The Earth Federation is on the brink of war with the rival Draconian Empire. When the TARDIS lands on an Earth spaceship in the midst of an ambush, the Doctor and Jo realise that the crew perceives the attackers to be Draconians when, in reality, they are Ogrons using a hypnotic device. Unfortunately, the brainwashing also convinces the humans that the Doctor and Jo are Draconian collaborators, and they are sentenced to spend the rest of their lives in a lunar penal colony. There they learn that it is the Master who's inflaming tensions between the two space powers. But why?

Early in 1972, the BBC gave the green light for Doctor Who's tenth season. Producer Barry Letts and script editor Terrance Dicks quickly began to formulate suitably celebratory plans, and settled on two key elements of the for the anniversary year. Its cornerstone would be an adventure which brought the two earlier Doctors, William Hartnell and Patrick Troughton, together with the current incumbent, Jon Pertwee; it was ultimately titled The Three Doctors. In addition, Letts wanted to challenge the record for longest Doctor Who story, held by 1965's twelve-part The Daleks' Master Plan. He and Dicks consulted with its director, Douglas Camfield, who described the significant difficulties such a lengthy production had presented. Dicks also worried about maintaining the audience's attention over the course of three months, having previously grappled with the same concerns on the ten-part The War Games in 1969.

As such, it was decided to instead develop two interconnected six-part stories, each of which would feature one of the Doctor's two most popular enemies: first the Master, then the Daleks. The writer chosen for the opening serial was Malcolm Hulke, who had already written for the Master on two occasions: 1971's Colony In Space and 1972's The Sea Devils. The BBC had recently acquired a library of spaceship models from Gerry Anderson and Century 21, creators of various marionette science-fiction programmes like Thunderbirds and UFO. As such, Hulke was encouraged to write a grand space opera, the likes of which Doctor Who had not attempted since the Sixties -- and even then on a relatively small scale, as with The Space Pirates in 1969.

Malcolm Hulke wanted to develop an intergalactic parallel with the ongoing Cold War between the USA and the USSR

The storyline for “Frontiers In Space” was commissioned on April 14th, 1972, and had to satisfy a number of requirements. First, to reduce costs on what was shaping up to be an expensive season, the Master could only feature in the last four of its six episodes. This way, actor Roger Delgado would only have to be contracted for two out of the three studio blocks. The evil Time Lord was to ally himself with the Ogrons, who had been introduced in Day Of The Daleks the previous year. Letts and Dicks felt them to be an entertaining and effective monster, and their presence would also foreshadow the climactic revelation that the Master was in the employ of the Daleks. This, in turn, would link into the subsequent serial, Terry Nation's Planet Of The Daleks. For his part, Hulke wanted to develop an intergalactic parallel with the ongoing Cold War between the United States and the Soviet Union.

Hulke was commissioned to write his six scripts on May 4th, under the slightly amended title of Frontier In Space; the pluralised form would continue to be used occasionally in the lead-up to production. The rival Hulke had originally devised for the Earth Federation was the Andromedan Empire; it became the Draconian Empire. The author had intended their culture to be like the post-Napoleonic Hapsburgs, although their eventual execution was more akin to a Japanese shogunate. The Doctor's discovery that the attacks in space were being committed by Ogrons initially came much later, after the Master had liberated him from prison. The notion of the hypnosound was developed to replace the physical masks the Ogrons wore in Hulke's storyline. At the lunar penal colony, Patel was originally called Doughty. At Dicks' suggestion, the President of Earth became female, with Hulke taking care to note that she was not the first woman to hold the office.

Although Frontier In Space was scheduled to be the third story of Season Ten in broadcast order, it would be the first serial recorded as part of Doctor Who's tenth production block. The season premiere, The Three Doctors, could not be recorded until November and December 1972 due to Patrick Troughton's availability. Meanwhile, Carnival Of Monsters, which would air immediately before Frontier In Space, was being held over from the preceding production block. Assigned to direct the space saga was Paul Bernard, who had worked on both Day Of The Daleks and The Time Monster during Season Nine, and therefore had experience with the Daleks, the Ogrons and the Master. This would be Bernard's third and final Doctor Who serial.

Frontier In Space required considerable model filming, which occurred on seven days between August 14th and 25th. Visual effects assistant Ian Scoones felt that freelance cameramen were more effective for model work than those employed directly by the BBC. However, he had faced considerable pushback when he invited a freelancer to work at BBC facilities for The Curse Of Peladon the previous year. As such, the model work for Frontier In Space took place at Bray Studios in Water Oakley, Berkshire.

