Many proposals are being made for cleaner, more sustainable forms of energy production. Terrestrial solar photovoltaic farms (SPFs) could potentially deliver large quantities of energy to the grid, although these are limited to daytime use. The output from these SPFs could be enhanced, particularly around dawn and dusk, by the use of orbiting solar reflectors (OSRs) in near-polar orbit. These would reflect an image of the solar disk, or solar image (SI), onto the SPFs to augment their energy output. Pointing requirements are therefore to ensure that reflected sunlight is delivered to the terrestrial SPF, avoiding the losses incurred by an offset of the SI and the SPF itself. The SI would typically be of order 10 km for a reflector in a 1000 km orbit. Given the potentially large size of the reflectors, this presents a challenge for the attitude determination and control system (ADCS) to ensure that the maximum quantity of energy can be delivered to a SPF, typically requiring large control moment gyro actuators. In addition, there exist numerous sources of error in the ADCS which can cause further degradation in the quantity of energy delivered to the SPF. These errors can manifest in the resolution of the various sensors, flexible structural modes, manufacturing inaccuracies, and misalignments due to vibration during launch. This paper will investigate the effects of pointing error sources (PES) on the reflector ADCS and so on the quantity of energy delivered to the SPF. With the application of a PD controller with feedforward compensation, and the set of noise characteristics defined in this paper, numerical simulations will show the typical losses in energy delivered to SPFs of 0.015% when the model accounts for PES in onboard sensors, actuator uncertainty and flexible structural modes.

Orbiting solar reflectors (OSRs) are flat, thin and lightweight reflective structures that are proposed to enhance terrestrial solar energy generation by illuminating large terrestrial solar power plants locally around dawn/dusk and during night hours. The incorporation of OSRs into terrestrial energy systems may offset the daylight-only limitation of terrestrial solar energy. However, the quantity of solar energy delivered to the Earth's surface remains low due to short duration of orbital passes and the low density of the reflected solar power due to large slant ranges. To compensate for these, this paper proposes a constellation of multiple reflectors in low-Earth orbit for scalable enhancement of the quantity of energy delivered. Circular near-polar orbits of 1000 km altitude in the terminator region are considered in a Walker-type constellation for a preliminary analysis. Starting from a simplified approach, the equations of Walker constellations describing the distribution of the reflectors are first modified by introducing a phasing parameter to ensure repeating pass-geometry over solar power farms. This approach allows for a single groundtrack optimisation to define the constellation, which was carried out by a genetic algorithm for single and two reflectors per orbit with an objective function defined as the total quantity of energy delivered per day, to existing and hypothetical solar power projects around the Earth. When full-scale constellations are considered with a number of reflectors, the quantity of solar energy delivered is substantial in the broader context of global terrestrial solar energy generation.

Orbiting solar reflectors may be a useful assets to illuminate solar power farms to enhance their utility when direct sunlight is not available. The assessment of their feasibility for a variety of applications requires accurate calculations of how much solar energy can be delivered from a variety of orbits. This paper presents a generic, three-dimensional semi-analytical model that outputs the quantity of solar energy for a given circular orbit and solar power farm position at the beginning of a pass. The model extends previous studies by including new phenomena such as the Earth's oblateness, rotation, shadow on the reflector and orbit around the Sun, in addition to time-dependent geometric and atmospheric losses. These additions provide new analytical insights into the delivery of reflected solar energy delivery and demonstrate the importance of high-fidelity modelling. The strengths of the model are illustrated for a 1000 km altitude Sun-synchronous orbit throughout, as well as a range of other orbits and solar power farms located at different latitudes and longitudes.

Orbiting reflectors offer the possibility of illuminating large terrestrial solar power plants to enhance their output, particularly at dawn and dusk when their output is low but energy spot prices can be high. While the concept of orbiting solar reflectors has been considered in various forms in the past, there is now a timely overlap of rapidly growing global demand for clean energy services, falling launch costs through reusability and the emergence of in-orbit manufacturing technologies to enable the fabrication of large, ultra-lightweight space structures. This paper provides an end-to-end analysis of a possible minimum initial architecture to deliver such global clean energy services. The analysis will cover orbit selection, attitude control requirements, structural analysis and economical viability, followed by a discussion on regulatory issues, future improvements and further applications.

Orbiting solar reflectors (OSRs) are flat, thin and lightweight reflective structures that are proposed to enhance terrestrial solar energy generation by illuminating large terrestrial solar power plants locally around dawn/dusk and in night hours. The incorporation of OSRs into terrestrial energy systems may offset the daylight-only limitation of terrestrial solar energy. However, the quantity of solar energy delivered to the Earth's surface remains low due to short duration of orbital passes and the low density of the reflected solar power due to large slant ranges and the projected image of the solar disk. To compensate for these, this paper proposes a constellation of multiple reflectors in low-Earth orbit to enhance the quantity of energy delivered and extend pass durations. Circular near-polar orbits of 1000 km altitude in the terminator region are considered in a Walker-type constellation as a preliminary analysis to avoid eclipses and to include Sun-synchronous orbits. Starting from a simplified approach, equations of Walker constellations describing the distribution of the constellation reflectors is modified to ensure scalable expansion of the constellation by a phasing parameter between the reflectors. Thanks to this approach, a single groundtrack optimisation is sufficient to describe the constellation. This optimisation was carried out for single and two reflectors per orbit, with an objective function defined as the total quantity of energy delivered per day to existing and hypothetical solar power projects around the Earth. When full-scale constellations are considered with 5, 10 and 20 reflectors, the quantity of solar energy delivered linearly scales with the number of reflectors and considerable in the broader context of global solar energy.

