Interstellar Teleportation Mechanics

[Guest]

Assume a spaceship drive that essentially teleports the ship from one star to another, like the Jump Drive from Battletech. The specifics aren't entirely important but I'm curious how things would work if, say, the drive didn't scrub its current universe-relative velocity and instead carried it with the vessel. Let's say we're orbiting a planet in System 1 and perform a jump to System 2 into orbit of the primary. What happens in System 2? How about if we jump into orbit of a planet in System 2?

I imagine this could result in some very awesome hilariousness as well as some devastating kinetic weaponry if a jump was calculated just so...

[UmbralRaptor]

Relative velocities of nearby stars seem to run from <10 to >250 km/s. Not sure what the galaxy's rotational curve as a whole is, but I assume for a retrograde star or a cross galaxy jump, up to 400-600 km/s would be possible. And in rare cases, one could have silliness from hypervelocity stars or jumping near a double-degenerate binary system to abuse gravitational slingshots.

[Guest]

Oh man, I totally forgot about star motion... That makes it even more powerful, and potentially more useless.

E: But then again, if you account for that motion and know what the target system looks like at any given moment, you can plan ahead and enter into the correct orbit for a Hohmann transfer or something, so maybe not so useless. Would probably take a pretty powerful computer, though.

[Rune]

Relative velocities of nearby stars seem to run from <10 to >250 km/s. Not sure what the galaxy's rotational curve as a whole is, but I assume for a retrograde star or a cross galaxy jump, up to 400-600 km/s would be possible. And in rare cases, one could have silliness from hypervelocity stars or jumping near a double-degenerate binary system to abuse gravitational slingshots.

If you can jump quick enough, you don't need to bother with slingshots: let yourself drop almost-into a black hole and/or big giant enough times, and you will go relativistic in short order. Then hop to the target planet, drop rocks, hop back to the other side of the black hole to decelerate. Unstoppable fireworks ensue.

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Oh man, I totally forgot about star motion... That makes it even more powerful, and potentially more useless.

E: But then again, if you account for that motion and know what the target system looks like at any given moment, you can plan ahead and enter into the correct orbit for a Hohmann transfer or something, so maybe not so useless. Would probably take a pretty powerful computer, though.

As I said, if you can change your position at will, you can accelerate in any direction you desire to any velocity you desire by using any gravity well, then drop yourself where you match orbital parameters. Haven't you seen people playing with warp drives in KSP?

Rune. That's a nifty unintended doomsday weapon. Kzinti lesson anyone?

[Guest]

As I said, if you can change your position at will

Specifics include a long time between jumps, a maximum distance, and a prohibition against jumps within "significant" gravity, in true sci-fi fashion, but it's still far more powerful than I originally thought. Jump near black hole or sufficiently large star, build up decent velocity while recharging, jump to target.

E: Oh, hrm... Well, you'd still have your relative star motion to take into account, even if jumps were prohibited deep in a gravity well....

[Bill Phil]

Relative velocities of nearby stars seem to run from <10 to >250 km/s. Not sure what the galaxy's rotational curve as a whole is, but I assume for a retrograde star or a cross galaxy jump, up to 400-600 km/s would be possible. And in rare cases, one could have silliness from hypervelocity stars or jumping near a double-degenerate binary system to abuse gravitational slingshots.

If it's truly like BT's drive, then there's a max range of 30 light years per jump. There's not that much relative velocity on average withi that range, right?

At least for the most part.

There's also a recharge time, as well as a requirement of low gravity.

In effect, all of space is a valid jump point except for the space near celestial bodies.

However, if velocity is kept when you jump, then there is almost no effect if you have the correct velocity relative to the target and choose to jump to the point above the zenith or nadir of the star.

You can't jump at will unless you have the drive charged and are in a valid jump point.

[UmbralRaptor]

If it's truly like BT's drive, then there's a max range of 30 light years per jump. There's not that much relative velocity on average withi that range, right?

Well, there are a few halo stars that close, so...

[Guest]

If it's truly like BT's drive, then there's a max range of 30 light years per jump. There's not that much relative velocity on average withi that range, right?

