Optical configuration and optical tests of the HartRAO Lunar Laser Ranger N. Nkosi 1, 2, L. Combrinck 1, 2, M. Akombelwa 2 1. Hartebeesthoek Radio Astronomy Observatory (HartRAO), South Africa. 2. Programme of Land Surveying (Geomatics) School of Engineering, University of KwaZulu- Natal, South Africa. 10 th Inkaba yeAfrica/!Khure Africa (AEON) Conference/Workshop Lord Milner Hotel, Matjiesfontein - Karoo 29 September – 3 October 2014

OUTLINE Introduction LLR telescope Telescope Mirrors: Cleaning and coating Coude path Measurements, tests and simulations

INTRODUCTION The HartRAO LLR will be a highly accurate system, consisting of integrated optical, mechanical, electronic and software units Requires the development of several new subsystems, including characterization and constant monitoring of the optical systems Characteristics under investigation includes: -Various reflection coefficients -Optical path environmental conditions (temperature, pressure, humidity) -Overall system parameters Output data will aid system monitoring, validation and quality checks

LLR TELESCOPE Figure 1: 1-m Classical Cassegrain telescope Figure 3: Parabolic primary mirrorFigure 2: Convex hyperbolic secondary mirror

LLR TELESCOPE…. cont Both the primary and secondary mirrors are of a honeycomb design Figure 4: Honeycomb mirror design Figure 5: Whiffle-tree support system The substrates are made from Schott Zerodur ceramic glass material through a technique of fusing glass plates and a core together at high temperatures. The primary mirror is held in place by an 18 point whiffle-tree floatation cell( Figure 5)

TELESCOPE MIRRORS: CLEANING AND COATING During laser ranging, the telescope is exposed to dust and other particles. This reduces the reflectivity of the mirrors, hence limiting the capability of observations Studies have revealed a direct relationship between the detection capability of a telescope and the cleanliness and efficiency of the coatings (Dierickx, 1992). To ensure maximum reflectivity, mirror surfaces have to cleaned and re-aluminized from time to time Mirror cleaning is a delicate process and one should avoid damaging the optics during this process.

TELESCOPE MIRRORS: CLEANING AND COATING..cont A visual inspection of the primary mirror’s coating was done by illuminating the mirror from behind with an LED light source. This revealed major degradation of the coating Attempts to remove coating off primary mirror failed. Potassium hydroxide solution Ferric Chloride Hydrochloric acid & Copper Sulphate Nitric acid Figure 6: Coating degradation on primary mirror Figure 7: Mirror surface after failed attempts to remove coating

Coudé Path Dielectric coudé mirrors Diameter = 50 mm Flatness = λ/ nm(λ) Capability ≥ GW Mirror Mounts Kinematic precision Angular resolution = 0.1 Arcseconds Path purge adapters Join delivery tubes Purge dry nitrogen gas into system Dry Nitrogen gas Removes dust and contaminants

Coudé Path Insulation Polyethylene pipe insulation Operating temperature= -40˚C to 90˚C Thickness = 15 mm Conductivity = to W/mK Delivery tubes OD= 65mm Black anodized to prevent reflection Protective cover Galvanised steel

Measurements, Tests & Simulations

We appreciate support towards this project from the Inkaba yeAfrica project, the NRF and HartRAO Acknowledgements