“Hard” SF is science fiction that makes a conscious effort to make the science and technology in the story stick to what we know, or at least surmise, and tries to be modest in its extrapolations.  The resulting “hardness” of the SF falls on a continuum: the less extrapolation and the more established the science, the “harder”… the farther out and more speculative, the “softer”, until at the far end of the spectrum you get “science fantasy”, which is essentially magic in technological drag. Allowance is often made for implausible science needed to make the story work, such as  faster-than-light travel or time travel, but even there “harder” SF deliberately tries to reduce the number of impossibilities and often to disguise the ones it has by at least cloaking it in not-yet-absolutely-disproved speculative science.  Sometimes that the whole point of the story: what would it be like if everything we knew for a fact was still the same, but easy and cheap teleportation was possible? (This is often contentious where it shouldn’t be, because people confuse their taste for harder or softer SF for the quality of the story and get tangled in arguments over whether this or that is “really” SF, but I’m going to ignore all that.)

SF RPGs are often on the soft side, if not outright fantasy, with some notable exceptions such as Blue Planet and Traveller.  Partly this is because RPGs tend to be inspired by action-adventure stories and, particularly in the movies and comics, verisimilitude has never been a high priority compared to thrills; partly it’s because making games seem like Hard SF sounds like a lot of work, and likely to be boring to the players or the GM, and GMs aren’t always confident that their knowledge of science is up to the task and would rather spend time working on the setting than doing research.  Visions of players actually being required to calculate orbits, or long arguments at the table over the scientific accuracy of particular features of the setting make Hard SF RPGs seem like more trouble than it would be worth for a little bit of extra S in the SF ambience.

Neither strict scientific rigor nor big swaths of in-game tedium are necessary to have a game that feels like Hard SF, and any system or setting can be tweaked to move it at least a little farther towards the hard end of the spectrum if that’s your goal.   Hard SF can be easy, if you keep a few principles in mind.

Verisimilitude, Not Accuracy

Very few games in any setting deal with things at a sufficient level of detail that you could really check the accuracy, even if you wanted to, and players by and large don’t want to as long as you can avoid gross implausibilities that shatter their willing suspension of disbelief.  Even in a strictly modern day RPG with no SF or magical elements, nobody tracks, say, how much fuel is in their car, what their mileage is at what speeds, and when and how much they have to refuel; running out of gas might come up as a plot point, but if it’s not important to the immediate action players are perfectly willing to assume that because cars must be refueled regularly, they’re doing so “off screen.” The fact that they never have to play out getting gas without some specific reason to focus on that scene doesn’t lead them to question whether the cars they drive are realistically requiring fuel, let alone that the mileage they’re getting fits in with what is known about that model of car.  The same principle applies to make-believe tech in an SF setting.  As long as you establish that the tech has certain constraints, such as space-ships needing to refuel, you don’t need to make the players track their fuel or calculate its consumption or provide accurate details of what specific impulse their engines deliver.  At most you may have to make sure to remind them once in a while, since you won’t be able to rely on the common knowledge that (hopefully) prevents players in a modern day setting from proposing to drive their Ford Focus from LA to New York without ever stopping or spending money on gas.

If It’s Broke, Fix It

Since one of the goals is to avoid tripping the players up with thoughts of “that couldn’t possibly be true”, or “well, I guess since this is just fiction…”, if somebody has a problem with something that strikes them as implausible given what’s known, fix it then and there.  In a setting with magic and gods it’s routine for the PCs to encounter phenomena that are completely beyond their ken, and for only the GM to know the principles that govern magic if indeed there are any, but in Hard SF you’re trying to avoid that.  Even if the PCs encounter a mysterious phenomenon in a Hard SF setting, the assumption is that it can in principle be understood, and they will be able to figure it out if they work at it.  That means that as the GM you should try hard to keep things congruent with what the players know, and you should attempt to reward their efforts to reason from what they know about real-world science and technology as well as what they’ve learned about stuff that you’ve made up for the setting.  If it seems plausible to them that given how you’ve described forcefields as working, you ought to need an air supply to use a personal forcefield for more than a few minutes, then you should roll with that or correct them immediately, not leave it dangling or mysterious whether that’s true.  If they notice a contradiction or hole in the setting that you didn’t, try to fix it or retcon it, rather than putting on your inscrutable GM face and pretending that it’s all part of a deeper truth that they aren’t privy to.

