Praise must be given to Roger Murray-Leach, one of the most talented set designers that Doctor Who ever had. His designs for Space Station Nerva are staggering in their scale. The main incubation room is a marvelous design, cleverly using mirrors to make the set look much larger than it actually is. The corridors (or should I say corridor, which is just as expertly shot by director Rodney Bennett) are equally as impressive. They are, for the most part, transparent - open enough to see the vast emptiness of space beyond the station, and claustrophobic enough to emphasize the isolation the humans are feeling.
The fact that this story is so gripping and tense, however, completely belies the effectiveness of the sets. Everything is white - the doors, the walls, the floors, the uniforms, everything. Only in select situations is the lighting dimmed (and, when it is, it's due to power failures explained in the script). Compare this to a future story with a similar look to it, Warriors of the Deep. That story is often derided for its bright look, but it has much in common with The Ark in Space.
The key is the sheer lack of characters in The Ark in Space. Rogin and Vira are the only two human regulars who survive for more than five minutes. Noah, the main villain, is rarely seen in the same room with our heroes, and it's his absence from normal proceedings, along with the rest of the Wirrn in all their larval and pupal stages, that makes this story so exciting. We can't see the Wirrn, so we don't know what they're up to. And not knowing what your enemy is planning is the scariest notion of all.