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how powerful of an explosion would be starships large enough to carry about 2 armoured divisions each accelerated to about half the speed of light and instead of decelerating so that they can attack a planet they kept going so that they would hit the planet?
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At the very least, I'd think you need to decide the mass of the starships and the atmosphere of the planets. Probably the size of them, too.
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Hitting a planet at 0.5c has got to hurt, as would being accelerated up to 0.5c by an explosion Posts: 7593 | Registered: Sep 2006
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Hyper-science this scenario up to avoid physics criticism. Remember that if accelerating mass to shove it into planets at extreme speeds causes a lot of damage, then you either have to invent a specific technology or hindrance that prevents people from doing this except in extremely convenient conditions, otherwise everyone would just be plowing piggybacked mass into each other's planets in wartime.
Posts: 15421 | Registered: Aug 2005
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Propulsion system would indeed play a huge part in this scenario, as would the intended use of the ships (shuttle, interplanetary, or intergalactic)...
The problems with using spaceships as aimed projectiles is that due to their standard usage their volume tends to be primarily composed of empty space. Think of it as the difference between throwing a baseball at someone's head vs. throwing a wiffleball at someone's head.
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Oh there is no doubting that. I thought about going after the 1/2 c, but that seemed to be a more arbitrary part of the conversation.
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addition to what Samprimary and Architraz have said:
1) If you don't want this happening you don't even have to have "Hyper-Science" per-se to explain it. It can pretty easily be limited as some sort of interstellar political moritorium on the use of mass-driver technology on populated worlds (i've seen that explanation used before and it makes sense, since there is so much possibility for planet-wide cataclysm similar to agreements not to use nukes)
2) It definately would be bad tactics (in general) to use ships as projectiles, both because of their hollowness (though that would have little effect at these speeds) and because of their enormous cost compared to just strapping some engines (and associated support structure) onto asteroids.
3) In addition to the above concerns, there is likely an issue with aiming this ship accurately enough at those speeds to hit a planet. It wouldn't necessarily be impossible, so much as likely improbable/difficult.
4) That being said, suppose you have a story or scenario where there is a ship/ships which in a desparation move does what you propose (breaking whatever laws/avoiding whatever shielding) then to get some sort of rediculously rough ballpark figure on the collision, just do an energy calculation: m*v^2 and compare it with other big booms (I'm guessing there's proposed numbers on the asteroid(s) that may have wiped out the dinosaurs, created the gulf of Mexico etc... my guess is that the ship would be a lot less massive, but also moving a lot faster than these, so it would probably be a lot more energetic collision.
general likely situation for a direct impact would be massive tectonic/entironmental cataclysm potentially causing the complete devastation of the planet.
Other potential outcomes could include planetary debris forming asteroid fields/small moons.
If you want to still have the collision but don't want as bad results, then make it a glancing blow skipping off the atmosphere and/or surface which could be anywhere from as bad as a full-on collision to an EMP over one hemisphere...
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Blayne Bradley
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I'm not writing a science fiction story out of it (although if I ever do get around to one it would make an interesting plot point) it is just that in the novel Homeward Bound by Harry Turtledove, Humans supassed the "Race" technologically with FTL travel while the "Race" still can only travel through traveling at sublight speeds and cryogenic freezing of the passengers. So inorder not to look completely helpless Fleetlord Atvar threatened that if in a war of extermination all they would have to do is accelerate ships into projectiles to render Tosev 3 (Earth) uninhabitable.
Out of curiosity I was wondering its plausibility I know in the Haloverse the UNSC uses MAC guns on its starships that accelerate a slug of tungsten to about 3/4 of c to combat the Covenant ships.
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quote:Originally posted by Blayne Bradley: I'm not writing a science fiction story out of it (although if I ever do get around to one it would make an interesting plot point) it is just that in the novel Homeward Bound by Harry Turtledove, Humans supassed the "Race" technologically with FTL travel while the "Race" still can only travel through traveling at sublight speeds and cryogenic freezing of the passengers. So inorder not to look completely helpless Fleetlord Atvar threatened that if in a war of extermination all they would have to do is accelerate ships into projectiles to render Tosev 3 (Earth) uninhabitable.
