The 400th episode of Doctor Who airs on BBC1. This story marks the Cybermen’s first story since the Troughton era, and closes out both the series’ 12th season and the “Nerva” plotline.
This timeline entry leads to an entry covering this entire Doctor Who serial; there are plans to write new episodic entries in the future. You can support this effort!
Order Earl Green’s book VWORP!1 from theLogBook.com Store
The fifth episode of the children’s science fiction series Sky airs on ITV, created and written by Bob Baker and Dave Martin (later the creators of K-9 for Doctor Who). 
The TV movie-of-the-week The Invisible Man airs on NBC, starring David McCallum (The Man From UNCLE, Colditz), Melinda Fee, and Jackie Cooper. This is the first TV series to credit Harve Bennett (of The Six Million Dollar Man and Star Trek II) as one of its creators, alongside Steven Bochco, for whom The Invisible Man is his second such credit. The movie achieves a high enough rating to merit a series pickup later in 1975.
NASA launches Explorer 53, renamed Small Astronomy Satellite C, from an Italian-owned offshore launch platform off the coast of Kenya. SAS-C is a smaller spacecraft than NASA’s larger Orbiting Astronomical Observatory (OAO) series, but can be aimed very precisely at any cosmic X-ray sources that it detects. One of SAS-C’s discoveries is MXB1730-33, a binary star giving off rapid X-ray bursts. SAS-C will remain in orbit and functional until it re-enters Earth’s atmosphere in 1979.
The fourth episode of Terry Nation’s post-apocalyptic series Survivors airs on BBC1.
The 401st episode of Doctor Who airs on BBC1. This story marks the Cybermen’s first story since the Troughton era, and closes out both the series’ 12th season and the “Nerva” plotline.
This timeline entry leads to an entry covering this entire Doctor Who serial; there are plans to write new episodic entries in the future. You can support this effort!
Order Earl Green’s book VWORP!1 from theLogBook.com Store
The sixth episode of the children’s science fiction series Sky airs on ITV, created and written by Bob Baker and Dave Martin (later the creators of K-9 for Doctor Who).
The seventh and final episode of the children’s science fiction series Sky airs on ITV, created and written by Bob Baker and Dave Martin (later the creators of K-9 for Doctor Who). Bernard Archard guest stars.
The sixth episode of Terry Nation’s post-apocalyptic series Survivors airs on BBC1. This episode introduces the adversaries that the series regulars will face off against several times for the rest of Survivors’ run.
Soyuz 18 is launched toward space station Salyut 4 by the Soviet Union. Cosmonauts Pyotr Klimuk and Vitali Sevastyanov set a new Soviet record for long-duration stays in space, remaining about Salyut 4 for two months. They are also aboard Salyut 4 during the entirety of the Apollo-Soyuz Test Project, and are able to contact that international mission’s Soviet crew in another Soyuz vehicle. (Two mission control centers are used to prevent any confusion between the two Soyuz crews.) At the time the Soyuz 18 crew abandons Salyut 4 in July, the station’s environmental systems are failing, allowing the atmosphere inside the station to become humid enough for mold to begin growing on surfaces in the crew compartment; no further human crews will visit the station.
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