Of all the projects talked about on this site, with the exception of Skylark, Black Knight had the distinction of being the only one that had clearly defined objectives and which met those objectives as planned. It was also technically highly successful, was relatively cheap, and was subject to few delays. The budget for Black Knight in 1956 was of the order of £5million, and some estimates were made that suggested that an individual rocket cost £41 000 on leaving the Saunders Roe factory at Cowes, which included £15 000 for the Armstrong Siddeley engine. To that should be added about £7 000 for testing and setting up at High Down and in Australia. A Ministry of Supply memo of 9th April 1959 noted that the Black Knight programme "is being carried out in a most economical manner."! It's true that it slipped from the original schedule, but given the inevitable delays, the schedule was not too far out. One obvious source of delay is that after acceptance trials at High Down on the Isle of Wight, the rocket had to be dissembled, crated, then shipped to South Australia - a journey by sea of 5 to 6 weeks, before re-assembly and static testing at Woomera.So what was the purpose of Black Knight? Its functions were set out in a early memorandum -24th October 1955 - as follows :
"This missile will employed as a test vehicle for the following purposes:
a) Investigation of re-entry of heads in to the atmosphere. These tests will be under the control of R.A.E.
b) testing components and systems being developed for Blue Streak. This will include development for the ground radar installation. These component tests will be under the control of the main missile contractor (de Havilland)
c) Black Knight may also be used to investigate the physics of the upper atmosphere but these tests will be of minor importance compared to (a) and (b) above"
A schedule was also given whereby the first launching would be in August 1957, with the second in October, the third in December, and so on - although this was a distinctly optimistic timetable. The HTP rocket motors were tried and tested, but nothing else was. It was Britain's first completely indigeneous rocket project.But to put it another way, the point of Black Knight was give Britain experience in rocketry, in setting up the facilities at Woomera such as radar tracking, and most importantly of all, investigating re-entry. In 1955 there was no experience at all of hypersonic speeds, yet ballistic nuclear warheads with ranges of several hundred nautical miles would encounter such conditions. It was less of a problem at launch, since the vehicle could rise vertically at the start and so leave the denser parts of the atmosphere before pitching over for the ballistic lob. By the nature of rockets, acceleration was also least at launch, so the main change in velocity would happen in the less dense part of the atmosphere. But on re-entry, deceleration would be rapid, and almost all of the kinetic energy of the re-entry vehicle would be dissipated as thermal energy. In addition, the re-entry vehicle is unguided, and needs to have a shape which will be aerodynamically stable - i.e., not tumble. In other words, it was a proving vehicle for a lot of the Blue Streak equipment. The idea was that it was a good deal cheaper - and saved a lot of time - if these tests could be done on Black Knight rather than the full scale Blue Streak. In any event, Blue Streak wouldn't have been ready for testing until 1961 or 1962. Black Knight would give invaluable experience and data.
While the early Black Knights were simple single stage rockets, later ones had a solid fuel rocket motor added, derived from the highly successful Skylark rocket. This could be configured so that it threw the re-entry vehicle higher, or so that it was fired on the descent, forcing the vehicle into the atmosphere faster. This configuration must have made Black Knight unique in having the second stage pointing downward!
This is what the arrangement looked like:
Looking at the sketch plan of Black Knight at the top of the page, then this may be taken as an enlargement of the very top of the rocket. At the bottom is the electronics bay just above the kerosine tank, then the re-entry vehicle, attached to the solid fuel rocket motor by a ring with 4 attached struts to a second ring on the rocket. Those are shown as dashed lines on the diagram on the left.The odd feature to modern eyes looking at the original 1957 layouts is the use of imperial units. It must have made the later co-operative effort of ELDO and Europa even more interesting!
The re entry head had its own control system of air jets that operated in the vacuum during free fall to ensure the correct head orientation. For flight control during powered ascent the control system comprised an autopilot with gyroscopes to keep the missile on a constant heading. Tracked by a constant radar beam, any deviation from course could be corrected by a perturbation signal transmitted to the autopilot from a ground transmitter. The radio link also had provision for fuel cut off signals in the event of any major problems, and explosive was fitted in a ring round the HTP tank in case it was necessary to destroy the rocket in flight. This was to be the undoing of BK01!
Here we see its intended trajectory, using only the first stage. The rocket is fired vertically until the engines are throttled back, then the head separates and is lobbed up 600 miles before falling back down again. The engine could be throttled so that the acceleration and final velocity were predetermined, although problems were encountered on the flights which didn't arise in static testing : the kerosine tended to run out early, and the motors continued decomposing HTP only. This was refered to as "cold" thrusting.We can do some simple calculations as to the re-entry velocity, assuming a fall of (600-40)miles. But let us use SI units :
v2=u2 + 2as;
and a = 10m/s2; s = 560miles = 900 000m approx;
so v2 = (2 x 10 x 900 000)m2/s2;
v = 4200m/s.
I have, incidentally, taken the acceleration as being constant : g will be appreciably less at a height of 1000km, where it will have the value of around 7.5m/s2.
