Slow then FTL travel speeds

[jaz0nj4ckal]

Folks,
I am not sure if this is covered in any of the books, but I have drafted a solar system that has a few planets and moons within the 1-parsec hex. I need something that allows me to match slower then FTL travel speeds to ship size and engine rating. For example: how long would it take a ship to travel from Earth to Mars, is roughly 54,00,000 or 400,000,000 km depending on their rotation cycle.


Thanks!!!

 

[drkem99]

Reactionless thrusters (thruster plates or whatever you choose to call them) make excellent torchship drives and fully open a typical star system to STL travel. (In fact, per canon they permit long-duration STL travel between star systems. Many systems in canon space have been settled in just this way.) This Dropbox link is to a file that provides your answers and the simple physics formulas you need for calculation. It is from one of the original Traveller LBB. There is a great deal of value to a GM in the old Traveller materials; they are available and well worth purchase from: http://www.farfuture.net

Dropbox link: http://dl.dropbox.com/u/14464683/Answer.jpg
File will be hosted for 14 days; it's too big to upload here.
See copyright disclaimer below.

If your Traveller universe permits in-system jumps, then they generally will be the preferred mode of travel for trips taking longer than 1 week. Targets far out in the Kuiper Belt or Oort Cloud can exceed on-board life support. (Oops.) It is also educational to calculate your turn-around (peak) velocities and then read Nyrath's excellent Atomic Rockets site (specifically): http://www.projectrho.com/rocket/spacegunexotic.php#relativistic

Try not to damage too many planets.

Copyright disclaimer: This single page of material was reproduced for non-commercial use (to answer a rules question) and no challenge to copyright is intended. The Traveller game in all forms is owned by Far Future Enterprises. Copyright 1977 - 2008 Far Future Enterprises.

 

[jaz0nj4ckal]

Thanks for the link, but how do I know my ship's max. G- Acceleration? Does the ‘#-G’ category corresponds to the Jump Drive rating of the ship?

 

[renski]

http://www.nbos.com/products/astro/astro.htm

^ AstroSythesis allows you to construct star systems and calculate the time based on trust rating (1g = 1 thrust) among many other things, though its a little buggy and costs $34.95 US.

I personally found it very useful, but it takes a little getting used to.

Renski

 

[Rikki Tikki Traveller]

Thanks for the link, but how do I know my ship's max. G- Acceleration? Does the ‘#-G’ category corresponds to the Jump Drive rating of the ship?

No, for sublightspeed travel use the Manoeuvre Drive rating (M-Drive), not the Jump Drive. The M-Drive rating is in G's of acceleration.

 

[jaz0nj4ckal]

Thanks for the link, but how do I know my ship's max. G- Acceleration? Does the ‘#-G’ category corresponds to the Jump Drive rating of the ship?

No, for sublightspeed travel use the Manoeuvre Drive rating (M-Drive), not the Jump Drive. The M-Drive rating is in G's of acceleration.

Oh...ok I got you...I was over looking that!!! my fault.

thanks.

 

[far-trader]

You might find this page useful too:

http://www.cthreepo.com/lab/math1.shtml

The first formula calculator (Newtonian Constant Acceleration in g's.) is what you want for in-system travel. Just put int he Gs in the first box and HALF the distance in the last box and it will give you the time to the roll over for deceleration. Double that for total trip time.

Or use it for calculating a full thrust flyby (or intercept, like for missiles). Again just put in the Gs in the first box but use the total distance, the time will be when you pass (miss) or hit your target.

As a bonus it gives you the velocity (in the purple box at the end of the formula line), in case you want to calculate something like the size of the BOOM from the kinetic energy when it hits (you'll have to track down other calculators for that though).

There are formulas below that for interplanetary trips using M drives that account for relativity in case you need to do that. And other interesting and helpful formulas.

 

[drkem99]

Let's take a trip to Pluto as an example. (Be careful; there's an Imperial Research Station on Pluto.)

