The Soviet Union detonates its first hydrogen bomb, code named RDS-6s, in its first thermonuclear weapons demonstration. The bomb is estimated to have a yield of 400 kilotons, thanks to a layered design devised by nuclear physicist (and later political exile) Andrei Sakharov, though Sakharov’s design is incapable of being scaled up, ending its use in later Soviet nuclear weapon designs.
The experimental communications relay satellite Echo 1 is launched into orbit by NASA. A 100-foot metalized Mylar balloon, Echo 1 is a demonstration of passive signal relay, carrying no powered transmitters of its own; its reflective surface simply bounces signals back to Earth. Microwave signals, radio, telephone and TV signals are all successfully relayed via Echo 1; it remains in orbit for four months.
The Soviet Union launches Vostok 4 with Pavel Popovich aboard, while Andrian Nikolayev orbits overhead in Vostok 3. The two vehicles pass within four miles of one another, but with no precision maneuvering, rendezvous or docking equipment, there’s little practical engineering value in the tandem space flight, other than to prove that ground controllers can handle two simultaneous flights. Popovich returns to Earth after nearly three days.
ITV airs the third episode of Ace Of Wands, starring Michael McKenzie, Tony Selby and Judy Loe. David Prowse (Star Wars) guest stars. This episode, like the rest of the series’ first two seasons, is now missing from the archives.
Released from its 747 Shuttle Carrier Aircraft in mid-air for the first time, and airborne on its own for the first time, the Space Shuttle Enterprise takes wing over the dry lake bed at Edwards Air Force Base for a test landing. With no engines on board (a test shuttle that will never go into orbit, Enterprise isn’t equipped with them) and only one shot at a safe landing, Enterprise successfully touches down on the runway after a flight lasting only a few minutes, validating the unpowered approach method of landing a shuttle just returned from space. 
NASA launches the first High Energy Astronomy Observatory satellite in Earth orbit, continuing the survey of the sky with sensitive detectors designed to find gamma ray and X-ray sources. HEAO-1 will remain in service through January 1979, and will re-enter Earth’s atmosphere in March 1979.
The third in a series of three International Sun-Earth Explorer satellites, a joint effort between NASA and the European Space Agency, is launched aboard a Delta rocket from Cape Canaveral. Unlike the other ISEE satellites, ISEE-3 is intended to take up a “halo” orbit at the L1 LaGrangian point between the sun and Earth, the first man-made space vehicle to do so. There it will study the interaction between the solar wind and Earth’s own magnetosphere. Once its mission is completed in the early 1980s, it will be redirected and renamed to become the first Earth spacecraft to study a comet at close range.
IBM Model 5150, developed under the code name “Chess” but better known as the IBM Personal Computer, is released, including the original PC edition of Microsoft’s MS-DOS. This not only marks the ascendency of Microsoft as a maker of operating systems, but a sudden shift away from a multitude of other computer platforms (especially the Apple II series) toward the IBM PC. Within a year, the first IBM PC-compatible machine will arrive on the market, but while that begins to cost IBM its hardware market share, it popularizes the Intel-8088-based architecture and makes it the standard of the computer industry.
ITV airs the 26th episode of P.J. Hammond’s science fiction series Sapphire & Steel, starring David McCallum and Joanna Lumley.
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The ninth episode of The Max Headroom Show airs, starring Matt Frewer. (This is the music video/talk show series, not the American-made drama series featuring the same character.) Oliver Green guest stars. 
The Doctor Who-related fan production Mindgame is released on VHS, starring Sophie Aldred and Miles Richardson. Though not BBC-sanctioned, UK copyright law allows the filmmakers to license the characters of the Sontarans and Draconians for this video’s commercial release.
The Doctor Who-related fan production Mindgame Trilogy is released on VHS, starring Sophie Aldred and Miles Richardson. Though not BBC-sanctioned, UK copyright law allows the filmmakers to license the characters of the Sontarans and Draconians for this video’s commercial release.
The 21st episode of Witchblade airs on cable channel TNT, based on the Top Cow comic book of the same name, starring Yancy Butler, David Chokachi and John Hensley. Eric Roberts (Heroes) guest stars.
The Röyksopp album Melody A.M. is released, featuring the singles “Epie” and “Remind Me”.
The 178th episode of Stargate SG-1 airs on the Sci-Fi Channel, starring Ben Browder, Amanda Tapping, Christopher Judge, Beau Bridges, and Michael Shanks. Claudia Black (Farscape) guest stars.
Sci-Fi Channel airs the 24th episode of Stargate Atlantis.
Sci-Fi channel airs the 18th episode of Ronald D. Moore’s re-imagining of Battlestar Galactica. Rick Worthy and Richard Hatch guest star.
Free Clyde Records releases Joel Goldsmith’s soundtrack from the TV movie Stargate: Continuum.
Sci-Fi Channel airs the 28th episode of the science fiction series Eureka, starring Colin Ferguson, Salli Richardson, and Joe Morton. Alan Ruck (Ferris Bueller’s Day Off, Star Trek: Generations) guest stars.
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Eureka now streaming on Amazon Prime
American pay cable channel Starz airs the 37th episode of Russell T. Davies’ science fiction series Torchwood, with a season subtitle of Miracle Day. Bill Pullman (Independence Day) and Ernie Hudson (Ghostbusters) guest star.
Thee audio drama box set Doctor Who: The Fifth Doctor Box Set, starring Peter Davison, is released by Big Finish, featuring the story Psychodrome. This set reunites the complete cast of Davison’s first season, including Janet Fielding, Sarah Sutton, and Matthew Waterhouse.
Streaming service CBS All Access releases the 11th episode of Star Trek: Lower Decks, created by Mike McMahan (Rick & Morty) and starring Tawny Newsome (Space Force), Jack Quaid (The Boys), Noel Wells (Craig Of The Creek), Eugene Cordero (Other Space), Dawnn Lewis (A Different World, Futurama), and Jerry O’Connell (Sliders). Jonathan Frakes (Star Trek: The Next Generation), Neil Casey (Other Space), and Phil LaMarr guest star in the second season premiere.