JUSTIFICATION FOR FUNDS REQUESTED

1. NATURE OF THE EQUIPMENT

The Lovell Telescope (LT) is a unique astronomical instrument, owned, maintained and operated by the University of Manchester. It is the largest fully-steerable radio telescope in the UK and the second largest in the world. For many of the research projects in which it is involved, no alternative exists. The unique status and national importance of the Lovell Telescope was recognised in 1988 when it was declared a Grade 1 Listed Building.

The LT has operated for more than 40 years, with one major upgrade almost 30 years ago. The present proposal is for a refurbishment project, costing a small fraction of the rebuilding cost, which will both extend the operational life of the telescope well into the next century and greatly improve its technical performance to meet the new challenges in radio astronomy.

2. THE MAIN PROJECT ELEMENTS

2.1 New Reflecting Surface

The Lovell Telescope was first commissioned in 1957 and had a major upgrade in 1970 in the form of a new reflector and strengthened support structure. The reflector consists of 336 panels with curved steel angle frames, surfaced with mild steel sheets which are attached by plug welds at intervals of 150 mm. After nearly 30 years, the surface sheets are suffering from corrosion due to the retention of moisture between the sheets and the supporting frames. The sheets are also severely distorted due to rust lifting them away from the frames. Fortunately the frames themselves have not suffered significantly, and we propose to use these as the foundation of a new reflecting surface.

Three panels have recently been the subject of a trial to investigate the proposed replacement technique and also to study the likely precision of a new surface (Figure 1a). Figure 1b shows work in progress on one of these panels. After removal of the old sheets, the frame has been cleaned and painted and new galvanised sheets are being secured in place on a bed of mastic with self-drilling/self-tapping screws.

Figure 1 (a) & (b)
The present surface, showing three trial panel replacements. Installing a trial galvanised steel plate.

A detailed technical review of the proposed replacement method by AEA Engineering in June 1998 concluded that it would `undoubtedly provide a reflector surface with a better corrosion performance than the existing surface'. Since the existing surface was installed in 1970, the new one may be expected to have a lifetime in excess of 30 years. AEA also suggested a number of ways to refine and validate the proposed technique. Based on this advice, some details of the technique have been modified and a sample has been submitted for accelerated corrosion testing to verify the expected increase in lifetime. Further trials to optimise access and working procedures are planned for Summer 1999.

With the surface sheets removed, good access is available to the panel `adjusters': threaded rods and nuts which were used to manipulate the large-scale profile of individual panels and the surface as a whole. These adjusters have also suffered badly from corrosion and have seized, so that it is no longer possible to reset the profile of the reflector. We propose to replace all the adjusters with new devices, plated to avoid future corrosion.

The repair of the trial panels has resulted in a large improvement in the profiles of all three. We have surveyed these panels as well as a sample of unmodified panels over the whole surface. The rms intra-panel deviations from the ideal profile, measured on the unmodified panels, ranged from 2.0 mm to 9.1 mm with a mean value of 4.7 mm. For the repaired panels the range was 1.1 mm to 2.4 mm with a mean value of 1.7 mm.

2.2 Surface adjustment

The main limit on the high-frequency performance of the telescope is the presence of large- scale deviations of the surface profile from a paraboloid of revolution. The present surface was set in the early seventies using conventional surveying techniques and gives 80% of the sensitivity for an ideal reflector at the specified operating frequency of 1500 MHz. The repaired surface will be capable of operation to much higher frequencies once it has been reset, using the renewed adjusters, to a profile determined by modern surveying techniques.

We have now developed a radio holographic technique for surveying the profile of the reflector. This involves the use of another radio telescope and a strong cosmic radio source (Padin, Davis & Lasenby, 1987, MNRAS, 224, 685). Figure 2 shows the result of such a survey of the LT conducted last year, at a resolution of about 1 m and with an accuracy of better than 1 mm. This diagram shows that the largest deviations are about 20 mm above (red) and below (dark blue) the ideal shape. The standard deviation from the ideal is 6.5 mm. Such an image will be used after the new reflecting surface has been installed in order to establish the adjustments which will be required for each of the 2500 adjusters.

Figure 2
Holographic measurements of the deviations of the present surface from a perfect paraboloid.

The measurements indicate that the inter-panel profile can be set with an rms accuracy of about 1 mm. Together with the intra-panel deviations of about 1.7 mm, we expect an overall rms deviation from the ideal of less than 2 mm. As shown in Figure 3, the sensitivity will then be at least 85% of that of an ideal surface at 5 GHz and a useful 50% at 10 GHz, equivalent to a perfect 54-m telescope.

Figure 3
The predicted improvement in the sensitivity of the Lovell Telescope, showing the relative performance as a function of frequency both before (lower curve) and after (upper curve) the proposed resurfacing.

