by Damien Burke
In practice, one drawback of AGC was that it rendered the scanner incapable of imaging sudden changes in the terrain, in particular the change from over-water imaging to coastal areas. The AGC took several seconds to cope with the change, valuable seconds in which the imagery would not be of acceptable quality. Thus reconnaissance of coastal targets would have been extremely problematic. Early testing of the active linescan system also found that contrast was much lower than expected, challenging the haze filters, and only after a fruitless investigation into the characteristics of the light source being used was it realized that the main problem was simply the lack of any shadows, the light source always pointing directly at any one point on the scanned line. Thus the RAF’s preference for the ‘more natural’ illuminated scene actually resulted in an entirely unnatural image. It is noteworthy that other linescan systems produced after the TSR2 project was cancelled went with IR imaging, rather than natural light or active illumination.
Linescan airborne radio link (ARI.23135)
With one of the TSR2’s primary purposes for reconnaissance being tactical support of the army on the battlefield, timely reception and processing of reconnaissance information was essential. Accordingly the lines-can system needed to be able to transmit its data in real time if at all possible, or, at the very least, shortly after scanning and before the aircraft returned to base. The transmitter would use one of five frequencies in the C-band (around 4,600Mhz), pre-selected on the ground before the sortie.
Linescan radio-link ground stations
Requirement ASR.2153 covered the requirement for mobile, air-transportable installations capable of receiving and processing signals from the linescan radio link called for in OR.343. Each station was to receive linescan pictures transmitted via HF from TSR2 aircraft, process the data into photographic imagery suitable for first-stage interpretation, in real time, and to provide display facilities for this imagery. A range of up to 110nm (125 miles; 200km) to the transmitting aircraft was specified, with acquisition of the aircraft at 120nm (140 miles; 220km). All of the information received was to be recorded for later re-use and processing to a permanent negative or positive image on 5in film as fast as possible (no more than a two-minute delay being allowed).
High-frequency communications for the receipt of linescan information would be supplemented by UHF facilities and telephone/telex links along with display units, tables and seating for operators/ interpreters. Air-conditioning and filtration and, of course, power supplies and lighting, would also be required. All of this was to fit within a standard Signals Container Body Mk 6, with all external mountings able to be stored inside for air transportation in an Armstrong Whitworth Argosy or similar aircraft. Rough estimates on the number required gave a total of twelve at a cost of £50,000 each, four of which were to be located in Germany. Each station would only be able to work with a single aircraft at any one time, and the aircraft would need to remain within range throughout its transmission. This would require some careful traffic control within a busy battlefield environment. Ground stations would also need to be able to deal with downloaded information provided from landed aircraft that had been unable to transmit while airborne.
In the early months of 1965, as part of the desperate cost-cutting exercises being undertaken to try to stop the project from being cancelled entirely, the requirement for live linescan data transmission was unceremoniously dropped, and all work on the transmitter and ground station came to a sudden halt.
Sideways-looking reconnaissance radar (ARI.23136)
The reconnaissance pack also contained a high-resolution Q-band SLR for reconnaissance, with 15ft (4.6m)- long aerials on the port and starboard sides. Each aerial could be shortened to an effective length of 8ft (2.4m) via a mechanical shutter, and each could be tilted in the roll axis between 10 and –20 degrees from the horizontal, the navigator being able to select one of five positions throughout this range (both aerials would tilt to the same setting). At low altitude the lateral coverage for each aerial was between 2 and 5nm (2.3 and 5.75 miles; 3.7 and 9.25km), rising to around 10nm (11.5 miles; 18.5km) at medium altitude. The dead zone directly beneath the aircraft, in between the port and starboard radar coverage zones, could be filled by use of the linescan (at low level), or by overlapping passes to get 100 per cent radar coverage.
