Planetary Defense Research Articles

The 59th Colloquium on the Law of Outer Space at the 67th International Astronautical Congress

The 59th International Institute of Space Law (IISL) Colloquium on the Law of Outer Space was held from 27–30 September 2016 in Guadalajara, Mexico, in conjunction with the 67th International Astronautical Congress (IAC). Comprised of seven technical sessions and one session for interactive presentations, the Colloquium focused on a range of thematic issues in space law, and featured papers from almost seventy presenters. Topics discussed included the legal aspects related to the remote sensing principles, regional cooperation and Latin American space activities, large satellite constellations, space resource utilization, planetary defence, and spectrum management. The 8th Nandasiri Jasentuliyana Keynote Lecture was delivered by incoming IISL president Kai-Uwe Schrogl, entitled ‘Space Law and Diplomacy’. The Manfred Lachs Space Law Moot Court semi-finals and world finals were also held in Guadalajara, as well the General Assembly of the IISL.

Study on Trajectory Optimization Method of Spacecraft as an Impactor for Asteroid Deflection Exploiting Impact Geometry Analysis

Study on Trajectory Optimization Method of Spacecraft as an Impactor for Asteroid Deflection Exploiting Impact Geometry Analysis

Calculating the momentum enhancement factor for asteroid deflection studies

The possibility of kinetic-impact deflection of threatening near-Earth asteroids will be tested for the first time in the proposed AIDA (Asteroid Impact Deflection Assessment) mission, involving NASAs DART (Double Asteroid Redirection Test). The impact of the DART spacecraft onto the secondary of the binary asteroid 65803 Didymos at a speed of 5 to 7 km/s is expected to alter the mutual orbit by an observable amount. The velocity transferred to the secondary depends largely on the momentum enhancement factor, typically referred to as beta. We use two hydrocodes developed at Los Alamos, RAGE and PAGOSA, to calculate an approximate value for beta in laboratory-scale benchmark experiments. Convergence studies comparing the two codes show the importance of mesh size in estimating this crucial parameter.

Modeling impact outcomes for the Double Asteroid Redirection Test (DART) mission

The Double Asteroid Redirection Test (DART) is a NASA mission concept currently in Phase-A study, which will provide the first full-scale test of a kinetic impactor deflection mission for planetary defense. The DART spacecraft will target the moon of Didymos (Didymos-B, or “Didymoon”) and impact the smaller body at ~6 km/s with ~500 kg mass. The change in orbital period of the moon will then be measured using ground-based observations, which can be used to estimate the momentum enhancement of the moon from the impact. Impact modeling provides a basis for interpretation of the DART impact and observations (including the calculation of the momentum enhancement, β, the period change, and ejecta mass for a given impact scenario). Here, we present results from simulations using the shock physics codes CTH and Spheral of a DART-like impact into an asteroid target. Variations in target composition and porosity are simulated to examine their effect on β. A variety of methods are used to calculate β, and these simulations suggest that β can be calculated using any of them, depending on what type of simulation is performed, and provide consistent results. The results also indicate that varying the target composition (e.g., whether the target is made up of something granite-like or more akin to basalt or pumice) does not significantly affect the results. More significant changes are seen when parameters such as porosity are varied: increased porosity decreases β, alters the crater shape, and increases ∆v. Simulations also suggest that the form of porosity is important: macro-porosity has a significant effect on the cratering process that is different than equivalent micro-porosity.

THERMAL TOMOGRAPHY OF ASTEROID SURFACE STRUCTURE

ABSTRACT Knowledge of the surface thermal inertia of an asteroid can provide insight into its surface structure: porous material has a lower thermal inertia than rock. We develop a means to estimate thermal inertia values of asteroids and use it to show that thermal inertia appears to increase with spin period in the case of main-belt asteroids (MBAs). Similar behavior is found on the basis of thermophysical modeling for near-Earth objects (NEOs). We interpret our results in terms of rapidly increasing material density and thermal conductivity with depth, and provide evidence that thermal inertia increases by factors of 10 (MBAs) to 20 (NEOs) within a depth of just 10 cm. Our results are consistent with a very general picture of rapidly changing material properties in the topmost regolith layers of asteroids and have important implications for calculations of the Yarkovsky effect, including its perturbation of the orbits of potentially hazardous objects and those of asteroid family members after the break-up event. Evidence of a rapid increase of thermal inertia with depth is also an important result for studies of the ejecta-enhanced momentum transfer of impacting vehicles (“kinetic impactors”) in planetary defense.

