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Orbital bombardment

  1. Mar 7, 2017 #1
    For my story i wonder about a situation where Mars try to gain independence from Earth.
    I specified that fusion ships should have around 100MW for 100 ton in order to maintain miliG acceleration for months.
    So a destroyer's cannons could fire 10MJ x-ray beams in every second for a while (laser focusation equipment more sensitive to heat than thrusters, a laser cannon could be damaged by a scale smaller one).
    Fleet around Mars counts 15 various kinds of ships, battleship too. I estimated 400 MJ in every second. As far as i know, Martian atmosphere swallows at most 10-20% of x-rays.

    Question, is it a bit plausible, that a reinforced government building (no energy shields) could withstand such a siege for a minute?

    After the fleet leave, orbital fighters still remain. Low orbital speed around Mars is 3km/s. So a squadron of fighters could do even more damage in a second with kinetic bombardment, than the fleet's cannons, but they cant attack continously (only with 1-2 MJ cannons).

    Would the thin atmosphere of Mars cause any significant trouble in guiding kinetic bombs at orbital speed?
     
  2. jcsd
  3. Mar 7, 2017 #2
    I - or rather, my cousin, came up with a better idea: if you place an electro-conductive metal thruster between two magnetic fields - say, those of two worlds - you have an electric current, which can then be rode, like a surfboard on an ocean wave, to your destination.
     
  4. Mar 7, 2017 #3
    I wouldnt rule out beamriding, but only for short ranges, since beams scatter.
    Tell your cousin that magnetic fields and electric currents connecting interplanetary distances are total irreal.
     
  5. Mar 7, 2017 #4
    It is almost certain that any settlement on Mars will be underground until the atmosphere is terraformed to become breathable, at which point it will absorb probably even more X-rays than Earth's atmosphere.
    If the building is several meters under ground, it will be almost impossible to dig it out using lasers since a deep thin hole would close itself. You'd have to vaporize hundreds of tons of sand, which would take at least several hours unless I'm making an order of magnitude error.
     
  6. Mar 7, 2017 #5
    I think about lead glass covered streets on the surface. (Additional protection during solar storms)

    http://www.space.com/23875-mars-radiation-life-manned-mission.html

    (I didnt find crackpot in that one)
    http://www.universetoday.com/14979/mars-radiation1/
     
  7. Mar 7, 2017 #6

    Ryan_m_b

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    Lets try and work it through: How much energy does it take to melt a cubic metre of lead? Wiki tells me that the molar heat capacity of lead is 26.65J/mol/K, given one mol of lead would be 82 grams and the density is 11.34g/ml one cubic centimeter would require 3.686J to be raised one degree; a cubic meter would therefore take ~3.7MJ. Lead melts at 327°C, assuming a starting temperature of -100°C (Mars night average) to melt a cubic meter of lead would require ~1.56GJ of energy.

    If the Government bunker had a 100m2 roof with a 10cm thick layer of lead on it and the fleet is hitting it evenly with 320MJ of energy it would take 48.75 seconds to melt it all.

    There's a couple of assumptions in there that will change the time, it assumes a perfect transfer of energy uniformly throughout the led (rather than pulsing the laser and ablating the roof into gas/plasma, layer-by-layer) and it assumes the bombardment is uniform. It also assumes that the melted lead will be enough (because it will either melt through into the building or flow off, exposing a more vulnerable surface).

    If the lead had to be boiled off then it would need to be raised in temperature by another 1400°C. In total that would be a little over 4 minutes of bombardment.

    Just bear in mind that this is a theoretical, imperfect way of going about it. In reality you'd more likely focus on key points with the goal of burning through and hitting key targets inside (like load bearing walls).
     
    Last edited: Mar 7, 2017
  8. Mar 7, 2017 #7
    Looks like it isnt that fearful as i thought.
    The key target could be members of Parliament just announcing independence.
    Drill through multiple stories is easier than melting the roof, so reach the council chamber. Could beams possibly create an explosion, by vaporizing part of the floor?
     
