With the end of the TV show, I was finally tempted to read the books, and I've been pleasantly surprised by how good they are. Whilst I appreciate the hard sci-fi aesthetic, I was worried the books were going to be full of cod-physics and maths, turns out they're space opera with a Newtonian veneer.
Anyway, I really like the setting, and it's giving me an itch to want to do something with it. Is anyone playing with it? I know there's an official RPG, but the AGE system looks a bit crap, and it's not like there's a shortage of half decent systems out there.
So what are people using?
Orbital 2100 could do it think. It's Zozer Games and runs Cepheus Engine, which is a Traveller clone.
The official game is actually good. I'd use it.
Quote from: KingofElfland on February 01, 2022, 01:19:02 PM
Orbital 2100 could do it think. It's Zozer Games and runs Cepheus Engine, which is a Traveller clone.
Traveller has a certain reputation - how heavy is it?
Quote from: Batjon on February 01, 2022, 02:19:20 PM
The official game is actually good. I'd use it.
Are you aware of anyone who's run a lengthy game with it? Any decent writeups of actual play?
Quote from: Kiero on February 01, 2022, 05:24:06 AM
Anyway, I really like the setting, and it's giving me an itch to want to do something with it. Is anyone playing with it? I know there's an official RPG, but the AGE system looks a bit crap, and it's not like there's a shortage of half decent systems out there.
So what are people using?
The official game is quite good... at least from a one shot I played in a few weeks ago.
As to Orbital, it uses a trimmed down version. I think they release a free pdf for classic 2d6 Sci-Fi to make Cepheus Engine play more like original LBB classic Traveller. I know their Hostile line is very easy to grasp and go
Quote from: squirewaldo on February 01, 2022, 03:14:16 PM
The official game is quite good... at least from a one shot I played in a few weeks ago.
Did you use some published adventure, or something the GM came up with? What were your impressions of how the licensed system evokes the setting?
Quote from: KingofElfland on February 01, 2022, 03:50:20 PM
As to Orbital, it uses a trimmed down version. I think they release a free pdf for classic 2d6 Sci-Fi to make Cepheus Engine play more like original LBB classic Traveller. I know their Hostile line is very easy to grasp and go
Is this (https://www.paulelliottbooks.com/orbital.html) it?
Quote from: Kiero on February 01, 2022, 04:37:34 PM
Quote from: squirewaldo on February 01, 2022, 03:14:16 PM
The official game is quite good... at least from a one shot I played in a few weeks ago.
Did you use some published adventure, or something the GM came up with? What were your impressions of how the licensed system evokes the setting?
Quote from: KingofElfland on February 01, 2022, 03:50:20 PM
As to Orbital, it uses a trimmed down version. I think they release a free pdf for classic 2d6 Sci-Fi to make Cepheus Engine play more like original LBB classic Traveller. I know their Hostile line is very easy to grasp and go
Is this (https://www.paulelliottbooks.com/orbital.html) it?
It was a free Quick start on DriveThruRPG: https://www.drivethrurpg.com/product/247982/The-Expanse-RPG-Quickstart?affiliate_id=474082
If you're going to play in any sort of semi-realistic game set in our solar system, I'd recommend downloading the map from a boardgame called High Frontier. It is an energy map of the solar system where distances are measure in number of burns (i.e. velocity) rather than meters. The map includes just about every solar object we currently know about as well as including information about other navigation hazards like erratic spins, debris fields, and radiation zones. It does almost all the math work for you. It even includes slingshot info.
(https://i.imgur.com/IgyPULt.jpg)
[The sizes of objects is on a logarithmic scale. A size 3 asteroid is twice as big as a size 2]
Quote from: Kiero on February 01, 2022, 03:01:49 PM
Quote from: KingofElfland on February 01, 2022, 01:19:02 PM
Orbital 2100 could do it think. It's Zozer Games and runs Cepheus Engine, which is a Traveller clone.
Traveller has a certain reputation - how heavy is it?
Quote from: Batjon on February 01, 2022, 02:19:20 PM
The official game is actually good. I'd use it.
Are you aware of anyone who's run a lengthy game with it? Any decent writeups of actual play?
Lots of good reports here: https://www.facebook.com/groups/182815575923462
Quote from: hedgehobbit on February 01, 2022, 06:48:25 PM
If you're going to play in any sort of semi-realistic game set in our solar system, I'd recommend downloading the map from a boardgame called High Frontier. It is an energy map of the solar system where distances are measure in number of burns (i.e. velocity) rather than meters. The map includes just about every solar object we currently know about as well as including information about other navigation hazards like erratic spins, debris fields, and radiation zones. It does almost all the math work for you. It even includes slingshot info.
(https://i.imgur.com/IgyPULt.jpg)
[The sizes of objects is on a logarithmic scale. A size 3 asteroid is twice as big as a size 2]
That's a pretty cool map. How's the board game play?
I have it. It's fun, if you like that sort of thing, and it's scalable from a family dinner-table game to the sort of thing you spend weeks on. The assorted addons can take it from a cooperative building/acheivement game to a full on competitive 4x style with warships, if that's your thing.
Quote from: Kiero on February 01, 2022, 03:01:49 PM
Traveller has a certain reputation - how heavy is it?
You can check it out for free with Cepheus
The original SRD
https://www.drivethrurpg.com/product/186894/Cepheus-Engine-System-Reference-Document
Lite-rules variations
https://www.drivethrurpg.com/product/371207/Cepheus-Light-Upgraded
I am focusing more on Cepheus because it more focused on settings other than the Third Imperium. Including a bunch of products that focus on the science fiction subgenre that the Expanse is part of. Like Hostile.
https://www.drivethrurpg.com/product/377186/Hostile-Rules
And Green Ronin's Expanse RPG is worthy of a look as well. It uses a 3d6 roll high system.
Quote from: Batjon on February 02, 2022, 01:11:53 AM
Quote from: Kiero on February 01, 2022, 03:01:49 PM
Quote from: KingofElfland on February 01, 2022, 01:19:02 PM
Orbital 2100 could do it think. It's Zozer Games and runs Cepheus Engine, which is a Traveller clone.
Traveller has a certain reputation - how heavy is it?
Quote from: Batjon on February 01, 2022, 02:19:20 PM
The official game is actually good. I'd use it.
Are you aware of anyone who's run a lengthy game with it? Any decent writeups of actual play?
Lots of good reports here: https://www.facebook.com/groups/182815575923462
Oh, please. That is like me saying that there are a lot of good reports about Traveller here: https://www.facebook.com/groups/travellerrpg
How about some source with a little less bias?
Fun fact about The Expanse universe...
The Expanse universe was created by a homebrew sci-fi rpg campaign the writers played using d20 Modern with all the D20 Modern sci-fi books.
Quote from: KingofElfland on February 01, 2022, 03:50:20 PM
As to Orbital, it uses a trimmed down version. I think they release a free pdf for classic 2d6 Sci-Fi to make Cepheus Engine play more like original LBB classic Traveller. I know their Hostile line is very easy to grasp and go
Is this (https://www.paulelliottbooks.com/orbital.html) it?
[/quote]
Yes
Quote from: hedgehobbit on February 01, 2022, 06:48:25 PM
If you're going to play in any sort of semi-realistic game set in our solar system, I'd recommend downloading the map from a boardgame called High Frontier. It is an energy map of the solar system where distances are measure in number of burns (i.e. velocity) rather than meters. The map includes just about every solar object we currently know about as well as including information about other navigation hazards like erratic spins, debris fields, and radiation zones. It does almost all the math work for you. It even includes slingshot info.
