Planetary Defense Research Articles

NEOROCKS project: surface properties of small near-Earth asteroids

ABSTRACT We present new results of the observing program which is a part of the NEOROCKS project aimed to improve knowledge on physical properties of near-Earth Objects (NEOs) for planetary defense. Photometric observations were performed using the 1.2-m telescope at the Haute-Provence observatory (France) in the BVRI filters of the Johnson–Cousins photometric systems between June 2021 and April 2022. We obtained new surface colours for 42 NEOs. Based on the measured colours, we classified 20 objects as S-complex, nine as C-complex, nine as X-complex, two as D-type, one object as V-type, and one object remained unclassified. For all the observed objects, we estimated their absolute magnitudes and diameters. Combining these new observations with the previously acquired data within the NEOROCKS project extended our data set to 93 objects. The majority of objects in the data set with diameters D < 500 m belongs to a group of silicate bodies, which could be related to observational bias. Based on MOID and ΔV values we selected 14 objects that could be accessible by a spacecraft. Notably, we find D-type asteroid (163014) 2001 UA5 and A-type asteroid 2017 SE19 to be of particular interest as possible space mission targets.

Asteroid deflection bags award

The Physics World 2022 Breakthrough of the Year goes to the first demonstration of “kinetic impact” by successfully changing the orbit of an asteroid, as Hamish Johnston reports.

The Political Dimension of Space Exploration

Space exploration is essential for global security and technological development, yet political leaders often disregard its importance. This policy paper demonstrates the role of space exploration in global security and technological development and the necessity for political support, as space exploration is costly, relying primarily on federal funding. Political support is motivated by political circumstances. When winning the space race was an important demonstration of power, political support was at its highest. However, political interest in spacefaring faded after the Cold War ended, and funding decreased. Political disinterest has global consequences. Space hazards constitute a severe global threat to planetary defense and come in different forms, such as space rocks, artificial space debris, and space weaponization. These hazards threaten satellites in orbit with a significant role in global operations, including communications, surveillance, and navigation. Additionally, nearEarth objects such as asteroids or comets seriously threaten global security. A catastrophic impact of a near-Earth object could threaten life on Earth and even become an extinction event. The national space program also plays an important role in mitigating climate change, a significant current threat to global security. Therefore, setting the right direction for the space program and ensuring sufficient funding for spacefaring is essential to global security. Using qualitative secondary analysis and the causal explanation method, this policy paper analyzes political support by comparing NASA’s budget and national space policies over several decades and how funding affects technological advances and development. The paper concludes by generating policy recommendations to establish the optimal conditions for a national space program to thrive and fulfill its role in maintaining global security

Neural network for determining an asteroid mineral composition from reflectance spectra

Context.Chemical and mineral compositions of asteroids reflect the formation and history of our Solar System. This knowledge is also important for planetary defence and in-space resource utilisation. In the next years, space missions will generate extensive spectral datasets from asteroids or planets with spectra that will need to be processed in real time.Aims.We aim to develop a fast and robust neural-network-based method for deriving the mineral modal and chemical compositions of silicate materials from their visible and near-infrared spectra. The method should be able to process raw spectra without significant pre-processing.Methods.We designed a convolutional neural network with two hidden layers for the analysis of the spectra, and trained it using labelled reflectance spectra. For the training, we used a dataset that consisted of reflectance spectra of real silicate samples stored in the RELAB and C-Tape databases, namely olivine, orthopyroxene, clinopyroxene, their mixtures, and olivine-pyroxene-rich meteorites.Results.We used the model on two datasets. First, we evaluated the model reliability on a test dataset where we compared the model classification with known compositional reference values. The individual classification results are mostly within 10 percentage-point intervals around the correct values. Second, we classified the reflectance spectra of S-complex (Q-type and V-type, also including A-type) asteroids with known Bus–DeMeo taxonomy classes. The predicted mineral chemical composition of S-type and Q-type asteroids agree with the chemical composition of ordinary chondrites. The modal abundances of V-type and A-type asteroids show a dominant contribution of orthopyroxene and olivine, respectively. Additionally, our predictions of the mineral modal composition of S-type and Q-type asteroids show an apparent depletion of olivine related to the attenuation of its diagnostic absorptions with space weathering. This trend is consistent with previous results of the slower pyroxene response to space weathering relative to olivine.Conclusions.The neural network trained with real silicate samples and their mixtures is applicable for a quantitative mineral evaluation of spectra of asteroids that are rich in dry silicates. The modal abundances and mineral chemistry of common silicates (olivine and pyroxene) can be derived with an accuracy better than 10 percentage points. The classification is fast and has a relatively small computer-memory footprint. Therefore, our code is suitable for processing large spectral datasets in real time.