Two modes of operation were provided for; firstly, moving-target indication (MTI), primarily at low level, using the 8ft aerial length and comparing successive pulses to ascertain whether contacts had moved, and, secondly, medium-altitude reconnaissance without MTI, using the full aerial length. MTI recording would be available up to 10,000ft (3,000m) and 800kt (920mph; 1,480km/h) ground speed, with the non-MTI role being available from 5,000ft (1,500m) upwards through the aircraft’s full speed range. The radar transmitter/ receiver, modulator and power units were developed from the Red Neck radar system that had been intended for use on the Handley Page Victor, but which never entered service. Several modifications had been made, most notably to the pulse-repetition frequency (PRF), to enable better detection of moving targets travelling at speeds characteristic of military vehicles.
Beam configuration and coverage of SLR. Damien Burke
Continuous recording of the radar returns would be carried out along with data from the aircraft’s navigation system: altitude, heading, pitch angle, timebase delay, latitude and longitude. The actual recording was carried out using a similar ‘Heath Robinson’ means to that of the navigation SLR display, radar returns being displayed on a pair of 3in (7.6cm) CRT monitors, and the output being recorded on photographic film running at a speed varying with the aircraft’s ground speed. Three separate 80mm f/4 lenses would record the CRT traces, the central one recording non-radar data from a smaller 2in (5cm) CRT, while the outer lenses recorded the radar returns (left and right radar returns only in non-MTI mode, or half-width tracks showing radar returns and MTI traces if MTI was in use). Exposure would automatically vary with the speed at which the 5in-wide film strip was transported past the lenses. Unlike the linescan unit, radio transmission of radar data was not considered practical or necessary, and post-flight processing and interpretation of radar reconnaissance data would be the only means of getting at this data. Unlike the aircraft’s on-board navigation SLR, there was no rapid processing unit to enable near-real-time display of the reconnaissance radar. Instead, a rapid processing and development unit (RPDU) would be part of the ground station supporting TSR2 reconnaissance operations.
The reconnaissance pack control panel in the navigator’s cockpit. This panel would have occupied the ‘role panel’ slot at bottom left of the navigator’s instrument panel. BAE Systems via Warton Heritage Group
The amount of coverage possible from the SLR was limited by two things. First of all, the length of the film strip dictated the distance that could be covered on the track (25ft (7.6m) of film gave 1,500nm (1,725 miles; 2,775km) of cover at 5nm per inch), and secondly the altitude flown at and angle of the SLR aerials dictated the lateral depth of the coverage. The aerials could be set at five angles ranging between 10 degrees above the horizon to 20 degrees below, with the angle chosen not just to vary lateral coverage width, but also to make best use of available radar power. With 5, 10 and 20-mile (8, 16 and 32km) time bases, the lateral coverage could vary between 866 and 28,580ft (264 and 8,710m) with a 5-mile time base, and from 28,020 to 82,040ft (8,540 to 25,000m) with a 20-mile time base. The gap of no coverage below the aircraft would therefore vary from 1,732 to 56,040ft (530 to 17,080m). The film scale would vary between 5 and 9 miles per inch.
The MTI feature could only detect objects with a perpendicular movement component of at least 3.5 mph (5.6km/h). A moving vehicle could theoretically go entirely undetected if it was heading along a track parallel to that of the aircraft. In practice this was unlikely to have been a major problem, as reconnaissance sorties would have been planned to avoid flying parallel to the track of any roads or rail lines of interest, and targets moving over open cou
ntry would be unlikely to stick to a straight line for long, minimizing the already small chance that their track would coincide with that of the aircraft.
The SLR requirements were particularly demanding in terms of reliability; up to 6hr continuous airborne use, and 200hr between maintenance checks, without any loss in accuracy.
Photographic reconnaissance
While OR.343 initially specified a front-facing camera mounted in the aircraft, this was changed when it was pointed out that the average time between the pilot spotting a target and needing to get the camera pointing at it would be around 1/10th of a second, which was simply not possible in most circumstances. The results from forward-facing cameras on existing reconnaissance types were proving to be extremely limited as a result. A downward-facing camera was substituted instead, along with two side-facing cameras giving oblique coverage. These were all Vinten F.95 Mk 7s, the downward-facing one being fitted with a 1.5in (38mm) lens and the obliques with 4in f/1.8 lenses tilted down at 15 degrees from the horizontal. Shutter speed was 1/1500 at six frames per second, or 1/3000 at twelve frames per second, with image movement compensation. The film magazine on each camera could accommodate 100ft (30m) of film, enough for 40sec continuous coverage at the highest frame rate.