(https://i.imgur.com/IgyPULt.jpg)
[The sizes of objects is on a logarithmic scale. A size 3 asteroid is twice as big as a size 2]
That's really cool. Any idea what one burn is?
Quote from: estar on February 02, 2022, 08:26:27 AM
You can check it out for free with Cepheus
The original SRD
https://www.drivethrurpg.com/product/186894/Cepheus-Engine-System-Reference-Document
Lite-rules variations
https://www.drivethrurpg.com/product/371207/Cepheus-Light-Upgraded
I am focusing more on Cepheus because it more focused on settings other than the Third Imperium. Including a bunch of products that focus on the science fiction subgenre that the Expanse is part of. Like Hostile.
https://www.drivethrurpg.com/product/377186/Hostile-Rules
And Green Ronin's Expanse RPG is worthy of a look as well. It uses a 3d6 roll high system.
Thanks for those.
Quote from: Kiero on February 09, 2022, 09:11:04 AM
That's really cool. Any idea what one burn is?
2.5 km/sec of delta-vee.
From the rule book.
QuoteBURN SPACES show the velocity increment required to travel between orbits, often called delta-v. Each game Burn is 2.5 km/sec of delta-v. The delta-v of a rocket is defined by the rocket equation: Delta-v = Ve ln (Wet Mass/Dry Mass), where Ve is the exit velocity of the propellant in km/sec. Assuming a minimum energy (Hohmann) transfer, the delta-v to fly from LEO to some nearby destinations is: Nereus = 4.5 km/sec, Venus capture = 5.5 km/sec (neglecting aerobrake), Phobos/Deimos = 5.6 km/sec, lunar base = 5.7 km/sec, Earth's surface = 9.5 km/sec, and Mars base = 10.2 km/sec (again assuming no aerobraking). Notice that the martian moons are closer to us than our own moon, in terms of fuel and energy.
Quote from: estar on February 09, 2022, 09:21:06 AM2.5 km/sec of delta-vee.
Just for reference, the Saturn V could generate about 16,900 delta V (and that is with lots of complicated staging). Which is about 6 burns. In game terms, that's three burns from the surface of the Earth to orbit. Two burns from orbit to the Moon. And one burn from the Moon back to Earth. The rest was done with atmospheric braking.
Now in The Expanse, ships are capable of performing a 1g burn for hours at a time. The Saturn V could do it for less than 30 minutes then it's dead in space. Even the most advanced rocket ever built, the nuclear powered NERVA, could only produce a 1g burn for about twice as long. I hope that puts into perspective just how reality-defyingly good those Epstein drives actually are. An hour at 1g would give you a delta V of 35,280 m/s and in The Expanse, that doesn't seem to go through a significant portion of the ship's fuel reserves.
The introduction of something like an Epstein drive would completely shatter the economics of space travel and exploitation.
Quote from: hedgehobbit on February 10, 2022, 11:10:55 AM
Quote from: estar on February 09, 2022, 09:21:06 AM2.5 km/sec of delta-vee.
The introduction of something like an Epstein drive would completely shatter the economics of space travel and exploitation.
That was the point of having the Epstein drive in the novels.
Last night I sat down with the latest iteration of the High Frontier map and worked with it and figured out the following.
.3 G = 2 days per burn
1 G = 1 day per burn
7 G = 1/3 day per burn
12 G = 1/4 day per burn
It correlates highly with travel times using the average separation distance.
You have to keep in mind that the High Frontiers map is a ENERGY map not one based on strict distances. So the procedure is.
Starting at the destination, count up all your burns including any hohman pivots which count as two burns each. But SUBTRACTing any burns you get from a flyby. The total number of burns is the total travel time.
If something was to happen mid journey then you need to figure out when it happen proportionally. For example if it take 5 burns to get to Mars thus 5 days at 1G. And something was to happen 2 day in. Then you need trace the path until your are 20% of the way there and that where it happens.
The map is more of a slide rule to help calculate how much energy and time it takes to travel somewhere. In the normal HF rules. A turn is a year and your engine's thrust ratings is how many burns you can do in that time. The movement is basically you can move as far as you want as long as you have the burns (and fuel to make the burns). If you run out of burns (and still have fuel remaining) you have to stop in the space prior to the next burn in the sequence and deal it with it in the movement phase of the next turn (and adding a year of travel).
With the Epstein Drive the Energy paths still matter as it still take time for the drive to build up speed, flip and decelerate. But since the drives are so efficient it can be handled quicker. Hence the travel time is measured not in turns of a year but how many burns must be made. And most inner system destination can be reached in days. And the outer system within weeks.
There are still issue with the HF Map in that there is a lot of stuff on it tailored for the game itself. That gets in the way of using it as an aide for the Expanse RPG (or any other solar system setting). I am going to redraw the maps to remove the unneeded clutter and see how that works.
Quote from: RebelSky on February 02, 2022, 03:09:10 PM
Fun fact about The Expanse universe...
The Expanse universe was created by a homebrew sci-fi rpg campaign the writers played using d20 Modern with all the D20 Modern sci-fi books.
A friend of mine knows the authors. He mentioned they used Traveller. Maybe he was wrong. Other fun fact. The rpg Expanse campaign was run my GRRM.
Quote from: estar on February 10, 2022, 11:44:08 AMThat was the point of having the Epstein drive in the novels.
I haven't read the books as I've only watched the Amazon show but I don't think the ramifications of the Epstein drive are fully realized in the setting. IOW, some of the things that are present in the setting, such as belters having a distinct language or water being rare, aren't particularly realistic considering the low cost and speed of travel that the Epstein drive provides. To me it is sort of like having huge areas of "Unexplored Regions" in Star Wars even though ships can easily fly across such areas in a matter of hours.
Quote from: soundchaser on February 10, 2022, 12:20:29 PMA friend of mine knows the authors. He mentioned they used Traveller.
That's totally believable. Maintaining a constant 1g burn and doing the "flip and burn" maneuver at your halfway point are two things that are in Traveller (even if they don't really make sense).
Quote from: hedgehobbit on February 10, 2022, 02:02:33 PM
Quote from: estar on February 10, 2022, 11:44:08 AMThat was the point of having the Epstein drive in the novels.
I haven't read the books as I've only watched the Amazon show but I don't think the ramifications of the Epstein drive are fully realized in the setting. IOW, some of the things that are present in the setting, such as belters having a distinct language or water being rare, aren't particularly realistic considering the low cost and speed of travel that the Epstein drive provides. To me it is sort of like having huge areas of "Unexplored Regions" in Star Wars even though ships can easily fly across such areas in a matter of hours.
Quote from: soundchaser on February 10, 2022, 12:20:29 PMA friend of mine knows the authors. He mentioned they used Traveller.
That's totally believable. Maintaining a constant 1g burn and doing the "flip and burn" maneuver at your halfway point are two things that are in Traveller (even if they don't really make sense).
I always questioned that The Expanse was originally based on a d20 Modern/Future game and not Traveller. The way that the ships of The Expanse maneuver is definitely not what is in the d20 rules, but more like Traveller.
I also disagree with water is rare bit as well. From everything I've read, water is pretty common in easy to reach spots and forms once you get beyond the snow line. Not to mention indications of water ice in craters on the Moon and Mercury.
