Slashdot Mirror
The Physics of Space Battles
An anonymous reader writes PBS' It's OK to be Smart made this interesting video showing us what is and isn't physically realistic or possible in the space battles we've watched on TV and the movies. From the article: "You're probably aware that most sci-fi space battles aren't realistic. The original Star Wars' Death Star scene was based on a World War II movie, for example. But have you wondered what it would really be like to duke it out in the void? PBS is more than happy to explain in its latest It's Okay To Be Smart video. As you'll see below, Newtonian physics would dictate battles that are more like Asteroids than the latest summer blockbuster. You'd need to thrust every time you wanted to change direction, and projectiles would trump lasers (which can't focus at long distances); you wouldn't hear any sound, either."
no one can hear you explode.
Go check out the GoG site for the two i-War games which feature "correct" space based combat.
Good old games, that were overlooked at the time.
I seem to recall that the Starfury of Babylon 5 got the physics (more or less) right.
Short bursts of thrust to get around? Wrong! Space is big... very big. Getting around a solar system would take days.
No fireballs in space? Wrong! Spaceship occupants need atmosphere.
Close in naval battles are a no-no? The is the distances lasers might be effective.
OK so we have long range battles... They say sci-fi lasers aren't possible but rockets are? It would probably be much easier to evade a rocket in space (a rocket that will probably fly past you at a crazy speed as it's course corrections have to fight inertia).
...I can tell you another thing about space battles: you don't see anything aside from a few tracks on a computer screen. If you have a telescope pointed in the right direction at the exact right time you see a very unimpressive and quick flash.
The ranges, timing, and velocities involved are far too great for human perception.
I am very small, utmostly microscopic.
Actual space battles would be extremely boring to watch. It would all take place at such distances that nothing could really be observed very well or viewed as a whole. Assuming energy / laser type weapons, it's purely a matter of how sensitive and accurate the telescopes are that identify the enemy ships and direct the weapons where to fire. Stealth and cloaking would be where the real arms race would be.
Better known as 318230.
Demonstrating the physics of space fighters with Kerbals in them:
https://www.youtube.com/watch?...
Poul Anderson, The Star Fox
Larry Niven, Protector
C.J. Cherryh, Downbelow Station
I remember seeing something a few years back that made the case that Ship to Ship space battles would be fought by AI Drones. Due to the extreme 3D maneuverability of small craft with thrusters , humans wouldn't stand a chance against machines capable of making advanced tactical calculations in milliseconds. Whether or not projectiles would trump high powered energy weapons would depend on the sorts of shielding and materials in use to create spacecraft with. However, a rapid fire rail gun does seem like it would be ideal for close quarters combat and require less energy to penetrate shielding and armor. But perhaps more exotic ammo than slugs would be more useful, imagine a round that on impact would release rapidly replicating nano-bots that eat through the ship's hull until there was no ship or deliver an EMP to disable the systems.
My first encounter with realistic space battle physics was with Antares Dawn: a great book by Michael McCollum... Great stuff.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
"First things first -- but not necessarily in that order"
-- The Doctor, "Doctor
Why not skip the ships and just have massive barrages of guided missles? They could approach from all angles, split MIRV style and fly random patterns closer to impact. If they could coordinate their behavior it'd be like trying to stop a swarm of bees.
Missiles travel very, Very, VERY slow (in space). Even if they are under constant acceleration.
Lasers travel very, Very, VERY fast. But they lose energy/focus over space-type distances.
So it comes down to how well the writer understands economics and what technological advances they are postulating.
Not to mention WHY there is a war in the first place if both sides have that kind of technology available to them.
I read a rebuttal to that which was fairly compelling: http://scienceblogs.com/builto...
The equation given isn’t derived. We have no idea where they’re getting that 13.4 proportionality constant. Dimensionally it’s correct, and it’s pretty easy to derive the equation up to that constant which will depend on the sensitivity of the detector. That equation modulo some uncertainty with respect to that constant is accurate as far as it goes given a spacecraft of hull temperature T and cross-sectional area A.
I would take you through the steps of the derivation, but it would be pointless because the assumption that the hull temperature has anything to do with the interior temperature is simply flat wrong. We can prove this with a potato.