Solar-Sail Trajectory Design for a Multiple Near-Earth-Asteroid Rendezvous Mission

The scientific interest for near-Earth asteroids as well as the interest in potentially hazardous asteroids from the perspective of planetary defense led the space community to focus on near-Earth asteroid mission studies. A multiple near-Earth asteroid rendezvous mission with close-up observations of several objects can help to improve the characterization of these asteroids. This work explores the design of a solar-sail spacecraft for such a mission, focusing on the search of possible sequences of encounters and the trajectory optimization. This is done in two sequential steps: a sequence search by means of a simplified trajectory model and a set of heuristic rules based on astrodynamics, and a subsequent optimization phase. A shape-based approach for solar sailing has been developed and is used for the first phase. The effectiveness of the proposed approach is demonstrated through a fully optimized multiple near-Earth asteroid rendezvous mission. The results show that it is possible to visit five near-Earth asteroids within 10 years with near-term solar-sail technology.

Distributed integrated navigation systems for planetary defense against asteroids

The main objectives of this paper are to give an interdisciplinary overview of the current status of the research on planetary defense against asteroids, which is a real challenge, and consider technical proposals on the development of a multilevel planetary defense system based on modern space technologies, providing for the application of projectile asteroids to deflect target asteroids’ trajectories and distributed integrated navigation systems, the navigation equipment of which is supposed to be installed on many different objects. The composition of such navigation systems and their accuracies are discussed. This work is based on the results obtained by the international Research Laboratory of Space Research, Technologies, Systems and Processes [1], founded at Moscow Institute of Electronics and Mathematics (MIEM), Branch of Higher School of Economics (HSE) in 2011. The project was supported by the grant of the Government of the Russian Federation (2011–2013) [2, 3]. We have also used pioneering ideas from the course of lectures Models of planetary defense [4], prepared at the Department of Mechanics and Mathematical Modeling, MIEM NRU HSE in 2014 [4].

Implementation of a Systems Engineering Approach to the Management of a Planetary Defense Team Project in an Intensive Space Studies Program Using IPPD

AbstractPlanetary Defense is an important and challenging topic, and long‐term mitigation of asteroid impacts have been discussed by governments and space agencies; however, short‐term solutions of comet impacts are rarely considered. 34 participants from 17 countries tackled this problem, a comet impact two years after detection, at the 2015‐Space Studies Program and produced the Roadmap for EArth Defense Initiatives (READI). The Integrated Product and Process Development (IPPD) methodology was used to identify the mission statement, define requirements and needs, and provide possible solutions. This paper concentrates on how the IPPD was applied as a systems approach to each phase of our project, where the whole system was Planetary Defense, and its architectural decomposition was divided into five key elements: detection and tracking, deflection techniques, global collaboration, outreach and education, and evacuation and recovery. The importance of applying human factor concepts throughout the project is addressed through challenges faced, solutions applied, and lessons learned. Verification and validation of selected options are presented, along with the use of various project management tools. Furthermore, we discuss our results and recommendations for Planetary Defense, as they are products of our analysis using the IPPD approach to systems engineering.

The NEOTωIST mission (Near-Earth Object Transfer of angular momentum spin test)

We present a concept for a kinetic impactor demonstration mission, which intends to change the spin rate of a previously-visited asteroid, in this case 25143 Itokawa. The mission would determine the efficiency of momentum transfer during an impact, and help mature the technology required for a kinetic impactor mission, both of which are important precursors for a future space mission to deflect an asteroid by collisional means in an emergency situation. Most demonstration mission concepts to date are based on changing an asteroid's heliocentric orbit and require a reconnaissance spacecraft to measure the very small orbital perturbation due to the impact. Our concept is a low-cost alternative, requiring only a single launch.Taking Itokawa as an example, an estimate of the order of magnitude of the change in the spin period, δP, with such a mission results in δP of ~4min (0.5%), which could be detectable by Earth-based observatories.Our preliminary study found that a mission concept in which an impactor produces a change in an asteroid's spin rate could provide valuable information for the assessment of the viability of the kinetic-impactor asteroid deflection concept. Furthermore, the data gained from the mission would be of great benefit for our understanding of the collisional evolution of asteroids and the physics behind crater and ejecta-cloud development.