The design was for an actual re entry velocity of 12 000feet per second, or just under 4000m/s. By comparison, low earth orbit velocity is 7500m/s and escape velocity is 11 000m/s.
The duration of the powered flight was between 140 and 145 seconds, with a takeoff acceleration of 1.3g.
Inside the re-entry vehicle were various pieces of equipment, and I imagine that the most important would have been some form of accelerometer, and probably temperature probes. The re-entry vehicle had then to be retrieved for further study.
Black Knight Structure and Dimensions.
The basic shell of the rocket can be seen on the right. It used four HTP [High Test Peroxide, 85% H2O2] and kerosine combustion chambers, which were mounted in the engine bay, which was easily detachable from the tank section. There had been a steady evolution of the use of HTP/kerosine as a rocket fuel which would continue through to other projects. Silver deposited on Ni gauze is used as a catalyst to decompose the HTP into superheated steam and oxygen in the combustion chambers and in a turbine steam generator. In the combustion chambers the oxygen is used to burn the injected kerosine, whilst in the turbine steam generator the decomposition products are expanded thru nozzles to drive the impulse turbine. This makes for a slightly odd design : normally the oxidiser and fuel are mixed straightaway, but here it is a 2 stage process. The chemistry of the process means that the ratio HTP to kerosine was 8.2 to 1! This made for a HTP tank over 17foot long as compared with a kerosine tank of 4foot [the ratio is mass not volume. Kerosine density is 785kg/m3, whereas HTP is 1375kg/m3].The 4 combustion chambers were linked in pairs for control purposes, and were angled inwards slightly : the dotted lines on the plan at the top of the page represent the thrust lines of the motors.
As you can see from all the pictures, the rocket itself was a simple tube, the fuel tanks themselves being of quite thin metal with rib stiffeners externally. It is a point about rocket design that is not widely appreciated - the pressure in the tanks themselves transmit the forces upward, and these pressures are relatively small. There is a large area. The stiffening stringers which give the rocket its characteristic appearance were not there in the original design, but were added after a report about Woomera's weather noted that there could be jetstreams of up to 200knots. In these early days of rocket design SaundersRoe decided to err on the safe side.
The rocket bay bolts on to the bottom, with four fins. There are two transponder pods on the fins, one of which is a dummy. The fins themselves had no control function, this being done by swivelling the engines, but were there for aerodynamic reasons. The single stage variety was a plain cylinder with a conical nose cone : addition of the second stage made it slightly less elegant, as can be seen from the plan at the top of the page.
The single stage version - numbers 1 to 9 - were 1 inch short of 34foot high, and 3 foot diameter; the two stage version - numbers 10 to 25 - were over 38foot tall. The solid fuel motor in the second stage was the Cuckoo motor as designed for the Skylark rocket and was 17.25inches diameter and 4foot long [for the metricated among us, 12inches added up to one foot. There are approx. 39inches to the metre, or 1inch = 2.5cm!] Its burn time was around 4 seconds.
In the original single stage design, the head weight was 225lb, but in the 2 stage version it had increased to 700lb. Accordingly the single stage engine thrust of 16000lb was uprated to 16800lb for the 2 stage version. The gas pressure in the HTP tank was increased to take the extra load, and some extra strengthening added at the top of the kerosine tank.
Flight testing
For the testing of the missile in the UK, a old site was redeveloped at High Down on the Isle of Wight, on land already owned by the military. This is close to the Needles Battery and overlooks Scratchell's Bay : anyone who sails past the Needles lighthouse can look up and see the concrete blast deflectors which are still there. It is highly unlikely that anyone would be able to build such a test site in an area like that today! The work was carried out by Saunders Roe, who were based at Cowes, and had earlier built the SR53, a hybrid jet rocket interceptor, using HTP/kerosine technology.When the site was completed, the first rocket was brought to the island for testing. Since the rocket had to be dissembled for transport to Australia, it had to be modular in design. The engine bay was designed to be bolted to the tanks, the missile static tested, and it could then be taken off again for transport. The upper nose cone sections could be fitted later, and weren't needed for the static testing. This can be seen in the picture above right, with the engine bay bolted to the main tank section, then further bolted to its work stand.
There were 9 initial test firings of the Gamma 301 engine from 16th April to 31st May 57, which were basically successful. Such testing had its technical problems : the fuel lines were initially filled with nitrogen, then HTP introduced under pressure to the generator for the turbine which powered the main pumps. If there was to be a 15second test, then at the end of the 15seconds, the fuel valves would be closed, and nitrogen used to force the remainder of the fuel through. HTP is nasty stuff to handle, and so the lines had to cleared as far as possible. After the engines had cooled and been inspected, then the tanks and lines had to be washed thru and dried. Once the missile had been accepted, it had to be dissembled for shipment. Here is the engine bay ready to be crated for shipment, and detached from the fuel stage. To give an idea of scale, this is 3 foot [slightly less than 1 metre] diameter, as is the tank section. There was a technical report published in 1964, which gives a very useful summary of the results of the majority of the launches : I have prepared a lightly edited version of it.
Nicholas Hill.