Quote from: hedgehobbit on February 10, 2022, 02:02:33 PM
I haven't read the books as I've only watched the Amazon show but I don't think the ramifications of the Epstein drive are fully realized in the setting. IOW, some of the things that are present in the setting, such as belters having a distinct language or water being rare, aren't particularly realistic considering the low cost and speed of travel that the Epstein drive provides. To me it is sort of like having huge areas of "Unexplored Regions" in Star Wars even though ships can easily fly across such areas in a matter of hours.
The Expanse comes across to me as an old and developed civilization. Both in the novel and the show. They have dozens of ships like the Canterbury working the ice rings of Saturn to supply water for millions.
As for the speed of the Epstein drive. The situation at the start of Leviathan Wakes is that it takes days to travel between major settlement. You can think of the Expanse Solar System as the Pacific Ocean with the different settled planets, moons, stations, and asteroids islands dotting the ocean. Sure it wasn't hard for the Polynesians to travel but it wasn't easy either. Leading to different sections of the Pacific to develop in its own way. And beyond Saturn it still takes weeks to get anywhere.
Quote from: jeff37923 on February 10, 2022, 02:14:36 PM
I always questioned that The Expanse was originally based on a d20 Modern/Future game and not Traveller. The way that the ships of The Expanse maneuver is definitely not what is in the d20 rules, but more like Traveller.
Why can't you run d20 Modern with Traveller Starship rules?
Quote from: jeff37923 on February 10, 2022, 02:14:36 PM
I also disagree with water is rare bit as well. From everything I've read, water is pretty common in easy to reach spots and forms once you get beyond the snow line. Not to mention indications of water ice in craters on the Moon and Mercury.
1) Ceres is right on the inner edge of the frost line in the Solar system.
2) It was stated that all the water was mined from Ceres and it requires imported water to keep things going.
Quote from: estar on February 10, 2022, 02:18:00 PM
Quote from: jeff37923 on February 10, 2022, 02:14:36 PM
I always questioned that The Expanse was originally based on a d20 Modern/Future game and not Traveller. The way that the ships of The Expanse maneuver is definitely not what is in the d20 rules, but more like Traveller.
Why can't you run d20 Modern with Traveller Starship rules?
Well, you can do it that way. I just consider it to be heresy. ;D
Quote from: estar on February 10, 2022, 02:18:00 PM
Quote from: jeff37923 on February 10, 2022, 02:14:36 PM
I also disagree with water is rare bit as well. From everything I've read, water is pretty common in easy to reach spots and forms once you get beyond the snow line. Not to mention indications of water ice in craters on the Moon and Mercury.
1) Ceres is right on the inner edge of the frost line in the Solar system.
2) It was stated that all the water was mined from Ceres and it requires imported water to keep things going.
What about the Jovian Trojans? The delta vee to get from there to Ceres can't be greater than going from Saturn to Ceres.
(I know, I'm quibbling.)
Quote from: jeff37923 on February 10, 2022, 02:35:13 PM
Well, you can do it that way. I just consider it to be heresy. ;D
Sorry man, hybrids are the norm not the exception.
Quote from: jeff37923 on February 10, 2022, 02:35:13 PM
What about the Jovian Trojans? The delta vee to get from there to Ceres can't be greater than going from Saturn to Ceres.
(I know, I'm quibbling.)
Well it does take as much delta-vee to reach Deimos or Phobos as it does to land on the moon. So it all depends on how the energy plot looks.
According to HF map and my rules it would take 9 burns and 9 days at 1 G to reach Low Callisto Orbit.
To reach Ceres or more accurately the Gefion family of asteroids it would take 8 burns.
To reach the Trojan Jupiter group it would take 10 burns.
To reach the Greek Jupiter group it would take 9 burns.
There is an alternative path to the Greek to the L3 Mars-Sol point that only takes 8 burns.
Quote from: estar on February 10, 2022, 03:19:44 PM
Quote from: jeff37923 on February 10, 2022, 02:35:13 PM
What about the Jovian Trojans? The delta vee to get from there to Ceres can't be greater than going from Saturn to Ceres.
(I know, I'm quibbling.)
Well it does take as much delta-vee to reach Deimos or Phobos as it does to land on the moon. So it all depends on how the energy plot looks.
According to HF map and my rules it would take 9 burns and 9 days at 1 G to reach Low Callisto Orbit.
To reach Ceres or more accurately the Gefion family of asteroids it would take 8 burns.
To reach the Trojan Jupiter group it would take 10 burns.
To reach the Greek Jupiter group it would take 9 burns.
There is an alternative path to the Greek to the L3 Mars-Sol point that only takes 8 burns.
Is there a larger HF map that I can access online? I can't really read the numbers for the image on Imgur and I'm left with mathing it out which will take me a bit of time I don't have right now.
What about taking a leaf from GURPS Terradyne? I bought it at the end of my GURPS cycle so I never played it it, but IIRC it had a strong "let's colonise the Solar System - realistically!" vibe.
Quote from: jeff37923 on February 10, 2022, 04:08:40 PM
Quote from: estar on February 10, 2022, 03:19:44 PM
Quote from: jeff37923 on February 10, 2022, 02:35:13 PM
What about the Jovian Trojans? The delta vee to get from there to Ceres can't be greater than going from Saturn to Ceres.
(I know, I'm quibbling.)
Well it does take as much delta-vee to reach Deimos or Phobos as it does to land on the moon. So it all depends on how the energy plot looks.
According to HF map and my rules it would take 9 burns and 9 days at 1 G to reach Low Callisto Orbit.
To reach Ceres or more accurately the Gefion family of asteroids it would take 8 burns.
To reach the Trojan Jupiter group it would take 10 burns.
To reach the Greek Jupiter group it would take 9 burns.
There is an alternative path to the Greek to the L3 Mars-Sol point that only takes 8 burns.
Is there a larger HF map that I can access online? I can't really read the numbers for the image on Imgur and I'm left with mathing it out which will take me a bit of time I don't have right now.
This is the highest resolution you can download. However you will need an account (free) in order to get access to it.
https://boardgamegeek.com/image/5605558/high-frontier-4-all
Quote from: Reckall on February 10, 2022, 04:48:26 PM
What about taking a leaf from GURPS Terradyne? I bought it at the end of my GURPS cycle so I never played it it, but IIRC it had a strong "let's colonise the Solar System - realistically!" vibe.
I have it and to be honest it is pretty boring compared to the Expanse.
Quote from: estar on February 10, 2022, 09:21:23 PM
Quote from: jeff37923 on February 10, 2022, 04:08:40 PM
Quote from: estar on February 10, 2022, 03:19:44 PM
Quote from: jeff37923 on February 10, 2022, 02:35:13 PM
What about the Jovian Trojans? The delta vee to get from there to Ceres can't be greater than going from Saturn to Ceres.
(I know, I'm quibbling.)
Well it does take as much delta-vee to reach Deimos or Phobos as it does to land on the moon. So it all depends on how the energy plot looks.
According to HF map and my rules it would take 9 burns and 9 days at 1 G to reach Low Callisto Orbit.
To reach Ceres or more accurately the Gefion family of asteroids it would take 8 burns.
To reach the Trojan Jupiter group it would take 10 burns.
To reach the Greek Jupiter group it would take 9 burns.
There is an alternative path to the Greek to the L3 Mars-Sol point that only takes 8 burns.