Directed energy missions for planetary defense

Directed energy for planetary defense is now a viable option and is superior in many ways to other proposed technologies, being able to defend the Earth against all known threats. This paper presents basic ideas behind a directed energy planetary defense system that utilizes laser ablation of an asteroid to impart a deflecting force on the target. A conceptual philosophy called DE-STAR, which stands for Directed Energy System for Targeting of Asteroids and exploration, is an orbiting stand-off system, which has been described in other papers. This paper describes a smaller, stand-on system known as DE-STARLITE as a reduced-scale version of DE-STAR. Both share the same basic heritage of a directed energy array that heats the surface of the target to the point of high surface vapor pressure that causes significant mass ejection thus forming an ejection plume of material from the target that acts as a rocket to deflect the object. This is generally classified as laser ablation. DE-STARLITE uses conventional propellant for launch to LEO and then ion engines to propel the spacecraft from LEO to the near-Earth asteroid (NEA). During laser ablation, the asteroid itself provides the propellant source material; thus a very modest spacecraft can deflect an asteroid much larger than would be possible with a system of similar mission mass using ion beam deflection (IBD) or a gravity tractor. DE-STARLITE is capable of deflecting an Apophis-class (325m diameter) asteroid with a 1- to 15-year targeting time (laser on time) depending on the system design. The mission fits within the rough mission parameters of the Asteroid Redirect Mission (ARM) program in terms of mass and size. DE-STARLITE also has much greater capability for planetary defense than current proposals and is readily scalable to match the threat. It can deflect all known threats with sufficient warning.

Dynamics of a Tether System Connected to an Irregularly Shaped Celestial Body

The problem of pendular oscillations of a tether attached to an irregularly shaped celestial body is studied in this paper. The dynamic analysis of the system is performed by examining the phase plane trajectories. The effect of the tether length as well as the higher order terms in the gravitational potential of the celestial body on the tether dynamics is investigated. It is demonstrated that consideration of the finite size of the celestial body can have significant effects on the tether dynamics, while the effect of the asphericity of the celestial body on the tether dynamics is negligible. This study is of practical relevance for asteroid deflection using tethers, as well as for the development of space elevators on small planets/moons.

Effect of the finite size of an asteroid on its deflection using a tether–ballast system

Potentially hazardous near-Earth objects which can impose a significant threat on life on the planet have generated a lot of interest in the study of various asteroid deflection strategies. There are numerous asteroid deflection techniques suggested and discussed in the literature. This paper is focused on one of the non-destructive asteroid deflection strategies by attaching a long tether–ballast system to the asteroid. In the existing literature on this technique, very simplified models of the asteroid-tether–ballast system including a point mass model of the asteroid have been used. In this paper, the dynamical effect of using a finite size asteroid model on the asteroid deflection achieved is analyzed in detail. It has been shown that considering the finite size of the asteroid, instead of the point mass approximation, can have significant influence on the deflection predicted. Furthermore the effect of the tether-deployment stage, which is an essential part of any realistic asteroid deflection mission, on the predicted deflection is studied in this paper. Finally the effect of cutting the tether on the deflection achieved is analyzed and it has been shown that depending on the orbital properties of the asteroid as well as its size and rotational rate, cutting the tether at an appropriate time can increase the deflection achieved. Several numerical examples have been used in this paper to elaborate on the proposed technique and to quantitatively analyze the effect of different parameters on the asteroid deflection.

