Warp (Hyperjump) and momentum

[Michael Thayne]

I noticed that Psionic Powers has a useful little clarification regarding Warp: "If your destination has a different relative velocity (e.g., warping into a moving vehicle, or warping safely to the ground when falling), you automatically match it, but this imposes a -5 penalty to your Body Sense roll." While none of the builds in Psionic Powers include the hyperjump limitation, there's no obvious reason not to apply this rule to that version of Warp. This has some interesting implications: it means that if a ship has a cargo hold that's been emptied of air, you should be able to jump to the inside of the cargo hold regardless of how fast the ship is traveling relative to any nearby celestial bodies. Presumably it also applies to jumping to the surface of a ship, station, or airless celestial body, meaning you can hyperjump straight from, say, the surface of Ceres to the surface of Luna, no problem!

Finally, if you're jumping to a point above a planet, presumably you match the velocity of the planet (perhaps this is true out to the limit of the planet's hill sphere?) In some situations, this could be inconvenient because you won't be "in orbit". On the other hand, you won't need to worry about a deorbit burn. A spaceship with Warp (Hyperjump) might be able to make a round trip from Earth to Mars with less than 2 mps delta-V (for achieving a suborbital trajectory from the surface of either planet, and for a propulsive landing on Mars).

Thoughts on this interpretation? It seems significantly different from how people often want FTL drives to work, but a lot of fiction seems to routinely ignore orbital velocity, so maybe that's not so bad? Plus lets you get interplanetary travel without making all your drives uber torch drives that logically ought to vaporize the landing site.

[AlexanderHowl]

I keep conservation of momentum and vector in my games, so jumping long distances is often fatal without proper planning. For example, the average rotational velocity on Earth is around 320 m/s, so a miscalculated jump may cause someone to slam into the ground at 640 mph. Space is more forgiving (usually) because there is a lot of void, but it should always be a concern in unfamiliar space.

[Michael Thayne]

Originally Posted by AlexanderHowl

I keep conservation of momentum and vector in my games, so jumping long distances is often fatal without proper planning. For example, the average rotational velocity on Earth is around 320 m/s, so a miscalculated jump may cause someone to slam into the ground at 640 mph. Space is more forgiving (usually) because there is a lot of void, but it should always be a concern in unfamiliar space.

What does "proper planning" consist of? If you're warping around on the earth's surface, even warping 100 miles could lead to you being launched several yards up into the air, and that doesn't look avoidable.

[AlexanderHowl]

100 miles is much worse than that. A 100 miles at the equator would average roughly a 70 mph difference in velocity (depending on longitude and latitude). Since that translates to Move 35, a 10 HP person would take around 7d crushing damage from a collison.

[Rupert]

I get about 25 miles per hour difference for a 100 mile jump east or west along the equator, with most of the vector being horizontal, so the main risk would be slamming into something at ~12 yards/s. Going east you'll have some lift, making this very hard to control. Going west you'll be pushed into the ground and thus probably snatched off your feet and you'll roll. It's probably a soft collision for 1d (1d+1 if you prefer) if there's nothing hard in the way, otherwise a hard collision for 2d (or 2d+1) if there is.

Going north or south the vector is effectively entirely horizontal, and is about 6 inches per second. A roll to not fall over is all you'd need.

Things get more dire with many bigger jumps, of course. However, from a given latitude north to the same south (or vice versa) along a constant longitude gives no change in velocity relative to Earth's surface. Also, at higher latitudes shifts east-west are less dangerous.

Research into the landing point is clearly indicated for most jumps, however, as is wearing protective gear. Many are outright contra-indicated.

[dcarson]

In _The Witling_ by Vernor Vinge a planet has low tech natives that can teleport. Long distance is done in sealed boats with internal padding and suspensions from lake to lake. They still limit it to a few hundred miles a hop. The lakes are spaced at convenient distances because the tiny percentage who are very powerful teleports ported in rocks from their moon to make them.

[clu2415]

Your supposition is that if there’s no air in the cargo hold, there will be nothing to transfer forces from the ship to you, so the ship wouldn’t count as having any velocity, right? But if you’re explicitly not matching the ship’s relative velocity, you still retain your own velocity and risk smacking the side of the cargo hold.

[Not another shrubbery]

Originally Posted by clu2415

Your supposition is that if there’s no air in the cargo hold, there will be nothing to transfer forces from the ship to you, so the ship wouldn’t count as having any velocity, right?

I think it's because Hyperjump doesn't work in an atmosphere.

[Pomphis]

GURPS Traveller (3e) has rules on p.84/85 thát assumed that retaining momentum is a limitation, so without such a limitation it is presumably not retained. It also limits changes in altitude (gravitational potential) by saying that energy loss/gain is balanced by a corresponding change in body temperature.

[Michael Thayne]

The Traveller approach seems to be one that makes intuitive sense to a lot of people, but it enables surprise high-speed attack runs, which seems possibly undesirable. It's not even really physics-respecting, unless like Traveller psis you're limited to small changes in gravitational potential energy, which Traveller seems to only apply to psis, not spaceships.