National Science Foundation Open Skies
Past proposals submitted to the NSF Open Skies proposal process are available here .
- Current Proposal Requests
- Proposed Changes for Green Bank Observatory Operations 
The National Science Foundation’s (NSF’s) Division of Astronomical Sciences (AST) in its Mathematical and Physical Sciences (MPS) Directorate, funds world-class facilities that use cutting-edge technology providing images that rival the view from space. The NSF built the Green Bank Observatory and funded its operation for more than 50 years. Today the NSF still owns the facility and funds part of the operations, including time for “open skies” science on the 100-m GBT. The principle of “open skies” science is to maximize the scientific output of an instrument or facility through allowing any scientist in the world to apply for time on that instrument through a peer-reviewed process. Currently, roughly 66% of the GBT’s time is funded by the NSF for open skies proposals, although that percentage is anticipated to be reduced over the next two years.
in 2012 the National Science Foundation received a recommendation to divest the Green Bank Telescope from its budgetary portfolio by FY2017. Over the past few years we have worked closely with the National Science Foundation to redefine the future of the Green Bank facility. Across this time a number of new partnerships have emerged, most prominently with West Virginia University, the NANOGrav Consortium, and Breakthrough Initiatives.
Across the past four years the GBT has also continued to grow and improve both in its performance and in the instruments available for scientific research. A recent paper was published comparing the GBT as it was in 2012 (when the divestiture recommendation was received) with the telescope as it is today. That paper, entitled The National Science Foundation’s AST Portfolio Review of 2012 is Not Relevant to the Green Bank Telescope of 2017  can be found online at https://arxiv.org/abs/1610.02329. 
A second paper, looking at the impact of the GBT on high frequency (20-116 GHz) science, was also just released. It is entitled “The Case for a Publicly Available, Well-Instrumented GBT Operating at 20-115 GHz” and is here 
In 2012 the budget for Green Bank Observatory was almost entirely funded through an NSF contract for site and facility operations. This included funding for the site, the 100-m GBT, and the education and outreach programs which take place here. Currently the funding for the facility is at about 60%. Depending upon the final decision made by the NSF in the coming years, that number may go to as little as 30% or less. There are a couple ways of looking at the impact of that change. The simplest is to look at the over-subscription rate of the GBT with time. This essentially tells you how many hours of telescope time is request for every hours available. In other words, an over-subscription rate of 2.0 mean twice as much time was requested for science on the telescope as is available. A second means for understanding how the decrease in NSF-funded open-skies time will affect the science community is by looking at a two week period for the telescope schedule.
To better illustrate the two issue raised in the previous paragraph, below are three images. The first shows the measured over-subscription rate for the GBT of the past five years, and a predicted over-subscription rate, assuming the average number of hours requested for GBT science does not change in the upcoming three years. Following that, and to understand better the impact of that change, below are two versions of the GBT telescope schedule. The first shows the GBT schedule as it is today, with the open (white) space showing the time available for scientific proposals from the worldwide astronomy community. The second image shows the likely telescope schedule if only 30% of the available observing time were given to “open skies” proposals.
The effects of reducing the NSF funded open skies time on the GBT for pulsar science is described here .