Second-order variational equations forN-body simulations

First-order variational equations are widely used in N-body simulations to study how nearby trajectories diverge from one another. These allow for efficient and reliable determinations of chaos indicators such as the Maximal Lyapunov characteristic Exponent (MLE) and the Mean Exponential Growth factor of Nearby Orbits (MEGNO). In this paper we lay out the theoretical framework to extend the idea of variational equations to higher order. We explicitly derive the differential equations that govern the evolution of second-order variations in the N-body problem. Going to second order opens the door to new applications, including optimization algorithms that require the first and second derivatives of the solution, like the classical Newton's method. Typically, these methods have faster convergence rates than derivative-free methods. Derivatives are also required for Riemann manifold Langevin and Hamiltonian Monte Carlo methods which provide significantly shorter correlation times than standard methods. Such improved optimization methods can be applied to anything from radial-velocity/transit-timing-variation fitting to spacecraft trajectory optimization to asteroid deflection. We provide an implementation of first- and second-order variational equations for the publicly available rebound integrator package. Our implementation allows the simultaneous integration of any number of first- and second-order variational equations with the high-accuracy IAS15 integrator. We also provide routines to generate consistent and accurate initial conditions without the need for finite differencing.

Impact risk assessment and planetary defense mission planning for asteroid 2015 PDC

In this paper, an integrated utilization of analytic keyhole theory, B-plane mapping, and planetary encounter geometry, augmented by direct numerical simulation, is shown to be useful in determining the impact risk of an asteroid with the Earth on a given encounter, as well on potential future encounters via keyhole passages. The accurate estimation of the impact probability of hazardous asteroids is extremely important for planetary defense mission planning. Asteroids in Earth resonant orbits are particularly troublesome because of the continuous threat they pose in the future. Based on the trajectories of the asteroid and the Earth, feasible mission trajectories can be found to mitigate the impact threat of hazardous asteroids. In order to try to ensure mission success, trajectories are judged based on initial and final mission design parameters that would make the mission easier to complete. Given the potential of a short-warning time scenario, a disruption mission considered in this paper occurs approximately one year prior to the anticipated impact date. Expanding upon the established theory, a computational method is developed to estimate the impact probability of the hazardous asteroid, in order to assess the likelihood of an event, and then investigate the fragmentation of the asteroid due to a disruption mission and analyze its effects on the current and future encounters of the fragments with Earth. A fictional asteroid, designated as 2015 PDC – created as an example asteroid risk exercise for the 2015 Planetary Defence Conference, is used as a reference target asteroid to demonstrate the effectiveness and applicability of computational tools being developed for impact risk assessment and planetary defense mission planning for a hazardous asteroid or comet.

Electric Solar Wind Sail Kinetic Energy Impactor for Asteroid Deflection Missions

An electric solar wind sail uses the natural solar wind stream to produce low but continuous thrust by interacting with a number of long thin charged tethers. It allows a spacecraft to generate a thrust without consuming any reaction mass. The aim of this paper is to investigate the use of a spacecraft with such a propulsion system to deflect an asteroid with a high relative velocity away from an Earth collision trajectory. To this end, we formulate a simulation model for the electric solar wind sail. By summing thrust vectors exerted on each tether, a dynamic model which gives the relation between the thrust and sail attitude is proposed. Orbital maneuvering by fixing the sail’s attitude and changing tether voltage is considered. A detailed study of the deflection of fictional asteroids, which are assumed to be identified 15 years before Earth impact, is also presented. Assuming a spacecraft characteristic acceleration of 0.5 mm/s 2, and a projectile mass of 1,000 kg, we show that the trajectory of asteroids with one million tons can be changed enough to avoid a collision with the Earth. Finally, the effectiveness of using this method of propulsion in an asteroid deflection mission is evaluated in comparison with using flat photonic solar sails.

Nuclear cycler: An incremental approach to the deflection of asteroids

This paper introduces a novel deflection approach based on nuclear explosions: the nuclear cycler. The idea is to combine the effectiveness of nuclear explosions with the controllability and redundancy offered by slow push methods within an incremental deflection strategy. The paper will present an extended model for single nuclear stand-off explosions in the proximity of elongated ellipsoidal asteroids, and a family of natural formation orbits that allows the spacecraft to deploy multiple bombs while being shielded by the asteroid during the detonation.