Is there a larger HF map that I can access online? I can't really read the numbers for the image on Imgur and I'm left with mathing it out which will take me a bit of time I don't have right now.
This is the highest resolution you can download. However you will need an account (free) in order to get access to it.
https://boardgamegeek.com/image/5605558/high-frontier-4-all
Thank you.
Rough number crunching of Hohmann transfers gives me an 8.2 km/sec for Jupiter Trojans to Ceres while it gives me 13.1 km/sec for Saturn to Ceres but that is not including the plane changes. Now, something I didn't think of are the Hilda asteroids, which only need a 5.2 km/sec for delta vee. Most of the Hildas are C-type and should have plenty of water.
Come to think of it, why isn't the water recycling taking up a lot of slack for the belter population? I know, because plot.
EDIT: It should be known that you don't have to get into this kind of nitty-gritty math/science/engineering to play Traveller. I do it because I dig it and it allows me to run games in that system with more depth, but I don't impose this on players (they'd hate it for the most part).
Quote from: estar on February 10, 2022, 11:44:08 AM
I am going to redraw the maps to remove the unneeded clutter and see how that works.
Please keep us updated. I'd be really interested in what you do with it!
Quote from: estar on February 10, 2022, 02:15:06 PM
The Expanse comes across to me as an old and developed civilization. Both in the novel and the show. They have dozens of ships like the Canterbury working the ice rings of Saturn to supply water for millions.
Yeah, space travel is centuries old in the setting, even the Epstein drive has been around about a century. Mars traded it with Earth for their independence. Ships like the Cant were former colony ships for the most part, converted to alternative uses rather than break them up.
Lots of old ships were retrofitted with Epstein drives, which extended their useful life by decades or more. Most of the warships are 30-40 years old, some of the UNN ones even as old as a century.
Quote from: estar on February 10, 2022, 02:15:06 PMAs for the speed of the Epstein drive. The situation at the start of Leviathan Wakes is that it takes days to travel between major settlement. You can think of the Expanse Solar System as the Pacific Ocean with the different settled planets, moons, stations, and asteroids islands dotting the ocean. Sure it wasn't hard for the Polynesians to travel but it wasn't easy either. Leading to different sections of the Pacific to develop in its own way. And beyond Saturn it still takes weeks to get anywhere.
This is something the books make much clearer than the show, travel times are measured in weeks and months around the solar system. Even comms has delays of minutes or hours.
That's another reason why there are no interceptor/fighter-sized craft, they wouldn't be comfortable to travel any of the distances that events take place in.
Quote from: Kiero on February 12, 2022, 05:32:41 PM
That's another reason why there are no interceptor/fighter-sized craft, they wouldn't be comfortable to travel any of the distances that events take place in.
Seems like there was a use case for having some short range ones with nukes or some sort of rock busting capabilities. ;D
Quote from: KingCheops on February 12, 2022, 07:06:10 PM
Quote from: Kiero on February 12, 2022, 05:32:41 PM
That's another reason why there are no interceptor/fighter-sized craft, they wouldn't be comfortable to travel any of the distances that events take place in.
Seems like there was a use case for having some short range ones with nukes or some sort of rock busting capabilities. ;D
The Razorback proved they could have made fighters. It wouldn't have been to.hard to see them putting a few missiles and PDCs on a similar hull.
Quote from: HappyDaze on February 12, 2022, 07:26:27 PM
Quote from: KingCheops on February 12, 2022, 07:06:10 PM
Quote from: Kiero on February 12, 2022, 05:32:41 PM
That's another reason why there are no interceptor/fighter-sized craft, they wouldn't be comfortable to travel any of the distances that events take place in.
Seems like there was a use case for having some short range ones with nukes or some sort of rock busting capabilities. ;D
The Razorback proved they could have made fighters. It wouldn't have been to.hard to see them putting a few missiles and PDCs on a similar hull.
Fighters work in real life because they are faster, smaller, longer range, and cheaper and pack the firepower to kill a naval ship by itself.
That not the case with spacecraft. Anything with people will have the same range and speed regardless of size. Any drone regardless of size will have the same range and speed. Unless the smaller engine has a vastly different Thrust to weight ratio the rocket equation mean the different that exist on a planetary surface doesn't exist in space.
There is a size limit and that is because of heat. Build something too large then you won't have the surface area to dump the heat that generated. The same problem exist with living things.
Quote from: estar on February 12, 2022, 10:53:27 PM
Quote from: HappyDaze on February 12, 2022, 07:26:27 PM
Quote from: KingCheops on February 12, 2022, 07:06:10 PM
Quote from: Kiero on February 12, 2022, 05:32:41 PM
That's another reason why there are no interceptor/fighter-sized craft, they wouldn't be comfortable to travel any of the distances that events take place in.
Seems like there was a use case for having some short range ones with nukes or some sort of rock busting capabilities. ;D
The Razorback proved they could have made fighters. It wouldn't have been to.hard to see them putting a few missiles and PDCs on a similar hull.
Fighters work in real life because they are faster, smaller, longer range, and cheaper and pack the firepower to kill a naval ship by itself.
That not the case with spacecraft. Anything with people will have the same range and speed regardless of size. Any drone regardless of size will have the same range and speed. Unless the smaller engine has a vastly different Thrust to weight ratio the rocket equation mean the different that exist on a planetary surface doesn't exist in space.
There is a size limit and that is because of heat. Build something too large then you won't have the surface area to dump the heat that generated. The same problem exist with living things.
The Razorback exists in the setting. It is a racing ship with a very high acceleration, but it appears to be quite capable of long duration trips too. It has no weapons, but it could have formed the basis of a light armed ship skin to a fighter with a little ingenuity. Dumping heat isn't something that the Expanse focused upon.
Relevant:
http://toughsf.blogspot.com/2019/10/the-expanses-epstein-drive.html
Quote from: HappyDaze on February 13, 2022, 12:21:15 AM
The Razorback exists in the setting. It is a racing ship with a very high acceleration, but it appears to be quite capable of long duration trips too. It has no weapons, but it could have formed the basis of a light armed ship skin to a fighter with a little ingenuity. Dumping heat isn't something that the Expanse focused upon.
Again there is no advantage to arming the Razorback. Or the ship that tried to shoot the Ring. That class of ship was built to have as high thrust to weight as possible. It trivial to build a drone that can exceed what the Razorback can do. In fact from Chapter 31 of Nemesis Games when Alex was talking about what was needed to use the Razorback to escape a Free Navy ambush.
Quote
"Not going to be enough. If we're burnin' all the way to Earth... we can probably outrun the enemy ships, but their missiles don't have to worry about keeping anyone inside from getting squished by thrust. And it ain't like there's anything out here to hide behind."
Quote from: estar on February 13, 2022, 08:47:41 AMAgain there is no advantage to arming the Razorback. Or the ship that tried to shoot the Ring. That class of ship was built to have as high thrust to weight as possible. It trivial to build a drone that can exceed what the Razorback can do.
Unfortunately, the "just use a drone" argument can be used to explain why none of the ships we see make logical sense. Gunships, destroyers, battleships would all be inferior to a missile armed drone. This is especially true because of the vast amount of destructive energy that can be imparted into a simple mass via the Epstein drive. Even those cargo transports would be more effective if they were crewless drone ships.
At some point you just have to draw the line and accept the rule of cool.
