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Space Marines

  1. Jul 3, 2015 #1
    I wonder, could they be employed in hard SF, if yes, how?
    If one intends to capture a planet (example: Mars with a few cities, capital on south pole) the defenders only doomed if big ships can reach low orbit and burn them with lasers.
    Big surface lasers can easily outpower even the biggest ships, but can there be any reason why were they ineffective against surface units?
    Anti-satellite missiles can be a serious threat to any big ship coming close, while fast agile shuttle craft can be hard to hit, especially if the attackers can kill orbital recon, and cleanse a landing belt from radars. (The defenders could put those missiles to satellites also, but then they would be very vulnerable to small delta-V missiles and orbital fighters launched from high orbit)
    Extrapolating present day results, how big mass driver would be needed to throw serious amount of projectiles (with a minimal delta-V to track ships) to low orbit from martian surface?
  2. jcsd
  3. Jul 3, 2015 #2
    I understand you want a better explanation than a planet is round, while the laser light goes in straight line? :D

    Maybe because land units can also load some amount of ice as a coolant?

    Americans tested a railgun which offered 1988 gs... (https://en.wikipedia.org/wiki/Railgun)

    OK that's not the limit...

    The limit would be toughness of launched object.

    What about making it survive at least 10gs? (F-16 are intended to operate with not much more than 9, but it is because of weakness of flesh inside ;) )

    Escape velocity 5km/s

    d = vt + (1/2)at^2,


    26 km to let it escape from Mars orbit... (shorter also OK) So my answer is less than that, how much less - pending on your expectations
  4. Jul 4, 2015 #3
    If they put the lasers on top of Olympus Mons for example horizont distance is around 400 km. Using ice as coolant can be good :) I also thought about using local resources to produce a kiloton of cheap steel coilgun slugs.
    26km for escape velocity, even if i divide it with ten, it is still too big to effectively serve military purpose if not bombing a fixed location...

    How could they land troops in relative safety? I suppose a mothership has a radius of at least 100m to mimic gravity. It could mount a launch loop to erase horizontal orbital speed.
    So, question about orbital dynamics, if the mothership is at a high orbit around Mars, with orbital velocity 1km/s, what would be the speed of a free falling drop pod?

    Maybe they could carry lots of empty shuttles, and fill them with Phobos and Deimos rocks and dust, so only third of the shuttles have troops, even if defence destroys half of the shuttles only sixth of landing force killed. They have to land in an area outside laser reach, then they can start construction.
  5. Jul 4, 2015 #4


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    The same way they employ them today. Clear out the anti-ship defenses, then land the transports. Small teams of special forces can be sent in prior to the main attack to disrupt the enemy's defenses plus I assume the military has plenty of other weapons/vehicles at its disposal to take out defenses.

    Assuming a drop from about 100 km and ignoring air resistance, the velocity of the drop pods near the surface would be about 1.1 km/s, but only 0.1 of that 1.1 km/s would be in the vertical direction.

    I hope this wasn't a serious suggestion. You aren't going to counter a laser with some ice.
  6. Jul 4, 2015 #5
    My problem is, if they clear out all anti-ship defences, big ships could reach low orbit, and i guess they could mount enough laser power to penetrate the atmosphere from low orbit, wouldnt it make marines obsolete? (They can employ kinetic bombardment from high orbit, but its possible to defend against it more or less, and a precise space to surface missile isnt cheap, and they cant just replace them far from the base.)
    Small teams of special forces, do you mean secret intelligence agents? Before main attack, orbital recon is tight enough that one cant just land troops.
    Otherwise, yes they dont only land infantry, but tanks, artillery etc.

    Thanks, although i am not sure i understood it fully. I think i wasnt clear enough. The mothership should be at high orbit, where 1km/s is enough for stabil orbit, at Mars, that is much bigger than 100km.
    I wondered about the possibility of vertical landing, instead of going around the planet.

    Ice isnt meant to be armor, but coolant for coilguns, lasers.
    Last edited: Jul 4, 2015
  7. Jul 4, 2015 #6


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    Certainly not! Nothing can replace having boots on the ground. One of the things your warships can't do is clear out and take over structures that you don't want to destroy. This includes factories, communication centers, random civilian buildings, etc. Why destroy an enemy's research and manufacturing complex when you can take it over and use it yourself instead? It's certainly MUCH cheaper and easier to do so than to build one from scratch, and you can see short-term/long-term gains with very little economical investment (assuming you don't lose massive amounts of troops or ships in the process).

    No I mean troops similar to Navy Seals, Army Rangers, British SAS units, etc.

    It might be difficult to land a few special forces teams, but I don't think it's believable to say that there's utterly no way of getting onto the surface without being detected. But that's just my personal opinion.

