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Void travel time


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#1 Red Bart

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Posted 03 April 2012 - 10:28 AM

I couldn't find anything about the time it takes for a ship to move through the void. Does anybody know of any rules, or of any fluff that gives an idea of how many days it takes for a ship to travel from planet to planet or from warp point to planet?



#2 WhiteLycan

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Posted 03 April 2012 - 08:39 PM

 Not trying to be a smart ass but there's a very obvious indicator of how fast a ship can move through the void. Its speed.



#3 Errant

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Posted 03 April 2012 - 10:15 PM

Fluff is inconsistent on this point; some pieces indicate that it takes weeks to get to the goldilocks zone of a system from the outer fringes, while in others it's bare hours. I tend to hedge it at about a week at full burn.

As a sidenote, if you assume a Speed of 8 VU, one VU being 10,000km, it would take approximately 4.21 years to get from Earth to Pluto.



#4 Red Bart

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Posted 03 April 2012 - 10:17 PM

I completely overlooked that, but you're very right

However if I set the speed of an average ship (about 6) and the length of a void unit (10,000km) against the distance in our own solar system the voyage gets to be rather long. A warp translation point is, I think, always at the edge of a solar system, so (according to wikipedia) the farthest distance of pluto to the sun is about 50AU, or 7,500,000,000km (to get really clear of the solar system you'd probably have to travel even further). An average ship would travel 60,000km per half our, or 2,88 million km per day. To get to earth you'd have to travel at least 49AU, or 73,500,000,000km, making it a trip lasting about 70 years, and then you would have to make a return trip to travel to a warp translation point...



#5 Red Bart

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Posted 03 April 2012 - 10:22 PM

Errant said:

Fluff is inconsistent on this point; some pieces indicate that it takes weeks to get to the goldilocks zone of a system from the outer fringes, while in others it's bare hours. I tend to hedge it at about a week at full burn.

Actually I could live with an inconsistency like this. That would just mean that I as a GM could decide the amount of time they'd spent inside a system, and make it anything from a couple of hours to a couple of weeks. However having to make it anything from 4 years to 70 years for a one way trip would make the characters rather short lived

 



#6 Trader Austin

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Posted 04 April 2012 - 03:16 PM

ships can make 2 warp jumps. 1 to get to the system and another to get close to ,relatively speaking, to planets. look at frozen reaches. the orks jump into the middle of your fleet. it is insanely close to the planet,within hours, but jump in a day or two away from the one you want after you have taken a look from out system. it's more dangerous but it saves a lot of time. 



#7 Errant

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Posted 04 April 2012 - 03:24 PM

 Yeeees, but about six of the nine vessels that attempt that are torn apart by the system's gravity well. I doubt most Rogue Traders would be terribly happy with those odds



#8 Trader Austin

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Posted 08 April 2012 - 06:50 AM

that was my point about the distance from the planet the orks jumped. they jumped into real space within 12 hours of the planet. they lost around 1/4 of their ships as written in the adventure. jump to 2 days out from the planet. outside the planetary and moons grav well but still much closer than pluto's orbit. 



#9 WhiteLycan

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Posted 08 April 2012 - 07:46 PM

 I'm 95% certain the adventure specifically states that the ork role are torn apart by the STAR's gravity well, not the planet's. 

 

Anyway, I found a paragraph that talks about void travel outside of combat. It pretty much leaves it up to the GM but says ships should move a lot faster out of combat than in combat, similar to combat speed and narrative speed for vehicles.I'm pretty sure the paragraph was in RT core but I'm not positive.  



#10 Blargh

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Posted 09 April 2012 - 09:57 AM

Page 183 on in the core rulebook talks about traveling through the warp 



#11 Tron_18

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Posted 09 April 2012 - 06:54 PM

Red Bart said:

I completely overlooked that, but you're very right

However if I set the speed of an average ship (about 6) and the length of a void unit (10,000km) against the distance in our own solar system the voyage gets to be rather long. A warp translation point is, I think, always at the edge of a solar system, so (according to wikipedia) the farthest distance of pluto to the sun is about 50AU, or 7,500,000,000km (to get really clear of the solar system you'd probably have to travel even further). An average ship would travel 60,000km per half our, or 2,88 million km per day. To get to earth you'd have to travel at least 49AU, or 73,500,000,000km, making it a trip lasting about 70 years, and then you would have to make a return trip to travel to a warp translation point...

I think one could argue that in narrative time you can continue to accelerate and accelerate for hours and hours, eventually reaching speeds faster than speed x VU.  I think going 1/4 the speed of light could be reasonable, making 50 AU's take only a few days.  I believe the book says it takes several weeks to cross a planetary system (which I would interpret as the full width of it).



#12 Darth Smeg

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Posted 10 April 2012 - 08:35 PM

If you are trying to bring real-world physics into this, you're in for some pain.

Remember, there is no air-resistance in space, the only "drag" you have to worry about is inertia. And once overcome, a moving object will keep moving at a constant velocity without any further thrust.

At "Full burn", you're not measuring a constant "max speed", you're measuring a constant "max acceleration". As long as you're working those engines, you will keep going ever faster and faster, until you eventually approach light speed and relativity kicks in and limits your effective speed.

So for practical purposes I'd rule that the speed value for a ship (ie 6 VU p Combat turn) is an approximation of the distance a ship can cover while turning and maneuvering (and thus not benefiting from extended acceleration). But for long trips, no ship will be limited to this limit.

Even at a modest 1G acceleration, you will travel 1 AU in the first 2 days. At that point, your speed will be over 6 million kilometers pr hour (about 609 Void Units/hr), or about 1 AU / day. Keep accelerating, and you'll hit 2 AU / day after 4 days, 4 AU after 8 days, and so forth.

