-mars-mission-death/2016/06/11/id/733387/
    You are correct, Mars One is doing volunteers, Spacex wants to fly them. Elon Musk is just the CEO and cheerleader.
     
  8. Feb 21, 2017 #7

    mfb

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    The headline is stupid. It is as meaningful as "[random car company] wants death volunteers for buying cars."
    Yes he said that it is dangerous and that people will die, but that is true for traffic as well. People die in traffic every day.
    SpaceX doesn't want to fly Mars One volunteers (well, not more than any customer that is willing to pay). They probably don't care about Mars One because that project was never realistic.
    Musk has the majority of SpaceX. He is not just CEO, it is literally his company. And it matters: If a publicly traded company decides to send a spacecraft to Mars just for R&D that might pay off in 20+ years, shareholders will protest. If Musk decides that SpaceX will do that, it will do that.
     
  9. Feb 22, 2017 #8

    stefan r

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    http://www.huffingtonpost.ca/2013/03/11/sxsw-interactive-2013-elon-musk-mars-spacex_n_2855562.html
    More recently:
    http://www.businessinsider.com/elon-musk-mars-risks-death-spacex-2016-9
    The vast majority of commuters come home from the trip. The number that do not return may be alarming and sad but this is different.

    We are talking about one way trips with return trips sometime in the distant future when things get rolling. The fuel is also the radiation shield so passengers from Mars to Earth weigh a lot. The life support systems would be extremely valuable to people on Mars. On the outward trip the radiation shield is the gas for the return leg. Cosmic radiation shortens your life expectancy. Micro gravity does severe damage to your bones. If you do not want to retire on Mars why subject yourself to the first leg?
     
  10. Feb 22, 2017 #9

    mfb

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    I don't see the relevance of that quote. Musk wants to move to Mars and live there for the rest of his life. How is that related to the discussion here?
    No we are not. The key point of ITS is a re-use of the spacecraft. They have to fly back to Earth. Apart from a retirement of spacecrafts after many flights, they will always have the same capacity in both ways. A large fraction of the capacity towards Mars will be used by cargo. In terms of passenger capacity, the way back has actually more than the way to Mars.
    ITS in transit only has fuel for landing, the amount is very similar in both directions.
    Could you please inform yourself about the very basics of the system you want to discuss? ITS produces the fuel for the return trip on Mars. Carrying the fuel for the return trip to Mars does not work with the system, the required delta_v would be way too large.
    We don't have public numbers about the radiation shielding, but the additional lifetime cancer risk from a trip would probably be below 1%. Smoking is far more dangerous than radiation on the trip to Mars. Why do people smoke?


    And what does all that have to do with the comparison with a Ceres flyby?
     
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