Science is Universal

Whatever is true for the PCs and their civilization ought to be true at all places and times; even if different alien races and cultures have different tech, that tech should obey the same physical laws, and the PCs ought to be able in principle to understand and use it (and vice versa), even if there are practical difficulties such as being built by methane breathers out of substances that are unstable in the presence of oxygen.  Apparent violations of this rule ought to cause consternation, and perhaps even become the focus of the adventure.

TANSTAAFL

As Heinlein put it, There Ain’t No Such Thing As A Free Lunch.  I’ve mentioned this before, in Clarke’s Law and SF Roleplaying, but it bears repeating and emphasizing: one of the biggest things about science and technology in the real world, and so one of the biggest things to emphasize if you want your made-up science and technology to feel realistic, is that there are always trade-offs.  In technology, this is often expressed as the engineer’s trilemma: Fast, Cheap, Good, pick two.  In your game, this can be expressed in a lot of ways to make the technology feel more real: bigger vehicles can be slower  and less maneuverable, or require a lot more fuel; more powerful weapons can be more expensive and require more expensive ammo; more advanced technology can require a lot more maintenance and crew (think about what it takes to keep an F-16 flying compared to a Piper Cub, or a Sopwith Camel);  more advanced tech can also require more support infrastructure (you can land a Camel in an open field, an F-16…not if you want to be able to take off again); cybernetic implants can require a regular supply of drugs to keep the body from fighting them, or people with them can be more susceptible to disease and infection because their immune systems are compromised. Medical technology should have drawbacks: if limbs can be regrown, perhaps it requires rehabilitation before you can learn to use them again; drugs to regenerate nerve damage can be addictive; nanites that destroy cancer cells can work, but still need the destroyed cells to be flushed from the body regularly through blood filtration in the sick-bay, etc. Even completely make-believe science like psionic powers can be made to feel “harder” by presenting it as having major drawbacks, which probably explains why it’s so common to depict using them as causing nosebleeds….

Another aspect to TANSTAAFL relates to how technology is presented as being used in the setting.  If star-ships require regular refueling, then places where you can do that are going to place constraints on the routes ships take and how far they can go, even if the tech doesn’t limit them to travelling along predefined paths (as with star-gates or hyperspace jump lines).  This kind of thing can make the limits of the technology used visible to the players without requiring any book-keeping at all on their part to track fuel consumption.  One easy thing to do that applies to almost any sort of tech is give it a limited duration or fixed number of uses: spacesuits, airplanes, cars, laser pistols, power plants, forcefield belts, teleportation pads.  Even if you don’t make them track it, as long as the players have to consider whether their proposed use falls within the time constraints of the equipment and plan around that, it will make even the most exotic technology feel more grounded in physical reality.

