Jump to content
Sign in to follow this  
Sebastian Yorke

Real space travel time

Recommended Posts

Usually while reading the pre-made adventures and endeavors, there will be noted that in-system travels from a jump point to a planet can take weeks sometimes.

 

Considering the group's colony and other endeavors depending on the passing of time, I think it's important I keep a track of time passed, specially since the individual PCs can also use that time stuck in the ship (Master of Whispers can solidify his networks inside the ship, AdMech have time to do crazy stuff with a manufactorum or lab, etc...).

 

Warp travel time is fine, perfectly described in Navis Primer with all I need to know.

 

But, I can't find rules for Real Space travel time, are there any? Anywhere? Did I miss something?

Share this post


Link to post
Share on other sites

Well, there is no such item as "max speed" in space when you have kind of unlimited power, anti gravity (so you can not to worry about acceleration compensation) and A MASSIVE VERY POWERFUL FUSION TORCHES. Ahem. Sorry. So you're limited by acceleration. Saber can get 4.4G, so to take light speed you need ((300000/(0.001*4.5), and it's kind of 2 years, gravitational maneuvers not included. Luckly, you have warp drives, so light speed rarely can be useful. With limited speeds you can travel in system with some good speeds on modern spacetravel technology, yet.

So I believe times as "some days on Mars, kind of week to the warp point" is good. Yeah, it's a kind of magic.

Share this post


Link to post
Share on other sites

I would just wing it, maybe have them roll a Scholastic Lore (Astromancy), Trade (Voidfarer) or Operate (Voidship) as they steer the ship or calculate trajectories for optimum usage of nearby planetary gravitational wells and so on, adjusting in-system travel from between a week (planet-to-planet) to one or two months (travelling cross-system or out of the system) based on that.

 

I realize that that might not be too helpful and that you want a clear answer, but I don't think there is one. Different ships will probably differ wildly depending on model and make and how much they want to push their engines and plasma generators.

I would say that if it's really necessary, the tech-priests should be able to pull overtime and with tech-use tests boost the engines similar to the shipboard actions in combat, making the maximum speed of any ship being able to leave a system within a week, during particularly panic-inducing events.

There's a lot of opinion and personal perception in this, so make of it what you will.

Share this post


Link to post
Share on other sites

I'd note that if the players have a colony and you're tracking time spent, then you'll probably want to modify some of the colony rules.

 

By the book you roll for colony changes every 90 days. Considering that 1 day of warp travel is on average 12 real-time days (RT book, page 184), that leaves the characters 7.5 days of warp travel. That's for both there and back, so realistically about 3 days of warp travel out, then 3 days back.  That's not a lot of time. Most warp travels take weeks.

 

Now a colony size change doesn't always occur, and the characters can use Background Endeavors using the colony governor. But even so the rate of change is rather drastic.  If the governor fails it could be a couple more "cycles of change" before the characters get back to their colony and by then it's too late.

 

I've seen it mentioned elsewhere in these forums that it's probably a good idea to change the rate at which colony changes to every 1 year. That also makes it line up better with the rate at which Resource depletion happens (SoI book, page 28).  Personally, I also think a year is just a more realistic amount of time for a colony (potentially) changing size.

Share this post


Link to post
Share on other sites

Thanks for the feedback, I will probably reach a house rule line at some point.

Like, depending on the Star you get different jump-point distances from the farthest planetary body, and between each planetary body you have a distance of "1" or "2", and then I will sum stuff together, divide by Speed and reach a house rule for how many weeks a real space travel takes.

 

Once I have it, I will post it here or in House Rules.

Thanks for the feedback guys.

Share this post


Link to post
Share on other sites

I use 1-2 weeks to travel between stellar zones.  Usually a few days to a week between planets in a stellar zone. 

 

I use a number of house rules for colonies, including one year per cycle.  It works out a lot better.  My players also leave the materials for Infrastructure Upgrades in their colonies in case the colony grows while they are gone.

Share this post


Link to post
Share on other sites

I use a number of house rules for colonies, including one year per cycle.  It works out a lot better.  My players also leave the materials for Infrastructure Upgrades in their colonies in case the colony grows while they are gone.

1 year sycles make much more sense indeed.

