Inspirations - The Invisible Enemy

In the latter years of the 1970's, and on into the 1980's, many Sci-Fi films and TV series insisted that some sort of cute robot be included amongst the central characters. Buck Rogers had Twiki, Battlestar Galactica had Daggit, Disney's The Black Hole had V.I.N.CENT, and so on and so forth. This was all a reaction to the inclusion of the hugely popular C-3PO and R2-D2 in Star Wars.
That film was released in the US in May 1977, and did not hit the UK until December of that year.
The Invisible Enemy was produced in April 1977, and screened that October - so the arrival of K9 in Doctor Who was most assuredly not down to the influence of Star Wars.
Besides, K9 was originally only going to appear in this single story as a one-off character - which explains why the machine is under repairs for the next story. He simply wasn't in the original story brief.
Now, Star Wars was filmed in the UK, and many of the VFX gang at the BBC would have known about the film from colleagues working at Pinewood Studios, but it is unlikely that writers Bob Baker and Dave Martin would have known much about it.
K9 is the personal computer of Professor Marius, who is played by Frederick Jaeger. Jaeger was a friend of Baker and Martin, and they had given the name Jaeger to the scientist character in their 1972 story The Mutants. He did not get the part named after him, although he had already appeared in the show back in the 1960's, playing Jano in The Savages. More recently, he had featured as Professor Sorenson in Planet of Evil.

Baker and Martin took as their starting point a story about an alien infection. Doctor Who had always shown the human race venturing out into space, colonising new worlds, but the risks of unknown viruses and illnesses posing a threat, instead of aliens and monsters, had rarely been touched upon.
The Ark had shown what might happen if a TARDIS traveller introduced the common cold to a people from the future who no longer had any immunity to it, whilst The Moonbase had featured a throwaway line from the Doctor about the TARDIS being a sterile environment, and that he and his companions were generally illness-free. Illnesses in the programme tended to come in the form of biological weapons, deliberately engineered by the enemy to attack humans - be it the Cybermen and their neuroptropic viruses, or plagues concocted by Daleks or Silurians.
The virus in this story floats about in space in the vicinity of Saturn, waiting to infect a passing spaceship which can carry it to someplace where it can incubate and then spread throughout the colonists. It is said to be noetic - relating to mental activity or intellect. After infecting a space shuttle crew, who will be tasked with setting up a home for it, the virus then attacks the TARDIS - the most intelligent thing it comes across. It quickly transfers itself to the Doctor. It ignores Leela, as she is all animal instinct and intuition. Later, it will be seen to temporarily infect K9.
The Doctor is taken over but manages to fight off its influence for a time, and guides the TARDIS to the nearest hospital - the Bi-Al Foundation which is built into an asteroid. This is where Professor Marius works alongside his computer K9. He is a dog lover, but could not afford to transport his real dog to the Foundation with him - and so built his computer in the shape of a canine, named K9.

The VFX designer on this story was the late, great Ian Scoones, assisted by Mat Irvine due to the amount of FX required. Also brought on board was Tony Harding, and it was he who designed and built K9. The first version he came up with was a large, doberman-style animal, with legs, but was then asked to make it simpler, and went for what is basically a box with a dog-like head. Adjustments had to be made as the script was developed - such as the addition of the ticker tape dispenser beneath the nose.
For a Sci-Fi show, Doctor Who had rarely ventured into outer space. Spaceships had been seen briefly in space in stories such as The Sensorites, but spaceships were usually just there to get the aliens to a planet where the real story would take place. The Wheel in Space was the first story to be set entirely off-planet, and had featured the titular space station W3, as well as the Silver Carrier rocket and a Cyberman spaceship. A number of spacewalks were also shown. A short time later we had the first real attempt at what is commonly known as "space opera", with The Space Pirates.
Much of the action in The Invisible Enemy takes place in space - either in various shuttles or within the asteroid hospital. The other main location is the refueling station on Saturn's moon Titan.
Not a lot was known about Titan at the time, so it is presented as being similar to our own moon, with no atmosphere. We now know that it is in fact the only moon in our Solar System which does possess an atmosphere, as it is shrouded in a dense orange fog of organonitrogen. (When this story was released on DVD it came with optional new CGI effects, and the black star-scape is replaced with an orange haze. Unfortunately, these changes failed to be carried through thoroughly, and there are scenes set inside the base where you can still see the star-scape through the windows). We also now know that because of this it has weather systems - a methane cycle rather than a water cycle - and the surface is not all rock and ice. There are lakes of liquid hydrocarbons.

Once at the Bi-Al Foundation, the Doctor comes up with a plan to use the TARDIS dimensional stabilser, plus clones of himself and Leela, to delve into his own body and fight the Nucleus of the virus there. This section of the story has a movie inspiration - 1966's Fantastic Voyage, which starred Donald Pleasence, Stephen Boyd and Raquel Welch. The film was based on a story by Otto Klement and Jerome Bixby. In this, a medical team are miniaturised within a submersible craft and injected into the body of a scientist defector from the Soviet Union who has been injured in an assassination attempt. The team have to sort out a blood clot in his brain which has rendered him comatose. Among the many hazards the team has to negotiate is attack by antibodies from the body's immune defence system - just as Leela and the clone of Lowe are attacked here.

This is the first story to be produced under the vision of new producer Graham Williams. He wanted to take the show into more hard Sci-Fi areas, and it is noticeable that spaceships feature prominently in his era of the show. He had also been tasked with getting rid of the Gothic horror trappings which had characterised his predecessor's reign, as well as injecting more humour into the proceedings. Ironically, this story features one of the staples of the Hinchcliffe era - body horror and physical and mental possession. Robert Holmes is still Script Editor, after all - although he is about to step aside for Anthony Read.
One thing Williams did not like was the Jules Verne-style wooden TARDIS console room design. He asked this story's designer to return it to a more traditional futuristic look. The designer in question was Barry Newbery - the man who had come up with the wooden console room in the first place. Long before the notion that the ship has "desktop themes", the Doctor blames the similarity of the new console room to the original one on the ship's lack of imagination.
Apparently the shots of the Nucleus' eggs in their tank on Titan were derived from test footage which the BBC VFX crew had prepared for an intended Quatermass remake - presumably Quatermass II, which features alien organisms being prepared in environment tanks.
And this is the second story from Baker and Martin to feature a catchphrase from the characters. Previously they had people stating "Eldrad must live!" in The Hand of Fear, and here those infected claim "Contact has been made".
Next time: Graham Williams' third story in charge, and he just can't get away from Hammer Horror. He almost had vampires for his first story, and now we have black magic rituals deep in the English countryside...