The UAE’s Emirates Mission to the Asteroid Belt (EMA) is scheduled to launch later this decade. The mission will rendezvous with the water-rich asteroid (269) Justitia, and along the way will flyby 6 different main belt asteroids. The EMA mission goals combine both scientific investigation on the nature of water-rich asteroids and determining the resource potential present in asteroidal bodies. While all of the asteroid flybys will be too fast to enable precise mass estimates, the rendezvous with Justitia will include estimating its mass, gravity field and internal density distribution as a main scientific goal. The approach to be taken will mimic other asteroid rendezvous missions such as NASA’s NEAR, Dawn and OSIRIS-REx missions. Specifically, a combination of optical navigation images along with radio metric tracking from the Earth during an orbital phase will be combined to determine the asteroid precise spin state, total mass, and gravity field coefficients. Upon arrival at Justitia, the EMA spacecraft will first have a few flybys of the asteroid to determine its overall mass. Following this will be an extended mission phase where it will orbit the asteroid to measure its higher gravity coefficients. After the gravity field is appropriately mapped, the mission will focus on observations of its surface with multi-spectral instrumentation. While the first orbital phase is driven by navigation needs, gravity science will process tracking and optical navigation measurements through all of the orbital phases of the mission in order to produce the highest fidelity gravity field feasible. This talk will introduce the specific challenges that the EMA mission will need to overcome at Justitia. Challenges and opportunities exist for the orbital phase of the mission, as depending on the precise spin state and total mass of the body, a sun synchronous orbit may be feasible and advantageous for the other imaging instruments. A key scientific result will be the bulk density measurement and comparison of the measured gravity field with the overall shape model of the asteroid, enabling constraints on the internal distribution of material in this body. The talk will also review the expected performance based on mission design and current knowledge of Justitia’s likely shape, spin and density range. Funding support for the EMA project was provided by the United Arab Emirates Space Agency and its knowledge partner, the University of Colorado Boulder’s Laboratory for Atmospheric and Space Physics.

This study explores the potential utility of flying a gravity gradiometer to directly sense the gravity field of a small body, in particular it focuses on the asteroid Bennu using the OSIRIS-REx mission as motivation. The gradiometer formulation and dynamic environment of the spacecraft are discussed as part of the study too. The measured values of the gravity tensor along the orbit are used to obtain a model of the gravity field using a Batch filter.

Binary asteroids originate from a wide range of evolutionary pathways, and are the targets of several previous and upcoming spacecraft missions. Differential heating and radiation on asymmetric asteroids can cause measurable changes in their rotation rates and spin axes, collectively known as the Yarkovsky- O'Keefe-Radzievskii-Paddack (YORP) effect. In binary systems, such radiation-driven torques can cause changes to the mutual asteroid orbits, termed the binary YORP or BYORP effect. To study how binary asteroid shapes and thermophysical properties affect surface temperatures and BYORP, we developed a new 3D thermophysical model. This model can be applied to binary asteroid systems, solitary asteroids, and other airless bodies with complex topography. The model balances direct insolation, 1D conduction, visible light reflection, and mutual heating through scattered infrared radiation. Using 3D ray tracing, we include eclipses, shadowing from horizons and topography, as well as the mutual radiation exchange between the primary and secondary asteroids. Using this model, we perform global temperature modeling of the binary asteroid (175706) 1996 FG3, a target of the Janus mission. At perihelion, we find that the 1996 FG3 system experiences temperatures between similar to 100 and 475 K. We also find that eclipses and thermal inertia can alter surface temperatures on the secondary by up to 14%, with a mean difference due to radiation from the primary of just over 1%. These radiative effects decrease with higher thermal inertia. We also present a model for calculating the BYORP effect using the results of the binary thermophysical model. This model compares well to analytical approximations of the BYORP coefficient B, and suggests that thermal effects such as eclipses and thermal inertia can reduce torque in the 1996 FG3 system and alter the BYORP coefficient B by up to several percent. Though small, these second-order effects may produce significant dynamical changes. For 1996 FG3, eclipses alter B by approximately 7%, resulting in a lower torque on the secondary. In the absence of tidal effects, this change would reduce the contraction of the semimajor axis by about 20 meters over 10,000 years. Mutual radiation from the primary also causes a small nonzero change to B, although of an order of magnitude smaller. Our findings suggest that thermal effects can alter temperatures and BYORP calculations sufficiently that they should be included when modeling binaries, and the relative importance of each effect is predicted to vary with the properties of the system being studied.