Ground Your Science and Technology in the Familiar

You want the players to be able to say “that sounds like good science” and “if it works like X, then it stands to reason that Y”  In particular, you want to use existing names and ideas when possible.  A lot of technology doesn’t become obsolete that easily, and the science behind it almost never does.  Telescopes have been around since at least 1608, and the principles behind them described as far back as the 13th century.  We’ve made major advances in constructing them, using them for wavelength unknown back then, putting them in space, adding innovations (themselves dating back to 1868) in using multiple telescopes and a bunch of math to simulate a much larger telescope… but they’re still telescopes.  Your star-ships could employ vaguely-named and vaguely-described “sensors”, but it’s more concrete to call its various instruments telescopes, spectrometers, radar, and so on.  This serves a dual purpose in both keeping the science of the setting tightly coupled with real science, and with letting the players recognize and employ their knowledge appropriately without needing to give them an “info dump” on make-believe technology.  Even with new, make-believe technology, see if you can analogize it to existing tech: “subspace radio” suggests that your FTL communications works in a way similar enough to radio that the players can assume, or at least not be surprised by, it broadcasting in all directions and detectable and maybe decipherable by anybody in range with the proper equipment, that its power falls off with distance, that it can be interfered with either deliberately (jamming) or by natural phenomena (ion storms or the like), perhaps even that its bandwidth makes it more suitable for audio than full duplex video.  On the flip side, if the tech doesn’t work anything like that, avoid names that would suggest false analogies and come up with something obviously new such as when Ursula Le Guin’s coined “ansible” for an FTL communication device that instantaneously transmits from one device fixed to a planet or other large body to an attuned device at a known location anywhere in the cosmos.

Keep a Sense of Scale

Space is big. You just won’t believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space. -Douglas Adams

Even with FTL, planets and stars are a long, long way away…and there are a whole lot of them.  Our galaxy is 100,000 light years across.  That means that at 1,000 times the speed of light (somewhere between Warp Factor 8 and 9 in StarTrek) it would take the Enterprise 100 years to cross the Milky Way. We now know of a star system within 20 light years of us that has a planet within the “Goldilocks Zone” where water can exist in liquid form.  That doesn’t mean it’s habitable, or even that it does actually have water, but it’s right on top of us, galactically speaking.  If two such planets (us and them) in such a tight space are typical, then there could be millions in our galaxy.  Space. Is. Big.

A Hard SF game will emphasize that. It might forbid FTL travel completely, or even interstellar travel without generation ships, but even if it doesn’t, it will take significant chunks of time to get from system to system, and even if known space in the setting is huge, it will likely cover an insignificant fraction of the galaxy.  A galactic empire that spanned a thousand star systems would still be just peanuts to space.

Even a single planet is huge.  Just look at the incredible variety of different terrains on Earth, and that’s before you start adding various ecologies, man-made structures and cultures.  As Larry Niven has written:

“It was raining on the planet Mongo.” Lots of SF feels claustrophobic, as if planets were all about the size of a village. It makes the storytelling easier for a lazy writer.

You can easily make your planets seem bigger, and the SF harder, by making the habitats, whether they’re planets, space stations, or futuristic cities more varied.  Even if you have a world that’s locked in ice, or a completely dry desert, you can still have a large variety of different terrains… look at Mars.  No, literally, do a quick Google for some of the terrain features of Mars, ranging from the largest mountain in the solar system, to enormous systems of canyons 4000 km long and up to 7km deep, or a crater 2000 km in diameter and 6 km deep. If the world has water and supports life, layer a bunch of different ecosystems on top of that, modeled after the ones on Earth, appropriate to where they’re situated: near the poles, the equator, in a giant crater, ranged up and down the walls of the canyons, on the mountain slopes, and so on.  If you add human or alien habitations, even if they’re just scientific outposts and not full fledged cities, you can make a sketch of a single planet that seems large and varied enough to support an entire campaign.  You don’t need to work it out in any detail until and unless the players elect to spend a lot of time there, but if you do this for the first few places they’re likely to encounter and then every one that they spend any significant time interacting with, it will be easier for them to accept the illusion that the whole galaxy is filled with places just as varied and interesting.  It doesn’t matter if they know it’s an illusion, and that you sometimes might have to call for a halt while you work out some more detail on the place they want to visit next; what’s important is that they can know that as they’re actually playing the places they go will have variety and they won’t land on Mongo to find it’s raining all over the planet.

