Modelling and Assessment of the Impact of Gas Convection and Conduction within the Power Laser Head Enclosures of the ATLID and ALADIN Spaceborne Lidars
Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Spaceborne lidar are a promising new technology with the potential to provide significant information about the climate of Earth and other planetary bodies. Europe’s first spaceborne lidars are due to fly as primary payloads on both ADM-Aeolus (Aladin) and EarthCARE (ATLID) within the next few years. During vacuum tests, Aladin was found to malfunction due to complications from the phenomenon of laser inducedcontamination. Consequently, ESA and Astrium SAS identified a need for an oxygen purge system onboard ADM-Aeolus to allow the Power Laser Heads (PLHs) to function nominally. In response Astrium Ltd proposed an in-situ cleaning system (ICS), which involves the enclosure of the PLH components in a 40 Pa oxygen environment. ATLID, being earlier in its design phases has learned from Aladin and plans to fully pressurise the instrument with air to atmospheric pressure.A key challenge for the implementation of these instruments is the impact of convection and conduction of the gas medium on a system with stringent optics temperature stability requirements in an environment with highly dissipative items. On-ground, the potential occurrence of convection may also lead to a markedly different thermal performance than the gas conduction effects in microgravity or vacuum, requiringcorrelations between the cases to be known. These effects must be understood and characterised prior to passing the Aladin Qualification Review and for the successful operation of both of these payloads.This thesis addresses this need by numerically investigating the impact of convection and conduction of the gases on the thermal environment of the PLHs of Aladin, with applications to ATLID. Both parametric models were generated and the available reduced models of the Aladin PLH and its amplifiers modified to assess the impact of the gas on the laser diode stack, crystal slab and master oscillator bench temperatures. Simulations were run for the conditions of laboratory testing (101,325 Pa) and vacuum testing (40 Pa) as well as for the in-orbit conditions of 40 Pa and zero gravity. Through these simulations, the performance of a new manual numerical techniques in ESATANto model the fluid is presented and verified by theoretical analyses in MATLAB and existing models in ANSYS. Experimental verification is anticipated to occur in the coming years or months as hardware testing resumes.The results demonstrate that the ICS has minimal detrimental effect on system performance and in many instances acts to thermally stabilise the system, enabling some strict requirements on the design to be relaxed. However, it was identified that there may be a critical issue resulting from contact conductance effects that warrants further investigation, particularly at the amplifier level.
Place, publisher, year, edition, pages
2010. , 180 p.
Technology, Lidar, Aladin, ATLID, ESA, Laser, EarthCare, Aeolus, Convection, ESATAN, ESARAD
IdentifiersURN: urn:nbn:se:ltu:diva-52455Local ID: 99410d7b-63dc-4cf6-992f-f0f23f787abbOAI: oai:DiVA.org:ltu-52455DiVA: diva2:1025825
Subject / course
Student thesis, at least 30 credits
Space Engineering, master's level
Ejemalm, JohnnyKingston, Jenny
Validerat; 20131014 (global_studentproject_submitter)2016-10-042016-10-04Bibliographically approved