Specialised optical ground station infrastructure will be required for the comparison of optical atomic clock timescales between ground and space. The optical ground station is required for precise pointing, acquisition, and tracking of the spacecraft carrying the clock, it needs have a sufficiently large collecting area to receive the spacecraft’s timing incoming laser signal on phase-sensitive detectors, efficiently couple this laser light into single mode fibre, transmit a coherent laser timing signal of sufficient optical power at an independently steerable point-ahead angle to hit the spacecraft, be able to remotely access or support a locally hosted ground-based timescale, and ideally be located in an optimal site in terms of environmental and operational conditions.

The Astrophotonics group at University of Western Australia (UWA) has established the TeraNet optical ground station network in Australia (www.teranet.space). This network includes the TeraNet-2 (TN-2) optical ground station located at Geoscience Australia’s Yarragadee Geodetic Observatory (YGO). TN-2 is specifically optimised to support high-precision timing between ground and space.

The TN-2 ground station comprises a Planewave Instruments, 70-cm aperture, RC700 telescope, with gold-coated optics that are well-suited for 1550nm operations. The telescope is housed within a 4.6m two-storey Gambato observatory dome, which is connected to an adjacent building that includes a temperature-controlled laser laboratory and local control room. A HartSCI ClearStar LC adaptive optics system is coupled to one of the telescope’s Nasmyth ports to enable efficient single mode fibre coupling. The adaptive optics system includes a separate optical fibre-fed 15-cm transmit telescope with integrated point-ahead capability that includes first-order uplink pointing calibration and correction capability.

The other Nasmyth port supports a state-of-the-art, dual-wavelength, kHz-class pulsed satellite laser ranging system, but it also has the provision for a free-space Coudé path to the adjacent temperature-controlled laser laboratory. The laboratory has an optical table and equipment rack to support future installations of specialised state-of-the-art optical atomic clocks. The laser laboratory includes coaxial cable links to the YGO’s local timescale, comprising a suite of geodetic-grade GNSS equipment and a hydrogen-maser atomic clock, and the site is connected via a multi-path AARNet dark fibre network to the UWA campus, ESA’s New Norcia Deep Space Tracking Facility, and the Australian Square Kilometre Array telescope site, which operates its own UTC(k).

YGO is one of the world’s premier locations for ground-space links. It is a fundamental geodetic observatory that includes the world’s most productive satellite laser ranging facility, NASA’s MOBLAS-5, a 12-m geodetic VLBI antenna, DORIS transmitter, and geodetic-grade GNSS equipment. The site has a favourable climate with very low annual cloud cover, and especially over the six summer months, and it is centred on a nationally legislated no-fly zone. It has surprisingly decent astronomical seeing, typically around 1–3 arcseconds. The site is connected to high-speed redundant AARNet internet, grid power, has security controls, and is staffed by Geoscience Australia personnel.

In 2027, the Astrophotonics group plans to conduct the first coherent laser link demonstration via reflection off the Ajisai geodetic satellite, utilising the group’s velociraptor high-Doppler phase-tracking technology [1, 2] referenced to a commercial-grade portable optical atomic clock. These demonstrations will be used to validate the specific suitability of TN-2 to support future state-of-the-art optical atomic clock fundamental physics space missions, with TN-2 forming the blueprint for the required deployment of similar specialised optical ground station infrastructure around the world.

Satellite quantum networks offer a path towards global-scale quantum communication, owing to the quadratic loss scaling of space–Earth optical links, in contrast to the exponential attenuation of optical fibre. To support this, a network of high-precision optical ground stations (OGSs) is required to sustain the line-of-sight optical link between space and ground segments. To date, most OGSs are situated in remote locations away from population centres to mitigate the effect of anthropogenic light pollution on QBER. However, this approach limits access to the infrastructure and connectivity necessary for practical OGS deployment, creating a fundamental trade-off between low-background operation and urban accessibility.
The Singapore Optical Ground Station (SOGS) was commissioned in 2024 as a quantum-capable facility located on a metropolitan site. We present experimental characterisations of SOGS against link-loss models to validate its feasibility for sustaining a space–Earth quantum link. This includes passive tracking of low-Earth-orbit satellites with tracking precision ranging from tracking precision ranging from 1.04” to 3.64”, approaching Singapore’s atmospheric seeing limit of approximately 2”-3”. Sky background measurements yielded noise levels of 200–1200 cps, varying primarily with lunar phase and angular separation from the Moon, and remaining within operational bounds even under high lunar illumination. SOGS’s tracking precision, background levels, and detector performance compare favourably against a reference link budget shown to yield secure key rates of 19.2 kbit per pass.
In tandem with its quantum networking capabilities, SOGS’s equatorial location provides frequent access to a broad range of orbital inclinations, making it an attractive testbed for optical space situational awareness, including passive satellite monitoring and orbit refinement. To date, the SOGS has successfully optically tracked various space assets including equatorial and MEO CubeSats. Taken together, these capabilities position SOGS as an experimental hub for both quantum networking and the growing space ecosystem in Singapore. This represents a key step towards the deployment of satellite quantum links in the region.