Time-optimal trajectories to circumsolar space using solar electric propulsion

The aim of this paper is to explore the capabilities of a solar electric propelled spacecraft on a mission towards circumsolar space. Using an indirect approach, the paper investigates minimum time of transfer (direct) trajectories from an initial heliocentric parking orbit to a desired final heliocentric target orbit, with a low perihelion radius and a high orbital inclination. The simulation results are then collected into graphs and tables for a trade-off analysis of the main mission parameters. Finally, a comparison of the performance between a solar electric and a (photonic) solar sail based spacecraft is discussed

Trajectory Design with Hybrid Low-Thrust Propulsion System

A novel mission concept based on a hybrid low-thrust propulsion system is proposed and discussed. A solar electric propulsion thruster is coupled with an auxiliary system providing an inverse square radial thrust In this way the spacecraft is virtually subjected to a reduced gravitational solar force. The primary purpose of this paper is to quantify the impact of the reduced solar force on the propellant consumption for an interplanetary mission. To this end the steering law that minimizes the propellant consumption for a circle-to-circle rendezvous problem is found using an indirect approach. The hybrid system is compared with a conventional solar electric thruster in terms of payload mass fraction deliverable for a given mission. A tradeoff between payload size and trip time is established

Fast E-sail Uranus entry probe mission

The electric solar wind sail is a novel propellantless space propulsion concept. According to numerical estimates, the electric solar wind sail can produce a large total impulse per propulsion system mass. Here we consider using a 0.5 N electric solar wind sail for boosting a 550 kg spacecraft to Uranus in less than 6 years. The spacecraft is a stack consisting of the electric solar wind sail module which is jettisoned roughly at Saturn distance, a carrier module and a probe for Uranus atmospheric entry. The carrier module has a chemical propulsion ability for orbital corrections and it uses its antenna for picking up the probe's data transmission and later relaying it to Earth. The scientific output of the mission is similar to what the Galileo Probe did at Jupiter. Measurements of the chemical and isotope composition of the Uranian atmosphere can give key constraints to different formation theories of the Solar System. A similar method could also be applied to other giant planets and Titan by using a fleet of more or less identical probes.Comment: 14 pages, 5 figures, Meudon Uranus workshop (Sept 16-18, 2013) special issue of Planetary and Space Scienc

Thrust and torque vector characteristics of axially-symmetric E-sail

The Electric Solar Wind Sail is an innovative propulsion system concept that gains propulsive acceleration from the interaction with charged particles released by the Sun. The aim of this paper is to obtain analytical expressions for the thrust and torque vectors of a spinning sail of given shape. Under the only assumption that each tether belongs to a plane containing the spacecraft spin axis, a general analytical relation is found for the thrust and torque vectors as a function of the spacecraft attitude relative to an orbital reference frame. The results are then applied to the noteworthy situation of a Sun-facing sail, that is, when the spacecraft spin axis is aligned with the Sun-spacecraft line, which approximatively coincides with the solar wind direction. In that case, the paper discusses the equilibrium shape of the generic conducting tether as a function of the sail geometry and the spin rate, using both a numerical and an analytical (approximate) approach. As a result, the structural characteristics of the conducting tether are related to the spacecraft geometric parameters

Venus-Centered Heliosynchronous Orbits with Smart Dusts

This paper deals with the problem of determining an analytical control law capable of maintaining highly elliptical heliosynchronous polar orbits around Venus. The problem is addressed using the Smart Dust concept, a propellantless propulsion system that extracts momentum from the solar radiation pressure using a reflective coating. The modulation of the thrust magnitude is performed by exploiting the property of electrochromic materials of changing their optical characteristics through the application of a suitable electrical voltage. The propulsive acceleration can, therefore, be switched from a minimum to a maximum value (or vice versa) so as to obtain a simple on–off control law. The required Smart Dust performance is described in closed form as a function of the semimajor axis and eccentricity of the working orbit. The soundness of the analytical control law is validated through a numerical integration of the equations of motion, in which the orbital perturbations due to the oblateness of Venus and to the gravitational attraction of the Sun are also included

Multi-Revolution Transfer for Heliocentric Missions with Solar Electric Propulsion

An extension of the classical method by Alfano, for the analysis of optimal circle-to-circle two-dimensional orbit transfer, is presented for a deep space probe equipped with a solar electric primary propulsion system. The problem is formulated as a function of suitable design parameters, which allow the optimal transfer to be conveniently characterized in a parametric way, and an indirect approach is used to find the optimal steering law that minimizes the required propellant mass. The numerical results, obtained by solving a number of optimal control problems, are arranged into contour plots, characterized by different and well-defined behaviors depending on the value of the initial spacecraft propulsive acceleration, the final orbit radius, and the thruster's specific impulse. The paper presents also a semi-analytical mathematical model for preliminary mission analysis purposes, which is shown to give excellent approximations of the (exact) numerical solutions when the number of revolutions of the spacecraft around the Sun is greater than five. An Earth Mars cargo mission has been thoroughly investigated to validate the proposed approach. In this case, assuming a propulsion system with a specific impulse of 3000 s (comparable to that installed on the Deep Space 1 spacecraft), the results obtained with the semi-analytical model coincide, from an engineering point of view, with the numerical solutions both in terms of total mission time (about 8.3 years) and propellant mass fraction required (about 17.5%). By decreasing the value of the specific impulse, the differences between the results from the semi-analytical model and the numerical simulations tend to increase. However, good results are still possible if the number of revolutions of the spacecraft around the Sun is close to an integer number

Optimal Planetary Rendezvous with an Electric Sail

The aim of this paper is to discuss Electric Solar Wind Sail-based missions towards Venus and Mars. The analysis takes into account the real three-dimensional shape of the starting and arrival orbits and the planetary ephemeris constraints, using the JPL planetary ephemerides model DE405/LE405

Optimal solar sail transfers to circular Earth-synchronous displaced orbits

The aim of this paper is to evaluate the minimum flight time of a solar sail-based spacecraft towards Earth-synchronous (heliocentric) circular displaced orbits. These are special displaced non-Keplerian orbits characterized by a period of one year, which makes them suitable for the observation of Earth’s polar regions. The solar sail is modeled as a flat and purely reflective film with medium-low performance, that is, with a characteristic acceleration less than one millimeter per second squared. Starting from a circular parking orbit of radius equal to one astronomical unit, the optimal steering law is sought by considering the characteristic acceleration that is required for the maintenance of the target Earth-synchronous displaced orbit. The indirect approach used for the calculation of the optimal transfer trajectory allows the minimum flight time to be correlated with several Earth-synchronous displaced orbits, each one being characterized by given values of Earth- spacecraft distance and displacement over the ecliptic. The proposed mathematical model is validated by comparison with results available in the literature, in which a piecewise-constant steering law is used to find the optimal flight time for a transfer towards a one-year Type I non-Keplerian orbit

Solar Sail Optimal Transfer Between Heliostationary Points

This Note analyzes the transfer between two heliostationary points that are the same distance from the sun. The problem is addressed within an optimal framework in which a constraint is enforced on the minimum sun–spacecraft distance along the transfer trajectory