Many of those ships if I recall carried nuclear weapons. Many ships carrying many nuclear bombs could theoretically do a lot of damage.
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The problems I've having with the speeds involved is that at half the speed of light, even the upper most fringes of the atmosphere are going to be equivalent to a solid. My training is far from that of an astrophysical nature, but my intuition is that any non-solid (as in a single solid mass) object would wind up being atomized before it impacted the ground.
That brings up another interesting alternative... That much disruption in an atmosphere (occurring in the span of milliseconds) could be destructive in new and interesting ways, including reducing / eliminating it entirely (it being the atmosphere of the planet, which is somewhat fragile as it is). The pressure wave it caused would probably kill / destroy most non-fortified creatures and structures over most unprotected areas of the planet.
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suffice it to say that it would probably be an effective threat by Atvar. It is quite possible that such a collision would wipe out Earth (either through direct collision with the ground/ocean or through severely destabilizing the atmosphere. Either way it's likely that it would take quite a while for anyone to difinitively do the calculations to say that the human race could survive such an impact.
My question about his threat though would be how long it would take him to get his ships going that fast and to Earth, I would imagine their propulsion systems would involve generally slow accelleration which built up during the long interstellar trips. Even if the ships were at Earth already they would probably have to wander around for 50 years (or whatnot) before they'd build up that kind of speed... of course I could be guessing wrong about their propulsion systems. I don't remember any detailed descriptions of them from the first couple books in that series, but I may just be forgetting.
Posts: 1038 | Registered: Feb 2006
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quote:Originally posted by Blayne Bradley: I'm not writing a science fiction story out of it (although if I ever do get around to one it would make an interesting plot point) it is just that in the novel Homeward Bound by Harry Turtledove, Humans supassed the "Race" technologically with FTL travel while the "Race" still can only travel through traveling at sublight speeds and cryogenic freezing of the passengers. So inorder not to look completely helpless Fleetlord Atvar threatened that if in a war of extermination all they would have to do is accelerate ships into projectiles to render Tosev 3 (Earth) uninhabitable.
If humans have faster than light travel, isn't it reasonable that they could detect and destroy the ships long before they got close to earth.
No hyper-science would really be needed. Realistically, detection would have to be the primary way to deal with any sort of mass driver weapon. While they would be devastating if it hit, the build up time for that sort of speed should be long enough that if you have defenses in place. Of course, if you aren't defended, you're pretty much dead, but that's been the way that advanced advanced weapons work for a while now. I mean, if an attack helicopter showed up and you didn't have any anti air weapons to fight with you'd be pretty much hosed. Nothing new there except the scale of the destruction.
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quote:If humans have faster than light travel, isn't it reasonable that they could detect and destroy the ships long before they got close to earth.
Nothing of the sort. Space is a sphere; the volume you have to cover to get warning at distance x grows as the cube of x. At one-half c, even ten seconds' warning is a huge volume, and filled with all kinds of debris at that.
quote:The problems I've having with the speeds involved is that at half the speed of light, even the upper most fringes of the atmosphere are going to be equivalent to a solid. My training is far from that of an astrophysical nature, but my intuition is that any non-solid (as in a single solid mass) object would wind up being atomized before it impacted the ground.
Both untrue and irrelevant. Firstly, the stmosphere is a very thin skin; at 0.5c, you pass through it in less than a millisecond. There isn't time for the spaceship to disintegrate. Second, even if the atmosphere were made of iron, the spaceship would still penetrate for some considerable depth into it. Third, even if it did disintegrate, the energy has to go somewhere; radiation is a very inefficient transfer, so basically you're still putting all that energy into the Earth, with bad effects. After all, a nuclear weapon disintegrates too!
