This paper presents an analysis of optimal impact strategies to deflect potentially dangerous asteroids. In order to compute the increase in the minimum orbit intersection distance of the asteroid due to an impact with a spacecraft, simple analytical formulae are derived from proximal motion equations. The proposed analytical formulation allows for an analysis of the optimal direction of the deviating impulse transferred to the asteroid. This ideal optimal direction cannot be achieved for every asteroid at any time, therefore an analysis of the optimal launch opportunities for deviating a number of selected asteroids was
This paper investigates the effect of planetary oblateness and solar radiation pressure on the orbits of high area-to-mass spacecraft. A planar Hamiltonian model shows the existence of equilibrium orbits with the orbit apogee pointing towards or away from the Sun. These solutions are numerically continued to non-zero inclinations and considering the obliquity of the ecliptic plane relative to the equator. Quasi-frozen orbits are identified in eccentricity, inclination and the angle between the Sun-line and the orbit perigee. The long-term evolution of these orbits is then verified through numerical integration. A set of 'heliotropic' orbits with apogee pointing in the direction of the Sun is proposed for enhancing imaging and telecommunication on the day side of the Earth. The effects of J 2 and solar radiation pressure are exploited to obtain a passive rotation of the apsides line following the Sun; moreover the effect of solar radiation pressure enables such orbits at higher eccentricities with respect to the J 2 only case.
This paper investigates how perturbations due to asymmetric solar radiation pressure, in the presence of Earth shadow, and atmospheric drag can be balanced to obtain long-lived Earth centered orbits for swarms of micro-scale "smart dust" devices, without the use of active control. The secular variation of Keplerian elements is expressed analytically through an averaging technique. Families of solutions are then identified where Sun-synchronous apse-line precession is achieved passively to maintain asymmetric solar radiation pressure. The long-term orbit evolution is characterized by librational motion, progressively decaying due to the non-conservative effect of atmospheric drag. Long-lived orbits can then be designed through the interaction of energy gain from asymmetric solar radiation pressure and energy dissipation due to drag. In this way, the usual short drag lifetime of such high area-to-mass spacecraft can be greatly extended (and indeed selected). In addition, the effect of atmospheric drag can be exploited to ensure the rapid end-of-life decay of such devices, thus preventing long-lived orbit debris.
Current debris evolutionary models usually neglect fragments smaller than 10 cm because of the high computational effort they add to the simulation. However, small debris objects can also be dangerous to operational satellites. This work proposes an analytical approach to describe the evolution of a cloud of small fragments generated by a collision in Low Earth Orbit. The proposed approach considers the cloud globally and derives its evolution analytically, in terms of the change in the spatial density under the effect of atmospheric drag. As a result, the analytical approach allows the representation of small fragments and noticeably reduces the computational time under 10% compared to the numerical propagation of all the fragment trajectories.For altitudes above 800 km the relative error compared to the numerical method is lower than 10%. R E = Earth's radius [km]
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