MITM11
Session assets
Introduction: Kinetic impact deflection is one of the strategies for addressing the threat of near-Earth small body impacts. The DART mission has confirmed the effectiveness of deflection and demonstrated the generation and morphological evolution of ejecta. However, what happens to the remaining asteroid shortly after the impact remains a blind spot for in-situ detection. The propagation of residual kinetic energy within the remaining rubble-pile asteroid, and the possible internal structural damage, are crucial for understanding the subsequent evolution of the remaining asteroid. Using a proof-of-principle numerical model, we simulated the response within rubble-pile asteroids to residual impacts and found that the propagation strongly depends on the inherent internal stress chains. Such chains occur in three- and two-dimensional aggregates and we mainly study this phenomenon in 2D.
Methods: We first establish the 2D granular aggregate model and show the existence of initial stress chains based on the particle-scale stress tensor calculation1–3. Velocity perturbations are applied in the form of pulses to particles in strong stress chains or weak stress regions, and then we observe the propagation of particle speeds, normal and shear stresses, and contact failure events. The dependences of propagation patterns on the magnitude and direction of perturbation velocity, the location of perturbed particles, and the particle size distribution of aggregates are investigated. All the numerical simulations are employed using discrete element code DEMBody4–6.
Results: In bi-disperse granular aggregates (Fig. 1a), we observed that particle speed response preferentially propagates along the initial (pre-impact) stress chains than in the direction of perturbation velocity (Fig. 1b). The dynamic normal and shear stresses propagate faster and are higher along the inherent stress chain structure (Fig.1c). According to the probability scatter map in Fig.1d, particles under high dynamic shear stress are highly likely to have initially high stress levels, which means that they belong to initial stress chain structures. The heterogeneity of the initial stress chain structure causes anisotropy in the propagation of impact responses, as demonstrated by the D (it characterizes the mean propagating distance of particle speed response) evolution in the 8 sectors around disturbed particle I (Fig. 2).
Figure 1. (a) Initial stress distribution of the bi-disperse aggregate. Particles are colored by the trace of stress tensor Tr(σ0) and the negative sign means the compressed state. The redder the color, the larger the stress. Yellow circles and arrows denote the disturbed particles and directions of perturbation velocities respectively. (b) The particle speed (blue-red) at τ=6.6×10-4 superpose on the initial stress Tr(σ0) in grey. Particles with u≤0.01 are invisible. (c) The post-impact particle stress trace Tr(σ). (d) The bi-variate probability scatter map in the ε-ζ plane at τ=6.6×10-4. ε=Tr(σ0)-Tr(σ0)med and ζ=σ12-σ12med with (•)med denoting the median value. All the quantities are non-dimensional.
Figure 2. (a) A zoom on Tr(σ0) around the location I, with the region divided into 8 sectors. (b) The evolution of D in the 8 sectors under impact perturbation b. All the quantities are presented in dimensionless form.
We also noticed that sliding and rolling failure events frequently occur in weak stress particles that are in contact with particles in the initial stress chains (Fig. 3a and 3b). When the magnitude of the perturbation velocity is large, the preference for response propagation remains unchanged, but particles near the disturbed particle exhibit significant displacement, and the particles scattered by the impact (coordinate number = 0) are predominantly distributed in the cavities formed by the initial stress chain structure (Fig. 3c).
Figure 3. Impact perturbation is applied on particle II along the direction d, as shown in Fig. 1a. (a) Particles that undergo sliding failure (yellow) superpose on the initial stress chains. uimpact=1.0, τ=6.6×10-3. (b) Particles that undergo rolling failure (green). The same condition and moment as panel (a). (c) Particles with coordinate number = 0 (red). uimpact=100.0, τ=6.6×10-3.
Impact perturbation simulations conducted in bi-disperse aggregates with surface boulders and power-law-distribution aggregates exhibit the same response propagation patterns. All the quantities are presented in dimensionless form.
Conclusion and Discussion: To conclude, the response to impact perturbations propagates preferentially along the initial stress chains, which bear the majority of the load induced by the residual impact kinetic energy. It suggests the impact disturbance may travel further than expected along these invisible paths, rather than dissipated uniformly in all directions from the impact crater. Particles in the weak stress regions enclosed by the initial stress chains are more easily scattered by impacts. Downstream of this work, we will focus on the extent and patterns of structural damage in the remaining rubble-pile asteroids and their dependency on impact perturbations.
Acknowledgments: C.H. is grateful for the hospitality of Imperial College London, where this work was carried out. C.H. is supported by the international joint doctoral education fund of Beihang University. Y.Y. acknowledges the financial support provided by the National Natural Science Foundation of China Grants No. 12272018.
Reference:
1. Ball, R. C. & Blumenfeld, R. Stress Field in Granular Systems: Loop Forces and Potential Formulation. Phys. Rev. Lett. 88, 115505 (2002).
2. Blumenfeld, R. Stresses in Isostatic Granular Systems and Emergence of Force Chains. Phys. Rev. Lett. 93, 108301 (2004).
3. Nicot, F., Hadda, N., Guessasma, M., Fortin, J. & Millet, O. On the definition of the stress tensor in granular media. Int. J. Solids Struct. 50, 2508–2517 (2013).
4. Cheng, B., Yu, Y. & Baoyin, H. Collision-based understanding of the force law in granular impact dynamics. Phys. Rev. E 98, 012901 (2018).
5. Cheng, B., Yu, Y. & Baoyin, H. Numerical simulations of the controlled motion of a hopping asteroid lander on the regolith surface. Mon. Not. R. Astron. Soc. 485, 3088–3096 (2019).
6. Cheng, B. et al. Reconstructing the formation history of top-shaped asteroids from the surface boulder distribution. Nat. Astron. 5, 134–138 (2021).
How to cite: Huang, C., Yu, Y., Cheng, B., King, P., and Blumenfeld, R.: Structure-dependent impact response propagation in residual rubble-pile asteroids after ejecta, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-431, https://doi.org/10.5194/epsc2024-431, 2024.
The NASA DART mission impacted the asteroid Dimorphos, the satellite of the asteroid Didymos, at 23:14 UTC on September 26, 2022, as a planetary defense test. This marked the first hypervelocity impact experiment on an asteroid relevant to planetary defense. The Italian Space Agency's LICIACube captured crucial imagery before and after the impact, aiding in studying the ejecta's distribution in inertial space. The data returned by LUKE camera aboard LICIACube thus enabled the characterisation of the orientation and geometry of resultant ejecta [1,2,3], which are closely related to the calculation of how effective the impact has been in imparting momentum to the asteroid (parameter β) [4].
LUKE images acquired at different vantage points with respect to the ejecta, allowed the characterisation of the global ejecta structured in the aforementioned studies, by approximating it to a hollow cone. Nevertheless, the real structure of the ejecta is intricate and contains complex structures. Given the availability of LUKE images, we attempt to recover the three-dimensional structure of the ejecta by coregistering them to a Dimorphos-centred coordinate system. We trace two-dimensional ejecta shapes [5] as projected onto LUKE images and then place these 2D shapes (scaled with distance) along LUKE boresight at different distances to create depth so that we capture all the possible theoretical planes where different parts of ejecta structure could reside (Figure 1). Once we obtain such 3D profiles for four different images obtained at various vantage points, we intersect them in an inertial J2000 space. The material common to all the intersections then provides us with a three dimensional structure that is compatible with the images used as input to trace two dimensional profiles on the LUKE images. Then, we bring the resulting structure back to LUKE image space and visualise them with the original images to see how they compare.
Fig.1. Top panel: Left: A perspective view of the three dimensional profile of the ejecta structure recovered using 3 scaled planes (image acquired at '2022-09-26T23:17:03.004' UTC) placed at the location of LICIACube, at the centre of Dimorphos and away from Dimorphos in the same line of sight between LICIACube and Dimorphos. Right: Planes removed to highlight the ejecta structure. Bottom pane: The same for the image acquired at '2022-09-26T23:17:18.000' UTC.
In this way we’re able to validate the three dimensional model we obtained by intersecting three dimensional profiles derived from LUKE images. In order to check its accuracy, the model will be cross-checked against the solutions of Deshapriya et al., 2023 and Hirabayashi et al., 2024 which are compatible with each other. The model will later be refined to remove any resulting artifacts. The result of this work will allow us to understand the three dimensional distribution of ejecta material in inertial space and hence will help constrain models of ejecta propagation following planetary impacts.
Acknowledgments: This research was funded by the Italian National Astrophysical Institute (INAF) - Call for Fundamental Research 2022. The LICIACube team acknowledges financial support from Agenzia Spaziale Italiana (ASI, contract No. 2019-31-HH.0 CUP F84I190012600).
References
[1] Dotto et al., Nature, 627, pages 505–509 (2024)
[2] Hirabayashi et al., submitted to Nature Communications
[3] Deshapriya et al., Planet. Sci. Journal. 4, 231 (2023)
[4] Cheng et al., Nature, 616, 457 (2023)
[5] Zinzi et al., Planet. Sci. Journal. 5, 103 (2024)
How to cite: Deshapriya, J. D. P., Hasselmann, P. H., Gai, I., and Dotto, E. and the LICIACube team: Reconstruction of Ejecta Shape from LICIACube Data, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-436, https://doi.org/10.5194/epsc2024-436, 2024.