Switch your oven to the “Bake” setting at a temperature of 350 F. After preheating, put in the potato. The interior of the oven, and eventually the potato, are maintained at a constant temperature of 350 degrees. How hot is the exterior surface of the oven? Depends on how well insulated your oven is, but I can guarantee it’s a lot less than 350 degrees.
The key is the understanding the relationship between heat and energy. Put hot coffee in a thermos – the hot coffee is hot because it contains thermal energy. If the energy can’t leave, the coffee will stay hot because the energy stays inside the thermos. The outside of the thermos stays at the temperature of the surroundings. Now neither the thermos nor the oven is a perfect insulator. Some energy leaks out of the oven’s interior, cooling it down. The oven thus has to pump energy into the heating elements to make up for this loss. Equilibrium is reached when the rate of energy being put into the oven equals the rate of loss through the insulation.
For a spacecraft in a vacuum, the pretty much the only way to lose energy from the interior is by radiant heat. The higher the temperature of the outside, the higher the rate of energy loss via radiation. But the temperature itself is irrelevant, since just like the oven and the thermos it’s not necessarily related to the actual temperature inside the cabin at all. It is always and everywhere a function of the total power passing through the hull. If the temperature inside the cabin is constant, the power leaving the hull by radiation is exactly equal to the power being generated inside the hull.
So how far away can we detect a given amount of emitted power? According to Wikipedia, a telescope of 24 aperture can detect stars of magnitude 22 after a half-hour exposure. I think this is a pretty good realistic limit for detection with reasonable equipment in a reasonable time frame. Now we need to compare this magnitude to something of known power output. How about the Sun? The sun has magnitude -26.73 as seen from the Earth’s surface (smaller magnitude is brighter), for a difference in magnitude of 48.73. The exponent used for magnitude is 2.512, so the difference in power per unit area of telescope is 2.512^48.73 = 3.1 x 1019. Since the Sun radiates about 1000 watts per square meter at the distance of the earth, the smallest radiant power we can reasonably detect in our telescope is about 3.123.1 x 10-17 watts per square meter.
Our hypothetical spacecraft is radiating that power into space, evenly distributed over the surface of a sphere of radius r, where r is the distance to the detector. When that power-per-area is the same as the limit of our telescopic capability, that gives us the maximum detection range. Mathematically,
Where rho is the sensitivity of our detector. Solve for r:
So what’s the power? Well, each human on board is going to produce about 100 W just from basic bodily metabolism. Computers, life support, sanitation, and all the rest will contribute more. We might assume 10,000 watts total for a futuri
https://en.wikipedia.org/wiki/Inverse-square_law
Energy weapons in space all have the same problem. The distances involved mean that they get real weak real fast.
At best they'd be useful in a fixed-site-defense scenario. Such as putting them on moons to defend against incoming ships.
But then you have the problem where your defeneses are not manoeuvrable. So asteroid bombardment becomes an option.
I would guess they will turn out more like battles between submarines. Whoever gets detected first loses. And one hit and you're dead.
If you're going to have reaction drive style thrusters for maneuvering, you're going to run out of fuel very quickly, dissipating mass, unless your thrusters are thrusting out little bits of mass at VERY high speed, in which case they could be used as weapons themselves. (Sci Fi writer Larry Niven came up with the idea of a reaction drive as a weapon, google the 'Kzinti Lesson' for more info.)
I think it would be interesting to have space battles where several fighters were somehow connected to each other via some sort of tractor beam, so they maneuvered by transferring momentum between each other instead of dissipating mass into the vastness of space; they might look a bit like bolas circling each other but with quick changes snapping in and out as they went in to battle, or maybe they would be tethered to a mother ship, somewhat like World War II aircraft carrier that sends out figher planes to do the fighting. The mother ship would have enough mass to let the fighters seem to be free to zap around easily.
