As demand for high-bandwidth data transmission continues to increase, future satellite constellations can leverage the benefits of free space optical communication, which provides significant advantages compared to traditional radio frequency systems. Despite the development of satellite laser communication terminals (LCTs) in recent years, one major challenge remains; coupling the incoming signal into an optical fiber. In addition, most terminals use intensity modulation to encode data, which is limited in its ability to reach high data rates. So-called coherent modulation schemes offer superior performance but are not widely implemented in satellite LCT’s yet. A system that avoids fiber coupling while using coherent modulation could simplify designs, reduce complexity, and improve performance. This thesis presents the design, implementation, and evaluation of such a coherent free space optical detection system. Differential Phase Shift Keying (DPSK) was chosen as the modulation scheme due to its balance of power efficiency and implementation simplicity, delivering performance comparable to other coherent schemes with a less complex receiver architecture. The system was implemented using bulk optics and tested in a laboratory environment. A Delay Line Interferometer (DLI) was used for DPSK demodulation. The system successfully achieved a data rate of 100 [Mbit/s], demonstrating the feasibility of DPSK-based coherent free space detection. Some performance limitations were identified, with DLI instability emerging as the most notable, which is primarily caused by the long length required for this data rate. This instability resulted in intermittent bit error rate values exceeding the required threshold. These findings show that DPSK demodulation using bulk optics is favored toward higher data rates, and thus shorter delay lines. Recommendations for future work would be to operate at a higher data rate, and implement active stabilization for operational systems.

Future Very High-Throughput Satellites are foreseen to implement optical ground-to-satellite feeder links to achieve multi-terabit-per-second data rates. Optical links however, are highly susceptible to atmospheric losses caused by turbulence, absorption, and scattering, especially at low elevation angles. Despite prior confirmation of the feasibility of cloud-free network availability, high-latitude stations have been notably absent from optical feeder link studies due to the limitation of Geostationary orbits in providing sufficiently high link elevation angles. Tundra orbits present a promising alternative to Geostationary orbit, requiring two satellites to ensure uninterrupted coverage of high-latitude regions like Europe and Canada with link geometries highly suitable for optical communication. This paper addresses optical feeder link implementation aspects in Tundra orbits and selects a suitable orbit to service Canada while considering aspects such as coverage, radiation environment, pointing angles, and delta-v impact. End-to-end simulations, including downlink and uplink amplitude statistics, are presented to assess dynamic turbulence penalties. These simulations focus on angular anisoplanatism and highlight the link geometry impact on adaptive optics efficacy. This analysis anticipates a mean 4.1 and 4.7 dBm link budget advantage for Tundra configurations for two and three satellites respectively. These findings highlight Tundra constellations' potential to enhance satellite communication infrastructure, providing robust, efficient service in regions where Geostationary orbits faces limitations.

Since their first use during the Apollo 15, 16, and 17 missions, laser altimeters have become indispensable for planetary exploration, enabling topographic mapping of rocky bodies throughout the solar system. The latest European contributions in this field are represented by the BepiColombo Laser Altimeter (BELA) and the Ganymede Laser Altimeter (GALA), developed by the DLR Institute of Planetary Research and currently en route to Mercury and the Jovian moons, respectively. However, to date, such instruments have only been deployed on large satellites, failing to meet miniaturised systems' SWaP (Size, Weight, and Power) requirements.

This thesis investigates the adaptation of laser altimeter technology for smaller platforms, focusing on the NLA (New Laser Altimeter) developed for the SER3NE (Selene's Explorer for Roughness, Regolith, Resources, Neutrons, and Elements) mission proposal. The instrument aims to improve the precision of Lunar topographic data to support the characterisation of future landing sites for crewed missions from a 12 U microsatellite. To meet the stringent SWaP constraints, the design will feature a transceiver and a single-photon detection system — an approach never previously applied to topographic altimeters.

This thesis aims to develop an optical design that fits the instrument within a 3 U volume. Given the innovative nature of the design, a trade-off analysis was conducted to evaluate several configurations based on their compactness, cross-coupling between the laser source and detector, footprint size at the target, co-alignment between the transmitter and receiver, and transmission losses. The selected design stood out in providing a footprint size in the range allowed by the requirements, reducing the probability of damage to the detector due to internal reflections from the laser, and guaranteeing a more stable co-alignment between the transmitter and receiver paths. It includes a transmitter with two 45° folding mirrors, a borehole mirror that allows the laser to pass while deflecting the returning signal, and a shared telescope.

A test campaign is then conducted on a dedicated optomechanical design to assess 1) its compliance with some trade-off criteria and 2) its functionality. The expansion performance is demonstrated as predictable and reliable, guaranteeing the desired divergence and footprint at the target. On the other hand, the transmittance is increased above the constraints by varying the angle of incidence of the light on the band-pass filter. For the functional tests, the quality of the wavefront is first evaluated, resulting in an aberration-free transmitter and a slightly worse receiver, but still acceptable for altimetry applications. Finally, the prototype is aligned thoroughly and tested for timing measurements with single-pixel detectors, successfully providing the range to the target.

