The pilot episode of Space: 1999 went through multiple iterations until it became the episode Breakaway.
There was one pilot script, and one storyline, prepared in early 1973 before Landau and Bain were cast (July/August 1973). These seem to have been half-hour episodes.
Zero G "First Draft" by producers Gerry and Sylvia Anderson, dated 1973. 33 pages. Set on Moon City, with the characters of Space Commander Steve Maddox and Doctor Marc Miller. Minor characters are Lt. Caron, head of reconnaissance, and Dr. Gordon, the female medic.
Ending
Untitled 4 page story outline. The only named characters are Commander John Koenig, Professor Sabatini, and the politician Grivas. We are on the Moonbase (not Moon City). Introduces the concept of nuclear waste blowing the Moon out of orbit.
George Bellak was recruited in August 1973, but left the production in October. On 3 September he produced a writer's guidelines, and these full scripts must have been in September.
The Void Ahead, "first draft copy" (71 pages), unmarked version (83 pages) and "temporary final" (82 pages). Koenig, Helena and Bergman are all in place. The Main Mission "adjutant" (Koenig's assistant) is Vorkonen. The pilot is Sergio Catani. The previous commander is named Grodno (he doesn't appear at all in the first draft). The Commissioner is Symonds. Other characters are Dr Fujita and analyst Sabatini, the tech chief Murneau and depot chief Gundlach. The first draft only mentions spaceships and "modules"; the final names them as Modular Transportation Unit (MTU) and renames Vorkonen as "Bob" Morrow.
Opening (unmarked copy)
Opening (temporary final)
Series titles (unmarked)
Series titles (temporary final)
Koenig and Helena (temporary final)
Koenig and Grodno (unmarked)
Koenig and Helena (unmarked)
Koenig, Bergman and Symonds (unmarked)
Out of orbit (first draft)
After Bellak left in October, Christopher Penfold took over, although the scripts are now uncredited (Bellak's name remains as the on-screen credit).
Turning Point, "final shooting script", dated 5 November 1973, 71 pages. The Eagle is now named, as is Paul Morrow, commander Gorski and commissioner Simmonds. Data analyst is Sandra Sabatini. The pilot is still Captain Catani, and Helena's assistant is Dr Fujita.
Opening
Series titles
Koenig and Gorski
Out of orbit
Just over two weeks after Turning Point, the script is retitled, with most pages amended in blue pages.
Breakaway (formerly titled "Turning Point") "amended blue pages" dated Thursday, 22nd November, 1973, 71 pages. Names as before, we still have Captain Carlo Catani, Sandra Sabatini and Dr. Fujita.
Opening
Koenig and Gorski
Rehearsals began Monday 26th November, with first filming the following Monday, 3rd December.