[Spaceships] Solar System Travel Table

[malloyd]

Originally Posted by Agemegos

There appear to be a number of errors in the "Solar System Travel Table" on p.37 of GURPS Spaceships.

1. The orbital radius of Ceres is 2.77 AU, which ought to be rounded to 2.8 AU rather than 2.7 AU.

Orbits aren't circular. Ceres semimajor axis is 2.7670258 AU and it's heliocentric distance ranges from 2.5572913 to 2.977 AU. It's possible this table is simply computed for a particular date (most likely Jan 1 2100 and borrowed from something compiled for Transhuman Space) or simply uses some other sort of average than the semimajor axis.

5. Periodic comets are associated with the Scattered Disk with orbital radii perhaps about 100 AU, not with the Oort Cloud and orbital radii about 10,000 AU.

6. The orbital period of "Oort Cloud" objects at 10,000 AU ought to be about 1,000,000 years, not 200 years. The minimum possible orbital period for any object of which its orbit takes it to 10,000 AU would be over 350,000 years.

This stuff is actually *entirely speculative*. Unless there is quite recent data, i.e. well after the publication of Spaceships, there are exactly zero actual observations of anything in the Oort Cloud or Hills Disk.

[Agemegos]

Originally Posted by malloyd

This stuff is actually *entirely speculative*. Unless there is quite recent data, i.e. well after the publication of Spaceships, there are exactly zero actual observations of anything in the Oort Cloud or Hills Disk.

If you're going to report speculations at all, you might as well report them correctly.

Kepler's Third Law, relating orbital radius to orbital period, is not speculative. The 200-year orbital period for "Oort Cloud" is quite impossible, and wrong by a factor of 5,000.