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.
The NRAO Green Bank Telescope (GBT), located in Green Bank, West Virginia, is supported by 16 steel wheels which
rest upon a composite steel and concrete Azimuth Track, 210 feet (64 meters) in diameter. From the start of observing in
February 2001, the Azimuth Track design presented an operational problem for NRAO. By the spring of 2001, slippage
of the top plate on the base plate was causing hold-down bolt failures. In July 2002, wear between the top and base
plates (fretting) had become evident around the entire track circumference. NRAO engineers took immediate action to
reduce both the track slippage and wear problems. But in January 2003, cracks were discovered in two adjacent top
plates; by 2006 the top plates were cracking at a rate of almost one a month - an alarming rate given the design service
life of 20 years. This paper will summarize the engineering analysis efforts that were subsequently conducted to assess
the root cause of the GBT track degradation problem. We will also discuss a trial modification section that was installed
in June 2004. Finally, we will discuss the design solution that was developed to remedy the track performance problem.
The azimuth track of the Green Bank Telescope did not perform as designed. Relative movement of components was
noted during construction; in addition, fretting of the base plate and wear plate faying surfaces, fatigue cracking of the
wear plates, fatigue failure of wear plate fasteners, and deterioration of the cementitous grout layer occurred at a rapid
pace during the first few years of operation. After extensive failure analysis, a new system of components was designed
and fabricated, and installation of the components was performed during 2007 (Symmes, Anderson, and Egan,
"Improving the service life of the 100m Green Bank Telescope azimuth track", SPIE 7012-121). The highlights and
lessons learned during the fabrication and installation phases are described herein. This information will benefit any
organization performing a similar replacement, and may be helpful in new installations as well.