[Space/Spaceships] Getting the velocity/Delta V I want with the tech I want

[Johnny1A.2]

Originally Posted by scc

OK, I'm working on a so far hard Sci-fi setting and I've got two planets that are 400 AU apart, +/- 44 AU. Now according to my math that means that at a velocity of ~300 mps it will take a ship 4 years to move between the two planets.

This is an odd situation to start with. If this is a relatively 'hard' setting, then it's very odd to have two inhabited worlds 400 AU apart, varying only by 44 AU. Four hundred AI is a big gap, it's about 2 light-days. For comparison, the entire Inner Solar System, from Pluto to the far side of Pluto's orbit, is about 11 light-hours. If they orbit the same star, it must be a monster, and that 10% variation is odd, too.

My problem is that I want there to be somewhat regular trade between them (In fact one's supposed to be settled from the other).

Now the basic issue here is drives, the tentative TL for the setting is TL9, but I'm thinking that most of the freighters use older systems, such as Ion Drives.

No I'm thinking that lithobraking can be used at the journeys end to slow the ship down, but that still leaves me trying to figure out how to get the ship moving that fast.

I assume you mean aerobraking, lithobraking would be slowing down by slamming into the surface of the planet.

Boosters/upper-stage's are just sort of wrong for the setting, there's supposed to be a lot of traffic so it doesn't work out. Catapults could work, but how long would a human usable one be? Increasing the amount of delta-v is out, at least for Ion Drives, from what I can see the specific thrust they get is Spaceships is twice as high as it should be. Mag-sails are an option, but both they a Ion Drives have an acceleration problem, though I might be able to get by that with Mag-sails.

The truth is that none of the above is going to be very useful for 400 AU trips in a short time. Ion drive in theory can give you constant accelation for a long time, but at a very low acceleration. At 1g, in a straight line flight (which is oversimplified) you'd need nearly two months 1 way to cover 400 AU. Ion drive, realistically, isn't 1g.

So what do you suggest I do?

We need to know a little more about the setting, and how close you want to stick to realistic phsysics, you may need to rework your star system.