FTL Assumptions [Space]

[Pomphis]

I decided to build FTL drives as in G:Traveller, simply so that I could use all the existing ship designs and the design rules. But they work differently. Jumps are instantaneous, drives need 1 hour rest between jumps, and jumps need jump fuel as in GT but do not comsume it. So I do not have the weeks in jump space /Orient Express situations, but I do have ships spending significant time in deep space where they can be intercepted or encounter stuff like wrecks or rogue planets. Jump Fuel is needed simply so that I can use GT ships, but it is not consumed so that ships have greater range.

Jump Limits are: Near Limit: Fourth Root of (object´s mass as multiple of earth´s mass) x 1 million miles, Far Limit: Fourth Root of (object´s mass as multiple of earth´s mass) x 1 AU

Solar system limit multiples: Sol: 24.1, Mercury: 0.48, Venus: 0.96, Earth: 1, Mars: 0.63, Jupiter: 4.23, Saturn: 3.13, Uranus: 1.96, Neptune: 2.04, Triton 0.24, Pluto: 0.22

Outside the Far Limit jump distance is 0.1 pc/JNo.
Between Near and Far Limit jump distance is square root of (JNo+sAccel) AU

This means ships need thrusters to reach Near Limit, then between 8 (J4M4) and 18 (J1M1) jumps/hours to reach Sol´s Far Limit, and then can go to 0.1 pc/JNo. In-System ships need J1, but ususally it is cheaper to increase sAccel than JNo to get greater in-system jump distances, so interstellar and interplanetary ships are designed differently. Pluto is an important spaceport. As it is outside Sol´s Far Limit interstellar ships can get really close at full speed and waste little time in in-system travel. Farports outside the local star´s Far Limit are common as interstellar ships can avoid days of in-system travel by using them.

Ships arrive at rest relative to the object exercising the greatest gravitational pull on the point of arrival, so surprise drive by attacks are not really possible. Attackers must accelerate towards their target and defenders have time to counter them. Also I don´t have to care about relative speeds/vectors of systems and planets.

[RyanW]

Originally Posted by Nereidalbel

And in a galactic version of the Geneva Conventions, it has been deemed that anybody employing such tactics will see every planet they own being sterilized immediately. MAD works, man.

MAD works when only megastates can play. When WMDs are available from every junk dealer on Tatooine, we'll see how well it holds up.

[naloth]

Originally Posted by Nereidalbel

And in a galactic version of the Geneva Conventions, it has been deemed that anybody employing such tactics will see every planet they own being sterilized immediately. MAD works, man.

If only the military had ships that might work. When anyone with a grievance and a ship can easily do it, you'll have individuals going postal in that way. People that don't care of they survive that want to hurt others will do so in the most flashy destructive way they can. It won't be a "civilized" warfare issue. It will be a civilian control one.

[copeab]

Ultimately, I prefer the stutterwarp drive of 2300AD as a FTL drive. It's a teleportation drive (cycling hundreds if not thousands of times a second). It has an effective velocity of up to several times the speed of light (0.5 ly/day for old commercial ships to over 4 ly/day for military couriers, with most warships in the 1.5-2.5 ly/day range). Despite this relative velocity, the drive produces no actual (felt) thrust, which means crews are either strapped in or floating in zero-G. One major limitation is that after travelling 7.7 ly, the ship must enter orbit around a world for 40 hours to discharge a static charge building up around the drive. Failure to do so causes a charge buildup in the drive that will melt it and produce radiation lethal to the crew).

Speaking of gravity, the drive only allows FTL speeds under very weak gravity (the asteroid belt and further out). Closer to the sun and it drops drastically, but still much higher than a fusion rocket. In a strong gravity well (planetary orbit) stutterwarp struggles to keep the ship in orbit (it is useless in landing or taking off from a world).

Combat isn't possible at FTL speed, as lasers and particle beams are too slow (although missiles have stutterwarp drives as well, their endurance if far below that of a ship).

[AlexanderHowl]

Originally Posted by Michael Thayne

This feels annoyingly arbitrary to me, though certainly it's necessary to avoid the problems ericthered points out. Personally, I'd rather use a square root, such that a small sphere's "hyperspace shadow" will have a radius less than that of the sphere.

A square root formula would work, it would end up creating a 57.4 AU hyperspace shadow for the Sol System. Of course, that much lead allows for a lot of acceleration...

[Humabout]

Originally Posted by AlexanderHowl

I have decided to share my assumptions about TL10 FTL travel. First, I assume that objects have a hyperspace shadow equal to the eighth root of the mass in Earths × 0.1 AU (creating a hyperspace shadow roughly equal to 0.1 AU for the Earth and 0.5 AU for the Sun). Second, I assume that hyperspace jumps only preserve sufficient velocity to maintain the orbit of where they are traveling to, with excess kinetic energy being transformed into electromagnetic energy at the point of origin (insufficient kinetic energy causes the hyperspace jump to settle in the appropriate orbit instead of the destination orbit). Third, FTL velocity is equal to square root of drives × 100c and FTL communications do not exist.

