Small body surfaces are covered by granular material of varying particle sizes and depths. This material is observed to be easily mobilised from the surface through natural processes or spacecraft interaction. The material can escape or re-impact to the surface as a result of this process. The latter may be considered as a low-speed cratering activity under microgravity. In this paper, a set of simulations of normal impacts at 5–10 cm/s under 9.81 × 10⁻⁵m/s² is presented with gravel-type realistic material properties. The simulated craters are investigated for their qualitative impact outcomes, as well as quantitatively for the coefficient of restitution and crater and ejecta scaling properties. The results are compared with the results of impacts in glass beads type materials from authors’ previous work under the same conditions and wider literature experimental and observational literature. It was shown that most impacts result in a rebound with non-negligible coefficient of restitution values. The crater sizes are smaller compared to those in glass beads material and follows the crater scaling relationships across different impact energies with a μ coefficient of 0.55. Ejection is shown to continue beyond the final size with a significant quantity of material mobilised at speed below escape speed under the selected gravity level. The depth-to-diameter ratio of the craters is within the range of small craters of asteroid Bennu, with qualitative impact outcomes displaying similarities with those found in this paper. These results suggest a possible low-speed impact and secondary cratering activity in small bodies as a result of natural and artificial particle ejection events, such as in the case of Bennu and Didymos.

Space sails are a continuum of near-planar technologies related to solar sails. There exist various synergies among space sails, with scope to be further leveraged towards practical interplanetary and interstellar missions. Accordingly, the objective of this study is to answer two questions. Firstly, how big is the technological gap between present state-of-the-art space sailing and future proposed interplanetary and interstellar missions? Secondly, what are the major risk areas, and how can eventual bottlenecks be overcome? These questions are addressed through a focus on three planned missions with different Technology Readiness Levels, types of stakeholders, and destinations: Solar Cruiser, Project Svarog, and Breakthrough Starshot. Gaps between these missions and currently achievable technologies on subsystem- and system-levels are assessed using the Advancement Degree of Difficulty (AD2[jls-end-space/]) scale, and potential ways forward are proposed. A database of parameters achievable with present technologies is obtained from prior work by the authors. Key risk areas for each mission are mapped out, with attitude control, sail material, and subsystem integration being identified as major ones. It is highlighted that testing of high-risk components in intended environments is essential for lowering the AD2 levels. Moreover, cross-sectoral collaboration and cross-pollination between different types of space sails as well as other technologies is highlighted as a key for finding alternatives to high-risk technologies.

Orbiting solar reflectors (OSR) are large, thin, flat and ultralightweight structures proposed to extend the operational hours of solar power farms (SPF) beyond the daylight hours by locally illuminating them at night from orbit. They operate with the principle of intercepting incoming sunlight and reflecting an image of the solar disk onto a ground target by tracking. It has been previously shown that a constellation of modest number of OSR in circular, Sun-synchronous low-Earth orbits can increase the efficiency of terrestrial SPF considerably [1]. The design of such constellations typically relies on circular orbits due to the reduced complexity of orbit selection and optimising the constellations for a given objective, where analytical expressions are available for simple constellation patterns. Introducing nonzero eccentricity to orbit shape immediately multiplies the complexity of the optimisation problem as the number of available orbits are in principle infinite, but their employment in the design would enhance the flexibility in mission design and may offer an improved performance. This paper therefore investigates the design of optimal OSR constellations with elliptic Sun-synchronous orbits with an objective to maximise the daily quantity of energy delivered. An analytical approach is used to simplify the design process by placing reflectors in different orbit planes that allow reflectors to follow the same pass geometry over a given target, reducing the constellation optimisation to effectively a single groundtrack optimisation, carried out by a genetic algorithm for full orbital element space except semi-major axis. The results demonstrate that introducing eccentricity at three different semi-major axis values increase the daily quantity of energy delivered by up to 20%, offering flexibility in constellation design with reduced complexity that can be applied applications beyond terrestrial space-based solar power.

