McAnally's (The Community Pub) > Author Craft

I broke physics and now it's being obnoxious.

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Aminar:
So, for the YA Sci-Fi project I'm working on I have a psuedo-magic system based around the concept of gates(read portals from portal, but with more room to play.)  There's quite a bit of backstory behind this, and more than a little Significantly advanced tech/life is magic.(I'm probably at a 2.5 on the Sci-Fi Hardness scale, but spaceflight itself is leaning towards a 3.5(works with physics at a basic level, but I'm not going to start throwing theoretical physics around much, just account for relativistic time dilation and the like.)
Anyway here's the situation.
Ship A(The Captain doesn't like to name ships.) is running low on fuel.  They have enough to either A-Get to travelling speeds(.9C) or B, slow down from (.9C) but not both.  The ship is being pursued, and is somewhat damaged from a run in with another pirate vessel.  They took the attacking pirate vessel without major harm to it via sabotage and portals.  Now the Pirate ship, Queenswyrd, needs to tow the other ship to travelling velocity.  They'll deal with the fuel trouble of that later, but they don't have the hull integrity to pull this off(because why would you have the hull integrity to tow a ship 6 times your size to .9C)  So what I want to do is put a gate on the back of the ship, fire the magnetic grapple through the gate, and then have it come out at a 180 degree angle to itself, so that the magnet hits a forward facing wall(that is involved in bracing the engines) on the Queenswyrd.)

However, depending on the perspective I take this gets really weird.  If I go from Ship A's perspective it should be getting towed, but if you go from the perspective of the grapple it looks like the cable should be slackening, but then if the cable slackens the two ships will be getting closer together, but if that happens its getting towed.

I'm pretty sure I'm overthinking things, but I can't be certain and it's slowly driving me nuts.

Wordmaker:
I'm not sure what ".9C" means, but I'm assuming these are starships you're talking about.

Now, most real-world physics kinda goes over my head, even more so when it comes to space and faster-than-light travel. I'm a big fan of warp speed and hyperdrives and anything that makes it easier to just get on with the story.

So this advice comes completely from the perspective of a lay person and what I'd be looking for as a reader.

I would say, just let the ship be towed without the portal. The average reader probably isn't going to worry about, or even notice, details like hull integrity and whether or not one ship can tow another. What's important is that the ship gets towed, so stick to the simplest way of making that happen.

Haru:
I think if you consider levers and pulleys rather than portals, it might be easier. Basically, what you could do with a pulley is pull something up with less force than you'd need if you lifted it directly, but you will have to pull on a lot longer string. I believe it is antiproportional, so if you want to use half the force to lift, you'll need to pull on the string twice the length you want to lift the object. Portal-engineers probably figured out how to do something like this.
In your case, that would mean you'd need a portal-pulley that reduced the effective mass of the towed ship to a 6th, which in return would mean that for every 6 meters the pirate ship moves, Ship A would move 1 meter. You should be able to adjust this difference by portals as well.

On the other hand, you are not thinking 4th dimensionally, Marty.  ;)

The first thing that came to mind was to create a portal loop for a ship as a runoff. Imagine a slope, and on the bottom you put a portal that leads back to the top. If you roll something down there, it is basically an endless slope, and the object will gather more and more speed as it goes along (in an atmosphere [and by the friction of the slope], that is limited, but you won't have to worry about that in outer space).
Now a slope is probably not the best thing to use for a space ship, but since we are in space, we don't need to use one. We'll just let ourselves be pulled straight towards the nearest sun, portal back a few miles and use that to increase the speed to where we want it. Then you shift the exit portal so that you are facing the direction you want to go and there you have it. You'll have to adjust your trajectory every now and again, but you won't have to use any fuel to get to the speed you want. You'll need quite a large sun to get to the big speeds in a useful amount of time, but you could use smaller ones or even just planets to gather enough speed to get to a bigger system and jump from there.

For example: You'll need 318 days in the gravitational pull of the earth to reach .9C. The gravitational pull of our yellow sun would be able to do it in 46 days. And I think our sun is one of the small ones.

Wordmaker:
 ???

That went right over my head, but it sounded smart, so if that works, go with it.

Haru:
Well, look at it this way. If you are in a car and you accelerate, your speed increases. If the rate of acceleration is constant, and you have a long enough road ahead of you, you could, in theory, accelerate to somewhere near the speed of light. Of course, in your car, you have the problem that friction on the road, friction against the air, friction in the engine itself will only allow for a limited speed.

Now the earth gravity is a source of constant acceleration. If you let a ball fall 2 seconds, it will have double the speed as if you would let it fall only 1 second. Of course the problems remain the same, friction against the air will reduce its speed, and there is a break even point known as "terminal velocity", where the force from the friction cancels out the gravitational force that would accelerate the ball. Also, you can't have it fall endlessly, at some point it is going to simply crash into the ground.

Now if you are in space, there is no air, so there is no (or far far less) friction to stop you. And with the portals, you can create an endless fall, gathering more speed with every second you spend in there. From that point on, it is just a waiting game, and how long you have to wait depends on the size of the planet/sun you use.

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