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posted by martyb on Saturday September 22 2018, @01:38PM   Printer-friendly
from the powered-exoskeleton? dept.

If we wish to colonize another world, finding a planet with a gravitational field that humans can survive and thrive under will be crucial. If its gravity is too strong our blood will be pulled down into our legs, our bones might break, and we could even be pinned helplessly to the ground.

Finding the gravitational limit of the human body is something that's better done before we land on a massive new planet. Now, in a paper published on the pre-print server arXiv, three physicists, claim that the maximum gravitational field humans could survive long-term is four-and-a-half times the gravity on Earth.

Or, at least you could if you are an Icelandic strongman – and Game of Thrones monster – who can walk with more than half a metric ton on your back. For mere mortals, the researchers say, it would need to be a little weaker.

[...] For the maximum gravity at which we could take a step, the team turned to Hafþór Júlíus Björnsson, an Icelandic strongman who once walked five steps with a 1430 pound log on his back, smashing a 1,000-year-old record[*].

[*] YouTube video.

What's the Maximum Gravity We Could Survive?


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  • (Score: 2) by Immerman on Sunday September 23 2018, @04:07PM (11 children)

    by Immerman (3985) on Sunday September 23 2018, @04:07PM (#738878)

    There is a significant military application for high-G troops in space combat though. Unless your combat ships are all fully autonomous drones, the light-speed delays means you'll need at least some troops to be right in the thick of the fight. In which case they will be the limiting factor on the maneuverability of any ship they're on. A ship that can only accelerate at 0.1 g is a sitting duck in a fight against ships that can handle a sustained 4g.

    Even if it's only a single drone-oversight command ship with a crew in any given encounter, that ship is the limiting factor on how fast the entire fleet can move.

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  • (Score: 2) by Arik on Sunday September 23 2018, @05:26PM (10 children)

    by Arik (4543) on Sunday September 23 2018, @05:26PM (#738898) Journal
    Hmm let's take this bit by bit.

    "Unless your combat ships are all fully autonomous drones"

    Why wouldn't they be? Start with off-the shelf autonomous mining drones, upgrade weapons and logic, program for mission and launch.

    "the light-speed delays means you'll need at least some troops to be right in the thick of the fight."

    Ok, I'll actually give you a point here. While of course we'd do as much of any fighting that had to be done as possible with autonomous military bots, yes there still might be a need to have a human relatively near for C&C overwatch.

    "In which case they will be the limiting factor on the maneuverability of any ship they're on. A ship that can only accelerate at 0.1 g is a sitting duck in a fight against ships that can handle a sustained 4g."

    But again, I still don't see this as being so important. Acceleration? Maneuverability, essentially, in a vacuum. Why do you think that is so blamed important?

    If there's no FTL, then c is still your speed limit. Greater accel could get you there faster, get you back down faster, but interstellar distances being what they are most of the trip would be spent at c either way, and your advantage is small. And that's assuming we don't come up with some nice sleep ships that can first suspend us and then safely accelerate more rapidly than your guys can do.

    It would be handy in a tactical situation in that it might give you the ability to flee, or to preclude flight, by the enemy. Assuming you detect them from outside of either sides effective weapons range, at least.  Ok, that's actually pretty big. But still not nearly as big as you seem to think.

    And again, if we have FTL, we almost certainly have some associated tech to render this moot.

    But beyond that it's pretty nearly useless. Space combat would be taking place at astronomical distances. The likely weapons include lasers, and there's no way to dodge a laser (short of time-machine level stuff.) And another likely sort of attack would be to launch a wave of autonomous weapons - call them suicide drones, or just guided missiles, it's the same thing. They set a collision course, get as much speed as possible, and then self destruct at the last moment, turning into an expanding cloud of shrapnel. Moving at a significant fraction of light speed, anything they touch would be toast.

    Who can detect the other first, who can launch an effective strike first, would almost certainly determine who won. Little, perhaps nothing, else matters.

    So I don't think your accel is likely to come into it, even under your best scenarios.