Share this post


Link to post
Share on other sites

I think an important limitation to keep in mind regarding travel speed in real space is that whatever speed you manage to crank up to you have to take about as much time to slow back down or you'll just blow past your destination. I don't remember where but I believe they actually stated so in one of the books somewhere or at least they should have if they didn't.

 

In any case for practical purposes space ships should fly at the speed of plot but there should be consistancy, well except when dealing with warp travel in which case you should avoid consistancy. I've been working with the assumption that flying a frigate from Sol to Pluto in real space would take a week and I just sort of bull all my other travel times from that starting point.

Share this post


Link to post
Share on other sites

1g = 186,471 miles per second (aka light speed).

Pluto is 29 AU from Earth, approx 2.75 billion miles.

A Meritech Shrike-class Raider is capable of 5.9g max sustainable acceleration. That's right at 1,100,179 miles per second.

Under normal mass-reactive drives (non-Warp), the Meritech can travel from Earth to the outer reaches of the system in approximately 2499. 6 seconds, or just over 40 minutes.

Uh-huh, sure. Obviously you'd wanna reserve that kind of burn for the wide-open void.

 

Methinks the "fluff" of vessel speeds/accelerations is based on out-of-my-ass science.

 

Anyway...

It took the Apollo launches approximately 4.5 days to reach Earth's moon (236,121 miles).

The return trip (on average) took a little less than half that time.

At Apollo speed, it would take approximately 31.7 years to reach Pluto. 

 

By using Apollo as a benchmark, you could say in-system travel takes less time, because the vessel would be aided in its approach by the system's gravity well, and out-system travel takes more time because the vessel's drives work harder to escape the system's gravity well.

 

The average between the two extremes is (calculates some out-of-my-ass math) 93.4 days from Earth to Pluto, 46.7 days from Pluto to Earth. Cut that by a third for Imperial mass-reactive drive tech and safe piloting (we don't want to scuff the surface of Mars) it would take a month to travel out-system to a suitable jump point, and 15 days to travel in-system from point of translation.

Edited by Brother Orpheo

Share this post


Link to post
Share on other sites

I thought 1g was relevant to earths gravity and not the speed of light?

Edit: I'm not saying I don't agree with you. I do, whole heartedly. But I'm not a math genius so I'm just going to hand wave it like you mentioned. I mean heck, the person in charge sits on a Golden Throne powered by human sacrifices, daemons can actually kill you, and humans use flying cities traveling in another dimension to commonly get around. ;)

Edited by Nameless2all

Share this post


Link to post
Share on other sites

g is gravitational acceleration, not light speed (which is c).  Remeber that g is a unit of acceleration (9.8m/sec/sec), not speed.   If you were to accelerate constantly until halfway, and decelerate the rest of the way the following formula would give you travel time:

 

Time=2*Square root of Distance      

                                     Acceleration

 

For a trip of one AU at 1g that works out to 68 hours.  That should be equivalent to traveling from Primary Biosphere to Inner Cauldron.  Travel further out in the system has longer distances, and orbital position can easily double that again.  I assume that most RTs aren't going to be doing max accleration the whole time and instead allow orbital mechanics and momentum do a lot of the work for them (as we do now).  Long burns like that are both hard on the drives and very expensive in terms of fuel.  In an emergency you can do a pretty much straight line, full burn, trip to the Earth from the Kuiper Belt on the outer edge of the system in 230 hours (in your Sword class Frigate, accelerating at 4.5g).  Note that you will be doing about 10% of light speed at midpoint transition.  Even a single such maneuver would probably exhaust your ships fuel reserves, if they even lasted that long.  The exact distance for transition from the Warp is a little fuzzy, so I expect it is less than that.

Share this post


Link to post
Share on other sites

1g = 186,471 miles per second (aka light speed).

Pluto is 29 AU from Earth, approx 2.75 billion miles.

A Meritech Shrike-class Raider is capable of 5.9g max sustainable acceleration. That's right at 1,100,179 miles per second.

Under normal mass-reactive drives (non-Warp), the Meritech can travel from Earth to the outer reaches of the system in approximately 2499. 6 seconds, or just over 40 minutes.

