[Spaceships] Designing Hyperspace / FTL for space opera (and implications)

[Pragmatic]

I prefer a two-tier system.

A bunch of "wormhole"-connected systems, where travel takes a normal sublight engine. There may be anywhere from three to three-hundred systems in each "network," and any particular system may have one to five or more "wormholes." (More along the lines of the "Lost Fleet" universe than the "Starfire" universe. Not instantaneous like Starfire, but not as long as the Lost Fleet.)

And a "jump drive" that allows jumps of medium-range distances, taking about a week. (Think "BattleTech" or "Star*Drive.")

Thus, stellar empires will tend to grown quickly through the "wormhole networks," but there's the possibility of "jumping" to a nearby network. "Jumpships" would have to carry additional systems (batteries and jump drive and what-not), so would either have unarmed "carrier" ships, or weak combat capabilities.

[Pomphis]

Originally Posted by Molokh

I also found that Reactionless drives seem too cheap/efficient/fast-accelerating on average when compared to Reaction drives of the same TL.

I'm not sure I 'get' what is so special about the Probability Drive.

a) Yes. But have you actually run the numbers for interplanetary trips with reaction drives ? We are talking months.

b) Only that it is a canonical jump drive that does not need jump points.

[weby]

In my own scifi setting there are actually 3 types of FTL travel in use.

The normal travel distances are quite long with distances of hundreds of pc between inhabited worlds being normal.

Jump gates:
These are huge structures consisting of huge powerplants and capacitors due to high power requirement. They allways work in pairs and have a 30pc maximum range. The need to have the large gate at both ends makes these the feature of the "main routes" where they are in chains.
Benefits:
-Move to target instantly
-No FTL drive needed in the ships traveling
Disadvantages:
-Need the huge structures. (Smallest possible gates are 20 000 tons)
-The huge energy demands put a limit on mass transmitted at one time and mass transmitted over a given time period for given gate.

Warp(microjump) drives:
Are the drives used by most exploration and military craft. They are bulky,heavy,Very expensive and very mass sensitive but capable of moving the ships at 5pc/day(typcical heavy warship) to 20pc/day(fast courier/scout).

Also used in the main ship to ship weapons as that is the only thing capable of catching a warp drive ship..

Benefits:
-Move fast where there are no gates.
-Huge combat advantages from ability to move at FTL speed in combat.
-Can operate at FTL speeds anywhere outside atmospheres.
Disadvantages:
-Require huge machinery(about 20% mass for a heavy warship 80% mass for a fast courier)
-Very expensive due to manufacturing difficulty.

Hyper drives:
These are used by everything else. They are small(typical requirement 0.2-1% of ship mass) and fairly cheap. They can move ships at 0.2pc/day to 1pc/day depending on the generation of the drive. They cannot be used close to large masses.

They are used in places where the gates do not go and for bulk non persishable cargoes even along gate routes as transporting things that way basically costs nothing except time.

Also most military craft have hyper drives as backup and even military smallcraft routinely have hyperdrives.

Benefits:
-Very Cheap
-Does not take much space/weight.
Disadvantages:
-Slow
-Easy to track. The source and target vectors of any jump is detectable for weeks afterwards in most cases from quite far away. (Military craft, pirates and smugglers can activate several hyperdrives at same time confusing the track a lot, making it very hard, but not impossible)
-You cannot change destination or see outside when traveling. (Though you can drop out of hyper anywhere along the plotted route)

FTL communication along the Jump gate route is very fast. The gates have constant high bandwith link between them. Thus messages travel at maybe 300pc/second along such routes.
Elsewhere the speed is slower:
-the high bandwith communications and imaging FTL radar travels at 10pc/day
-Low bandwith communications and FTL radar travels at 30pc/day.

The low bandwith communication is basically only good for simple text messages(think telegrams). The high bandwith is enough for several channels of HD video.

FTL communication ranges are long though, a (large)backpack sized communicator can reach 100pc(high bandwith)/1000pc(low bandwith) shipboard systems way further.

[vicky_molokh]

Originally Posted by Pomphis

a) Yes. But have you actually run the numbers for interplanetary trips with reaction drives ? We are talking months.