Introduction: The NASA Double Asteroid Redirection Test (DART) impact [1], was the first space mission that successfully demonstrated the kinetic impactor technique for planetary defense. It was at the same instant, on 26th September 2022, when ASI/Light Italian Cubesat for Imaging of Asteroids (LICIACube) [2] was the first Cubesat to image the plume coming from Dimorphos, the smaller body of the binary asteroid (65803) Didymos. The DART impact into Dimorphos [3] caused ejecta plume propagation with high velocity and very filamentary structure, composed of dust particles from μm to cm sizes in size [4]. The large aperture and observed spikes did not prevent propagation of larger excavated material, namely, boulders up to ~2 m [5]. Far-field observations such as HST clearly showed dust tail formed from the low-speed ejecta dust due to solar radiation pressure (SRP) [4].
The scientific objectives: The estimation of the size distribution and velocity distribution of the plume in close vicinity to Dimorphos, captured in the LICIACube images is still an unanswered question. While the long-term monitoring of the tail can reveal the size distribution up to tens of cm in size, the impact simulations can constrain the initial velocity of the excavated material. Near and mid – field simulations considering different dynamical properties at local scale can address the complex collimated but inhomogeneous distribution of the dust within the plume. Here, we discuss some of the dynamical properties of the plume using the available observational DART and LICIACube data of the plume propagation. We try to constrain the particle sizes within the collimated plume structures.
The model: We apply the 3D+t model – LIMARDE [6,7] constrained with laboratory observations [8], impact simulations and near- and far- field observations such as the LICIACube [9] images and HST [2] dust observations, respectively. The model computes single particle trajectories, the dust rotational frequencies and velocity as well as the particle orientation at any time and distance. We compute the dust velocity distribution based on the physical properties (size, mass and shape) derived from the LICIACube observations. The results are useful to check what is the role of the fragmentation of the particles and to constrain the physical properties based on the dynamical properties of the ejected dust in the near- and mid- environment.
Fig. 1. The dust speed and rotation frequency of particles with different shapes as constitutes of the dust clumps shown in the observations of ASI/LICIACube/LUKE, 2022-09-26T23:17:04.
Discussion: The LICIACube observations suggest that we have the locations of accumulation of different particles along the collimated plume streamers. The latter may contain particles of the same density and shape but with different velocity and rotation due to the initial ejected position and form not-linear motion within the collimated filament – like structures. In Fig. 1 we show LIMARDE simulations with particles of different shapes that result with different velocities suggesting a scenario where the dusty clumps could occur at the same location due to motion of particles with different shapes. The study discusses what is the probability that these dust clumps are formed owing to fragmentation, or their location is a result of their motion history of the ejected particles.
Acknowledgements: This research was supported by the Italian Space Agency (ASI) within the LICIACube (ASI-INAF agreement AC n. 2019-31-HH.0).
References: [1] Rivkin, A.S. et al. 2021, PSJ, 2, 24pp; [2] Dotto, E. et al. 2021, PSS 199, [3] Daly, R.T. et al. (2023) Nature. [4] Li, J.-Y., et al. (2023) Nature. [5] Farnham et al. LPSC abs. [6] Ivanovski et al. 2023, u.rev.; [7] Fahnestock et al. 2022, PSJ; [8] Ormo et al. 2022, E&PSL [9] Dotto et al. 2023, Nature
How to cite: Ivanovski, S. L., Hasselmann, P. H., Zanotti, G., Bertini, I., Deshapriya, P., Ieva, S., Lucchetti, A., Pajola, M., Perna, D., Poggiali, G., Dotto, E., Della Corte, V., Herreos, M. I., Ormo, J., Ferrari, F., Li, J.-Y., Amoroso, M., Pirrotta, S., Zinzi, A., and Brucato, J. R. and the LICIACUBE and a part of the DART team: Dust Clumps Dynamics of the Dimorphos Ejecta Plume, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1168, https://doi.org/10.5194/epsc2024-1168, 2024.
Introduction: In 2022, the NASA DART spacecraft performed a kinetic impact on the asteroid Dimorphos. This first attempt of asteroid deflection was highly effective and demonstrated the feasibility of modifying an asteroid trajectory. The on-board camera, DRACO, captured images of the binary asteroids Didymos and Dimorphos during the approach. These images showed Didymos to have a relatively smooth equatorial region compared to the polar terrains. Linear groove-like features perpendicular to the equator can be seen.
In this work, we use the DRACO images and boulder tracks visible on the surface to apply a previously validated geotechnical approach [1] and estimate the bearing capacity of the surface of the primary asteroid Didymos. Our findings have been accepted for publication at Nature Communications [2].
Geotechnical properties of asteroids affect their geology and evolution [3] and are important parameters in numerical models of the formation and history of small bodies. Moreover, they are also important for any space mission involving surface operations or interactions [4]. The ultimate bearing capacity is the maximum pressure that a surface can withstand without experiencing shear failure [5].
Methods: Image processing solutions were used to visualize and measure the boulder tracks. We applied a Laplacian filter that increases the visibility of the contours by enhancing the zones with high intensity gradients. To quantify the influence of image resolution on our measurements, we conducted successive degradations of resolution that showed measurement errors up to ~10%. The bearing capacity estimate takes into account a possible error of one pixel (~50% error) on the track width measurements.
The values for Didymos’ size, mass, gravity field and spin rate [6] show a very small effective gravity, that combines both gravitational and centripetal accelerations. The topographic data from [7] provides evidence for a change in gravitational potential on the surface of Didymos. The surface presents a minimum of geopotential at the equator (Fig. 1) due to the fast rotation of Didymos, supporting the hypothesis of the observed lineaments being tracks formed by boulders moving on the granular soil. The coordinates in latitude and longitude of these tracks were measured using the Small Body Mapping Tool [8] to locate them on the gravitational potential map (Fig. 1). The change in gravitational potential along each track is reported in Fig. 1, and shows a lower gravitational potential at the end of all the tracks, indicating that the boulders would have moved towards the equator to minimise their geopotential.
Results: From the DRACO images, 15 possible boulder tracks are identified on the surface of Didymos, shown in Fig. 2b, among which 9 are chosen to be studied further. We measure manually the width and length of each track in the processed images. The track widths have a mean and standard deviation of 8.9 +/- 1.5 m.
Using the track width measurements, we applied the Terzaghi equation, previously applied to the lunar soil [1, 9], that relates the shear strength of the soil to the material properties and the track measurements. We performed Monte Carlo simulations to account for the uncertainty in the key parameters (friction angle, cohesion and density) which we vary within their expected ranges found in recent studies [6, 7, 10, 11]. We find an average bearing capacity of 70 N/m² (Fig. 3).
Conclusion: The linear features observed on Didymos seem to be tracks formed by boulders moving down the gravitational slope towards the equator. From the 9 tracks identified, we find an average boulder track width of 8.9 +/- 1.5 m. Using a geotechnical approach, we estimated the mean bearing capacity of Didymos to be 70 N/m². This means that every 1 m² of Didymos’ surface can support only ~70 N of force before experiencing shear failure. This is at least 1000 times smaller than the bearing capacity of dry sand on Earth (~105 N/m²). The upcoming ESA Hera mission will return on site in 2026 and provide high resolution images of Didymos. This will provide confirmation that the observed features are indeed tracks formed by boulders.
Our work will also be put into practice through an experimental project that was selected for the ESA Academy Experiment Programme, led by a student team from ISAE-SUPAERO in France. Sinkage experiments in low gravity conditions will be conducted using the ZARM drop tower, in order to measure the bearing capacity of surface materials and test the influence of cohesion.
Acknowledgements: We acknowledge funding support from the French Space Agency (Centre National d’Etudes Spatiales; CNES), support from the French ANR Tremplin-ERC ‘GRAVITE’, and funding from the European Union (ERC, GRAVITE, 101087060).
References:
1. Bickel, V. T. et al. Analysis of Lunar Boulder Tracks: Implications for Trafficability of Pyroclastic Deposits. Geophys. Res. Planets 124, 1296–1314 (2019).
2. Bigot, J., Lombardo, P. et al. The bearing capacity of asteroid (65803) Didymos estimated from boulder tracks. Nature Communications, accepted (2024).
3. Sánchez, P. Asteroid Evolution: Role of Geotechnical Properties. Proc. Int. Astron. Union 10, 111–121 (2015).
4. Zacny, K. et al. Chapter 8 - Geotechnical Properties of Asteroids Affecting Surface Operations, Mining, and In Situ Resource Utilization Activities. in Primitive Meteorites and Asteroids (ed. Abreu, N.) 439–476 (Elsevier, 2018).
5. Terzaghi, K. Theoretical Soil Mechanics. (J. Wiley and Sons, Inc.; Chapman and Hall, Limited, New York, London, 1943).
6. Naidu, S. P. & Chesley, S. Dimorphos orbit solution, JPL Memo s542. (2023).
7. Barnouin, O. S. et al. The geology and evolution of the Near-Earth binary asteroid system (65803) Didymos. Nature Communications, accepted (2024)
8. Sargeant, H. M. et al. Using Boulder Tracks as a Tool to Understand the Bearing Capacity of Permanently Shadowed Regions of the Moon. Geophys. Res. Planets 125, (2020).
9. Ernst, C. M. et al. The Small Body Mapping Tool (SBMT) for accessing, visualizing, and analyzing spacecraft data in three dimensions. LPSC 49, abstract #1043 (2018)
10. Pajola, M. et al. Evidence for multi-fragmentation and mass shedding of boulders on rubble-pile binary asteroids. Nature Communications, submitted (2024).
11. Robin C. Q. et al. Mechanical properties of rubble pile asteroids (Dimorphos, Itokawa, Ryugu, and Bennu) through surface boulder morphological analysis. Nature Communications, accepted (2024)
How to cite: Bigot, J., Lombardo, P., Murdoch, N., Scheeres, D. J., Vivet, D., Zhang, Y., Sunshine, J., Vincent, J.-B., Barnouin, O. S., Ernst, C. M., Daly, T., Sunday, C., Michel, P., Campo-Bagatin, A., Lucchetti, A., Pajola, M., Rivkin, A. S., and Chabot, N. L.: Estimating the bearing capacity of asteroid (65803) Didymos using boulder track measurements, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-395, https://doi.org/10.5194/epsc2024-395, 2024.
