shmodot/scripts/orbits/Planet.cs

using Godot;
using System;
using Vim.Math3d;

[Tool]
public class Planet : Spatial, IPointMass
{
    [Export]
    public double Mass { get; set; }

    private DVector3? _position;
    public DVector3 Position
    {
        get
        {
            if (_position.HasValue) return _position.Value;

            var t = Translation;
            return new DVector3(t.x, t.y, t.z);
        }
        set
        {
            _position = value;
            Translation = new Godot.Vector3
            {
                x = (float)value.X,
                y = (float)value.Y,
                z = (float)value.Z
            };
        }
    }
}