I was thinking more like 10 but, still, a lot can be done with that. If the jump has to happen near the orbit of Pluto, or at a similar point in any given gravity well, that limits it a bit further, but you still have the problem of slingshotting around a halo star for added velocity as UmbralRaptor points out. It's an interesting twist in the device because it makes every poorly-piloted tramp freighter a weapon of mass destruction and if the drive is only operated by a certain group they have a (E: different sort of) monopoly on force.

E: Actually, the more I think about it the more I think that would be a very interesting stardrive.

Edited June 18, 2015 by regex

[Zucal]

Motion within superclusters would be interesting, when you start thinking about what stuff like the Great Attractor would do with this system.

[Guest]

Okay, let me lay out some specifics. Let's say the drive has a maximum range of about 10 ~ 11 light years, can only be operated (jump in/out) around or outside the orbit of Jupiter (or a similar gravitational acceleration), preserves universal velocity vector on jump (aggregate), is expensive in materials, requires a large amount of infrastructure to manufacture, has a payload fraction of around 5% (drive + power system + fuel + radiators, not including crew, facilities, in-system drives, etc...), and generates massive amounts of heat on jump while requiring a lot of stored power to actually perform a jump (recharge, cooling time). Keep in mind to make a useful jump you need good knowledge of the destination and some good computers to calculate when would be the best time to jump. Existing radiator mass and payload fraction encourage in-system drives like a fission-fragment rocket or similar which would mainly be used for orbital correction while the craft is met by in-system craft for off-loading.

Obviously you're not going to be terribly inclined to use this as a weapon, although the option is very much there. Any other silly holes we can punch in it?

[TheSaint]

The only question you haven't answered is: How accurately can you place your arrival in the target system? If you're travelling over a distance of ten light-years, having a CEP (or in this case I guess it would actually be SEP) measured in AU would not be out of the question. (At lower levels of technology, some might call that "amazingly accurate".) It would also mean the difference between "I'm going to just drop my ship right into this nice tight little orbit here," and, "I'm going to plot my arrival in the Oort cloud to make absolutely sure I don't run into the red giant."

[Guest]

The only question you haven't answered is: How accurately can you place your arrival in the target system? If you're travelling over a distance of ten light-years, having a CEP (or in this case I guess it would actually be SEP) measured in AU would not be out of the question. (At lower levels of technology, some might call that "amazingly accurate".) It would also mean the difference between "I'm going to just drop my ship right into this nice tight little orbit here," and, "I'm going to plot my arrival in the Oort cloud to make absolutely sure I don't run into the red giant."

Great point. I suppose that really depends on computing power. Let's say that minimum SEP is 150,000km (1/1000 AU), at absolute best, and that a reasonable max SEP that any self-respecting captain would call a limit would be 1,500,000km (1/100 AU), with a good value considered about 200,000 ~ 300,000km (1/750 ~ 1/500 AU). This pretty much mandates that the carrier ship carry a maneuvering engine.

[Zucal]

Whatever its purposes, it'll be terrible for stealth if it generates that much heat on jump and moves at relativistic velocities afterwards as well. Secondly, this makes objects like rogue planets really interesting as an operating base, because they won't have a nearby gravity well to be attacked with or attack with.

[Rakaydos]

Whatever its purposes, it'll be terrible for stealth if it generates that much heat on jump and moves at relativistic velocities afterwards as well. Secondly, this makes objects like rogue planets really interesting as an operating base, because they won't have a nearby gravity well to be attacked with or attack with.

If you arrive more light minutes out than your drive's charge time, you dont need stealth. You sit there, watch, and before any of the enemy you can see (who obvously could not know you were coming) can reply even with lightspeed weapons, you tactically jump and go back to watching.

Larry niven had at least 3 fleets doing this at once in one of his later Ringworld books.

[Shpaget]

First you jump near your own star and let the gravity accelerate you to the relative 0 velocity for your destination (or whatever velocity you want to have upon arrival).

Then you jump to the other system.

