The whole galaxy and all the planets were generated on the fly from a few small sets of strings and a pseudo-random number generator. The fact that the number generating sequence always started with the same seed meant it always made the same names and planets!
It's actually quite easy to do something similar in BASIC, using RANDOMIZE and RND.
Make a string like "KAKEKIKOKUFAFEFIFFOFULALELILOLUOSONAX"
Start with a seed via RANDOMIZE - say RANDOMIZE seed+planet.no
Generate a number with RND to be the length of the name, and with a FOR loop, generate a random odd number, and add the 2 characters in the above string starting at that position to the planet name until you hit the needed length.
The above string will give you names like "Kafila", "Liax", "Nakefi", and "Kukuos". The more combinations you add, the more diverse the names.
Generate all the random data you want for that planet - tech level, planet size, whatever. You can make some based on formulas, like population based on size x tech level or whatever suits your purpose. Get as complex as you want.
Now, the trick is, because computer random number generators are not truly random, every time you start a RANDOMIZE with the same seed, you'll get the same planet, no matter how much data you generate! This way its possible to have literally thousands of planets, which will always be the same, yet only have the data for the one current planet in memory or even stored on disk.