Blue Streak – The Origins
The story of Blue Streak divides into two phases, phases which are very sharply divided from each other: the military and the civil. The civil phase was an afterthought, a by-product from the military. Blue Streak was cancelled as a military weapon in 1960, and its life as a civil project began with the intention of creating a satellite launcher from what had been intended as a Medium Range Ballistic Missile (MRBM). But after 14 years and hundreds of millions of pounds of expenditure (much to the despair of the Treasury) neither programme yielded useful results – but that was not the rocket’s fault. Technically, the design was excellent. Almost every launch was flawless. But it spent most of its life in search of a role.
The original intent behind Blue Streak was to produce a guided weapon capable of carrying a megaton range warhead to the strategically important parts of the USSR. Design work began in 1955 and the final result was a technological snapshot of rocketry progress circa 1957. In principle and design it was very close to its American and Russian counterparts, and very much their equivalent. But to realise this, we have to look briefly at the history of guided weapons.
The V2 was notoriously inaccurate, and given in addition its limited payload (1 tonne of high explosive), it was not an effective military weapon. Following the war, both the Americans and the Russians pressed on with improved designs, based around the V2 concept. The British devoted relatively little effort to large rockets at this stage, and such work was, in the main, theoretical, although three captured V2s were fired off in Cuxhaven, Germany (Operation Backfire) in what was effectively a familiarisation exercise. However, the post-war rocketry effort in the three countries began to solve some of the three major problems of guidance, accuracy and range.
Most of the work done in the UK in the early 1950s simply consisted of studies of possibilities. The technologies of the time were changing fast, and the problems were firstly to choose which would be the most fruitful, and secondly, to try and estimate how far the technologies could be usefully developed. One of the first significant British developments in this field of long-range delivery
systems was a report commissioned from the English Electric Company Ltd.1 Work on the report, entitled ‘Long Range Project’, by LH Bedford, started in March 1952, and the completed report was delivered in July 1953. The first consideration was that of range and accuracy. The report took a range for the weapon of 2,000 nautical miles with circular error probability (c. e.p.) of the order of 1,500 ft as the target to be aimed for (c. e.p. refers to the probability of 50% of the missiles landing that distance from the aiming point). Three types of missiles were considered: the ramjet, the glide rocket and the ballistic rocket. The guidance system for all of these was taken to be integrating accelerometers using gyroscopes. The times of flight were calculated as 16 minutes for the ballistic rocket, 25 minutes for the glide rocket and 50 minutes for the ramjet. The significance of this was that the accuracy of the system decreased as time of flight increased. Thus the ballistic rocket was to be preferred on two counts: that of accuracy and that of invulnerability. Intercepting a warhead from a ballistic missile is a task that even today is extremely difficult. Indeed, if attempted operationally on a system with even rudimentary decoys, it is well-nigh impossible.
The two major problems of the ballistic rocket were identified firstly as obtaining a sufficiently high S. I. from the rocket motors, and secondly the problems of re-entry into the atmosphere. In neither case were practical solutions offered, nor was there any attempt to suggest design features such as the fuel to be used. The report was still theoretical and speculative.
The RAE was conducting its own studies into the same areas as the English Electric Report, and it is interesting to note the estimated all-up weights of the three options2:
(Range is given in nautical miles; weights in thousands of pounds)
This has important implications for the design of any ballistic missile: a mass of 210,000 lb implies a lift-off thrust of at least 250,000 lb. It was noted that the ballistic missile would be much heavier than the others, and that if it were to be chosen it would be because of its much greater chance of survival against enemy defences. The calculations were done assuming liquid oxygen and kerosene as propellants, and give a remarkably accurate prediction for the weight of what would become Blue Streak.
As a consequence of these deliberations, the RPD at Westcott pressed ahead with design studies on larger motors. But even at the end of 1954 no formal summary had been made of the RPD’s overall policy on the ballistic missile, as it was felt the position was constantly changing. At the same time, research was continued on a series of rocket engines that went under the generic name of Delta. Despite RPD’s earlier dislike of kerosene as a rocket fuel, these were lox/kerosene fuelled, and mainly for research purposes. There was no firm design for a missile at this stage, although speculative drawings of how to fit several motors together for such a missile were made.
Commercial firms were also interested in the concept: during a meeting between the RAE, RPD and Rolls Royce, the company stated that:
In their own studies they had assumed a warhead of 10,000 lb and minimum range of 2,500 miles and had produced a preliminary design. This design was a single stage missile with an all-up weight of 250,000 lb and empty weight 18,000 lb giving a mass ratio (empty/all up) of 0.072. Thirty-three chambers of 10,000 lb thrust each were used.
Apart from the number of chambers, again this sounds very much like Blue Streak.
At around this time the ramjet and the glide rocket drop out of consideration. The glide rocket was never a very serious candidate. The ballistic missile with separating warhead and self-contained guidance system has the great advantage that it was, and still is, almost invulnerable to defensive counter measures. A missile is also much better equipped to carry decoys; in other words, dummy reentry vehicles or devices that would look the same as a re-entry vehicle to enemy radar. Decoys have been an on-going area of research up to the present day.