Uh-huh, sure. Obviously you'd wanna reserve that kind of burn for the wide-open void.

 

Methinks the "fluff" of vessel speeds/accelerations is based on out-of-my-ass science.

The vessel speed/accelerations are certainly pulled out of thin air, but so's the stuff above. Sorry.

 

1g is an acceleration of 9.8 m/s^2. Light speed would be 1c.

The whole point of Warp travel is that without it, faster-than-light movement is not possible. Indeed omce you pass 0.01 c relativistic effects become large enough that you can't just ignore them.

 

Even worse, starships in RT do not move according to real life physics. No-where near it.

Remember, this is a game company where double digit subtraction is considered "hard math" to be replaced with single digit subtraction in their next game, and we're playing a game where the space combat is explicitly  designed to resemble BFG which was explicitly inspired by WWI-era naval battles (IIRC).

So ships are instead given a speed stat. This is rules - the max accel is purely there for fluff.

 

Ofcourse, this speed stat is in arbitrary units, but they do kinda suggest that a VU is about 10k kilometers.

From this and some back of the envelope math, you'll get that it takes a speed 10 raider about 2 weeks to move from earth-orbit to pluto-orbit at max speed (unless I dropped a zero somewhere, which is entirely possible).

 

But please, keep real physics out of this! And I say (write, technically) as a trained physicist.

Whatever did real life physics do to you to get into this setting? About the only thing acknowledged is the hard limit of light speed.

Edited by Tenebrae

Share this post


Link to post
Share on other sites

Weeks to get from a planet to the jump zone is just kind of ridiculous given fusion-powered ships. 

 

I wouldn't worry about it unless the plot requires something to happen en route to the jump, or between jumping in and making the planet. The rest I'd hand wave because it's likely not very interesting to play that out over and over.

Share this post


Link to post
Share on other sites

Weeks to get from a planet to the jump zone is just kind of ridiculous given fusion-powered ships.

Not so sure about that.

 

Let's ignore my post above, and use slightly more realistics physics.

 

Pluto Orbit is an elipse, with a minor axis of about 30 AU. Since an AU is just over 8 light-minutes, that makes 240 light-minutes to Pluto Orbit. Actually closer to 250 to be honest, but who'd counting.

 

240 minutes is 4 hours.

 

Let's assume we don't want to go faster than 0.01 c. Why not? Because that would mean relativistic effects became non-negligible. Why would this be a problem? I could easily see the Imperium as having lost the ability to perform the calculations to take these relativistic effects into account and then simply observe that "When we go faster than this, things don't work out the way they should - clearly doing so angers the machine spirits!"

But to be honest, I'm really just too lazy to even bother with a relativistic model.

 

So, at 0.01c, it takes us 400 hours to travel 30 AU, that's just over 4 days of constant travel at 0.01 c, with no acceleration or deceleration. To reach the closest point of Pluto Orbit.

Since the major axis of Pluto Orbit is about 49 AU, making it about 7 days.

 

Still not several weeks, but remember that we've ignore acceleration completely.

We could do a model based on constant acceleration, but that sort of thing would be horribly expensive in fuel (see "Rocks Are Not Free") and I'd need to take into account the general theory of relativity as well as the differential equation that gives us our max acceleration, since that would depend on the mass of the fuel in the tanks. And personally, I can't be arsed to do neither. Feel free to post the results if you do though :)

 

But the real kicker is that we have no idea how far out the jump zone is!

Some fluff-authors seem to think it's just about means you need to clear the atmosphere, while others indicate that it is so far out-system that the "gravetic influence of the star is negligible."

I personally like to use Pluto Orbit for back-of-the-envelope calculations like these, because it's a number and we can certainly know that the gravity well of our sun still matters at that distance. For all I know, the jump limit is even further away.

 

Further more, if the jump distance is based on gravity, it should scale with the mass of the star, and Sol isn't exactly a big star.

 

I wouldn't worry about it unless the plot requires something to happen en route to the jump, or between jumping in and making the planet. The rest I'd hand wave because it's likely not very interesting to play that out over and over.

I have found a few uses for it.

First of all, it means that wounds inflicted while the characters are in the Goldylock-zone will be fully healed* by the time of the Warpjump - so we don't have to worry about that.

