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.
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Figure 1 (a) & (b) The present surface, showing
three trial panel replacements. Installing a trial galvanised steel plate.
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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.
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Figure 2 Holographic measurements of
the deviations of the present surface from a perfect paraboloid.
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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.
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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.
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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 telescope’s drive and control system using
a specification developed from the recommendations in Comsat’s
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.