Current trends in astronomical research necessitate a large number of small to medium sized telescopes be commissioned
to support and augment the science goals of larger ground-based observatories and space observatories. The science
mission requirements for these telescopes vary widely, yet the critical design requirements for the telescopes are largely
consistent across many missions. This paper clarifies the critical functional and performance parameters of a gimbaled
telescope system as dictated by three significant classes of telescope missions: laser transmission, wide area surveys and
pointed surveys. Within these classifications several specific example science missions are considered from which
specific telescope functional requirements are derived. Detailed telescope performance requirements are then evaluated
from a systems engineering perspective, highlighting typical performance that may be expected from a modern
telescope. Additional commentary is provided on the probable feasibility of upgrading older facilities in contrast to
commissioning new telescopes systems.
Based on the predictions of the NSF / NOAO sponsored ReSTAR report, it is assumed that the demand for highobservation-
volume pointed surveys will increase rapidly within the next ten years. A case is made for the high science
value of high gimbal slew rates on the basis of effective throughput in pointed survey applications.
Friction is a well-known performance limitation for gimbaled EO director systems. While much research study has been directed to bearing friction, the well-known friction models in literature, being represented in time, position, and rate domain, are not amenable to most LOS jitter analysis. Furthermore the type of mission profiles to which large gimbals are subjected have received limited attention in this field of research, so the selection of an appropriate friction model is not obvious. This paper fits popular friction models to experimental data, and studies the models in frequency domain.
Wind is a well known performance detractor for telescope pointing. A dome is often used for larger telescopes to minimize the wind load on the telescope. However, the dome does not eliminate the impact of wind but rather alters its static and dynamic load on the telescope structure. Unfortunately, predicting the interaction of the wind and dome on telescope performance is quite difficult so even a dome design that mitigates wind effects does not allow the telescope control designer to ignore the wind load. The control system must be prepared for on-site modifications to accommodate a dynamic wind disturbance and the combined telescope control and structure design dictate available control solution methods and their effectiveness. This paper quantifies the impact of wind induced jitter at the system level and examines the nature of the wind disturbance and control system solution alternatives. While the chosen solution is straightforward, its practical implementation involves subtleties in the control and structure cooperative design. The author employs recent test data to support the conclusions.
Optical tracking of airborne targets typically involves initial acquisition by radar at long range and relatively high measurement error. The target is then passed to an electro-optical tracker with a WFOV and precision tracking begins. The problem can include a second handoff to a NFOV sensor for additional resolution. A stringent mission time line requires these handoffs to be executed quickly. In this paper, traditional approaches to these handoff problems are reviewed and a new solution is presented at the system level. The authors discuss problems uncovered in the integration and testing phase and show results from an extensive HWIL testing platform.
Large gimbal systems often demand high accuracy pointing and smooth travel. Feedback control is employed to guarantee this performance in the face of wind, bearing and other disturbances. Both small and large gimbal performance is affected by many common factors. However, in smaller gimbal system, the foundation has little impact on the performance of the gimbal feedback control and can be neglected. For larger gimbal systems, this is not the case. Fortunately, the control system designer can use simplified analytical models to characterize foundation designs assess the impact on the system. This information can be coupled with modern control design techniques to improve the performance under less than ideal foundations. Analytical work is supplemented with test results from two large terrestrial gimbal telescopes with significantly different foundation designs.