---
("Cough Cough") I wrote an unpublished Sci Fi Novel (I did send it to a bunch of publishers at the time, over 10 years ago), where interstellar travel used 'draggers'. There was no faster than light travel so it took years and years to go between even nearby stars, (The travelers themselves would be in an accelerated frame of reference so it wouldn't be so long for them.) In the novel it took a long time to set up a system between two solar systems, similar to the way it takes a long time to set up a railway between two cities, but then you could use it very efficiently. A vessel would attach itself to a dragger, and be quickly accelerated (that's the hard part, dealing with the sudden accleration that would flatten everything against the back wall like you were in a super cream separator), the dragger, much more massive than the vessel, would be slowed down some, but then, at the other end, as the dragger wheeled around a star, the vessel would transfer it's momentum back to the dragger and slow down to become part of the other solar system.
The thing about conservation of momentum is that it means the center of mass of a closed system doesn't change. If two solar systems and the draggers going between them were a closed system, then the center of mass would shift as the vessel moved between one and the other, but, if the vessel returned to the original system again, then the original center of mass would be restored, and the energy used to move between them could be recycled, plus there wouldn't be reaction mass being spewed out all over the place.
In theory, theory and practice are the same; in practice they're different. (Yogi Berra & A. Einstein)
The only two "giveaways" would be the heat signature from its power source (not just propulsion, but life-support) and whatever it accidentally occults as it moves across the background of stars. The heat can be drastically reduced by towing the power source a long way behind the main craft and having it very, very dispersed so the Watts per square metre of I.R. are very small. The occultation problem can be reduced by choosing a path that stays away from the galactic plane.
So most battles would be ones of sneak attacks and defensive fire. It might be possible to devise some sort of A.I. mines, or even simply fire a cloud of sand in the general direction (assuming the relative velocites of target + sand are high enough, that could be all that's needed).
However, I have a feeling that most "wars" in the future, whether in space on on Earth, will be economic in nature and "fought" over decades rather than wham-bam shooting battles.
politicians are like babies' nappies: they should both be changed regularly and for the same reasons
If you're going to swallow the idea of FTL drives, tractor beams and shields -- among other things -- then it's not really that much of a stretch to swallow the idea of inertial control, too. Which would make such battles not resemble a game of asteroids at all.
As for sound, presuming your vehicle maintains atmospheric integrity, you'd hear anything that causes the the craft's atmosphere to be jolted into motion. Debris hitting your vehicle, the stress caused by a sealed compartment being ruptured, people screaming when they get fried, crushed or otherwise insulted as a consequence of direct or indirect battle damage or loss of, for instance, inertial damping, equipment failures and power supplies having problems. You would also hear something if a force field of any kind was imposed upon your vehicle in such a way as to deliver any kind of uncompensated-for energy in mechanically coupled framework(s) producing direct or indirect vibrations in the audio range. And furthermore , presuming a ship has sensors to detect things like the energy outputs of other vehicles as they maneuver, seems to me that converting that to audio as a handy sound cue/warning would be hardly any trick at all. Just as one example.
Likewise, perhaps *we* can't focus a laser today, but that's not an inherent limitation of lasers even by today's known physics, that's a limitation of our technology, so that objection is kind of dead on the doorstep, so to speak. Not that a visible future beam weapon is necessarily carrying its punch in the form of light anyway. Could be just a side effect, or an aiming aid. This is the future, we're talking an imaginary scenario resulting from science and technology we don't presently have and so may speculate upon (using current knowledge... pretty boring... we can barely get off the planet's surface, much less engage in space battles... that's why most SF has at least a few pure fantasy elements in it.)
And along the lines of what we accept and what we don't, if you are blase' about the idea of a magic camera floating around your space battle and instantly changing perspective from A to B to C, perhaps it's just a little bit silly to complain about, for instance, a whoosh, or what "lasers" can do. That's entirely outside of what might be realistic in terms of what the movies subjects are up to.
So yeah, it's ok to think, but don't let someone else do your thinking for you. If there are space battles as depicted in most SF(fantasy) movies, the rules as we know them right now have long since been trashed, so there doesn't really seem to be any reason to worry about it.
All of the above is why I can really enjoy Star Wars, Firefly, Trek, etc, btw. Even though I'm fairly well grounded in how we think things work at present.
