Jodrell Bank Observatory: Mark II Telescope, Lower Withington, Cheshire East

Summary

Radio telescope. Designed 1960, built 1962-1964 and constructed to designs by Sir Charles Husband of structural engineers Husband and Company of Sheffield to the requirements of Sir Bernard Lovell. Constructed by Arrol & Co. New, circular bowl surface mounted on top of the original elliptical bowl in 1987.

Description

MATERIALS: concrete, structural steel, welded steel sheet, with later aluminium panels (1987).

PLAN: circular, ground-floor base building containing roller track and alt-azimuth mount with rectangular engine room projecting on south-east side; concrete bracket on top of circular base building supporting an elliptical dish; rectangular first-floor room located between the base of the bracket; separate, small, engine room situated on the rotating structure of the telescope.

EXTERIOR: the base building, ground-floor engine room (known as the Ward Leonard Room), first-floor central room (known as the Turntable Lab) and telescope bracket are constructed of pre-stressed concrete. The buildings have flat concrete roofs, some covered in asphalt. All the windows have Georgian-wired glazing.The ground-floor engine room is known as the Ward Leonard Room after the Ward Leonard Motor Generator System which used to be the standard system for producing Direct Currant (DC) power for rotating the telescope. It is well-lit by large, metal-framed windows. In the centre of the north-west side is a small, square projecting room with windows in all three elevations. On both sides of this room are wide, full-height doorways with timber double doors, that to the right with a wicket door. The circular base building is lit by four horizontal, metal-framed windows. On the south side is a tall, wide, doorway with timber double doors. On the east side there is a flight of concrete steps with metal pipe handrails with diamond wiring infill leading up to the roof of the circular building on which the telescope bracket stands. It has a similar metal pipe railing (without the wiring infill) around the perimeter. The flat-roofed Turntable Lab has concrete braces across to the outward-leaning telescope bracket. The room is well-lit by tall, vertical windows with metal frames. There are wide, full-height doorways with timber double doors at the right-hand ends of both long elevations. Situated on the rotating structure of the telescope is a small engine room known as the Elevation Drive Cabin. It has a deep, concrete engine-bed base, and the walls and flat-roof are constructed of riveted steel panels with a sliding, steel-panel doorway on one side. The elliptical reflector bowl has a lattice-work, steel frame supported on the concrete bracket with concrete counter-weights to the rear. The elliptical, paraboloidal bowl is constructed of welded steel sheet with a major axis of 125ft (38.1m) and minor axis of 83ft 4in (25.4m). Overlaying this is the 1987, circular surface of aluminium panels. The aerial with a focal point of 40ft (12m) is supported by four lattice-work legs standing out from the edge of the bowl structure; the lower, right leg incorporates a narrow flight of steps to access the aerial focal point with a hanging flight of steps to allow access from the roof of the Elevation Drive Cabin.

INTERIOR: the Ward Leonard Room contains the original azimuth gearbox on a deep concrete engine bed, since modified. It bears a plaque for Crofts (engineers) Ltd, Bradford and is stamped ‘AUG 30 62 3Hz’. It powers a vertical driveshaft, gear chain and cogs which move rollers to control the horizontal position of the alt-azimuth mount in the circular base building. On the east side of the gearbox are the two original motors of the control system for the telescope, now replaced by control cabinets along the south-west side of the room. The circular base building contains the alt-azimuth mount which sits on 54 steel rollers in a 12.8m (42ft) diameter on a concrete foundation block in a spoke chamber. There is a narrow walkway around the outside. The first-floor Turntable Lab contains a central, full-height, circular cabinet of riveted steel panels known as a ‘twister’ through which the telescope wires are threaded to prevent their tangling. The room also retains the original circular, enamelled light shades. It has a small, 500kg travelling crane above a trap door in the floor through which the alt-azimuth mount can be reached. The Elevation Drive Cabin contains a motor and gearbox which drives a vertical driveshaft which controls the vertical position of the telescope.

History

The observatory at Jodrell Bank was one of the earliest planned sites for radio telescopes in the world. As such it had a pivotal role in the development of the new science of radio astronomy which was one of the first steps towards modern Astrophysics, revolutionising our understanding of the Universe. The site was first used for academic purposes in 1939 when the University of Manchester's Botany Department purchased three fields in the Cheshire countryside covering around 11 acres. The earliest use of the site for radio astronomy occurred in December 1945 when Bernard Lovell, who worked for the university’s Physics Department, moved here to escape the radio interference that occurred in Manchester city centre. His first observations used ex-army radar equipment located at the south end of the site, close to two pre-existing botany huts. Subsequently his team expanded northwards with the continuing construction of more permanent buildings, aerials and telescopes. Jodrell Bank’s status as a world-class centre of ongoing scientific research continues to this day with the construction of the global headquarters for the Square Kilometre Array project linking hundreds of telescopes and aerials in South Africa and Western Australia.