Three FX.126 cameras were intended to be fitted within the rear half of the reconnaissance pack, with a variety of lens sizes to enable a mixture of imagery resolutions from various altitudes: one with a 6in f5.6 lens, and the others with either 24in f5.6 or 36in f6.3 lenses. Shutter speeds could be 1/250, 1/500 or 1/1000, and film capacity for this 9 × 9in (23 × 23cm)-format film was 250ft (76m) of film or 320 exposures. Latitude and longitude would be recorded on each frame, and markers recorded on the SLR traces to show where each photographic frame was taken (if the SLR was operating). One drawback of traditional photographic film was its susceptibility to radiation, and given the nuclear environment in which the aircraft could expect to be operating in a full-scale European war, provision was made for filtration of the air entering the reconnaissance pack camera bay to stop radioactive contaminants accumulating on or around the film cassettes. In peacetime the filters would be bypassed owing to the expense and maintenance hassle of fitting and removing them all the time.
Mobile photographic-interpretation units were intended to be located with TSR2 units at forward airfields, enabling all air-reconnaissance imagery to be passed through human interpretation before being communicated to the Army. There would, however, never be enough of these to go round, so the idea was they would be located at a handful of ‘master’ airfields rather than attempting to provide facilities at every dispersed site.
Self-protection: passive electronic countermeasures
While TSR2’s primary defence against detection was low-level flight, there would still be plenty of opportunity for the aircraft to be blown out of the sky by sufficiently advanced missiles, and the loft attack in particular exposed the aircraft to radar detection and lock-on. The Guided Weapons Department at Vickers produced a report at the end of January 1959 which concluded that active jammers should not be carried by the TSR2 except in exceptional circumstances, that a warning receiver would be essential, that the natural radar echoing area of the aircraft should be kept as low as possible, and passive measures such as applying radar camouflage material to the airframe and carriage of Window (chaff) would be useful. A Sub-Committee on Electronic Countermeasures was formed and examined this area in detail.
An FX.126 camera with 12in lens. Development of the camera lagged behind that of the TSR2 but continued after the aircraft’s cancellation, airborne trials starting in 1967. With automatic focus, exposure and image stabilization, plus the ability to record navigational information alongside the images, this was an advanced piece of equipment. A&AEE
Missile warning system (ARI.18203)
To give the aircrew some indication that they were the subject of a radar-guided-missile attack, a passive RWR fit was to be integrated within the airframe. An outline requirement for this was drawn up in May 1960, and detailed a system that was to weigh no more than 50lb (23kg), nor exceed one cubic foot (0.03cu m) of space. The system was to indicate the presence of lock-on radars of all polarizations, whether airborne or ground; indicate and discriminate between S-, X-, J- and Q-band signals; discriminate between continuous-wave and pulse signals; give all-round cover; give aural and visual indications of a lock-on, and be ready by June 1963. Competitive study contracts were placed with Marconi and Ferranti in August 1960. Tenders were submitted in November and the job was given to Ferranti at the end of December. Incredibly, it then took the MoA a full year to negotiate a contract with Ferranti, a ridiculous length of time, beating even its own normally slothful standards. Consequently the development of the system did not begin until late in 1961, nearly two years after the TSR2 project as a whole had begun.
