MUSTANG 2 is a 223 element focal plane that operates between 75 and 105 GHz on the 100 meter Green Bank Telescope. It shares many of the science goals of its predecessor, MUSTANG, but will have fifteen times the sensitivity and five times the field-of-view. Angular scales from 900 to 60 will be recovered with high fidelity providing a unique overlap between high resolution instruments such as ALMA and lower resolution single dish telescopes such as ACT or SPT. Individual TES bolometers are placed behind feedhorns spaced by 1.9λ f and are read out using a microwave SQUID multiplexing system.
We report on the development of Argus, a 16-pixel spectrometer, which will enable fast astronomical imaging over the 85–116 GHz band. Each pixel includes a compact heterodyne receiver module, which integrates two InP MMIC low-noise amplifiers, a coupled-line bandpass filter and a sub-harmonic Schottky diode mixer. The receiver signals are routed to and from the multi-chip MMIC modules with multilayer high frequency printed circuit boards, which includes LO splitters and IF amplifiers. Microstrip lines on flexible circuitry are used to transport signals between temperature stages. The spectrometer frontend is designed to be scalable, so that the array design can be reconfigured for future instruments with hundreds of pixels. Argus is scheduled to be commissioned at the Robert C. Byrd Green Bank Telescope in late 2014. Preliminary data for the first Argus pixels are presented.
This document will discuss the efforts and progress made in understanding, modeling, quantifying, and mitigating the stresses and behavior induced by creep motion in the 100 meter Green Bank Telescope's (GBT) azimuth track. From its commissioning the GBT azimuth track has been plagued by the side effects of creep motion induced by the 1,000,000 lb rolling load of each of its wheels. This paper will discuss the degrading effects of creep motion, similarities seen in other track systems, and the mitigation efforts employed to maintain track performance. It will also discuss efforts to understand and numerically model the track behavior, efforts to bound stresses using classical calculations, and suggest the direction for further work.
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.