First, a scale of hard sci-fi:

http://www.kheper.net/topics/scifi/grading.html

Generally speaking, everything I want to do falls into the "Very Hard SF" or harder categories. No FTL travel, no warp bubbles, no time travel, no wormhole travel (sure, wormholes might be a real thing, but you almost certainly wouldn't want to enter one), no teleportation, no handwavium, no cloaking devices (you can't hide life support systems or engines in space), no icy doom when spaced without a suit (you die from no air and no pressure, not by freezing), etc., etc., etc.

Just looking for any kind of advice, info, links, etc., you want to give. I'm probably going to roll my own system, but I'm still open to reviewing good medium-crunch stuff; even if I won't use it wholesale, I'll pillage it for systems and ideas. I was looking at Savage Worlds, until I realized that SW isn't OGL; for some reason I'd rather roll my own than use a generic system that isn't OGL.

I'm especially interested in tools for building space habitats, star systems, planets, ecologies, societies, critters, etc.

I posted a thread some time back at some shitty forum where I was subsequently banned for not being a complete, total, abject soy boy, or for not being wrong about the definition of hard SF...I'm not really sure. In any event, here is a roundup of the systems/settings that were suggested to me:

Jovian Chronicles
Blue Planet
Cyberpunk 2020 (Near Orbit and When Gravity Fails)(Deep Space)
Classic Traveller (3 core books plus Supplement 4: Citizens of the Imperium)
Diaspora
Spacemaster Privateers
Star Cluster 3
Traveller (Orbital Setting)
GURPS Terradyne
GURPS Transhuman Space
Cyberpunk 2020
2300AD
Traveller 2300
Orbital 2100
Shadows Over Sol
Eclipse Phase
Mindjammer
Albedo RPG (Platinum Catalyst edition)
The Expanse (upcoming)

Previous or subsequent searches have revealed a few more:

Coriolis
Stars Without Number
Fading Suns
Thousand Suns
M-Space
Savage Worlds - Interface Zero
Savage Worlds - Seven Worlds

(I really have to give Seven Worlds a shout-out for their dedication to writing a hard SF RPG; they took time to do their research and write scientific explanations of their choices, which I really appreciated)

Traveller, 2300 AD, Eclipse Phase, and Coriolis all involve FTL and/or other elements you are trying to avoid.

I always liked Heavy Gear. Reasonable mecha (small, lightly armored). FTL exists but is extremely rare and expensive as hell. And a deadly system.

Happy, yeah, but this is as much about mining a system for good stuff as it is about choosing a system to run. Moreso, really.

Lord, yeah Heavy Gear always gets mentioned in sci-fi system threads, I'll have to take a look.

What kind of system do you really like playing? What do you find the most exciting about a system?

Why OGL? You want to publish this? SWADE has a content creator program on DTRPG. So does HERO now. Cypher system, Gumshoe, Torg...  If you want to publish under a known property you should check out all the programs on DTRPG.

You'll want to look at 1st or 2nd ed. 3rd ed they tried to take it d20 and that just ruined it.

HG is the same company (Dream Pod 9) as Jovian Chronicles.

I've seen Classic Traveller used well for "very hard scifi" because one of the major elements between "hard scifi" and "space fantasy" is what happens when a human body gets hit with higher tech weapons. In Traveller, those bodies mostly go splat.

Also, Traveller's chargen works well to simulate the randomness of human learning and development. It's not perfect, but its a great system if you are looking for a system that takes back seat to the setting you are designing. In fact, I am 100% sure there are published Traveller settings that might be "very hard" enough for you. IIRC, there was one called ORBITAL.

I'm a space horror fan. I've run Traveller campaigns stripping down the tech to "realistic", keeping everything in our solar system, and enforcing the laws of physics and biology, and then adding Mythos nightmares into the "realism."

So, simple Hard Traveller patch.  There is no jump drive or antigravity, this volume is now wings and thrust vectoring and higher G worlds tend to have thicker atmospheres so it all works out.  Ships that don't enter atmospher trade in the jump drive for an ion drive that puts out, 1/10 G and is ten times more efficient than the maneuver drive.  The fuel tankage is 1 G-hour per 10% of the ship's volume.  Sure mass would be more realistic but this is a simple patch.

All hard sci-fi really means is that space helmets are required.

Cepheus Engine is OGL Traveller and may be dialed in quite hard for Sci-Fi. You already mentioned the Orbital and Orbital 2100 settings which are for Mongoose Traveller 1e and Cepheus Engine respectively. To really get the Hard Science feel, I'd suggest getting the Spacecraft Design Guide for Cepheus Engine which will allow you to design spacecraft with chemical rockets, solid rockets, NERVA drives, and realistic fusion rockets that do not use grav plating but spin habitats to avoid the effects of prolonged lack of gravity (the Vehicle Design Guide for Cepheus Engine is also not too shabby). The only drawback that I can think of is the lack of some of the wackier but plausible spacecraft drive types, like Robert Zubrin's Nuclear Saltwater Rocket.

As a general reference work for you, I highly recommend the Atomic Rockets website. Chock full of some of the best material you could ever want about the science in science fiction space travel.

Have fun!

You should check out Stellar Wind . The basic system is nothing to write home about (somebody's homebrewed d20) but the spacecraft construction and travel rules will be right up your street. Somebody has basically already done the work for you of turning Atomic Rockets into gameable rules.

If you can find it, Cthulhu Rising, a hardish-SF setting for (you guessed it...) Call of Cthulhu. There is FTL but you could easily ignore it - there is a wealth of setting detail just about the Solar System. The same author later did River of Heaven using OpenQuest rules (a slightly simplified BRP/d100 system), which is very Alastair Reynolds in feel.

Speaking of which, you've heard of Eclipse Phase, right?

Traveller: The New Era is much harder SF than Classic. Oh the joys of calculating Bingo Fuel...

Quote from: Shawn Driscoll;1120256All hard sci-fi really means is that space helmets are required.

Nah, it means heat sinks are required.

We had a similar thread a few weeks ago.

So once more. Personal Go-Tos for hard SF RPGs.

Star Frontiers+Knight Hawks: No artificial gravity. No psionics. Alien races are few and some are the product of past seeding of the area by beings unknown. Just pretend Zebulons Guide never existed. Thats what 90% of the SF fanbase does. Has a hyperspace. But its mildly unsafe.
Albedo: Even harder SF than Star Frontiers. No lasers. No anti gravity. No aliens. Practically no alien fauna even. No lasers. There is a psi power but it exists so rare only less than a handfull of NPCs have it. Combat is brutal and war is hell. Has a hyperspace. But its VERY unsafe.

Others I like being
CP2020 Near orbit: Not a bad little expansion to CP2020 out into the solar system. The second book takes it out into the galaxy and is less hard SF.

Wayyyy back Dragon Magazine did some space themed articles for Top Secret. Hard SF overall.

Quote from: trechriron;1120229Why OGL?

Probably because he has his own setting in mind that he doesn't want to have locked up behind a restrictive Community Content license. With Genesys and possibly Hero Game being exceptions.