I am especially surprised to notice errors of continuity which I had
missed during the past thirty years of viewing these same episodes. You've
possibly noticed all of these but I thought I'd mention some for your possible
interest.
The Fireball XL5
spaceship was designed jointly by Reg Hill and Derek
Meddings. Originally the ship and the television program
were both to have been called 'Century 21' but Gerry
Anderson, inspired by a brand of motor oil called
'Castrol XL', changed the name to Fireball XL5. The XL5
is part of a huge fleet of XL class patrol ships operated
by the World Space Patrol. These ships are launched from
Space City on a long rail. This was an idea taken from
the Russians who originally announced to the world during
the 1950s that they planned to launch their early rockets
into space this way. The Russians may have been inspired
by German V1 'Buzz Bomb' scientists captured from
Peenamunde by the Red Army after the war.