Solar Radiation Pressure–Based Orbit Control with Application to Small-Body Landing

Orbit-attitude coupled motion around small bodies: Sun-synchronous orbits with Sun-tracking attitude motion

Navigation for low-cost missions to small solar-system bodies

Asteroids and other Small Solar System Bodies (SSSBs) are of high general and scientific interest in many aspects. The origin, formation, and evolution of our Solar System (and other planetary systems) can be better understood by analysing the constitution and physical properties of small bodies in the Solar System. Currently, two space missions (Hayabusa2, OSIRIS-REx) have recently arrived at their respective targets and will bring a sample of the asteroids back to Earth. Other small body missions have also been selected by, or proposed to, space agencies. The threat posed to our planet by near-Earth objects (NEOs) is also considered at the international level, and this has prompted dedicated research on possible mitigation techniques. The DART mission, for example, will test the kinetic impact technique. Even ideas for industrial exploitation have risen during the last years. Lastly, the origin of water and life on Earth appears to be connected to asteroids. Hence, future space mission projects will undoubtedly target some asteroids or other SSSBs. In all these cases and research topics, specific knowledge of the structure and mechanical behaviour of the surface as well as the bulk of those celestial bodies is crucial. In contrast to large telluric planets and dwarf planets, a large proportion of such small bodies is believed to consist of gravitational aggregates ('rubble piles') with no -- or low -- internal cohesion, with varying macro-porosity and surface properties (from smooth regolith covered terrain, to very rough collection of boulders), and varying topography (craters, depressions, ridges) [...].

Investigation of small planetary bodies is now attracted and some missions on asteroids and comets have been realized. Such bodies are full of geographical features that next demand would be direct surface investigation by a rover. In order to navigate the rover to the specific points, the localization of the rover is required. However, conventional localization method is not adequate on small bodies whose size is less than 1[km]. One of the conventional methods, localization by camera images obtained on the rover needs a map made by a mother spacecraft. The resolution of the map is not enough for the rover's local view. Another method, localization by observing the movements of stars and the sun has little accuracy. Global positioning system (GPS) is not practical for small planetary bodies because it needs several orbiters. In this paper, we propose a reasonable method which localizes the rover on a small body with reasonable accuracy, with reasonable time and with reasonable resource. This method measures two way range between a rover and a mother spacecraft repeatedly. Even this method uses only one orbiter, the localization accuracy is estimated about 1[m] assuming ITOKAWA-size asteroidwhoseradiusisatmost600[m].

The equation of motion of a small isolated body that moves in translational motion through a fluid which is itself in unsteady and nonuniform motion is established on the assumption that actual forces acting on the body can be split up in gravity; a drag component, which accounts for viscosity and vorticity effects; and an inertial force with the same formal expression as the force that would act on the body if the flow were irrotational (this force is obtained for an unrestricted irrotational flow in the appendix). By assuming that flow acceleration is small compared with that due to gravity and that ϵ = wƒω/g ≪ 1, which defines what here is called “very small body” (wƒ being still water terminal fall velocity, ω angular frequency, and g acceleration due to gravity), some approximate equations are obtained using a perturbation scheme. Subsequently, a simple expression is derived for the leading order approximation of the velocity of very small bodies in water waves. This solution shows that, at least under certain conditions, the hypothesis of some delay time (Kennedy and Locher, 1972) is sound, although this time is not the same, in general, for the vertical velocity component as for the horizontal one. From a practical point of view, owing to the assumptions involved in this derivation, the applicability of the solution must be restricted to suspended sediment particles in low concentrations and to reasonably well‐behaved wave conditions, including superposition of linear waves (particularly standing waves and irregular wave fields), slightly nonlinear waves, and weak currents superimposed on waves. The direct application of the results of this investigation to flows with a high degree of turbulence intensity must be precluded because of the existence of large flow accelerations.

Phase curves of nine Trojan asteroids over a wide range of phase angles

Seismology on small planetary bodies by orbital laser Doppler vibrometry

Compared with planets and their moons, small bodies retain the characteristics of their early formation. Therefore small bodies, especially Near Earth Asteroids (NEA), have become one of the most valuable targets in space exploration. This paper presents a review of the current status of small body exploration, including the science objectives, main optical imaging instruments and the main scientific results obtained from the relevant exploration missions in the past two decades. Then, it outlines and discusses future missions to small bodies by different space agencies, including those already planned and under development. Finally, it discusses the trend of optical imaging instrument development for exploring small bodies.

In recent years, missions for exploring small bodies such as asteroids, comets, and meteorites have received a significant attention all over the world. The rovers which hang around the surface of such small planetary bodies can provide in-situ surface observations on the various points of the target body. So the research and development of exploration rovers for small planetary bodies are very important.Under the micro gravity environment such as on the surface of small planetary bodies, traditional wheeled rovers are not expected to move effectively due to the low friction and the inevitable detachment from the surface. This paper discusses the friction-based mobility around the surface of small bodies and proposes a new mobility mechanism that drives the rover by hopping. The hop angle and the velocity are analyzed by numerical simulations, which show the effectiveness of the new mobility system.

