The Compact Hybrid Optical Rf User Segment (CHORUS) project is a collaborative research partnership between SmartSat CRC, DST Group, EOS Space Systems, EM Solutions, Shoal Group, the Australian National University, University of South Australia, and Lyrebird Antenna Research. The project has developed a prototype terminal capable of simultaneous operation in both radiofrequency and optical frequency bands through communications systems integrated into the same tactical platform. A full-size engineering model was developed and tested at the DST Group laser range at Edinburgh South Australia. The terminal is a modified existing platform from EM Solutions currently employed widely in the international defence sector focusing on maritime applications. The modifications made within this project include the integration of a custom aluminium mirror in the centre of the RF antenna. The optical communication signal is received at prime focus and a novel method for separating the RF and optical signals was designed, tested, and integrated. We report on the terminal design specifications and verification through field testing including performance of the optical and RF systems, pointing accuracy, and future technology directions.
The Australian Nation University (ANU) Quantum Optical Ground Station (QOGS) has been constructed in Canberra, Australia. Instrumentation is under development to enable lunar communications with QOGS. A receiver system and beacon transmitter will be installed on the telescope that is compatible with the Optical to Orion (O2O) terminal that will be onboard the Artemis II mission. Communication with spacecraft beyond the Moon is also possible by moving the receiver hardware to a larger telescope. The ANU operates Siding Spring Observatory where a 3.9 m or 2.3 m telescope could be used for deep space communications.
Dome seeing is an often overlooked avenue for seeing improvement for a telescope. Because most existing telescope domes have not been characterized for turbulence, there is an opportunity to improve the overall seeing by minimizing the dome contribution, thereby optimizing scientific productivity and operations. A dome turbulence sensor has recorded data in the Anglo-Australian Telescope (AAT) over the past year. The instrument consists of a collimated laser beam that propagates (and double passes) between the AAT’s primary mirror box and a flat mirror on the secondary strut. The angle-of-arrival fluctuations are used to derive a dome-seeing-proxy in arcsec. We found the dominant effects to be the temperature gradients and wind speed. Convection conditions are considerably more detrimental to the dome-seeing-proxy than thermal inversion conditions. Unlike other large telescopes, there is no discernible relationship between the dome-seeing-proxy and relative wind direction. Concerning telescope operations, it would be worth considering lowering the air-conditioning set point temperature to include a higher proportion of observations under thermal inversion. Nevertheless, this must be carefully weighed with the risk of condensation in the dome, a major concern for a site with frequent high relative humidity.
KEYWORDS: Transmitters, Telescopes, Receivers, Optical communications, Signal detection, Design and modelling, Prototyping, Free space optics, Space operations, Mirrors
The Australian National University (ANU) Optical Communications Ground Station (OCGS) is currently under development at Mt. Stromlo Observatory in Canberra, Australia. The OCGS will be compatible with a range of wavelengths, coding schemes, and techniques to cover satellites in Low Earth Orbit to Lunar and deep-space, and provide a platform for quantum communication from satellites. We have conducted a feasibility study and preliminary design review for the development of an instrument to support the CCSDS high photon efficiency (HPE) standard so the OCGS can support future lunar missions featuring optical communication terminals. The development of lunar communication capabilities in Australia offers site diversity and increased visibility, allowing for improved optical link availability during missions. We present the preliminary design for the transmitter and receiver which will integrate on the 70 cm telescope in the OCGS. A lab prototype of the transmitter has been built to demonstrate the generation of a pulse position modulation (PPM) waveform which is compatible with the CCSDS high photon efficiency (HPE) standard. The transmitter is made up of four 15 cm apertures which is mounted by a piggyback to the telescope. Each can operate as an independent channel with fine steering control through a fast steering mirror. The apertures are separated by characteristic atmospheric turbulence length r0 to minimise fading at the spacecraft. The receiver is installed at the Nasmyth port of the 70 cm telescope. The receiver features a fast steering mirror to maximise coupling into a multimode fibre. The signal is split with a photonic lantern and sent to several superconducting nanowire single photon detectors (SNSPD).
