Have a look at this link, which struck me as having vague relevance to space exploration and hence Rogue Traders:-

http://www.wired.co.uk/news/archive/2011-02/21/kepler-galaxy-census

According to this, the most recent galaxy survey, there are an estimated 50 billion planets in the galaxy, 500 million of which are in the potential "goldilocks" habitable zone. They got these figures based on these ratios:-

"Kepler chief William Borucki and his colleagues realised that one of every two stars has planets orbiting it, and one of 200 stars has planets in the habitable zone."

So you could actually do a pretty realistic exploration table, like the one in the GM screen pack, to represent this, but based on the latest scientific evidence. Upon encountering a star, roll on the following tables :-

Table 1: Star system (roll d100)

01-50 - The star has no planets

51-00 - the star has planets: roll on table 2

Table 2: habitable zone planets. Roll a d1000 (3 rolls of a d10)

001-995 the star has no planets in the habitable zone

995-000 the star has a planet in the habitable zone.

er...ok, I appreciate that will take the narrative glamour and excitement out of the process, but it is at least realistic!

I do like to add a sense of realism to my games, so this is a very interesting piece of news. However, the problem with such raw statistics is, as you say, that they drain the narrative flair and excitement somewhat, if you;re mechanically going through the various systems your players explore.

This doesn't mean you should just discard your random tables. If your players suffer a warp misjump or the likes they can end up in all sorts of places. Depending on how long you want to run through such incidents, you could use this table to provide a basis for qa new viable system, or even a lonely star, burning away it's reserves of hydrogen alone in the void (currently I run a brief 1 hour WHAT DO YOU DOOOOOO style session with minor hazards, but plan to step up to multi-session life threatening stellar phenomenon stories as we move up and onwards).

there's no reason to totally discard science in the name of any fictional system, but you also need to make sure that the players like it that way, and realise that although you value scientific factuality in many game elements, it cannot override important narrative points (for instance they MIGHT be able to drift their ship sideways towards an opponent firing macro broadsides in newtons take on physics, but the combat mechanics don't take it into account, and that is a lot more Babylon 5 than Warhammer 40,000.

I agree - basic science should have a place in 40k. I have absolutely no scientific background, but I do feel the setting is weakened when there is constant "handwavery" used to explain away scientifically impossible aspects. I can accept stuff like the warp - which is (as far as we currently know) completely unscientific, as this is a willing suspension of belief, and fundamental to the background. But when incidental things like lasers just don't seem to operate in any kind of rational way, my inner nerd starts scowling. But that's just me!

Anyway, that aside, and returning to space exploration, one imagines that the scanning/auspex equipment on most Rogue Trader vessels would be powerful enough to enable them to scan at least the dozen nearest stars while simply stationary in space. Humanity has found hundreds of exoplanets so far using equipment far less sophisticated.

Perhaps standard operating procedure for a Rogue Trader would be to pick a star that is as much like Sol as possible, head there, and from a stationary position a light year or so out, scan that star and then scan all the others within a 5 light year radius or so for any hint of planets in the "goldilocks" zone. If there's any sign, they'd move in and inspect it. If not, they'd simply chart the star and move on the next one. In this way, you could chart perhaps 50 or 60 systems a year, maybe? So maybe every 4 or 5 years, you'd hit a habitable world? These are just speculative musings, really...

Good points - I am currently running the Simkin's Reach meta Endeavour, and my players have made it up to the stage where they are doing just that - dropping warp into interstellar space, close enough to the cluster that their auspex can locate favourable systems (the Stellar Survey objective) without interference from anything in the interstellar medium (dust clouds, nebulae etc).

For flavour, i will likely take on board the facts you presented in the OP, and state that there are a lot of systems with nothing of note, before presenting the five systems i have generated, two of which are unfavourable to human life but possess resources that would be incredibly lucrative if harnessed, and three of which house civilizations of various kinds (leaving out tech level and species as my players read this board, but they know they're going there to find out if anything lives there or if the legendary Simkin did found his colony).

But yes, I will be quiet now as I feel we basically agree on this: science has a place in our description of events and general over view - but we must focus on the player-centric 'exciting' elements of that truth. As an RT you are that 0.0000005% of important things happening in the galaxy, and you should be experiencing the extraordinary, described against a backof the mundane.

Ever one for the impossible question Lighbringer!

Canon wise in 40k there are a "million imperial worlds" with the uncalculable hoplessly out of date variations at the administratum, depending on the Xeno of the week planetary invasion or a lowly scribe accidentally shredding or misfiling a tithe ledger thus dooming a planet to bureaucratic oblivion.The thread on the range of auspex sensors that I started sort of touches on this as it would obviously make it a lot easier if the imperium were able to make a qualified guesses on the feasbility of a star system with habitable planets, rather than having to visit every emperor forsaken star system and making an augur scan. This is especially important for for Rogue traders as its kind of their main raison d'etre in the 40K universe, bringing in new planets into the emperors realm.

