Visual Effects and Miniatures
Derek Meddings did some truly seamless visual effects work on this, much of the space stuff reminiscent of Superman with nods to Thunderbirds (numbered satelites).
The scene in which William Prince and Bruce Davison go on the elevator drop or when the drive in theatre turns into a satelite base are 100% seamless miniatures. They get so much screen time but the audience will never know!
The late Ray Caple did some an amazing matte painting for when they cross the desert into the Russian mountains. You couldn't have done better with a digital matte painting today.
The Brits were up there with ILM, Boss film and Apogee back in the early days of the post-Star Wars VFX revolution.