    --
    If laughter is the best medicine, who are the best doctors?
    • (Score: 2) by Immerman on Monday September 24 2018, @12:01AM (9 children)

      by Immerman (3985) on Monday September 24 2018, @12:01AM (#739010)

      No one's getting anywhere close to c for anything other than interstellar voyages - at 1g it'd take almost a year to get to that speed, in which time you'd have long since exited the solar system. Even at 10g you'd have traveled about 50x the diameter of Neptune's orbit before you reached relativistic speeds.

      And I'm guessing most people would want to avoid releasing fully autonomous killing machines in as free-flowing a battle-ground as space, unless they're actually conscious AIs (which brings up a whole different set of problems). It's just too easy to lie to a machine. And too easy to extract its knowledge if captured (at the very least you get it's tactical/strategic decision-making algorithm, rendering it easy to exploit.) The friend-versus-foe identification system alone would be ripe for exploitation.

      Now, for the importance of acceleration, suppose we have two armies of roughly equal size, but once can handle 10x the acceleration of the other. I'll call them F(ast) and S(low)
      F decides they want to capture a location, so they launch their entire military at a juicy-enough target in the opposite direction. S launches at least most of their military to the same spot - anything less would be a pointless suicide mission. Halfway there, F changes course to attack the original location. They get there long before S can hope to do so, capture it, and then proceed to the next target - all while S is stranded in the interplanetary void unable to do anything remotely useful

      Meanwhile, S decides to attack, and F can consolidate their armies at their destination from anywhere remotely close - when your army's movements can't be hidden, the faster army wins. F's army can effectively be in multiple places at once.

      It all boils down to the equation of motion: d=1/2*a*t^2, or t = sqrt(2d/a). 10x the acceleration, means you can traverse 10x the distance in the same amount of time, or the same distance in a third the time.

      • (Score: 1) by Arik on Monday September 24 2018, @04:38AM (8 children)

        by Arik (4543) on Monday September 24 2018, @04:38AM (#739063) Journal
        "No one's getting anywhere close to c for anything other than interstellar voyages"

        Those would be the voyages that are important here though. That's the limiting factor for exploration, for colonization, and yes for invasion.

        If you're talking about tactical mobility; again, little if any advantage actually accrues there, because our robots still don't have any difficulties with accel, and they're the tactical pieces, not manned ships.

        --
        If laughter is the best medicine, who are the best doctors?
        • (Score: 2) by Immerman on Monday September 24 2018, @02:27PM (7 children)

          by Immerman (3985) on Monday September 24 2018, @02:27PM (#739173)

          Acceleration is largely irrelevant for interstellar invasion. Unless you're imagining combat between galaxy-spanning empires - but without FTL such a thing even existing seems extremely unlikely.

          Distances are so vast that the time taken to reach cruising speed is largely irrelevant, top speed is determined by propellants specific impulse and the rocket equation. And it's relatively easy to hide in interstellar space, so nobody is going to see you coming. Well, not until your braking burn announces your position I suppose - in which case the Slows give 10x as long a warning to get ready to fight them. But that's going to be months or years even for the fasts - making it strictly relevant to how many additional defenses can be built.

          It's warfare within a solar system where acceleration matters. If you really think tactical AIs will be so advanced that human insight has no value in a military engagement, then perhaps it's not important. But with several minutes to hours of communication lag, probably relatively easily jammable locally, if human insight has anything to offer then you're going to want humans nearby.

          • (Score: 2) by Arik on Monday September 24 2018, @06:22PM (6 children)

            by Arik (4543) on Monday September 24 2018, @06:22PM (#739314) Journal
            "Distances are so vast that the time taken to reach cruising speed is largely irrelevant"

            Yes.

            "And it's relatively easy to hide in interstellar space, so nobody is going to see you coming."

            Not so sure about that. New detection methods might be in play by that point, and even with 1960s tech we should be able to spot an incoming fleet just fine once they start their decel burn.

            "If you really think tactical AIs will be so advanced that human insight has no value in a military engagement, then perhaps it's not important."

            Given the distances and velocities involved I suspect ONLY a tactical AI will be able to function in traditional front line roles.

