Measuring and analyzing thermal deformations of the primary reflector of the Tianma radio telescope
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The primary reflector of the Tianma Radio Telescope (TMRT) distorts due to the varying thermal conditions, which dramatically reduces the aperture efficiency of Q-band observations. To evaluate and overcome the thermal effects, a thermal deformations measurement system has been established based on the extended Out-of-Focus holography (e-OOF). The thermal deformations can be measured in approximately 20 min with an illumination-weighted surface root mean square (RMS) accuracy of approximately 50 μm. We have measured the thermal deformations when the backup and front structure were heated by the sun respectively, and used the active surface system to correct the thermal deformations immediately to confirm the measurements. The thermal deformations when the backup structure is heated are larger than those when the front structure is heated. The values of half power beam width (HPBW) are related to the illumination-weighted surface RMS, and can be used to check the thermal deformations. When the backup structure is heated, the aperture efficiencies can remain above 90% of the maximum efficiency at 40 GHz for approximately two hours after one adjustment. While the front structure is heated, the aperture efficiencies can remain above 90% of the maximum efficiency at 40 GHz, and above 95% after one adjustment in approximately three hours.
KeywordsRadio telescope Thermal deformations Active surface system Extended out-of-focus holography
We are grateful for the assistance of the TMRT operators during the observations. This work was supported by the National Natural Science Foundation of China (Grant No. 11503070, U1631119, 11590780, 11590781 and 11590784), the Knowledge Innovation Program of CAS (Grant No. KJCX1-YW-18), the Scientific Program of Shanghai Municipality (Grant No. 08DZ1160100), the Key Laboratory for Radio Astronomy of CAS, the Astronomy-Financial Special of CAS, and the Youth Innovation Promotion Association of CAS. National Key Basic Research and Development Program (Grant No. 2018YFA0404700).
- 4.Prestage, R. M.: The green Bank telescope. Ground-based and Airborne Telescopes, Proc. SPIE, vol. 6267, pp. 626712 (2006)Google Scholar
- 6.Smith, D.R., Souccar, K., Magana, C.A., et al.: Performance testing of the LMT/GTM primary surface actuators. Advances in optical and mechanical Technologies for Telescopes and Instrumentation. Proc. SPIE. 9151, 91512C (2014)Google Scholar
- 7.Jian Dong, Huiliang Jin, Qian Ye., et al.: The active surface control system for the tian ma telescope, Proc. SPIE 9913, Software and Cyberinfrastructure for Astronomy IV, 991306 (2016)Google Scholar
- 10.Nikolic, B., Prestage, R.M., Balser D, S., et al.: Out-of-focus holography at the green bank telescope. A&A. 465, 685–693 (2007)Google Scholar
- 11.Nikolic, B., Hills, R.E., Richer, J.S.: Measurement of antenna surfaces from inand out-of-focus beam maps using astronomical sources. A&A. 465, 679–683 (2007)Google Scholar
- 15.Prestage, R.M., Constantikes, K.T., Balser, D.S., et al.: The GBT precision telescope control system. Ground-based telescopes. Proc. SPIE. 5489, 689 (2004)Google Scholar
- 16.John M. Ford, Richard M. Prestage., et al.: Marty Bloss, Experiences with the design and construction of wideband spectral line and pulsar instrumentation with CASPER hardware and software: the digital backend system, Proc. SPIE 9152, Software and Cyberinfrastructure for Astronomy III, 915218 (2014)Google Scholar