A yellow-striped tube stretched away into the part of Quarantine set aside for people who, like them, were returning from the surface of Earth. A few meters in, they were confronted by a one-way door, constructed so that only one person at a time could pass through it. Hanging on a rack nearby were a number of hard bracelets, color-coded to indicate that they were intended for Survey personnel, also striped with machine-readable glyphs. Kath Two selected one and ratcheted it around her wrist. After a moment, a red diode began to blink on its back and digits began to count time. She waved it at the door, which unlocked itself and allowed her to pass into the tube beyond.