Security, Policy and Legal Challenges of Planetary Defense

Security, Policy and Legal Challenges of Planetary Defense

Constraining the Limitations of NEATM-like Models: A Case Study with Near-Earth Asteroid (285263) 1998 QE2

Near-Earth asteroids (NEAs) are a key test bed for investigations into planet formation, asteroid dynamics, and planetary defense initiatives. These studies rely on understanding NEA sizes, albedo distributions, and regolith properties. Simple thermal models are a commonly used method for determining these properties; however, they have inherent limitations owing to the simplifying assumptions they make about asteroid shapes and properties. With the recent collapse of the Arecibo Telescope and a decrease of direct size measurements, as well as future facilities such as LSST and NEO Surveyor coming online soon, these models will play an increasingly important role in our knowledge of the NEA population. Therefore, it is key to understand the limits of these models. In this work we constrain the limitations of simple thermal models by comparing model results to more complex thermophysical models, radar data, and other existing analyses. Furthermore, we present a method for placing tighter constraints on inferred NEA properties using simple thermal models. These comparisons and constraints are explored using the NEA (285263) 1998 QE2 as a case study. We analyze QE2 with a simple thermal model and data from both the NASA IRTF SpeX instrument and NEOWISE mission. We determine an albedo between 0.05 and 0.10 and thermal inertia between 0 and 425J m−2 s−1/2 K−1. We find that overall the simple thermal model is able to well constrain the properties of QE2; however, we find that model uncertainties can be influenced by topography, viewing geometry, and the wavelength range of data used.

On the predictability horizon in Impact Monitoring of Near Earth Objects

AbstractThe Impact Monitoring (IM) of Near Earth Objects (NEOs) is a fundamental part of the planetary defense strategy. Current NEO IM systems (Aegis, NEODyS and Sentry) scan the Confidence Region (CR) of each observed object looking for Virtual Impactors (VIs) with a time horizon of about 100 years. This procedure is performed regardless of the uncertainty with which the orbit of the object is known, and without considering whether a scattering encounter is present in the propagation time span. In view of the likely future increase of the IM workload due to higher future NEO discovery rates, it might be more reasonable to adapt the predictability horizon of the impacts to each object, taking into account the orbit uncertainty and the close encounters experienced. In this paper we discuss the problem of estimating a reasonable predictability horizon when multiple close encounters are present and start to address the problem proposing a formal mathematical definition of scattering encounter.

Kinetic impactor for a short warning asteroid deflection

In this paper, GMV as a major AOCS (Attitude Orbit Control System)/GNC (Guidance, Navigation and Control) system provider presents its work on the development of a GNC system for a Kinetic Impact mission. Asteroid impacts on Earth are a known source of extinction and played an important role in the evolution of life on Earth. This comes as no surprise given the high number of objects orbiting in Earth’s vicinity—asteroid impacts become a question of “when” rather than “if”.This comes as no surprise given the high number of objects orbiting in Earth’s vicinity—asteroid impacts become a question of “when” rather than “if”. Under this motivation, thousands of potentially hazardous asteroids (PHAs) are monitored around the globe and naturally the question on the next step rose: What can we do when an incoming asteroid is identified as being on collision course with Earth? This is the motivation behind the field of Planetary Defence. Several mitigation strategies are being studied, but most of these have technology readiness levels still far off from the required. The one that comes closest is the kinetic impactor concept, which is the focus of this work. The concept is simple from a theoretical standpoint - a spacecraft (impactor) is sent into a collision course against the hazard NEO transferring enough momentum through kinetic energy to slightly change the NEO’s trajectory and causes it to miss the Earth.The main component of kinetic impactors is the GNC, due to the necessity of a fully autonomous system. The major elements are the camera and the guidance, since they will allow detecting the target and modifying its trajectory to have a successful impact, respectively. This study includes the implementation of the required algorithms as well as an analysis of their performance in the impact scenario.The main variables that control the simulations have been examined in order to determine the design limits. The sensitivity analysis illustrates that the errors introduced in the model were chosen conservatively, inasmuch as the impact could be reached introducing higher uncertainties and errors in the systems considered. In general, even with the not excessively complex algorithms employed, the performance of the GNC is good. This study opens the door for the development of a kinetic impactor mission.

