2.3 Modern Large Radio Telescopes
53
in a fixed direction with a 150-m tower to hold equipment at the focal point. Later, to
meet the application requirements in research areas of radio astronomy, atmospheric
science and radar astronomy, the design was revised into a dish-shaped spherical
reflector with a diameter of 305 m. Gordon selected a sinkhole with the karst topography located in the municipality of Arecibo, Puerto Rico, to put the very large dish.
Areciboradio telescope was built in 1963, and its dish surface was made of 38,778
perforated aluminum panels, each about 1 m by 2 m, supported by a mesh of steel
cables. Since the reflector is spherical, and not parabolic, the reflected signals will
not focus on a focal point so that the method of adjusted mirror or linear feed source
is used to collect energy. To aim the device, the receiver is moved to intercept signals
reflected from different directions by the spherical dish surface of 270-m radius. The
receiver is located on a 900-ton platform suspended 150-m above the dish by 18
cables running from three reinforced concrete tower, one 111-m tall and the other
two 81-m tall, placing their tops at the same elevation. The platform has a rotating,
bow-shaped track 93-m long, called azimuth arm, carrying the receiving antennas
and secondary and tertiary reflectors. This allows the telescope to observe any region
of the sky in a 40° cone of visibility at the local zenith. The observational strip formed
in the sky with the Earth rotating is between −1° and +38° of the declination. The
working wavelength range of the Arecibotelescope is from 3 to 100 cm, and its focal
length is 132.6 m. From its construction in the 1960s until 2011, the observatory
was managed by the University of Cornell. Under cooperative agreement with the
U.S. National Science Foundation, it is currently being operated by the University
of Central Florida, Yang Enterprises, and Metropolitan University (in Puerto Rico).
For more than 50 years, the Areciboradio telescope had always been the world’s
largest single-aperture one. Until 2016, it was surpassed by the Five-hundred-meter
Aperture Spherical Telescope (FAST) built in China.
Moreover, the Green Bank Telescope is the world’s largest fully-steerable radio
telescope, located in Green Bank, West Virginia, near the heart of the U. S. National
Radio Quiet Zone, and completed in 2002. The telescope is 148 m tall and its working
frequency range is from 290 MHz to 100 GHz; its surface is an elliptical cross section
with 110 by 100 m, intercepted from the symmetric rotational paraboloid with a
diameter of 208 m; it is unusual for radio telescopes that the primary reflector is an
off-axis segment of a paraboloid, and its focal point and feed horn are just located
at the side of the dish. The advantage of the off-axis design is that without any
obstruction above the dish, the radiations from celestial objects can directly arrive
at its surface to improve the effective collection areas, and cancel the reflection and
diffraction effects possibly from the arms or holders of the telescope. The reflector’s
surface is together joined by 2004 active metal panels, each of which can adjust its
position by an individual small motor. The surface deformation resulting from the
discrepancies of gravity, wind and temperature can be determined in real time by the
laser ranging system. And then, the computer sends control instructions to the motor
to adjust the position of corresponding panel. In the telescope rotating, the parabolic
shape can be kept by real-time adjusting the surface.
Beginning in the 1980s, a series of radio telescopes have successively been built
in China, such as Miyun synthesis radio telescope with an array of 28 nine-meter
53
in a fixed direction with a 150-m tower to hold equipment at the focal point. Later, to
meet the application requirements in research areas of radio astronomy, atmospheric
science and radar astronomy, the design was revised into a dish-shaped spherical
reflector with a diameter of 305 m. Gordon selected a sinkhole with the karst topography located in the municipality of Arecibo, Puerto Rico, to put the very large dish.
Areciboradio telescope was built in 1963, and its dish surface was made of 38,778
perforated aluminum panels, each about 1 m by 2 m, supported by a mesh of steel
cables. Since the reflector is spherical, and not parabolic, the reflected signals will
not focus on a focal point so that the method of adjusted mirror or linear feed source
is used to collect energy. To aim the device, the receiver is moved to intercept signals
reflected from different directions by the spherical dish surface of 270-m radius. The
receiver is located on a 900-ton platform suspended 150-m above the dish by 18
cables running from three reinforced concrete tower, one 111-m tall and the other
two 81-m tall, placing their tops at the same elevation. The platform has a rotating,
bow-shaped track 93-m long, called azimuth arm, carrying the receiving antennas
and secondary and tertiary reflectors. This allows the telescope to observe any region
of the sky in a 40° cone of visibility at the local zenith. The observational strip formed
in the sky with the Earth rotating is between −1° and +38° of the declination. The
working wavelength range of the Arecibotelescope is from 3 to 100 cm, and its focal
length is 132.6 m. From its construction in the 1960s until 2011, the observatory
was managed by the University of Cornell. Under cooperative agreement with the
U.S. National Science Foundation, it is currently being operated by the University
of Central Florida, Yang Enterprises, and Metropolitan University (in Puerto Rico).
For more than 50 years, the Areciboradio telescope had always been the world’s
largest single-aperture one. Until 2016, it was surpassed by the Five-hundred-meter
Aperture Spherical Telescope (FAST) built in China.
Moreover, the Green Bank Telescope is the world’s largest fully-steerable radio
telescope, located in Green Bank, West Virginia, near the heart of the U. S. National
Radio Quiet Zone, and completed in 2002. The telescope is 148 m tall and its working
frequency range is from 290 MHz to 100 GHz; its surface is an elliptical cross section
with 110 by 100 m, intercepted from the symmetric rotational paraboloid with a
diameter of 208 m; it is unusual for radio telescopes that the primary reflector is an
off-axis segment of a paraboloid, and its focal point and feed horn are just located
at the side of the dish. The advantage of the off-axis design is that without any
obstruction above the dish, the radiations from celestial objects can directly arrive
at its surface to improve the effective collection areas, and cancel the reflection and
diffraction effects possibly from the arms or holders of the telescope. The reflector’s
surface is together joined by 2004 active metal panels, each of which can adjust its
position by an individual small motor. The surface deformation resulting from the
discrepancies of gravity, wind and temperature can be determined in real time by the
laser ranging system. And then, the computer sends control instructions to the motor
to adjust the position of corresponding panel. In the telescope rotating, the parabolic
shape can be kept by real-time adjusting the surface.
Beginning in the 1980s, a series of radio telescopes have successively been built
in China, such as Miyun synthesis radio telescope with an array of 28 nine-meter