The dual challenges of escalating operational costs linked to fossil fuel consumption and the urgent need to mitigate carbon emissions necessitate innovative strategies for energy sustainability and resilience. Space-based solar power technologies, particularly orbiting solar reflectors (OSRs), have emerged as an advanced solution to extend solar energy availability by reflecting sunlight from space to terrestrial solar power farms (SPFs) beyond daylight hours. This paper presents an approach to reduce power grid fossil fuel costs and carbon emissions by optimally integrating OSRs with a terrestrial SPF. The methodology employs a modified IEEE test system and optimal power flow analysis within a MATLAB framework to determine the optimal placement and sizing of the SPF for minimising active power losses, fossil fuel costs and carbon emissions. The research evaluates multiple operational scenarios, ranging from conventional generation to the combined operation of the SPF and OSRs. The results confirm that OSR integration substantially enhances SPF energy output during dawn and dusk hours, leading to lower fossil fuel costs, decreased carbon emissions, and improved voltage stability across the power grid. These findings underscore the potential for substantial economic and environmental benefits in future energy systems by seamlessly integrating OSRs technology with terrestrial SPFs.

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.

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.

The transition to clean energy resources such as solar energy is critical for the battle against climate change and to achieve net zero emission goals. However, one of the challenges solar energy faces is its dependence on daylight hours only for energy production. This challenge restricts the availability of solar energy after daylight hours which leads to reliance on fossil fuel generators during peak demand periods, thus, increasing CO2 emissions. To overcome this challenge, orbiting solar reflectors (OSRs) were proposed as a future technology which can reflect sunlight to terrestrial solar power farms (SPF) from space during dawn and dusk. This paper aims to explore the integration of OSRs into SPFs to extend the availability of energy after hours of sunlight and reduce carbon emissions by reducing dependency on fossil fuel generators. Furthermore, the paper discusses how OSRs can contribute to the stability of the voltage of the power grid. The results show that the OSR could significantly boost the energy output of a SPF during these periods, thereby extending the availability of solar energy and decreasing the reliance on fossil fuel generators. This technology has the potential to reduce carbon emissions, which contributes to global efforts to reduce climate change. Furthermore, the findings illustrate how OSRs can help maintain voltage stability in the power grid by providing more energy during the peak demand period.

Space sails are a continuum of lightweight, thin, large-area, deployable technologies which are pushing forward new frontiers in space mobility and exploration. They encompass solar sails, laser-driven sails, drag sails, magnetic sails, electric sails, deployable membrane reflectors, deployable membrane antennas, and solar power sails. Some have been flight tested with operational heritage, while some are concepts planned to reach maturity in the coming decades. The number of flown and planned missions has increased rapidly in the past fifteen years. In this context, it is time to recognise the advantages of space sails for supporting the achievement of a wide range of major space exploration goals. This paper evaluates, for the first time, synergies between the broad spectrum of space sail technologies, and major space exploration ambitions around the world. The study begins by looking to the past, performing a global, historical review of space sails and related enabling technologies. The current state of the art is mapped against this technological heritage. Looking to the future, a review of major space exploration goals in the next decades is conducted, highlighting domains where space sails may offer transformational opportunities. It is hoped that this paper will further the ongoing transition of space sails from a promising flight-proven technology into a go-to component of space mission programme planning.

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.

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.

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.

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.

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.

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.