The ramjet is not as vulnerable to guided missiles as the manned aircraft, but does not begin to compare with a free falling re-entry vehicle at velocities of several thousand ft per second. Height is also a factor here: today’s turbofan subsonic cruise missile is designed to fly as low as possible since terrain following radar and accurate guidance have subsequently been developed to make this possible. Supersonic ramjets would be high flying and more vulnerable to defensive missiles.
In 1954 the Sandys/Wilson agreement was signed between the UK and the US, whereby the two countries agreed to collaborate on long range missiles; the British concentrating on medium range weapons whilst the Americans would aim for intercontinental ranges. However, to produce an effective military weapon, there were several important problems to be solved other than simply building a big enough rocket. For the missile to fulfil its function, all the systems had to work together. Loss of just one would render the weapon impotent.
The first of these problems was that of guidance. Radio/radar guidance during the launch phase was possible. However, such external guidance could easily be jammed or destroyed, particularly during a nuclear attack. The answer lay in internal inertial guidance, using gyroscopes and accelerometers to determine the vehicle’s heading and speed accurately. The American Atlas missile used a form of radio guidance, but all other missiles carried inertial guidance. A form of radio guidance for Blue Streak was also developed for a time before being abandoned as too easy to jam and too easy to destroy, and also because there was an economy drive on! There were many obstacles to an accurate inertial guidance system in the 1950s, before the advent of transistors and when electronics depended on power-hungry thermionic valves for amplifiers. Suitable gyroscopes were difficult to manufacture, and eventually, partway through the project, gyros had to be bought from the American firm Kearfott. To give some idea of the accuracy which was needed over a range of 2,500 nautical miles, it was stated early in the programme that there was
a requirement for a 50% circular error no greater than 8,000 feet at all ranges. If this requirement should result in undue delay in the introduction of the missile into service the Air Ministry will be prepared to accept a 50% circular error of no greater than 3 miles at all ranges in the first instance.3 [8,000 ft is around one and a half miles.]
A novel feature of these designs for ballistic missiles was that at the moment the engines cut, some two to three minutes after launch, the warhead and its reentry vehicle would separate from the empty rocket shell and travel along a ballistic path outside the atmosphere towards its target. After a flight time of some tens of minutes, the re-entry vehicle would descend on its target at very high speed – perhaps as much as 15,000 miles per hour. It had to re-enter the atmosphere at this speed, which led to the other unknown of the time: what would happen to such a vehicle? Would it survive re-entry or would it burn up like a meteor? In parallel with Blue Streak, the Black Knight programme was set up to investigate the problem. Guidance and re-entry were the two major imponderables, for which a good deal of work had to be done in parallel to the main project. But what of the rocket itself?
After the Sandys/Wilson agreement had been signed, the US and the UK set out to design missiles which were complementary to each other. Initially, the Americans were to produce the long-range Atlas missile, the British the medium- range Blue Streak. A team of Americans visited the UK in April 1955 to discuss progress. Sir Steuart Mitchell (CGWL) described the British plans, which involved the RAE as the principal designer for the first two years, control being passed to the firms in the second year. The American team was not impressed by this idea. The VCAS (Vice Chief of Air Staff) noted that he had been told in private that
They felt themselves that unless we give it to industry with a free hand it might delay the project greatly. They voiced the opinion at the meeting that the British Technical Civil Service was of a much higher calibre than the American, but that a scheme such as that proposed by Mitchell would just never work in the US.
Whether this was the case is difficult to judge, but certainly, progress in 1956 seems to have been slow. On the other hand, uncertainties as to the warhead, as we shall see, contributed to the delays.
It is also noticeable that the many technical reports that came out of the RAE at this time were also speculative and academic. Typically, a half dozen different design solutions would be carefully evaluated in these reports, but they did not lead to a direct practical design in the way that an aircraft design team might work. British aircraft designers of the time would start with quite detailed sketches, which would be refined up to the final solution. A commercial firm was also under pressure to produce a prototype as soon as possible in a way that the RAE was not.
At the same time, a British team from RAE had visited America, and produced a report defining the problems more clearly. As a result of this, the Air Staff felt sufficiently confident as to issue an Operational Requirement (OR 1139) for the missile in 1955, which stated a requirement to deliver a megaton range warhead over a distance of up to 2,500 miles. An OR is one thing, a design is another. Throughout 1955 and 1956, whilst work started on Black Knight and on other aspects of the programme, arguments went back and forward as to the details of the design. The crucial point, from which all else flowed, was: should it have one motor or two? The motor under consideration, an American design, had a thrust of 135,000 lb. This implied a missile weight of no more than 100,000 lb with only one motor. A two motor design could be double that mass. The critical factor, and an unknown factor, was the payload, and the payload was, of course, a megaton warhead and its re-entry vehicle.
With only one motor and a warhead weight of 2,000 lb, the maximum range that could be expected was only 1,900 miles – not enough. There was a further snag: Britain did not have a thermonuclear warhead weighing only 2,000 lb. Indeed, Britain did not have a thermonuclear warhead at all – in 1955, the design of such a warhead was only just beginning. It would not be until late in 1957 that such a device would be tested successfully. The only warhead that might have done the job weighed 4,500 lb – far too much. Some lateral thinking would be needed.