Data from Spectrum files withheld.  Because of security reasons, the Spectrum organisation will not release many of the specific details of the Spectrum Detector Van.

Inside of Detector van, as seen in 'Manhunt'.

Also known as 'Radar vans", eight of these directional, long-range, Geiger counter vans exist. They were used to detect and track the radioactive presence of Captain Black, after his break-in at the Culver Atomic Centre (episode 4 "Manhunt").

The large spinning "parabolic reflector" on the roof is used in conjunction with other vans, to triangulate the position of the intended target. 

The detector van runs on a special type of fuel collected by the Spectrum refinery at Bensheba. The equipment inside is powered by Hydro-Genical fuel-injection cells, a combination of ambient air and the Hydrogenic fuel generates electricity to power the electric motors.

The van is a five seater vehicle (two persons as driver and navigator, with three as passenger/technicians), constructed by an unknown firm for the Spectrum organisation. 

The van is presumably made from conventional motor vehicle materials (with internal "roll-cage" and bracing) and are blue in colour.

(Sources: TV Century 21 material (Annuals, books and magazines), Engale Marketing's Century 21 magazine, Issue 15, Winter 1995, Fleetway Magazines, Captain Scarlet & the Mysterons book by Chris Drake & Graham Bassett, Complete Book of Captain Scarlet by Chris Bentley… all related to TV Century 21 material - Photo-montages provided by Keith McNeill's 's Space Model Photography.)