NSF Award
1836009
The Green Bank Telescope (GBT) is the world's largest fully-steerable telescope and a unique asset for the US scientific community. Its surface, which is larger than a football field, must be adjusted very precisely to bring the incoming radio waves into focus, so the surface was designed with more than 2000 individual panels mounted on precise motors. The motors can move the panels to compensate for any deviations from the perfect shape. While this works quite well at night, it can be very difficult to make this adjustment during daylight hours, when sunlight falling on different parts of the dish causes temperature changes and unpredictable distortions that cannot currently be measured. These distortions limit use of the GBT at its highest operating frequencies, where tolerances on surface accuracy are the tightest. The current project will implement a laser ranging measurement system on the GBT that will measure any surface distortions very accurately, allowing the GBT to be focused precisely both day and night. This will increase the available usable time of the telescope at its highest operating frequencies by as much as 1,000 hours every year, with a corresponding increase in the scientific output of the GBT and its utility to the US scientific community for a broad range of investigations. The Green Bank Observatory also supports a wide range of public outreach activities through its visitor center. <br/><br/>Enhancements to the Green Bank Telescope (GBT) metrology system are planned that will enable expanded operation in the 3mm wavelength band during daylight hours. This work will increase the usable telescope time at 3mm by as much as a factor of two, and increase available time on the molecule-rich inner Galactic plane and the Galactic center by up to a factor of four. Recent technological advances in commercial metrology make it possible to purchase a Terrestrial Laser Scanner (TLS) which, when mounted near the prime focus of the GBT, can scan the entire dish in one to two minutes, producing ~10 million data points with individual range accuracies of the order of a few mm. A least-squares fit to these data provides an estimate of the surface with accuracies ~30 microns rms, significantly better than the current method of "out-of-focus holography" and well in excess of the accuracy needed. The measured surface would be compared to the ideal surface to produce commands to the surface panel actuators to compensate for the thermal distortions.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