    Ohhh, you're right. If my calculations are accurate, the orbital radius of an object traveling 1 km/s around Mars is 39,000 km.
    That would put the velocity of a drop pod at around 4.8 km/s near the surface, ignoring air resistance, etc.

    That wasn't the meaning I got from Czcibor's post, but even so, I can't see how you'd use ice for coolant. First and foremost, ice is a solid, and you'll need to circulate coolant. Ice is also a decent insulator, so if you try to use it as a heat sink to pull the heat from your coolant you'll run into problems.
  8. Jul 5, 2015 #7


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  9. Jul 5, 2015 #8
    Yes, capture buildings is not so epic as WW three on an exoplanet, but that is infantry job. Martian domed cities makes firefight more difficult... (i am still reading the paper Czibor sent, but at this point, i think if Mars could had so much resources for terraforming, the invaders wouldnt have a chance, not so high tech level) If the defenders dont want the domes ruined, they cant prevent the attackers from entering, but once they are in, they can fire from angles that dont damage the domes, and probably they can have lots of repair bots to seal a small bullet hole.
    Maybe i write two-phase, the first phase is when only the giant (and fragile) defence lasers is taken out, but digged-in missile silos still operational, and big ships dont risk coming close... If they fire a great number of missiles to the shuttles or drop pods, then the fleet can handle the rest of missiles, and with their laser support, the rest of troops, that managed to land, only need to prepare for building-fight.
    Second phase when the troops entered into the capital, and crush opposition from building to building.

    That was another topic, stealthy entry into atmosphere, i reread it. Getting near to the planet isnt unsolvable i think, use neutral merchant ship, and the attackers from Mercury, the Sun's proximity can mask heat signs of launch.

    Thanks. That would mean a mass ratio around e with liquid fuel to decelerate.

    Well, it is easy to convert ice into water. :)

    Thought about that also, but it is extremely difficult with newtonian dynamics, speed in space, let alone ship defences. At first i wrote my pirates simply cut the cargo bay with lasers, i planned only one entering, when they want to capture a VIP.
    Last edited: Jul 5, 2015
  10. Jul 5, 2015 #9
    Under assumptions that no stray laser beam made a big hole that quite quickly reduced the pressure. Under such conditions fighting with fire would be actually quite easy...
    (story hint - try to save a few people trapped inside or compound from burning? ;) )

    If you need Mars semi-terraformed for story reasons (those biological armies being a match for robots) I see here a way:

    Realistically, in such huge projects you don't use much of your own cash. You either take a huge loan or make a consortium. So all Mars need is finding a group of investors... presumably some long term bonds for retirement funds. Maybe offer also some payment in kind and offer investors land that would be at seaside after terraforming...

    ...such big project might have been started earlier...

    ...when the political situation was calmer, while during a war no-one would lend 5% of such cash...

    Of course it changes the dynamic, as one of force would be the investors

    Shouldn't they just evacuate civilians, put on pressure suits and let the game start?
    Shouldn't one build laser arrays out of plenty tiny ones? To reduce the mentioned fragility?
    (but such weakening defence sounds good)
  11. Jul 5, 2015 #10
    Sorry i thought about fighting with firearms. Not put out flames.

    I thought about a few big laser domes, that have some armor (but still not that much in order to easily turn around) and lots of lasers that can move on railways. The domes surely need to be destroyed before surface units get near, the rest of the laser array can be handled by ground based artillery. If they have lots of tiny lasers, they are still vulnerable to shrapnels.

    Evacuating civilans, depends on terraformation progress, if most of the planet cant support human life, they cant just evacuate a big city.

    Terraforming, plant GMOs that can survive and slowly produce oxygen, i think that isnt the most difficult part, with the expertise of mr gene modifier megacorp. Increase greenhouse effect, it can be solved. Increase pressure, that would need LOTS of redirected comets...
    It is also good for story purposes if Mars is indebted to banker alliance and gene modifiers, they will be crippled by the scientist characters (exposing illegal human experiments, hack main system and destroy lunar Vault by reversing mega cannon that protects it with intimidation)
  12. Jul 5, 2015 #11
    What about declaring one base an open city (like Paris during WW2) and fight the rest?
    (no idea)

    OK, you evaporate polar caps, which would give you roughly 2 times denser atmosphere:

    7.5 mb to 15 mb...

    It would move water boiling temperature on surface to 10 C and 21 C in the deepest depression...

    Concernig story - in Real Life such big projects have an awful tendency to run over budget... That can make the story even grimmer...