For the original question, rough sketch: Taking the mass of a tank as 50 tons, letting an armoured division be 200 tanks, doubling the mass to account for various incidentals, and tripling to account for the spaceship, you get a mass of 600 million kg per spaceship. At 0.5c you have a gamma of 0.5*sqrt(3)=0.866, and kinetic energy is mc^2(1/gamma-1), giving (6*10^8 kg) * (3*10^8 m/s)^2 * (0.15) = 8.1 * 10^24 Joules; roughly two thousand teratons of TNT. The effects of such an explosion are unknown - zero experimental data - but I think it fair to say that Atvar's threat is quite frightening.
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Blayne Bradley
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The distance between Tau Ceti (race homeworld) and Earth takes about 20 of our years for the Race's ships to travel across.
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The only recourse in a situation like that is to threaten to do the same thing in retaliation. A case of Mutually Assured Destruction.
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It depends on the actors contracts. If they are regulars who are expected back next season, it will not be possible to hit their home planet or have them on board the spaceship when it happens. Furthermore, it woudl be considered immoral for the ...
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In this case the ships are already in Earth orbit, and have been there for at least half a century, if not a couple decades longer. For those not familiar with the series The Race came to Earth during WWII, but they evolve technology much slower then us. The influx of alien technology actually sped us up and surpassed them in many cases including said fater then light drive.
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but Stephan, the problem still arises that it would take them a long time to speed up, so being at earth doesn't really buy them much.
likely statement about their propulsion technology (especially since it's not FTL) would be that the 20 year voyage involves 10 years acceleration and 10 years decelleration (approximately) So, even assuming that they can actually get up to .999 the speed of light somewhere in that 10 years it means that it would still take them at least a few years starting at earth to start on some curved trajectory back to the planet at the necessary speed. even if they only do it at .1c (which is probably more than sufficient to devastate us) it would take at months.
That being said, the issues with detection could still be an issue.
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Blayne Bradley
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uuuumm Stephan.... you do realize that there is an interstellar trade of sorts between Home and Tosev, there are starships in Home's orbit which they could send to Earth.
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Nope, that wouldn't work, because such a thing could only be ordered in retaliation for a devastating attack on Home. (By the moss-grown imperial bureaucracy which has just gotten bombed out of its comfy offices, and anyway takes a century to decide what it wants to wear for the ceremony that's starting in a millennium or two, but that's a separate issue.) That means that the Earth ships which just destroyed Home can track the starships, intercept them before they accelerate very much, and destroy.
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Blayne Bradley
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your saying that the entire orbital defence fleet of Home cant defend itself from one-two starships in orbit?
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quote:For the original question, rough sketch: Taking the mass of a tank as 50 tons, letting an armoured division be 200 tanks, doubling the mass to account for various incidentals, and tripling to account for the spaceship, you get a mass of 600 million kg per spaceship. At 0.5c you have a gamma of 0.5*sqrt(3)=0.866, and kinetic energy is mc^2(1/gamma-1), giving (6*10^8 kg) * (3*10^8 m/s)^2 * (0.15) = 8.1 * 10^24 Joules; roughly two thousand teratons of TNT. The effects of such an explosion are unknown - zero experimental data - but I think it fair to say that Atvar's threat is quite frightening.
Yeah, that's what I was thinking, but I didn't want to do the math. Without experimental data, you could just do a rough estimate of how much temperature increase this much energy would do to an earth sized planet. That might give us an understandable reference.
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quote:your saying that the entire orbital defence fleet of Home cant defend itself from one-two starships in orbit?
No, you're saying that. Why would Atvar retaliate with weapons of mass destruction if he hadn't already lost the war? So if he has any kind of reason to do such a thing, then yes, the Home defense fleet is gone.
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"Use your imagination. Propulsion system could play a critical factor.
