Problem of math

[Umbran]

From the center of our system to the outer reaches of the Oort is about 1.5 LY. I would presume that AC has about the same around it though I have no time to research it right now- sorry, typing one handed while rocking a baby.

Ah, I gotcha. I usually only see things within the bounds of the Kuiper Belt (out to 50 AU) to be called "in the system".

I require nothing of no one. I ask that you be kind, and respectful, but its not a requirement.

My apologies - I was just using your own words: "I still have some campaign ideas that would require the PCs to travel some 60,000 AUs"

As far as why- there is a mega plot element out there, and I would rather not give it away before I use it.

Well, please allow me to rephrase. Can you tell us why that plot element is out at 60,000 AU? Why specifically that distance, roughly one lightyear from the star? Is the number really important, or can you define it as "far, as the PCs measure travel"?

I tend to follow a simple design philosophy - which is to not overspecify. Otherwise, you get things like this, where you are designed into a corner, and need to come up with ways to work around your earlier definitions.

You are not working in the Sol system. You are not fixed to the numbers we have here. You are able to put planets and objects wherever you like, within some broad limits for verisimilitude. Rather than define your positions, and then try to figure out how to make travel times work out, why not figure out your travel times, and then place the objects where you want them to be?

Following Sol as a very rough model: We could say that you've got a couple or few really useful planets within 2 or 3 AU of the star. The longest distance between these will be 6 AU or less. Decide how long you want them to take to travel between these objects. You'll then have other objects scattered from 3 AU out to perhaps 30 AU (Neptune's orbit-ish) or 50 AU (the outer edge of the Kuiper Belt).

a) If inner-system travel is in terms of days, travel out to the outer system will probably be on the order of weeks, or tens of days. (You seem to think this is a bit fast)

b) If it takes a week to get across the inner system, it'll take two or three months to reach the outer system. (From the sound of it, you probably want this option)

Now, decide how long you want them to take to get to this distant plot element. That'll give you a distance. If they can travel one AU a day (they take a week to get across the inner system, and a couple months to go one-way from the inner system to the outer system), and you want one way travel alone to be a year, the object is out around 300 to 400 AU. For the Sol system, that'd be out far beyond the Kuiper Belt, beyond anything folks would call "in the system" from a practical day-to-day point of view.

 

[Pbartender]

~Stuff that I generally agree with.~

This reminds me of an anecdote about J. Michael Straczynski... whenever someone asks him how fast any specific spacship in Bablylon 5 can go, he always replies, "They travel at the speed of plot." In other words, if it helps the storyline that the ship should arrive in time, then it does. If the plot is better off having the ship get there later, then it does. The ship arrives at the dramatically appropriate time... Specific speeds and distances, aside from "fast", "slow", "far" or "nearby", aren't necessary.

In other words, and taking J. Michael Straczynski's advice to heart...

Harmon's players: "How far away is the Distant Plot Element?"
Harmon: "It's about three plotlines away... It might take you a few months to get there."

 

[Someone]

I don't think I've seen it proposed in the thread, but one alternative is acceleration.

In space you don't need a very good push to archieve very high speeds. Since there's no friction that opposes movement any force causes an acceleration. Speed keeps building and you get as much speed as you want, as long you wait enough for it. Obviously, the stronger the force (the push) the better, but remember that it's possible to archieve great speed without a very potent rocket.

Also we all know that once you have that speed you want you can just disconnect the engines and the ship will keep it. (Of course, we're not taking planetary masses into consideration here)

Now, atmospheric flight is a horse of a different color. Air friction builds very quickly with speed, and is a force that opposes movement. As your speed increases, so does friction: once the braking from he air equals the push from the rocket, the net force on the ship is zero, and there's no more acceleration; your speed does not increase. To get more speed, you need a more potent engine. I know nothing of plane construction, but most probably atmopsheric fight at high speed also requires an specific structure.

Now, suppose you have two alternatives with engines. One can give a strong acceleration, but can work for small amonts of time beacuse it burns a lot of fuel. The other engine can work for, in practice, unlimited amounts of time, but the push is smaller. In interplanetary flight, the second can be preferred, depending on the actual numbers (and notice that you would need to start deccelerating [/i]at mid point of the travel[/i]. The constant force applied would also provide artificail gravity, so this is a good option if you want to keep your game relatively low tech)

If you go with the "actually, engines in ship are less potent than you imagine" option, you also will need a way to scape from the planets' gravity well, like a space lift connected with a space port or shuttles.

