Main Worlds and Eccentricity

While working on the Express Boat Network post, I found eleven systems on the network with class E starports. I was curious about how x-boat stations in those systems would be refuelled. While reviewing them, I noticed that some of the main worlds had very high eccentricities. Harmony in Reft, for example, ended up with an eccentricity of 0.9.

If Harmony had a circular orbit, the mean temperature would be about 10°C. With an eccentricity of 0.9, the temperature swings from −55°C to 365°C. Settling a planet with temperature swings that extreme would be difficult.

I could not find any mention of restricting eccentricity for main worlds in the World Builder’s Handbook. But I think the generator should produce main worlds without that kind of temperature swing. To that end, My Traveller Universe has two additions.

Campaigns now support a Limit Populated World Eccentricity option. When enabled, any stellar object with a population code of 3 or higher has its eccentricity capped at 0.09.

If the system generator assigned the maximum eccentricity of 0.09 to Harmony, the temperature range would be −10°C to 15°C, which seems more reasonable for a settled planet. As a comparison, Earth’s eccentricity is 0.0167, which results in a temperature swing of about 5°C due to orbit.

Population codes 1 and 2 are excluded so the system generator can still create cases like a space station orbiting a high eccentricity object.

Second, the build configuration for a body can explicitly set the eccentricity.

  name: Test System
  primary:
    type: G2
    class: V
    bodies:
      - uwp: terrestrial
        orbit: hzco
        mainWorld: true
        eccentricity: 0.02
      - uwp: gas giant
        eccentricity: 0.3

If Your Traveller Universe has populated worlds with high eccentricity, you don’t have to make any changes to your campaign set up or build configurations.