First off, I'm sorry if this is posted in the wrong part of the forum, feel free to move it if it is.

I'm currently designing a skyship for my campaign on Solomon (As described in the House of Dust and Ash adventure), and got to thinking about hos such a ship would be powered.

I figure the the two propelers providing thrust are probably promethium powered, but the ship probably needs some sort of generator for the skimmer fields (Grav plates? I don't remember what they're usually called). Is a basic prometheum reactor enough? Other options I've been considering is a Plasma Reactor, or a Fission Reactor (as that technology is already prevalent on Solomon).

The pro's of a prometheum reactor would be its relative simplicity, so the ship's engineers wouldn't have to be as well trained, but on the other hand, a prometheum reactor would use up a lot of fuel, which would cut down on the space available for crew, cargo and passengers.

A plasma reactor on the other hand, is not simple at all, but it is likely a lot less bulky (or at least it's fuel probably is).

A fission reactor I'm guessing would be somewhere between the two, with the least bulky fuel, but by far the most bulky machinery, due to all the radiation shielding and such.

What do you guys think?

I limit promethium to being used by vehicles comparable to modern internal-combustion-driven vehicles, and make up sci-fi-sounding power sources for vehicles beyond what modern science can produce. Skyships- massive anti-gravity vehicles- would be a good candidate for some kind of atomic reactor. The crew shouldn't be able to take the Skyship's technology for granted, but rather should reguard it with almost superstitious awe, in my opinion...

That's pretty much how I feel too (even though some kind of smoke belching, prometheum fuelled behemoth would be pretty cool ).

Which brings the choises down to two, Plasma or Fission.

I've always figured that Plasma Reactors are highly refined variations on Fusion technology, and they feel a bit too clean and futuristic for a low-cost, down and dirty bulk cargo ship, but a Fission reactor might be perfect.

Fission is high-tech enough to be problematic (to say the least) for any ship's mechanic to fix, meaning a Tech-Priest needs to be brought in for periodic maintenance. Its fuel lasts for a long time, but is exotic enough to be a bit hard (perhaps even a short adventure) or expensive to get hold of.

Also, there are all kinds of funny effects of shoddy maintenance that can be thrown in to hurt any players on the ship.

Besides including an reactor of its own (which I normally only due in -massive- vehicles) their is the option of an depleteable energy storage.

The 40K-universe now methods of storing insane amout of energies. Otherwise, Las weapons would not exist. So how about something like fuel cells (similiar to those used on modern submarines... so I think these are actually auxilarry systems)? These cells provide the energy for some eletronic engine or are directly feeding the anti-grav mechanics keeping the vehicle aloft. After X km (which might be every three journeys or something similiar) the fuel cells need either to be replaced or reloaded.

A cell might be much lighter then an actual reactor (since you do not need to consider things like cooling equipment or radiation shielding) but has the ultimate drawback of being depleteable. In addition, if the fuel cells are just for the anti-grav, you can still have the joy of a regular, smoke belching combustion engine in order to keep the propellers moving.

Almost all void-ships are powered by plasma generators. Highly unstable and dangerous its one of the only Imperial technologies capable of providing the required energy output of void and warp travel.

Note: plasma in 40k is 'the purest form of energy available, the component material of stars, completely ionised matter. It is little used in the Age of the Imperium , the safety margins for its containment are too tight. Regarded as old fashioned, it is still used to power steam or photon technology and is used for space drives (40k:RT 1st Ed. p270).

The other common power systems are;

Crystal batteries (manufactured crystals that absorb energy that changes their crystalline structure and then slowly releases it as that structure reverts to normal) (40k:RT 1st Ed. p270).

'Conventional' (petroleum, solar, wind, atomic/nuclear fusion/fission, tidal, fossile fuels, animal-powered, etc.) (40k:RT 1st Ed. p270). Later 'promethium' was added and i guess i'd put it into this category. (40k:RT 1st Ed. p270).

Ultimately its up to you.