Gravitational stresses on the structure cause the profile of the reflector to change slightly with elevation. We propose to set the profile for optimum performance at an elevation of 40 degrees. At the important operating frequency of 5 GHz, this will result in a sensitivity greater than 70% of the optimum for all elevations between 15 degrees and 80 degrees. We anticipate that recent developments in receiver technology will soon provide the means to compensate electronically for much of the gravitational distortion of reflector, restoring the full sensitivity at all elevations.

2.3 New Pointing Control System

The approximately four-fold increase in operating frequency achieved by the repair and adjustment of the reflector will result in a corresponding decrease in the angular size of the primary beam of the telescope. In order to point this narrower beam accurately at a radio source, the precision with which the control system guides the telescope must be improved.

A study of the control system by Comsat RSI Precision Controls was commissioned in 1995. Comsat are recognised world-wide as leading experts in the control of large radio telescopes. They concluded that `the Lovell Telescope celestial tracking capability can be improved significantly' by means of `individual control of all ten drive motors and appropriate motor controller and front-end loop closure electronics/algorithms'. We have obtained budgetary prices for upgrading the telescopeís drive and control system using a specification developed from the recommendations in Comsatís report.

2.4 Refurbishment of the Track and Foundations

Surveys of the azimuth rail tracks and their reinforced concrete foundations were commissioned in 1990. The surveys were undertaken by AEA Engineering and Gantry Railing Ltd respectively, the latter being updated in 1999.

The concrete survey `revealed a material generally consistent with the original concrete specification, well compacted and showing a present compressive strength of 20N/mm minimum'. It noted that `The defects in the concrete are confined to the exposed surface of the beams and slab of the outer ring' and `recommended that the areas of defective concrete be repaired and then the surface be protected with a proprietary sealant'.

The track survey recommended replacement of the outer rail and the replacement of soleplates, rail clips, holding-down bolts and grout on both the inner and the outer tracks.

We have obtained budgetary prices for refurbishing the telescope's track and foundations in accordance with the detailed recommendations of the above reports.

3. CONTRIBUTION TO RESEARCH INFRASTRUCTURE

The LT currently spends about 25% of its time operating as part of the MERLIN National Facility and as the UK element of European and global VLBI networks. Observing time for these activities is allocated purely on scientific merit through national and international peer review. MERLIN is the key radio element of the national strategy to provide access to state- of-the-art observational facilities across the electromagnetic spectrum. It is a world-class facility, with unique capability for the high resolution imaging of radio sources at a resolution which is matched to that of the Hubble Space Telescope and the planned next generation of new telescopes. The upgraded LT is expected to spend up to half of its time on these activities and will greatly enhance the science achievable, for instance more than doubling the sensitivity of MERLIN at 5 GHz.

Apart from the researches conducted by University of Manchester astronomers, the LT is available for use by other UK institutions. For example, the University of Wales at Cardiff are currently using a newly-developed multibeam receiver system for a neutral hydrogen search for low surface brightness `crouching giant' galaxies. In the future, the high- frequency spectral capability will also make the LT a valuable instrument for the burgeoning UK star-formation community. The LT is also involved in the most sensitive search ever for signals for extra-terrestrial intelligence, being undertaken in collaboration with the SETI Institute. The improved performance of the refurbished telescope will widen the scope of that search substantially.

4. EQUIPMENT OPERATING COSTS

The University of Manchester will continue to operate the Lovell Telescope as at present, using income from research grants and access charges as well as internal funds. The improved performance of the refurbished telescope may be expected to increase its capacity for revenue generating activities. No contribution to the cost of future operations is requested from JIF.

5. THE COSTS REQUESTED

Cost estimates for the main project elements have been assembled from the best available quotations and budgetary estimates, with adjustment where appropriate to current prices. The preliminary trial plate replacements have established the viability of most of the proposed procedures and appropriate contingencies. All costings have been subject to independent scrutiny by Gleeds Construction Consultants, a copy of whose report is available from the University. Although allowance for indexation is not normally included in JIF equipment awards, consideration of this is requested for this bid because of the unusual nature of the equipment procurement. Final costs will, of course, be dependent on the results of the detailed tendering process.

6. INVESTMENT AND OPTION APPRAISAL

The University's Financial Regulations require that an investment and option appraisal be undertaken for all projects where the cost exceeds a threshold set by Council; at present this limit is 150k. Such appraisals include cost/benefit, risk and financial assessments and utilise guidance issued by the Treasury, suitably amended for the University's environment. All reports produced, for this purpose, are scrutinised by the Capital Monitoring Group and approved by, or on behalf of, Finance Committee and Council, the University's governing body. Full details of the appraisal in relation to this project are attached as an Appendix to this submission.