But they have unlimited delta-V. They're a better investment in the long run. Thus they should somehow be worse elsewhere. As of now, they aren't terribly expensive, yet they seem better than reaction drives in all areas.

[David Johnston2]

Originally Posted by Molokh

But they have unlimited delta-V. They're a better investment in the long run. Thus they should somehow be worse elsewhere..

Not really. They're superscience. They don't exist as an alternative to more realistic drives, but as a replacement for them.

[Ulzgoroth]

Originally Posted by Molokh

But they have unlimited delta-V. They're a better investment in the long run. Thus they should somehow be worse elsewhere. As of now, they aren't terribly expensive, yet they seem better than reaction drives in all areas.

Reactionless drives are generally going to blow high-impulse reaction drives away unless you make them have significantly lower acceleration, or very expensive, because even high-impulse rockets almost never can have as much impulse as they'd like.

High thrust is another thing, though. A high thrust water-burning fusion torch gets 3g per system. The delta-V is a bit limited at TL10, but the thrust ratio is hard to beat (you'd need a high-thrust Orion or a high thrust water-burning antimatter plasma torch).

Since high-impulse is usually what matters for trade, the only place I can see fusion torches beating any kind of reactionless much is for ships that need planetary take-off capability.

[thtraveller]

Originally Posted by Pomphis

a) Yes. But have you actually run the numbers for interplanetary trips with reaction drives ? We are talking months.

Maybe for the outer planets at low TL. You can do Earth-Mars in 5 weeks at TL9 http://forums.sjgames.com/showthread.php?t=56322

[Kelly Pedersen]

I'm designing a space setting for my next campaign, so these are questions that have been on my mind lately. :-)

Originally Posted by Molokh

For one, 'lighter' space games (such as space opera) should probably avoid scenarios where a one-hit kill will destroy a civilizations. Thus, fast sublight drives should be out of the question.

The problem with this is that it tends to make the solar system too huge. Without high acceleration and high delta-v ships, trips to other planets take months or years. You're left with a scenario where either there's only one "interesting" planet per system, or else using the FTL drive for pretty much all travel, with drives confined to maneuvering. Neither is a result I like, personally.
The suggestion to use pseudo-velocity can help, of course, but pseudo-velocity has its own issues for me - I don't like the image of space combat it creates, with ships stopping instantly when they hit a pebble, or colliding with each other without effect.
In my setting, I'm using reactionless thrusters, but I'm also allowing force screens. I'm just assuming that anything too big to dodge a relativistic rock will have extensive force screens in an anti-kinetic "Whipple" configuration, capable of stopping most impactors.

Originally Posted by Molokh

Jump gates are even worse in terms of blockades, as they can be powered down if needed . . . or sabotaged by jumping a bomb from the other side, if their mechanism prevents shutdown somehow.

On the other hand, jump gates do have some advantages for a space setting. They essentially provide space with more "terrain" - jump gates are the Thermopyleas and Straits of Malacca of space. They provide dramatic potential for players to guard, to sneak past, to get stopped at for customs, etc. etc. Of course, it's true that if they're too easy to interdict, things get boring. In my setting, I'm making some asssumptions about jumpgates:

• Jumpgates are expensive - it takes the resources of a major industrial nation to build one. So there are major disincentives to just destroying one to prevent an attack.
• They're not easy to open, once you shut one down. It takes a lot of exotic matter to restart a shut-down gate, taking about 5 years to collect. Again, a disincentive to shut down a gate to avoid an attack.
• Gates are "one way". If you have an active gate, you can go to the destination, regardless of whether there's an active gate at the other end (an active gate at the other end just lets you get back). So, destroying a gate in your system doesn't prevent an invaison anyway - you have to destroy the gate on their side.
• It's not necessary to go through the physical gate to make use of the wormhole. A gate "weakens" space in an volume within 100,000 miles of the physical terminus. Reactionless drives, which operate on a similar principle to the jumpgates, can be manipulated to punch through into the wormhole(called "gatecrashing"). You have to make a skill roll, unlike just going through the physical gate, but it lets smugglers, invading fleets, pirates, and various and sundry others go through without having to crunch down to such a narrrow area.