Doppelgänger is a 1969 British science-fiction film directed by Robert Parrish and starring Roy Thinnes, Ian Hendry, Lynn Loring and Patrick Wymark. Outside Europe, it is known as Journey to the Far Side of the Sun, which is now the more popular title.
In the film, a joint European-NASA mission to investigate a planet in a position parallel to Earth behind the Sun ends in disaster with the death of one of the astronauts (Hendry). His colleague (Thinnes) discovers that the planet is a mirror image of Earth.
Travelling through the Solar System in 2069, the unmanned Sun Probe locates a planet that lies on the same orbital path as Earth but is positioned on the opposite side of the Sun. Dr Kurt Hassler (Herbert Lom) of EUROSEC (EUROpean Space Exploration Council) has been transmitting Sun Probe flight data to a rival power in the East, but Security Chief Mark Neuman (George Sewell) uncovers the betrayal and shoots Hassler dead in his laboratory. EUROSEC director Jason Webb (Patrick Wymark) convinces NASA representative David Poulson (Ed Bishop) that the West must launch astronauts to investigate the planet before Hassler's allies in the East. With EUROSEC member states France and Germany unwilling to offer financial support, Webb obtains majority funding from NASA. American astronaut Colonel Glenn Ross (Roy Thinnes) and British astrophysicist Dr John Kane (Ian Hendry), head of the Sun Probe project, are assigned to the mission.
Launched from the EUROSEC Space Centre in Portugal in the Phoenix spacecraft, Ross and Kane pass the first half of their six-week round trip in stasis, with "Heart Lung Kidney" machines managing their life functions. Three weeks after launch, the astronauts are revived in the orbit of the planet. Scans for the existence of extraterrestrial life prove to be inconclusive, and Ross and Kane decide to make a surface landing. While the astronauts descend through the atmosphere, an electrical storm damages their Dove lander shuttle, which crashes in a mountainous region that is revealed to be Ulan Bator, Mongolia. When an air-sea rescue unit returns Ross and Kane, the latter fighting serious injuries, to the Space Centre in Portugal, it is apparent that the Phoenix mission has been terminated after three weeks and that the astronauts have arrived back on Earth.
Neuman and EUROSEC official Lise Hartman (Loni von Friedl) interrogate Ross, who denies that he aborted the mission. Shortly after, Kane dies from the injuries that he sustained in the crash. Eventually, Ross assembles a series of clues that point him to the conclusion that he is not on Earth, but indeed on the unknown planet – a Counter-Earth that is a mirror image of his. (This has been foreshadowed a number of times; for instance, an oscilloscope is seen scanning from right to left, a tape deck's reels turn clockwise, and at one point while driving at night Ross almost collides with another vehicle that he believes to be on the wrong side of the road.)
Many, including his wife, Sharon (Lynn Loring), are baffled by his claims that all aspects of life on the planet – from the print in books to the plan of his apartment – are reversed. However, Webb is convinced of the truth when Ross demonstrates the ability to read aloud from a sign, without hesitation, when it is reflected in a mirror. Later, X-rays from Kane's post-mortem examination reveal that his internal organs are located on the wrong side of his body. Ross conjectures that the two Earths lie parallel, which would mean that the Ross from the Counter-Earth is living through similar experiences on the far side of the Sun.
Webb suggests that Ross recover the flight recorder from Phoenix, and then return to his Earth. EUROSEC constructs a replacement for Dove that is designed to be compatible with the reversed technologies of Phoenix. Modifications include the reverse-polarisation of electric circuits, although neither Ross nor the scientists can be certain that the differences between the two Earths extend to the direction of electric current. The shuttle is re-christened Doppelganger, a term denoting a duplicate of a person or object in the original German. Lifting off and entering orbit, Ross attempts to dock with Phoenix. However, Doppelganger experiences a technical malfunction, indicating that current is constant after all. The shuttle detaches from Phoenix and loses contact with EUROSEC, falling through the atmosphere towards the Space Centre with Ross struggling to disengage automatic landing control. EUROSEC is unable to repair the fault from the ground, and Doppelganger crashes into a parked spacecraft. Ross is incinerated in the collision and a chain reaction obliterates the Space Centre, killing personnel and destroying all records of Ross's presence on the Counter-Earth.
Decades later, a bitter Jason Webb, long since dismissed from EUROSEC, has been admitted to a nursing home. In his dementia, the old man spies his reflection in a mirror mounted on a window. Rolling forwards in his wheelchair, and reaching out to touch his image, Webb dies when he crashes through the mirror.
The later books have a sad amount of rehash (I think Tubb was under tight deadlines and used a good deal of filler unfortunately).
