Project Cyclops, A Design... - Department of Earth and Planetary ...

APPENDIX
G
BACK-UP
STRUCTURES
There are four primary methods for limiting the
deflections of an antenna structure 'that appear to be
usable for the Cyclops design.
MAXIMUM STIFFNESS APPROACH
This is the time-honored procedure that has been
used by structural engineers for designing buildings,
bridges, etc. It has the distinct disadvantage of requiring
more material compared with other methods, to achieve
the desired result. This method is useful to the Cyclops
design only if structural members can be incorporated
for multiple use-for example, incorporating the reflector
surface and backup structure into some sort of
semimonocoque type of arrangement.
ENVIRONMENTAL
SHIELDING
A radome may be placed over the antenna to shield it
from wind and thermal effects. According to reference
1, this approach gives a total structural cost that may be
appreciably below the typical cost curves for all current
existing antenna designs. (Although our study here does
not necessarily confirm this finding.)
BEST-FIT
PROCEDURE
It is possible to reduce the rms deviation by fitting a
paraboloid of revolution to the distorted surface for the
various angles of tilt of the dish. The so.called "homologous
design" as discussed in reference 2 is a further
exploration of this method. Figure 8-2 from reference 2
shows the so-called "natural" limits that exist for a
steerable antenna. Assuming that the rms deviation for
the Cyclops antenna elements is between 1 mm and 3
mm, it can be observed from Figure 8-2 that it is
possible to construct dishes with a diameter of 40 to 70
m without violating the gravitational limit. For dishes in
excess of these dimensions, it is necessary to employ a
refinement in structural analysis or design to meet the
requirements of rms deviation. Regardless of the size of
the dish to be selected, a best fit procedure should be
used to minimize the rms error and total structural
weight.
THE USE OF MECHANICALLY
ELEMENTS
ACTIVATED
If the antenna element is fitted with force or
deformation compensating devices so that excessive
deflections can be removed, then the structural elements
can be made much lighter. These compensation devices
can consist of hydraulic jacks, that are properly arranged
counterweights. According to reference 1 it is possible to
accomplish proper compensation with as few as three
opposing force systems. This approach seems to lack
appeal for the Cyclops array because, with the large
number of elements, the problem of maintenance
appears to outweigh any savings represented by initial
cost
savings.
REFERENCES
1. A Large Radio-Radar Telescope Proposal for a
Research Facility. (4 vol.) Northeast Radio Observatory
Corp., June 1970.
2. A 300 Foot High High-Precision Radio Telescope.
National Radio Astronomy Observatory, Green
Bank, West Virginia, May 1969.
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