I am curious about why you decided on the eight root. That is a specific and odd root to use in general, but you may have reasons.

Also, have you noticed that using such a high root tends to make very small things have very big shadows and very big things have relatively small shadows? Frex, 433 Eros (1 billionth the mass of Earth) has a shadow 0.0076 AU (7.6% the size of Earth's); while R136a1 (the most massive star known) has a hyperspace shadow of 1 AU or 10 times that of Earth.

I'm not saying you're wrong to do this, but what's you're reasoning behind it?

Originally Posted by AlexanderHowl

So, what do you think? Do you use similar assumptions in your settings with FTL? If not, what assumptions do you use for FTL in your setting?

I use a penalty on Navigation (Hyperspace) based on how close to a solar-size mass the ship is at time of departure or arrival. So you could theoretically plop into LEO from halfway across the galaxy with enough skill, but it's really more suicidal than anything to attempt it.

This ends up covering both of your concerns simultaneously, while keeping the biggest cost of FTL travel being time. I allow spending Time Spent, but with a base of 30 minutes and distance penalties often being quite high, too, jumping is never fast, far, and accurate. Typical ships jump to the edge of a solar system and then execute a series of shorter jumps to close in on their destination before ultimately shifting to subluminal propulsion.

I do use the 'no FTL comms' assumption. I like preserving the pre-radio feel for interstellar distances and the time lag is a nice reminder that space is big.

[Rupert]

Originally Posted by Nereidalbel

And in a galactic version of the Geneva Conventions, it has been deemed that anybody employing such tactics will see every planet they own being sterilized immediately. MAD works, man.

That won't stop terrorists.

[Rupert]

Originally Posted by copeab

Ultimately, I prefer the stutterwarp drive of 2300AD as a FTL drive. It's a teleportation drive (cycling hundreds if not thousands of times a second). It has an effective velocity of up to several times the speed of light (0.5 ly/day for old commercial ships to over 4 ly/day for military couriers, with most warships in the 1.5-2.5 ly/day range). Despite this relative velocity, the drive produces no actual (felt) thrust, which means crews are either strapped in or floating in zero-G. One major limitation is that after travelling 7.7 ly, the ship must enter orbit around a world for 40 hours to discharge a static charge building up around the drive. Failure to do so causes a charge buildup in the drive that will melt it and produce radiation lethal to the crew).

Note that such a drive, as with many pseudo-velocity drives, can be used to build up huge real velocities over time. Let the ship fall, turn the drive on and fly out, let the ship fall...

[Rupert]

Originally Posted by Humabout

I am curious about why you decided on the eight root. That is a specific and odd root to use in general, but you may have reasons.

Also, have you noticed that using such a high root tends to make very small things have very big shadows and very big things have relatively small shadows? Frex, 433 Eros (1 billionth the mass of Earth) has a shadow 0.0076 AU (7.6% the size of Earth's); while R136a1 (the most massive star known) has a hyperspace shadow of 1 AU or 10 times that of Earth.

I'm not saying you're wrong to do this, but what's you're reasoning behind it?

I'm a fan of the cube root. For bodies of similar density, this gives a limit proportional to diameter. Less dense objects will have smaller limits than their size suggests. Thus is works roughly like Traveller, but with smaller shadows around stars and gas giants than Traveller assumes. As the tidal force from gravity varies as a cube root of distance, this can be used as the excuse - you can't jump (safely) when space is too curved.

I do use the 'no FTL comms' assumption. I like preserving the pre-radio feel for interstellar distances and the time lag is a nice reminder that space is big.

I normal use this too. However, I sometimes go with FTL comms being big, expensive, and finicky, requiring many relays, etc. Thus only major systems (and those between them that have relay stations) will have FTL comms, while poorer systems won't be able to afford them. Information will travel a bit like how it did when the telegraphs followed the railway network - fast along the rails, at the speed of a horse (or in this case, a spaceship) when off the lines.

This should still give the players a fair freedom of action within most systems, but will make it hard for them to outrun their reputations and (mis)deeds over the medium to long term.

[copeab]

Originally Posted by Rupert

Note that such a drive, as with many pseudo-velocity drives, can be used to build up huge real velocities over time. Let the ship fall, turn the drive on and fly out, let the ship fall...

That's the thing, it doesn't have any real velocity. You can't "build up" velocity with it.

If you are talking about falling from orbit, no, it won't work. It's going to fall at the same velocity whether it has a stutterwarp drive or fusion rocket with empty tanks.