Characterisation and mitigation of atmospheric turbulence is critical for free space optical communication that relies on adaptive optics such as high bit rate coherent modulation or quantum key distribution. Turbulence profiling, i.e. measuring turbulence at different altitudes, provides more detail than typical seeing monitors and supports sophisticated AO and the possibility to forecast conditions. We present the implementation of a Ring-Image Next Generation Scintillation Sensor (RINGSS) instrument that profiles turbulence with a novel approach of defocused ring images introduced by A. Tokovinin (2021)1 . RINGSS is exceptionally low-cost, small, and fully automated, requiring significantly simpler equipment than previous turbulence profilers. We have demonstrated preliminary results that demonstrate the capability of this instrument for measurements of seeing and a low resolution turbulence profile. Future work is outlined that includes cross-calibration with a Stereo-SCIDAR instrument recently commissioned on the ANU 2.3m telescope at Siding Spring Observatory and plans for deployment at prospective optical ground station sites for an Australia-New Zealand optical network.
Two major contributors to the overall seeing that degrades astronomical images are turbulence from the atmosphere and turbulence within the telescope dome structure. Dome seeing generally contributes less than 1 arcsec to the overall seeing. However, most existing telescope domes have not been characterized for dome seeing; there is an opportunity to significantly improve the overall seeing by optimizing the dome seeing. An instrument that measures a proxy to dome seeing was installed at the Anglo-Australian Telescope (AAT) at Siding Spring Observatory in Australia. The instrument is based on a similar ’dome seeing monitor’ built and tested by Bustos and Tokovinin for the 4 m Blanco telescope in 2018. The instrument consists of a collimated laser beam that propagates from the AAT’s primary mirror box, reflects off a flat mirror on the secondary strut, back down to the primary mirror box, and is imaged by a camera. The angle-of-arrival fluctuations are used to derive the seeing proxy in arcsec. Meteorology is recorded in parallel to the dome seeing proxy, including inside, outside, and mirror temperature, humidity, pressure, wind speed and direction, and telescope azimuth and elevation. These meteorology variables were tested for correlation to the dome seeing proxy. There are 77 nights worth of data, spanning from August 2021 to May 2022. The highly correlated variables were the outdoor/indoor and indoor/mirror temperature difference, the wind speed and humidity. Poorly correlated variables include the wind-to-dome slit angle, the sky/ambient temperature difference and elevation. Thermal convection conditions were found to significantly affect the dome-seeing-proxy compared to thermal inversion conditions.
The Mount Stromlo LGS facility includes two laser systems: a fiber-based sum-frequency laser designed and built by EOS Space Systems in Australia, and a Semiconductor Guidestar Laser designed and built by Aret´e Associates in the USA under contract with the Australian National University. The Beam Transfer Optics (BTO) enable either simultaneous or separate propagation of the two lasers to create a single LGS on the sky. This paper provides an overview of the Mount Stromlo LGS facility design, integration and testing of the two sodium guidestar lasers in the laboratory and on the EOS 1.8m telescope.
This paper presents a preliminary analysis of the first results we have obtained from the adaptive optics systems built for EOS 1.8 m telescope at Mount Stromlo. This presentation focuses on the single-camera stereo-SCIDAR for monitoring the atmospheric seeing. We briefly summarize the system, describe its on-sky performance during commissioning, compare results to numerical simulations and evaluate the remaining challenges going into the future.
Space debris in low Earth orbit (LEO) below 1500 km is becoming an increasing threat to spacecrafts. To manage the threat, we are developing systems to improve the ground-based tracking and imaging of space debris and satellites. We also intend to demonstrate that it is possible to launch a high-power laser that modifies the orbits of the debris. However, atmospheric turbulence makes it necessary to use adaptive optics with such systems. When engaging with objects in LEO, the objects are available only a limited amount of time. During the observation window, the object has to be acquired and performance of all adaptive optics feedback loops optimised. We have implemented a high-level adaptive optics supervision tool to automatise time-consuming tasks related to calibration and performance monitoring. This paper describes in detail the current features of our software.
As space debris in lower Earth orbits are accumulating, techniques to lower the risk of space debris collisions must be developed. Within the context of the Space Environment Research Centre (SERC), the Australian National University (ANU) is developing an adaptive optics system for tracking and pushing space debris. The strategy is to pre-condition a laser launched from a 1.8 m telescope operated by Electro Optics Systems (EOS) on Mount Stromlo, Canberra and direct it at an object to perturb its orbit. Current progress towards implementing this experiment, which will ensure automated operation between the telescope and the adaptive optics system, will be presented.