Quote from: estar on February 13, 2022, 08:47:41 AM
Quote from: HappyDaze on February 13, 2022, 12:21:15 AM
The Razorback exists in the setting. It is a racing ship with a very high acceleration, but it appears to be quite capable of long duration trips too. It has no weapons, but it could have formed the basis of a light armed ship skin to a fighter with a little ingenuity. Dumping heat isn't something that the Expanse focused upon.
Again there is no advantage to arming the Razorback. Or the ship that tried to shoot the Ring. That class of ship was built to have as high thrust to weight as possible. It trivial to build a drone that can exceed what the Razorback can do. In fact from Chapter 31 of Nemesis Games when Alex was talking about what was needed to use the Razorback to escape a Free Navy ambush.
Quote
"Not going to be enough. If we're burnin' all the way to Earth... we can probably outrun the enemy ships, but their missiles don't have to worry about keeping anyone inside from getting squished by thrust. And it ain't like there's anything out here to hide behind."
Real world fighter aircraft can't outrun missiles either, but they are still widely used today.
Quote from: hedgehobbit on February 13, 2022, 11:38:07 AM
Quote from: estar on February 13, 2022, 08:47:41 AMAgain there is no advantage to arming the Razorback. Or the ship that tried to shoot the Ring. That class of ship was built to have as high thrust to weight as possible. It trivial to build a drone that can exceed what the Razorback can do.
Unfortunately, the "just use a drone" argument can be used to explain why none of the ships we see make logical sense. Gunships, destroyers, battleships would all be inferior to a missile armed drone. This is especially true because of the vast amount of destructive energy that can be imparted into a simple mass via the Epstein drive. Even those cargo transports would be more effective if they were crewless drone ships.
At some point you just have to draw the line and accept the rule of cool.
Unless they are completely autonomous, a drone ship will still need a controller. Then you have communications lag, so any distance greater than 300000 km (or even 150000 km for transmit and return) is going to really complicate your control of that drone.
Quote from: jeff37923 on February 13, 2022, 03:16:08 PM
Quote from: hedgehobbit on February 13, 2022, 11:38:07 AM
Quote from: estar on February 13, 2022, 08:47:41 AMAgain there is no advantage to arming the Razorback. Or the ship that tried to shoot the Ring. That class of ship was built to have as high thrust to weight as possible. It trivial to build a drone that can exceed what the Razorback can do.
Unfortunately, the "just use a drone" argument can be used to explain why none of the ships we see make logical sense. Gunships, destroyers, battleships would all be inferior to a missile armed drone. This is especially true because of the vast amount of destructive energy that can be imparted into a simple mass via the Epstein drive. Even those cargo transports would be more effective if they were crewless drone ships.
At some point you just have to draw the line and accept the rule of cool.
Unless they are completely autonomous, a drone ship will still need a controller. Then you have communications lag, so any distance greater than 300000 km (or even 150000 km for transmit and return) is going to really complicate your control of that drone.
You don't need active remote control. Simply dictating targeting priorities and mission objectives can be enough if the drone has low level AI just like controlling units in RTS games by setting a stance (aggressive, defensive, avoidance) and a destination. A few seconds of lag shouldn't matter much as, lacking much stealth in space (the show does highlight some exceptions), you'll have a lot of warning (hours or even days) of anything approaching.
Missiles/torpedoes themselves already fulfil the "armed drone" role, in the setting. They can loiter, reassess and change targets, cover huge distances (because they have Epstein drives of their own).
Countermeasures are mostly inferior to the AI driving them, which is why ships use either counter-missile fire or PDCs as a defense against them. Unless a fighter is mounting a PDC of it's own, it's extremely vulnerable to missiles.
Quote from: estar on February 10, 2022, 11:44:08 AM
There are still issue with the HF Map in that there is a lot of stuff on it tailored for the game itself. That gets in the way of using it as an aide for the Expanse RPG (or any other solar system setting). I am going to redraw the maps to remove the unneeded clutter and see how that works.
Would any pre-existing (if not so pretty) delta-v maps be of help? Like these?
https://drive.google.com/file/d/13Qhtxlnhd_vYRQoldieKDy1ePakHC1nj/view?usp=sharing
https://drive.google.com/file/d/1ma3XSSjm87K9EEP_fjIIsnAh1DB9qRcv/view?usp=sharing
I think pretty much any group familiar with the source material, playing in the setting, would likely want a Martian gunship for their "PC ship". After all, that's what the protagonists of the series do, which sets them apart from any other lot with a civvy ship mounting external torpedo racks and a jury-rigged PDC. And let's be honest, no one wants a UNN vessel.
It has to be a smaller one that can run with a relatively small crew, and that's another reason for an ex-military ship, which is designed with redundancies in mind. Something that can be crewed effectively by 6 or less. Which puts the cruisers needing dozens of personnel out of the reckoning.
So how might they get one?
If the game is set around the time of the first book, that makes it rather difficult. Various exceptional circumstances combined to allow Holden et al to escape on the Tachi and claim it as "legitimate salvage". And they suffered legal problems for a while afterwards until the Martian government gave up.
With the Earth Mars war that starts over Ganymede, you have a richer vein of possibility with wrecks that could be salvaged. You could come up with any number of ways a frigate or destroyer could have been abandoned after enemy action that would allow the PCs to seize it after the fact. That could easily be the seed of a major plot arc in it's own right.
If you're following the plotline of the books, there's the Inaros-OPA faction's attack on the Martian naval shipyard on Callisto for another way something could get "lost". The shipyard was destroyed, which may also mean records of what was there were compromised.
Then later, with the opening of the ring gates, we have the sudden appearance of MCRN tech, all the way up to ships, on the black market. Lots of the gunships that could be carried in the belly of the Donnager battleships "disappeared", many being diverted to the Free Navy. Which in itself could be a way the PCs get hold of one, as well as other nefarious means.
Quote from: Kiero on February 18, 2022, 09:08:20 AM
I think pretty much any group familiar with the source material, playing in the setting, would likely want a Martian gunship for their "PC ship".
In AD&D1e, I always wanted a +5 vorpal sword.
Players don't always get what they want. Sometimes they even have to make a plan to go and get it - and it might not even succeed. And that's where we get adventures from.
Quote from: Kyle Aaron on February 18, 2022, 10:06:54 PM
In AD&D1e, I always wanted a +5 vorpal sword.
Players don't always get what they want. Sometimes they even have to make a plan to go and get it - and it might not even succeed. And that's where we get adventures from.
Granted, my point was it's a tangible starting goal in which there are varying plausible openings that could make it
possible. Before some of the events of the books, it's in the realms of impossible.
Go steal a warship from a vigilant and competent naval power who would forcefully seek it's return or destruction is not a good starting premise without any of those nuances.
So here is my work in progress. Remember this is a energy/delta-vee map. Not a physical map of the Solar System although there is a relationship between distance and energy.
The way it works is that you generally start out on the green dots. For example Low Earth Orbit. The each pink dots you pass through takes 1 burn which equal 1 day of travel at a 1G Burn. White dots are free to move through. A pivot can be made at any intersection and cost 2 burns (and 2 days of travel). Blue circle with a -number means you subtract that number of burns from your total thus reducing your travel time due to the free delta-vee you gain. White circle with a skull indicate a hazard roll needs to be made.
