A star to steer her by

More about Shayla's world.

Last time I talked about the spread of star systems, so I thought today I should delve into the actual space travel bit.

Space travel in Shayla's world depends on two things:

Folded space

This is a sci-fi staple. The idea is that our familiar 4-dimensional space-time is embedded in a higher-dimensional space. If our universe is folded up in these higher dimensions then it might be possible to take a shortcut across the gap, allowing you to disappear from one point and reappear somewhere else. Interstellar travel depends on you finding shortcuts that allow you to travel vast distances in our universe for very little actual distance in the higher dimension.

In Shayla's world, I've decided that this folding of space happens very tightly, so folds are very close together, and is also fractal in nature. In other words, space is folded up on all sorts of scales from subatomic up to light years.

This part is important, but before we get to that I need to talk about...

Gravitational fields

Yes, Shayla's technicians can manipulate gravity. Another sci-fi staple.

This one mechanism is put to several uses.

For conventional travel, everything from small air cruisers to the secondary drives of large starships, an artificial field can be made to interact with a surrounding field of a planet or star for propulsion. In its simplest form, the device producing the field generates lift, and anything else bolted on gets lifted with it.

An extension of the same principle, usually only used in larger craft, can enclose a volume of space in a gravity field isolated from the outside world. This simultaneously produces artificial gravity for habitation, and protects the inhabitants from the crushing accelerations - anything up to 40g - used by starships maneuvering in normal space.

Bring the two together

Because gravity isn't confined to our visible world, but "leaks" into the higher dimensions, a variation on the gravitational field is able to pull a volume of space across those higher dimensional folds.

The principle is very simple. You are sitting on one side of a fold in space. Lying right next to you in higher dimensional terms, but invisible to your eyes, are neighboring folds in all directions. Reach a few atoms-width "sideways" and you might hit a patch of space a few feet away. Stretch further, and you can reach into space miles distant.

All your gravity drive has to do is reach across, anchor itself to one of those folds, and haul your ass across the gap.

This is where things get interesting. Flinging something the size of a starship from one fold to another, you have to be darned careful that every patch of space you are moving into lines up exactly with the patch you just left.

Or bad things happen.

Very bad things.

In practice, imperfections are inevitable but are managed within safe limits. But the further you try to reach, the less perfect the fit. Once you go beyond safe limits, it affects biological and electrical systems a bit like radiation damage. Push your luck even further and you start getting large scale structural failure.

Luckily, those clever engineers have figured out how to tune the drive to make sure things line up pretty darned good, but this puts a practical limit on how far you can safely jump in one go.

Practicalities

The primary hopper drive typically jumps hundreds or thousands of miles at a time, depending on the power and quality of the drive. That may not sound impressive, but the field cycles fast - anything up to a million times a second. This gives practical speeds ranging from 1,000 to 10,000 times the speed of light.

Hopping becomes increasingly dangerous in the distorting presence of a gravitational field. Within approximately 2 AU of a sun-sized star, safe hop lengths reduce to less than a mile bringing speeds down to just over light speed. Get closer, and the dangers mount up in exactly the same way as stretching too far in open space. This means ships usually have to drop into real space and switch to secondary drive some distance out from their destinations.

When a ship hops, it jumps sideways from one point in space to another. Momentum in real space is conserved so it will reappear with the same velocity it started off with. This means a ship will almost certainly need to spend time adjusting its velocity at its destination.

The most efficient way to approach a planet is to hop to somewhere "upstream", so your existing velocity carries you straight in. All you have to do is slow down at the right time.

Direct approaches like this are generally frowned upon by planetary authorities, partly because of the potential danger an incoming ship would pose if it lost power, but mainly because that kind of approach is usually the sign of an attack.