We present the status of the site-characterisation campaign at Mount Stromlo Observatory. The main goal of the project is to aid the development and operation of new adaptive optics (AO) systems for space debris tracking and pushing as well as satellite imaging. The main method we use for the characterisation is based on the SCIntillation Detection And Ranging (SCIDAR) technique. We have designed a unique version of the SCIDAR instrument: a stereo-SCIDAR system that uses a roof prism to separate beams from a double-star system to obtain two isolated pupil images on a single detector. The instrument is installed on the 1.8 m telescope of Electro-Optic Systems (EOS), sharing facilities with the adaptive optics systems we are currently building. The SCIDAR instrument will be operated intermittently, weather and availability permitting, until sufficient amount of data has been collected to characterise the site. This paper reports the current status of the project: we have recently started the commissioning phase and obtained first measurements with the instrument.
Satellite tracking and imaging is conducted by the ANU Research School of Astronomy and Astrophysics (RSAA) and Electro-Optic Systems at Mount Stromlo as part of the Space Environment Management Cooperative Research Centre to support debris tracking. To optimally design adaptive optics systems for those applications, it is important to know the atmospheric profile, i.e. how the turbulence is distributed as a function altitude. We have designed a new stereo-SCIDAR instrument1 to conduct a site characterisation campaign at Mount Stromlo site. This paper summarises our current progress: specifications, design choices and post-processing techniques. In particular, we compare two different post-processing algorithms for stereo-SCIDAR, using simulated data cubes. One of the codes is implemented by the RSAA, the other by the Centre for Advanced Instrumentation, University of Durham. The comparison shows that the current implementations of both codes produce decent results. However, we can see potential for further improvements.
Satellite tracking and imaging is conducted by the ANU Research School of Astronomy and Astrophysics and Electro-Optic Systems (EOS) at Mount Stromlo Observatory, Canberra, Australia, as part of the Space Environment Management Cooperative Research Centre (SERC) to support the development in space situational awareness. Atmospheric turbulence leads to distortions in the measured data. Adaptive optics (AO) systems counteract those distortions and improve the resolution of the tracking and imaging systems. To assist in the design of the AO systems, we need to gather information on the atmosphere at Mount Stromlo: r0, τ 0, and the turbulence Cn2 profile. With the SCIntillation Detection And Ranging (SCIDAR) Technique the scintillation of two stars is measured and their autocorrelation function is computed, providing a measurement of the turbulence profile. This technique usually uses one detector recording the two images of the stars simultaneously. However, the images overlap leading to an underestimation of the Cn2 values. The introduction of stereo-SCIDAR1 over- comes this issue by separating the two stars and imaging them on two separate image sensors. To reduce costs, we introduce a new stereo-SCIDAR system separating the beams from the two stars, but using only one single detector. This has been shown for a Low Layer SCIDAR (LOLAS) system with wide double stars (200 arcsec). We investigate this technique by detecting the scintillation patterns of double stars with separation from 10 to 25 arcsec, allowing some flexibility in the altitude span and resolution, while retaining a simple optical setup. We selected a low noise sCMOS camera as the imager. We show the current design of this system and investigate its feasibility for further development.
So far, concepts for three dimensional biomedical imaging rely on scanning in at least one dimension. Single-shot
holography1, in contrast, stores three-dimensional information encoded in an electro-magnetic wave scattered back from
a sample in one single hologram. Single-shot holography operates with simultaneous recordings of holograms at
different wavelengths. While the lateral sample information is stored in the interference patterns of individual
holograms, the depth information is obtained from the spectral distribution at each lateral image point, similar to
Fourier-domain optical coherence tomography2. Consequently, the depth resolution of the reconstructed image is
determined by the bandwidth of the light source, so that a broadband light source is needed to obtain high depth
resolution.
Additionally, the holographic material, in which the holograms are stored, restricts the useable bandwidth. A thick
photorefractive crystal can store several holograms of different wavelengths at once. As the crystal works best when
using a source with a discrete spectrum, a light source is needed that has a spectrum with well distinguishable laser
lines.
In a proof-of-principle experiment, we use colliding pulse mode-locked (CPM)3 laser diodes as light sources with a
comb-like spectrum to demonstrate the concept of single-shot holography by storing multiple holograms at the same
time in a photorefractive Rh:BaTiO3 crystal.
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