The Advanced Topographic Laser Altimeter System (ATLAS) will be the only instrument on the Ice, Cloud, and Land Elevation Satellite -2 (ICESat-2). ICESat-2 is the 2nd-generation of the orbiting laser altimeter ICESat, which will continue polar ice topography measurements with improved precision laser-ranging techniques. In contrast to the original ICESat design, ICESat-2 will use a micro-pulse, multi-beam approach that provides dense cross-track sampling to help scientists determine a surface's slope with each pass of the satellite. The ATLAS laser will emit visible, green laser pulses at a wavelength of 532 nm and a rate of 10 kHz and will be split into 6 beams. A set of six identical, thermally tuned optical filter assemblies (OFA) will be used to remove background solar radiation from the collected signal while transmitting the laser light to the detectors. A seventh assembly will be used to monitor the laser center wavelength during the mission. In this paper, we present the design and optical performance measurements of the ATLAS OFA in air and in vacuum prior to their integration on the ATLAS instrument.
The Laser Retroreflector Array for Lunar Landers (LRALL) is a small
optical instrument designed to provide a target for precision laser
ranging from a spacecraft in lunar orbit, enabling geolocation of the
lander and its instrument suite and establishing a fiducial maker on
the lunar surface. Here we describe the optical performance of LRALL
at visible and near-infrared wavelengths. Individual corner cube
reflectors (CCRs) within LRALL were tested for surface flatness and
dihedral angle values. We also imaged the far-field diffraction
patterns of individual CCRs as well as the entire retroreflector array
over the range of possible incident angles to extract the optical
cross section as a function of viewing angle. We also measured the
optical properties of one of the CCRs over the lunar temperature range
(100–380 K) and found no significant temperature-dependent variance.
The test results show LRALL meets the design criteria and can be
ranged to elevation angles above 30° with respect to the
instrument base from an orbital laser altimeter such as the Lunar
Orbiter Laser Altimeter on the Lunar Reconnaissance Orbiter. This work
summarizes the test data and serves as a guide for future laser
ranging to these retroreflector arrays.
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