Effects of Impact and Target Parameters on the Results of a Kinetic Impactor: Predictions for the Double Asteroid Redirection Test (DART) Mission

The Double Asteroid Redirection Test (DART) spacecraft will impact into the asteroid Dimorphos on 2022 September 26 as a test of the kinetic impactor technique for planetary defense. The efficiency of the deflection following a kinetic impactor can be represented using the momentum enhancement factor, β, which is dependent on factors such as impact geometry and the specific target material properties. Currently, very little is known about Dimorphos and its material properties, which introduces uncertainty in the results of the deflection efficiency observables, including crater formation, ejecta distribution, and β. The DART Impact Modeling Working Group (IWG) is responsible for using impact simulations to better understand the results of the DART impact. Pre-impact simulation studies also provide considerable insight into how different properties and impact scenarios affect momentum enhancement following a kinetic impact. This insight provides a basis for predicting the effects of the DART impact and the first understanding of how to interpret results following the encounter. Following the DART impact, the knowledge gained from these studies will inform the initial simulations that will recreate the impact conditions, including providing estimates for potential material properties of Dimorphos and β resulting from DART’s impact. This paper summarizes, at a high level, what has been learned from the IWG simulations and experiments in preparation for the DART impact. While unknown, estimates for reasonable potential material properties of Dimorphos provide predictions for β of 1–5, depending on end-member cases in the strength regime.

Asteroid interception and disruption for terminal planetary defense

Modern techniques for planetary defense from comets and asteroids involve the deflection of the bolide via kinetic, gravitational, ablative, or radiative means. While potentially effective, none of these methods are capable of operating in a terminal interdiction mode wherethe threat is discovered with little time prior to impact. We present a practical and effective method for planetary defense which enables extremely short interdiction time scales, but can also operate within longer time scales and can be effective for extremely large threats. Called PI (“Pulverize It”), the method makes use of an array of hypervelocity penetrators which uses the kinetic energy of the asteroid or comet to disrupt it. In the terminal interdiction mode, the fragments of maximum ∼10 m diameter disperse laterally as they continue towards the Earth, and then enter the Earth’s atmosphere where they burn up as a series of airburst events which spatially and temporally de-correlate the energy of the original parent bolide for any arbitrary observer on the ground in the form of acoustical shockwaves and optical pulses. We show that terminal interdiction modes ranging from 2 minutes prior to impact for 20-meter class bolides (such as the Chelyabinsk asteroid), 1 day prior to impact for 100 m-class asteroids, 10 days prior to impact for Apophis-class asteroids (∼370 m), and even 60 days prior to impact for 1 km-class threats are all possible, though longer warning times are always preferred. Using only technologies readily available today, the PI method allows for a cost-effective and practical roadmap towards robust planetary defense capability.

Stability Analysis on the Moon’s Rotation in a Perturbed Binary Asteroid

Numerical calculation provides essential tools for deep space exploration, which are indispensable to mission design and planetary research. In a specific case of binary asteroid defense such as the DART mission, an accurate understanding of the possible dynamical responses and the system’s stability and engineers’ prerequisite. In this paper, we discuss the numeric techniques for tracking the year-long motion of the secondary after being perturbed, based upon which its rotational stability is analyzed. For long-term simulations, we compared the performances of several integrating schemes in the scenario of a post-impact full two-body system, including low- and high-order Runge–Kutta methods, and a symplectic integrator that combines the finite element method with a symplectic integral format. For rotational stability analysis of the secondary, we focus on the rotation of the secondary around its long-axis. We calculated a linearised error propagation matrix and found that, in the case of tidal locking of the secondary to the primary, the rotation is stable; as the perturbation amplitude of the spin angular velocity of the secondary increases, the rotation will lose stability and will be prone to being unstable in the long-axis direction of the secondary. Furthermore, we investigated the one-year-long influences of the non-spherical perturbations of the primary and the secondary.

After DART: Using the First Full-scale Test of a Kinetic Impactor to Inform a Future Planetary Defense Mission

NASA’s Double Asteroid Redirection Test (DART) is the first full-scale test of an asteroid deflection technology. Results from the hypervelocity kinetic impact and Earth-based observations, coupled with LICIACube and the later Hera mission, will result in measurement of the momentum transfer efficiency accurate to ∼10% and characterization of the Didymos binary system. But DART is a single experiment; how could these results be used in a future planetary defense necessity involving a different asteroid? We examine what aspects of Dimorphos’s response to kinetic impact will be constrained by DART results; how these constraints will help refine knowledge of the physical properties of asteroidal materials and predictive power of impact simulations; what information about a potential Earth impactor could be acquired before a deflection effort; and how design of a deflection mission should be informed by this understanding. We generalize the momentum enhancement factor β, showing that a particular direction-specific β will be directly determined by the DART results, and that a related direction-specific β is a figure of merit for a kinetic impact mission. The DART β determination constrains the ejecta momentum vector, which, with hydrodynamic simulations, constrains the physical properties of Dimorphos’s near-surface. In a hypothetical planetary defense exigency, extrapolating these constraints to a newly discovered asteroid will require Earth-based observations and benefit from in situ reconnaissance. We show representative predictions for momentum transfer based on different levels of reconnaissance and discuss strategic targeting to optimize the deflection and reduce the risk of a counterproductive deflection in the wrong direction.

