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Building a Science Fiction Universe: Beginnings

What’s this universe for, anyway?

Ok, so you want to create an SF universe – what’s it being used for?  I want to tell the story of a ship, the UES Achilles.  It might be a novel, or a tabletop RPG, or a series of novels.  Fortunately, many of the worlds built for role-playing are also good for novels – they lend themselves to the media format switch well since both are basically a print media, and telling a story over a period of several (or several dozen) hours.  The major difference is when crafting gaming supplements, which should not railroad the players into one specific path – not a consideration for a novel, where the narrative is whatever you set it to.  So basically, we need to get down to the details of what should be in this universe. (again, the purpose of this site is to illustrate the process I am taking to create my setting, take or leave what you will of this)

In my case, I want something which is reasonably hard-SF.  Something “harder” than the BSG reboot, or The Expanse.  Something that spans multiple star systems, and something where travel takes a fair amount of time, but typically not years.  A big part of that is going to be the jump drive.  Jump drives are fairly common in SF.  Battlestar Galactica and Babylon-5 both have them, and they can basically be engaged at any time – and the Galactica used it frequently to get out of sticky situations.  The parameters of the jump drive in BSG were not clearly-defined, but it was damned accurate if you had a good plotter to set the coordinates, and it couldn’t generally be used for “tactical” jumps – we only see it used in that fashion a couple times in the series, and it’s not clear whether that was due to the other ships in the fleet being civilian ships, or some other reason.  Another type of jump drive is the one found in C.J. Cherry’s “Alliance-Union” setting. (In “Downbelow Station”, the “Chanur” books, and “Cyteen”, among others) I am a big fan of Ms. Cherryh’s books, especially “Tripoint”, “Rimrunners”, and “Hellburner”.  Jump drive in the “Cherryh-verse” involves making one’s way to a “jump point” to another system (there is one for each linked system) which is not clearly defined, but once there, you go into jump space and travel in a straight line until the gravity of the destination star pulls you out into normal space.  You have to be drugged unconscious or jump space will drive you mad, and it takes a month or more to get there. There’s a lot of additional details, but basically that’s it, plus the “jump vanes” on your ship can be pulsed to speed up or slow down prior to or after jump – which gives you a lot of ∆V (Delta-V) for free and greatly reduces travel time.  The combination of sleeping in jump space and occasional relativistic travel means that characters who are in space a lot are younger than their stationside age would otherwise indicate.  In Tripoint, Tom is 23, ship-time, but he was born almost 40 years ago as stationers keep time.

One big change allowed

They say that in “good” SF, you’re allowed to change one major thing and still hold the reader’s suspension of disbelief.  (typically most SF authors agree you can also sweep 1-3 minor items under the rug) For most settings, that’s a Magic Space Drive (TM) – frequently some form of FTL – and in my case, it’s the jump drive.  My details can be found here, but that page doesn’t explore all of the nuances.  Here’s a couple of mine, with the key details repeated:

  • No explanation: I don’t want to have to explain why jump drive works.  So I don’t.  An object crashes on Earth in 2158.  Or maybe 2058, who knows.  It’s filled with 15 metallic spheres packed well enough to survive impact. (another dozen are damaged / destroyed) No one survived the impact, but the ship contained extraterrestrial bipeds.  The impact is in northern Canada, and once the major world powers get there and look around, they immediately lock it down.  The ship is taken apart and disappears into several research sites, and the world’s major powers publicly blame each other but secretly share research and eventually figure out how to make more of the devices, which acquire the name “jump governor”.
  • Instant FTL: Jump drives travel to another star almost instantaneously, taking microseconds to move light years.  They seem to require only a few kilowatts per tonne to jump, and it means that the fastest form of communication between stars is a sort of Pony Express. (Traveller would call it the XBoat network)
  • Size limits: Jump drives have several thousand parts inside, and many can’t be made smaller than a certain size.  The distance between components matters also, and so the parts can be scaled in a linear fashion until the point where they are too far apart for the jump governor to work.  This means there is both an upper and lower size limit to the governors.  A governor of a given size can move a certain range of mass, so this also means ship size is similarly constrained – from roughly 1,500 tonnes (that’s “metric tons” for you unrepentant Imperialists) to about four million tonnes.  No jump fighters in this setting, and no Star Destroyers. Also, larger ships exit and enter farther from the star or planet than smaller ones. (as gravitational force doubles when ship mass doubles – 4x the mass = twice the distance)
  • Repeat jumps take time: The drive takes several hours to cool down, forcing a limit to how fast jumps can occur.
  • Tactical FTL: Any gravity gradient of a certain strength (force, not acceleration) will haul a ship down out of jump space back into our reality – including brown dwarfs, Jupiter, Ceres, or even a small moon – although for small asteroids, it would cause a ship to exit jump space close enough to overlap with the asteroid itself, causing an impressive explosion.  This means a ship which jumped to Sol and exited jump at the jump space boundary (typically 1.5-2AU from the Sun) could spend 6 hours cooling the drive and then jump directly to Jupiter. (assuming it was outside the sun’s jump limit, and that a straight line to Jupiter didn’t cross the boundary again)
  • No WMD: It’s a simple fact that any reactionless drive or technology that allows ships to move multiple kilometers per second = a weapon of mass destruction, based on kinetic energy alone.  Rick Robinson puts it this way: “An object impacting at 3 km/sec delivers kinetic energy equal to its mass in TNT.”  Meaning a 33,000 tonne warship (one of my bigger ones) moving at 10km/s = would hit with the force of 100 kilotons of TNT – equal to 5x the power of the nuclear weapon dropped on Nagasaki, Japan.  That’s bad enough, and could still happen without a reactionless drive – the Apollo missions returned from the moon at 10-11km/s, but were a lot smaller.  My jump drive avoids that by forcing a ship leaving jumpspace to enter normal space at rest respective to the gravity peak which caused it to exit jump space.  In the case of Jupiter or Saturn, you are immediately at rest respective to that planet, but far enough out that your ship may naturally fall into an orbit around it, (due to the Sun’s gravity) depending on your entry vector.  In the case of the Sun, you fall straight towards it, but not very fast.

