Speaker
Mr
Fabio Ferrari
(Politecnico di Milano)
Description
The Asteroid Impact Mission (AIM) is a mission by ESA, planned to be the first to rendezvous with a binary asteroid. AIM mission objectives includes both scientific investigations and technological demonstrations. The mission is part of the Asteroid Impact & Deflection Assessment (AIDA), a joint cooperation between ESA and NASA, devoted to assess the effectiveness in deflecting the heliocentric path of a threatening Near Earth Asteroid (NEA) for planetary defense purpose. The target of the mission is near-Earth binary asteroid 65803 Didymos. The goal of AIDA is to study the effects of a kinetic impact on the surface of the smaller secondary asteroid of Didymos couple, informally called Didymoon. To this purpose, together with AIM, the AIDA mission includes DART (Double Asteroid Redirection Test), the kinetic impactor, designed by NASA.
The primary objectives of AIM include the detailed study and characterization of the binary couple. Among these, the internal composition of the smaller asteroid will be determined by means of low frequency radar tomography. Similarly to what done with the CONSERT instrument, on board the ESA's Rosetta mission, the radar will include a lander-orbiter architecture to host both transmitters and receivers. Rosetta mission highlighted the challenges of designing close proximity trajectories and to land a probe on the surface of an extremely irregular body such as comet 67P/Churyumov-Gerasimenko, whose shape and mass distribution were completely unknown and unexpected during the mission design phase. In that case, the Philae lander release was challenged by the highly perturbed dynamical environment in the proximity of the comet and its very low and irregular gravity field. In analogy with the Rosetta mission, AIM will deploy a small and passive probe (MASCOT-2, with clear heritage from MASCOT, Hayabusa 2 mission) that will reach the surface of a largely unknown object after a purely ballistic descent. MASCOT-2 lander do not feature any anchoring mechanism and this makes the release even more challenging since Didymos system's gravity field is expected to be weaker, with an escape velocity from Didymoon's surface of about 4-6 cm/s, being the asteroids estimated to be nearly two orders of magnitude less massive than comet 67P/Churyumov-Gerasimenko. In addition, the presence of two gravitational attractors makes the gravity field in the close proximity of the couple highly unstable and chaotic.
The paper proposes an effective strategy for MASCOT-2 release, beneficial for the mission analysis and operations design points of view. The AIM scenraio is presented as a perfect case of study, but the methodology applies to any asteroid/small body scenario. In particular, the landing trajectory and dynamics of MASCOT-2 is studied during close-proximity operations using the highest up-to-date fidelity model of Didymos. The paper presents some updates on the work the authors are currently performing during the phase A/B1 design of AIM, under ESA contract, in consortium with OHB System AG, and Spin.Works. From the orbital mechanics point of view, the binary system is naturally modeled as a three-body system and solutions are studied within the frame of the Restricted Three-Body Problem modeling. Shape-based models are used to model the gravitational contribution of the two asteroids refined models are built by combining them to reproduce the gravity field in the proximity of the binary couple. The purpose of the design strategy is to take advantage of the presence of two gravitational attractors to find effective landing solutions. The increased complexity because of the two gravity sources is here read as a potential opportunity to be exploited through the three-body problem modeling, which opens to a variety of dynamical solutions not available whenever a single attractor is dealt with. Three-body solutions are computed for Didymos binary system and suitable trajectories to land MASCOT-2 on the surface of the secondary are selected. More in detail, the motion close to the Lagrangian points is exploited: stable manifolds associated to Halo and Lyapunov orbits, have been propagated in the high-fidelity dynamical environment and suitable solutions are selected to guarantee soft landing on the secondary asteroid. The dynamics of the lander is propagated from release up to rest on the surface of the asteroid. Results show that the extremely low gravity environment does not guarantee the lander to stay on the surface after touch down, but MASCOT-2 will most likely bounce until reaching a stable position of Didymoon. Successful landing probability is assessed for the case of study and landing dispersion is evaluated. Compared to classical Keplerian solutions, three-body dynamics are shown to be effective to lower the risk of rebounding on the surface of the secondary, and to increase the safety of the overall release maneuver to be performed by AIM.
| Applicant type | First author |
|---|
Primary author
Mr
Fabio Ferrari
(Politecnico di Milano)
Co-authors
Mr
Ian Carnelli
(ESA)
Prof.
Michelle Lavagna
(Politecnico di Milano)