Perhaps cyrstal batteries? The ship's 'sails' actually gather photonic energy (starlight) focussing it into the crsytal core which releases that energy into an ion drive emissions array? Something like that?

I truly hadn't considered stored power, thanks.

I feel that managing batteries might bee too easy though, with too little mystery and danger for what I'd like, and besides, the ship is pretty huge, with a length of about 55 meters. It will need a lot of energy to manage all the lift needed.

I think the propellers will be Prometheum fuelled though both because it's easily available, and because it handily limits the ship's maximum flight length. It also increases the risks of funny fires if the ship is attacked by Wreckers.

Sorry Luddite, I wasn't really clear, it is not a starship, but a skyship (pretty much a steampunk/40k blimp with counter-grav instead of lighter than air gas).

Thank you for the Rogue Trader references though, I will definately look them up.

No worries.

55 meters is pretty small by 40k standards though eh? I guess what we're looking at here is the 40k version of Jabba's Sail Barge from Star Wars.

http://images.wikia.com/starwars/images/d/d4/Sailbarge-chron2.jpg

I'd go with Crystal battery storage that provides energy through a heat exchanger to a steam engine. This powers the ship's gravity plating for lift and locomotive turbine blades for thrust.

Nice and 40k, with a real mix of tech. And options for all manner of malfunctions as befitting the 'everything in decline' 40k meme...

55 meters is basically in the range of a small cruise ship, so it's still pretty big (far larger than any vehicle, apart from Titans, regularly used on imperial battlefields). But of course, with Imperial technology stored energy is still a possibility, especially if the propellers are left promethium fuelled. My main concern is that, for the group using the ship, getting hold of fuel will be far too easy (even if the ship's endurance is reduced, which can also be a good thing).

By the way, Jabba's barge is about 30 meters long, so it's considerably smaller.

* also:

The ship will be a light cargo ship, capable of carrying more than 2300 m3 of cargo and up to five passengers, with a crew of about 15.

Generally, there's "high grade" promethium and "low grade" promethium IMO. The higher-grade stuff (like having hydrogen isotopes) is used as fuel for fusion reactions whereas low-grade you'll find directly powering things like tanks, used as flamer fuel, or included in many different industrial products (like plasteel).

I made up a couple of classes of combat airships used by a jump-brigade of IG and they're essentially the same as boomers and hunter subs with one or two nuke reactors, steam turbines, grav plate suspension systems and electric turbines for direction... just with some artillery pieces, bomb racks and other go-away weapons. That's the upper tier of the technology, depending on what's available, the imperium will power it locally, so it could very well be solar panels and batteries, IC engines running on gas, kero, diesel or petrol, all the way up to a mini plasma reactor.

Quite a lot of the imperial vehicles run on IC, something like a Rhino has 4 (extremely compact and efficient) engines coupled up to a reserve battery strings and electic motors much like the driveline of a train. Majority of others are your usual multi-fuel diesel motor, gearbox and driveshaft

I dunno, I could see tech priests with arachnid-like servos giving them extra arms in addition to their normal limbs scuttling back and forth over vast banks of batteries hooked to mechanical circuit breakers. As the ship draws power the crystals overload and flip their breakers, which must be constantly reset to keep the ship afloat. The "engine room" would be banks upon banks of these things, hundreds of them (thousands if they used something insane like lasgun packs... gotta love salvage punk), with tech priests rushing back and forth trying to keep the disconnected cells within design tolerance limits (no more than 10% of the batteries can be off at any given time to remain stable, and the batteries trip pseudo-randomly). The room would be a cacophony of electric crackles and sizzles as the breakers threw, it'd smell of ozone, and the very best tech priests would speak of the spirit of the ship, able to predict which cells she'd throw next (having figured out the way the ship draws power). Once done flying huge umbilicals deliver massive amounts of power back to the cells to charge them up again and run the anti-grav systems while docked.

Hmm... I'm going to have to write that one down. It seems like about the kind of salvaged solution a culture experiencing a dark age of technology might resort to... brute force instead of elegance.