I have more trouble with obvious errors that don't take into account technologies we already have. For instance, in Red Mars, some of the characters "hide" from satellite surveillance by moving over long distances in a large hollow rock (or perhaps a thing that looks like I rock, I forget), something we would spot in an instant *today* by the simple expedient of image subtraction; Take two shots under the same or similar conditions but separated by time, align them, and subtract them. Everything that's in the same place turns to black; anything that has moved will be bright. This is *trivial* surveillance technology, and has been in use since *at least* the 1970's. And the kicker is this would work even better on Mars than it does here -- thinner atmosphere. Caused me a few snickers, that one did.
I've fallen off your lawn, and I can't get up.
Any colonization of Space would drop the population density. With out a dense population you cannot support a large military. So you have two scenarios, a very local one and a distant one. This is much closer to the Paleolithic then to any modern or near modern history.
The local one would be like what we have today. If everything is one polity then you have police functions. It there is more then one polity then you have militaries. The Blue and Green colonies of Mars fighting over something. What they are doing is trying to change the nature of how power and resources are controlled by the polities. This is some sort of permanent reshuffling. You have to remember that the instability of the Middle East is driven by large, poor, young, male heavy populations.
In a distant scenario you get hit and run tactics. Mars colony wants the ore that Europa colony has, so it launches a raid. Grab the ship and go. It doesn't try to change the nature of Europa's or it's own polity. This is what you see for most warfare in most of human history. This means a totally different kind of technology and tactics.
I tend to think that Firefly got it most right. Space Wars are Civil Wars and the military exists to maintain the status quo. Fighting will take place within the Polity.
I recommend The Lost Fleet book series by Jack Campbell to anyone interested in realistic space battles, that take into account relativistic aspects and the speed of light. Also the 90's TV show Babylon 5 nailed newtonian physics, but the ships engaged in close battle for the sake of visual entertainment. You can see Starfuries and White Stars strafing like the Asteroids video game.
Where there are people, particularly in large groups separated by distance (and by proxy culture), there will be war. The harshness of the environment or emotional and physical costs to the soldiers, history has proven, is irrelevant.
Combat ships will be largely unmanned, with several (for redundancy) manned "overseers" nearby to give the drones a sentient strategic advantage. Remote oversight wouldn't be able to respond quickly enough due to communications lag, although the overseers would be in two-way communication with more distant officers coordinating the combat groups general strategy.
Assuming the technology to efficiently and compactly generate incredible amounts of power has progressed equally with all other fields relevant to space colonization, energy weapons would be favored over more conventional chemically-propelled/detonated ordinance like bullets, missiles and bombs. Conventional ordinance requires mechanical fidelity and precision to fire, is limited in quantity to due to the mass required to be effective, travels slowly over great distances, may be easily impeded by other ordinance or energy weapons, suffers from intertia and can result in friendly fire if it is disabled, misses its target, or is fragmented by defensive countermeasure. Energy weapons reach their target nearly instantaneously, may track their target for sustained, precision delivery, and use only enough energy to obtain the desired effect. Their vector can be controlled non-mechanically, allowing sensors to maintain a lock on a rapidly and unpredictably moving target. They may not be impeded by other energy weapons and travel too quickly to be countered by dynamically-deployed mass-based countermeasures.
The precision and accuracy of combat drones' movement and energy weaponry combined with the tiered progression from automated drone to human overseer would, with the exception of any extreme tactical choices by central command, product a general lack of chaos that is atypical of conventional battles. The primary focus would be to edge out the opponent by obtaining slight defensive advantages through technological superiority, use of unique environmental factors (planets, moons, stars, gravitational or radiological fields, asteroids), the purposeful introduction of unpredictable or chaotic elements (literally gambling that the increase in chaos will be favorable), or psychological tactics such as deliberate attacks on civilians, propaganda and public (broadcast) executions and torture.
The bottom line is that less people would die. Once the enemy drones have been decimated there's really no reason to go on slaughtering the general public. Once that happens the first few times, history will keep the losers of the future in line outside of the inevitable (but manageable through surveillance and information control) insurgencies.
Buy your next Linux PC at eightvirtues.com