Many proposals are being made for cleaner, more sustainable forms of energy production. Terrestrial solar photovoltaic farms (SPFs) could potentially deliver large quantities of energy to the grid, although these are limited to daytime use. The output from these SPFs could be enhanced, particularly around dawn and dusk, by the use of orbiting solar reflectors (OSRs) in near-polar orbit. These would reflect an image of the solar disk, or solar image (SI), onto the SPFs to augment their energy output. Pointing requirements are therefore to ensure that reflected sunlight is delivered to the terrestrial SPF, avoiding the losses incurred by an offset of the SI and the SPF itself. The SI would typically be of order 10 km for a reflector in a 1000 km orbit. Given the potentially large size of the reflectors, this presents a challenge for the attitude determination and control system (ADCS) to ensure that the maximum quantity of energy can be delivered to a SPF, typically requiring large control moment gyro actuators. In addition, there exist numerous sources of error in the ADCS which can cause further degradation in the quantity of energy delivered to the SPF. These errors can manifest in the resolution of the various sensors, flexible structural modes, manufacturing inaccuracies, and misalignments due to vibration during launch. This paper will investigate the effects of pointing error sources on the reflector ADCS and so on the quantity of energy delivered to the SPF. With the application of a PD controller with feedforward compensation, and the set of noise characteristics defined in this paper, numerical simulations will show the typical losses in energy delivered to SPFs of 37.50% when the model accounts for pointing error sources in onboard sensors, actuator uncertainty and flexible structural modes. Improvements in sensor noise characteristics, as well as application of a more robust controller, could improve upon this result.

Constellations of orbiting solar reflectors on Sun-synchronous repeat ground track orbits can in principle illuminate large terrestrial solar power plants after sunset or before sunrise. This will enhance the number of hours per day during which such solar power plants can deliver clean energy to the grid. In order to develop and deploy such large-scale in-orbit infrastructure, a number of technology demonstrations will be required to de-risk the technology and build confidence for investment. This paper considers potential technology demonstration activities for orbiting solar reflectors, from laboratory-scale testing to high altitude balloon flight and sub-scale in-orbit demonstration. The key technological requirements for orbiting solar reflectors are identified and the utility of each demonstration step evaluated. An integrated technology development, technology demonstration and investment roadmap is then presented.

Constellations of orbiting solar reflectors on Sun-synchronous repeat ground track orbits can in principle illuminate large terrestrial solar power plants after sunset or before sunrise. This will enhance the number of hours per day during which such solar power plants can deliver clean energy to the grid. In order to develop and deploy such large-scale in-orbit infrastructure, a number of technology demonstrations will be required to de-risk the technology and build confidence for investment. This paper considers potential technology demonstration activities for orbiting solar reflectors, from laboratory-scale testing to high altitude balloon flight and sub-scale in-orbit demonstration. The key technological requirements for orbiting solar reflectors are identified and the utility of each demonstration step evaluated. An integrated technology development, technology demonstration and investment roadmap is then presented.

The delivery of global clean energy services represents a key challenge for the 21st century. In order to deliver such services, it is clear that large-scale solar power farms will continue to grow both in number and size. In principle, ultralight membrane orbiting solar reflectors can illuminate large-scale solar power farms during the critical dawn/dusk hours of the day, enhancing the utility of terrestrial solar power. The key advantage is that only a relatively modest mass needs to be delivered to Earth orbit. This paper discusses the technical challenges associated with the development, deployment and operation of such a space-based energy service. Business development models are discussed along with regulatory issues and finally an integrated technology demonstration roadmap is presented.

Orbiting Solar Reflectors (OSRs) can be used to reflect sunlight locally to terrestrial solar power plants to enhance solar energy generation. Displaced polar orbits can, in principle, change the geometry of passes of OSR over terrestrial solar power plants. Such non-Keplerian orbits can be obtained by orienting the reflector at a fixed pitch angle with respect to the Sun-line, such that the solar radiation pressure (SRP) induced force would shift the orbit plane in the anti-Sun line. This, in principle, would allow extending night-time or high-latitude solar energy delivery without eclipses. This paper investigates a range of displaced highly non-Keplerian orbits for OSRs and assesses their operational use. Displaced polar orbits are generated in the two-body problem using a rotating reference frame considering the Earth's oblateness up to J₂ and the SRP force. Their stability is reviewed and an optimal control scheme is presented with reflector area control. As a novel application, a compound reflector system is proposed, which consists of a large Sun-facing parabolic collector in a polar orbit displaced in the anti-Sun direction and a smaller free-flying flat director placed near the focus of the parabolic collector, displaced by the reflected SRP in the Sun direction. The conditions for the synchronized motion and the sizing of the reflectors are investigated. The quantity of solar energy delivered to the Earth is calculated for both the compound and single reflector systems and it is shown that the displaced polar orbits could enhance solar energy delivery significantly.