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The impact of nonspherical bodies is complex, even at low velocities where contacting bodies are assumed to be rigid. Models of varying complexity (e.g. finite element methods) can be used to evaluate such impacts, but it is advantageous to use impulsive models such as that by Stronge , which are computationally inexpensive and governed by (fixed) material interaction coefficients. Stronge's model parameterizes nonspherical rigid-body impacts with energetic restitution and Coulomb friction coefficients. This model was successfully used in large-scale simulations of ballistic lander deployment to asteroids and comets, whose trajectories involve dozens of chaotic bounces. To better understand the complex dynamics of these bouncing trajectories, this paper performs a dedicated study of idealized bouncing in two dimensions and on a flat plane, in order to limit the involved degrees of freedom. Using a numerical implementation of Stronge's model, the motion of a bouncing square is simulated with different impact conditions: the square's impact attitude, velocity, and mass distribution as well as the surface restitution and friction coefficients. The simulation results are used to investigate how these conditions affect the bouncing motion of the square, with a distinction between first impacts with zero angular velocity and successive impacts in which the square is spinning. This reveals how a single "macroscopic" bounce that separates two ballistic arcs may often consist of multiple micro-impacts that occur in quick succession. For the different impact conditions, we show how the number of micro-impacts per macro-bounce varies, as well as the normal, tangential, and total kinematic restitution coefficients. These are different from the energetic material restitution coefficient that parameterizes the impact. Finally, we examine how the settling time and distance of the bouncing trajectories change. These trends provide insight into the bouncing motion of ballistic lander spacecraft in small-body microgravity. [ABSTRACT FROM AUTHOR]

This paper investigates the equatorial cavities found on asteroids 2008 EV5 and 2000 DP107 Alpha. As the likelihood of these cavities being impact craters is demonstrated to be low, the paper presents a fission mechanism that explains their existence as a scar of past fission events. The dynamical environment of “top-shaped” asteroids is such that, at high spin rates, an identifiable equatorial region enters into tension before the rest of the body. We propose hypothetical past shapes for 2008 EV5 and 2000 DP107, with mass added within the cavity to recreate a smoother equatorial ridge. The dynamical environment of these hypothetical parent bodies reveal that this modified region is indeed set in tension when spin is increased. The fission process requires tensile strength at the interface between the ejecta and the remaining body, at the moment of fission, between 0 and 2  Pa for 2008 EV5 and between 0 and 15  Pa for 2000 DP107, depending on the precise fission scenario considered. Going back to the spin-up deformation phase of the asteroids, the paper examines how kinetic sieving can form predominantly rocky equators, whose tensile strength could be much lower than that of the rest of the body. This process could explain the low cohesion values implied for this fission mechanism. [ABSTRACT FROM AUTHOR]

Following their success in low Earth orbit, nanospacecraft weighing less than 25 kg may soon contribute to the exploration of the Solar System. This paper outlines the necessary technologies that enable these small satellites to be placed on an interplanetary trajectory. Propulsion is a key aspect of this problem but is only part of it; because a nanospacecraft does not choose its launcher and its injection orbit, launch opportunities and propulsion systems must be considered together. Specifications of present and upcoming electric thrusters and the limits of electric propulsion are described. Especially, the use of such nanothrusters on a nanospacecraft are considered with the realistic constraint of limited thrusting time, which restricts the very large ΔV that can be obtained otherwise. Then, given the present state of rideshare opportunities along scientific or commercial missions, the paper analyzes the possibility of nanospacecraft escaping Earth on their own from common orbits. The paper concludes on technological and system developments required for nanospacecraft to change the paradigm of interplanetary Solar System exploration. [ABSTRACT FROM AUTHOR]

This paper investigates the sensitivities of spherical lander deployment to small bodies. Previous work established methods to simulate the motion of such landers in the gravitationally and topographically complex small-body environment. These methods are extended, primarily through the inclusion of a "persistent" rock model that accounts for the observed distribution of rocks and boulders on the small-body surface. The resulting framework is applied to investigate the effects of relevant environmental and hardware parameters on trends in the deployment of a lander. In the dynamically favorable environment of asteroid Itokawa, variations in the surface interaction, rock distribution, and lander mass distribution scale the settling time, slope, and surface dispersion of a given deployment scenario. In the more challenging environment of asteroid 1999 KW4 Alpha, these parameters determine the success rate with which landers are delivered to the surface, and they should be carefully considered during deployment design. The current results underscore the importance of high-fidelity modeling, may provide guidelines for the hardware and mission operations design of lander spacecraft, and may prioritize particular studies and observations of the small-body (sub)surface. [ABSTRACT FROM AUTHOR]