So, what are some of the ramifications of this?  That’s a good question.  One thing it does is allow me to get around some of the limitations of my propulsion system. (see below) Since ships can basically jump to an outer planet or very close to one of the large main belt asteroids, I can retain a setting with realistic propulsion systems and still get from Earth to Jupiter in months rather than years.

Speaking of engines… (propulsion)

Atomic Rockets has a great list of engine types and expected performance. In an ideal world, I would select something with the ∆V and thrust ratio that I wanted, and build from there, but most of the propulsion types cataloged not only don’t exist today, but their engineering details haven’t been worked out.  We know the limits from a scientific perspective, (such as chemical rockets being limited to no more than a specific impulse of about 500 seconds) but we haven’t worked out the engineering details – can the reaction chamber take the pressure at this level? How much waste heat is produced, and will that melt the nozzle? Will the cooling requirement mean huge coolant pumps?  Things like that.  Incidentally, this is one of the things which the game Children of a Dead Earth excels at – allowing you to change all the details of your engine to figure out exact performance and what will and will not work – whether your ship runs on Hydrogen and Oxygen, or Methane, Decane, or other fuels.  Basically, the two “performance” options are Chemical Propulsion, or Nuclear Thermal Propulsion (NTP).  In either case, my ships will likely have somewhere from 3kps-10kps total ∆V – probably a methane NTR, and there will be a lot of methane tankers running around the Solar System.  This assumes, of course, that I don’t build ships with Nuclear Pulse Propulsion (NPP), like the 1960s Project Orion. Orion-style NPP engines have 3x-6x as much ∆V as NTR, but they also use up the very bombs the military might want to lob at other spaceships. It’s also worth pointing out that we’ve built and tested an NTR on the ground, whereas Orion never made it past proof of concept.

Summary so far…

  • My major change: FTL travel in the form of a jump drive
  • Jump drive size limits: 1,500 tonnes – 4,000,000 tonnes
  • Instant travel, with a delay before traveling again
  • No “planet-buster” relativistic rocks (Buy the T-Shirt of this from Ken Burnside!) – the Magic Space Drive (TM) should not allow 100kps planet strikes
  • Cheap travel to the outer system
  • We don’t have to explain how the Magic Space Drive works, because… someone else built it and we’re just trained monkeys
  • “normal” travel is still with “realistic” technology – NTRs and chemical drives, and possibly Orion.


So, what does all the above mean?  First off, I have a spreadsheet I created to do the math for the jump drive.  Ships can’t initiate a jump if the force due to gravity is above a certain limit, (I’m still defining the exact limit) and that limit means if you’re inside the boundary of that sphere, (let’s call it the jumpshell) you can’t enter jump space.  If you’re outside the shell, then when you contact it, your ship falls out of jump space at that exact point, and re-enters normal space completely stationary in regards to the object that caused you to exit jumpspace.  This means you can’t hit something at light speed. (or indeed, at all, with one exception) The Jump Shell Boundary (JSB) distance depends on the gravitational force, not gravitational acceleration.  Take 2 bricks – a 1kg brick (2.2lbs, fellow Americans) and a 4kg brick.  If you drop them off a building at the same time, and stick around to see it, (and no one calls the cops) then they will hit the ground at the same time – acceleration is constant, because accel = force / mass. (derived from F= M\cdot{}A ) There is 4x the force, however.  Gravitational force is found by F=G\cdot}\frac{M_{1}\cdot{}M_{2}}{ r^{{2}}}  meaning that the force is quadrupled if you either quadruple the mass or half the range. (and the inverse of that is true – to get 1/4 the force, quarter the mass, or double the range)