    Yay! I found terraforming calculation I was looking for:

    You may calculate from it how many nuclear reactors you need ;)

    (counting 2.5 MWe each, something like 20... for raising temperature by 40 Celsius... that part is good...)
  13. Jul 7, 2015 #12
    I would think an army capable of traveling through space would not use marines or traditional warfare. I imagine a more blitzkrieg style attack with robots. Hollywood always depicts an alien invasion like our ships vs theres in a devastating battle in a David v Goliath style showdown. I imagine it more like all of a sudden a trillion machines destroy every piece of military technology on the planet in the first sixty seconds in a Godzilla v Bambi slaughter. An alien species will hit a limit with technology, you can only make a weapon so powerful before it simply becomes more efficient to produce two smaller ones.
  14. Jul 7, 2015 #13


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    I think it's too hard to predict what future warfare will be like with any real degree of confidence. There are a great many factors that influence what can and can't be done with various types of weaponry along with even more factors that determine how an army will fight, what they will be armed with, and to what extent they will go to to defeat their enemy. One enemy may be content to bombard the entire planet from orbit, while another may send in ground forces and avoid as many civilian casualties as possible.

    That being said, I absolutely agree that hollywood's depiction of an alien invasion is far from believable. For example, in Battle Los Angeles (I think that's the name) the battle was won by destroying a massive drone controller, rendering every drone in the area dead. Which is utterly silly. Our own drones don't simply fall out of the sky if they lose connection with their operators, so there's no reason a highly advanced species would design theirs that way. But there has to be some hope for the defenders, otherwise there wouldn't be a movie, so I'm not complaining too terribly much.
  15. Jul 7, 2015 #14
    Ugh, I hated that movie. They also came to Earth specifically for water... opposed to just collecting the trillions and trillions of tons of it floating around the outer solar system *facepalm*
  16. Jul 7, 2015 #15
    Alien invasion, yeah Earth dont has a good chance... but depends on. For example, it is possible that if the aliens so violent, they destroyed their own planet with a nuclear war, only one ship managed to survive, they dont want to nuke another planet from orbit... than they descend with not terrible big amount of resources.
    Whether using robots or marines, that can depend on mentality, one factor for developing robots is : masses of dead soldiers bad for reelection. If aliens has insect like mentality, probably they dont care about such things.

    Otherwise i thought about the following equipment for marines : pressurized powered exo skeletons is basic, recon/communication drone escort, missile jammers on shoulders (Heinlein had the idea to counter homing on jamming with multiple jammers that randomly turn on/off), heavy rifles firing explosive armor piercing ammo, guided grenades, anti-air missiles fired from backpacks (aimed with eye-movement) coilguns portable by two men when disassembled, and a heavy microwave emitter, that can be used for radar or EMP.

    It looks like to me, that target size matters, how vulnerable to current. I imagine the EMP good against small recon drones, and temporary hinders point range defence sensors.
    (They could also blind humans with lasers, so i expect advanced sensor arrays on bigger units, multiple sensors different wavelenghts, sensitivity, based on liquid crystal that can be rearranged.)

    Czibor : if you dont mind i copy your links to my other topic about Mars in the astronomy section. Maybe it is best for my setting, that they already managed to rise pressure to human toleratable, but not enough oxygen.
  17. Jul 7, 2015 #16
    Sure, please use them.

    A few thoughts:
    1) The article about Mars terraforming with calculation concerning energy needed used to be a source on Wiki, but someone removed it. It looks professional, but theoretically there may be some flaws.
    2) For terraforming you need:
    - nuclear energy
    - mining equipment
    - minerals processing facilities
    I think about building normal, standardized nuclear power plants. And just move mining equipment and processing facilities. The processing facilities would be connected to grid, truck would presumably have to use flywheels:
    (batteries are not durable enough, you don't worry too much about energy density)

    3) Terraforming results:
    -you have plenty of nuclear plants and not so bad grid... just add lasers :D
    -you have a few really big holes - strip mining (which may end up as lakes) or mine shafts (potential shelters). Because of lower gravity and seismically dead planet you may easily dig a few dozen km deep, that would mean not so bad atmospheric pressure at the bottom of such pit
    -nuclear power plants produce waste heat - you may use it to heat up area around a base and build an equivalent of an oasis nearby
    -I really think about lakes of salty water (lower freezing point) with some algaes
    -the idea that I dislike is that water would very easily evaporate and try to condense at poles
    -there would be very, very little oxygen - maybe a GMO animal that uses it is apathetic most of time, but activates some reserves of oxygen for fight? Like whales hemoglobine, except that here it would not be used for an hour diving, but one short attack

    4) Terraforming politics:
    -presumably one needed referendum for that and an extra tax
    -presumably such a big loan gives the creditor some supervision... collateral? There may be some additional strings attached - like not only interests, but those built nuclear plants get gov guaranteed a contract to sell electricity at good price for 100 years... even if after terraforming the demand for electricity would be presumably low...
    -high expenditure on terraforming? painful cuts on other sectors, including military ;)
    -those who invested their money in Mars, would like to abuse local business partners, however would be really unhappy if someone endangered their business. So it would look Moon Bankers vs Mercury, unless Mercury would make them certain that their investment is safe... (no confiscation... even minor collateral damage would cause furry)
    -there would be voters who would treat terraforming as bad idea and clear sign of megalomania a white elephant of planetary scale :D
  18. Jul 7, 2015 #17
    Yes, all rather weird.

