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.
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:
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.
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.
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 ) There is 4x the force, however. Gravitational force is found by 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 post I’ll go into the whole “modular” thing, and what I think that means.