SSPA is involved in numerous small body missions. Our involvement ranges from the development of instruments specifically for the exploration of small bodies, to the physical properties and internal structure of asteroids and their geophysical evolution.
The AIDA mission: Asteroid Impact and Deflection Assessment (DART + Hera)
The NASA Double Asteroid Redirection Test (DART) mission will reach Didymos in September 2022 and steer itself into Dimorphos at a speed of approximately 6.6 km/s. The last thing DART will transmit back to Earth in advance of the collision will a close-up of Dimorphos’s surface features. Post-impact investigations will be performed initially from Earth and then by the other component of AIDA, ESA’s Hera mission (planned for launch in 2024). Hera’s (Michel et al., 2017) detailed post-impact survey will turn the large-scale impact experiment into a well-understood and repeatable planetary defence technique.
Overall results from the two missions should provide a baseline for planning any future planetary defence strategies, offering insight into the kind of force needed to shift the orbit of any incoming asteroid, and better understand how the technique could be applied if a real threat were to occur.
DART and Hera are self-standing; each mission on its own will provide valuable knowledge. However, when combined together this knowledge will be multiplied considerably.
SSPA’s involvement in these mission is two-fold: to help prepare the close proximity operations of the Hera mission, specifically with regards to the landing and operational strategy of the CubeSats, and to prepare the scientific analyses of the DART and Hera missions, specifically with regards to the geophysical properties of Didymoon (internal structure and surface mechanical properties). Naomi Murdoch is a co-I of the Hera mission and a collaborator for the DART mission.
The MMX rover to Phobos
The Japan Aerospace Exploration Agency, JAXA, Martians Moons eXploration (MMX) mission will investigate the Martian Moons Phobos and Deimos, and return samples from Phobos to Earth. As part of this mission a small ( 25 kg) rover, contributed by the Centre National d’Etudes Spatiales (CNES) and the German Aerospace Center (DLR), with additional contributions from INTA (Spain) and JAXA, will be delivered to the surface of Phobos. The rover will demonstrate the technology of locomotion on a regolith-covered, low gravity planetary surface. In addition, the rover will provide scientific data on the regolith properties (mechanical, mineralogical and thermal), provide ground truth for the MMX orbiter instruments, give context information for the returned samples, and contribute to reducing the risk of the landing and sampling operations of the MMX mission.
One of the four scientific instruments on board the rover are the WheelCams (PI: Naomi Murdoch). These cameras will observe the properties of the regolith compaction and flow around the rover wheels, and the resulting trenches in order to characterise the mechanical properties of the regolith itself.
In the SSPA team we are studying the feasibility and the expected performance of a wheeled vehicle on the surface of a Phobos, in addition to preparing for the data analysis of the WheelCams.
H2020 NEO-MAPP Project
NEO-MAPP stands for Near Earth Object Modelling And Payload for Protection. This project is funded by the H2020 program of the European Commission and addresses the topic "Advanced research in Near Earth Objects (NEOs) and new payload technologies for planetary defence" (SUSPACE-23-SEC-2019). The main goal of NEO-MAPP is to support the development and data analysis of NEO missions, as Hera and provide significant advances in both our understanding of the response of NEOs to external forces (in particular a kinetic impact or a close planetary approach), and in the associated measurements by a spacecraft (including those necessary for the physical and dynamical characterization in general).
The NEO-MAPP objectives, include:
(1) Pushing the limits of numerical modelling of the response of NEOs to a kinetic impact, as well as of their physical and dynamical properties while maturing European modelling capabilities linked to planetary defence and NEO exploration;
(2) Increasing the maturity of multiple spaceborn and landed European instruments directly related to planetary defence, while focusing on measurements of surface, shallow sub-surface and interior properties of NEOs;
(3) Developing algorithms and simulators to prepare for closeproximity operations and
payload data analyses and exploitation;
(4) Developing innovative and synergetic measurement and data-analysis strategies that combine multiple payloads, to ensure optimal data exploitation for NEO missions;
(5) Developing and validating robust GNC strategies and technologies enabling surface interaction and direct response measurements performed by CubeSat or small/micro-lander
The NEO-MAPP team will dedicate considerable resources to developing important and innovative synergies between the two sub-topics. As such, NEO-MAPP will provide significant advances in our understanding of NEOs while at the same time build upon and sustainably increase expertise of European scientists and engineers in both planetary defence efforts and small-body exploration.
Here are some SSPA research topics related to small bodies:
The dynamics of the surface material are also involved in the evolution of small bodies in our Solar System and are critical for the design and/or operations of landers, sampling devices and rovers to be included in space missions.
- Asteroid landing: The understanding of surface-lander interactions is important for all asteroid landers as these considerations influence the deployment strategy, the mission design and operations, and even the choice of payload. To simulate landing on an asteroid we have developed an Atwood machine: a variable gravity drop tower (Sunday et al., 2016). With the tower we perform low velocity collisions in low gravity conditions. The results of our experiments indicate that the lower gravity collisions lead to a more fluidized behaviour of the grains (Murdoch et al., 2017). To watch an experiment about the Drop Tower simulates asteroid landing.
- Rolling in low gravity: Using a DEM code that we have improved and validated to model the specific interactions of a wheel with the regolith of a small body (Sunday et al., 2020), we are studying how sinkage, traction and (simplified) maneuverability vary in different types of regolith, at different levels of gravity. The results will be used directly for the MMX rover operations planning, and interpretation of the wheel motion and interaction with the regolith on Phobos.
Understanding the internal structure of an asteroid has important implications for interpreting its evolutionary history, for understanding its continuing geological evolution, and also for asteroid deflection and in-situ space resource utilisation. There is strong evidence that asteroids are seismically active (see Murdoch et al., 2015 for a review). The SSPA team studies the natural seismicity (tidal forces, impacts, thermal cracking, …) of asteroids to understand the consequences for their evolution and internal structure, and for future asteroid seismic stations (Garcia et al., 2015; Murdoch et al., 2017).
Instrumentation for probing the physical properties (surface and interior) of asteroids
By measuring the ground displacement due to seismic activity on the surface of asteroids a geophone can provide constraints on the layering and mechanical properties of the subsurface, in addition to the typical size of subsurface heterogeneities.
Seismology has long been considered a key technique for understanding a planetary body and its interior. However, despite the evidence that asteroids are seismically active and the obvious need to further our understanding of their internal structure, no seismic experiment has been performed on an asteroid’s surface.
To achieve the goal of performing seismology on the surface of a small body, we are developing an instrument that is adapted to the small body environment. Our low mass, low power seismometer can fit inside a small asteroid lander (e.g. a CubeSat) and function in the challenging environment of the asteroid surface.