The Hera mission, which is part of the Space Safety Program of the European Space Agency (ESA), will launch on 7 October 2024 (baseline date) from Cape Canaveral with a Falcon 9 from the Space X company. The launch window runs for 3 weeks. At the time of the presentation, the spacecraft will already be at Cape Canaveral for the launch campaign taking several weeks, after leaving Europe by early September. Once launched and after a first phase of commissioning, the first milestone will be a flyby of Mars in March 2025, which will allow the in-flight calibration of the instruments onboard the spacecraft by taking images of Mars and Deimos.
Hera will perform a rendezvous with Didymos in the fall of 2026 and investigate it over 6 months. With NASA’s DART mission, Hera will offer the first fully documented asteroid deflection test. DART successfully impacted Dimorphos, the 150 meter-sized moon of Didymos, on 26 September 2022 at approximately 6.1 km/s. The DART impact resulted in a decrease of 33 minutes from the original 11 hours 55 minute orbital period of Dimorphos around Didymos. However, many questions remain and although Hera returns to the system already visited by DART, the properties of the system will have changed in a way that may surprise us. In fact, it is clear that the Dimorphos that we know from DART’s images before impact will be very different when Hera sees it, reflecting how the DART impact modified it. Thanks to the great efforts of the DART team, the surface properties of the hemisphere of Dimorphos that was imaged before impact are well known, and it will be extremely interesting to see how those properties were changed by the impact. Among the questions that Hera will answer, the most important ones are: (1) What is the mass of Dimorphos, telling us momentum transfer efficiency of the DART impact? (2) What are the internal properties of Dimorphos, largely influencing the interpretation of the outcome of the DART impact? (3) What is the final state of Dimorphos, i.e., what is the size of the crater left by the DART impact or was Dimorphos globally or in large parts reshaped by the impact? (4) What is the rotational state of Dimorphos? Did the impact cause it to tumble?
The Hera mission will provide answers to these important questions that will lead to an unbiased interpretation of the outcome of the DART impact, and the possibility to fully validate numerical impact models aimed at reproducing the impact. With its mother spacecraft, which carries five instruments including a thermal infrared imager contributed by JAXA, and its two cubesats, Juventas, devoted to geophysics and Milani, devoted to mineralogy and dust analysis, Hera will investigate Didymos’ and Dimorphos’ state after the DART impact in great detail and provide measurements that have never been obtained for an asteroid so far. In particular, thanks to the low-frequency radar JuRa onboard the Juventas Cubesat, the first measurements of subsurface and internal properties of an asteroid will be achieved. Moreover, Hera will also perform the first landing of a Cubesat on a body as small as Dimorphos, offering an opportunity to measure the surface mechanical response of an asteroid in a very low gravity environment. Thanks to its detailed characterization of the binary system, Hera will answer key questions regarding the formation of small asteroid binaries and the geophysics of small bodies.
The working groups of the Hera Science Team are, adjusting their investigation plans to account for the new and important knowledge provided by DART and LICIAcube, to support the asteroid phase, including the possible surprises that Hera will offer during its visit to Didymos in late 2026-2027.
P.M. acknowledge support from ESA and CNES.
About half the size of a Smart car, the cubic Hera spacecraft is seen with its solar arrays folded up on each side. Hera’s ‘top deck’ is visible, hosting most of its instruments, including its Asteroid Framing Cameras – seen left top – and the dispensers for its two CubeSats in the middle. Its main antenna used for communicating with Earth is seen to the right. Credit: ESA - S. Blair
How to cite: Michel, P., Küppers, M., Martino, P., and Carnelli, I.: The ESA Hera mission to the binary asteroid (65803) Didymos: a few weeks from launch, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-56, https://doi.org/10.5194/epsc2024-56, 2024.
ASPECT is a flexible hyperspectral imager based on tunable Fabry-Perót interference filter (Näsilä and Kohout 2020). It consists of three independent Vis-NIR imaging channels, one single-point SWIR spectrometer, and a dedicated data processing unit (DPU) based on Xiphos Q7 (Table 1). ASPECT is the prime payload of Milani CubeSat carried by ESA Hera mission (Michel et al. 2022, Kohout et al. 2018) to binary asteroid Didymos-Dimorphos and is also considered for RAMSES and Satis missions to asteroid Apophis.
Table 1. ASPECT specifications
Aspect will conduct global hyperspectral mapping of the target asteroids with a resolution of 1 m/px from 5 km. The spectral domain contains key information on surface composition and maturity. Combined with high spatial resolution lateral variations in surface properties can be mapped. To extract such information from ASPECT observations we developed two machine learning convolutional neural network (CNN) codes (Korda et al. 2023ab, 2024) to extract scientific information from ASPECT observations.
The first code quantitatively detects silicate mineral composition (olivine, orthopyroxene, clinopyroxene modal abundances and their Fe, Mg, and Ca content). The second code evaluates space-weathering level based on spectral match score to the spectral type Q (fresh silicate asteroid) or to the type S (space-weathered). The codes were tested on legacy spatially resolved spectra of the asteroid (25143) Itokawa revealing local space-weathering trends in both mineralogy and space weathering indicators (Fig. 1). The apparent correlation between reduction in olivine content with increasing surface maturity is due to higher olivine susceptibility to space weathering-induced damage and related progressive removal of its diagnostic spectral absorption bands relative to these of pyroxenes.
Fig. 1. Local variations in surficial space weathering (left) and olivine content (right) on asteroid Itokawa revealed by the machine learning analysis. Spectral data are obtained by NIRS (Near Infrared Spectrometer) instrument on the Hayabusa (JAXA) spacecraft. The space-weathering level is expressed as a match score to spectral S-type with higher values (redder) being more mature.
The codes will be applied on hyperspectral observations of Didymos-Dimorphos or Apophis asteroids to produce composition and space-weathering maps, detect fresh impact events, map ejecta extent, or to detect local resurfacing. The web interface to access the codes for online user spectra classification can be found here:
https://sirrah.pythonanywhere.com/upload
References:
Michel et al. 2022 DOI 10.3847/PSJ/ac6f52
Näsilä, Kohout 2020 DOI 10.1109/AERO47225.2020.9172437
Kohout et al. 2018 DOI 10.1016/j.asr.2017.07.036
Korda, Kohout 2024, DOI 10.3847/PSJ/ad2685
Korda et al. 2023a DOI 10.1051/0004-6361/202346290
Korda et al. 2023b DOI 10.1051/0004-6361/202243886
How to cite: Kohout, T., Korda, D., Penttilä, A., Rajamäki, L., and Palamakumbure, L.: Detection of composition, space weathering, and local resurfacing using ASPECT hyperspectral imager of ESA Hera / Milani mission, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-316, https://doi.org/10.5194/epsc2024-316, 2024.
Introduction
The cosine* HyperScout-H (HS-H) instrument will fly aboard the ESA/Hera spacecraft. This mission [1], focused on planetary defense, aims to thoroughly characterize the (65803) Didymos near-Earth binary asteroid following the impact of the NASA/DART mission. It will launch in October 2024 and it is expected to reach the target by February 2027.
HS-H captures hyperspectral images over 657 - 949 nm wavelength range. Each macropixel, made of a 5 x 5 matrix of pixels, records the signal across 25 different narrow bands, with each band corresponding to a pixel. These measurements will represent a key element for understanding the Didymos - Dimorphos system, including its composition, the space-weathering effects and the potential presence of exogenous material. Also, they will complement the data obtained by the main camera (Asteroid Framing Camera) used for geomorphological studies, and for searching the presence of boulders near the two asteroids. Moreover, HS-H will provide high spatial resolution images of the crater resulting from the NASA DART impact. Another use of the instrument may occur in March 2025, during the cruise phase, when the spacecraft will perform a swing-by of Mars. It is expected that Phobos and Deimos, the two natural satellites of Mars, can be spectrally characterized by Hera/HS-H.
This presentation will provide an overview of the ongoing scientific activities to exploit this instrument. Its focus will be on cross-calibrating HS-H in the laboratory using meteorite samples.
Experiment setup
Two bulk meteorite samples were received from Archaeology, Environmental Changes, and Geo-Chemistry (AMGC) in Belgium. One piece, approximately 6 x 3 cm in size, originated from the El Hammami meteorite, an H5 ordinary chondrite. The other piece, measuring about 4 x 3 cm, was a fragment of the Sayh al Uhaymir (SaU) 001 meteorite, also an ordinary chondrite but of L5 subtype.
The reference spectra were obtained over the 550 - 4200 nm with a dedicated setup using the SHADOWS spectro-goniometer at Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), France. The sample area measured was about 5.2 mm x 5.2 mm covered with 7 optical fibers of around 1.3 x 1.7 mm each. The optical arm of the spectro-goniometer was set at the nominal geometry of incidence 0° and emergence 30°, to simulate the most common viewing geometry of asteroids from the Earth [2].
The HS-H instrument was used to obtain hyperspectral images of the two samples, in the laboratory facilities of ESTEC (Noordwijk). The setup is shown in Fig. 1. A halogen lamp was used to illuminate both the sample and the spectralon. A number of 45 images were acquired, 15 for El Hammami, and 30 for SaU 001. Different exposure times were used, 500 ms, 1 sec, and 1.5 sec. In order to reduce the read-out time, we acquired subframes (regions of interest).
