Kinetic Impactor Research Articles

Characterization of the LCROSS impact plume from a ground-based imaging detection

The Lunar CRater Observation and Sensing Satellite (LCROSS) mission was designed to search for evidence of water in a permanently shadowed region near the lunar south pole. An instrumented Shepherding Spacecraft followed a kinetic impactor and provided--from a nadir perspective--the only images of the debris plume. With independent observations of the visible debris plume from a more oblique view, the angles and velocities of the ejecta from this unique cratering experiment are better constrained. Here we report the first visible observations of the LCROSS ejecta plume from Earth, thereby ascertaining the morphology of the plume to contain a minimum of two separate components, placing limits on ejecta velocities at multiple angles, and permitting an independent estimate of the illuminated ejecta mass. Our mass estimate implies that the lunar volatile inventory in the Cabeus permanently shadowed region includes a water concentration of 6.3±1.6% by mass.

Conceptual design of a hypervelocity asteroid intercept vehicle (HAIV) and its flight validation mission

An intercept mission with nuclear explosives is the most effective of the practical mitigation options against the impact threat of near-Earth objects (NEOs) with a short warning time (e.g., much less than 10 years). The existing penetrated subsurface nuclear explosion technology limits the intercept velocity to less than approximately 300m/s. Consequently, an innovative concept of blending a hypervelocity kinetic impactor with a subsurface nuclear explosion has been developed for optimal penetration, fragmentation, and dispersion of the target NEO. A proposed hypervelocity asteroid intercept vehicle (HAIV) consists of a kinetic-impact leader spacecraft and a follower spacecraft carrying nuclear explosives. This paper describes the conceptual development and design of a baseline HAIV system and its flight validation mission architecture for three mission cost classifications (e.g., $500M, $1B, and $1.5B).

Impact Hazard Protection Efficiency by a Small Kinetic Impactor

In this paper the ability of a small kinetic impactor spacecraft to mitigate an Earth-threatening asteroid is assessed by means of a novel measure of efficiency. This measure estimates the probability of a space system to deflect a single randomly generated Earth-impacting object to a safe distance from the Earth. This represents a measure of efficiency that is not biased by the orbital parameters of a test-case object. A vast number of virtual Earth-impacting scenarios are investigated by homogenously distributing in orbital space a grid of 17,518 Earth-impacting trajectories. The relative frequency of each trajectory is estimated by means Opik’s theory and Bottke’s near-Earth objects model. A design of the entire mitigation mission is performed and the largest deflected asteroid computed for each impacting trajectory. The minimum detectable asteroid can also be estimated by an asteroid survey model. The results show that current technology would likely suffice against discovered airburst and local damage threats, whereas larger space systems would be necessary to reliably tackle impact hazard from larger threats. For example, it is shown that only a 1000 kg kinetic impactor would suffice to mitigate the impact threat of 27.1% of objects posing similar threat than that posed by Apophis.

Scale Size Effect in Momentum Enhancement

When an impactor strikes a body at hypervelocities the momentum transferred to the impacted body is greater than the initial impactor momentum. This effect is due to the crater ejecta, and when the impacted body's mass provides some of the momentum change, the effect is referred to as momentum enhancement. The small amount of data on this question implies that there is a scale effect – that is, as the projectile size increases there is an increase in the imparted momentum beyond that anticipated due to the increase in projectile size. Recently, experimental data was gathered on the increase in momentum caused by crater ejecta when 4.45-cm diameter aluminum spheres struck granite targets. The amount of momentum enhancement (characterized by the ratio β) was greater than 2 for 2km/s impacts. Compared with other data at much smaller scale, these tests imply an impactor scale and an impactor density effect for hypervelocity strikes into rock. The implied impactor size scale effect is surprisingly large – to a 0.4 power – and extrapolation indicates that a 1-meter aluminum sphere striking a consolidated rock surface at 10km/s could have a β exceeding 40, supposing the scale size effect does not saturate on the order of 10cm. Such a large momentum enhancement shows that kinetic impactors can be very efficient at deflecting asteroids.

The European Union funded NEOShield project: A global approach to near-Earth object impact threat mitigation

Although discussions are underway within the Action Team 14 of the United Nations COPUOS, there is currently no concerted international plan addressing the impact threat from near-Earth objects (NEOs) and how to organize, prepare and implement mitigation measures. We report on a new international project to address impact hazard mitigation issues, being the subject of a proposal submitted to the European Commission in response to the 2011 FP7 Call “Prevention of impacts from near-Earth objects on our planet”. Our consortium consists of 13 research institutes, universities, and industrial partners from 6 countries and includes leading US and Russian space organizations. The primary aim of the project, NEOShield, is to investigate in detail the three most promising mitigation techniques: the kinetic impactor, blast deflection, and the gravity tractor, and devise feasible demonstration missions. Furthermore, we will investigate options for an international strategy for implementation when an actual impact threat arises.The NEOShield project was formally accepted by the European Commission on 17 November 2011 and funded with a total of 5.8 million Euros for a period of 3.5 years. The kick-off meeting took place at the DLR Institute of Planetary Research, Berlin, in January 2012. In this paper we present a brief overview of the planned scope of the project.

