I recall reading something by either Lem or Asimov that popular fiction’s idea of space combat is impossible because ships wouldn’t be able to intercept each other. Maybe, I don’t remember the quote properly, but I’m pretty sure the gist of it was that it would be impossible for one ship to meet up with another in space.
Could someone please explain this to me? And please bear in mind that you are dealing with a dullard who based his entire academic career on avoiding math and science classes.
Also, is there any popular science fiction that gets the science of space combat right (from the physics standpoint). I’m posting this in GQ because I’m looking for factual answers, not a review of SF combat scenes, but please move as needed.
If I was any good at math or science, I would not have had to go to law school.
However, we’ve demonstrated an ability to hook up the shuttle and the space station, and even sent a probe to an asteroid. If we can do that, why could we not intercept a space ship? As long as we can detect it and track it, we oughta be able to intercept it…
I’m not sure what is meant by “not intercept each other” or “not meet in space”. As far as I can tell, this is patently false; the Gemini and Apollo missions pretty much proved that. So I must be misunderstanding this…
Combat certainly wouldn’t look like it does in the movies. The sound factor aside, many of these really have the look of air combat (e.g. barrel rolls, streamlined banking). In space I don’t really see how well-designed combat ships can ever get in a position where one can approach another from a vulnerable direction for any length of time (i.e. as they do in air combat, where the main tactic is to chase from behind). A ship attacked like this could presumably do a quick 180 with steering rockets, or pretty much instantly push force at a 90 degree angle to the direction of travel.
Of course, it’s difficult to find anything in space, so all of this presumes a locational apparatus somewhat better than just looking out the window, and 2D radar just ain’t it. This is probably the biggest obstacvle to anykind of combat, and so my guess then is that stealth technology vs. location technology would be one of the biggest determiners in space combat. I’d also guess fuel consumption would be a factor, and so efficient use of fuel in high-maneuver combat–likely determined by computers–could offer another edge.
Combat in orbit offers a few additional challenges. Here I think there is a clear advantage in attacking “from above” (i.e. from a higher orbit) that the pursued ship can’t easily overcome. Fuel consumption would definitely be an issue here–no matter if you’re boosting to a higher orbit or braking for a lower one, I’d bet you use the same amount of fuel. Keeping these transfers fuel-efficient is obviously one goal, but I believe the edge you would get in making quicker orbital transfers might be worth burning extra fuel.
I would guess that what the author (could it perhaps be Niven instead? in question was saying it that it’s impossible to match vectors and board a hostile spaceship, because all it has to do is vary thrust. It’s not terribly hard to intercept another craft; indeed, laying a field of small iron balls at orbital velocities to intercept an incoming craft would be sufficient to destroy any vessel imaginable by foreseeable technology.
It’s certainly possible for spacecraft to meet up in space; we’ve been doing it since the Gemini-Agena Target missions (even without fancy digital control systems) and it’s more or less routine for the Space Shuttle or an automated Progress supply ship to dock with the ISS. It does require careful trajectory calculations so that you don’t wiz past your target, but hardly impossible.
Thanks guys. Obviously a coordinated effort to intercept is possible as it has happened. But what I am referring to is one ship chasing down and attacking another ship that is actively trying to evade.
My non-scientist way of looking at it is that the issue relates to speed of the craft. It’s possible for one craft (‘target’) to be moving in space with a very high speed relative to another (‘interceptor’)
Hence to ‘catch’ up the interceptor craft has to build up a lot of speed. Increasing speed requires an increase in it’s energy ie it has to accelerate. For example burning fuel in engines to create an accelerating force.
Taking a straight line path the interceptor would infact have to move faster than the target. Like a cop chasing a crook down the motor way.
Humans can only withstand a limited amount of acceleration before passing out/dying. The interceptor craft would therefore need sufficient fuel and sufficiently powerful engines to be able to exceed the speed of the target craft for sufficient time for it to ‘catch up’. Obviously the target craft would potentially be looking to use it’s engines to increase it’s speed making the interceptors job harder.
I don’t think the original concept even thought THAT far. The idea is describing combat as in SciFi to be impossible, you know, you arrive at a solar system, track down the enemy ship hiding behind some moon and blast away with your space lasers. Basically, if everybody has ships fast enough to execute maneuvres like those , they would never play out like that. To paraphrase Douglas Adams, space is really really really really mindbogglingly big and we are incredibly small. If your space ship is an orbital craft about as fast the space shuttle, it’s one thing - if you can somehow get accross the solar system in a couple of days, and then back, the relativistic effects alone would make strategic warfare a nightmare. Not even talking about how the hell are you going to find a ship? What magic space radar is going to even give you a vague idea where something the size of a locomotive is that’s three light hours away and actively trying not to be found?
