Inspirations - Frontios

Frontios was written by the series' ex-script editor Christopher Hamilton Bidmead. On joining the programme he had fought for more "hard science" in the show, so his stories tend to be based on scientific principles gleaned from his love of computing or the pages of New Scientist magazine. Something else which interested him was the TARDIS, which he felt ought to feature more. Instead of simply the machine which gets the Doctor and his companions from one adventure to the next, there was a huge amount of potential to be gotten out of the ship itself. Once thought of as having an infinite capacity, it was Bidmead himself who actually limited its dimensions by having specific percentages of it jettisoned - first Romana's bedroom to break free of the Master's time bubble (Logopolis), then a whole 25% to escape Event One (Castrovalva). You can't have 25% of Infinity, so the TARDIS has to have its limits.
The role which the TARDIS plays in Frontios is three-fold. First of all we see it go beyond "temporal parameters". It turns out that Time Lords are not supposed to venture too far into the future. Clearly this is a rule or law and not some physical barrier - otherwise the TARDIS would have been unable to travel that far ahead in the first place. What might be the reasons for such a law? Using the hindsight of more recent stories, these days we could surmise that perhaps the Time Lords might have had a Matrix premonition that they and Gallifrey might end up in a bubble universe at the end of time for their own protection, and so didn't want anyone drawing attention to this time. However, something which Bidmead himself might have thought at the time was that even the Time Lords couldn't see that far into the future (which might include their own ultimate fate) and so wanted to avoid it.

The second function of the TARDIS in this story is to be destroyed - thus giving us some idea of the severity of the situation the Doctor has found himself in and the threat level of his latest adversary, as well as providing the age old excuse of trapping the Doctor and companions somewhere until the threat has been resolved.
To be honest, Frontios is actually a fairly run-of-the-mill story, and one suspects that the "We're going too far into the future!" and "Oh no! The TARDIS has been destroyed!" bits were added just to make it look more important than it is.
The third function of the TARDIS is to provide the resolution. The Doctor only defeats the Tractators by tricking the Gravis into reassembling the ship with him inside it - cutting him off from his minions.
The design of the Tractators derives from woodlice. Apparently Bidmead's flat had suffered an infestation of these insects. He took the name from "traction". It was originally intended that they would be able to wrap themselves around their victims and roll up into a ball, and dancers were hired to play the creatures, but the heavy costumes proved to be far too rigid.

One inspiration often mentioned for this story is Star Trek's 'The Devil In The Dark'. This depicted an alien creature which dwelt underground and spent it's time burrowing through rock, leaving perfectly spherical mineral nodules behind. The Tractators endlessly burrow, even when not under the control of their Gravis, and we see large spherical objects in their caverns as well.
Another influence is our old friend Nigel Kneale again, as Turlough is seen to suffer a nervous breakdown brought on by a race memory of the Tractators. Race memory is a key component of Quatermass and the Pit, and has surfaced in earlier Doctor Who stories such as The Silurians and Image of the Fendahl.
Many have pointed out that this story also plays like a Hartnell one (as with Four to Doomsday). There are hints of The Web Planet (mindless insect creatures under the thrall of a governing intelligence), The Ark (human survivors of a catastrophe in search of a new home) and even The Dalek Invasion of Earth with its Blitz analogies. Like the Hartnell era (and the early Davison period), we have a cliffhanger ending to lead into the next story.
Some of the character names appear to reflect their personalities. The revered commander of the colony was Captain Revere, and his First Officer is the brassbound Brazen, who rigidly follows procedure. Revere's son and prospective heir, who will take over the colony after him, is Plantagenet - named for the royal dynasty which ruled England from 1133 to 1485.
Next time: Davros and the Daleks are back, in a story that should have been part of Season 20...