Momentum enhancement from aluminum striking granite and the scale size effect

An unknown in deflecting an asteroid on a collision course with Earth is the quantitative effectiveness of various deflection techniques. For example, when an impactor strikes a body at hypervelocities the momentum transferred to the impacted body is greater than the initial impactor momentum due to the crater ejecta. When the impacted body’s mass provides some of the momentum change, the effect is referred to as momentum enhancement. The small amount of data on this question implies that there is a scale effect – that is, as the projectile size increases there is an increase in the imparted momentum beyond that anticipated due to the increase in projectile size. Recently, experimental data was gathered on the increase in momentum caused by crater ejecta when 4.45-cm diameter aluminum spheres struck granite targets. The amount of momentum enhancement (characterized by the ratio β) was greater than 2 for 2 km/s impacts. Compared with other data at much smaller scale, these tests imply an impactor scale and an impactor density effect for hypervelocity strikes into rock. The implied impactor size scale effect is surprisingly large–to a 0.4 power–and extrapolation indicates that a 1-m aluminum sphere striking a consolidated rock surface at 10 km/s could have a β exceeding 40, though the scale size saturation may be just larger than the tests we performed, which would reduce this value. Such a potentially large momentum enhancement shows that kinetic impactors can be very efficient at deflecting asteroids. Also, the failure strain is shown to depend on the scale size to the −2/3 power.

Physical properties of Near-Earth Objects that inform mitigation

Various methods have been proposed to avoid the collision of a Near-Earth Object (NEO) with the Earth. Each of these methods relies on a mitigation concept (deflection or fragmentation), an energy source (e.g. kinetic, gravitational, solar, thermal, etc.) and a mode of approach (e.g. remote station and interaction). The efficiency of each method depends on the physical properties of the considered NEO that influence the way the body will respond to the considered energy source. While the knowledge of properties such as the mass, spin rate and obliquity as well as the shape is generally required for all mitigation methods, there are other properties that are important to know for some methods and that have no great influence for other ones. This paper summarizes the current knowledge of main physical properties of NEOs and their importance for the most usual mitigation strategies that have been proposed, i.e. the kinetic impactor, the gravity tractor, strategies based on anchoring or depositing material on the surface, and strategies aimed at modifying the thermal properties of the NEO in order to either modify or cancel the Yarkovsky effect, or cause surface vaporization.

NEOShield - A global approach to NEO Impact Threat Mitigation

AbstractNEOShield is a European-Union funded project coordinated by the German Aero-space Center, DLR, to address near-Earth object (NEO) impact hazard mitigation issues. The NEOShield consortium consists of 13 research institutes, universities, and industrial partners from 6 countries and includes leading US and Russian space organizations. The project is funded for a period of 3.5 years from January 2012 with a total of 5.8 million euros. The primary aim of the project is to investigate in detail promising mitigation techniques, such as the kinetic impactor, blast deflection, and the gravity tractor, and devise feasible demonstration missions. Options for an international strategy for implementation when an actual impact threat arises will also be investigated.The NEOShield work plan consists of scientific investigations into the nature of the impact hazard and the physical properties of NEOs, and technical and engineering studies of practical means of deflecting NEOs. There exist many ideas for asteroid deflection techniques, many of which would require considerable scientific and technological development. The emphasis of NEOShield is on techniques that are feasible with current technology, requiring a minimum of research and development work. NEOShield aims to provide detailed designs of feasible mitigation demonstration missions, targeting NEOs of the kind most likely to trigger the first space-based mitigation action.Most of the asteroid deflection techniques proposed to date require physical contact with the threatening object, an example being the kinetic impactor. NEOShield includes research into the mitigation-relevant physical properties of NEOs on the basis of remotely-sensed astronomical data and the results of rendezvous missions, the observational techniques required to efficiently gather mitigation-relevant data on the dynamical state and physical properties of a threatening NEO, and laboratory investigations using gas guns to fire projectiles into asteroid regolith analog materials. The gas-gun investigations enable state-of-the-art numerical models to be verified at small scales. Computer simulations at realistic NEO scales are used to investigate how NEOs with a range of properties would respond to a pulse of energy applied in a deflection attempt. The technical work includes the development of crucial technologies, such as the autonomous guidance of a kinetic impactor to a precise point on the surface of the target, and the detailed design of realistic missions for the purpose of demonstrating the applicability and feasibility of one or more of the techniques investigated. Theoretical work on the blast deflection method of mitigation is designed to probe the circumstances in which this last line of defense may be the only viable option and the issues relating to its deployment. A global response campaign roadmap will be developed based on realistic scenarios presented, for example, by the discovery of an object such as 99942 Apophis or 2011 AG5 on a threatening orbit. The work will include considerations of the timeline of orbit knowledge and impact probability development, reconnaissance observations and fly-by or rendezvous missions, the political decision to mount a mitigation attempt, and the design, development, and launch of the mitigation mission. Collaboration with colleagues outside the NEOShield Consortium involved in complementary activities (e.g. under the auspices of the UN, NASA, or ESA) is being sought in order to establish a broad international strategy.We present a brief overview of the history and planned scope of the project, and progress made to date.The NEOShield project (http://www.neoshield.net) has received funding from the European Union Seventh Framework Program (FP7/2007-2013) under Grant Agreement no. 282703.

