Journey to the Far Side of the Sun

Some may remember that the first live action show made by the 1960s puppet master and creator of Thunderbirds and Captain Scarlet Gerry Anderson was the early 1970s show UFO. Well, it wasn't. Anderson's first foray into live action production was this 1969 film Doppelgänger, released in the US as Journey to the Far Side of the Sun.
Scientists have discovered a new planet in our solar system, in the same orbit as the earth, but on the opposite side of the sun.
Roy Thinnes (The Invaders) plays one of the astronauts assigned to the mission to explore this new planet. They travel to the other planet and crash on it -- or they think they have. It seems that somehow they've crash landed back on earth.
But then they discover that they have landed on the other planet and it is -- omigod! -- an exact double for Earth!
Except that -- omigod!² -- it's a mirror copy of Earth!!! People drive on the wrong side of the road! Clocks go around the wrong way!
The movie takes its own sweet time getting going. There's a spy discovered, behind the scenes maneuvering, astronaut training, one astronaut's marriage goes on the rocks -- we're 43 minutes into the flick before these guys even take-off! And it's only a 100 minute film!
The "Gerry Anderson style" is evident from the first moment, and it feels like it fits perfectly into that milieu. The titles are in the same futuristic font that would be used for Space: 1999. The musical score seems exactly the same as for UFO and Space: 1999, which makes sense as Barry Gray scored all three projects. Many of the props and sets would eventually be recycled on UFO. Many of the smaller roles are played by actors who would appear in other Anderson projects; for instance, Ed Bishop who would star in UFO has a small role as a NASA liaison here.
The special effects take after the more cruder effects Thunderbirds than the later more realistic effects of Space: 1999, and they feature those crazy but surprisingly logical planes and rockets of Thunderbirds.
Despite its faults, it's a well done and engaging film, with a bit of a twist ending.