For example if you start out in Low Earth Orbit and want to go to Eureka towards the bottom right edge of the map. It will take 4 burns or 4 days at 1 G. You pass through the Transfer Orbit burn point then through the radiation hazard of the Van Allen Belt. The make another burn near Geosynchronous Orbit which can take you to the L2 Earth_Luna Lagrange Point. You then continue through the L5 Sol Mars Lagrange point. You then make two burns, and have to make a hazard check to match Eureka spin and latch on with grapples. Now you are station keeping with Eureka.
https://en.wikipedia.org/wiki/5261_Eureka
(https://www.batintheattic.com/images/Expanse_Map.jpg)
Is it even worth accounting for the varying orbits of the planets? As in the distances between them are in flux.
Quote from: Kiero on February 20, 2022, 05:17:07 PM
Is it even worth accounting for the varying orbits of the planets? As in the distances between them are in flux.
What he said.
The map is awesome, but what if the planets are in opposition?
Quote from: Kiero on February 20, 2022, 05:17:07 PM
Is it even worth accounting for the varying orbits of the planets? As in the distances between them are in flux.
It does to a point because it is a energy map not a position map. Since we are talking torch ships capable of continuous thrust with applies to Traveller or the Expanse it is about as realistic as it gets for something that playable. Each pink dot represent 2.5 km of delta fee.
The game I adapted this from is used turns of a year because the focus on real world drives. With Traveller or Expanse style drive we are talking days.
It's graphically very satisfying, but with 1G of constant boost it seems like 4 days to L2 is a bit weird. Maybe if you set it to something like .1g for a more realistic setting. With 1G and no realistic restrictions on delta-v budget, the whole inner solar system is your oyster regardless of opposition within a couple days tops. Earth/Mars on average would be 2 days with flip and stop, for instance.
There are limits on burn time in The Expanse. They're mentioned in the books and discussed in the article I posted.
http://toughsf.blogspot.com/2019/10/the-expanses-epstein-drive.html
The limits on burn time are less obvious in the TV show than books, because we naturally assume that whenever people are seen walking on decks they're under acceleration. However, usually they're just clamping down with their magnetic boots, and other microgravity effects aren't shown because nobody can be bothered with it and 99% of the audience won't notice. It's the same as how we only once saw a coriolis effect on Ceres, with Miller's drink being poured and it twisting to one side - this was never shown again.
Most of the time we see people moving around on the Rocinante they're under microgravity or relatively low acceleration. As the blog article notes, a full use of the fuel would get them 0.1g for 40 days. That's 3,456km/sec of delta-V, covering about 80AU if they didn't turn and flip and decelerate at the halfway point.
So it's not unlimited, it's just fucking huge compared to anything we've got now. But the calculations tell us it'd be a 100TW drive, vs 18TW for all of Earth today. Using five times the entire current energy output of the human race just to have half a dozen people zip around having adventures is pretty nuts, but that's scifi for you.
Quote from: Panzerkraken on February 20, 2022, 11:52:43 PM
It's graphically very satisfying, but with 1G of constant boost it seems like 4 days to L2 is a bit weird.
Which L2?
Quote from: Panzerkraken on February 20, 2022, 11:52:43 PM
Maybe if you set it to something like .1g for a more realistic setting. With 1G and no realistic restrictions on delta-v budget, the whole inner solar system is your oyster regardless of opposition within a couple days tops. Earth/Mars on average would be 2 days with flip and stop, for instance.
I go by the table here as being more accurate than what in the Expanse RPG book. It pegs Earth to Mars as a 4 day trip as a 1G Brachistochrone trajectory.
Spaceship Handbook Mission Table
http://www.projectrho.com/public_html/rocket/appmissiontable.php
Here some posts explaining the High Frontier Map
https://boardgamegeek.com/thread/868735/why-are-planets-static-high-frontier
The explanation of the High Frontier Map is down aways
http://www.projectrho.com/public_html/rocket/spacemaps.php
Quote from: estar on February 21, 2022, 12:37:52 AM
I go by the table here as being more accurate than what in the Expanse RPG book. It pegs Earth to Mars as a 4 day trip as a 1G Brachistochrone trajectory.
Spaceship Handbook Mission Table
http://www.projectrho.com/public_html/rocket/appmissiontable.php
That table is for a round trip, it even says so.
Quote from: http://www.projectrho.com/public_html/rocket/appmissiontable.php link=http://www.projectrho.com/public_html/rocket/appmissiontable.php
Delta-v and Travel Time for ROUND Trips To or From Terra's Surface
(i.e., the "Mars" row gives data for both the TERRA-MARS-TERRA and the MARS-TERRA-MARS missions
I'm guessing the parachute icons represent aerobraking opportunities. Maybe I'm reading this wrong, but it seems to me like you put in an aerobrake from Mars flyby to Mars orbit, but NOT one for actually landing? What's the reasoning behind that?
Quote from: Premier on February 21, 2022, 08:31:03 AM
I'm guessing the parachute icons represent aerobraking opportunities. Maybe I'm reading this wrong, but it seems to me like you put in an aerobrake from Mars flyby to Mars orbit, but NOT one for actually landing? What's the reasoning behind that?
I omitted landing sites and landing burns from the High Frontier in favor of just a low orbit notation. Figuring that folks can figure out which method works best for getting to the surface including aerobraking landing if there is an atmosphere. But this is just a first pass so I may change my mind on that.
Quote from: Panzerkraken on February 21, 2022, 07:10:52 AM
That table is for a round trip, it even says so.
You are right that I misread it so in that case I recommend the following
.3 G = 1 days per burn
1 G = 1/2 day per burn
7 G = 1/6 day per burn
12 G = 1/8 day per burn
Quote from: estar on February 21, 2022, 12:37:52 AMIt pegs Earth to Mars as a 4 day trip as a 1G Brachistochrone trajectory.
The problem with that table is that getting from the Earth's orbit to the Martian orbit in 4 days is only helpful is Mars is there when you arrive. And that still requires Earth and Mars to be in a precise alignment which only happens once every 26 months. So you'll still need some math to determine how long it takes for the other 25 months out of every Earth/Mars cycle. At that point you've just using charts to calculate travel times and the map becomes useless.
Although, I do like the idea of Earth/Mars traffic being concentrated on a once in two years cycle, where a whole fleet of ships launch at the same time and, effectively, travel together. Sort of a wagon train to the stars but with the potential that they might not all be friendly with one another. This is a game scenario that really doesn't occur in any other genre since you can normally just leave whenever you want if traveling by horse, ship, or aircraft.
Quote from: estar on February 21, 2022, 10:04:50 AM
You are right that I misread it so in that case I recommend the following
.3 G = 1 days per burn
1 G = 1/2 day per burn
7 G = 1/6 day per burn
12 G = 1/8 day per burn
The show doesn't deal with speeds at all, beyond the occasional "here comes the juice" moment to tell you they're burning hard. But the books deal with speeds all the time and it's pretty consistent. For reference:
- 0.1g is slow, a stately pace when you've got nowhere to go.
- 0.3g is a standard, sustainable pace that most travel takes place in, unless you have a reason to go slower.
- 1g is a moderate burn, can be uncomfortable for those used to lower gravities, but can be kept up for hours at a time, with breaks at a lower speed when the crew need to eat and change stations. People can still move around the ship at 1g.
- Anything over 3g is a "hard burn" which requires everyone in acceleration couches and pharmacology to reduce the risk of people stroking out and such. When Eros sped up to 4g and didn't look like it would have any trouble keeping that speed indefinitely, trying to keep pace with it for more than a brief period was a potential death sentence. 3-4g is the standard speed for hard maneuvers in combat.