So basically, a ship 9 times as massive has to travel 3x as far from the sun before it can jump.  I want UES Achilles to mass about 18,000 tonnes, because it’s about the size of a US Navy cruiser or a large submarine. (I might change this later, but it’s my aiming point) My spreadsheet does the math according to the Gravity equation, to calculate what range gravitational force exceeds the limit for jump.  For my target ship the Achilles (which I previously called a “Cornwallis Block II Frigate”) that is 7Mkm from Jupiter, or 758LS (light-seconds) from Sol. (roughly the orbit of Mars) Recycle time after a jump is about 6 hours.  During that time, the ship would “fall” towards the central object that pulled it out of jump space.  In 6 hours, (21,600 seconds) that would be about 600km towards the Sun or Jupiter, or whatever – assuming nothing is done.  Actual gravitational acceleration is about 0.0025m/s2, (1/400g) so countering that acceleration would be trivial – it would cost around 0.055km/s of ∆V if we wanted to “hover” – that’s practically a rounding error. The jumpshell distance varies with the mass of the ship, so it could be an issue if one were to miss the Jupiter SOI and hit the solar jumpshell at the distance of Jupiter directly in front of it, since Jupiter circles the sun at 13km/s.  Also, the ∆V to get to the inner planets inside the jumpshell will not be trivial, but it would be within the fuel load of a given ship if a low-fuel trajectory is used.  This means a travel time in months to the inner planets, unless your ship is small enough that the jumpshell is inside Earth’s orbit. (your ship must be lighter than about 8,500 tonnes)

What this means is I have created a setting where the following is true: ships that are smaller than 8,500 tons can jump from lunar orbit (as long as they steer 30,000km clear of Luna itself) to anywhere farther out – Mars, Jupiter, Saturn, the belt.  They can do it for very little energy, using no fuel, and can jump again after 6 hours.  This makes travel very, very easy once out of Earth’s gravity well. (which as Heinlein said, is half the effort to get anywhere) Meaning a spaceship less than 1/6 the size of Paul Allen’s yacht can go pretty much anywhere – now we have a reason for tramp freighters.  Passenger ships would more closely resemble airliners, or perhaps Amtrak – sleeper cars which would let you travel in relative luxury, getting to your destination in no more than a few days. (6 hours per jump means 8 jumps in 2 days)  I’ll talk about it later, but this SF setting will have lots of modular ships, so it’s likely some of the transports would be a jump “carrier” which can accommodate several (or dozens) of modules and move them from one location / station / whatever to another.  imagine something the size and shape of the Destiny lab on the ISS which you live in (maybe with 1-3 other people) and that you own.  The module would be your house, similar to in this award-winning design (by a Toronto high-schooler, no less) for a space station – Asten.  Asten would have thousands of these living modules (see pages 19-20) based on NASA’s inflatable Transhab concept.  Now imagine that the modules could be inflatable like those, or rigid like Destiny, and that you could disconnect from the orbital station and be attached to a chemical rocket, then thrust to another orbit where a tug would again detach your house and link it to a jump carrier.  Zip!  Now your house is in Mars orbit, or Saturn, or Tau Ceti e, or Wolf 359.  That’s the kind of future I want to write about.  Not everything would be modular, but the modules would be what allows a huge and mobile society.  It’d be as if the shipping container house fad that’s currently in vogue were extended so that you were loaded on a truck, then a ship, then you’re living in West Africa, or Hawaii, or Singapore.

This type of jump drive also means space “patrol” ships are practical.  Not the traditional “space fighter” (which I didn’t want anyway) but something analogous to a Coast Guard cutter or a corvette – a small, limited-duration ship – because they can get closer to the inner planets now, instead of 6 weeks (or 6 months) from now. They also would be able to stay close to a base and not devote a lot of volume/mass to things like crew amenities. It also means piracy is practical under certain circumstances. If you want to move large amounts of material in bulk, then there needs to be a large cargo port further out – Saturn would be a good location in the Solar System for one where you could jump Supertanker-sized cargo ships.  In general, however, the economics at first glance would seem to favor somewhat smaller ships.

Next up – Modular Space, it’s not just for the 1970s anymore…

Next post I’ll go into the whole “modular” thing, and what I think that means.