Like other early episodes of "Thunderbirds", "Trapped in the Sky" was originally 25 minutes long. This running time was doubled after a preview screening that was attended by Lew Grade, APF's owner and financial backer. Grade was so impressed with the story and effects that at the end of the screening, he declared "That's not a television series, that's a feature film!" and ordered Gerry Anderson to re-write and expand all episodes to fill a one-hour timeslot. He later increased the series' budget per episode from £25,000 to £38,000.