I think we probably need to define whats habitable....an earth like temperate world where humanity can quite happily make a fist of surviving with not too much, trouble or do we mean some hell hole where humanity grimly holds onto existance with only their sturdy flashli...sorry their lasgun and their "faif in der Emprah!" to keep them going. Bera in mind that in teh past the Imperium colonised High gravity and low gravity worlds as well as pleasant and inviting worlds such as Catachan where habitable is a ephemism for a life of unending combat against a planet's biosphere that considers you to be food or a parasite. Or does it mean a planet where the very air is corrosive, but the gravity is such that people can survive quite happily in domes cities (Mars in total recall anyone) The permutations are endless.

Then we have to define worlds....do we mean planets or even planet sized moons that can support life?

My guess is that a planet has to have something to go about it for a rogue trader to settle there in either goods or materials. If they want to colonise a planet with no discernable quick payoff they might just create "trading stations" for equipment or supplies on major trade routes, and if these are important enough to warrant it the planet doesnt even have to be that habitable.

Once I tries to Figure out the subdivisions of the Imperium using some of the early fluff from Space Fleet (Jervis Johnson, Andy Jones, Simon Forrest & Rick Priestley (White Dwarf 139 &140) )

1000000 worlds in a galaxy which is 75000 light years edge to edge (west to east fringe? Not sure this is actually scientifically correct BTW)

200000 worlds per segmentum (5), this is at best a guess...bear in mind that this is because "Although intended for purposes of fleet administration and shipping controls, the Segmentae have evolved into administrative divisions of the Adeptus Terra." you would imagine they divide up into divisons that the administratum can bureucratically manage which often mean equally. Again this is a guess

Sectors "Each Segmentum is divided into sectors. The size of a Sector varies according to local demands and stellar density. A typical sector might encompass 7 million cubic light years, equivalent to a cube with sides almost 200 light years long."

Subsectors: "Sectors are divided into sub-sectors, usually comprising between 2 and 8 star systems within a 10 light year radius (some may encompass more systems - others only 1). This size is governed by the practical patrol ranges of spaceships. Because sub-sectors are divisions of worlds (rather than volumes of space) there are vast numbers of star systems within each sector which do not fall with in a sub-sector. These are referred to as inter sectors - and are commonly known as wilderness zones, forbidden zones, empty space and frontier space. Inter-sectors may contain gas or dust nebulae, inaccessible areas, alien systems, unexplored systems, uninhabited systems and uninhabitable worlds."

I cant be arsed to do the maths right now...(any maths majours out there?) but Im pretty sure someone can calculate the amount of subsectors sectors and with the RT rules on what constitutes as 'vast' a guess at how many planets fall between the sectors.

If anyone can figure out how big the koronus expanse its, they may be able with the information above to have a guesstimate at how many planets could be feasibly colonised in the koronus expanse given what the Imperium has achieved so far in the galaxy. And bear in mind that the imperium has a wide margin for what is habitable.

Lightbringer said:

This is very interesting information, and I thank you for bringing it to my attention.

Apart from ruining the narrative flow, there is one fairly important issue I would take with these charts, however: statistically speaking, most systems will be devoid of anything interesting. That may very well be realistic, but it's not exciting at all. In a game, I image the players would quickly become tired of jumping from system to system and not finding anything. Perhaps that's what you meant.

I wouldn't use a chart like this to randomly generate systems while the PCs are exploring, not even for a bad warp jump, simply because I would prefer if my PCs had at least a reasonable chance to land somewhere interesting, even if it was by accident.

Where I WOULD use a chart like this, however, is while building my campaign world, to avoid needing to think about how many interesting planets there should be and where they should go. I'd just nominate a number of stars for the sector (probably by rolling d100+20 or something) and then randomly generate each system using these charts, and maybe a couple others to generate specific planet details for those systems that contain something useful. Then I would probably nudge a few things around to avoid having excessively large expanses of nothing interesting in one place.

Having predetermined everything in the sector, I would then set my PCs loose and let them explore it.

www.cbc.ca/news/health/story/2011/02/19/planet-census.html

Habitable zone

Borucki and colleagues figured one of two stars has planets and one of 200 stars has planets in the habitable zone, announcing these ratios Saturday at the American Association for the Advancement of Science annual conference in Washington.

The Associated Press

As for the size of the Koronus expanse, i'd say it is much bigger than the Calixis Sector, maybe three of four times as huge, maybe ten times as huge.

Of course, much of it might not be as useful as the calixis sector. The expanse is noted as having lots of dead stars, dead worlds, etc and this seems more common here than in the calixis sector.