[Guest]

That makes the charge time crucial in terms of using it as a weapon, which is fine. I hope it's sufficiently interesting not only as a means of transportation but also as a plot device. One of my goals of posting here was to see if there were any overt problems with the device in terms of realism (ignoring the fact that you're teleporting between stars).

You really have to know what the target system looks like to use it effectively, which means that probing target systems becomes a big deal if your computers don't know what to expect. I imagine early exploration was quite an experience and most likely done by automated science probes. Once again, charge time is crucial since you can reasonably expect a safe jump, given the operation parameters, but have no idea what to expect once you're there. So basically you'd send the probe on a good vector to place it into orbit of the target system, collect as much data as possible on possible jump destinations and anything that might cause problems, and hopefully be able to jump to relative safety before you actually do run into problems.

Ships with this device probably have Brayton generators, enormous radiators, a nuclear reactor of some type for initial spin-up (since you could use the waste heat for helping with recharge at the target), and high-isp maneuvering drives that require as little reaction mass as possible (like a fission fragment rocket).

I'm curious whether the consensus is that this would be a interesting drive for relatively low-tech space exploration where fusion power is still a pipe-dream.

[Scotius]

Fission fragment rocket indeed has very high ISP, but its thrust is minuscule. Your interstellar behemots would require much...heftier interplanetary propulsion. Maybe MHD plasma drive, or even fusion torch engine to give it half-decent acceleration and maneuverability.

[Guest]

Fission fragment rocket indeed has very high ISP, but its thrust is minuscule. Your interstellar behemots would require much...heftier interplanetary propulsion. Maybe MHD plasma drive, or even fusion torch engine to give it half-decent acceleration and maneuverability.

:ugh: I wanted to avoid that if at all possible, but you're probably right. I imagine these carrier ships as pretty much staying where they end up and instead bringing along riders or large cargo pods that would be handled by the more efficient in-system craft since the payload fraction is so small. In that sense they are true starships, rather than spaceships (is that a valid distinction?)

[Scotius]

I...don't think it would work. Reloading goods from a carrier to several smaller shuttles would be pretty labour and time consuming. It's better to bring that freighter down to space elevator station and gradually unload it there. If you really want to keep big ship in deep space, make it modular - a core containing engines, power plant, crew quarters and cargo containers surrounding it. Then you could send a fleet of interplanetary tugs (possibly with empty containers). Tugs would haul away full containers, clip empty to the core and carrier would be ready to go, while fleet of tugs would return to the planet with cargo.

[Guest]

Okay, let me lay out some specifics. Let's say the drive has a maximum range of about 10 ~ 11 light years, can only be operated (jump in/out) around or outside the orbit of Jupiter (or a similar gravitational acceleration), preserves universal velocity vector on jump (aggregate), is expensive in materials, requires a large amount of infrastructure to manufacture, has a payload fraction of around 5% (drive + power system + fuel + radiators, not including crew, facilities, in-system drives, etc...), and generates massive amounts of heat on jump while requiring a lot of stored power to actually perform a jump (recharge, cooling time).

I...don't think it would work. Reloading goods from a carrier to several smaller shuttles would be pretty labour and time consuming. It's better to bring that freighter down to space elevator station and gradually unload it there. If you really want to keep big ship in deep space, make it modular - a core containing engines, power plant, crew quarters and cargo containers surrounding it. Then you could send a fleet of interplanetary tugs (possibly with empty containers). Tugs would haul away full containers, clip empty to the core and carrier would be ready to go, while fleet of tugs would return to the planet with cargo.

That's pretty much what I was suggesting. I requoted the drive specifics since they are now important to the discussion. Given a payload mass outside of the interstellar drive of around 5%, I think these ships would end up being fairly massive on their own and would prefer to avoid maneuvering as much as possible since they would have to bring along enough reaction mass to do the job. This is one reason why I think fission-fragment rockets would be preferred for station-keeping/correction engines, especially since they already sport some massive radiators to handle all the heat they're generating already.

Hopefully I'm not digging a huge hole here, lol. If it's not workable, it's not workable.