Fig. 1 The setup used to obtain the hyperspectral images of the two meteorites samples with HS-H. The left image shows a piece of El Hammami, while the right one corresponds to SaU 001.
Data analysis and results
The pre-processing of the data includes the dark subtraction and the flat field correction. Then, in order to obtain the spectral data, we applied the demosaicking algorithm that takes into account the pixel position and its corresponding wavelength (the central wavelength of each narrow band filter). The reflectance spectra are computed by dividing the spectrum of the meteorite by the one obtained for the spectralon.
The first approach was to consider a wide region of 10 x 10 macropixels over each sample (red squares in Fig. 2). The resulting curves show an excellent match between the reference spectra and the data obtained with HS-H. The comparison is shown in Fig. 2.
The second step was to consider the spectral curve resulting for each macropixel of HS-H. To analyze these measurements, we generated a taxonomic classification map (Fig. 3), using the classification system developed by [2]. We also determined the spectral slopes across the surface and an estimation of the depth of the absorption band at 1 µm. This surface mapping shows clear patterns consistent with the compositional variation across the meteorite.
Fig. 2 Comparison between the spectra obtained with HS-H (in blue), and the reference spectra obtained in the laboratory (in red). The corresponding HS-H image is shown on the left of each plot. The red square on each image marks the macropixels used to retrieve the meteorite spectrum.
Fig. 3 The taxonomic type (using the Mahlke [3] classification system) assigned to each macropixel .
References
[1] Michel, P. et al. (2022) Planetary Science Journal, 3, id.160;
[2] Potin S. et al.(2018) Applied optics, 57(28), 8279-8296, (2018);
[3] Mahlke, M. et al. (2022) A&A, 665, id.A26;
* https://www.cosine.nl/
How to cite: Popescu, M., de León, J., Goldberg, H., Kovács, G., Krämer Ruggiu, L., Nagy, B., Prodan, G. P., Grieger, B., Kohout, T., Licandro, J., Karatekin, Ö., Esposito, M., and Küppers, M.: Hyperspectral imaging of meteorites using the HyperScout-H instrument, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-586, https://doi.org/10.5194/epsc2024-586, 2024.
Introduction:
The Double Asteroid Redirection Test (DART [1]) was a NASA space mission that impacted the moonlet of the Didymos binary asteroid (Dimorphos) on 26th of September 2022. The data collected prior to the collision by the spacecraft provided extraordinary information about Dimorphos and has been analysed by several scientists around the world, allowing the extraction of Dimorphos’ characteristic properties before impact, including physical and morphological properties, among others.
The European Hera mission [2] will continue exploring Didymos with a launch scheduled in October 2024. Hera will get the first images of Dimorphos after impact by the end of 2026. Along its trajectory, Hera will be able to deliver precious information about Mars, Deimos and Phobos.
The Austrian contribution to the Hera mission mainly consists of supporting the scientific camera instruments´ teams (TIRI, HSC, AFC, and ASPECT) by reconstructing, visualizing and analysing the data acquired with the different instruments on board. For this purpose, several tools have already been partly developed and will be improved and completed up until arrival for rendezvous with the asteroid in late 2026. For the first phase of the project (April 2023-June 2024) two uses cases were defined, namely Mars-fly-by and Dimorphos visualization and analysis with a 3D-GIS (Geographic Information System). In order to evaluate the tools in the most realistic way, a MARS MOLA shape model [3], the results of the DART mission available on its repository [4] and the Hera planned trajectories (SPICE kernels, [5]) calculated by ESAC in September 2023 were used.
PRo3D-GIS
PRo3D-GIS is the Austrian tool designated to support the instruments´ teams for the evaluation and analysis activities during the mission. The tool is based on PRo3D, an interactive 3D visualization tool to allow planetary scientists to work with high-resolution 3D reconstructions [6] [7]. It has major heritage from ExoMars and Mars 2020, but up to recently only supported single planets. To this end, we extended its capabilities to deal with celestial bodies as required for the Hera mission forming the PRo3D-GIS extension. To work with high-quality reconstructions, Pro3D-GIS uses the Ordered Point Cloud (OPC) format [8].
The visualization elements of PRo3D-GIS can be classified into three groups, namely:
- Structural layer (Digital Elevation Model – DEM)
- Texture layers
- Primary texture layer (ortho image)
- Secondary texture layers (derived products, e.g.: hyperspectral map)
- Annotation layers: comprises observations, annotations and measurements
After adding the 3D reconstructions (from DEM) called surfaces to PRo3D, users associate the surface with the SPICE kernel by assigning it a celestial body and reference frame. Given an observation time, PRo3D aligns all 3D data accordingly and fetches the required data. Depending on the visualization properties configured by the user, PRo3D automatically loads the corresponding layers, computes necessary derived products (such as contour lines) and provides an 3D visualization which can be explored interactively. Supported by the visualization layers (e.g. contour lines) users can author annotations and measurements and create screenshots or author videos.
DART repository data for Dimorphos multilayer OPC
Based on the PRo3D-GIS visualization elements mentioned before, following data were taken from the DART repository and converted into OPC format for visualization and analysis:
- OPC Dimorphos structural layer: “g_01960mm_spc_obj_dimo_0000n00000_v003.obj”, i.e.: DART Dimorphos shape model (Figure 1, left)
- OPC Dimorphos texture layers:
- OPC primary texture layer: “dart_0401930042_08549_01_iof.fits”, DRACO image which was projected on DART shape model with a projective transformation (Figure 1, right)
- OCP secondary texture layers: “g_01960mm_spc_dtm_dimo_0000n00000_v003.fits”, i.e. 17 DART Dimorphos information layers contained in the FITS file. An example is displayed in Figure 1, centre (i.e.: elevation layer)
Since DART data offers more than one texture layer, the OPC data scheme was enhanced to support them (i.e.: multilayer OPC), and the data import interfaces were adapted. Furthermore, the PRo3D-GIS tool was improved to allow multi-layer analysis and visualization. Additionally, the integration of large coordinates of the celestial bodies’ and the several coordinate systems provided in the SPICE kernels encountered in all mission phases, involved modifications to the design and implementation of PRo3D-GIS.
Visualization and analysis of the use cases
The Hera 3D-GIS has to support the two uses cases proposed for this phase of the development, namely:
- “Mars fly-by,” which main objectives are: The calibration of the instruments on board (e.g.: AFC, HyperScout and TIRI), the possibility to perform science observations of Deimos far side, and the observation of Mars for a couple of hours at good spatial resolution, and for several days with good phase angles
- “Visualization and analysis of Dimorphos” with information provided by the instruments teams, ordered in several information layers, in the validation process using the DART multilayer OPC as simulation example
Mars fly-by
Figure 2 (top) shows three bookmarks selected at different days and times in March 2025 (13th March at 00:00, 16th March at 14:00 and 17th March at 01:00). At the bottom of Figure 2, the approach of Hera (observer, grey colour) to Mars (target, red colour) is visualized. The meta kernel used for this simulation in PRo3D-GIS was “hera_study_PO_EMA_2024.tm” and the reference frame was the ecliptic plane.
Visualization and analysis of Dimorphos
A simulation of the approach of Hera to Dimorphos on 24th July 2027 can be seen in Figure 3. The selected times are shown on the top. At the bottom in the simulated views, Hera is represented as a grey small point in the centre of the image and Dimorphos multilayer in grey and brown colours, due to the combination of two information layers, namely the texture and elevation layers. The meta kernel file used for this simulation was “hera_study_PO_EMA_2024.tm”.
Additional analysis of the Dimorphos multilayer OPC with the available tools of the 3D-GIS was done. Some of the GIS applications available in PRo3D-GIS are shown in Figure 4, namely: layers superimposition visualization, annotations, measurements and scale analysis.
Summary and further work
Acknowledgement
References
[1] https://iopscience.iop.org/article/10.3847/PSJ/ac91cc/pdf
[2] https://iopscience.iop.org/article/10.3847/PSJ/ac6f52
[3] https://tharsis.gsfc.nasa.gov/MolaRcvrPaper.pdf
[4] https://dart.jhuapl.edu/SOC/DRA/
[5] https://s2e2.cosmos.esa.int/bitbucket/projects/SPICE_KERNELS/repos/hera/browse/kernels
[6] https://doi.org/10.1002/2018EA000374
[7] https://doi.org/10.1002/9781119313922.ch3
[8] https://www.researchgate.net/publication/228716045_Towards_True_Underground_Infrastructure_Surface_Documentation
[9] https://www.vrvis.at/publications/pdfs/PB-VRVis-2022-017.pdf
[10] https://www.vrvis.at/publications/pdfs/PB-VRVis-2023-002.pdf
[11] https://meetingorganizer.copernicus.org/EPSC2021/EPSC2021-73.html
[12] https://doi.org/10.5194/epsc2020-123
[13] https://az659834.vo.msecnd.net/eventsairwesteuprod/production-atpi-public/2387daf11cb14198bb064e103ee9747a
How to cite: Caballo-Perucha, P., Nowak, R., Steinlechner, H., Paar, G., Traxler, C., and Vincent, J.-B.: PRo3D-GIS tool for Hera: visualization and analysis of two use cases, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-322, https://doi.org/10.5194/epsc2024-322, 2024.
Introduction The successful DART mission has validated kinetic impact as the most effective method for deflecting or disrupting potentially hazardous asteroids [1]. The impact produced unexpectedly intense material ejection, expanding our understanding of asteroid response to hypervelocity collisions [2]. What insights might this violent fragmentation and ejecta reveal about Dimorphos's material strength and structural composition? Exploring these aspects before the upcoming Hera mission [3] can optimize mission design and interpretation.
