Tracking, Characterisation and Identification of Space Objects

Project lead: EOS Space Systems

Researchers: Mark Blundell, Craig Smith, Daniel Kucharski, James Bennett

Participants: EOS Space Systems, SERC

R1.1 has met its stated objectives of designing and developing passive and active track sensors for objects in GEO. This includes technologies for telescopes, beam directors, detectors, lasers, timing systems, optical systems and command & control software.

The SERC GEO tracker telescope at Mt Stromlo is now in routine operation in support of the RP1 and RP3 programs. The SERC GEO tracker telescope is collecting space object track data in support of  CATW and on-sky experiments. A high-speed photometry system (Lumini) has been integrated into the telescopes and control systems across the EOSSS Space Situational Awareness (SSA) network to enable spin characterisation of space objects of interest. A photon counting detector has also been developed and will be rolled out across the network. This detector will replace the Lumini detector system due to its higher sensitivity and superior signal to noise ratio.

The specifications and capabilities of SERC GEO tracker telescope and detectors are provided below:

Telescope specifications:

• PlaneWave Instruments Corrected Dall-Kirkham (CDK) 700
• 0.7m primary mirror
• Dual Nasmyth ports
• Steerable tertiary mirror for port selection
• Independent focusers and derotators for each Nasmyth port
• 15 degree/s maximum velocity (note: practically limited in azimuth by dome maximum slew rate, which is 4 degrees/s)

Camera specifications (primary Nasmyth port):

• Finger Lakes ProLine 4240
• Mid-band, back-illuminated scientific CCD
• 2048 x 2048 pixels, giving 0.61 arcseconds per pixel (1/2 degree FOV, without focal reducer) or 0.88 arcseconds per pixel (1/3 degree Field of View, with focal reducer)
• Thermoelectric cooling plus plumbed liquid cooling with heat exchanger
• Mechanical shutter
• Remotely controllable filter wheel
• EOSSS precision timing system (referenced to GPS time)

Lumini High Rate Photodetector:

• Optical sensor Hamamatsu PMT H11901
• Spectral response 230-920 nm
• Cathode peak sensitivity at 630 nm; luminous sensitivity 500 µA/lm
• Sampling rate 50-100 kHz
• GPS time server
• Mounted with a 5x focal reducer
• Linux operating system

Photon Counting Detector:

• Optical sensor Hamamatsu Micro-PMT H12406
• Spectral response 300-850 nm
• Dark count rate 45 counts-per-second
• Pulse-pair resolution 20 ns
• GPS time server
• Linux operating system

EOSSS control system:

• Fully automatic, unattended operations with automatic protection from weather, sun, power loss, etc
• Remotely controllable via the Internet
• Able to integrate with other telescopes and sites in the EOSSS Space Surveillance Network
• Tracking of satellites and debris (with integration with SERC SOC), sidereal Right Ascension/Declination (RA/DEC), or deep space (RA/DEC track), plus weather balloons
• Automatic mount pointing error correction via astrometry software

Project lead: EOS Space Systems

Researchers: Mark Blundell, Craig Smith, Daniel Kucharski, James Bennett

Participants: EOS Space Systems, SERC

The SERC SOC is fully operational. Tracks of over 1,000 space objects of relevance to SERC are routinely being collected by the SERC and EOSSS sensors and stored in the SERC SOC.

The system is routinely running TLE orbit determinations (OD) and using the results to characterise an initial state of regular ODs. The results are also being used as an input to the post processing of optical observations to maintain consistency with the observations. 

Multiple upgrades to the SOC database architecture and hardware have been implemented to improve speed and ease of use. Some of the improvements include:

• Addition of a dashboard server. The dashboard server permits the user to see the number of observations or tracks received. The dashboard server also permits the user to determine how effectively the observations are being correlated and corrected. 
• Automation of the mount model correction allowing for continued tracking of the telescope mount stability. The correction is based on astrometric observations. 
• SOC and server upgrades. These upgrades allow a greater number of post processing and orbit determination nodes. The upgrades have improved throughput and robustness of the data in the SOC. 
• Improvements to the SOC user interface to provide a more seamless micro-services architecture. This update has allowed browsers such as Chrome to use the interface. The upgrade has also allowed for smarter behaviour of the user interface (UI) to detect when some applications are failing. 
• Framework upgrades to speed up the SOC database. This has involved the creation of a connection pool that is managed internally allowing for a database transactions to be executed in milliseconds rather than seconds. This has significantly sped up the SOC and its associated servers. In addition, the test suite now runs in half the time it had previously allowing for a faster release cycle.

Project lead: ANU

Researchers: Francis Bennet, Michael Copeland, 

Visa Korkiakoski

Participants: Australian National University (ANU)

This output draws on SERC adaptive optics and sensor developments to obtain high resolution (diffraction limited images) of satellites and space debris. Having information about geometry, stability and surface condition allows much better estimation of orbit parameters in RP2 and RP3.