Not really. Blayne's just described a planet killer. How much the propulsion system overkills the planet is a moot point. Doing it the quick and dirty way... Let's start with the explosive power of 1gram of antimatter is equivalent to 43kilotons of TNT... and the Wiki figure sounds too low according to vague memories of fusion bombs. So lets look up fusion in the Sun, and we get: the explosive energy of 10megatons of TNT is equivalent to the total conversion of 47grams of mass. (10,000,000 divided by 47) So the total conversion of 1gram of mass is equivalent to the explosion of 212,766 tons of TNT What the heck, I'm too lazy right now to do the arithmetic, and I trust a university astronomy class more than Wiki.
What does this have to do with anything? Well, 1gram of mass contains the same amount of energy whether the mass is 1gram matter or 1gram antimatter. And the total conversion of mass into energy involves equal amounts of matter and antimatter.
Which leads to relativistic speeds, relativistic mass increase, and the energy of relativistic collisions.
Mv = relativistic mass at speed Mo = mass at rest (zero speed) v = speed c = lightspeed Mv = Mo/(1-[v^2/c^2])^0.5 : ie relativistic mass equals rest mass divided by the square root of (1 minus [{speed times speed} divided by {lightspeed times lightspeed}])
Hokay... Your starship is running at half of lightspeed, so v = 0.5 And lightspeed is lightspeed, so c = 1 [{0.5 times 0.5} divided by {1 times 1}] equals [0.25 divided by 1] [v^2/c^2]= 0.25 Then (1-[v^2/c^2]) equals (1-0.25) equals 0.75 and taking the square root of (1-[v^2/c^2]) equals 0.75^0.5 equals 0.866 which is a lot of typing to get to (relativistic mass at half lightspeed) equals (rest mass) divided by 0.866 or since dividing by 0.866 is the same as multiplying by (1 divided by 0.866) which is equal to 1.1547 : the (relativistic mass at half lightspeed) equals 1.1547 times (rest mass) At half lightspeed, Mv=1.1547Mo, or 1gram at half lightspeed has a relativistic mass equivalent to 1.1547grams at zero speed.
Here's where it gets cute. We know from Thermodynamics that "Mass&energy can be neither created nor destroyed." So where did the extra 0.1547grams come from? It didn't if you are thinking that the 0.1547grams is matter. That extra 0.1547grams is the (mass equivalent of the KineticEnergy) of that (1gram of matter traveling at half lightspeed) via Einstein's E=MC^2 : (Energy) equals (Mass) times the (speed of light) squared. So (relativistic mass) equals (rest mass) plus the (mass equivalent of the KineticEnergy) From Newton's "For every action, there is an equal and opposite reaction.", we know that the extra equivalent mass came from 1/2 of the total energy that was expended to accelerate that 1gram to 0.5 lightspeed. Using a "spherical cow" example...You annihilate 0.1547grams of matter with 0.1547grams of antimatter to get the (KineticEnergy equivalent of 0.1547grams of mass) traveling with the 1gram of mass at half lightspeedand the (KineticEnergy equivalent of 0.1547grams of mass) traveling as "rocket exhaust" in the opposite direction.
Since 1gram of matter at half lightspeed has the KineticEnergy equivalent of converting 0.1547grams of mass into energy, and total conversion of 1gram of mass produces energy equivalent to 212,766tons of TNT, then 1gram of matter traveling at half lightspeed has the (kinetic)energy of (0.1547 times 212,766)tons of TNT. Or at half lightspeed, the energy from a 1gram collision is equivalent to an explosion of 32,915tons of TNT,
ie KineticEnergy at half lightspeed 1gram : ~33kilotons of TNT 1kilogram : ~33,000kilotons of TNT : ~33megatons of TNT 1tonne : ~33,000megatons of TNT : ~33gigatons of TNT 1 (Abrams) main battle tank with a mass of 63tonnes : 2,074gigatons of TNT : ~2.1teratons of TNT 1teraton of TNT : Richter10 earthquake : {without calculating, Wiki's example bolide feels WAY too large) 1 Abrams : ~2.1teratons : Richter10.2earthquake 12to57 Abrams : 25to119teratons : Chicxulub : KT extinction (which killed a LOT more than just dinosaurs) The 25teratons is the amount of energy necessary to have displaced the rock/etc from Chicxulub. How much of the 94(extra)teratons of explosion actually occurred in the crater's creation depends on other calculated assumptions made**.