Predicting Asteroid Material Properties from a DART-like Kinetic Impact

NASA’s Double Asteroid Redirection Test (DART) mission is the first full-scale test of the kinetic impactor method for asteroid deflection, in which a spacecraft intentionally impacts an asteroid to change its trajectory. DART represents an important first step for planetary defense technology demonstration, providing a realistic assessment of the effectiveness of the kinetic impact approach on a near-Earth asteroid. The momentum imparted to the asteroid is transferred from the impacting spacecraft and enhanced by the momentum of material ejected from the impact site. However, the magnitude of the ejecta contribution is dependent on the material properties of the target. These properties, such as strength and shear modulus, are unknown for the DART target asteroid, Dimorphos, as well as most asteroids since such properties are difficult to characterize remotely. This study examines how hydrocode simulations can be used to estimate material properties from information available post-impact, specifically the asteroid size and shape, the velocity and properties of the impacting spacecraft, and the final velocity change imparted to the asteroid. Across >300 three-dimensional simulations varying seven material parameters describing the asteroid, we found many combinations of properties could reproduce a particular asteroid velocity. Additional observations, such as asteroid mass or crater size, are required to further constrain properties like asteroid strength or outcomes like the momentum enhancement provided by impact ejecta. Our results demonstrate the vital importance of having as much knowledge as possible prior to an impact mission, with key material parameters being the asteroid’s mass, porosity, strength, and elastic properties.

Mass-Optimized Gravity Tractor for Asteroid Deflection

A method for asteroid deflection that makes use of a spacecraft moving back and forth on a segment of a Keplerian orbit about the asteroid is studied with the aim of optimizing the initial gross mass of the spacecraft. The corresponding optimization problem is formulated as a discrete nonlinear optimal control problem where the parameters of the orbit segment are the control variables. A hypothetical asteroid deflection problem is solved numerically using the method of dynamic programming, and it is shown that a gravity tractor can be obtained that is significantly more efficient in terms of deflection attained per unit mass of the spacecraft, as compared to similar gravity tractors in the literature. It is further shown using a numerical approach that the results may be applied to a slowly rotating asteroid that is assumed to have an ellipsoidal shape.

DART: Planetary Defense in the Introductory Physics Curriculum

The Double Asteroid Redirection Test (DART) is a National Aeronautics and Space Administration–European Space Agency collaborative mission to test the feasibility of defending Earth from a catastrophic asteroid impact by using a spacecraft to deflect the asteroid away from the planet. Launched on Nov. 23, 2021, the DART spacecraft will intercept the binary asteroid 65803 Didymos in late September or early October 2022, colliding (nearly) head-on to modify its motion measurably.

Reshaping and ejection processes on rubble-pile asteroids from impacts

Context. Most small asteroids (< 50 km in diameter) are the result of the breakup of a larger parent body and are often considered to be rubble-pile objects. Similar structures are expected for the secondaries of small asteroid binaries, including Dimorphos, the smaller component of the 65 803 Didymos binary system and the target of NASA’s Double Asteroid Redirection Test (DART) and ESA’s Hera mission. The DART impact will occur on September 26, 2022, and will alter the orbital period of Dimorphos around Didymos. Aims. In this work we assume Dimorphos-like bodies with a rubble-pile structure and quantify the effects of boulder packing in its interior on the post-impact morphology, degree of shape change, and material ejection processes. Methods. We used the Bern smoothed particle hydrodynamics shock physics code to numerically model hypervelocity impacts on small, 160 m in diameter, rubble-pile asteroids with a variety of boulder distributions. Results. We find that the post-impact target morphology is most sensitive to the mass fraction of boulders comprising the target, while the asteroid deflection efficiency depends on both the mass fraction of boulders on the target and on the boulder size distribution close to the impact point. Our results may also have important implications for the structure of small asteroids.