            Yes you'll want and need human oversight at the strategic level but that's a relatively small issue. Ok, our command ships are slow beasts that can't really run. Just gives our guys more incentive to make sure they win. And if you take a command ship out, sure, that's human casualties, I'm sure it will piss us off more than losing the robots, but we lose one command ship and you lose a whole manned fleet, we're still going to feel ok about the way things are going I am thinking.

            --
            If laughter is the best medicine, who are the best doctors?
            • (Score: 2) by Immerman on Monday September 24 2018, @08:47PM (5 children)

              by Immerman (3985) on Monday September 24 2018, @08:47PM (#739392)

              You want to spot a broad-spectrum vanta-black ship coasting against the blackness of interstellar space? Good luck - we can barely spot things the size of a planet when we get *extremely* lucky. But maybe eventually - which would rob high-acceleration ships of their advantage on that front. Until then though, they're likely invisible until they start their deceleration burn - at which point the Slows would give their target 10x as much warning as the Fasts. How much of an advantage that would really be though? How much additional military can you you really build in a year or three? Especially compared to the size of fleet necessary for a credible shot at an interstellar invasion?

              Yeah, but you're not going to be throwing your automated fleets against their manned ones - you're going to be throwing your automated fleets against their automated fleets, in an effort to take out each other's strategically important command ships. And ultimately, while people get upset over casualties, it appears to be cost of replacing hardware that wins modern wars. Soldiers are cheap until things have been going really badly for a while.

              • (Score: 2) by Arik on Tuesday September 25 2018, @04:21AM (4 children)

                by Arik (4543) on Tuesday September 25 2018, @04:21AM (#739542) Journal
                "You want to spot a broad-spectrum vanta-black ship coasting against the blackness of interstellar space?"

                Sure, and your stealth-paint isn't going to make it any harder. If anything, it might make it easier.

                We aren't likely to detect it directly, reflected light or radio waves or whatever, even if you mirror-polished it instead. That's just not going to be the method of detection, so the countermeasures against it won't matter either.

                How will we spot it? One of two ways. Either via occultation (we notice that this one star blinked out at this time, and then this one a little later, and then this one a little later... ohhh I see a pattern here!) or a direct detection once the decel burn starts.

                The decel burn, whatever type of engine you use, is still going to involve releasing massive amounts of energy, and that's visible, there's no way to avoid it.

                "How much of an advantage that would really be though? How much additional military can you you really build in a year or three?"

                Obviously that depends on how long ago you got the colony started and how efficiently you've worked it, what's on hand, etc. But 1-3 years might well be enough time to prepare, or to evacuate if necessary. Even with lower accel tolerance.

                Remember we don't colonize planets. We live in HOMEs and exploit the surface robotically. We'll have a relatively small human population to worry about, and none or virtually none will need to worry about packing up or reaching escape velocity - we're already packed and ready to go. HOMEs can be moved just like any other spacecraft.

                "And ultimately, while people get upset over casualties, it appears to be cost of replacing hardware that wins modern wars"

                Sure.

                And war machines made in zero-g, from materials mined in zero-g, are just going to require orders of magnitude fewer calories to produce than machines made on a planet and then boosted to space, or even those made in space using raw materials boosted from a planet.

                --
                If laughter is the best medicine, who are the best doctors?
                • (Score: 2) by Immerman on Tuesday September 25 2018, @02:18PM (3 children)

                  by Immerman (3985) on Tuesday September 25 2018, @02:18PM (#739677)

                  Yes, I've twice agreed with the decel burn - that's when you light the "here we come" beacon and give the targets not only warning of your coming, but a probably pretty good estimate of your mass. Unless you approach out-of-plane with

                  And again I say - we're barely able to detect entire planets by occultation when we get very, very lucky, we don't see any of the probably billions of Oort cloud objects that way. You really think we'll be able to detect something as tiny as space ships?

                  Also, infrared would probably be the bigger giveaway, but sufficient layers of directional reflective shields should render ships effectively invisible at the distances involved.