AIDA: Asteroid Impact and Deflection Assessment

AbstractAIDA (Asteroid Impact and Deflection Assessment) is a project of a joint mission demonstration of asteroid deflection and characterisation of the kinetic impact effects. It involves the Johns Hopkins Applied Physics Laboratory (with support from members of NASA centers including Goddard Space Flight Center, Johnson Space Center, and the Jet Propulsion Laboratory), and the European Space Agency (with support from members of the french CNRS/Cte dAzur Observatory and the german DLR). This assessment will be done using a binary asteroid target. AIDA consists of two independent but mutually supporting mission concepts, one of which is the asteroid kinetic impactor and the other is the characterisation spacecraft. The objective and status of the project will be presented.

Earth-Impact Modeling and Analysis of a Near-Earth Object Fragmented and Dispersed by Nuclear Subsurface Explosions

Although various technologies, including nuclear explosions, kinetic impactors, and slow- pull gravity tractors, have been proposed for mitigating the impact threat of near-Earth objects (NEOs), there is no consensus on how to reliably deflect or disrupt such hazardous NEOs in a timely manner. This paper describes the orbital dispersion modeling, analysis, and simulation of an NEO fragmented and dispersed by nuclear subsurface explosions. It is shown that various fundamental approaches of Keplerian orbital dynamics can be effectively employed for the orbital dispersion analysis of fragmented NEOs. This paper also shows that, under certain conditions, proper disruption using a nuclear subsurface explosion with shallow burial is a feasible strategy, providing considerable impact damage reduction if all other approaches fail.

An Overview of the Lunar Crater Observation and Sensing Satellite (LCROSS)

The Lunar Crater Observation Sensing Satellite (LCROSS), an accompanying payload to the Lunar Reconnaissance Orbiter (LRO) mission (Vondrak et al. 2010), was launched with LRO on 18 June 2009. The principle goal of the LCROSS mission was to shed light on the nature of the materials contained within permanently shadowed lunar craters. These Permanently Shadowed Regions (PSRs) are of considerable interest due to the very low temperatures, <120 K, found within the shadowed regions (Paige et al. 2010a, 2010b) and the possibility of accumulated, cold-trapped volatiles contained therein. Two previous lunar missions, Clementine and Lunar Prospector, have made measurements that indicate the possibility of water ice associated with these PSRs. LCROSS used the spent LRO Earth-lunar transfer rocket stage, an Atlas V Centaur upper stage, as a kinetic impactor, impacting a PSR on 9 October 2009 and throwing ejecta up into sunlight where it was observed. This impactor was guided to its target by a Shepherding Spacecraft (SSC) which also contained a number of instruments that observed the lunar impact. A campaign of terrestrial ground, Earth orbital and lunar orbital assets were also coordinated to observe the impact and subsequent crater and ejecta blanket. After observing the Centaur impact, the SSC became an impactor itself. The principal measurement goals of the LCROSS mission were to establish the form and concentration of the hydrogen-bearing material observed by Lunar Prospector, characterization of regolith within a PSR (including composition and physical properties), and the characterization of the perturbation to the lunar exosphere caused by the impact itself.

