hi hi At the risk of being contrary, I must disagree with my esteemed predecessor and say that Jupiter will not be useful at all for interstellar commerce. Space is very very big and Jupiter, while very large by planetary standards, is a very small and remote target for stellar vehicles. In almost all cases, getting your spacecraft into Jupiter's gravity well will expend more ∂V than you will get back out of the slingshot maneuver. Additionally, going out of your way will likely cause the trip to take more time. The Voyager mission was able to make use of what is called a [url=http://en.wikipedia.org/wiki/Planetary_Grand_Tour]Planetary Grand Tour[/url], an astronomical event that will not occur again until the year 2146 and Jupiter's synodic period in most planet to planet interactions is several years in length at least, so your window of opportunity is not very large either. Even the Bulk Carrier, the slowest interplanetary vessel in Eclipse Phase with it's 40 km/s ∂V budget, has more than enough propellant to make a direct hohmann transfer to any planet in the solar system (although the synodic periods for some of those flights are prohibitively long, so bulk transports would probably be only used in the inner system) Jupiter's orbital velocity is 13.07 km/s, this is the maximum velocity you can gain out of a gravity assist relative to the sun, but the surface gravity of Jupiter (surface gravity being defined as the place where atmospheric pressure equals that on Earth's surface) is only 24.5 m/s so that will give you some indication of how slow you need to be going to make use of that acceleration. Given the low thrust and high speed of Eclipse Phase ships, the Oberth Effect will not be very useful either since it requires a large ∂V expenditure at periapsis. For ships in Eclipse Phase like the standard transport with it's whopping 400 km/s ∂V budget, that is not a significant boost. Gravity assists are most certainly not multiplicative, the faster you are traveling, the less time you are going to be inside the planet's effective gravity well, and thus the less ∂V will be imparted on your vessel. Given the ∂V budgets of common space craft and the long synodic periods involved, most commerce will likely just fly straight to their destination.

hi hi I suppose commerce might benefit from a short term boost due to planetary alignment, but that was really more of an example. The windows for origins other than Earth are going to be different. On the extreme side of things, the synodic period between Neptune and Pluto is 499 years, 4 months and 9 days. Suffice to say, they're probably not going to be using gentle hohmann transfers.

hi hi Jupiter wouldn't be a bad place to stop and refuel if you didn't care about making the trip all on one tank. For bulk carriers coming out of the inner system, it might be preferable to make a Brachistochrone transfer to Jupiter, refuel, then make a Brachistochrone transfer to one of the other outer planets instead of trying for a direct Hohmann transfer. In fact, they might need to make several stops along the way. (I'm not really sure why bulk carriers have so much lower ∂V than the standard transport, but who am I to argue.)

Arenamanoutanevanidad brings up the strongest argument, I think. Excepting when Jupiter, by great happenstance, is close to the course you were taking anyway, it's not a huge amount of use. However, Jupiter's gravity well also means it has a ton of STUFF there, including a lot of habitats and moons. Going planet by planet, I would guess that Jupiter probably has the highest population of any of them, just because of how much stuff is there waiting to be turned into a habitat (reducing the cost of living). And of course, the Junta, because of it's restrictive laws and cultural values, may have difficulty producing certain products, and will be a HUGE value to smugglers of all stripes. So I would expect they're a big, fat trading target.

One of a fallacies I have noticed when people talk about the Jovian system is that they make it out to be a Luddite enclave of nut jobs. If anything I can see these people producing some of the best tech around. They are paranoid, scared, and aggressive. War tends to breed innovation, and the Republic is basically focused around its militaristic might. Sure, they probably suck at producing really cool BioMorphs. But their robotics are going to be insane, with their Jammer units being some of the best in the System. To utilize the vast power stored in the Jovian system they probably are conducting some serious research into generation tech. And just because they say they don't touch TITAN tech doesn't mean that they don’t have black divisions hidden out in the black with enough guns pointed at it to blow up a small moon if it all goes wrong.

Extrasolar Angel wrote:

I would make Jovian Republic the major producer of antimatter in the system due to both possible high-tech engineering background of their population and access to energy sources in Jovian system.

I've always liked this idea. It gives the Jovian Republic a solid industrial base that doesn't rely on the much less solid tariffs-that-they-have-trouble-enforcing mentioned in the core book. It also gives them a fuel source for their ships and every other political body the chills to think that the Jovian Republic is sitting on so much antimatter.

Extrasolar Angel wrote:

Jovian Republic gets its revenue from the traffic, but in my view, they are rather closed economy, and probably try to rely on themselves in economic matters.

Because of the huge cost of production, EVERYONE will be a closed economy if they have any say in the matter. However, if you outlaw certain technology, certain production methods or end products won't be available (or won't be available as cheap as it is elsewhere). I'm sure Jupiter also produces a lot. It seems more politically stable than most of the system and certainly bigger. All that means that trade is still a huge thing. If I'm a smuggler, I can probably make more shipping PETALs from Extropia to Jupiter than I can shipping water from Venus to Mercury.