Primary mirror figure maintenance of the Hobby-Eberly Telescope using the Segment Alignment Maintenance System

Rakoczy, John; Hall, Drew; Howard, Richard T.; Ly, William; Weir, J.T.; Montgomery, Edward; Adams, Mark T.; Booth, John A.; Fowler, James R.; Ames, Gregory H.

doi:10.1117/12.456734

Cited by 10 publications

(4 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…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

View full text Add to dashboard Cite

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.

show abstract

Section: Introductionmentioning

confidence: 99%

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

2023

View full text Add to dashboard Cite

show abstract

“…The MARS was part of this effort, along with the Segment Alignment Maintenance System (SAMS) 3,4 and the Dome Ventilation System (DVS). The MARS was part of this effort, along with the Segment Alignment Maintenance System (SAMS) 3,4 and the Dome Ventilation System (DVS).…”

Section: Introductionmentioning

confidence: 99%

Mirror Alignment Recovery System (MARS) on the Hobby-Eberly Telescope

Wolf

Palunas²,

Booth³

et al. 2003

SPIE Proceedings

Self Cite

View full text Add to dashboard Cite

The Mirror Alignment Recovery System (MARS) is a Shack-Hartmann based sensor at the center of curvature (CoC) of the Hobby-Eberly Telescope (HET) spherical primary mirror used to align the 91 mirror segments. The instrument resides in a CoC tower next to the HET dome, a location which provides a challenging set of problems including wind shake and seeing from two different domes. The system utilizes an internal light source to illuminate the HET and a reference mirror to provide focused spot locations from a spherical surface. A custom lenslet array is sized to the HET pupil image, matching a single hexagonal lenslet to each mirror segment. Centroids of the HET mirror segment spots are compared to the reference spot locations to measure tip/tilt misalignments of each segment. A MARS proof-ofconcept (POC) instrument, tested on the telescope in 2001, utilized a commercial wavefront sensor from Adaptive Optics Associates. The final system uses the same concept, but is customized for optimal performance on the HET.MARS replaces previous burst-antiburst alignment techniques and provides a more intuitive method of aligning the primary mirror for telescope operators. The POC instrument has improved median HET stack sizes by 0.3″ EE50, measured at the CoC tower. The current alignment accuracy is 0.14″ rms (0.28″ rms on the sky), resolution is 0.014″, measurement precision is 0.027″ rms, and segment capture range is ± 5″. With continuing improvements in HET dome ventilation and the addition of software customized for removal of tower motion during measurement, the alignment accuracy is expected to reach approximately 0.04″ rms in the final MARS, to be installed in late 2002.

show abstract

“…This algorithm is analogous to the classical feedback control laws that are typically used to actively control large ground telescopes; [24][25][26][27] it is similar to a proportional controller with a logic-driven gain operating on a 2-week timescale rather than continuously. It may seem inefficient or overly simplistic to simply discard six out of seven measurements.…”

Section: Baseline and Averaging Algorithmsmentioning

confidence: 99%

Improving active space telescope wavefront control using predictive thermal modeling

Gersh-Range

Perrin

2014

J. Astron. Telesc. Instrum. Syst

View full text Add to dashboard Cite

Abstract. Active control algorithms for space telescopes are less mature than those for large ground telescopes due to differences in the wavefront control problems. Active wavefront control for space telescopes at L2, such as the James Webb Space Telescope (JWST), requires weighing control costs against the benefits of correcting wavefront perturbations that are a predictable byproduct of the observing schedule, which is known and determined in advance. To improve the control algorithms for these telescopes, we have developed a model that calculates the temperature and wavefront evolution during a hypothetical mission, assuming the dominant wavefront perturbations are due to changes in the spacecraft attitude with respect to the sun. Using this model, we show that the wavefront can be controlled passively by introducing scheduling constraints that limit the allowable attitudes for an observation based on the observation duration and the mean telescope temperature. We also describe the implementation of a predictive controller designed to prevent the wavefront error (WFE) from exceeding a desired threshold. This controller outperforms simpler algorithms even with substantial model error, achieving a lower WFE without requiring significantly more corrections. Consequently, predictive wavefront control based on known spacecraft attitude plans is a promising approach for JWST and other future active space observatories. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

show abstract

Primary mirror figure maintenance of the Hobby-Eberly Telescope using the Segment Alignment Maintenance System

Cited by 10 publications

References 4 publications

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

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

Mirror Alignment Recovery System (MARS) on the Hobby-Eberly Telescope

Improving active space telescope wavefront control using predictive thermal modeling

Contact Info

Product

Resources

About