Scintillation Detection and Ranging (SCIDAR) 

To maximise the performance of the adaptive optics imaging (AOI) system, a SCIDAR has been designed and built. The generalised SCIDAR is used to characterise the atmospheric turbulence above Mount Stromlo. This information is then used to optimise the various AO systems developed by SERC researchers. To overcome the design limitation of this first generation SCIDAR, the system is being redesigned using optical ray-tracing software to decrease off-axis aberrations; increase the sensitivity of the system and increase the available field of view (FOV) from 5 arc seconds to 20 arc seconds. 

Adaptive Optics Imaging (AOI)

The AOI system is designed to capture high-resolution diffraction-limited images of satellites and space debris. High-resolution images give a smaller space object centroid which allows for a more precise orbit determination of the object. Two imaging modes are available via a flipper mirror. The flipper changes the effective FOV of the system from 75 arc seconds (acquisition mode) to 24-30 arc seconds (high resolution imaging mode). To optimise the performance of the AOI system, the Coudé path of the 1.8 m telescope has been realigned and AOI system aligned to the Coudé path. On-sky imaging using natural guide stars is underway and closed loop correction has been demonstrated.

Specifications of the AOI system and detectors are provided below:

AOI System:

• Design considerations: designed for 2 arc second seeing, altitude 600 km and above, compatible with natural guide star (NGS) and laser guide star (LGS) modes, 15 arc second FOV 
• ALPAO Deformable Mirror (DM277) 277 actuator deformable mirror
• NUVU Hnu 512 electron-multiplied CCD (EMCCD) imaging camera
• OCAM2k EMCCD camera
• Microlens array wave front sensor (WFS) (16x16 array, 300um pitch, 8mm focal length, 1.55 arc second/pix plate scale, total WFS field of view with 12x12 pixels per subaperture 18.6 arc second)
• 589 nm calibration laser source

Beam expander:

• f/5.3 parabolic primary with 2 custom collimating lenses
• Elliptical secondary 50 x 35 mm

Filters:

• 589+-10nm bandpass filter for LGS WFS
• 594+-12nm notch filter for broadband calibration source
• Neutral Density filters for the calibration and alignment laser

AO Supervisory Server:

The AO supervisory server has been tested and operates within specifications. All critical performance metrics such as calibrations, telemetry collection and system analysis are confirmed to be functioning within specifications.

Project lead: Australian National University

Researchers: Doris Grosse, Marcus Lingham, Celine d’Orgeville, Matthew Bold, Yue Gao, Mark Blundell, Andrew Gray

Participants: Australian National University, EOS Space Systems, Lockheed Martin

This research program has developed world leading AO capabilities that allow high intensity laser beams to be propagated through the atmosphere and is an enabling technology to support the remote manoeuvre experiment. The Adaptive Optics Tracking and Pushing system (AOTP) components have been fabricated and testing and integration are underway.

Laser Launch Telescope (LLT)

The LLT has been designed, constructed, aligned and has been installed on the 1.8 m telescope at Mount Stromlo. The LLT is piggy-back mounted to the main telescope and its function is to project, or launch, the GSL beam into space. Light from the artificial star created by the GSL is collected by the 1.8 m telescope.

Specifications of the LLT are provided below:

• Primary mirror: 360 mm diameter with clear aperture of 340 mm, 500 mm focal length, laser damage threshold 1 W per square centimetre
• Secondary mirror: 23 mm diameter with clear aperture of 22 mm, 25 mm focal length, laser damage threshold 500 W per square centimetre

Guide Star Laser (GSL)

The GSL design is based on the sum frequency generation of 1342 nm and 1050 nm wavelength lasers. The GSL output is frequency locked to the sodium D2 line (589.6 nm) using a sodium cell. The laser optics have been mounted on three carbon fibre breadboards and placed into their final configuration in the laser thermal enclosure mounted on the telescope. The control electronics for the GSL have been manufactured and are undergoing testing. Installation and commissioning on the 1.8 m telescope took place in the fourth quarter of 2019.

Deformable Mirror (DM)

The AOTP system uses a 177 actuator Xinetics deformable mirror with integrated tip-tilt stage to correct for atmospheric distortion and allow propagation of the high power laser during the photon pressure manoeuvre experiments. 

Prior to application of the high power coating to the DM surface, test coatings are being done on sample substrates to ascertain whether the coating has the necessary reflectivity (R) at the requisite wavelengths, and to measure the laser damage threshold. SERC researchers have developed cold coating techniques which will allow the DM surface to be coated whilst still attached to the actuators. The final coating is a pure dielectric coating and contains more than 29 layers. 