- The Tachi left the belly of the Donnager at 12g to escape the blast radius of the self-destruct, but that was for a few minutes and everyone passed out until the ship slowed down.
Quote from: hedgehobbit on February 21, 2022, 10:40:05 AM
Quote from: estar on February 21, 2022, 12:37:52 AMIt pegs Earth to Mars as a 4 day trip as a 1G Brachistochrone trajectory.
The problem with that table is that getting from the Earth's orbit to the Martian orbit in 4 days is only helpful is Mars is there when you arrive. And that still requires Earth and Mars to be in a precise alignment which only happens once every 26 months. So you'll still need some math to determine how long it takes for the other 25 months out of every Earth/Mars cycle. At that point you've just using charts to calculate travel times and the map becomes useless.
Although, I do like the idea of Earth/Mars traffic being concentrated on a once in two years cycle, where a whole fleet of ships launch at the same time and, effectively, travel together. Sort of a wagon train to the stars but with the potential that they might not all be friendly with one another. This is a game scenario that really doesn't occur in any other genre since you can normally just leave whenever you want if traveling by horse, ship, or aircraft.
See this comment by the designer
https://boardgamegeek.com/thread/868735/why-are-planets-static-high-frontier
This is the relevant reason for the Expanse.
QuoteA fourth reason is, for high ISP rockets (including most of the ones in the game) the difference in energy between the worse and best synodic positions is less than 15%. Only in low specific impulse rockets with miniscule delta-v (i.e. all NASA missions until Dawn) do such celestial billiards become significant.
And that leads to the question why bother with a map at all then? Well you bother with a map if you want to include a way for the players to change destination midway through the journey. Which a cross index table of distance values doesn't handle well. Also a energy map illustrates natural way points around which stations will be positioned notably the lagrange points.
Quote from: estar on February 21, 2022, 11:16:21 AMThis is the relevant reason for the Expanse.
QuoteA fourth reason is, for high ISP rockets (including most of the ones in the game) the difference in energy between the worse and best synodic positions is less than 15%. Only in low specific impulse rockets with miniscule delta-v (i.e. all NASA missions until Dawn) do such celestial billiards become significant.
All these energy calculations require that the target (i.e. Mars) be in the exact perfect spot of the elliptical orbit the ship is traveling. Which is a safe assumption since waiting for a proper alignment launch window takes no energy. In High Frontier, you're abstracting a two-year launch window in one-year turns. But, IMO, it completely breaks down when using turns of 1 day or 1 hour when your launch window is one day out of 700.
QuoteAnd that leads to the question why bother with a map at all then? Well you bother with a map if you want to include a way for the players to change destination midway through the journey.
If you want your space travel to be anywhere approaching realistic, then you're going to need an app to calculate position and travel times. But, I can see why that may not matter.
Quote from: hedgehobbit on February 21, 2022, 11:59:50 AM
All these energy calculations require that the target (i.e. Mars) be in the exact perfect spot of the elliptical orbit the ship is traveling. Which is a safe assumption since waiting for a proper alignment launch window takes no energy. In High Frontier, you're abstracting a two-year launch window in one-year turns. But, IMO, it completely breaks down when using turns of 1 day or 1 hour when your launch window is one day out of 700.
Again there is a difference but it inconsequential when talking about torch drives which is what I am focusing on. If we are talking chemical rockets with limited delta-vee budgets then we need to have turns that span a year just like the High Frontier game to marginalize the difference that windows make. And the Expanse uses torch drives.
I am well aware of what required and how it works. And programmed ships that were capable of continuous thrust like Traveller's Type-S Scout. It not a case of just point straight at the destination and go but it also doesn't require hitting a window every two years either. What it takes is point in the RIGHT direction which is usually off angle from the target. Sometimes a dogleg is required. The more Gs you can put out the more you can ignore the effects of gravity. A Free Trader with a 1G drive has to often take a counter initutive approach to reach a destination that I can best describe as a spiral and it is NOT a hohman transfer. Where a speeder ship capable of pulling 6G can almost but not quite just point at where needs to be and just go.
https://www.ibiblio.org/mscorbit/
Quote from: hedgehobbit on February 21, 2022, 11:59:50 AM
If you want your space travel to be anywhere approaching realistic, then you're going to need an app to calculate position and travel times. But, I can see why that may not matter.
Only if your delta-vee budget is limited.
Quote from: estar on February 21, 2022, 11:16:21 AM
Quote from: hedgehobbit on February 21, 2022, 10:40:05 AM
Quote from: estar on February 21, 2022, 12:37:52 AMIt pegs Earth to Mars as a 4 day trip as a 1G Brachistochrone trajectory.
The problem with that table is that getting from the Earth's orbit to the Martian orbit in 4 days is only helpful is Mars is there when you arrive. And that still requires Earth and Mars to be in a precise alignment which only happens once every 26 months. So you'll still need some math to determine how long it takes for the other 25 months out of every Earth/Mars cycle. At that point you've just using charts to calculate travel times and the map becomes useless.
Although, I do like the idea of Earth/Mars traffic being concentrated on a once in two years cycle, where a whole fleet of ships launch at the same time and, effectively, travel together. Sort of a wagon train to the stars but with the potential that they might not all be friendly with one another. This is a game scenario that really doesn't occur in any other genre since you can normally just leave whenever you want if traveling by horse, ship, or aircraft.
See this comment by the designer
https://boardgamegeek.com/thread/868735/why-are-planets-static-high-frontier
This is the relevant reason for the Expanse.
QuoteA fourth reason is, for high ISP rockets (including most of the ones in the game) the difference in energy between the worse and best synodic positions is less than 15%. Only in low specific impulse rockets with miniscule delta-v (i.e. all NASA missions until Dawn) do such celestial billiards become significant.
And that leads to the question why bother with a map at all then? Well you bother with a map if you want to include a way for the players to change destination midway through the journey. Which a cross index table of distance values doesn't handle well. Also a energy map illustrates natural way points around which stations will be positioned notably the lagrange points.
What about time, though? It will take less time at the same acceleration when two worlds are at closest approach then if those two worlds were at furthest distance.
In terms of energy (delta V), changing destinations mid-voyage may require a huge expenditure of energy to allow a rendezvous with a new destination. Those pesky belters and their torchships have a huge advantage with their drives in that area..
Quote from: jeff37923 on February 21, 2022, 03:06:56 PM
What about time, though? It will take less time at the same acceleration when two worlds are at closest approach then if those two worlds were at furthest distance.
As the author said the difference between the two amount to 15%. I am being handwaving it away in favor of playability.
Quote from: jeff37923 on February 21, 2022, 03:06:56 PM
In terms of energy (delta V), changing destinations mid-voyage may require a huge expenditure of energy to allow a rendezvous with a new destination. Those pesky belters and their torchships have a huge advantage with their drives in that area..
Any intersection is a hohmann pivot and you can change to another orbit at a cost of two burns or one day of travel at 1 G. Remember the map is a ENERGY map. Not a position map.
Also in the Expanse the Belters don't have any inherent advantage as everybody has access to torch drives and Epstein Drives.
Quote from: estar on February 21, 2022, 03:20:03 PM
Quote from: jeff37923 on February 21, 2022, 03:06:56 PM
What about time, though? It will take less time at the same acceleration when two worlds are at closest approach then if those two worlds were at furthest distance.
As the author said the difference between the two amount to 15%. I am being handwaving it away in favor of playability.