A 3 Point Action Agenda to Address Cosmic Hazards and Planetary Defense

ABSTRACT The IAASS and the JSSE gives its prime focus to astronaut safety and safe space transport, but one of its important areas of concern is that of cosmic hazards and planetary. This is a significant area because strategies for planetary defense could involve the safety of millions if not billions of people. This article addresses the latest information as to the nature of significant areas of cosmic risks, gaps in our knowledge, and an agenda for research to further planetary in future years. U.K. Royal Astronomer, Sir Martin Rees has noted: “Throughout its history, the Earth has been impacted by asteroids and comets and buffeted by solar flares. But the consequences of these natural phenomena are more catastrophic today, because the infrastructure on which our civilization depends is more elaborate and more vulnerable… …we have instruments, both on the ground and in space, that can give us forewarning of threatening flares and impacts. We are learning how to make our systems more robust and resilient. Moreover, we will not remain helpless in the face of these threats because we are empowered by advancing technology and engineering.” (Rees) But despite this quite hopeful statement by the U.K. Royal Astronomer, the truth is that there are many severe planetary risks ahead. Current space agency agendas, space instrumentation, changes to the earth’s magnetosphere, and research programs are, in fact, not fully responsive to the needs of a truly effective planetary defense. (Pelton and Allahdadi) This article sets forth some of the greatest lacks in current space programs and notes new or revised efforts that could better prepare our small six sextillion metric ton planet from cosmic dangers. Currently there are several cosmic concerns. These include asteroid and comet strikes from Near Earth Objects, solar flares and coronal mass ejections, and the build-up of orbital space debris that could endanger the safe launch of critical space infrastructure over the longer term future. This article focuses on potentially hazardous comets and asteroids and severe solar storms.

Autonomous Onboard Point Source Detection by Small Exploration Spacecraft

Small spacecraft platforms are a promising low-cost approach to accelerate exploration of small bodies, addressing the space community’s interest in origin science, planetary resources, and planetary defense. However, they can be challenging platforms for detecting and imaging low brightness targets. Difficulties include constrained bandwidth, which limits the volume of data that can be downlinked; attitude instability, which limits exposure time; small instrument apertures, which reduce sensitivity; and cosmic ray contamination, which creates illusory sources. Mission designers can address all these problems simultaneously by shifting image analysis across the communications gap. Spacecraft can use onboard data analysis to detect sources directly, or downlink parsimonious summary products for detection on the ground. One promising approach is to acquire stacks of short consecutive exposures, and then coregister and coadd them onboard. This work analyzes a coaddition algorithm that is designed to be robust against small spacecraft challenges. We evaluate factors affecting performance, such as attitude control and camera noise systematics, in regimes typical of small spacecraft missions. We motivate the algorithm design by considering its application to NEAScout, a mission representing a new generation of small (sub-50 kg) exploration spacecraft having very small instrument apertures and data rates below 1 kbyte s-1. Here, onboard analysis allows detection and rendezvous with far smaller and fainter objects, dramatically reducing the cost and complexity of primitive bodies exploration.

A New Vision for Fusion Energy Research: Fusion Rocket Engines for Planetary Defense

Abstract We argue that it is essential for the fusion energy program to identify an imagination-capturing critical mission by developing a unique product which could command the marketplace. We lay out the logic that this product is a fusion rocket engine, to enable a rapid response capable of deflecting an incoming comet, to prevent its impact on the planet Earth, in defense of our population, infrastructure, and civilization. As a side benefit, deep space solar system exploration, with greater speed and orders-of-magnitude greater payload mass would also be possible.

Mission analysis for the ion beam deflection of fictitious asteroid 2015 PDC

Based on a hypothetical asteroid impact scenario proposed during the 2015 IAA Planetary Defense Conference (PDC), we study the deflection of fictitious asteroid 2015 PDC starting from ephemeris data provided by the conference organizers. A realistic mission scenario is investigated that makes use of an ion beam shepherd spacecraft as a primary deflection technique. The article deals with the design of a low-thrust rendezvous trajectory to the asteroid, the estimation of the propagated covariance ellipsoid and the outcome of an ion beam slow-push deflection starting from three worst case scenarios (impacts in New Delhi, Dhaka and Tehran). Displacing the impact point towards an extremely low-populated, easy-to-evacuate region, as opposed to full deflection, is found to be a more effective mitigation approach. Mission design, technical and political aspects are discussed.