The Hayabusa2 extended mission, named Hayabusa2# (SHARP: Small Hazardous Asteroid Reconnaissance Probe), is planned to rendezvous with the fast-rotating asteroid 1998 KY26 in 2031. Hayabusa2# will be the first ever mission to rendezvous with such a rapidly rotating small asteroid, posing significant challenges because of its distinctive dynamical environment. In this paper, we investigate potential target marker (TM) deployment strategies, for both landing and orbiting scenarios, to maximize science acquisition. In particular, we model the surface and orbital environments to identify feasible target market operations and present landing site selection strategies and candidate insertion orbits considering realistic deployment errors. The TM is one of the only two remaining deployable payloads, and therefore, can play a critical role during the extended mission phase. Our results show that surface operations can be extremely challenging whereas orbit operations could help us gain valuable information on the asteroid’s gravity field. Overall, this research contributes to the exploration and characterization of extremely small bodies specifically through the use of artificial objects, in this case the target marker.

Phase space distributions outline regions of plausible spacecraft states in phase space given some degree of uncertainty. Under Hamiltonian dynamical flow, geometric features of these distributions become time-invariant and are referred to as Hamiltonian integral invariants. The shape and size of the distributions are correlated to our state uncertainty, so these geometric invariants provide unique, analytical insight into problems of uncertainty propagation. When a Hamiltonian system is perturbed by dissipative forces, the geometric features associated with integral invariants are no longer constant. Rather, they change in time, and the insight into problems of uncertainty propagation also changes. This paper explores how the geometric features of phase space distributions can be targeted with orbital and attitude guidance laws. For example, volume-collapsing guidance laws are designed to restrict both the translational and rotational spacecraft state. Alternative representations for regions of uncertainty are also considered via Monte Carlo and covariance matrix analysis. With these alternative representations, the targeted geometric behavior is validated.

Comet exploration missions represented by the Comet Interceptor mission have attracted our attention to unravel the origin of our solar system. However, it is difficult to know the details of orbital data about long period comets (LPCs) until their approach. Additionally, the amount of fuel consumption by the current intercept approach depends on the intersection points of cometary orbits with the ecliptic plane. To address these challenges, designing low-energy transfer trajectories suitable for the observation of LPCs is necessary. This paper introduces a novel approach by utilizing invariant manifold structures in the Sun-Earth circular restricted three-body problem for comet missions with multiple probes. As candidates for departure orbits, periodic orbits and quasi-periodic orbits are considered. Based on the optimal control theory, low-thrust trajectories to improve mission efficiency for enlarging the reachable domain of multiple probes are designed by leveraging invariant manifolds. The trajectories guided by invariant manifolds and optimal control theory facilitate formation flying, multi-point observations, and explorations of unknown comets by multiple probes.

The Earth–Moon L2 9:2 Near-Rectilinear Halo Orbit (NRHO) is a periodic orbit in the Circular Restricted 3-Body Problem that is representative of the lunar Gateway’s planned orbit. Accounting for the effect of the Sun has been known to change the behavior of periodic orbits, and can allow for easier transition into an ephemeris model. In this work, we use Melnikov theory and a continuation algorithm to transition this orbit into the Sun–Earth–Moon (SEM) system using the Hill Restricted 4-Body Problem (HR4BP). The set of periodic orbits corresponding to the 9:2 NRHO in the SEM HR4BP numerically foliate a 2D torus. We hypothesize this behavior constitutes a limiting case where the destruction of the torus by the 9:2 resonance in the SEM system is not numerically detectable. As this behavior is unexpected, we extend our analysis to other resonant periodic orbits and dynamical models. We find that the SEM HR4BP dynamical equivalents to the L2 7:2 NRHO and 5:2 halo orbit also exhibit similar behavior, and the 9:2 NRHO in the SEM Bicircular Restricted 4-Body Problem exhibits this behavior as well.

As space activities expand within the cislunar environment, developing efficient refueling strategies becomes essential for sustaining long-term missions. The multi-spacecraft refueling problem focuses on optimizing fuel consumption to extend mission lifetimes. A multi-fidelity modeling approach addresses varying levels of precision, using the two-body problem for initial trajectory estimation, the circular restricted three-body problem for reference orbits and transfers, and the bicircular restricted four-body problem with solar radiation pressure for realistic station-keeping costs. The refueling problem is formulated as an infinite-horizon Markov decision process (MDP), optimizing the refueling strategy while preventing fuel depletion. The refueling process consists of two phases: first, the refueler transfers into a temporary phasing orbit, followed by a final phasing maneuver to rendezvous with the target spacecraft. We map the available transfers between orbits using a fast sampling technique and select the phasing orbit to minimize fuel consumption within a limited synodic period. The case study samples orbits from the Lyapunov and Halo families around the Lagrange points of the Earth-Moon system, L1, L2, and L3. Simulations demonstrate that the MDP-based planning achieves a 36% reduction in fuel consumption compared to a greedy strategy.

