Black Arrow - Vehicle

Vehicle

The first and second stages of the Black Arrow were fuelled by RP-1 paraffin, burnt using high test peroxide as an oxidiser. Due to the optimum mixture ratio being about 7 a larger oxidiser tank was required compared to many contemporary launch systems. The oxidiser tanks were located below the fuel tanks, following the practice of putting the more dense propellent at bottom in order to lower the centre of gravity and make the rocket easier to control. This arrangement had been pioneered by Germany and the United States, whereas the Soviet Union had placed oxidiser tanks above fuel tanks, making it easier for the lower tank to be filled first.

Thrust vectoring was used to provide attitude control on the first two stages. The eight first stage combustion chambers were arranged in pairs which could gimbal either way along one axis. Two of the pairs were arranged perpendicular to the other two, and when all four pairs were used together, they provided roll, pitch and yaw control. The second stage had two combustion chambers, which could gimbal along two axes, providing the same level of control. During a coast phase after second stage cut-off, the rocket was controlled by a reaction control system. The third stage did not have an attitude control system, and was instead spin-stabilised.

The first stage was powered by a single Gamma 8 engine, which burned for 127 seconds. The Gamma 8 was an eight-chamber engine, derived from the Gamma 301 engine used on the Black Knight. It was 6.9 metres (23 ft) long, and had a diameter of 2 metres (6 ft 7 in), the same diameter as the French Coralie. Coralie was used as the second stage of the Europa rocket, and the decision to give Black Arrow the same diameter as Coralie was taken in order to make it compatible with Blue Streak, which was used as the first stage of Europa. This would have allowed Black Arrow's payload capacity to have been increased, and would also have allowed Britain to use the first stage of Black Arrow as a backup to the Coralie. For this reason, all dimensions in the original specification were given in imperial units except the first stage diameter, which was given in metres.

The first and second stages were connected by an interstage structure containing four Siskin IB separation and ullage motors, which separated and ignited seven seconds after the first stage had cut off. The interstage separated from the second stage six seconds later. The second stage, which was 2.9 metres (9 ft 6 in) long and measured 1.37 metres (4 ft 6 in) in diameter, was powered by a two-chamber Gamma 2 engine which ignited shortly after the separation motors, and continued to burn for 123 seconds. Three minutes after launch, during the second stage burn, the payload fairing separated.

About 257 seconds into the flight, the second stage cut off, and the rocket entered a coast phase to apogee. Immediately after cut-off, the second stage attitude control system was pressurised. During the coast the correct orientation for third stage separation was maintained by means of the attitude control system. Towards the end of the coast period, the third stage was spun up to a rate of 3 hertz (180 rpm) by means of six Imp rockets. Five seconds later, the third stage separated, and following ten more seconds of coasting, it ignited. The third stage was a Waxwing solid rocket motor, which burned for 55 seconds.

Just over a minute after the third stage had burned out, the payload was released, and gas generators were used to push the spacecraft and spent upper stage apart. The delay between burnout and separation was intended to reduce the risk of recontact between the upper stage and payload due to residual thrust. Despite this, following spacecraft separation on the R3 launch, the upper stage collided with the Prospero satellite, damaging one of the spacecraft's communications antennae; however the spacecraft was still able to successfully complete its mission. On the R3 launch, the ascent took 710 seconds (11.8 min) from liftoff to spacecraft separation.

Although none was ever built, several derivatives of Black Arrow were also proposed, as ways of increasing its payload capacity. One proposal added eight Raven solid rocket motors from the Skylark programme to the first stage as booster rockets. Another suggestion was to mount the entire rocket atop a Blue Streak missile, while a third proposal involved replacing the Gamma engines with the more powerful Larch.