If you have two ships with matching acceleration numbers and no “hyperjump”, your chase will likely not end until someone runs out of fuel or your machines or men break from wear or old age.
This is a bit of a hard one to answer, because we don’t know for sure what spaceships would look like by the time it comes to an actual space battle. But we can make some guesses.
In a realistic situation, you wouldn’t have the “magic” spaceships of Battlestar Galactica and Star Trek that appear to have nearly infinite amounts of fuel and capacities for acceleration. You’d have only a limited amount of “Delta-V”, that is, capacity to change your speed and direction. Your acceleration would also likely be fairly limited, both by the limitation of the human body to withstand it, and the desire to minimize fuel consumption.
Given this, consider the case where the ship you want to dock with or shoot down is approaching at, say, 90 degrees to the current course you are on, and is doing so at many thousands of miles per hour. You have to decelerate from whatever speed you are moving at and then accelerate onto the new course. Practically speaking, you’d pick a spot in space where you want to intercept and apply thrust in such a way as to accelerate to that point. Of course, at the time you get to the interception point, you have to be moving at the same speed and in the same direction as the ship you want to intercept (if you want to board) or at least fairly close to the same speed and direction (if you want to shoot). Pretty tricky, especially because the other guys, being no fools, will wait til you make your course correction and will then make their own course correction to make it more difficult to intercept. If you can’t match course, then you’ll probably sail by at several thousand miles per hour which doesn’t give you much of a window for shooting, even with missiles.
Truthfully, the above example really assumes better technology than what we have now. Today, the launch trajectories are very finely calculated to allow vessels to dock, and there isn’t a lot of fuel left over to be changing orbits with. It’s not like a space shuttle with a grudge against the Fox network could take it into its head to shoot down a satellite in geosynchronous orbit.
Of course – this all goes out of the window if we discover some kind of physics that allows “magic” spaceships – artificial gravity or inertia-less drives so high accelerations are a possibility and fuel becomes not an issue.
One of the main things to understand is that a “real-life” rocket moving through the solar system has a very very small ability to change its velocity relative to its velocity. Meaning, it has a rocket that can accelerate the ship at, say, 10 meters/sec/sec. But the ship itself is going thousands of meters/sec. No problemo, just keep the rocket blasting for longer.
Except rockets work by throwing hot gasses backwards to make the rocket move forwards. So you’ve only got a limited amount of fuel, and once you burn it you’re finished. No problemo, just bring more fuel.
Except adding more fuel means you have to haul around the extra fuel, so you’ll need extra rocket fuel to move the extra rocket fuel. You reach rapidly diminishing returns, when your ship is 90% fuel tank almost all your fuel is expended just moving around your fuel.
So when you’ve got a ship moving at orbital speeds around the solar system, it has a very limited ability to change that orbit. If you want to intercept an object in a stable orbit this isn’t difficult mathematically…you figure out where Mars will be in six months, and you blast your rocket to put you into an orbit that will put you in the place where Mars will be six months from now.
Except, what if Mars had a rocket too, and they didn’t want to meet you? They see you put yourself into an intercept orbit with them. But they’re chicken, so they fire their rocket to put themselves into an entirely different orbit, and now you’ll pass each other by millions of miles. No problemo, you just fire your rocket to match with their new orbit. Except by now you’re running low on fuel, you have very little ability to change your velocity relative to your velocity. Small changes at the start of the orbit make gigantic–shall we say astronomical–changes in your end position. And the same with “Mars”, which is really the enemy spaceship.
As long as the enemy spaceship can see you change velocity and calculate where you’ll end up, it is trivial for them to use a lot less delta-v to end up somewhere very far from that spot. And every burn you make to correct for their burns will use up much more fuel.
IIRC, the spaceships in Niven and Pournelle’s Mote in God’s Eye books have very standard propulsion systems, and this problem is discussed at length.
I’d suspect that battles will only happen when one side is attacking something that can’t move, like a planet, and the other needs to intercept. Thus battles will only happen by mutual consent.
I’d say that naval battles before airplanes were somewhat similar.