Results from the capacitive edge sensing system for the active alignment of the SALT primary mirror

Gajjar, Hitesh; Menzies, John; Swiegers, Jian; Rozière, Didier; Courteville, Alain; Buous, Sebastien; Luong, Bruno

doi:10.1117/12.672103

Cited by 6 publications

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“…Small improvements have been made to the system in an attempt _____A to meet the milestones: calibration in situ for the temperature correction, hardware reliability effort, using a bench of reference sensors in order to correct the environmental behaviour of the sensors. [5] 3. SENSOR OPTIMISATION…”

Section: Test 2 -High Rh Small Temperature Spanmentioning

confidence: 99%

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SALT segmented primary mirror: commissioning capacitive edge sensing system and performance comparison with inductive sensor

2008

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The SAMS (Segment Alignment Measurement System) is a capacitance-based edge sensing solution for the active alignment of the 10m SALT segmented primary mirror. Commissioning and calibrating the system has been an ongoing task in an attempt to counteract the unfavourable response of the sensors to high humidity conditions and high dust levels. Several solutions were implemented and tested including real-time feedback systems and the application of corrective functions.In parallel with the continuing efforts to improve the performance of the capacitive sensors, we have also been testing a prototype inductive sensor developed by Fogale Nanotech that is of a very similar flexible plate construction.In this paper we present the results obtained and performance gains achieved thus far with the capacitive edge-sensing system as well as a performance comparison of the Fogale inductive sensor to the capacitive edge sensor.

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Section: Test 2 -High Rh Small Temperature Spanmentioning

confidence: 99%

“…It consists of 3 identical capacitive truss sensors [5] bonded onto triangular Astrositall pieces, similar in shape to an actual segment. Astrositall is used because of its very good thermal stability in order to reduce any mechanical movement.…”

Section: Reference Sensorsmentioning

confidence: 99%

SALT segmented primary mirror: commissioning capacitive edge sensing system and performance comparison with inductive sensor

2008

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“…Except Keck and GTC (replica of Keck), all other telescopes (HET, SALT and LAMOST) based on segmented mirror technology have gone through troublesome period in maintaining the alignment. Even after commissioning, over many years, alignment of these telescopes could not be maintained, which has adversely affected telescope performance and hence their scientific productivity (Rakoczy et al, 2003;Gajjar et al, 2006). Another challenge with edge sensor based M1CS is the focus mode problem.…”

Section: Introductionmentioning

confidence: 99%

Building a large affordable optical-NIR telescope (I): an alternate way to handle segmented primary mirror

2023

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The use of innovative ideas and the latest technology have undoubtedly brought down telescope costs substantially. However, there are still ways to further reduce the cost of optical ground-based telescopes and make them affordable to much larger and wide spread astronomical communities. In this and subsequent papers we are presenting our studies carried out towards building affordable mid-size telescopes of 4.0-6.0m in size. In the present era, segmented mirror technology has become the first choice for building moderate to large-size telescopes. In any Segmented Mirror Telescope (SMT) the most important part is its primary mirror control system (M1CS). The conventional M1CS is based on edge sensors and actuators, but such a system introduces many design and implementation complexities. In this paper, we propose to make use of an Off-axis Alignment and Phasing System (OAPS), which is an active mirror kind of control system working in real time to maintain the figure of a segmented primary mirror without the use of edge-sensors. The alignment and phasing system which is an integral part of any segmented telescope can be used in the real time at the off-axis. Through extensive simulations we have explored the feasibility of using an OAPS for co-alignment, co-focusing as well as co-phasing of segmented mirror telescopes. From our simulations we find that the co-alignment and co-focusing of the segments can be achieved with a guide star as faint as 16-18 th magnitude. This implies that seeing limited performance for any segmented telescope can be easily accomplished without use of a complex edge sensor based control system. Whereas, to attain diffraction limited performance, mirror segments need to be cophased with an accuracy of few tens of nanometers. In our simulations we have used a dispersed fringe sensor based phasing scheme, which can effectively work up to guide stars of 14 th magnitude.

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SALT segmented primary mirror: inductive edge sensors

et al. 2014

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Results from the capacitive edge sensing system for the active alignment of the SALT primary mirror

Cited by 6 publications

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SALT segmented primary mirror: commissioning capacitive edge sensing system and performance comparison with inductive sensor

SALT segmented primary mirror: commissioning capacitive edge sensing system and performance comparison with inductive sensor

Building a large affordable optical-NIR telescope (I): an alternate way to handle segmented primary mirror

SALT segmented primary mirror: inductive edge sensors

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