Going to Mars: Yea or Nay

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Kylo Renskins, Nov 19, 2017.


should earthlings try to go to Mars?

  1. Yes

    7 vote(s)
  2. No

    0 vote(s)
  1. orcot Valued Senior Member

    What ever the reason we should wory a little bid abouth GW in general tough
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  3. Gawdzilla Sama Valued Senior Member

    We start small by enclosing side canyons of Valles Marineris. Do enough of those, perhaps deliberately isolated from each other, and we'd have some cache against Terra Fatalis.
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  5. iceaura Valued Senior Member

    There is no safe place on the moon - from anywhere on the moon, any city on earth can be destroyed simply by launching a couple of large rocks with a catapult.

    For that matter, something similar is possible from Mars or (even easier) one of its moons - not even counting the access to asteroids. Earth is "downhill" from Mars.

    I look forward far more to colonizing the ocean, and possibly Antarctica. We need space colonies only for immortality - and that's famous for being a bad motive.
    Last edited: Nov 20, 2017
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  7. orcot Valued Senior Member

    ah false let me explain. From any point other from earth itself and the back of the moon you are limited by your source of energy. In theory you could launch ?mass? at 99,99% speed of light to impact earth there is no defense possible against something like this. If you tried this from the back of the moon the mass would simply escape the solar system. So their is clearly a upper limit with means reaction time for earth to intercept the object. So what would be this max speed this rail gun could hit earth assuming the launched mass doesn't have a propulion system of it's owm the speed could not exceed that of a trans earth injection from the moon) this means a max speed of 3,25 km/s (for comparison: the meteorite that caused meteor crater had a minimum impact speed of 12,8 km/s.). this also means it would take several days meaning valuable reaction. I'm also guessing you could actually build hardware set's your rail gun in a fixed position where it is simply not possible to aim at earth and anything that get's launched in orbit for earth needs to be tugged there.
  8. billvon Valued Senior Member

    Not really. Targeting is difficult, and firing rocks large enough to survive re-entry is REALLY difficult. Keep in mind that the Chelabynsk meteor (one that didn't even reach the ground, and caused only minor damage to windows) weighed in at about 10,000 tons. For comparison, a Saturn 5 weighed only 3000 tons fully fueled.
  9. iceaura Valued Senior Member

    Targeting precisely would be difficult. But much smaller rocks than that one survive entry.
    Lifting the weight to Earth-capture is not nearly as difficult as that comparison implies - and the only reason the Chelabynsk meteor did as little damage as it did (far more than "rattling a few windows") was that by simple luck it exploded high in the air and far from big cities: https://en.wikipedia.org/wiki/Chelyabinsk_meteor.
    One hardly needs the 500 kiloton blast of that tonnage at that speed, to wreck a city. A few rocks much smaller and considerably slower would do just fine.
  10. Write4U Valued Senior Member

    There is a fifth future.

    A large industrial complex for building a aingle selfsustaining habitat for spacetravel. A city in the sky which could explore he rest of the milky way, until a suitable planet is discovered. IOW, using Mars not as a permanent habitat for a general population but as a giant factory designed only for building spacecrafts.

    Mars would make a good jump-off point because of it's low gravity. We would not have to build giant rockets to lift small payloads.

    We always speak of visiting aliens. How did they get here? Space travel by means of self sustaining space-cities, no?

    Time travel and Warp space seem very unlikely. If we are ever going to leave this planet, we'll have to do it the old fashioned way.

    Cryogenics is a possibility because it would take very little energy. Space itself is very cold, so no artificial refrigeration would be necessary . It's heating the environment that would take energy, but we already have nuclear submarines which can stay submerged for months and are basically self sustaining for long durations. So we do have the rudimentary knowledge of creating self-sustaning artificial environments designed for travel.

    It could be done, but who would fund such an effort without a guaranteed return on the investment?
    Last edited: Nov 20, 2017
  11. paddoboy Valued Senior Member

    Certainly for the time being and most probably within the next few hundred years or so. If we are still around in say another millenium, who knows?
  12. billvon Valued Senior Member

    And do almost no damage. A US woman, for example, was actually hit by a small meteor in 1954 - and was not killed, or even seriously injured. She recovered after some bruising.
    Take a look at the map there. It passed quite close to several towns, and during maximum luminosity passed almost directly over Pervomaiski, Korkino and Emanzhelinka.

    Now, fire these off regularly and you might well do some damage - broken windows, many injuries, the occasional death from flying glass or collapsing sheds. You might even crush a bus or something with the remnant of the meteor if you were very, very lucky. But it's going to be VERY hard to do. That meteor hit the atmosphere at about 42,000 mph. A typical minimum-energy orbit from the Moon hits the atmosphere at about 25,000 mph, which is only a third of the energy you saw from Chelabynsk.