 

[Pbartender]

The other engine can work for, in practice, unlimited amounts of time, but the push is smaller. In interplanetary flight, the second can be preferred, depending on the actual numbers (and notice that you would need to start deccelerating [/i]at mid point of the travel[/i]. The constant force applied would also provide artificail gravity, so this is a good option if you want to keep your game relatively low tech)

If you go with the "actually, engines in ship are less potent than you imagine" option, you also will need a way to scape from the planets' gravity well, like a space lift connected with a space port or shuttles.

While I didn't specify, this is generally the idea behind the "fusion ramjet" idea I posted above... A constant, steady, but relatively low acceleration for long-distance travel.

 

[Someone]

While I didn't specify, this is generally the idea behind the "fusion ramjet" idea I posted above... A constant, steady, but relatively low acceleration for long-distance travel.

Sorry I missed it.

Or you could use ion engines, the concept being equivalent.

 

[Pbartender]

Sorry I missed it.

Or you could use ion engines, the concept being equivalent.

Yep... The benefit of the ramjet, pseudoscientically speaking, is that you don't have to worry (quite so much) about fuel... you just scoop it up as you go along.

 

[Umbran]

Yep... The benefit of the ramjet, pseudoscientically speaking, is that you don't have to worry (quite so much) about fuel... you just scoop it up as you go along.

The other "benefit" of the ramjet, psudoscientifically speaking, is that you can work it well into the plot needs for havign differnet drive systems in different situations. For example:

The ramjet may function in the outer reaches of a gas giant's atmosphere, but it is easy to stipulate that the field breaks down when submitted to a density you'd call breathable. Or that it chokes when you feed it anything more than trace amounts of stuff other than hydrogen and helium. Or they tend to cause lightning strikes on the ship if you try to use them in an atmosphere...

However you do it, making it space-specific is pretty easy.

Or, you could just have ships using Orion drives - now there's a drive you don't want to use in the atmosphere of a habitable world.

 

[Jim Hague]

[PSEUDOSCIENCE=TECHNOBABBLE]
The Fusion Ramjet[/PSEUDOSCIENCE]

Woohoo, the SHARC Drive - Stellar Hydrogen Accumulator, Redirecting Collaminator! Requires constant motion to keep going, dies if it's slowed down...

Hey, what if you set up 'SHARC nets' - EMP 'mines' that disrupted the EM fields that powered a SHARC? Military or former military weapons, now sold on the black markets by unscrupulous supply folks...useful for piracy.

Just throwin' the idea out there. I really can't compare to PBartender's grasp of science, but my Rubber Science lingo's generall pretty good... Heck, Harmon, if you or other folks don't use it, I'll just keep the idea for myself.

 

[Pbartender]

The other "benefit" of the ramjet, psudoscientifically speaking, is that you can work it well into the plot needs for havign differnet drive systems in different situations. For example:

The ramjet may function in the outer reaches of a gas giant's atmosphere, but it is easy to stipulate that the field breaks down when submitted to a density you'd call breathable. Or that it chokes when you feed it anything more than trace amounts of stuff other than hydrogen and helium. Or they tend to cause lightning strikes on the ship if you try to use them in an atmosphere...

...Or the overload of fuel tends to make them explode?

Woohoo, the SHARC Drive - Stellar Hydrogen Accumulator, Redirecting Collaminator! Requires constant motion to keep going, dies if it's slowed down...

I kind of like that.

Hey, what if you set up 'SHARC nets' - EMP 'mines' that disrupted the EM fields that powered a SHARC? Military or former military weapons, now sold on the black markets by unscrupulous supply folks...useful for piracy.

Better yet, you simply use a fusion ramjet to scoop away all the available fuel within a given volume of space -- these things will need to scoop in interstellar hydrogen and helium from a swath several light seconds or light minutes wide in order to collect enough fuel. Ramjet passing through the area before it filled itself back in would suddenly die out.

What's more, a persuing ship would have to be careful not get caught in the tracks of its prey, lest they get the wind taken out of their sails, so to speak... A lead ship would leave a tunnel through the interstellar medium, with a thin, concentrated, but slowly expanding, trail of ionized/plasma exhaust down the middle of it. If you're not careful, a trailing ship could get stuck in the empty tunnel, without an operable ramjet.

But remember... Just because the ramjet dies out, doesn't mean you're dead in the water. You still have your forward momentum, and you still have any other drives and maneuvering you'd have available. You just lose the big, long-lasting efficient engines is all. You use your thrusters to get out of the dead zone, and fire up the ranjet again.

 

[Jim Hague]

So, riffing on the pseudoscience - what happens if you introduce heavier elements than hydrogen to the ramjet? Say, iron?