You should emphasize the size of planets, and other large objects the characters might encounter, by pointing out how long it takes to travel from place to place.  It’s easy enough to say that the characters are on a ship that’s ten kilometers long, but the players aren’t likely to really come to grips with that unless you remind them from time to time that it would take them two hours to walk from one end of the ship to the other, and that’s why the ship has trams, or turbo-lifts or however the crew actually get about.  Then if the ship comes under attack and the trams break, needing to get to the engine room becomes something they can’t just hand-wave past…  When travelling from place to place on a planet, the same considerations apply; just because in space there’s FTL travel doesn’t mean that crossing 600 km is negligible.  Even on a high-tech world, unless there’s some kind of teleportation system, it’s worth at least mentioning that it takes them an hour by maglev to get from the spaceport to Nova Paree, just to help them picture it, even if it doesn’t become a plot-point in the future.

Make Technology Commonplace (For the Setting)

Even if the equipment is capable of doing things like teleportation or matter duplication that we don’t have a clue how to achieve, to the characters it generally shouldn’t be mysterious or awe-inspiring.  Expensive as hell, maybe, impressive, even, but not astonishing or inexplicable. Unique, one-of-a-kind technology that confers vast powers should be the exception rather than the rule; if it exists at all it will probably be the thing that the whole campaign revolves around as the PCs get hold of it and either become the saviors of, or targets of, the rest of known space, or they will have to wrest it from the main villains of the setting before it’s too late.  Almost all the technology the PCs run into or use that’s not the focus of an adventure should be immediately recognizable and understandable, the kind of thing that you could purchase if you had enough money (or whatever passes for it in the setting)…even if only governments or giant corporations would actually have enough; the PCs should be able to assume that they’ll know what it is, and be able to look up its parameters…and if they find out they can’t, that is a mystery perhaps worth exploring.

Putting it All Together

To make the SF in your game “harder” you want to: aim for verisimilitude, not strict scientific accuracy; quickly fix any spots that the players notice strain that verisimilitude; ensure that whatever the tech and science you come up with applies everywhere and to everyone in the setting; emphasize that in your setting There Ain’t No Such Thing As A Free Lunch when it comes to technology; name things and employ existing technology and science such it seems familiar enough that players can reason correctly about in-game consequences;  remind them of the real-world scale of things in the game; and make the  technology in the setting to be commonplace for the characters unless the fact that it isn’t is what’s driving the adventure.  If you can do all these things, you can make practically any setting, using any system, feel more like Hard SF as it’s played.

Reversing the Polarity

What if you don’t want the SF to feel harder, but instead want to make your game wilder, wackier, and more like Science Fantasy?  Simple: you just reverse all the above advice.  Try to break verisimilitude by emphasizing things we know aren’t true, like air in space, space being filled with “ether”, perhaps even fire being caused by “phlogiston”; if the players notice an inconsistency or contradiction, don’t correct it, elaborate on it and invent some esoteric explanation for it (which may become a feature of the setting); make the rules that govern the setting arbitrary and vary from place to place or character to character; make the technology and science deliver free lunches to all, with equipment that inexplicably has no apparent trade off between power and weight and never needs maintenance, medicine that has no side-effects,  generators that create unlimited clean energy cheaply, perpetual motion machines, new elements with mysterious properties such as anti-gravity; make the science and technology unfamiliar, even it it’s just renaming things to seem exotic such as calling radio waves “etheric vibrations” or telescopes “panopticons”; ignore scale entirely, so that everything travels at the speed of plot…if the PCs have a rocket ship or etheric sailing vessel take it as given that they can get wherever they want to go by the next scene unless something interesting such as a ionic storm, shipwreck or attack by pirates intervenes, and reduce all the places in the setting to their single salient feature (the desert planet, the ice planet, the casino planet); make the technology in the setting arcane and unique whenever possible, don’t allow the players to assume that they know or can reason out what unfamiliar devices do…make them experiment.  The result will be quite far along the spectrum towards rollicking Science Fantasy.