The spectral properties of the coating are:

• Average R = 99.98% @ 1045 – 1100 nm
• R = 99.46% @ 589 nm
• Average R = 75.20% @ 450 – 570 nm
• Average R = 80.27% @ 610 – 750 nm
• Average R = 81.33% @ 750 – 850 nm
• Total thickness – 3.99 µm

Beam Expanders (BX)

Integral to the AOTP system is an off-axis beam expander. The BX consists of a primary and secondary mirror and its function is to increase the diameter of the high power laser output beam from less than 10 mm to more than 250 mm. 

Project lead: Australian National University

Researchers: Francis Bennet, Celine d’Orgeville, Michael Copeland, Liam Smith

Participants: Australian National University, Lockheed Martin

This program set out to develop an AO system that can reduce the point spread function of stars and targets (diffraction limit) so that higher accuracy astrometric solutions can be made to

determine the absolute position on the sky of the GEO target. This required development of high performance AO systems, sensors, calibration systems and algorithm development.

R1.5 is closely linked to developments undertaken in R1.3 as they use the same AO hardware. R1.5 is using the GEO Global Astronomic Interferometer for Astrophysics (GAIA) catalogue, a 3D catalogue of stars, as a natural guide star reference.

The method, concept, and expected performance of the GEO GAIA method has been developed. End-to-end modelling and simulation of the AO system, uplink and target engagement performance has been completed.

Lockheed Martin (LM) has provided additional data tables to other Participants. AO models have been upgraded to account for thermal blooming.

Project lead: EOS Space Systems

Researchers: Yue Gao, Yanjie Wang, Amy Chan, Matthew Bold, James Mason, Greg Madsen

Participants: EOS Space Systems, Lockheed Martin

This research program has developed high power laser technologies and techniques to combine and phase multiple lasers for increased power, beam shaping and beam control for use in the on-sky experiments.

SERC High Power Laser (HPL)

The SERC HPL is comprised of four IPG Photonics YAM-2000- SM fibre 2 kW amplifier modules, corresponding seed amplifiers and associated beam combination optical components. The individual 2 kW beams are combined spectrally using hybrid sandwiched volume Bragg gratings (VBG). SERC researchers have set a world record 2-beam combination efficiency of 98.7%, and 3-beam of 97.5%, with a seed oscillator spectral linewidth of 0.05 nm without the need for forced air or helium cooling of the VBGs. A seed oscillator linewidth of 0.1 nm would only provide a spectral combination efficiency of 85%. This increased efficiency translates into a 10% increase in the final laser output power.

The HPL optical table layout and incorporation of the LM 10 kW fibre laser has been completed.

Lockheed Martin 10 kW laser

SERC Participant Lockheed Martin has provided their IPG YLS- 10000 Ytterbium fibre laser system to SERC as a part of their in-kind contribution. This laser will provide 10 kW of fibre-fed laser power for spatial combination with SERC’s HPL.

The chiller for the 10kW laser has been installed on the new platform and electrical upgrades completed at the 1.8 m telescope cleanroom. The laser itself was relocated to the telescope laser lab from the AITC along with some other equipment (guide star laser) in October 2019.

The output collimator for the LMC 10 kW fibre laser has been designed and built. VBGs and sandwich windows are used to combine the LMC 10 kW output beam with the SERC HPL output beam. The additional windows have been procured and coated with anti-reflective coating. The spectral linewidth of the LM laser will necessitate spatial combining with the SERC HPL.

Laser – Telescope Control System Integration

Work on integrating the operating software for the high power lasers into the telescope control system has been completed.

Deformable Mirror (DM)

The AOTP system uses a 177 actuator Xinetics deformable mirror with integrated tip-tilt stage to correct for atmospheric distortion and allow propagation of the high power laser during the photon pressure manoeuvre experiments. 

Prior to application of the high power coating to the DM surface, test coatings are being done on sample substrates to ascertain whether the coating has the necessary reflectivity (R) at the requisite wavelengths, and to measure the laser damage threshold. SERC researchers have developed cold coating techniques which will allow the DM surface to be coated whilst still attached to the actuators. The final coating is a pure dielectric coating and contains more than 29 layers.

The spectral properties of the coating are:

• Average R = 99.98% @ 1045 – 1100 nm
• R = 99.46% @ 589 nm
• Average R = 75.20% @ 450 – 570 nm
• Average R = 80.27% @ 610 – 750 nm
• Average R = 81.33% @ 750 – 850 nm
• Total thickness – 3.99 µm

Following a range of coating problems and COVID related delays, a final coating to the DM surface is scheduled to take place in 2021.

Beam Expanders (BX)

Integral to the AOTP system is an off-axis beam expander. The BX consists of a primary and secondary mirror and its function is to increase the diameter of the high power laser output beam from less than 10 mm to more than 250 mm.