  9. Mar 7, 2017 #8

    Ryan_m_b

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    As I said there's a lot of assumptions there, the big one being that the energy from the laser is evenly distributed. It's entirely likely it wouldn't be. Instead you might pulse the laser, pumping as much power as possible into a short beam, to turn the surface layer to plasma. As the plasma expands it will damage the layer beneath. Exactly how powerful that would be I'm not sure. John Scalzi has a very similar scenario to yours in one of his books, the Human Division I think. A key world is about to declare independence from the military junta ruling human civilisation. As the vote is about to be cast in the planetary parliament a soldier parachutes towards the chamber ceiling. Just before they hit a ship in orbit rapidly ablates a hole for them, allowing them to arrive in the chamber in style and explosion to deliver the ultimatum not to leave.
     
  10. Mar 7, 2017 #9
    I hate to sound negative but members of parliament gathering in one place to vote sounds like 19th century, not 22nd.
     
  11. Mar 7, 2017 #10
    So put them in a segregated house area where they can walk to work without transport. Then meeting face-to-face would be less of a problem. It could a part-time resident, when government was in session.
     
  12. Mar 7, 2017 #11

    Ryan_m_b

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    I wonder if/when we'll see a permanently distributed national government, where for all debates/votes it's just done through VR.
     
  13. Mar 8, 2017 #12
    Good to know that we are in 19 century.

    Although i expect hero team to hack the security of Parliament (i dont know whether physically access cables between cameras and security hub is enough if they use quantum cryptography, but probably governor decided its better to steal the money and use the old way inside an already highly secure buliding) so technically remote voting becomes possible.

    Then Earth can say but the voting was hacked, but if rebellious MPs are hiding, they cant make them tell, it wasnt really us, it was a trick.
     
  14. Mar 8, 2017 #13

    Drakkith

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    If the effect is significant, they would necessarily have to account and correct for it if they have these weapons. Even if there are difficulties, I see no reason to think that they couldn't be overcome by a weapons designer. As usual, if you want the in your story, put them there.
     
  15. Mar 8, 2017 #14
    Since Mars dont have rainstorms, could it be bit realistic to escape from bombardment through sewer system?

    Im a bit confused, whether real sewers have enough place for humans or not?
     
  16. Mar 8, 2017 #15

    Drakkith

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    As far as I am aware, only the very old sewer systems are large enough to allow humans to pass through.
     
  17. Mar 8, 2017 #16
    There is this thing called https://en.m.wikipedia.org/wiki/Utility_tunnel. They seem to be more expensive than just burying the cables & pipes under ground but if you need it, it's perfectly reasonable to have them in a city.
     
  18. Mar 8, 2017 #17
    Wait, if you melt the top layer of lead, the next pulse will simply heat up the liquid on the surface more. You can't simply expect it to melt. What happens if you blast an ice cube with a blowtorch? If you add up all of the energy provided, it should be plenty to melt the ice cube, but in reality, you'll end up with a slightly smaller ice cube with a lot of very hot vapor and water. The better the insulating properties, the harder it is to melt something because the other layers deflect most of the energy. Dirt is a really good insulator.
     
  19. Mar 8, 2017 #18
    But with thin air melting and vaporization heat is close to each other isnt it?
     
  20. Mar 8, 2017 #19
    Thanks. I also thought, that they built bigger tunnels for the sake of protection if the city was attacked, lead glass breached.
     
  21. Jun 30, 2017 #20
    Story goes on. Mars rebels, Earth fighters (bigger ships has to go to Mercury) from Deimos base keep bombing rebels. What could be the methods to supply fighters, so they have to return to base for repairs only? If they launch a crate from base with a coilgun, and it would spiral into low orbit (or reach it another way), how much delta-V should be needed to capture it?
    (crate dont have any kind of thrusters, guidance, the point is to trust most recon/guidance/self defence to the orbital spacecrafts. )
     
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