This paper outlines the strategic approach to realize a human mission to an asteroid, focusing specifically on the proximity operations. The risks and challenges posed by asteroid surfaces to in-situ investigations force the proximity operations to be done by the intermediary of robotic explorers. In this architecture, a precursor is sent years in advance to a potential target asteroids. Its main goals are the characterization of the gravity field and of the surface behavior. If the target is found suitable, the manned mission then proceeds. With their main spacecraft stationed on a stable orbit around the asteroid, the astronauts are transported to the surface via a small, unpressurized spacecraft. Hovering a few meters above the surface, they deploy and command small robotic landers that perform scientific operations at the surface. [ABSTRACT FROM AUTHOR]

A comprehensive method for modeling the motion of a spherical pod at the surface of an asteroid is presented. Using triangular faceted surfaces, the largest features of the asteroid (global shape, monoliths, and large boulders) are modeled. The presence of smaller rocks is accounted for using a stochastic model of rock generation and collision. The contact dynamics on regolith or harder surfaces, including multiple contact points situations, are described. The force, torque, and coefficient of rolling resistance are introduced, explained, and estimated. Finally, this model is applied to a hypothetical deployment case on asteroid Itokawa. The numerical simulations show landing time around 5 h, with the main landing basin located in Muses Sea. It also proves the importance of each and every level of detail of the asteroid model for an accurate understanding of asteroid surface motion and the effective design of practical deployment strategies. [ABSTRACT FROM AUTHOR]

Abstract: The idea of deploying a lander on the secondary body of the binary primitive asteroid (175706) 1996 FG3 is investigated. 1996 FG3 is the backup target of the European sample return space mission MarcoPolo-R under assessment study at the European Space Agency in the framework of the M3 Medium-Class mission competition. The launch will take place in 2022–2024, depending on its selection at the end of 2013. A lander is indicated as an optional payload, depending on mass availability on the spacecraft. Obviously, the possible complexity of a lander deployment is also an important parameter to take into account. Here we demonstrate that, considering worst case scenarios and low requirements on the spacecraft GNC and deployment mechanism, the operations are easy to implement and safe for the main spacecraft. The concept of operations is to deploy a light lander from the L2 Lagrange point of the binary system, on a ballistic trajectory that will impact the secondary asteroid. The fundamental principles of this strategy are briefly presented and a detailed model of 1996 FG3 is considered, to which the strategy is applied. We show that the deployment is successful in 99.94% of cases. [Copyright &y& Elsevier]

The Discrete Element Method (DEM) is frequently used to model complex granular systems and to augment the knowledge that we obtain through theory, experimentation, and real-world observations. Numerical simulations are a particularly powerful tool for studying the regolith-covered surfaces of asteroids, comets, and small moons, where reduced-gravity environments produce ill-defined flow behaviours. In this work, we present a method for validating soft-sphere DEM codes for both terrestrial and small-body granular environments. The open-source code chrono is modified and evaluated first with a series of simple two-body-collision tests, and then, with a set of piling and tumbler tests. In the piling tests, we vary the coefficient of rolling friction to calibrate the simulations against experiments with 1 mm glass beads. Then, we use the friction coefficient to model the flow of 1 mm glass beads in a rotating drum, using a drum configuration from a previous experimental study. We measure the dynamic angle of repose, the flowing layer thickness, and the flowing layer velocity for tests with different particle sizes, contact force models, coefficients of rolling friction, cohesion levels, drum rotation speeds, and gravity levels. The tests show that the same flow patterns can be observed at the Earth and reduced-gravity levels if the drum rotation speed and the gravity level are set according to the dimensionless parameter known as the Froude number. chrono is successfully validated against known flow behaviours at different gravity and cohesion levels, and will be used to study small-body regolith dynamics in future works. [ABSTRACT FROM AUTHOR]

The Martian Moons eXploration (MMX) mission by the Japan Aerospace Exploration Agency, JAXA, will explore the Martian moons Phobos and Deimos. In addition to investigating the moons remotely and returning samples from Phobos, MMX will also deliver a small (about 25 kg) Rover to the surface of Phobos. The payload of the Rover consists of four scientific instruments: RAX, a Raman spectrometer to measure signatures of the mineralogical composition of the surface material, NavCam, a stereo pair of cameras to investigate the terrain and allow for navigation, miniRAD a radiometer to measure the surface brightness temperature of both, regolith and rocks, and two WheelCams which will observe the wheel-surface interface, and thus investigate the properties and dynamics of the regolith. The cameras, will serve both, technological and scientific needs. The rover will be deployed during the rehearsal phase of the landing operations for the main spacecraft and will thus land in proximity to the first sampling area. During its operational lifetime on Phobos (about 100 days), the in-situ measurements performed with the rover payload will provide scientific context for the returned samples, provide ground truth, study the surface heterogeneity and obtain information on the physical properties of undisturbed surface material. The MMX launch is planned for September 2024 and the Rover delivery is scheduled for 2027. The Rover is a contribution by the Centre National d'Etudes Spatiales (CNES) and the German erospace Center (DLR) with additional contributions from INTA (Spain) and JAXA. • In this paper we give an overview of the rover, which will be part of the MMX mission to Phobos. • The MMX rover will explore the surface of Phobos with cameras, a Raman spectrometer and a radiometer. • Scientific objectives and the mission outline are discussed. [ABSTRACT FROM AUTHOR]

