Optimal Transfer Performance Research Articles

Optimal circle-to-rectilinear orbit transfer with circumferential thrust

This paper investigates the optimal transfer trajectories from a circular parking orbit towards the apocenter of a rectilinear ellipse, where the spacecraft reaches a quasi-stationary condition relative to an inertial reference frame. The spacecraft is equipped with a propulsion system that provides a circumferential continuous propulsive acceleration, that is, an acceleration whose direction is perpendicular to the primary body-spacecraft line. The performance index to minimize is the total flight time, and an indirect method is used to analyze the transfer trajectories. In this context, the optimal transfer performance is obtained as a function of the spacecraft propulsive acceleration magnitude through an interpolation procedure of numerical simulations. The results obtained with a continuous thrust propulsion system are also compared with those derived from a multi-impulse transfer. Finally, the paper investigates a heliocentric mission scenario in which the spacecraft minimizes the flight time required to reach a rectilinear ellipse with a given value of the aphelion radius.

Semi-Analytical Method for the Analysis of Solar Sail Heliocentric Orbit Raising

L OW-THRUST trajectories are usually investigated within an optimal framework by minimizing a suitable scalar performance index, like the total mission time or the propellant mass consumption. Very often a preliminary mission analysis requires a considerable amount of simulation time to investigate the effect of different parameters on mission performance; therefore the availability of simple analytical and/or graphical means to describe the orbit evolution is very useful. These simplified tools are of great importance formission-design concepts and tradeoff studies because they can provide good estimates of fundamental mission parameters, like the total velocity increment, with a reduced computational effort. In this regard, a famous method was developed by Edelbaum [1] for the study of a circle-to-circle transfer under the effect of a constant and freely steerable propulsive acceleration. This method, especially in the variant proposed by Kechichian [2–4], has been succeedingly extended to deal with more complex mission scenarios [5–7]. An interesting alternative to Edelbaum’s approach is provided by the so-called Alfano transfer [8]. Assuming that the spacecraft is subjected to a constant propulsive thrust, the Alfano transfer basically uses the calculus of variations to minimize the flight time t required for a circle-to-circle transfer as a function of the initial and final orbit radii (r0 and r1, respectively) and of the propulsion system characteristics (in terms of initial acceleration a0 and constant propellant mass flow rate _ mp). Because, by assumption, the thrust acts continuously without any coasting phase, the minimum-time transfers coincide with minimum propellant mass consumption trajectories. The results of the optimization process are then collected into charts [9] that simplify the flight time evaluation as a function of themission characteristics for a number of parameters combinations, like r1=r0, a0, and _ mp=m0, where m0 is the initial spacecraft mass. The aim of these charts is twofold. On one side, they allow the designer to quickly obtain, in a graphical form, the optimal transfer performance, to estimate the sensitivity to a mission parameter variation, and to automatize his/her analysis with the aid of simple interpolations [10]. The second and more intriguing aim is to detect possible relationships to describe the variation of the performance index as a function of the mission parameters. Such information is useful both for validating already available analytical models [5] and to suggest new approximations. According toAlfano [10], in hismethod theflight time is not given explicitly, but it is represented in terms of total accumulated velocity change Va, that is