In the next instrument development phase, throughout the pre-phase A studies in collaboration with ESA (European Space Agency) and relevant companies, the prototype will be enhanced to verify the performance in the other criteria and test its functionality in a relevant environment with a flight campaign.

FSO satellite communication enables data transfer at high bandwidths, low latency, and high security. Due to these benefits, FSO communication services with satellite constellations can hugely improve global connectivity and bandwidth, while maintaining sufficient security. Modeling a global FSO satellite communication service is beneficial for gaining insight into, and performing preliminary analysis on such missions. However, these missions are complex problems with several physical processes occurring at different time scales. Macroscopic processes in the order of minutes to hours consist of relative platform dynamics (eg. aircraft and satellite motion) and atmospheric attenuation. Microscopic processes consist of atmospheric turbulence- and platform disturbances in the order of milliseconds and transporting photons/bits in the order of nanoseconds. To our knowledge, there are currently no end-to-end models that accurately and efficiently simulate a combination of all these processes. To overcome this, a multi-scale method is proposed that simulates and combines the physics of the microscopic and macroscopic processes of a global FSO satellite communication mission. A bi-directional air-to-space link is chosen as a use case. The proposed model simulates a 1.5 hours communication mission in 6 minutes with 8 Gb random access memory (RAM). Platform dynamics and jitter are the most dominant effects. Including microscopic processes results in a performance difference in signal power of 10 dB to 80 dB depending on the strength of the atmospheric channel. Using the multi-scale method, we can efficiently and realistically simulate an FSO communication service end-toend between an aircraft and a satellite constellation.

Laser satellite communications for ground-to-ground and ground-to space links is influenced by atmospheric turbulence. Typically, theoretical models are used to predict link performance and the influence of the atmosphere on variables such as beam wander, spot size and scintillation at the receiver. These variables are used as input for system design. However, the models, which predict the individual variables have not yet been empirically verified for their individual contributions. Therefore, this paper focuses on retrieving the individual variables estimated by theoretical models from measurements representing these variables. These measurements have been retrieved in a 10 km uplink path, ground-to-ground field test. In this test, the receiver plane is imaged. The spot location and size and the longitudinal, radial and on-axis scintillation indices are estimated from the measurements. Also, turbulence strength is measured along the path and are used as inputs for the theoretical models. For weak turbulence conditions the theory and test results fall within the same order of magnitude. For all effects, except on-axis scintillation, the values predicted by theory lie at a slightly higher value than retrieved with the field test for the weak turbulence regime. For strong turbulence conditions the difference in results between theory and data grows, up to order one. To the authors’ knowledge, this is the first time the turbulence variables have been experimentally investigated in so much detail. It is clear from the differences, that both the experimental setup and theory for horizontal ground-to-ground links need attention to close the gap between them, especially for turbulence conditions outside the Rytov approximation range.

The future will see an increase in missions headed for deep space. Advanced payloads will require higher data rates in more efficient spacecraft. Conventional space communication is facilitated through RF technology. Although it is very reliable, doubts arise on its future sustainability because of limited bandwidth, inefficiency and a saturated spectrum. Deep space optical communication (DSOC) can mitigate these issues and may present a sustainable future solution. In this thesis work, a concept is generated for the link and optomechanical design of a Deep space Optical Terminal (DOT), which is meant to be able of high data rate laser communication between the Moon and Earth. Emphasis lies on link analysis and design parameters required to realize the link. Subsystems and budgets are highlighted. The design process is discussed using systems engineering methods and tools.

Global internet traffic is subject to exponential growth. Free Space Optical communication can accommodate for this increase. Current communication systems prove to be capable of transferring Terabits/s of data per link to and from a satellite. This is done by coupling the laser beam into a fiber, which is connected to a computer capable of processing the data in the laser beam. The downside of these systems is that they require position sensors to accurately steer the beam into the fiber. These sensors limit the amount of light reaching the receiver and thereby limit data capacity. Furthermore, these sensors may drift due to thermal loads, causing the system to lose performance. By removing the position sensor and implementing the gradient-based algorithm Extremum Seeking Control, the same performance can be achieved without risk of fiber drift. Furthermore, this approach would reduce system complexity, relax tolerances imposed on these systems and most importantly, increase the average fiber coupling efficiency of satellite links by 40%. This is verified by a simulink model and breadboard experiment.

The resolution of ground-based telescopes is limited by the blurring caused by Earth’s turbulent atmosphere. Adaptive Optics (AO) is a technique used to correct atmospheric distortions, restoring images to diffraction-limited resolution. The main element of an AO system is the Deformable Mirror (DM), which compensates the distortions of the incoming wavefronts. There are several technologies available to actuate DMs. TNO has developed a novel DM equipped with electromagnetic actuators. Some of the design parameters of the DM have not yet been studied and are subject of optimization. A modeling approach is presented for studying the design sensitivities of the TNO DM. To increase optical performance, a study of optimal actuator layouts and mechanical parameters is shown. For the figure of merit in the optimization, a Fourier modal basis is used. Instead of the more commonly used Zernike basis from literature. This approach constitutes a blueprint for the design of electromagnetic DMs. Its use may be extended to other AO applications such as lithography or ophthalmology.