    Not sure why aliens would want to invade Earth. Any intelligence with interstellar flight technology would be capable of obtaining resources nearby at a fraction of a fraction of the effort of an invasion.

    As for terraforming Mars. Again, any group with such technology is so in advance that it would be a repeat of US/Soviet MAD strategy. A few buttons pressed and nuclear Armegeddon.

    We haven't yet mounted invasions of research stations in Antarctic. I assume that anyone on Mars is from Earth and eager to return to family, breath the air and feel the sunshine after a year of living in a concrete bunker.
  19. Jul 8, 2015 #18
    Nuclear Armageddon supposes two things : attack is clearly superior to defence, and no neutral parties who can ensure that the first ones using WMDs will be surely doomed.
    (Like Syria would have been doomed if they had used WMDs against rebels on large scale.)
    In my scenario of Mercury vs Mars, the first one has superior fleets, a digged in city with very strong defence, even if Mars could make one nuke to reach Mercury colony, they could still survive.
    Tech level is high enough, that people could brought family to Mars, they can see sunshine under lead-glass domes, and breath good air in parks. After adapted to low gravity (i speculated that this makes them very high but thin, with fragile bones, but i couldnt found data on effects of low, but not microgravity, it would be an interesting experiment to breed chicken and mice on Moon or a spin station mimic 1/3 g) they surely dont want to return to Earth so badly.

    Czibor : i will think about the other set of good ideas. :)
  20. Jul 22, 2015 #19
    Hmm, little derail to my own topic, mfb was skeptical about the terraformation and major climate change, and i also read recently that new models suggest, that Mars was rather dry and icy than wet...
    So it is quite questionnable whether anyone willing to spend lots of resources for terraformation... although the "Moon bankers" might have a malicious agenda, they give lots of money for terraformation, knowing that it wont be succesfull in any reasonable timescale, so Mars cant repay them with benefits of terraformation... unless they sell them everything.

    Maybe pressure level and temperature could rise due to mass dump smoke outside and vaporize polar caps by waste heat, maybe pressure could reach human toleratable level, but i dont think it wont be a really hostile environment.
  21. Jul 22, 2015 #20


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    Reminds me of the housing crash a few years ago. Banks gave out large sums of money that people ended up not being able to repay. It ended badly for everyone involved.
  22. Jul 22, 2015 #21


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    Corrected that for you ;)
  23. Jul 28, 2015 #22
    But as say people in middle of any big bubble - this time it is different :D

    GTOM - that's not how one make business. I mean more realistic approach for bank is:
    -we don't know whether your business is good or not;
    -if it's good you pay over the roof; (and that's what they hope)
    -if it's bad we take the collateral.

    I see a different possibility here - in case of big loan there would appear loan conditions... A few bank experts coming and helping to raise taxes and slash spending... Of course only in case if project cost would be over budget and tax revenue would be insufficient...

    It seems that I'm not so creative here:
  24. Aug 7, 2015 #23
    I see. Then i guess, even if waste heat, pollution, some minor terraforming etc raised pressure and heat a bit, the conditions are similar as today.

    Return to the question of orbital fire-support, how much martian atmosphere protects against UV-rays? (I expect the invader fleet uses UV-lasers. Well free-electron lasers can emit various wavelengths, but i dont know, whether it is easy to reconfigure them or not? And unless they reach low orbit, the beams already scatter in space.)
  25. Aug 25, 2015 #24
    About thin air and vacuum conditions :
    How long the oxygen supply of a present day spacesuit could last? How much plants (algae) it would require to turn Co2 back to O2?
  26. Aug 25, 2015 #25


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    Well, the primary life support on NASA's Extravehicular Mobility Unit (the suit the ISS astronauts use on EVA's) lasts 8 hours. Increasing the volume of the supply tank or the pressure of the gas would allow you to store more.

    According to this page, a single 2-liter bottle of algae can get rid of 11 kg of CO2 per year. In comparison, the human body produces about 1 kg of CO2 per day. You'd need about 33 of those two-liter algae bottles (66 liters) per person to generate enough O2 every day.
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