Something about that doesn't sound right. So you're saying the travel time between Earth and Mars is only 15% different between the cases when they're at closest approach versus the case where they're at opposite sides of the sun?
Quote from: Mishihari on February 21, 2022, 07:24:48 PM
Quote from: estar on February 21, 2022, 03:20:03 PM
Quote from: jeff37923 on February 21, 2022, 03:06:56 PM
What about time, though? It will take less time at the same acceleration when two worlds are at closest approach then if those two worlds were at furthest distance.
As the author said the difference between the two amount to 15%. I am being handwaving it away in favor of playability.
Something about that doesn't sound right. So you're saying the travel time between Earth and Mars is only 15% different between the cases when they're at closest approach versus the case where they're at opposite sides of the sun?
When using magically efficient rockets...
Something the books tease at, but never really deal with is what happens to munitions that miss. Newton's First Law still applies, after all, so railgun and PDC rounds that don't hit something carry on travelling.
Railgun rounds are probably something you can discount because there are so few of them. But PDC rounds are fired off at thousands at a time, lethal clouds spraying off each time they're used. All sorts you could do with that creating some unexpected hazard nowhere near the site of the original fight.
Quote from: Mishihari on February 21, 2022, 07:24:48 PM
Quote from: estar on February 21, 2022, 03:20:03 PM
Quote from: jeff37923 on February 21, 2022, 03:06:56 PM
What about time, though? It will take less time at the same acceleration when two worlds are at closest approach then if those two worlds were at furthest distance.
As the author said the difference between the two amount to 15%. I am being handwaving it away in favor of playability.
Something about that doesn't sound right. So you're saying the travel time between Earth and Mars is only 15% different between the cases when they're at closest approach versus the case where they're at opposite sides of the sun?
Something was lost in the conversation there. Technically, that information (with the 15% difference) is based on the Hohmann transfer formula and the delta-v required to successfully make the transfer. The idea is that it takes a certain amount of energy to accelerate the craft to sufficient velocity to be at the target body in order to make a capture. There's windows where it just doesn't work, although generally speaking, when talking about transfer orbits you can just ramp up the delta-v until you make whatever happen that you want to. The actual time required for a Hohmann transfer is ALWAYS 1/2 the period of the semi-major axis; you're either in the transfer or you're not. For Mars, this is about 259 days.
In the case of Expanse mechanics, where constant-thrust is a thing, you're really using Brachistochrone transfers (even at low thrust) which mean you're just boosting halfway and then decelerating the other half. Your target point isn't where the object IS, but instead where it's going to be (meaning you'll be captured in its gravity well). The calculation is pretty simple, since bodies have a uniform rate of movement in their orbits.
If you're talking about high-thrust applications (anything in the 1g+ range) you're only looking at days of travel time, so the planet won't move much during the transfer. At lower g applications (by that I mean in the .05g range) you might have to give it some lead time. The difference in travel time isn't much even at those levels though; for instance a 1g Brachistochrone transfer at perihelion would only take 29 hours, while at aphelion it would take 79 hours (assuming you fly through the Sun; a detour would add some time to that), while at .05g the perihelion B-stone transfer would be 132 hours, while an aphelion transfer would be 355 hours (about 14 days).
In the latter case, you'd want to shift your point of aim, since Mars has an orbital velocity of 29km/s; over the course of the longest passage the position of the planet would have shifted by 37 million km (about 7 degrees of its orbit). Again, it's a simple calculation to figure out what that point is and aim for it though.
All of that takes place in the easy areas of physics though, the reason orbital mechanics get hard is when you're talking about the seriously optimized minimum-energy transfers that are required for modern engineering. As HappyDaze said, if you have any kind of magical efficiency that leads to constant thrust, you're golden.
Quote from: Panzerkraken on February 28, 2022, 07:44:45 PM
If you're talking about high-thrust applications (anything in the 1g+ range) you're only looking at days of travel time, so the planet won't move much during the transfer.
The problem I found that unless we are talking Traveller style 6G drive. Is that the Brachistochrone trajectory is still impacted by gravity. The issue is not the amount of delta-vee you have, but the amount of time it takes to apply that delta-vee.
For example today's ion drives are capable of continuous thrust with a very high total delta-vee. But they are so low thrust they that have to take a spiral out of Earth orbit. For a 1 G the problem is not as bad but the issue still exist. This means some Brachistochrone trajectories being more optimal in terms of travel time than others. It gets better until at 6G you can basically ignore the local gravity fields.
I tried this in physics simulators like Orbiter Space Simulator with crafts that emulated Traveller style ships from 1G to 6G thrust. Played with the numbers until I got the thrust to mass ratio right and fussed with the ISP value until the on-board fuel could last 30 days at full thrust.
Honestly, three body problems are beyond the scope of RPGs. It's possible to plan ahead for things like making sure you're in excess of v=sqrt(GM/r^2) when you pass near a body, but while I'd be fine with playing in that game (math isn't a four letter word to me..) I've probably only played with a couple people in my entire life that would agree that it sounds like something they'd want to do.
Quote from: Panzerkraken on March 01, 2022, 04:14:18 PM
Honestly, three body problems are beyond the scope of RPGs. It's possible to plan ahead for things like making sure you're in excess of v=sqrt(GM/r^2) when you pass near a body, but while I'd be fine with playing in that game (math isn't a four letter word to me..) I've probably only played with a couple people in my entire life that would agree that it sounds like something they'd want to do.
Which goes back to why the map is a map of energy costs not one that show physical position.
For all that people say The Expanse is hard sci-fi, the books are much harder than the TV show. It strikes me the licensed RPG, from my cursory reading of it, is calibrated for the show's level of grittiness, not the books.
Something else that demonstrates that the licensed game was written for the TV show, not the books, is the mismatch with the opening fiction written by James SA Corey. That brings home some of the critical logistics involved in space travel - the crew are worried about water, air and (shedding) heat. They decide to turn ice prospector, risking limited fuel and potentially dangerous heat buildup, as a way to turn a quick buck.
But the licensed game doesn't even have rules or a discussion on life support systems on the ship or the effects of a deteriorating shipboard environment. Despite the fact that the books make clear time and again consideration of environmental systems are borderline religious in their sanctity for Belters.
Every online discussion of the setting seems to touch on the "why are there no fighters/interceptors" (there actually was a pair of stealth fighters defending the Thoth spin station in the first book), but there's a more fundamental one I haven't seen.
Namely, where are the robots? All the elements needed already exist in setting, you have AI and expert systems that could drive an autonomous mechanised body. There's bionics, power armour and mech frames. The advantages of a robot crewmate are obvious - they don't need to breathe, drink, eat or sleep. They can withstand environments humans can't.
So their absence is a clear design choice by the authors of the books.
I don't recall AI in the books or movies, Kiero. Unless you count the fucking black slime nonsense.
Quote from: Kyle Aaron on March 26, 2022, 02:34:17 AM
I don't recall AI in the books or movies, Kiero. Unless you count the fucking black slime nonsense.
There's AI in the books all the time. What do you think they're doing when they "talk" to the ship's computer and expert systems? What do you think is targeting and firing the PDCs under their normal mode of operation (without human intervention)? Or torpedoes, for that matter.
It's not self-aware, but it's more than capable of running a mechanised body. They look to have deliberately designed them as human-in-the-loop, but that's still AI. It's not a great leap for someone who doesn't care about the implicit ban on true AI to develop it with everything already available in the setting.