Galen Watts

The RadioAstron Green Bank Earth Station

We present the design, commissioning, and initial results of the Green Bank Earth Station (GBES), a RadioAstron data downlink station located at the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia. The GBES uses the modernized and refurbished NRAO 140ft telescope. Antenna optics were refurbished with new motors and drives fitted to the secondary mirror positioning system, and the deformable subreflector was refurbished with a new digital controller and new actuators. A new monitor and control system was developed for the 140ft and is based on that of the Green Bank Telescope (GBT), allowing satellite tracking via a simple scheduling block. Tools were developed to automate antenna pointing during tracking. Data from the antenna control systems and logs are retained and delivered with the science and telemetry data for processing at the Astro Space Center (ASC) of the Lebedev Physical Institute (LPI) of the Russian Academy of Sciences and the mission control centre, Lavochkin Association.

Advanced multi-beam spectrometer for the Green Bank Telescope

A new spectrometer for the Green Bank Telescope (GBT) is being built jointly by the NRAO and the CASPER, University of California, Berkeley. The spectrometer uses 8 bit ADCs and will be capable of processing up to 1.25 GHz bandwidth from 8 dual polarized beams. This mode will be used to process data from focal plane arrays. The spectrometer supports observing mode with 8 tunable digital sub-bands within the 1.25 GHz bandwidth. The spectrometer can also be configured to process a bandwidth of up to 10 GHz with 64 tunable sub-bands from a dual polarized beam. The vastly enhanced backend capabilities will support several new science projects with the GBT.

THE GBT 67–93.6 GHz SPECTRAL LINE SURVEY OF ORION-KL

We present a 67--93.6 GHz spectral line survey of Orion-KL with the new 4 mm Receiver on the Green Bank Telescope (GBT). The survey reaches unprecedented depths and covers the low-frequency end of the 3 mm atmospheric window which has been relatively unexplored previously. The entire spectral-line survey is published electronically for general use by the astronomical community. The calibration and performance of 4 mm Receiver on the GBT is also summarized.

Experiences with the design and construction of wideband spectral line and pulsar instrumentation with CASPER hardware and software: The Digital Backend System

NRAO recently designed and built a universal backend system for the Shanghai Astronomical Observatorys (SHAO) 65 meter radio telescope which was constructed near the city of Shanghai, China. The machine, called the Digital Backend System (DIBAS), was created from the design of the VErsatile GBT Astronomical Spectrometer (VEGAS) by adding nine incoherent pulsar search modes and eight coherent dedispersion timing modes to complement the 29 VEGAS spectral line modes. Together these modes cover all of the anticipated science requirements for the 65 meter except for VLBI.

A 4mm spectroscopic dual-beam receiver for the Robert C. Byrd green bank radio telescope

With a 100-meter aperture, and recent improvements to its surface accuracy and servo system upgrades, the Robert C. Byrd Green Bank Telescope is the most sensitive telescope operating at 90 GHz. A dual-feed heterodyne receiver is developed for observations at the lower frequency end of the 3-4mm atmospheric window (67 to 93 GHz). The science goals are primarily molecular spectroscopic studies of star formation and astrochemistry both internal and external to the Milky Way galaxy. Studies of the structural and physical properties of star-forming, cold-cloud cores will be revolutionized with molecular spectroscopy of the deuterium and other important species within the band. Essential for spectroscopy is the ability to remove slow gain and atmospheric variations. An optical table external to the cooled components rotates into the path of either beam an ambient temperature load, an offset mirror for viewing an internal cold load, or a quarter-wave plate that produces circular polarization for VLBI observations. A composite waveguide window comprised of HDPE, Zitex, and z-cut quartz provides a high-strength, low-loss medium for transmission of the signal to the cooled corrugated feed horn. An orthomode transducer separates the polarization components which are amplified by low noise HEMT amplifiers. Warm W-band MMIC amplifiers are required to compensate a negative gain slope and to reduce noise contributions from the down conversion to the GBT IF frequencies. Initial science results and receiver performance during commissioning observations will be presented along with details of the component design.

Satellite communications with NRAO Green Bank antennas

The National Radio Astronomy Observatory (NRAO) has new opportunities to partner with organizations in addition to the NSF using the assets at the Green Bank site. The 100 m Green Bank Telescope (GBT) is the worlds largest and most sensitive fully-steerable telescope, and can track at 20 deg min−1 in elevation and 40 deg min−1 in azimuth, providing the ability to track medium Earth orbit, geostationary, and deep space spacecraft. At X-band, its gain of 77 dB is unsurpassed by any fully steerable antenna. In addition to the GBT, the fully steerable, polar-mounted NRAO 140-ft telescope, with tracking rates of 20 deg min−1, and the 20 m telescope, with tracking rates of 120 deg min−1, provide a significant suite of instruments that can be deployed for spacecraft communications. Scheduled and target of opportunity observations are supported, allowing regular monitoring of and rapid response to targets.

A surface treatment for non-specular reflection

A method of treating reflective surfaces to reduce reflections causing signal drop-outs or antenna side lobes is described. The surface is constructed of small cells that reflect such that the relative phase of individual reflections is randomized and does not sum constructively or destructively. Tests of return loss and oblique reflection with comparisons to flat plates and RF absorber show performance similar to that of RF absorber.

Space situational awareness applications for radio astronomy assets

The National Radio Astronomy Observatory (NRAO) builds, operates, and maintains a suite of premier radio antennas, including the 100m aperture Green Bank Telescope, the largest fully-steerable antenna in the world. For more than five decades the NRAO has focused on astrophysics, providing researchers with the most advanced instruments possible: large apertures, extremely low-noise receivers, and signal processors with high frequency and time resolution. These instruments are adaptable to Space Situational Awareness (SSA) tasks such as radar detection of objects in near-Earth and cis-Lunar space, high accuracy orbit determination, object surveillance with passive methods, and uplink and downlink communications. We present the capabilities of antennas and infrastructure at the NRAO Green Bank Observatory in the context of SSA tasks, and discuss what additions and modifications would be necessary to achieve SSA goals while preserving existing radio astronomy performance. We also discuss how the Green Bank Observatory’s surrounding topography and location within the National Radio Quiet Zone will enhance SSA endeavors.