We carry out numerical simulations of a variety of impacts on a Dimorphos-like self-gravitating aggregate. These impacts have the same momentum, but we proportionally vary the velocity and mass of the impactor so that as velocity increases, so does its kinetic energy. This is done to explore the space of impacts on a binary secondary in order to gain insight into body deformation and energy dissipation in such a system. We use a soft-sphere discrete element method (DEM) code for this work and reach impact speeds of up to approximate to 1.5 km/s, bordering on supersonic where the results stop being realistic. We find that the amount of ejecta, as well as the momentum enhancing factor (beta) and the variation in the along-track velocity due to the impact (Delta v) increase with an increasing kinetic energy showing that our results point towards the values obtained by the DART mission. Additionally, we analyse how energy is dissipated over time, months after the impact, and evaluate the quality factor Q that characterises the energy dissipation rate.

The Hill Restricted 4-Body Problem (HR4BP) is a coherent time-periodic model that can be used to represent motion in the Sun-Earth-Moon (SEM) system. Periodic orbits were computed in this model to better understand the periodic orbit family structures that exist in these types of systems. First, periodic orbits in the Circular Restricted 3-Body Problem (CR3BP) representation of the Earth-Moon (EM) system were identified. A Melnikov-type function was used to identify a set of candidate points on the EM CR3BP periodic orbits to start a continuation algorithm. A pseudo-arclength continuation scheme was then used to obtain the corresponding periodic orbit families in the HR4BP when including the effect of the Sun. Bifurcation points were identified in the computed families to obtain additional orbit families.

Abstract Hypervelocity impacts play a significant role in the evolution of asteroids, causing material to be ejected and partially reaccreted. However, the dynamics and evolution of ejected material in a binary asteroid system have never been observed directly. Observations of Double Asteroid Redirection Test (DART) impact on asteroid Dimorphos have revealed features on a scale of thousands of kilometers, including curved ejecta streams and a tail bifurcation originating from the Didymos system. Here we show that these features result naturally from the dynamical interaction of the ejecta with the binary system and solar radiation pressure. These mechanisms may be used to constrain the orbit of a secondary body, or to investigate the binary nature of an asteroid. Also, they may reveal breakup or fission events in active asteroids, and help determine the asteroid’s properties following an impact event. In the case of DART, our findings suggest that Dimorphos is a very weak, rubble-pile asteroid, with an ejecta mass estimated to be in the range of (1.1-5.5)×107 kg.

Autonomous distributed space systems are receiving significant attention for their potential to reliably complete missions at reduced costs, and for their capability to enable novel science that cannot be achieved with a single spacecraft. One challenge inhibiting wider adoption of autonomous distributed systems is online navigation capabilities, which may not be as accurate as non-automatons systems which leverage powerful ground-based sensors. To bolster online navigation estimates, a spacecraft may maneuver to alter the sensing geometry within the distributed system and view new information. This work focuses on the study of optical-only navigation within a distributed space system and develops two analytical guidance policies that minimize relative range uncertainty. The first policy is a heuristic that is derived from a geometric analysis, and the second is an analytic solution to a surrogate cost function. The guidance policies are simulated in cislunar space and shown to closely approximate the true nonlinear solution. Additionally, the analytic guidance policy is combined with station keeping to reduce operational maneuvers.

The dynamical environment around binary asteroids has been studied in depth, but these models typically make assumptions about the eccentricity, shapes, or rotational stability of the asteroids. In this work, we develop a fully coherent dynamical model accounting for the gravitational influence of two arbitrarily shaped asteroids and the Sun, allowing for eccentricity and irregular spin states within the binary asteroid. We apply this model to Didymos after the DART impact to determine the stability of orbits in the perturbed system. We then study the behavior of ejecta and identify regions in which ejecta may be long-lived, a concern for the Hera mission. It is likely debris from the DART impact will survive in the system throughout the duration of the Hera mission, and these particles are generally at least 10 cm in diameter and found in wide, eccentric, and inclined orbits. The most likely region for Hera to encounter these particles is just outside the orbit of Dimorphos.

While contact binary objects are common in the solar system, their formation mechanism is unclear. In this work we examine several contact binaries and calculate the necessary strength parameters that allow the two lobes to merge without the smaller of the two being gravitationally destroyed by the larger. We find a small but nonzero amount of cohesion or a large friction angle is required for the smaller lobe to survive the merging process, consistent with observations. This means it is possible for two previously separated rubble piles to experience a collapse of their mutual orbit and form a contact binary. The necessary strength required to survive this merger depends on the relative size, shape, and density of the body, with prolate shapes requiring more cohesion than oblate shapes.