The passive warning receiver was initially to consist of two forward-facing missile-warning heads on the nose just in front of the windscreen, projecting at about 45 degrees on either side, and a rearward-facing pair of heads within the trailing edge of each of the down-turned wingtips. Each pair of heads could thus detect radar energy in both horizontal and vertical polarizations, and included three aerials to cover the microwave bands S, C/X and J. Detection of a missile lock would sound a tone in the aircrew headsets; an RWR display to show threat direction was not provided, though a simple left/right indicator was originally mentioned as being of use. However, difficulties were experienced with this equipment during development. First, reception of pulse signals caused overloading of a test unit, requiring considerable amplifier redesign, and then Ferranti’s aural signal, a relatively simple amplification of the received radar signal, was judged inappropriate, and a steady aural tone was required instead. This instantly meant the unit could not recognize a track-while-scan radar, as Ferranti had relied upon the distinct aural tones of such a radar to give the crew warning. Addition of a new circuit to cope with recognizing a TWS pattern and translating it to the standard aural warning tone was necessary.
The forward (nose) aerial of the missile warning receiver. Two of these would have been enclosed within a dielectric fairing on the nose, ahead and on either side of the windscreen, on production airframes. BAE Systems via Brooklands Museum
Then it was found that the proposed wingtip locations would interfere with the aircraft’s fluxgate compass, also mounted in the wingtip. As a result, the installation was downgraded to a single wingtip receiver, leaving a small gap in the rearward coverage which the Air Staff initially accepted but later objected to, forcing a rethink to see if a four-station unit could be made to work. The problem was insuperable, and a three-station system had to be accepted. By June 1963 the system was nowhere near ready. Flight trials were initially scheduled to take place on the ninth development-batch aircraft during late 1964, but the delays in development of both the RWR and the aircraft itself caused a decision to be made to transfer trials to the eleventh aircraft (these being scheduled for the spring of 1966). By April 1965, problems with the casings for the wingtip receiver had prevented the installation of a complete system in any TSR2 airframe; the project’s cancellation came days later.
The port wingtip trailing edge would have housed the third missile warning receiver aerial, in the area below the fuel vent/jettison pipe. Also evident here are the ILS aerial (bottom centre), fluxgate compass (bulged) and two ‘bonker’ plates (fitted only to some development-batch aircraft). Damien Burke
Chaff and flares
On the active countermeasures front there were no systems installed within the airframe, but various investigations were also carried out into the carriage of what was then called ‘rapid-blooming Window’ (RBW, now commonly called ‘chaff’). Window was the codename used by the RAF in the Second World War for foil strips used to confuse enemy radars. Rather than being thrown out in handfuls by aircrew, as was done during the war, modern jets needed the ability to eject RBW as and when required, preferably auto
matically. The main thrust of the investigation regarding use of RBW by the TSR2 was into masking the airframe during the loft attack, for which a forward-firing rocket was felt to be the best idea. The rocket would burst well in front of the aircraft and produce a cloud of Window that would hopefully either stop a radar lock-on from occurring, or break an existing lock.
The loft attack left the aircraft dangerously exposed to enemy radar and missiles. Firing a barrier of Window (chaff) was a way to try to prevent a missile lock during this vulnerable phase of a sortie. Damien Burke
Because BAC was initially frustrated on this front by lack of available data and existing equipment, it was agreed with the MoA that provision of firing circuits and pylons suitable to take a variety of rocket pods would be enough to fulfil the requirement. It did not take long for the MoA to come back to the subject and ask BAC for a detailed study. Early suggestions for RBW dispensers concentrated on the underwing carriage of dispensers on each side, whether by pylon, slipper pod or wingtip pod, all of which carried penalties in terms of loss of weapons carriage space, drag or excessive weight gain owing to a redesigned wingtip structure. Holding to the concept of projecting Window as far forward as possible, BAC also suggested a dorsal pack mounted above the fuselage, just ahead of the wing. However, the Air Staff were not keen on this addition, with its attendant ground-support requirements. (Loading the pack sections so high above the ground would require some sort of crane, and this went against the whole dispersed airfield and minimum-ground-support philosophy.) Despite the drawbacks of the loss of pylons for weapons carriage, and drag, the pylon-mounted dispensers were felt by the Air Staff to be the best option, and in July 1960 it was decided that pylon-mounted dispensers would be the way forward.