The Jovian Chronicles rulebook has a chart to find flight durations between the planets. That table uses minimum, average (mean) and maximum distances between the planets (start point and end point of journey). The game assumes that the travelling ship is going “in a straight line” from A to B, pretty much ignoring the fact that the planets move along individual orbits and the distance between them constantly changes dramatically. It also has the prerequisite that your ship is able to constantly accelerate until midpoint, then turn around and decelerate. The cost or energy efficient way would be to take the long way following a Hohmann Transfer Orbit. On top of that any ship will have to adjust the flight path to the gravity of the planet where it starts at (even in high orbit) and the sun.
We could assume that most ships would use Hohmann Transfer and accept the much longer travel times. Only ships with time crucial missions would use constant burn to head directly towards their targes (rescue mission, military mission, fast courier mission). Especially transport ships would most likely use Hohmann Transfer Orbits. It all depends on the availability of propulsion technology and fuel/reaction mass.
In Jovian Chronicles it seems that advanced drive technology and fuel are abundant and there is no need for long transfer orbits with short periods of thrust only.
The Jovian Confederation consists of the settlements in the planetary orbits of Jupiter and the Jovian moons as well as those in the huge asteroid clouds that move along the same orbital path of Jupiter, centered around the Lagrange Points L4 and L5. The distance between all Lagrangian Points is roughly the same, which means the distance between Sun and Jupiter equals the distance between Jupiter and L4 or L5.
In terms of traveling times this means that Jovian ships need as long to travel from Jupiter to Vanguard Mountain (L4) or Newhome (L5). The Trojans (astroids around L4) and The Greeks (asteroids around L5) are spread out in a long cloud along Jupiter’s orbital path. As we don’t know the exact position of important places or installations within these clouds (like Vanuard Mountain station) it is easier to always use the mean distance Sun/Jupiter for calculating travel times. For ships starting from other planets towards the Trojans/Greeks players should assume the travel distances to Jupiter.
An average slow trip from Jupiter to Newhome would take about 65 days or a bit over 2 months. A military ship burning at full rate would still need 5,5 days. Communication delay is at roughly 43 minutes.
This calculator is assuming that your vessel is going to accelerate constantly until midpoint (half of the travel distance), make a quick turnover maneuver and then decelerates at full thrust until it reaches it’s destination.
The calculator uses static distances between planets and ignores the fact, that they are constantly moving in relation to each other. In reality travel times would be higher due to the facts that relative distance and individual speeds are constantly changing. For the outer planets this can make huge differences in travel time.
Calculating orbital transfer routes is way too complex for roleplaying purposes. You would also need a complex computer software to calculate travel time for any given route, no way to handle this in a spreadsheet. You can find some info and an example here.
It get’s even more complicated when you pass other orbits on your journey that would be used for Hohmann-Transfer (slingshot) maneuvers.
The spreadsheet can be used by anyone (entering a required acceleration rating) here. It is recommended to use it on a large display, though.
Some other online Travel Time Calculators are:
- Space travel calculator (no Turnover)
- Relativistic Star Ship Calculator
- Space Travel Times Calculator (uses lightyears only)