The artificial impact experiment conducted by the Hayabusa2 mission demonstrated the influence of geological structures on cratering events [4, 5]. Similarly, understanding how the material and structural composition of an asteroid affect kinetic impact efficiency is crucial for planetary defense. To capture the detailed structure of asteroids, here we employ the Material Point Method (MPM), which excels in handling contact and interface problems, for modeling and simulation, aiming to address these critical questions.
Method The material point method (MPM) is a well-developed numerical technique in the mechanical industry, but remains underestimated potential in the field of planetary science. MPM discretizes the continuum body into Lagrangian material points and employs a rigidly attached Eulerian background grid at each time step, with the algorithmic flow illustrated in Fig. 1. By combining the strengths of both Lagrangian and Eulerian descriptions, MPM effectively eliminates numerical dissipation and expedites the search for neighbor points, resulting in an efficient, extendable, and robust shock-physics code. This feature makes MPM particularly well-suited for simulating complex geometries and contact interactions, which are common in planetary science applications.
To accurately capture the dynamical behavior of materials under hypervelocity impact, a modified pressure-dependent and damage-dependent Lundborg smooth yield model is adopted for the strength model, coupled with a quantitative plasticity correction. The Tillotson equation of state (EOS) is utilized in conjunction with a sound speed modification. Besides, a resolution-independent Grady-Kipp damage model is employed to simulate the fracture process. In the future, we plan to further develop the p-alpha equation to characterize the pore compaction effect.
These proposed algorithms and material models have undergone extensive benchmarking and validation, spanning a wide range of parameter spaces, demonstrating their capability to describe the potential dynamic behavior of small celestial body materials [6]. This comprehensive approach, combining state-of-the-art numerical methods and material models, paves the way for a deeper understanding of the dynamic properties of small celestial bodies and their constituent materials.
Simulation and Result Constrained by computational resources, we designed simulation scenarios based on China's upcoming kinetic impact mission [7]. A cubic spacecraft (1.5 m in size, 600 kg in mass) impacts a spherical target body (35 m in diameter) at a velocity of 10 km/s. Given the unknown material and structure of the target, we investigated the dynamic responses of small bodies with various structures (monolithic or rubble pile), geometries (spherical or ellipsoidal), and material compositions (rocky or regolith, solid or porous). Except for the solid rocky material with a density of 2700 kg/m3, all other target bodies have equal mass and a bulk density of 1200 kg/m3. Classic basaltic material parameters were used for all materials, except for the regolith, which has lower strength. The ejecta, damage, and velocity distributions after 0.5 s of impact are visually presented in Fig. 2. We further analyzed the momentum enhancement factor and the mass and velocity distributions of the fragments for each case.
Discussion and Conclusion The dynamic responses to hypervelocity impacts exhibit significant sensitivity to the target's material and structure, as evidenced by the ejecta intensity, ejection angles, fragment morphology, velocity, and angular velocity. Investigating the relationship between target structure and impact response is crucial for mission design and ejecta avoidance. Moreover, it helps unravel the physical properties of the target body from observational results. This study focused on perpendicular impacts and analyzed the results during the impact fragmentation phase. Future research may delve into the orbital dynamics of the fragments, evaluate the effectiveness of impact defense in mitigating Earth-threatening hazards, and explore the potential of oblique impacts to disrupt the target body through spin-up. These findings may also extend to impacts between asteroids and shed light on phenomena such as binary formation, which contributes to our understanding of the origin and evolution of small celestial bodies in the solar system.
Acknowledgment X.Y. and J.L. acknowledge support from the National Natural Science Foundation of China under Grant 12372047. X.Y. acknowledges support from the National Natural Science Foundation of China under Grant 62227901. P.M. acknowledges support from the French space agency CNES and from the French National Centre for Scientific Research (CNRS) through the exploratory research program of the Mission for Transversal and Interdisciplinary Initiatives.
References [1] Daly, R. T. et al. (2023) Nature 616(7957), 443–447. [2] Cheng, A. F. et al. (2023) Nature 616(7957), 457–460. [3] Michel, P. et al. (2022) Planet. Sci. J. 3(7), 160. [4] Arakawa, M. et al. (2020) Science 368(6486), 1–10. [5] Jutzi, M. et al. (2022) Nat. Commun. 13(1), 7134. [6] Yan, X. et al. (2023) ACM Conference. [7] Zou, Y. et al. (2024) J. Deep Space Explor. 11(2), 1-8.
How to cite: Yan, X., Zhou, W., Michel, P., and Li, J.: Assessing the influence of asteroid composition and structure on kinetic impact deflection efficiency: an MPM approach, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-260, https://doi.org/10.5194/epsc2024-260, 2024.
The objective: 99942 Apophis is a potentially hazardous asteroid with a diameter of about 370 metres that on 13 April 2029 will approach Earth’s surface at a distance that is closer than orbiting geosynchronous satellites (Fig. 1). Significant tidal torques will be exerted on the body of Apophis, with consequences that might include alterations of its rotation state and/or internal structure, measurable seismic waves and real-time surface disturbances.
This very close Earth flyby therefore presents an unprecedented planetary defense and science opportunity. A mission to Apophis could allow transforming our understanding of the mechanical response to external natural forces of the surface, interior and rotational properties of potentially hazardous asteroid, with both planetary defense and science implications.
Figure 1: Trajectory of Apophis during its close encounter with Earth on 13 April 2029, at a minimum distance of 31860 km from Earth’s surface.
The mission: Parallel ESA-funded studies for small missions to Apophis are ongoing. The first is “Satis”, a study based on a 12U CubeSat; in parallel a second small-satellite study (“RAMSES”, Rapid Apophis Mission for SpacE Safety) is exploring an adaptation of the Hera spacecraft design, to fit to the updated mission profile, while minimizing any new developments given the short timescale until launch.
To rendezvous with the asteroid before April 2029, the RAMSES spacecraft needs to launch in 2028 with a 3-weeks launch window opening on April 20th. Following a 10-months direct transfer, RAMSES will rendezvous with Apophis no later than March 1st, 2029, and will perform a detailed characterization campaign of the Asteroid. Initially RAMSES will run passively-safe hyperbolic arcs with pericentre at 20 km from Apophis, then will move into a pseudo-hovering position with fixed relative distance and phase angle with respect to the target asteroid. The distance will be decreasing in consecutive steps from 20 km to 10, 5 and finally 1 km, At the closest distance, global imaging at 10 cm resolution will be achieved (exploiting the Apophis rotation). This series of observations will be performed both before and after the close encounter with Earth.
In addition, during the close encounter, characterization of Apophis with high temporal resolution (1 picture per minute) will be performed in a safe hovering position at 5 km to observe in detail the abovementioned physical and dynamical alterations of the asteroid.
The Spacecraft: RAMSES is largely based on the Hera design. The key design drivers with respect to the original mission profile are: a much reduced distance from the Sun (allowing smaller Solar Arrays and reduced heater power), a closer distance from the Earth during critical operations (allowing a smaller antenna), but an increased delta-V demand (introducing the need for larger tanks and/or lower dry mass).
Payload: RAMSES will embark as a minimum two visible cameras with complementary Fields of View and two 6U-XL CubeSats which will be released in proximity of Apophis before the close encounter and will operate independently, using RAMSES as relay satellite. One of the two CubeSats could possibly land on Apophis before the close encounter, carrying relevant instruments such as, e.g., seismometers or gravimeters. Additional payloads will be accommodated either on RAMSES or on the CubeSats on the basis of available on-board resources. These might include a Thermal Infrared Imager, a Laser Altimeter, a Multispectral Camera onboard RAMSES, and/or a Low Frequency Radar, and other possible instruments of interest for planetary defense and/or science purposes.
International Cooperation: RAMSES will work in synergy with the NASA mission OSIRIS-APEX that will arrive at Apophis a few days after the closest approach of the asteroid to the Earth, allowing a comparison of the asteroid properties measured by the two missions and emphasizing the international cooperation that is at the heart of planetary defense.
Conclusion: The study of RAMSES will be instrumental to make an informed decision at ESA’s Council at Ministerial Level in 2025, both on the most effective technical solution as well as the best approach to reduce mission cost and allow fast implementation.
How to cite: Küppers, M., Martino, P., Carnelli, I., and Michel, P.: Status of ESA’s Rapid Apophis Mission for Space Safety (RAMSES) Concept , Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-199, https://doi.org/10.5194/epsc2024-199, 2024.
Introduction:
Satis is an ESA Phase A Planetary Defense mission study targeting (99942) Apophis, a Potentially Hazardous Asteroid (PHA) with a diameter of about 350 m. The mission consists of a stand-alone 12U-XL CubeSat that aims to rendezvous with Apophis prior to its Earth Closest Approach (ECA) at a distance from Earth's surface of 31,500 km on Friday, 13th April 2029. In addition, Satis serves as pioneer to demonstrate a completely new class of small, fast-response missions for planetary defense. Here, we present the Satis science objectives and the overall mission definition.
Science Objectives:
The flyby of Apophis in April 2029 will be a unique opportunity to observe a PHA closely. Its gravitational encounter with Earth will enable the direct observation of changes in the asteroid’s rotation, possible surface changes, as well as its long-term orbit. Satis will observe these parameters to assess the effects of an ECA on the evolution of asteroids.
Apophis is a tumbling body or a non-principal axis (NPA) rotator. The gravitational forces on Apophis during the ECA will likely change Apophis’ rotational speed significantly, by more than 30%, and will cause a wobble in the rotation [1-5]. These changes in rotation will allow us to infer the ratios of moments of inertia and provide information on internal mass distribution and structure (Sci-1). The interior structure of an asteroid carries the imprint of its collisional and accretion history and is important for planetary defense mitigation attempts and Hypothetical impact assessment [6].
