A 3.0 meter liquid mirror telescope
Dufour, Reginald J.
Doctor of Philosophy thesis
We constructed a 3.0 meter diameter f/1.5 Liquid Mirror Telescope (LMT) between 1990 and 1994 at the NASA Johnson Space Center, Houston, Texas. We have subsequently operated it since 1995 at the NASA Orbital Debris Observatory (NODO), Cloudcroft, NM. Employing an inexpensive rotating container of mercury as its primary parabolic mirror, the NASA LMT is a cost-effective alternative to telescopes utilizing glass mirrors. We detail criteria for mirror construction including environmental considerations via Hg vapor emission analysis. We describe performance optimization to the NODO site seeing limit of 0.8 arcseconds FWHM via analysis of perturbations to image quality from mirror angular velocity stability, dynamic balance, rotational axis tilt, and prime focus lateral and tilt displacements. We detail the behavior of the two prominent mirror surface wave phenomena---spiral and concentric forms. We demonstrate that the former probably results from vorticity in the air boundary layer above the mirror and show diffraction effects from the latter. We describe mirror stabilization in terms of boundary layer theory. The prime focus NASA-LMT utilizes corrective optics yielding a field of 46 arcminute diameter. Utilizing Micro-Channel-Plate (MCP) intensified video cameras we have obtained 750 hours of zenith staring orbital object event data with a limiting object diameter of approximately 1 cm at 1000 km altitude and 0.1 albedo. We have extended to 17.75 the lower magnitude limit of optical detections among the telescopes employed for orbital object surveys, further demonstrated the incompleteness of the SATCAT, and corroborated results of RADAR employed in orbital object detection. Utilizing CCDs we have conducted a 135 night broadband and multi-narrowband survey of 20 square degrees of sky at high galactic latitude down to a limiting magnitude of ∼22.0. The survey data will yield information on object morphology, spectral classifications, and large-scale structure to a redshift (z) of 0.5 with an accuracy of Deltaz ≤ 0.02. Broadband images from this survey are presented, demonstrating that the NASA-LMT optical performance is comparable to conventional telescopes of equivalent size located at a similar site.
Astronomy; Astrophysics; Optics