Four days of location filming began on September 10th at the Hayward Gallery in London's South Bank; Bernard felt that its brutalist architecture perfectly suited the futuristic Earth prison. The 11th and 12th were spent at Beachfields Quarry in Redhill, Surrey, for material on the Ogron planet. The same three Dalek casings used for Day Of The Daleks appeared in Episode Six. These days marked the first appearance of the Ogron Eater, which had a prominent role in Hulke's script for the concluding installment. Unfortunately, instead of the gargantuan lizard Hulke had described, the finished product was a formless, immobile blob; Bernard had little choice but to shoot around its limitations as best he could. Finally, September 13th took cast and crew to the home of BBC director Naomi Capon at Fitzroy Park in Highgate, London, which provided the gardens of the Draconian embassy. The spacewalk scenes were then filmed on September 14th at the BBC Television Film Studios in Ealing, London.

As usual, Frontier In Space was made in two-day studio blocks, held every fortnight. The first two sessions were held on Mondays and Tuesdays at BBC Television Centre Studio 4 in White City, London, during which Bernard allocated each day to a single episode. Episode One was recorded on October 2nd, Episode Two on the 3rd, Episode Three on the 16th, and Episode Four on the 17th. The final block was likewise intended to be taped on a Monday and a Tuesday, but a one-day delay pushed the work to a Tuesday and a Wednesday -- October 31st and November 1st -- with the venue shifting to TC3. Unusually, Episode Six was recorded on the Tuesday, alongside the cliffhanger ending to Episode Five. The penultimate installment was then completed on the Wednesday, since this was when sufficient make-up support would be available for the numerous Draconian characters required.

Barry Letts was unhappy with the ending of Frontier In Space, largely because of its reliance on the Ogron Eater. As written, Williams and the Draconian Prince were recaptured by the Ogrons following their escape, and the Master confronted the Doctor and Jo. The Doctor activated the hypnosound, and the Ogrons perceived him to be the Eater. The Master shot at the Doctor, only to have a panicking Ogron felled by the weapon instead. The Master escaped, pursued by Williams and the Prince, while the Doctor and Jo set off in the TARDIS on the trail of the Daleks. Letts now asked Terrance Dicks to revise the story's conclusion in a way that minimised the appearance of the Ogron Eater. This meant that any new material could only feature the Doctor and Jo, since it would have to be taped as part of the production of Planet Of The Daleks -- ultimately, on January 22nd, 1973 in TC4. Unfortunately, this lent a distinctly discontinuous feel to the televised climax of Episode Six.

Frontier In Space was originally assembled using the new “Delaware” arrangement of the Doctor Who theme music

Two characters in Frontier In Space were significantly affected by editing. In Episode Three, the President's assistant, Sheila, originally provided background information about the Earth-Draconia conflict and the role that General Williams played in igniting it. Actress Luan Peters retained her credit, despite all of her dialogue winding up on the cutting-room floor. Likewise, in Episode Six, Bill Mitchell was still listed as playing a newsreader, even though his material -- reporting on additional “Draconian” attacks on Earth spaceships -- was completely excised. As with Carnival Of Monsters, Frontier In Space was originally assembled using Paddy Kingsland's new “Delaware” arrangement of the Doctor Who theme music. The episodes were redubbed with the previous Delia Derbyshire version after Kingsland's efforts were belatedly rejected.

With the broadcast of Frontier In Space Episode One on February 24th, Doctor Who was now preceded by We Want To Sing and a news update, as had also been the case for part of Season Nine. The first two installments were still followed by The Wonderful World Of Disney, but that changed with Episode Three on March 10th, from when Doctor Who would be followed by a Tom And Jerry cartoon short and then the High Adventure movie strand, the latter having been brought forward from later in the evening. We Want To Sing was preempted before the last two parts of Frontier In Space and replaced with previews of the Eurovision Song Contest.

During production on Frontier In Space, Roger Delgado informed Barry Letts that he wanted to wind up his appearances as the Master. Many producers still believed that he was working full-time on Doctor Who -- as had been the case during Season Eight -- and were not considering him for other work, even though Delgado was now featuring in just one or two Doctor Who stories per season. It was agreed that Delgado would therefore appear in a single adventure during Season Eleven, in which the Master would sacrifice his life to save the Doctor. As such, Letts and Robert Sloman began developing “The Final Game” in early 1973. Sadly, this serial would never be made: on June 18th, Delgado died in a traffic mishap while being driven to a filming location in Turkiye. Frontier In Space would therefore mark the premature end of the beloved actor's involvement in Doctor Who.

• Doctor Who Magazine #201, 7th July 1993, “Archive: Frontier In Space” by Andrew Pixley, Marvel Comics UK Ltd.
• Doctor Who Magazine Special Edition #2, 5th September 2002, “Saturday Night's Alright For Fighting” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #19, 2017, “Story 67: Frontier In Space”, edited by Mark Wright, Hachette Partworks Ltd.
• Doctor Who: The Handbook: The Third Doctor by David J Howe and Stephen James Walker (1996), Virgin Publishing.
• Doctor Who: The Seventies by David J Howe, Mark Stammers and Stephen James Walker (1994), Virgin Publishing.