At your journeys half-way point, you would need to start decelerating at 1 G, in order to end up stationary upon your arrival. Whether this is necessary to perform a warp jump is not known, but let's assume so.

To travel 50 AU then, from standstill and to a complete stop, you would need to accelerate at 1 G for 10 days. This would take you 25 AU, and leave you with a top speed of some 3050 VU / hr. Then you simply hit the brakes (or more likely, turn the ship around and let the engines thrust as normal giving you the same deceleration as you had as acceleration). For the next 10 days you will cover the same distance, and end up stationary on the edge of our solar system after 20 days of travel.

If you did not need to slow down, you could be there after only 14 days at "full burn", but then you'd be moving at almost 4300 VU/h :)

And this is at 1 G. The level of acceleration you experience if you jump of something here on earth. With fancy-gravplating and inertial dampeners and other sci-fi tropes you could easily increase this, drastically reducing travel times. At 2G you'd just need 7 days before reaching your mid-point. At 3G, you're down to 6.

Of course, keeping this "full thrust" thing going would require a lot of fuel, which would require storage. Or some fancy extract-from-space-as-you-go thing. Or a lot of handwavium.


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#13 WhiteLycan

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Posted 12 April 2012 - 02:07 AM

Or instead of constant acceleration, just accelerate until you're satisfied and turn off your engines and then coast to your warp transition point. Would save a bunch of fuel. Take a little longer, but cost less fuel.



#14 Hygric

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Posted 14 April 2012 - 04:04 PM

As a GM, I go for approximately 2 weeks at "full burn" to get to safe warp tansit range for a normal star system (ie, like our own Sol star system).  Modify that time by the max G accel of the ship class (roughly), a 2g ship will take 2 weeks, a 1g ship 4 weeks etc.  A formula for that would be time in days = 28/g.  Seems to work in my campaigns, and makes faster ships (in strategic terms) have a bit of an edge with travel times.

As an example, take the Ambition and Dictator class cruisers, both have a combat speed of 5VU, but the ambition has 3g sustainable acceleration vs the dictators 2.5.  The Ambition can make a safe warp-point in 9 days and 8 hours while the Dictator can get there in 11 days and 5 hours.



#15 WhiteLycan

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Posted 14 April 2012 - 04:59 PM

Darth Smeg, any chance you could work up a light formula like the one Hygric uses? Going on your 1g = 20 days to clear the Sol system, something like

Small System: 10/G Days

Medium System: 20/G Days (Sol size)

Large System: 30/G Days

 

Would that be anywhere near accurate?



#16 Darth Smeg

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Posted 16 April 2012 - 01:14 AM

Problem is the equation is not linear. 

However, the formula is something like this: Time taken (in days) = Square root (408,9 / G)

 


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#17 WhiteLycan

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Posted 16 April 2012 - 09:45 PM

 What does 408.9 represent?



#18 Darth Smeg

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Posted 16 April 2012 - 11:49 PM

Time taken for the journey (in days) squared, then multiplied by the number of Gs in the acceleration.

This is just re-arranging the law of uniform acceleration, in order to solve for time (distance = 1/2 * Acceleration * time^2)

The value 408,9 is a bit arbitrary, but results mainly from your choice of units. Ie, we're talking Days and G's here. You might want to talk about Hours and other units of acceleration, in which case this factor would be different. It is also dependent on the distance traveled. In this case, 50AU.

Re-working to factor in distance as a variable, you divide 408,9 by 50, and then multiply with distance you want (in AUs).

So the new and improved (but still complicated) formula is then:

Time taken (in days) = Square root ((Distance * 8,2) / G)
 

I think that for practical game purposes, I would go for a simpler formula ala 28/g, or make a little table with "common" values.

 


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#19 WhiteLycan

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Posted 19 April 2012 - 03:31 AM

The complex formula is nice since due to time constraints and life, I can only play PbP games on RPOL.com.

After doing some light googling, I've learned that our solar system has a 60 AU diameter (out to the Kuiper belt only, not the oort cloud which is 190,000+ AU), plus a fraction. Half that would be 30. The hospitable zone of a solar system is (rounding) 1 to 3 AUs from the star. So with a Sol sized solar system, you're looking at 29 AU which translates into 7.5 days to reach warp safety for a Dauntless Light Cruiser and 9.75 days in a Lunar Class Cruiser (two common hull types players use)

I think all that's right!

Now for the big question, one that none of my googling turned up. How big, by comparison, is the Sol system? Are we big? Small? Average? Friggin huge?



#20 WhiteLycan

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Posted 19 April 2012 - 03:50 AM

Hm, just realized a flaw. A solar system's size has nothing to do with it. The only factor is the star's mass and consequently the size and strength of its gravity well. The larger the star, the further out you need to be before you can safely enter/exit the warp. I quote The Frozen Reaches as my example:

"....but this should serve as a graphic remind of the dangers of using a warp drive too close to a star."
     The Frozen Reaches, page 44, third paragraph from the bottom on the left side

What I get from that is that there is either a specific distance away from the star that you must be to enter the warp safely no matter how big/massive the star is or you have to be further out the more massive a star and thus the larger and stronger its gravity well is. If the latter is the case, then we really have nothing at all to go on unless there's some line in one of the hundreds of WH40K novels that an author states exactly how many AU away from Sol that the ship was before it entered the warp. Or at least how many days it took to reach that point as long as the ship's class type was identified so that we can do the math and find the distance ourselves.

Yes, I'm greatly overcomplicating this. But I love learning! And theory.






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