The Japanese MMX sample return mission to Phobos by JAXA will carry a rover developed by CNES and DLR that will be deployed on Phobos to perform in situ analysis of the Martian moon's surface properties. Past images of the surface of Phobos show that it is covered by a layer of regolith. However, the mechanical and compositional properties of this regolith are poorly constrained. In particular, from current remote images, very little is known regarding the particle sizes, their chemical composition, the packing density of the regolith as well as other parameters such as friction and cohesion that influence surface dynamics. Understanding the properties and dynamics of the regolith in the low-gravity environment of Phobos is important to trace back its history and surface evolution. Moreover, this information is also important to support the interpretation of data obtained by instruments onboard the main MMX spacecraft, and to minimize the risks involved in the spacecraft sampling operations. The instruments onboard the Rover are a Raman spectrometer (RAX), an infrared radiometer (miniRad), two forward-looking cameras for navigation and science purposes (NavCams), and two cameras observing the interactions of regolith and the rover wheels (WheelCams). The Rover will be deployed before the MMX spacecraft samples Phobos' surface and will be the first rover to drive on the surface of a Martian moon and in a very low gravity environment. [ABSTRACT FROM AUTHOR]

In the frame of Near-Earth-Object exploration and planetary defence, the two-part AIDA mission is currently studied by NASA and ESA. Being composed of a kinetic impactor, DART (NASA), and by an observing spacecraft, AIM (ESA), AIDA has been designed to deliver vital data to determine the momentum transfer efficiency of a kinetic impact onto a small body and the key physical properties of the target asteroid. This will enable derivation of the impact response of the object as a function of its physical properties, a crucial quantitative point besides the qualitative proof of the deflection. In the course of the AIM mission definition, a lander has been studied as an essential element of the overall mission architecture. It was meant to be deployed on Didymoon, the secondary body of the binary NEA system 65803 Didymos and it was supposed to significantly enhance the analysis of the body's dynamical state, mass, geophysical properties, surface and subsurface structure. The mission profile and the design of the 13 kg (current best estimate) nano-lander have been derived from the MASCOT lander flying aboard Hayabusa2. Differing from its predecessor by having an increased lifetime of more than three months, a surface mobility capability including directed movement, a sensor system for localization and attitude determination on the surface and a redesigned mechanical interface to the mother spacecraft. The MASCOT2 instrument suite consists of a bi-static, low frequency radar as main instrument, supported by an accelerometer, a camera, a radiometer and a magnetometer; the latter three already flying on MASCOT. Besides the radar measurements, the camera is meant to provide high-resolution images of the landing area, and accelerometers to record the bouncing dynamics by which the top surface mechanical properties can be determined. During the DART impact, MASCOT2 was expected to be able to detect the seismic shock, providing valuable information on the internal structure of the body. MASCOT2 was supposed also to serve as a technology demonstrator for very small asteroid landing and extended operations powered by a solar generator. In this paper, we describe the science concept, mission analysis of the separation, descent and landing phase, the operational timeline, and the latest status of the lander's design. Despite the fact that AIM funding has not been fully confirmed during the ESA Ministerial conference in 2016, MASCOT2 is an instrument package of high maturity and major interest for planetary defence and NEO science. With appropriate tailoring and optimization, it can be considered and studied for future missions. [ABSTRACT FROM AUTHOR]

This paper presents a mission analysis comparison of human missions to asteroids using two distinct architectures. The objective is to determine if either architecture can reduce launch mass with respect to the other, while not sacrificing other performance metrics such as mission duration. One architecture relies on chemical propulsion, the traditional workhorse of space exploration. The second combines chemical and electric propulsion into a hybrid architecture that attempts to utilize the strengths of each, namely the short flight times of chemical propulsion and the propellant efficiency of electric propulsion. The architectures are thoroughly detailed, and accessibility of the known asteroid population is determined for both. The most accessible asteroids are discussed in detail. Aspects such as mission abort scenarios and vehicle reusability are also discussed. Ultimately, it is determined that launch mass can be greatly reduced with the hybrid architecture, without a notable increase in mission duration. This demonstrates that significant performance improvements can be introduced to the next step of human space exploration with realistic electric propulsion system capabilities. This leads to immediate cost savings for human exploration and simultaneously opens a path of technology development that leads to technologies enabling access to even further destinations in the future. [ABSTRACT FROM AUTHOR]