    So to even equal that event you are going to have to accelerate something that's three times the weight of a Saturn 5 to something like 17,000 mph. There's no reason to design a lunar launcher to produce this amount of energy - lunar escape velocity is only about 5000 mph. Further, when launching material from the Moon, low energy orbits give you the freedom to do a lot of steering of the mass. At higher speeds you don't have much freedom to deflect the mass. And since the Earth doesn't move relative to the Moon's surface, that means that you have to build one linear accelerator with a fixed aim point for each latitude worth of targets - and it would be fairly useless for anything else. That's a lot of money to spend on a single use weapon.

    Note that you can do much more damage with hijacked airliners, as (sadly) we have seen - at about 1/100,000,000th the cost.
    Nope. See above.
  13. Write4U Valued Senior Member

    But all these problems would be solved by going underground on Mars.
  14. Write4U Valued Senior Member

    Of course. If we ever want to go out in space and settle another planet, we need time, lots of time. Thus minimizing our impact on the earth's ecosphere, we will be buying time to develop the technology to go into space en masse.

    Of course we can also make a decision to limit the human population on earth itself, in addition to start practicing clean energy. But we need to do this immediately.

    By the exponential function, if the the earth's population grows by just 1 %, it will take just 70 years for the earth's population to double in size and another 70 years to double in size again.

    It is clearly impossible for the earth to provide sufficient resources to sustain the presence of some 30 billion people in the span of just two lifetimes.
    Last edited: Nov 21, 2017
  15. iceaura Valued Senior Member

    The fact that meteors can also be tiny has nothing to do with it.

    Meteorites large enough to take out Manhattan Island's population can be launched from anywhere on the Moon by catapult, fairly easily - more easily than the 15 ton lunar landing vehicles were launched into lunar orbit, say, which required nothing like a Saturn.

    It's an interesting problem, come to think of it - there's an ideal size (and shape?): too small then too little mass survives entry at speed, too large and you have to target precisely because you have fewer shots. My guess is about a 3 meter launch diameter for spherical basalt or granite (ductile iron would be ideal, and there should be ore deposits on the moon) about twice the mass of the Apollo landers. Engineers?
    It didn't hit the ground. Lucky.
    Which was fortunate, in its way, because that speed at that shallow angle (and its looser constitution) shock/heated it enough internally to blow it up high in the air after distributing much of its kinetic energy over a long reentry path high above shock absorbing air.

    One third the energy of the Chelabynsk meteor would be about 150 kilotons, btw - just for intuition.
    To do thousands of times the damage per unit mass all you would need to do is come in more vertically and hit the ground.
    Even supposing one were shortsighted enough to not angle the launch track so that it covered a wide latitude range over time (the Earth's rotation axis is tilted relative to the moons orbit, https://eclipse.gsfc.nasa.gov/SEatlas/SEatlas-2/SEatlas-1999.GIF), and constrained enough in resources to neither build multiple tracks or shift one for aim, a quite narrow range of latitude properly chosen would do for most of the civilization of most countries, or even continents - a matter of timing (check a map).

    And an actual colony on Mars would offer phenomenal military opportunities - including major extortion demands, as the travel time of the big rocks would allow for extended negotiations. So there's that.
    Last edited: Nov 26, 2017
  16. orcot Valued Senior Member

    okay the moon Always shows the same side to the earth so from the back of the moon you can not see the earth.
    rocks from a catapult are on a fixed trajectory can't do any controlled speed up can't brake and can't change course in any way
    The moons escape velocity is 2,38km/s anything slower is going to crash somwhere on the lunar surface
    The orbital speed is 1,022km/s any fasther and it will simple leave the earth moon system yes?
    This gives you a speed of 2,39km/s and 3,4km/s to play with (2,38+1,022) lower then this crash into the moon fasther then this leave the earth moon system
    A railgun in basicly a train track with a inclined plane facing one direction, it's very expensive and for the near future can only be build by a "existing" country (or countries) all countries exist on earth all would be impacted by a meteor strike.
    No terorist can hold this place for long therfore they can't change the ramp, they can not change the power output by building additional power sources if they can other industries are there and a whole lot more people that can stop them.
    basicly they can not change the inclination they can not change the power output and there are going to be basic safty issues with measuring the weight so you can not launch a smaller cargo fasther. Also all this cargo will probably be stored in some sort of bullet sabot with a gps tracer on these people will need to build their own from scratch or use existing ones with GPS trackers on them.

    The backside of the moon is really the berst place for this.

    I'm curious abouth your timeframe? How far in the future are you thinking?

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