DESTINY⁺ is an upcoming JAXA Epsilon medium-class mission to fly by the Geminids meteor shower parent body (3200) Phaethon. It will be the world's first spacecraft to escape from a near-geostationary transfer orbit into deep space using a low-thrust propulsion system. In doing so, DESTINY⁺ will demonstrate a number of technologies that include a highly efficient ion engine system, lightweight solar array panels, and advanced asteroid flyby observation instruments. These demonstrations will pave the way for JAXA's envisioned low-cost, high-frequency space exploration plans. Following the Phaethon flyby observation, DESTINY⁺ will visit additional asteroids as its extended mission. The mission design is divided into three phases: a spiral-shaped apogee-raising phase, a multi-lunar-flyby phase to escape Earth, and an interplanetary and asteroids flyby phase. The main challenges include the optimization of the many-revolution low-thrust spiral phase under operational constraints; the design of a multi-lunar-flyby sequence in a multi-body environment; and the design of multiple asteroid flybys connected via Earth gravity assists. This paper shows a novel, practical approach to tackle these complex problems, and presents feasible solutions found within the mass budget and mission constraints. Among them, the baseline solution is shown and discussed in depth; DESTINY⁺ will spend two years raising its apogee with ion engines, followed by four lunar gravity assists, and a flyby of asteroids (3200) Phaethon and (155140) 2005 UD. Finally, the flight operations plan for the spiral phase and the asteroid flyby phase are presented in detail.

Ballistic landers enable orbiting asteroid missions to perform surface science at limited additional cost and risk. Due to asteroids’ weak gravity and irregular terrain, lander deployment trajectories will consist of several chaotic bounces. Although impacts on regolith-covered asteroids are numerically expensive to model, impacts on rocky asteroids can be modeled with simpler, impulsive contact models. One such model is that by Stronge, which was successfully used in large-scale Monte Carlo studies of asteroid lander deployment. This model parameterizes impacts with (fixed) material restitution and friction coefficients, but has not been validated for the low-velocity regime of an assembled, nonspherical body. This paper uses an air-bearing setup to perform 2D experiments of a rectangular floating assembly impacting a concrete block with V⩽25 cm/s. The impact velocity, assembly attitude, and block attitude are varied across 2,400 experimental runs of both normal and tangential impacts. Optical tracking is used to extract the pre- and post-impact velocities of the assembly. In a majority of cases, Stronge's model can be fit to the experiments to extract the corresponding restitution and friction coefficients. We find that the coefficients are not fixed with respect to the impact velocity and attitude, but that their variation is seemingly random. In some tangential impact cases, the model even fails to reproduce the observed behavior althogether. This suggests that there may not be a simple way to reconcile Stronge's fixed-material-coefficient model with reality, although it may retain practical use if the coefficients are randomly varied in each impact of a simulation.

The OSIRIS-REx mission collected a sample from the surface of the asteroid (101955) Bennu in 2020 October. Here, we study the impact of the OSIRIS-REx Touch-and-Go Sampling Acquisition Mechanism (TAGSAM) interacting with the surface of an asteroid in the framework of granular physics. Traditional approaches to estimating the penetration depth of a projectile into a granular medium include force laws and scaling relationships formulated from laboratory experiments in terrestrial-gravity conditions. However, it is unclear that these formulations extend to the OSIRIS-REx scenario of a 1300-kg spacecraft interacting with regolith in a microgravity environment. We studied the TAGSAM interaction with Bennu through numerical simulations using two collisional codes, pkdgrav and gdc-i. We validated their accuracy by reproducing the results of laboratory impact experiments in terrestrial gravity. We then performed TAGSAM penetration simulations varying the following geotechnical properties of the regolith: packing fraction (P), bulk density, inter-particle cohesion (σc), and angle of friction (φ). We find that the outcome of a spacecraft-regolith impact has a non-linear dependence on packing fraction. Closely packed regolith (P ? 0.6) can effectively resist the penetration of TAGSAM if φ ? 28° and/or σc ? 50 Pa. For loosely packed regolith (P ? 0.5), the penetration depth is governed by a drag force that scales with impact velocity to the 4/3 power, consistent with energy conservation. We discuss the importance of low-speed impact studies for predicting and interpreting spacecraft-surface interactions. We show that these low-energy events also provide a framework for interpreting the burial depths of large boulders in asteroidal regolith.