The world's largest radio telescope, the Five-hundred-meter Aperture Spherical Telescope (FAST), was launched on Sunday in China.
The radio telescope is nestled in a natural basin within a stunning landscape of lush green karst formations in the remote Pingtang county in southwest China's Guizhou province. It took five years and $180 million to complete and has 2 to 3 times the sensitivity of the 300-meter Arecibo Observatory in Puerto Rico, and five to 10 times the surveying speed.
FAST began test operations on Sunday September 25, 2016, and will be used to search for gravitational waves, radio emissions from stars and galaxies and signs of intelligent extraterrestrial life. It will take several years for the telescope to go fully operational, since it will take three years to calibrate the various instruments.
Construction
Construction began in earnest in March 2011. A 65-person village was relocated from the valley to make room for the telescope and an additional 9,110 people living within a 5 km radius of the telescope were relocated to maintain radio-silence.
FAST Design
FAST's surface is made of 4450 triangular panels, 11 m per side, in the form of a geodesic dome. Actuators underneath make it an active surface, pulling and pushing on joints between panels, deforming the flexible steel cable support into a parabolic antenna aligned with the desired sky direction.
Above the reflector is a light-weight feed cabin moved by a cable robot using winch servomechanisms on six support towers. The receiving antennas are mounted below this on a Stewart platform which provides fine position control and compensates for disturbances like wind motion.
FAST operates in the 70 MHz to 3.0 GHz frequency range using 9 receivers; the 1.23–1.53 GHz band around the hydrogen line is covered using a sensitive 19-beam receiver built by the CSIRO, Australia.
The data system, called the Next Generation Archive System (NGAS), was developed at the International Centre for Radio Astronomy (ICRAR) in Perth, Australia and the European Southern Observatory.
Radio Astronomy
Radio astronomy is the study of celestial objects that give off radio waves, which are electromagnetic waves with wavelengths longer than those of visible light. Celestial objects emits radiation in many wavelengths; also, wavelengths of emissions from very distant objects get longer due to the expansion of the universe.
Radio astronomy is conducted using large radio antennas referred to as radio telescopes, that are either used singularly, or with multiple linked telescopes utilizing the techniques of radio interferometry and aperture synthesis. The use of interferometry allows radio astronomy to achieve high angular resolution, as the resolving power of an interferometer is set by the distance between its components, rather than the size of its components.
Radio telescopes need to be extremely large in order to receive weak signals. Also since angular resolution is a function of the diameter of the "objective" in proportion to the wavelength of the electromagnetic radiation being observed, radio telescopes have to be much larger in comparison to their optical counterparts. For example, a 1-meter diameter optical telescope is two million times bigger than the wavelength of light observed giving it a resolution of roughly 0.3 arc seconds, whereas a radio telescope "dish" many times that size may, depending on the wavelength observed, only be able to resolve an object the size of the full moon (30 minutes of arc).
The Arecibo Radio Telescope
The Arecibo Observatory is a radio telescope in Puerto Rico. This observatory is operated by SRI International, USRA and UMET, under cooperative agreement with the National Science Foundation (NSF). From its construction in the 1960s until 2011, the observatory was managed by Cornell University.
Arecibo’s 305 meter dish is the second largest single-aperture telescope in the world. Unlike FAST, Arecibo has transmitters to perform Radar Astronomy. Radar Astronomy is a technique for observing nearby astronomical objects by reflecting microwaves off target objects and analyzing the reflections. Radar astronomy is a critical tool in observing and analyzing solar system objects, including near-Earth Asteroids. Radar images provide critical information about the shapes and surface properties of solid bodies, which cannot be obtained by other ground-based techniques.
The Arecibo observatory can perform radar astronomy using its 4 radar transmitters, which have effective isotropic radiated powers (EIRP) of 20 TW (continuous) at 2380 MHz, 2.5 TW (pulse peak) at 430 MHz, 300 MW at 47 MHz, and 6 MW at 8 MHz. Note that EIRP of 20 TW corresponds to a transmit power of 1 MW.
The observatory was built between mid-1960 and November 1963. Since then, the telescope has been upgraded several times.
The Arecibo facility has been struggling with funding in recent years. The NSF, which provides two-thirds of the observatory’s $12-million annual budget, is strapped for funds to build and operate new telescopes that are high priorities for the astronomy community, such as the Large Synoptic Survey Telescope now under construction in Chile. In 2006, an expert panel recommended that the agency close Arecibo unless someone else could be found to foot the bill. NASA began providing some funding five years ago and now contributes $3.7 million annually, but so far no other organization has stepped up to pay the rest. A 2012 expert report warned that unless the NSF slashes the amount it spends on large facilities such as Arecibo, research grants to astronomers could be "decimated."
In Nov 2015, the Arecibo Observatory director quit after frustrated attempts to secure funding www.nature.com/...
Notes
Main photograph attributed to Liu Xu/Xinhua via AP.
Other photographs attributed to fast.bao.ac.cn.
Also, please see my other diary www.dailykos.com/… on Asteroids and Planetary Defense and Arecibo’s role in it.