The Mark II Telescope was instigated in 1960 by discussions between Sir Bernard Lovell and Sir Charles Husband of structural engineers Husband and Co of Sheffield, who had previously designed the Mark I Telescope (since renamed the Lovell Radio Telescope), built in 1952-57. When approaching the design of this second telescope various issues were addressed. The idea of an oval (elliptical) reflector arose as a response to the design problems of constructing a very large reflector. Husband wanted to keep down the vertical size to avoid constructional and aerodynamic problems. He also preferred to construct the whole turntable of pre-stressed concrete rather than structural steel for reasons of rigidity and economy. It was intended as the prototype of a larger telescope, later referred to as the Mark IV, which was never constructed. Meanwhile, in 1960 the General Post Office asked Husband to build a radio telescope at Goonhilly, Cornwall, for transatlantic communication via the first active communication satellite, known as Telstar, with a summer 1962 deadline. Husband declared this impossible unless he was allowed to use the basic design for the Mark II Telescope, scaling the design so the bowl was circular with the diameter of the minor axis of the Mark II. It was subsequently built to the 1962 timescale and is recognised as the birthplace of satellite communication (Antenna No.1 at Goonhilly Satellite Earth Station listed Grade II*). Funding for the construction of the Mark II Telescope was requested on 19 December 1960, but the Research Council of the Department of Scientific and Industrial Research (RCDSI) did not pass this until December 1961.

The telescope was built on the site of the earlier 218ft Transit Telescope and was operational by summer 1964. It had a steel sheet paraboloidal reflecting bowl with an elliptical aperture of major axis 125ft (38.1m) and minor axis of 83ft 4in (25.4m). The focal length was 40ft (12.2m), the mounting was alt-azimuth with 420 degrees of travel in azimuth and 0 to 90 degrees in elevation. The drive was a Ward-Leonard system with digital computer control giving great accuracy of positioning. The Mark II was the first telescope in the world to be steered by digital computer. The computer used was the Ferranti Argus 104, which was one of the very first computers designed for real time control, with a storage capacity of 12 Kbytes.

A combination of greater surface accuracy of the bowl and the design of more precise control devices meant that the Mark II was able to observe higher frequency wave lengths in the 21cm band and shorter than the Mark I Telescope and thus complement it. As well as operating as a solo instrument, the telescope was intended to work as an interferometer with the Mark I Telescope (two or more telescopes that combine their signals to produce a resolution equivalent to that of a telescope of diameter equal to the largest separation between its individual telescopes). In 1971 the Mark II’s computer was upgraded to an Argus 400 computer, also capable of carrying out data acquisition for the telescope’s observing programs, with the original 104 transferred to the upgraded Mark I. During the 1970s the telescope worked in conjunction with the Mark III telescope (built to the same dimensions in 1966 at Wardle, Nantwich, Cheshire and intended to be portable but never moved). This work led to the development of the Multi Telescope Radio Linked Interferometer (MTRLI) and then Multi-Element Radio Linked Interferometer Network (MERLIN) arrays of which it is an integral part.

In 1974 a proposal was made to upgrade the Mark II to Mark IIA, by giving it a 100ft circular aperture which could be used on wavelengths down to 6mm. However, funding could not be secured.

In 1987 the bowl was upgraded with a circular surface of new aluminium panels mounted on top of the original steel surface. The new surface had an accuracy of 1/3mm and was set using a holographic technique. It was built in a collaborative project between Jodrell Bank and Racal Antennas and resulted in the telescope being able to observe at the 22GHz MERLIN frequency. In the late 1990s a new, more compact carousel for the receivers was installed in the aerial focus. The building was refurbished in 2014.

The Mark II Telescope continues in daily use with the majority of current observational time spent either on e-MERLIN (the upgraded MERLIN programme) or Very Long Baseline Interferometry (VBLI), joining radio telescopes around the world.

Reasons for Listing

The Mark II Telescope, Jodrell Bank Observatory, designed 1960, built 1962-66 and constructed to designs by Sir Charles Husband to the requirements of Sir Bernard Lovell, is listed at Grade I for the following principal reasons:

* Technological innovation: Husband designed a pre-stressed concrete mount for the reflector dish to improve on the rigidity and accuracy of the structural steel he had used for the Lovell Telescope, and as a more economic solution, the design of which he then used as the basis for the telescope at Goonhilly, Cornwall (Grade II*), built to receive the first live transatlantic television pictures from the Telstar satellite in 1962, the successful design then widely adopted in the development of international modern satellite communications. The Mark II Telescope was the first telescope in the world to be steered by a digital computer, the Ferranti Argus 104, one of the very first computers designed for real-time control;

* Historic interest: as an early, large-scale, fully steerable radio telescope and key component of the Jodrell Bank Observatory. One of the earliest planned sites for radio astronomy in the world, its construction enabled the development of scientific research through greater accuracy in observations both individually and in conjunction with the earlier Lovell Telescope (Mark I Telescope) to progress the technique of interferometry, a role it continues in a worldwide context to this day;

* Design interest: the bold concrete frame and striking elliptical reflector dish give the Mark II Telescope an impressive, sculptural appearance; together with the Lovell Telescope it has a dramatic visual quality which captures in physical form the excitement of radio astronomy at this pioneering site;

* Group value: the radio telescope has a strong functional and visual connection with the Lovell Telescope (Grade I), through the discipline of radio astronomy for which the Observatory has a long-standing international reputation.

External Links

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