1,721,084 research outputs found
Fuel-Optimal, Power-Limited Rendezvous with Variable Thruster Efficiency
No full textThe problem of minimum-fuel, time-fixed, three-dimensional rendezvous for a solar electric propulsion spacecraft
is discussed. The problem is solved via an indirect approach. The formulation takes into account both a
variable bounded specific impulse and a variable thruster efficiency and permits us to manage solutions with coast
arcs. The thruster efficiency is assumed to vary with the specific impulse through a polynomial approximation. The
optimal specific impulse control law is found to depend on the instantaneous values of the primer vector modulus, the spacecraft mass, the mass costate, and the thruster model. Optimal interplanetary trajectories toward Mars are discussed. It is shown that the inclusion of a variable efficiency thruster model has important effects on fuel
consumption. In particular, the classic constant efficiency thruster model overestimates the final spacecraft mass
Rapid Solar Sail Rendezvous Missions to Asteroid 99942 Apophis
No full textDifferent concepts for eliminating the threat of collision with a near-Earth object have been suggested in recent years. Most of them require that a probe is inserted in orbit around the object to obtain accurate physical and orbital
data. Asteroid 99942 Apophis is a member of the Aten group of asteroids, having orbital periods shorter than 1 year.
Such an asteroid is used here as a practical example to investigate the characteristics of new mission concepts and as a
candidate for a potential space agency project aimed to tag an asteroid either for scientific purposes or for a deflection mission decision. The purpose of this paper is to investigate the potentialities offered by a solar-sail-based rendezvous
mission toward Apophis. In particular, rapid transfer trajectories are studied, that is, missions whose transfer times are less than one terrestrial year. We show that a realistic near-term mission option, with a transfer time of about
300 days, requires a solar sail with a characteristic acceleration of 0.5 mm/s^2. A square solar sail with a side of about 90 m is needed for a payload of 50 kg, whereas a greater sail with a side of 160mis called for with a payload of 150 kg.
The solar sail performance is compared to that achievable with conventional propulsion systems
Trajectory Approximation for Low-Performance Electric Sail with Constant Thrust Angle
Full text linkAnalytic trajectories for a spacecraft subjected to a low, continuous, propulsive acceleration are available only for very special cases [1–3], even though these solutions find significant utility in preliminary mission design and optimization [4]. If a closed-form trajectory corresponding to a given thrust control law cannot be recovered, a possible option is to resort to a shape-based approach [5–7], or to suitably simplify the differential equations of motion [8–10].
Within the latter context, in this Note an analytical, albeit approximate, expression for the heliocentric trajectory of a spacecraft propelled by a low-performance electric sail [11, 12] is discussed. Using a two-dimensional model and under the assumptions of constant thrust angle and low propulsive acceleration modulus, the spacecraft heliocentric trajectory is obtained in a parametric way as a function of time. The effectiveness of the mathematical model is checked by comparing the analytic solution with a numeric integration of equations of motion
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