Minimum Earth-Pluto distance is 4.9 x 10 E 12 meters (roughly 5 billion km) according to Wolfram Alpha. We are in a 95 dT high-performance shuttle with a 5G maneuver drive. Our acceleration is thus 50 m/sec2. Using the formula in the file above, time (sec) = 2 x sqrt ( 4.9 x 10 E 12 / 50). It works out to 173.9 hours or roughly 7 1/2 days. Not too shabby; you can basically go anywhere in the system in a shuttle without using a jump drive (of course, trip time varies with relative positions of the planets, but this gives you the basic idea.)

There is a price to be paid for this type of easy in-system travel. At mid-point (where you turn and begin to slow down), your peak velocity is about 15,600 km per sec - or about 0.05 C (1/20th the speed of light.) A 1 gram speck of rock in your path will hit the shuttle with a force of 27 metric tons of TNT. Assuming a weight of about 700 metric tons for the shuttle, should some innocent moon wander into your flight path the shuttle will hit with an energy of 19 gigatons of TNT.

The entire "reactionless thrusters mean relativistic weaponry" discussion has been done to death over the years in many forums, and we should not reopen it here. Just keep in mind how big a crater one refugee from the enchanted land of nutjobs could blow in one of your campaign worlds with his starship.

Read more at: http://www.projectrho.com/rocket/spacegunconvent.php#id--Nukes_In_Space--Boom_Table

 

[far-trader]

Let's take a trip to Pluto as an example...

There is a price to be paid for this type of easy in-system travel. At mid-point (where you turn and begin to slow down), your peak velocity is about 15,600 km per sec - or about 0.05 C (1/20th the speed of light.) A 1 gram speck of rock in your path will hit the shuttle with a force of 27 metric tons of TNT.

True but let's not scare the gro-po pogs overly much

The odds of hitting anything in interplanetary space are incredibly remote. And Traveller (has in the past at least) includes some (largely undetailed, related to m-drive) form of hull effect to deal with radiation and presumably collisions with normal mircro-mass matter.

The entire "reactionless thrusters mean relativistic weaponry" discussion has been done to death over the years in many forums...

True again, though it will always be new to someone...

...and we should not reopen it here.

...but you have mate

I don't think it's a bad thing, as long as the flames are kept below a boiling point

I've always had handwaves to negate the threat of near-C rocks but a new (to me at least) one has just popped into my head. I should probably split it off into a new thread, but it's only just forming and needs more thinking. Basically limiting max speed to something reasonable based on local gravity. A built in maneuver drive governor if you will. One that is an effect of the gravity drive* itself. Something similar to the 100d precipitation effect on the jump drive. Such that as a grav drive nears a mass it brakes (possibly very HARD) to a limitation based on the local gravity. Anyone trying to approach at high velocity will find they run up against a wall before they hit the planet. So instead of a big crater the ship explodes (relatively) harmlessly, or is simply deflected, at some distance from the world.

You could still have terrorists, nut jobs, etc. doing serious damage by crashing a ship, but it wouldn't be multi-kiloton damage. And local defense forces in place might have a shot at stopping them before the impact.

...and I suppose it would be possible to ramp up a lot of speed and then shut down the drives, coasting at near-C and not having the drive governor effect. Of course (waving arms wildly... ) the drives could be such that if shut down the governor effect acts immediately canceling the ship's vector

* personally i think reaction drives need to be nerfed considerably for realism, at best they should be 10% the stated performance, and probably 1% would be better and still not that realistic, so instead of the table showing 1G etc. it should show 0.1G etc. or 0.01G etc.

 

[drkem99]

I tried, I just couldn't help myself. I knew it was a bad idea to start another Greenurple argument; I'll do my best to keep the flames to a minimum.

You are completely correct (at least in my opinion) that the drives need to be modified or hand-waved in some fashion to preclude relativistic weaponry. Nyrath quotes Jon's Law: "Any interesting space drive is a weapon of mass destruction. It only matters how long you want to wait for maximum damage."