The tides and strong rotational forces have the potential to cause changes in the surfaces due to geophysical processes, such as landslides. Investigating this possible resurfacing caused by the ECA is important for interpreting present observations and to understand the evolution of asteroid surfaces (Sci-2). Surface strength and cohesion are the main drivers for surface geophysical processes and are also critical for planetary defense, as they dictate the response of the asteroid to kinetic impacts.
The orbital perturbation from Earth's gravity on the Apophis orbit is likely to increase and change the orbit by increasing the semi-major axis and the perihelion distance (Sci-3). The change in the orbit due to ECA is expected to be large, but exact predictions are not possible due to uncertainties in the asteroid’s initial orientation. Flyby-induced changes to Apophis’ spin state and surface will also affect the asteroid’s Yarkovsky acceleration, which is a relatively small perturbation but relevant for long-term orbit and planetary defense.
Fig. 1: The modelled changes in Apophis’ gravity field due to ECA [1]
Mission definition:
The feasibility of the Satis mission concept was studied by an ESA CDF study [7] and since then the mission and system design further advanced [8]. The mission is designed to observe the asteroid before, during, and after the ECA in order to detect any changes induced by the effects of Earth’s gravity on this PHA, thus providing unique data for Planetary Defense purposes. The mission starts with an April 2027 launch on a dedicated micro-launcher equipped with a kick stage. The kick stage will be used to inject the CubeSat onto the required escape velocity vector. Following commissioning, the CubeSat will use a high-performance miniaturized electric propulsion system for the 2-year interplanetary transfer to achieve the rendezvous with Apophis. The mission duration will cover operations close to the asteroid two months before and at least two months after the ECA. Proximity operations will lead the spacecraft very close to Apophis’ surface to enable detailed analysis of the asteroid. Communication and navigation will be performed using a miniaturized X-band transponder interfacing with ESTRACK deep space ground stations. The payloads considered include a visual camera, thermal imager, radio science experiment as well as Hyperspectral, VIS/NIR imagers to fulfil the science objectives. The Mission Definition Review has been successfully completed and completion of Phase A of the mission study is foreseen for end of August 2024 with a Preliminary Requirements Review.
References: [1] Noiset, G. et al. (2023) 8th IAA Planetary Defence Conference, 3-7 April, 2003, Vienna. [2] Benson et al., (2023) Icarus, 390, 115324. [3] Scheeres, D. J. et al., (2006), Science, 314 (5803) [4] Souchay, J. et al (2018), Astronomy and Astrophysics, 617, 1–11. [5] Souchay, J. et al., (2014) Astronomy and Astrophysics, 563, 1–6. [6] Senel C. and Karatekin Ö. 8th IAA Planetary Defence Conference, 3-7 April, 2003, Vienna. [7] Satis CDF study (2022) ESA-TECSYE-HO-2022-003030. [8] Fogliano, V. et al. (2024) Small Satellites Systems and Services (4S) Symposium, 27-31 May, 2024, Palma de Mallorca.
How to cite: Karatekin, Ö., Ritter, B., Gundlach, B., Güttler, C., Patzek, M., Cabral, F. D. S. P., Catisanu, D. A., Fogliano, V., Holster, P., Simonetti, S., Walker, R., and Moissl, R.: Satis as fast-response missions for Apophis during its Earth close encounter in 2029 , Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-249, https://doi.org/10.5194/epsc2024-249, 2024.
Introduction: The tidal encounter of asteroid Apophis with the Earth in 2029 offers the ideal scenario for the first in-situ seismic investigation of an asteroid. A seismometer can be used to monitor the seismicity of Apophis due to tidal forces [1], and other natural sources such as micro-meteoroid impacts or thermal cracks; [2-4]. In addition, a seismometer can image Apophis’ sub-surface and internal structure [2] providing information about the asteroid’s physical properties that is critical for planetary defense, and for understanding the evolutionary history of asteroids. As a consequence, there is strong international support for the first seismic experiment on an asteroid.
We have developed a Compact Seismometer that is designed specifically to fit inside a small asteroid surface package and function in the challenging environment of the asteroid surface. The instrument team has extensive experience in developing, testing, and operating seismic [5,6] and acoustic [7] planetary instrumentation.
Scientific Objectives: The main science and technological goal of the Compact Seismometer is to perform the first ever in-situ seismic study on the surface of an asteroid. The specific compact seismometer science objectives are as follows:
Threshold science objectives:
(O1) Constrain the mechanical properties of the surface during landing
(O2) Measure the seismic background noise on the surface of Apophis
Baseline science objectives:
(O3) Quantify the seismicity of Apophis in response to tidal forces
(O4) Probe the subsurface and internal structure of Apophis
Bonus objective:
(O5) Perform the first active seismic experiment on an asteroid using the OSIRIS-APEX spacecraft – surface interactions
Compact Seismometer: The instrument consists of three commercial geophones that will each measure the ground motion along one axis, and dedicated electronics (Figs 1-2). The geophones are passive, contain no active electronics and are designed to withstand extreme environments (e.g., terrestrial boreholes). The analog electronics have been carefully designed and developed to have a high sensitivity and low intrinsic noise. The instrument is currently at TRL level 4/5 (4 for the electronics, 5 for the commercial sensors), and the development schedule is compatible with RAMSES schedule. The current best estimates of the instrument mass, volume and power budgets are ~1 kg, 0.8 L and ~ 2W, respectively.
Figure 1. (left) Schematic diagram of the Compact Seismometer. (right) The Compact Seismometer containing three geophones.
Operational scenario: The Compact Seismometer should be deployed to the surface of Apophis prior to the asteroid’s closest encounter with the Earth. In the lead up to the perigee, periodic measurements will be made for instrument commissioning and background noise measurements. Then, from 3 hours before to 6 hours after the perigee - when tidal-induced seismic activity is expected to occur [1] - continuous monitoring should be performed. Following the close encounter further periodic measurements should be made to monitor the evolution and diurnal variations of the background noise and seismicity. If the surface package can survive long enough, the OSIRIS-APEX excavation experiment using thrusters [8] would provide a unique opportunity to perform an active seismic experiment using the Compact Seismometer.
Figure 2. Possible concept of operations for the Compact Seismometer.
Surface coupling and levelling: The Compact Seismometer must land on the asteroid and be in contact with the asteroid’s surface. However, the Compact Seismometer can operate in any orientation and does not require levelling. The proposed solution is to not attempt to couple to the surface; any coupling attempt will only couple the instrument to the upper layer of regolith, which itself may not be coupled to the sub-surface. If any lofting occurs, these events can be used to characterize the surface properties during the subsequent touchdown.
Performance and environment testing: The expected noise level of the Compact Seismometer is <1.0E-9 m/s/sqrt(Hz) in the 5-200 Hz bandwidth (<1.0E-7 m/s2/sqrt(Hz) at 15 Hz). Performance tests of the Compact Seismometer have characterized the electronic noise floor, distortion, cross talk, and the integrated instrument performance. The performance evaluation of seismic instrumentation is particularly complex due to the terrestrial seismic environment. However, we rely heavily on the experience and expertise gained from the SEIS (InSight) instrument and ARTEMIS-4 geophone performance testing. Thermal vacuum (TVAC) testing of the Compact Seismometer (Fig. 3) sensors demonstrated that the sensors survived the environment testing and that the noise level and the transfer function before and after TVAC remain unchanged.
Figure 3 (left) Compact Seismometer performance testbed at ISAE-SUPAERO. (right) Compact seismometer sensors during TVAC testing.
Conclusions: The Apophis 2029 encounter with the Earth offers the ideal scenario for the first in-situ seismic investigation of an asteroid. There is a strong interest within the planetary science and seismology community, and large international support for the first seismic experiment on an asteroid. The Compact Seismometer – the result of over a decade of studies and development – is designed to fit inside a small lander and function in the challenging environment of an asteroid’s surface. The team has extensive experience in developing, testing and operating seismic and acoustic planetary instrumentation. The Compact Seismometer is currently at TRL 4/5 (4 for electronics, 5 for commercial sensors), and the development timeline is compatible with the ESA RAMSES mission schedule.
Acknowledgments: The authors acknowledge funding support from CNES and from the European Commission's Horizon 2020 research and innovation programme under grant agreement No 870377 (NEO-MAPP project).
References: [1] DeMartini, J. et al. (2024), EPSC. [2] Murdoch, N. et al., (2017) Planetary and Space Science, 144, 89-105., [3] Murdoch, N. et al., (2015) Asteroids IV, University of Arizona Press Space Science Series. [4] Compaire, N., et al. (2022). Geophysical Journal International, 229(2), 776-799. [5] Lognonné, P. et al., (2019) Space Science Reviews. [6] Mimoun, D. et al. (2017) Space Science Reviews, 211. [7] Mimoun, D. et al. (2023) Space Science Reviews, 219. [8] DellaGiustina, D. et al (2023) Planet. Sci. J. 4 198.
How to cite: Murdoch, N., Garcia, R. F., Sournac, A., Cadu, A., Wilhelm, A., Drilleau, M., Stott, A., DeMartini, J., Kawamura, T., Lognonné, P., Michel, P., Bousquet, P., and Mimoun, D.: An in-situ seismic investigation of asteroid Apophis, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-495, https://doi.org/10.5194/epsc2024-495, 2024.
Due to the increased performance of small satellites, their use in the exploration of asteroids is becoming increasingly more important. The DART mission with the CubeSat LICIACube or the Hera mission with the two CubeSats Milani and Juventas demonstrated this. Also, in the context of exploring the asteroid (99942) Apophis during its flyby of Earth in 2029 many concepts rely on the use of small satellites, which is illustrated i.e. by the plans for the RAMSES mission and the DROID mission.
