This science fiction/adventure film was one of the better works in the genre to emerge in the immediate wake of Stanley Kubrick's 2001: A Space Odyssey -- it was also notable as producer Gerry Anderson's first venture into science fiction involving live actors, as opposed to the marionettes that had previously populated his productions, on television series such as Captain Scarlet and Thunderbirds. The problem is that Anderson and his production team didn't sufficiently change their methods, techniques, or approaches to their work -- so that except for the performances by Patrick Wymark, Ian Hendry, and, to a lesser degree Roy Thinnes and George Sewell, none of what we see is terribly fast-moving or animated; and Herbert Lom is all-but-wasted in what amounts to an extended cameo appearance. Audiences were apparently supposed to be absorbed by the elaborate model work and effects -- especially the explosions that come up mid-way through the movie and at the end -- and in theaters these were probably very impressive; but on the small screen, they lose their impact. Additionally, the basic concept of the plot, an ultimately doomed (indeed, planet-altering) effort to explore a newly-discovered world on the far side of the sun, doesn't hold up under the treatment it receives here. The pacing is lethargic, and long stretches are given over to the quasi-psychedelic effects of suspended animation on the two (or four) space travellers involved. Those languid minutes kill the already shaky momentum behind the story, which is a fascinating idea, about two parallel, identical planets orbiting opposite each other around the sun -- what should have been a good sci-fi thriller ends up being more frustrating than anything else, for the opportunities that that missed. (And, apparently, the execution was so low-key, that the plot and content eluded one television production executive working for Turner Broadcasting in the 1980's -- the idea of two opposite, mirror-image Earths, on which everything is reversed, was achieved by "flipping" the film for the second half of the story; but some genius on WTBS, thinking the print had actually been flipped by mistake midway through, ordered it reversed and "corrected," so that those watching this movie in its early WTBS presentations couldn't see the mirror/reversal of the two worlds that unnerved Roy Thinnes's astronaut, and were almost as confused at home as the astronaut was supposed to be on the screen . . . . ).