Shape Modeling of Dimorphos for the Double Asteroid Redirection Test (DART)

The Double Asteroid Redirection Test (DART) is the first planetary defense test mission. It will demonstrate the kinetic impactor technique by intentionally colliding the DART spacecraft with the near-Earth asteroid Dimorphos. The main DART spacecraft is accompanied by the Italian Space Agency Light Italian CubeSat for Imaging of Asteroids (LICIACube). Shape modeling efforts will estimate the volume of Dimorphos and constrain the nature of the impact site. The DART mission uses stereophotoclinometry (SPC) as its primary shape modeling technique. DART is essentially a worst-case scenario for any image-based shape modeling approach because images taken by the camera on board the DART spacecraft, called the Didymos Reconnaissance and Asteroid Camera for Optical navigation (DRACO), possess little stereo and no lighting variation; they simply zoom in on the asteroid. LICIACube images add some stereo, but the images are substantially lower in resolution than the DRACO images. Despite the far-from-optimal imaging conditions, our tests indicate that we can identify the impact site to an accuracy and precision better than 10% the size of the spacecraft core, estimate the volume of Dimorphos to better than 25%, and measure tilts at the impact site over the scale of the spacecraft with an accuracy better than 7°. In short, we will know with excellent accuracy where the DART spacecraft hit, with reasonable knowledge of local tilt, and determine the volume well enough that uncertainties in the density of Dimorphos will be comparable to or dominate the uncertainty in the estimated mass. The tests reported here demonstrate that SPC is a robust technique for shape modeling, even with suboptimal images.

Asteroids and Their Mathematical Methods

In this paper, the basic classification of asteroids and the history and current situation of asteroid exploration are introduced. Furthermore, some recent research progress on the orbital dynamics of asteroids, including models of the gravitational potential field, the dynamics near asteroids, hopping motion on the surface, and bifurcations under varying external parameters, is reviewed. In the meanwhile, the future research development such as the configuration and evolution of binary or triple asteroid systems and near-Earth asteroid defense is briefly discussed.

Heliocentric Effects of the DART Mission on the (65803) Didymos Binary Asteroid System

The Double Asteroid Redirect Test (DART) is NASA’s first kinetic impact–based asteroid deflection mission. The DART spacecraft will act as a projectile during a hypervelocity impact on Dimorphos, the secondary asteroid in the (65803) Didymos binary system, and alter its mutual orbital period. The initial momentum transfer between the DART spacecraft and Dimorphos is enhanced by the ejecta flung off the surface of Dimorphos. This exchange is characterized within the system by the momentum enhancement parameter, β, and on a heliocentric level by its counterpart, β ⊙. The relationship between β and the physical characteristics of Dimorphos is discussed here. A nominal set of Dimorphos physical parameters from the design reference asteroid and impact circumstances from the design reference mission are used to initialize the ejecta particles for dynamical propagation. The results of this propagation are translated into a gradual momentum transfer onto the Didymos system barycenter. A high-quality solar system propagator is then used to produce precise estimates of the post-DART encounters between Didymos and Earth by generating updated close approach maps. Results show that even for an unexpectedly high β ⊙, a collision between the Didymos system and Earth is practically excluded in the foreseeable future. A small but significant difference is found in modeling the overall momentum transfer when individual ejecta particles escape the Didymos system, as opposed to imparting the ejecta momentum as a single impulse at impact. This difference has implications for future asteroid deflection campaigns, especially when it is necessary to steer asteroids away from gravitational keyholes.

Statistical Significance of Mission Parameters on the Deflection Efficiency of Kinetic Impacts: Applications for the Next-generation Kinetic Impactor

Understanding how to deflect an incoming asteroid is of great importance and a focus of research undertaken internationally by the planetary defense community. Deflection of an asteroid by a kinetic impactor is one such mitigation method that has a high degree of technological maturity. In 2022, NASA’s planetary defense mission, the Double Asteroid Redirection Test (DART), will provide the first full-scale technology demonstration of a kinetic impactor. However, the DART mission is just a single test of one kinetic impactor design, prompting the question: Is it possible to optimize the design of a kinetic impactor to make it the most efficient deflector that it can be? In this paper, we use high-fidelity hydrodynamic simulations to examine the effect of five mission parameters (impactor mass, impact velocity, impactor composition, impactor geometry, and target strength) on three observables related to deflection efficiency (crater morphology, ejecta distribution, and momentum transfer) resulting from kinetic impacts. We find that the most significant mission parameters for determining postimpact factors are the impact velocity, impactor mass, and target strength. The impactor geometry and impactor composition emerge as statistically nonsignificant. Overall, we find that the ogive impactor geometry results in the highest variance in predicting the momentum enhancement factor (β), and that generally, impactors with smaller volumes and flat leading edges (plates and rings) produce smaller craters and less ejecta mass compared to impactors with larger volumes and sharper leading edges (spheres, ogives, and cones).