Good ways to limit space travel?

[Fred Brackin]

Originally Posted by Shostak

If you want to limit travel to the third star, stay away from jump drive and stick with constant 1G acceleration

To keep the third star inaccessible, make refueling difficult. .

Just as a note this won't work at all (and the OP seems to understand that). One of the wonders of constant acceleration is that travel time is not linear with distance. It increases as the square root of the linear distance.

As a handy rule of thumb to remember a accel and decal trip of 1 AU takes about 3 days or 72 hours. A trip of 144 AU is of course, 144x as far in linear distance but only 12x as long in trip time at constant acceleration. So 36 days.

A trip 2x as far as that only takes 1.41 times as long rather than 2x as long. even if it absolutely is not possible to fit more fuel onto the ship than that 144 AU trip requires at 1G you can go farther by accelerating slower.

The square factor works with slower speeds as well so accelerating at 0.5G makes the trip last 1.41x as long. Traveling 2x as far still only takes 1.41x as long too. So if you can go 144 AU in 36 days at 1G you can go 288 AU in 72 days at 0.5 G on exactly the same amount of fuel.

If an alien cae and offered us a 0.01G constant acceleration drive I'd jump at it. You'd be accelerating 100x more slowly but trip time would only increase by a factor of 10. Only 3 weeks to Mars at close approach instead of the 6 months current planning is talking about.

As another note, refueling one ship from another ship or a space station requires matched velocities and mid voyage velocities for a constant 1G ship can be quite high. For that 36 day/1G trip they are around 5% of c. So there won't be a lot of refueling halfway through the trip unless you use a Bussard ramjet perhaps.