Asteroids and other Small Solar System Bodies (SSSBs) are currently of great scientific and even industrial interest. Asteroids exist as the permanent record of the formation of the Solar System and therefore hold many clues to its understanding as a whole, as well as insights into the formation of planetary bodies. Additionally, SSSBs are being investigated in the context of impact risks for the Earth, space situational awareness and their possible industrial exploitation (asteroid mining). In all these aspects, the knowledge of the geophysical characteristics of SSSB surface and internal structure are of great importance. Given their size, constitution, and the evidence that many SSSBs are not simple monoliths, these bodies should be studied and modelled as self-gravitating granular systems in general, or as granular systems in micro-gravity environments in particular contexts. As such, the study of the geophysical characteristics of SSSBs is a multi-disciplinary effort that lies at the crossroads between Granular Mechanics, Celestial Mechanics, Soil Mechanics, Aerospace Engineering and Computer Sciences.

Small icy bodies in the outer solar system have been shown to consist of ice‐silicate mixtures. The results of previous impact cratering experiments on ice‐silicate mixture targets showed that a crater volume decreases with increasing silicate content. Surface strength controls craterings in laboratory experiments and on small bodies with a certain degree of strength. In this study we measured the uniaxial compressive and tensile strength of the targets used in previous impact cratering experiments by uniaxial compression and Brazilian tests, respectively, at 263 K and calculated the shear strength from the measured values. We found the uniaxial compressive and tensile strength increased with silicate content, which explains why the crater volume decreases with increasing silicate content. Since the gradient of increase of the uniaxial compressive and the tensile strength was different, the difference between the tensile strength and the uniaxial compressive strength becomes smaller with the increase of silicate content up to 50 wt %. We show that the crater spall diameter is better scaled by the tensile strength to compensate the difference of the silicate content than by the uniaxial compressive strength.

Autonomy is becoming increasingly important for the robotic exploration of unpredictable environments. One such example is the approach, proximity operation, and surface exploration of small bodies. In this article, we present an overview of an estimation framework to approach and land on small bodies as a key functional capability for an autonomous small-body explorer. We use a multi-phase perception/estimation pipeline with interconnected and overlapping measurements and algorithms to characterize and reach the body, from millions of kilometers down to its surface. We consider a notional spacecraft design that operates across all phases from approach to landing and to maneuvering on the surface of the microgravity body. This SmallSat design makes accommodations to simplify autonomous surface operations. The estimation pipeline combines state-of-the-art techniques with new approaches to estimating the target’s unknown properties across all phases. Centroid and light-curve algorithms estimate the body–spacecraft relative trajectory and rotation, respectively, using a priori knowledge of the initial relative orbit. A new shape-from-silhouette algorithm estimates the pole (i.e., rotation axis) and the initial visual hull that seeds subsequent feature tracking as the body gets more resolved in the narrow field-of-view imager. Feature tracking refines the pole orientation and shape of the body for estimating initial gravity to enable safe close approach. A coarse-shape reconstruction algorithm is used to identify initial landable regions whose hazardous nature would subsequently be assessed by dense 3D reconstruction. Slope stability, thermal, occlusion, and terra-mechanical hazards would be assessed on densely reconstructed regions and continually refined prior to landing. We simulated a mission scenario for approaching a hypothetical small body whose motion and shape were unknown a priori, starting from thousands of kilometers down to 20 km. Results indicate the feasibility of recovering the relative body motion and shape solely relying on onboard measurements and estimates with their associated uncertainties and without human input. Current work continues to mature and characterize the algorithms for the last phases of the estimation framework to land on the surface.

Exhaustive evaluation of microgravity landing dynamics for small body exploration

Electrostatic dust lofting may be a common occurrence on small bodies in the solar system, whereby the upward electrostatic force on a grain is able to overcome the surface gravity and cohesion binding it to the surface. This electrostatic lofting may serve to redistribute and transport dust across the surface of these bodies to produce features such as dust ponds and lineations found on Eros, or even to rid bodies of small particles completely. Classical models, which distribute charge evenly across a dust grain, have historically predicted electric field strengths that are insufficient to loft dust. However, recent studies have developed grain-scale charging models that account for the buildup of charge in the microcavities of regolith and assume unequal distribution of charge on a dust grain. These models predict electric field strengths orders of magnitude larger than classical models, which may explain how electrostatic dust lofting occurs on small bodies. In this paper, we compare the grain-scale supercharging models developed by Zimmerman et al. and survey how the different parameters affect grain charging—namely, charge separation, grain size, and dielectric breakdown strength. Furthermore, we investigate how each of the charging models can be used to bound initial condition requirements such as charge and velocity for dust lofting to occur on these small bodies. Initial condition requirements are examined for a range of grain sizes, regolith cohesive strengths, and small body sizes.

Periodic orbit is one of the most important issues among all kinds of large-scale motion types, and has been regarded as the breakthrough of three-body problem by Poincare. Specifically, to orbital dynamics around small bodies, there are at least two reasons for us to focus on the periodic motion, which is related to orbital evolution of real small body system, and is crucial for mission design of approaching the target body. Differing from equilibrium points, to search periodic orbits in the phase space is still an art to date, especially for the highly dimensional systems like Eq. 2.23. The orbital motion equation near a small body Eq. 2.22 has similar formulation with the equation of CRTBP, which suggests that it might include periodic motion of the same level of abundance as the latter. This chapter starts with a specific asteroid. Section 4.2 proposes an algorithm to search large-scale periodic orbits around irregular bodies, which is then applied to find out the periodic orbital families of the target small body. Section 4.3 surveys the stabilities of these orbits, and Sect. 4.4 further describes the topologies of different orbital families, based on which a classification method is proposed to track the topological evolution. Section 4.5 discusses the general motion forms about the periodic orbits, which discriminates different orbital patterns according to the linearized map on the section.