Mitigation of asteroid impact threats

Although large asteroids and comets have impacted the Earth in the past, we do not want large ones to impact us in the future. Can we prevent this from happening? A considerable amount of work continues to be done in detecting asteroids that may pass near the Earth, but solving the engineering problem of how to actually conduct a mission to deflect an asteroid is still in its infancy. Of the many ways considered to deflect an asteroid, the methods currently in favor fall into three categories: (1) kinetic impactor, (2) nuclear standoff explosion, and (3) gravitational tractor. Other techniques such as landing machinery on the asteroid and shooting off material (mass driver), or parking a giant minor near the asteroid and focusing the sunlight on it to ablate material, are not strongly in favor at this time.

Multicriteria Comparison Among Several Mitigation Strategies for Dangerous Near-Earth Objects

In this paper a comparative assessment of the effectiveness of different deviation methods for Near Earth Objects is presented. Specifically, solar collector, nuclear interceptor, kinetic impactor, low-thrust propulsion, mass driver and gravity tug are modelled and compared. For each method, a mathematical model is developed in order to compute the achievable deviation. A multi-criteria optmization method is then used to construct the set of Pareto optimal solutions, minimizing the mass of the spacecraft at departure from the Earth and the warning time, i.e., the time from launch to the foreseen impact of the asteroid with the Earth, while at the same time maximizing the deviation. A dominance criterion is defined and used to compare all the Pareto sets for all the various mitigation strategies. Finally a Technology Readiness Level factor is associated to each strategy in order to estimate the required technological development.

Dynamics and Control of Gravity Tractor Spacecraft for Asteroid Deflection

Multiple gravity tractors in halo orbits and a hovering solar sail gravity tractor are proposed as an option for deflecting a certain class of near-Earth asteroids that may not require high-energy deflection techniques employing nuclear explosions or kinetic impactors. This paper presents the preliminary dynamic modeling and control analysis of such variants of the gravity tractor for examining their practical viability as applied to asteroid Apophis; however, detailed system-level tradeoffs are not treated in this paper. A system of orbiting multiple gravity tractors has many advantages over the hovering gravity tractor. They include'its larger total ΔV capability, multispacecraft redundancy, and mission design flexibility with smaller satellites equipped with lower-risk propulsion systems. A solar sail gravity tractor concept exploits the propellantless nature of solar reflectors despite its inherent drawback of requiring a particular hovering position with a 55-deg offset angle from the target asteroid's flight direction.

Performance Evaluation of the Sampling Head and Annular Kinetic Impactor in the Savannah River Site Alpha Continuous Air Monitor

ABSTRACT This paper describes evaluation and testing of the Savannah River Site (SRS) impactor-type alpha continuous air monitor (CAM) to determine the particle delivery and collection efficiency in the device using fluorescence-labeled, polystyrene latex spheres and liquid droplet aerosols. Particle sampling efficiency through the dome-shape sampling inlet for particles with aerodynamic diameters of 6.2 and 10 μm was 98% at 20 cfm (566 L/min), 90% at 32 cfm (906 L/min), and 87% at 40 cfm (1132 L/min) sampling flow rates. Internal delivery efficiency through the CAM was > 94% at 20 and 32 cfm for 0.5-, 1.1-, 2.2-, and 3.2-μm particles and > 90% for 6.2-μm particles. For 10-μm particles, the internal delivery efficiency was 91% at 20 cfm and decreased to 83% at 32 cfm and 77% at 40 cfm. The 50% cutoff aerodynamic diameter for the impactor was 3.2 μm at 20 cfm, 2.6 μm at 32 cfm, and 2.3 μm at 40 cfm. For a typical radioactive aerosol in the workplace (activity median aerodynamic diameter of 5 μm with a geometric standard deviation of 2), these cutoff diameters provide collection efficiencies of 74% at 20 cfm, 83% at 32 cfm, and 87% at 40 cfm. The normal grease layer of 1.5 mg that is routinely applied to the planchet of the SRS CAM was adequate to quantitatively retain all collected particles with diameters of 3.2 μm or less at flow rates of 20, 32, and 40 cfm. For particle sizes of 6.2 and 10 μm, approximately 80–85% of the particles were retained on the impactor planchet and 15–20% were re-entrained into the exhaust airstream due to particle bounce. The delivery and collection efficiencies in the SRS CAM can be combined to give overall efficiencies for detection of airborne actinide aerosols as a function of particle size. For 6.2 and 10 μm aerodynamic diameter particles, the total collection efficiency of the SRS CAM at 20, 32, and 40 cfm exceeds the conservative assumption of 50% efficiency for plutonium particle collection that has been traditionally used at SRS.

Performance Evaluation of the Sampling Head and Annular Kinetic Impactor in the Savannah River Site Alpha Continuous Air Monitor

Performance Evaluation of the Sampling Head and Annular Kinetic Impactor in the Savannah River Site Alpha Continuous Air Monitor