"Crater One Hundred And One," stylised as "Crater 101," is an instalment of Captain Scarlet And The Mysterons in which Captain Scarlet, Captain Blue, and Lieutenant Green are assigned both to destroy a complex that the Mysterons are building in crater 101 of the Humboldt "Sea" of Luna and to remove its power source so that its component matter cannot reverse itself. It is the second part of the "Lunarville Trilogy," of which Lunarville 7" is the first part and of which "Dangerous Rendezvous" is the third part.
Scenes from "Crater 101" appear as a flashback in the series finale, the clip show episode "The Inquisition". In 1981, the episode was re-edited for inclusion in the Captain Scarlet compilation film Revenge of the Mysterons from Mars.
Spectrum and the lunar authorities have made plans for the Mysteron complex in Crater 101, on the far side of the Moon, to be destroyed with a nuclear device. However, to prevent the Mysterons from simply reconstructing the complex, its power source will first have to be located and removed.
Having volunteered for this dangerous mission, Captain Scarlet, Captain Blue and Lieutenant Green return to the Moon and set off from Lunarville 6 in a Moonmobile. Arriving at Crater 101, they transfer to a smaller Lunar Tractor and make their final approach to the complex. Automated sentry vehicles move to attack them but are immobilised when Green destroys the control vehicle with the tractor's rocket launcher. Donning space suits and entering the complex, the Spectrum officers discover the power source to be a pulsating crystal surrounded by machinery.
Unknown to Spectrum, the Mysterons have killed and reconstructed Frazer, a Lunarville 6 colonist assigned to transport the nuclear device to Crater 101. While Scarlet, Blue and Green investigate the complex, Frazer leaves the device in the crater and departs in his Lunar Tank, having rigged the device to detonate two hours early to ensure the Spectrum party's demise. Crater 101 is beyond the radio range of Lunarville 6, so when controller Linda Nolan and fellow colonist Shroeder learn of Frazer's sabotage they attempt to warn Scarlet, Blue and Green by firing an unarmed CB29 rocket into Crater 101.
The CB29's arrival reminds Scarlet of the inscription on a good luck charm given to him by Nolan: in 2058, she oversaw the launch of a Neptune-bound CB29 space probe that reached its destination "ahead of schedule". Remembering this phrase, Scarlet realises that the nuclear device will detonate prematurely. He orders Blue and Green to return to the Moonmobile and clear the area while he attempts to extract the crystal. After much effort, Scarlet succeeds and escapes in the Lunar Tractor moments before the nuclear explosion engulfs Crater 101 and destroys the Mysteron complex. Scarlet, Blue and Green return to Earth with the crystal.
Tony Barwick's script stated that Lunarville 6 is smaller than Lunarville 7, the Moonbase that is destroyed in the episode of the same name. However, the two bases are introduced with the same establishing shot, which was recycled for "Crater 101". A new Lunarville model was built for the scene in which Frazer departs the base in the Lunar Tank; this re-used design elements from earlier episodes, including a Frost Line dome painting from "Avalanche" and a part of the Mini-Sat 5 space probe model from "Shadow of Fear". The Lunarville 6 control room console was a re-use of the Lunar Controller's console from "Lunarville 7".
For its appearance in "Crater 101", the Moonmobile model was fitted with a cargo module that an unfilmed scene would have shown houses the Lunar Tractor. The script described the Lunar Tank as running on "low-pressure independently-suspended ball tyres"; however, the filming model was fitted with caterpillar tracks. The Moonmobile cockpit seats were a re-use of the Thunderbird 2 and 3 cockpit seats from the film Thunderbirds Are Go (1966).
Dialogue in the episode states that the CB29 probe reached Neptune on 10 July 2058. Barwick liked to include references to 10 July in his scripts as that was his birthday.
The episode's on-screen title is rendered as "CRATER I0I" in the series' customary Microgramma font, with the letter "I"s substituted for the "1"s. This was done as it was thought that Microgramma "1"s were difficult to distinguish from "7"s and that rendering "101" entirely in numerals would have been confusing to viewers.
Although "Crater 101" is a direct continuation of "Lunarville 7", distributor ITC's official recommended broadcast order places it several episodes after "Lunarville 7" to conceal the fact that the puppet that plays Shroeder appears as the XK3 pilot in the earlier episode.
Anthony Clark of sci-fi-online.com comments that as with "Shadow of Fear" and "Dangerous Rendezvous", the pace of this episode "could hardly be described as breakneck"; however, he adds that it "[starts] an interesting story arc."
Paul Cornell, Martin Day and Keith Topping, authors of The Guinness Book of Classic British TV and The Doctor Who Discontinuity Guide, praise "Crater 101" for its creativity in "[taking] the fight to the Moon", considering it to be among the "finest pieces in the Anderson canon". They cite "Lunarville 7" and "Crater 101" as influences on the 1969 Doctor Who serial The Seeds of Death.
In a review of "Lunarville 7", "Crater 101" and "Dangerous Rendezvous" for the Gerry Anderson-centric publication Andersonic, Vincent Law comments positively on various aspects of "Crater 101". He notes that the episode's "discordant incidentals" imply that there is "something ominous about [the character] Frazer" and praises the scene of "Scarlet [making] a grab for the crystal" for demonstrating the puppet's mobility. Law also commends the role of Lieutenant Green in "Lunarville 7" and "Crater 101", observing that the character is given an opportunity to "get his feet stuck in on the action" and praising the scene in which he destroys the control sentry vehicle.
According to the British Board of Film Classification, "Crater 101" contains "infrequent, very mild" violence.
- Lieutenant Green - "Do I get a coconut?"
- Captain Scarlet - "If we ever get out of this Lieutenant, I'll buy you all the coconuts you can eat."