 

But more importantly, it isolates planets far more, especially those planets that are visited by only a few ships. This gives me a far darker feel, that works better for me.

 

 

 

* Unless extra bad

Share this post


Link to post
Share on other sites

I have found a few uses for it.

First of all, it means that wounds inflicted while the characters are in the Goldylock-zone will be fully healed* by the time of the Warpjump - so we don't have to worry about that.

 

But more importantly, it isolates planets far more, especially those planets that are visited by only a few ships. This gives me a far darker feel, that works better for me.

 

 

 

* Unless extra bad

 

 

The gentle, pleasing exit from a system is very important for the healing reason. Also the isolation matters because it is entirely possible when facing off a planetary engagement in a system with multiple planets that if you screw up deployment of forces, you could be forced to listen to a planet burn over the course of days from an Orkish Waagh before you can do anything to get there. Or you can try to travel there and hope your forces can hold on, only to realise that the enemy was moving on your planet and you didn't detect them in time. 

 

My quick and fast method for determining "distance" in a system is based on the Stars of Inequity classification of Outer Reaches, Primary Biosphere and Inner Cauldron.

 

Travel to anything within the same zone takes 1d5 days. Travel from one zone to another takes 1d10 + 1 days. Travel from anywhere in the Outer Reaches to the nearest Warp Point takes 1d5 days. If there are gas giants or gravitational anomalies, then the crew can attempt daring piloting manoeuvres to try and go faster. 

Share this post


Link to post
Share on other sites

Tenebrae, thanks for breaking down the real world physics. I really do find that stuff interesting. I just don't think it has a place in the in-setting considerations, I think it really overcomplicates things too much, and I don't think it's very fun for travel to the jump point taking potentially just as long as the warp travel to go partway across a sector. 

Share this post


Link to post
Share on other sites

Well, continuous acceleration is listed for the ships. Assuming straight line acceleration and decelaration, you can figure out a rough set of times for different values of acceleration. Most escort warships can burn at about 5G, merchants and capital ships about 2G.

 

 

I've got a table of transit times; worked out standing start, accelerate, turnover at 50% distance, and decelerate to rest. No account of relative orbits, but for high-speed manouvres like that you can ignore it in the noise - the difference in transit time for a 2.3 G ship to a 2 G ship is significantly more than the difference between taking into account orbital speeds and not doing.

 

 

That said - some data compiled for another science fiction game, but perfectly useable in Rogue Trader as narrative fodder:

 

Low planetary orbit to moon (Terra-Luna, ~400,000 Km)

2 1/2 hours @ 2G or 1 1/2 hours @ 5G

 

Transfer between close planetary neighbours (Terra-Mars, 45,000,000 Km)

26 hours @ 2G or 17 hours @ 5G

 

Transfer from planet to low solar orbit, or 1 AU above planet (Terra-Sol, 150,000,000 Km)*

2 days @ 2G or 30 hours @ 5G

 

Transfer from planet to gas giant orbit (Terra-Jupiter, 600,000,000 Km)

4 days @ 2G or 2.5 days @ 5G

 

Outer Reaches of System (Terra-Neptune, 1,000,000,000 Km)**

5 days @ 2G or 3 days @ 5G

 

* Dangerous-but-workable warp jumps at this point. Certainly warships with skilled navigators would risk this.

** 'Normal' warp jumps at this point, especially chartist merchants with no navigator.

 

Based on an unscientific divvy-ing up, that means a destroyer (fast warship) can make warp within 30 hours of breaking orbit, a cruiser (slow warship) about 2-4 days and a merchant about 5 days.

 

I quite like meaningful transit times, as it does make a faster ship genuinely 'faster' - rather than just being a means of carting the guy who makes Navigate (Warp) checks around.

Edited by Magnus Grendel

Share this post


Link to post
Share on other sites

I find all these numbers great in fact, my players are always using the spare time while in travel to do things around the ship (Explorators specially, but AM might sometimes start building an arena with gladiators and everything).

I also like to roll on random encounters sometimes (like setting a serial killer lose on the officer decks, or get them a Dark Heresy-like group roaming around the crew).

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

×
×
  • Create New...