                  And what makes you think calories will matter? If you're talking about civilizations capable of launching credible interstellar invasion fleets fast enough that their technology won't be hopelessly obsolete by the time they arrive, then the energy required to get a ship off a planet won't even be a rounding error. The limiting factor in rapidly expanding a fleet is industrial capacity and raw materials.

                  • (Score: 2) by Arik on Tuesday September 25 2018, @02:44PM (2 children)

                    by Arik (4543) on Tuesday September 25 2018, @02:44PM (#739691) Journal
                    "And again I say - we're barely able to detect entire planets by occultation when we get very, very lucky, we don't see any of the probably billions of Oort cloud objects that way. You really think we'll be able to detect something as tiny as space ships?"

                    Planets many light years away, oort cloud objects much closer but also much smaller. Your space ships can't afford to be too tiny - smaller than a planet but probably a good bit larger than a comet. Yes, I suspect that even our current feeble astronomical capabilities are quite capable of spotting something like that. Especially if you're talking about an 'invasion fleet' of dozens, even hundreds of such ships, I suspect there would be a noticeable pattern of occultation at considerable distance.

                    Today, it's my understanding that much of that data only winds up being analyzed months after it's been gathered, but that's an issue that could be solved very quickly and not very inexpensively, were there a will to do it.

                    "Also, infrared would probably be the bigger giveaway, but sufficient layers of directional reflective shields should render ships effectively invisible at the distances involved."

                    I don't see why you think infrared would be a bigger giveaway than occultation, but that aside, it is definitely another potential detection mechanism, and you CANNOT stealth it with shielding as you're proposing. You would cook. Everything you're doing in there, from biological movement to mechanical, even just powering the computers, all generates heat, and if there is no heat escaping then the temperature will rise until everyone is dead and everything is melted.

                    "And what makes you think calories will matter?"

                    What makes me think energy matters?

                    You realize that besides matter, energy is literally the only thing that matters? :)

                    Calories = joules = energy.

                    E=mc^2

                    Literally nothing else matters.

                    "If you're talking about civilizations capable of launching credible interstellar invasion fleets fast enough that their technology won't be hopelessly obsolete by the time they arrive, then the energy required to get a ship off a planet won't even be a rounding error."

                    Ok, so how did you to that level of technology to begin with then?

                    Certainly not by thinking that calories don't matter.

                    --
                    If laughter is the best medicine, who are the best doctors?
                    • (Score: 2) by Immerman on Tuesday September 25 2018, @11:29PM (1 child)

                      by Immerman (3985) on Tuesday September 25 2018, @11:29PM (#739933)

                      Hence *directional* shields - you can radiate anything you want away from enemy observation posts.

                      And yes, counting energy matters during development. But compared to the cost of getting ships out of the Sun's gravitational well, much less up to interstellar speeds, the cost of getting them off a planet is so close to zero as to make no difference. It's not going to be a limiting factor in building out additional combat capacity in a survival situation. The limiting factor will be your industrial capacity to convert non-essential resources into defenses.

                      • (Score: 2) by Arik on Wednesday September 26 2018, @01:18AM

                        by Arik (4543) on Wednesday September 26 2018, @01:18AM (#739975) Journal
                        "Hence *directional* shields - you can radiate anything you want away from enemy observation posts."

                        Perhaps, as long as you're sure where they are.

                        "And yes, counting energy matters during development. But compared to the cost of getting ships out of the Sun's gravitational well, much less up to interstellar speeds, the cost of getting them off a planet is so close to zero as to make no difference. "

                        *Perhaps* that's true, at the end of the tech tree. Even there I'm skeptical.

                        But at the tech levels we were talking about, this is just the most important thing. Because the challenge is the transition. Going from being a planet bound species to being a species that travels space and can spread from one star to the next. And the next, and the next.

                        Bridging that gap means large and intricate construction in space. And it's going to be many orders of magnitude more difficult to do if you don't get away from the idea of boosting stuff off the planet to work.

                        So we bridge the gap much more quickly than you, we have a dozen systems or more before you manage to go anywhere... that really seems a big enough advantage to cover any potential disadvantages.
                        --
                        If laughter is the best medicine, who are the best doctors?