I'll let you figure out how many tons of equipment&fuel&ammunition&food&water that an armored division has. All I could easily find was that during the KuwaitLiberation, the 1stArmoredDivision moved 17,400 soldiers and 7,050 pieces of equipment. Interesting sidelight: The average USMarine marching with full combat gear weighs ~100kilograms/220pounds: I've read that they weigh more. So using 100kilograms as the mass of a soldier with minimal life support, there is 1,740,000kilograms/1,740tonnes of mass in division personnel with minimal life support. And at half lightspeed, the KineticEnergy of (1,740tonnes of mass) times (32.915gigatons of TNT per tonne*) equals 57,272gigatons/~57teratons of TNT. So those soldiers with minimal lifesupport would collide with an energy equivalent to a Richter11.172earthquake all by themselves. Fortunately, it's just a flesh wound.
* A tonne denotes the metric 1000kilograms , ie ~2200pounds Whereas a (short)ton is the American 2000pounds , ie ~900kilograms And a (prefixed)ton of TNT is a defined measure of energy, and is only approximately related to either the tonne or the ton in terms of exploding a given weight of TNT on Earth.
** Calculated assumptions about how high that rock&etc was kicked up (including suborbital crash back to Earth, eventual orbital decay back down to Earth, and eventual escape from Earth), how much of that rock&etc was heated, how much was melted, how much was vaporized, how much was chemically decomposed (before recombining into new molecules), and how much energy escaped as light and other electromagnetic radiation.
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"An assault fleet leaves Mars going bearing 027 mark 3 at 0.4 times the speed of light. At the same time, an intercept fleet leaves Titan with a heading of bearing 217 mark 2 and traveling at 0.2 times the speed of light. Assuming a constant rate of transmission for subspace communications and no interceding spatial and temporal anomalies, at what time will either fleet commander receive the message that his fleet was decimated?"
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How fast must the fleet be traveling for the news to arrive that the fleet was decimated before the fleet is actually decimated, allowing said fleet commander to change his orders, saving his fleet, but creating a space/time paradox that eventually destroys reality?
Posts: 11895 | Registered: Apr 2002
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quote:Originally posted by Dan_raven: Extra credit:
How fast must the fleet be traveling for the news to arrive that the fleet was decimated before the fleet is actually decimated, allowing said fleet commander to change his orders, saving his fleet, but creating a space/time paradox that eventually destroys reality?
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Since faster then light travel is possible in Turtledove's universe, time travel should not be far behind. The humans could then just blow up the Race's planet long before they develop star travel, thereby creating our universe.
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Blayne Bradley
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Our Universe is the "alternate reality" where Atvar upon discovering that Humanity has advanced far more quickly then ever before realized turns the Conquest Fleet around as well as the Colonization Fleet via message back to Home, leaving us to our own devices hoping we destroy ourselves. (So far so good)
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But Tau Ceti, their home star system, is only 11 or 12 light years from Earth. We would have picked up radio signals sometime in the last 60 years.
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Once I post the answer: 42: I expect everyone will move fast enough to go backwards in time and post the correct answer in their test books, so once again, A's for everyone!!
Posts: 11895 | Registered: Apr 2002
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Blayne Bradley
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Unless upon discovering us they mask their radio signals as to prevent us from knowing of them and SETI/NASA I forget which HAS picked up Artificial Radio signals before but could never confirm it.
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quote:Originally posted by Blayne Bradley: Unless upon discovering us they mask their radio signals as to prevent us from knowing of them and SETI/NASA I forget which HAS picked up Artificial Radio signals before but could never confirm it.
If I remember correctly, Arecibo received *something*, and when it did I don't think it was under the jurisdiction of NASA.
Or maybe that's an X-Files I'm remembering...
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