## 2014-07-03

### Hyperdrive Reversion Velocities

Following on from the last post, there's the old question of whether you maintain a particular velocity upon hyperdrive exit.   That is to say, if you're doing 100 when you enter, are you doing 100 when you exit?

The question itself could be considered somewhat silly, really.   Consider that the apparent speed of the International Space Station as considered from the ground is something like 7.6 kilometers per second in its orbit.   But then consider that on the surface at the equator, the revolution of the Earth means that one sitting still on the ground is still whipping around at 0.44 km/s.  That's nothing compared to the planet's speed around the sun, which is more like 28.9 km/s.

So even if you could freeze the galaxy and stop its rotation, just going between two Earth-like planets in two Sol-like solar systems where the planets were still revolving around their suns in the same plane could involve a velocity difference of almost 60 kilometers per second if they happen to be going the opposite way at the time.

Of course, the galaxy isn't frozen.  In fact, we're out on one of the spiral arms doing about 220km/s around the galaxy, and in a bobbing motion over and under the plane (as measured over millions of years, anyway).  And if we considered that some sort of standard, then naturally we'd also have to recognize that solar systems closer in or further out are moving at different velocities (though dark matter theorists dispute this).   In any case, stars don't move around the galactic center in an orderly fashion, so there will be differences between systems in any event.

And, just for kicks, let's also note that the galaxy itself is trucking along at around 600 kilometers per second.

The point is, not only might you have a generic difference of 60 kilometers per second, but you could also have additional velocity differences between worlds you're traveling to via hyperdrive or other FTL means.

So, there's a question of frame of reference involved.

Generally speaking, Star Wars vessels seem to depart and arrive from planets at relatively low velocities relative to the planets themselves.  Certainly Solo's reversion to realspace near the Alderaan debris, said to be a planetary diameter out, was done at a sufficiently low velocity that his debris impacts were nothing near hypervelocity in nature.

The exit velocity may be a characteristic of hyperspace and its hyperlanes, or an effect afforded by the hyperdrive itself.   This is not clear.

Certainly even unusual reversions, such as the power-failure reversion of "Jedi Crash"[TCW1] or the emergency reversion of "A Sunny Day in the Void"[TCW5], seem to leave the ship at a relatively low velocity relative to the surroundings (for certain values of "relative", anyway).  That would seem to suggest that the hyperdrive cannot be used to, say, easily create a high-sublight kinetic missile.  (Indeed, it also seems that while hyperdriven ships ought not collide with things, the things themselves don't seem to mind much . . . otherwise, why create a Death Star?)

Consider a ship like a Republic Space Cruiser or Frigate, with a mass somewhere between ten and twenty thousand tonnes.  Even the low end of that gives the ship a kinetic energy of 10.75 gigatons at 1% of the speed of light (3000 km/s), which is as fast or faster than any ship we've ever seen in realspace in Star Wars.   Such a high-speed ship would be a tremendous weapon compared to any weapon in Star Wars other than the Death Star.   Certainly evildoers would have employed this technique if it was usable.

On the other hand, we have the Malevolence, which apparently did collide with a moon to seemingly tremendous effect, apparently while trying to go into hyperspace.

So even if exit velocity is somehow constrained by "hyperspace brakes", it seems a hypermissile can be made simply by timing the hyperdrive to attempt hyperspace entry in the direction of the offending planet.  That is, unless the Malevolence example is not what it appears to be.

In any case, especially in reference to "Jedi Crash", the canon strongly suggests a relatively low exit velocity is somehow tied to hyperspace itself.   That is to say, in "Jedi Crash" a ship hypers out of a planet's atmosphere and, when the hyperdrive is shut off via the power being cut, the ship is not traveling at relativistic velocity.  Certainly we might be tempted to expect relativistic speeds if the hyperspace exit were uncontrolled, but we don't see that.

The real question following on from the last post, however, is "can a ship accelerate via hyperdrive"?   I see no reason why not, within the limits apparent above.  Certainly a micro-jumping ship might be able to gain velocity on its way away from a planet, rather than toward it, and still maintain some semblance to the "hyperspace brakes" notion.

But, alas, there's no clear answer here.  I hate that.