The primary challenge for all mission concepts investigating (99942) Apophis is to secure funding and to meet the tight implementation schedule. In the context of the NEAlight project (Grant No. 50OO2413), carried out by IFEX at the University of Würzburg, these issues are addressed by examining three different mission concepts for a national small satellite mission in parallel: The concepts are designed to cover different mission complexities and cost constraints, and to allow utilization of different launch options, thus providing variation in implementation timescales.
RAMSES CubeSat Contribution
The first mission idea is the support of the European RAMSES mission by developing a CubeSat which aims to complement the science objectives of the RAMSES mission by providing valuable insights into the physical characteristics and possible surface changes in pre- and post- Earth closest approach (ECA) phase of (99942) Apophis. These are specifically done by observing the internal composition, shape, and dynamic state of the body. In addition, this mission concept aims to characterize the magnetization of (99942) Apophis and the plasma interactions as it passes through the Earth's magnetosphere. Table 1 shows an overview to said scientific contributions with specific instruments performing the respective measurements. Therefore, a suitable CubeSat bus must be capable of handling the deep-space environment, as well as operations in the close proximity of the asteroid. At this place the 6U+ SONATE-2 bus, which is developed and built inhouse at the University of Würzburg, serves as a viable foundation. This bus has flight heritage already and has been designed with future use in space exploration missions in mind, with a particular focus on mission autonomy and operating AI and advanced image processing hardware in space environment. Figure 1 shows an exemplary layout of this bus adapted for the mission.
|
Optical Observations |
Secondary measurements: Complementary observations from various angles alongside RAMSES observations. |
Camera system based on MASCAM, 1U-design, focal length ~35mm |
|
Radar Measurements |
Unique measurements as a direct contribution to the scientific objectives of RAMSES |
LFR based on JuRa instrument, BSPK-coded radar with 60MHz carrier, 1U electronic box plus cross-dipole antenna |
|
Magnetometer |
Distinct measurement beyond RAMSES scientific objectives, not covered by OSIRIS-APEX |
Set of vector-compensated 3-axis fluxgate magnetometers, mounted on deployable structure |
Tab. 1 Scientific Contributions to the RAMSES mission and respective instruments on the CubeSat
Fig. 1 Top level concept of the CubeSat to accompany the RAMSES Spacecraft based on the SONATE-2 bus.
Apophis Encounter Mission
An independent German small satellite could study (99942) Apophis, should the RAMSES mission not receive funding. The satellite is aimed to be designed in such a way that it can serve as a template for further missions to near-Earth asteroids (NEA) in cislunar space and beyond. One of the main tasks is the selection of the trajectory and the propulsion system for the autonomous deceleration at (99942) Apophis if no transfer vehicle can be used. The launch is estimated to be in 2028 at the latest, as otherwise the fuel or time constraints may not be met. In contrast to the SATIS mission, however, the focus is here on a small satellite in the size class of approx. 27U. Depending on the final design of the trajectory, an observation period of up to two months before the ECA is assessed to be possible. Based on current announcements the usage of commercial transfer vehicles might be feasible.
Apophis Interceptor Mission
The near-Earth fly-by of (99942) Apophis also offers the opportunity to conduct a relatively inexpensive mission using a small satellite. From a few kilometers away a set of high-resolution images of (99942) Apophis at its closest approach can be captured, while also demonstrating a versatile deep-space bus for future NEA fly-by missions. A key advantage is the flexibility in the launch window, including a launch option in 2029. Additionally, launching together with similar mission concepts can further reduce costs, making this concept even more feasible with restricted budgets.
Because of the comparatively low costs of this small satellite missions and the trend of increased launch opportunities into cislunar space in the coming years, these missions class seems ideal for the exploration of near-Earth asteroids in general. In this way, these missions could make a key contribution to understanding the formation and evolution of the solar system, as well as to planetary defense against potentially dangerous asteroids.
Acknowledgments: This work is part of the NEAlight project funded by the Federal Ministry for Economic Affairs and Climate Action (BMWK) through the German Aerospace Center (DLR) based on a decision of the German Bundestag (Grant No. 50OO2413).
How to cite: Männel, J., Neumann, T., Kayal, H., Riegler, C., and Amza, A. A.: Concepts for a German Small Sat Mission to (99942) Apophis, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1098, https://doi.org/10.5194/epsc2024-1098, 2024.
Introduction
Estimating the probability of a collision of asteroids with the Earth is an important task for planetary defense. There are systems that compute impact probabilities of near-Earth asteroids with the Earth on a regular basis: Sentry (Nasa, Jet Propulsion Laboratory) and CLOMON-2 (originally University of Pisa, now ESA). Here we present NEOForCE (Near-Earth Objects Forecast for Collisional Events) a new impact monitoring system which is being developed at Institut de mécanique céleste et de calcul des éphémérides (IMCCE, Paris Observatory).
Partial Banana Mapping method
The core of the new system is the Partial Banana Mapping method (PBM) [1] with the extension of a direct search for initial state vector that leads to a collision [2]. The basic principle of the Partial Banana Mapping method (PBM) is that the covariance matrix in curvilinear coordinate system, as described in [3] or in orbital elements much better represent the actual shape of the uncertainty region (see Fig.1) in the two-body formalism. To find the possible collision we can find on the main axis of the curvilinear uncertainty region the point, which is closest to the Earth (point B). In the extension of the PBM method we then are finding a state vector from the original uncertainty region (at epoch of observations) that leads to point B. Then we propagate the orbit of the found state vector until the time of possible collision and compute its probability. This approach can successfully find the virtual asteroid that leads to a collision.
Figure 1: The scheme of the banana shaped uncertainty region of the asteroid. Point A is the nominal position of the asteroid, point B — the virtual asteroid of the main axis of the uncertainty region, which is closest to the Earth. The bold line is the nominal asteroid’s orbit. The dashed arrow is the direction of the Earth’s relative velocity.
Line Of Variations approach
If the asteroid has close approaches with major planets then the linear analysis of collisions (like Partial Banana Mapping) can fail and nonlinear analysis is required. In NEOForCE we apply the concept of Line of Variations sampling to deal with it.
The uncertainty region of an asteroid at the epoch of observations is quite small and well represented by an ellipsoid (6 dimensional ellipsoid, since we have uncertainty in coordinates and velocities). The idea of Line of Variations approach [5,6] is to sample virtual asteroid on the main axis of this 6-dimensional uncertainty ellipsoid and integrate their orbits forward in time separately.
In NEOForCE each of the virtual asteroid is considered to be a representative of its vicinity of the uncertainty region (see Fig.2). The vicinity is found by dividing the largest eigen value of the covariance matrix that represents the uncertainty of the orbit. Then we proceed the analysis by the improved Partial Banana Mapping approach for each of the virtual asteroid.
Fig. 2. The schematic illustration of the uncertainty region at the epoch of observations. The horizontal line is the main line of the uncertainty ellipsoid (Line of Variations) and the black dots are the virtual asteroids. The green area is the vicinity of virtual asteroid that it represents.
Conclusion
The NEOForCE monitoring system will be using orbits of asteroids from DynAstVO database [6] and planetary ephemerids INPOP [7] from Institut de mécanique céleste et de calcul des éphémérides (IMCCE, Paris Observatory). The system has original approach of collisional analysis based on Partial Banana Mapping method. Hence the system provides an independent assessment of the impact probability, which is crucial for planetary defense campaign.
Acknowledgments
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 101068341 “NEOForCE”.
References:
[1] D. E. Vavilov (2020) MNRAS 492(3), 4546.
[2] D. E. Vavilov (2023) in Planetary Defense Conference 2023.
[3] D. E.Vavilov, et al. (2015) MNRAS 446(1),705.
[4] A. Milani, et al. (2002) Asteroid Close Approaches: Analysis and Potential Impact Detection 55–69.
[5] A. Milani, et al. (2005) Icarus 173(2),362.
[6] J. Desmars, et al. (2017) in European Planetary Science Congress EPSC2017–324.
[7] A. Fienga, et al. (2021) Notes Scientifiques et Techniques de l’Institut de Mecanique Celeste 110.
How to cite: Vavilov, D. and Hestroffer, D.: NEOForCE: Impact monitoring system of Paris observatory, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-544, https://doi.org/10.5194/epsc2024-544, 2024.
In April 2029, asteroid Apophis (2004 MN4) will flyby Earth and pass less than 32000 km from its surface. During this close encounter (CE), the asteroid will experience dynamical changes due to its gravitational interaction with the Earth ([1],[2],[3]). Several missions are currently being studied to observe and characterize Apophis before and during the CE ([4],[5]), and additionally the OSIRIS-APEX spacecraft will make a post-Earth-encounter rendezvous with the asteroid [6]. Apophis will also be observed by ground-based telescopes during its passage [7].
Apophis is a tumbling body or a non-principal axis (NPA) rotator. The gravitational forces of the Earth will likely change Apophis’ rotational speed significantly ([1],[2],[3],[8]). They may also alter its regolith configuration resulting in resurfacing due to local avalanches [9]. The variations of dynamical and orbital parameters, such as the spin, obliquity and longitudinal and latitudinal librations will provide unique insights about the behavior of such asteroids during their close flyby of planets. Resurfacing mechanics has important implications for interpreting surface observations, including space weathering effects on these bodies.
