Black Prince was a proposed British-led satellite expendable launch system. It would have made heavy use of the preceding Blue Streak missile and the Black Knight test rocket development programmes, as well as some new elements, to produce a British-built launcher capable of deploying medium-sized payloads into orbit. Popularly known as the Black Prince due to its assigned rainbow code, in official documentation, the platform was referred to as the Blue Streak Satellite Launch Vehicle (BSSLV).
The Black Prince originated from various ballistic missile programmes that were being conducted by the United Kingdom during the 1950s. As envisioned, it was to have been a multistage rocket, the first stage being the Blue Streak and the second stage being the Black Knight. This would have been mated to a variety of different interchangeable third stages, differing based upon the individual intended mission profile. According to performance projections, the Black Prince would have been capable of delivering a 960 kg (2,117 lb) payload to a 740 km (400 nmi) orbit.
The Black Prince gained several supporters, including official government backing following the termination of military involvement in the Blue Streak programme during early 1960. It was seen as a viable means of reusing existing development work, but one that would still involve significant costs. The British government promoted the concept to other potential partners across Europe and the Commonwealth of Nations, however it became clear that the necessary backing would not be forthcoming. Work on the Black Prince launcher came to an effective halt shortly after the formation of the European Launcher Development Organisation (ELDO) working group and a government decision to proceed with British participation in the multinational Europa launcher programme instead. During the late 1960s, it was proposed that elements of the Black Knight could be combined with the later Black Arrow launcher.