No AccessEngineering NoteGlobal Method to Compute Asteroid Equilibrium Points for Any Spin RateGavin M. Brown and Daniel J. ScheeresGavin M. BrownUniversity of Colorado, Boulder, Colorado 80309 and Daniel J. ScheeresUniversity of Colorado, Boulder, Colorado 80309Published Online:21 Dec 2023https://doi.org/10.2514/1.G007692SectionsRead Now ToolsAdd to favoritesDownload citationTrack citations ShareShare onFacebookTwitterLinked InRedditEmail About References [1] Tardivel S. C. V., "The Deployment of Scientific Packages to Asteroid Surfaces," Ph.D. Dissertation, Univ. of Colorado Boulder, Boulder, CO, 2014. Google Scholar[2] Brown G. M. and Scheeres D. J., "Temporal Evolution of the Dynamical Environment Around Asteroid (101955) Bennu," Icarus, Vol. 403, Oct. 2023, Paper 115632. https://doi.org/10.1016/j.icarus.2023.115632 Google Scholar[3] Hergenrother C. W., Maleszewski C. K., Nolan M. C., Li J. Y., Drouet d'Aubigny C. Y., Shelly F. C., Howell E. S., Kareta T. R., Izawa M. R. 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AcknowledgmentsThe authors acknowledge funding from the Solar System Exploration Research Virtual Institute and support from NASA grant number 80NSSC22K0240.PDF Received3 May 2023Accepted9 November 2023Published online21 December 2023

The exploration of small bodies in our solar system is of great interest for the planetary science community due to their high scientific value. However, their generally weak and irregular gravity fields increase the difficulty associated with close proximity operations. Moreover, solar radiation pressure (SRP) can significantly perturb the motion of objects in their vicinity, particularly for bodies with high area-to-mass ratios. In this work, we adopt the polyhedral gravity model and identify natural dynamical structures that can be used for mission operations. Further, we study forced periodic motion in the body fixed frame while accounting for the effect of SRP with eclipses. Overall, our work seeks to identify suitable orbits and locations in the vicinity of small bodies that can be exploited for the design of science orbits. To obtain periodic orbits in the model accounting for SRP perturbations, we use a Melnikov function to find orbits that satisfy resonances with the asteroid spin and show no net change in energy over the orbit. We then use a differential correction scheme to find numerical solutions in the time-periodic model. Our test cases are potentially hazardous asteroid 101955 Bennu and main belt asteroid 16 Psyche.

In this paper, the new equilibria realized by continuous optimal control inputs and the dynamic structure around them are studied. Using the Euler–Lagrange equation, which is a necessary condition for optimal control problems, the equations of motion of a dynamic system with optimal control inputs that minimize the quadratic cost function are described in terms of state and adjoint variables. Based on the equations of motion, equilibrium conditions are derived, and the properties of equilibria are analyzed for the two-body and Hill three-body problems. The stability and dynamic structure around unstable equilibria are also characterized to get insights into the properties of optimal trajectories.

Janus is a NASA SIMPLEx mission currently in Phase B. The SIMPLEx program is designed around the idea of using secondary launch opportunities to explore interplanetary destinations. The Janus mission concept plans to take advantage of the NASA Psyche launch to send two spacecraft to fly by Near Earth Objects of interest. A specific point design has been developed that sends two spacecraft to two binary asteroid systems, (175706) 1996 FG3 and (35107) 1991 VH, both of which have been observed repeatedly with photometry, spectrometry and radar. The Janus mission sends light-weight, low-cost spacecraft built by Lockheed Martin to encounter these high-science value small body targets. The science instruments are a visible and IR imager, from Malin Space Science Systems. The spacecraft will perform a rigorous remote sensing campaign when the object is a point source, and when resolved. The spacecraft will track the binary asteroid systems through closest approach, allowing for a combination of absolute surface resolution, relative resolution across the target asteroids and phase angle coverage unparalleled in previous asteroid flyby missions. Janus science will combine flyby observations of the target binary asteroids with ground-based observations, enabling the high resolution imaging and thermal data to be placed into a global context and leveraging all available data to construct an accurate topographical and morphological model of these bodies. Based on these measurements, the formation and evolutionary implications for small rubble pile asteroids will be studied. The science team members all have experience on asteroid missions or have made extensive ground based observations of NEAs. The industry team has extensive experience in the design, fabrication and operation of interplanetary spacecraft and instrumentation.Acknowledgements: The Janus mission is supported by NASA under a contract from the SIMPLEx Program Office. Part of this research was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.