For both the dynamical and the gravitational simulations, we use a radar-based shape model for Apophis [10] while the Earth is modeled by an ellipsoid of revolution. The surface accelerations for Apophis are computed using the polyhedron model with a constant density [11]. The gravitational interactions between the Earth and Apophis during CE are determined using the open-source GUBAS propagator implementing the full-two-body problem (F2BP) [12]. The simulations are propagated from when Apophis enters Earth’s sphere of influence. Preliminary analysis showed that depending on the initial ecliptic longitude, the rotational speed of Apophis can either increase of decrease. The CE also has a major influence on Apophis obliquity depending on initial conditions (Figure 1) [8].
Figure 1 Obliquity change with different initial conditions.
To assess the possible surface changes of Apophis during the CE, we investigate the variations of surface acceleration and dynamic slopes. We combine the self-gravity of Apophis with the contributions of the dynamics of the system (tidal forces and Euler acceleration). The dynamic slopes are defined as the angle between the surface normal and the surface acceleration vector. Initial results suggested changes of about 3% on surface gravity and less than a few degrees on slopes for the selected initial conditions [13]. Introducing a tumbling state of Apophis constrained by [14] shows slightly larger results [8].
Here we investigate the locations susceptible to resurfacing of Apophis during the CE under different initial orientation conditions, as the instantaneous orientation of the asteroid is not well determined unlike its orbital state. Compared to previous work [1], we consider a full tumbling state of Apophis constrained by observations [14] following the method shown by [7]. The influence of the initial orientation on the surface accelerations shows significant changes depending on the studied cases (Figure 2, Figure 3). These changes in Apophis rotation and local gravity, including potential localized resurfacing across its surface, are important parameters for planetary defense missions since they provide information on otherwise inaccessible interior and mechanical properties of the asteroids.
Figure 2 Slope changes for tumbling case at CE
Figure 3 Slopes changes for extreme obliquity change case at CE
[1] Souchay, J., Lhotka, C., Heron, G., Herv´e, Y., Puente, V., & Folgueira Lopez, M. (2018). “Changes of spin axis and rate of the asteroid (99942) Apophis during the 2029 close encounter with Earth: A constrained model”, Astronomy and Astrophysics, 617, 1–11.
[2] Souchay, J., Souami, D., Lhotka, C., Puente, V., & Folgueira, M. (2014). “Rotational changes of the asteroid 99942 Apophis during the 2029 close encounter with Earth”, Astronomy and Astrophysics, 563, 1–6.
[3] Benson C.J. et al. “Spin state evolution of (99942) Apophis during its 2029 Earth encounter” (2023) Icarus, Vol. 390, 115324
[4] Küppers M. et al. “STATUS OF ESA’S RAPID APOPHIS MISSION FOR SPACE SAFETY (RAMSES) CONCEPT” (2024), Apophis T-5 Years Workshop
[5] Karatekin Ö. et al. “SATIS MISSION STUDY FOR APOPHIS: Science objectives and mission definition.” (2024), Apophis T-5 Years Workshop
[6] Nolan M. C. et al. “THE OSIRIS–APEX MISSION TO APOPHIS” (2024), Apophis T-5 Years Workshop
[7] de León J. et al. “OPPORTUNITIES TO STUDY APOPHIS USING THE CANARIAN OBSERVATORIES BEFORE, DURING, AND AFTER ITS CLOSE APPROACH IN APRIL, 2029” 2024), Apophis T-5 Years Workshop
[8] Sert H. et al. “Changes in Rotational Dynamics and Surface Accelerations Induced by the Earth Encounter of Apophis » (2024), Apophis T-5 Years Workshop
[9] Yu Y. et al. “Numerical predictions of surface effects during the 2029 close approach of Asteroid 99942 Apophis” (2014), Icarus, Vol. 242, 82-96.
[10] Brozović et al. “Goldstone and Arecibo radar observations of (99942) Apophis in 2012–2013” (2018), Icarus, Vol. 300, 115–128.
[11] Werner R.A. and Scheeres D.J. "Exterior gravitation of a polyhedron derived and compared with harmonic and mascon gravitation representations of asteroid 4769 Castalia." (1996), Celestial Mechanics and Dynamical Astronomy 65.3, 313-344.
[12] Davis, A. B., Scheeres, D. J. “Doubly Synchronous Binary Asteroid Mass Parameter Observability” (2020a), Icarus, Vol. 341, 113439
[13] Noiset et al. “Changes in Apophis rotation and surface gravity during its 2029 Earth flyby” (2023), 8th IAA Planetary Defence Conference
[14] Pravec et al. “The tumbling spin state of (99942) Apophis” (2014), Icarus,
How to cite: Tasev, E., Sert, H., and Karatekin, Ö.: Changes in Apophis surface accelerations due to changes in its dynamical state during the 2029 Earth flyby, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-889, https://doi.org/10.5194/epsc2024-889, 2024.
DESIGNING THE NEXT GENERATION KINETIC IMPACTOR FOR PLANETARY DEFENSE
Raymond Lu(1*), Mallory E. DeCoster(1), Julie Peck(1), Tony Le(1)
(1)Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road Laurel, MD 20723,
*Raymond.Lu@jhuapl.edu
Keywords: Kinetic Impactors, Hypervelocity Impacts, Hydrocodes, planetary defense
ABSTRACT
On September 26, 2022, NASA successfully executed the Double Asteroid Redirection Test (DART) mission, a full-scale planetary defense demonstration of the kinetic impactor technology that intentionally collided a spacecraft into a small asteroid to change its orbit. However, the DART mission was a demonstration of one kinetic impactor design impacting a singular target morphology, begging the question: is it possible to optimize a kinetic impactor design to maximize deflection? Further, it remains an open question whether the kinetic impactor projectile can be optimized based on the intended target asteroid morphology and/or surface structure. To investigate this, we used CTH hydrocode simulations which examined the role of mass placement within a single projectile and a cluster of multiple projectiles on the deflection efficiency resulting from a hypervelocity kinetic impact with a variety of asteroid-like targets ranging from homogeneous monoliths to sandy rubble piles.
It is well known that the total projectile mass and impact velocity greatly influence the effectiveness of a kinetic impactor; however, these parameters are typically limited by the launch and target asteroid orbit considerations. For this work, we focused on the effects of mass placement within a spacecraft (projectile) design and performed numerical studies of projectiles of varying geometry while keeping the projectile mass constant. To systematically vary the projectile geometry, we considered both tall rods with varying aspect ratios (AR) (calculated as radius/length) and ogives where we varied the AR and the angle between the ogive leading edge and the target (α). Our results showed that the projectile geometry effect was subtle compared to the effects of target material parameters (cohesion, porosity, internal friction, etc.), which is in line with previous reports, however, when there is a projectile effect, it is most pronounced in weaker (i.e. yield strength of 1 MPa) granular (unconsolidated targets) compared to strong monolithic targets. While the role of α on deflection efficiency was complex, our results showed that for hypervelocity ( 6.65 km/s) impacts, smaller aspect ratios led to larger amounts of total ejecta mass and larger momentum efficiency factors (β). Figure 1 (a) indicates that by and large, tall rods and ogives resulted in similar β’s as a function of impact velocity, with the tall rods slightly outperforming the ogives except for when the AR was small (i.e., the tallest/skinniest projectile with AR=0.2). In this case, the tall rod drastically outperformed the ogive with equivalent AR by ~20%, and this projectile outperformed the other tall rods by 12%. Further, Figure 1 (b) illustrates that the projectile geometry effect on β was closely coupled to the target material properties, where the effect of projectile aspect ratio was more pronounced in weaker granular target compared to the strong competent target.
(Figure 1. (a) β resulting 500 ms post impact for simulations of impacts of tall rods (triangles) compared to ogives (squares) of varying aspect ratio at three different impact velocities (2.00 km/s, 6.65 km/s, and 15.00 km/s) into strong competent basalt targets. (b) β resulting 500 ms post impact for hypervelocity impacts of ogives of varying aspect ratio at three different impact velocities (2.00 km/s, 6.65 km/s, and 15.00 km/s) into two different types of targets (strong and weak basalt). The open symbols are indicative of impacts into weak granular basalt targets with a cohesion (Yo) of 1 Pa, and the solid symbols are indicative of impacts into strong competent basalt with a cohesion (Yo) of 80 MPa.)
In addition to the dominant role of target material properties in affecting deflection efficiency, recent work has shown that the near surface structure of the asteroid target also plays a crucial role in affecting β. Therefore, it may be possible to improve a kinetic impactor’s efficiency by using a set of clustered projectiles, rather than a singular projectile, to mitigate the armoring effect on β that an impact directly into a large surface boulder might have. We used CTH to investigate the effects of spacing and mass distribution (while keeping the total projectile mass constant) on a cluster of three spherical projectiles impacting homogeneous and rubble pile targets. Figure 2 shows three examples of the projectile clusters under consideration and outlines the full 2D axisymmetric test matrix. For each cluster of projectiles, we vary both the ratio between the mass of the side spheres and the central sphere (M) (while keeping the total mass constant) and the spacing between the spheres, reported as the ratio, S, between the center-to-center distance of the central sphere to the auxiliary sphere with respect to the diameter of the central sphere. Impacts performed into homogeneous and rubble pile targets will be useful to understand the role of near surface structure on projectile geometry optimization. These results will inform both future numerical efforts and future experimental investigations of kinetic impactor effectiveness.
(Figure 2. (top) Illustrations of projectile geometry clusters with varying mass ratios (M) and spacing ratios (S). (bottom) The full CTH test matrix for investigating the effects of projectile clusters on deflection efficiency into homogenous and rubble pile asteroid-like targets.)
How to cite: Lu, R.: Designing the next generation kinetic impactor for planetary defense, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-558, https://doi.org/10.5194/epsc2024-558, 2024.