Blue Joker

Blue Joker was an experimental moored balloon-mounted, airborne early-warning radar project developed by the British Air Ministry between 1953 and 1960. It might have been allocated the classification AMES Type 87, but since it did not enter service, the classification was later used for the Bloodhound Mark 2 guidance radar.

The system used balloons rather than aircraft because the stationary position avoided the problem of converting a moving radar plot to ground coordinates which was considered beyond the capabilities of the computers then available.

The system used two, later three, hydrogen-filled balloons positioned above each other along a common tether to support a 9-metre-diameter (30 ft), resin-bonded, terylene spherical radome inflated by a built-in fan to a pressure of 980 pascals (10 cm H2O). Each balloon generated 1,400 kg (3,100 lb) of lift, and the 1,660 kg (3,660 lb) radome was carried to an altitude of 1,500 metres (4,900 ft). Electrical power and control signals were provided to the gyroscopically stabilised radar system mounted inside the radome via the tether cable, and the radar-plot-video signal generated by it was transmitted to the ground using a microwave radio link.

The radar was developed by the Metropolitan Vickers Electrical Company and used moving target indication to eliminate the background clutter generated by the sea. During trials the radar successfully tracked an approaching Canberra jet bomber, 120 miles away (190 km).

Two prototypes were built and extensively tested at RAE Cardington, Bedfordshire and on a mountain site at Drum, Wales between May 1958 and mid-1960. There is still some evidence remaining on the Drum site in the Carneddau, which include the levelled hardcore area with access from the main track, two concrete foundation blocks, together with several metal pegs, which must have been used as anchor points to tether the units. The major problems were with high winds, particularly with hydrogen loss through the fabric then used for balloon construction and the maximum windspeed for safe handling on the ground of only 30 kn (56 km/h; 35 mph). Other issues were the life of the tether cable, the vulnerability to lightning strikes and the system's poor mobility.

By the end of the decade the perceived threat had changed from manned Soviet bombers to ballistic missiles, for which airborne radar was not so important because of their higher trajectory. Development of Blue Joker was stopped in mid-1960 and the prototypes mothballed, and the programme abandoned completely a couple of years later.