I went around and around when I developed my current campaign trying to explain why planets, large highports, and other 'fixed' targets weren't slagged right and left during various conflicts. I finally gave up trying to fix reactionless drives. I ended up with a modified jump drive and fusion drives stolen from Attack Vector: Tactical for maneuver drives (with short-duration high thrust for combat and 'torchship drive' thrust in the 5 to 10 milligee range.) I use lower amounts of fuel for jump and a shorter duration of time in jump to compensate for the increased reaction fuel requirements and increased travel time to the jump points; this keeps the basic flavor of the game intact. The other effect of this change is that it shortens combat ranges considerably; I've ended up with something similar to the old 2300 AD where torpedoes and missiles are long-range weapons and beam weapons are used at close range and for point defense. It works for me. I know that the fusion drives are just as magical as the reactionless drives (high thrust, high specific impulse, and with operating temperatures that make stars look cool), but that's easier to ignore. YMMV.

At the end of the day, I guess it needs to make enough sense to you and your players to suspend the rest of your disbelief and enjoy the game. That's why we play it, after all.

Ah, another hijacked thread. Maybe we had better move this if the discussion is to continue.

 

[SSWarlock]

What I've always found to be a severe challenge is calculating the time needed to intercept another ship. Anyone ever come up with something relatively (no pun intended) easy/quick to use during play?

 

[drkem99]

I think all GM's have trouble with this; determining contact ranges and closing rates in space combat is one of the most difficult things in Traveller.

There are so many possible factors to be considered that I just don't see how a simple math formula will be helpful. First, where is the combat going to happen? Is the combat in the space equivalent of the littorals in the ocean - planetary orbits full of highports, habitats, shipyards, powersats and comsats, factory workstations, defensive satellites, etc? This is a situation where encounter ranges are likely to be close, relative velocities low, and the fight sharp and quick. Or, is it an intercept in open space (near a jump arrival point, for example) where the fight will develop over hours (since you can detect a starship a very long way away) and it will take time to close (like a graceful battle between two ancient, sail-driven men of war?) Is it a pursuit, but one with short firing ranges and difficult targeting (like a chase sniping at each other through the atmosphere of a gas giant during a refueling run?) Second, why is the combat happening? Does one ship want to disable and board the other, or are both ships out to kill each other? Is the attack a surprise? Is the faster ship the aggressor, with escape from combat nearly impossible for the pursued ship and the faster ship controlling the range? Is the lower thrust ship the aggressor, starting from an advantage in position or initial velocity, who hopes to damage or disable the faster ship before it escapes weapons range? Finally, does one ship have a major advantage over the other (one ship has vastly superior sensors or weapons, or does the ship that wants to engage has a high velocity relative to the other ship or a marked superiority in maneuver drive, for example). It would take a large computer program to take all this into account.

I have always felt that at the end of the day, Traveller is a roleplaying game and not a starship miniatures game, and that answers to the questions above in your story should determine the initial range and relative velocities. Combat should emphasize the roles of the players and not just their ship's design. To do this, I generally assess the above factors, generate some simple seat-of-the-pants modifiers, and then roll an opposed roll (pilot vs. pilot for short-range combat and navigator vs. navigator for long-range engagements.) I set the closing velocity (expressed in number of combat turns to minimum range) and initial range to one favorable for the winner of the roll, and then proceed to resolve the combat focusing on shooting and damage control rather than maneuvering. At that point, I think maneuvering is not generally a factor - both computers have solved the math and determined the optimum approach early on - although I do let good pilot rolls provide a negative DM on that combat turn to hit.

Honestly, there are as many ways to do this as there are Traveller referees. ;-)

Even if you use some form of miniatures rules to resolve the combat, the initial situation falls to the referee to determine. This is where GM's earn their keep and where good ones shine - creating entertaining game situations quickly without using slow, complex rules to generate answers. Trust your instincts, not your math. Your game will be better for it.