Indirect low-thrust trajectory optimization with gridded ion thruster model

The work deals with indirect optimization of minimum-time and minimum-fuel interplanetary trajectories when gridded ion thruster models are considered. Using an accurate model of solar electric propulsion is beneficial in preliminary mission design, and allows including operational constraints. The maximum thrust and the specific impulse are expressed as a function of thruster input power, which is achieved by means of point-fitting lines that match the performance capabilities of the thrusters. Minimum-time and minimum-fuel problems are formulated to be solved by indirect optimization. In order to increase the accuracy and robustness of the shooting procedure, analytic Jacobians are derived, and a hybrid switching detection technique is used to improve the integration accuracy for minimum-fuel problems. Two examples of Earth-to-Mars transfer and Near-Earth rendezvous mission using the realistic NASA’s Evolutionary Xenon Thruster (NEXT) are given to substantiate the feasibility and effectiveness of the proposed method.

Trajectory Design for the ESA LISA Mission

The three Laser Interferometer Space Antenna (LISA) spacecraft are going to be placed in a triangular formation in an Earth-trailing or Earth-leading orbit. They will be launched together on a single rocket and transferred to that science orbit using Solar Electric Propulsion. Since the transfer Δv depends on the chosen science orbit, both transfer and science orbit have been optimised together. For a thrust level of 90 mN, an allocation of 1092 m/s per spacecraft is sufficient for an all-year launch in 2034. For every launch month a dedicated science orbit is designed with a corner angle variation of 60° ± 1.0° and an arm length rate of maximum 10 m/s. Moreover, a detailed navigation analysis of the science orbit insertion and the impact on insertion errors on the constellation stability has been conducted. The analysis shows that Range/Doppler measurements together with a series of correction manoeuvres at the beginning of the science orbit phase can reduce insertion dispersions to a level where corner angle variations remain at about 60° ± 1.1° at 99% C.L. However, the situation can become significantly worse if the self-gravity accelerations acting during the science orbit phase are not sufficiently characterised prior to science orbit insertion.

Precise Formation-Flying Telescope in Target-Centric Orbit: the Solar Case

We present the general concept of a telescope with optics and detectors mounted on two separate spacecrafts, in orbit around the telescope’s target (scopocentric or target-centric orbit), and using propulsion to maintain the Target-Optics-Detector alignment and Optics-Detector distance. Specifically, we study the case of such a telescope with the Sun as the target, orbiting at $\sim $ ∼ 1 AU. We present a simple differential acceleration budget for maintaining Target-Optics-Detector alignment and Optics-Detector distance, backed by simulations of the orbital dynamics, including solar radiation pressure and influence of the planets. Of prime interest are heliocentric orbits (such as Earth-trailing/leading orbits or Distant Retrograde Orbits), where thrust requirement to maintain formation is primarily in a single direction (either sunward or anti-sunward), can be quite minuscule (a few m/s/year), and preferably met by constant-thrust engines such as solar electric propulsion or even by solar sailing via simple extendable and/or orientable flaps or rudders.

Solar Wind Measurements from the Planetary Magnetometer Onboard the BepiColombo Spacecraft

<p>BepiColombo is en-route to Mercury. The boom carrying the planetary magnetometers (MPO-MAG instrument) was deployed in space on 25th of October in 2018. After the deployment, the magnetic disturbances arising from the spacecraft have been greatly decreased. Since the deployment, the fluxgate sensors have been monitoring the magnetic field continuously except for the solar electric propulsion phase. Extensive calibration and data processing activities have since enabled us to greatly decrease spacecraft-generated <br>disturbances in the magnetic field observations; these activities constitute a key step towards making the data <br>suitable for scientific analysis. We present a few cases of identified magnetic disturbances, discuss the challenges <br>they pose, and compare methods to clean the data. We also compare MPO-MAG measurements to observations by the <br>Advanced Composition Explorer (ACE) solar wind monitor, thereby highlighting the small-scale nature and rapid <br>evolution of interplanetary magnetic field (IMF) variations. We conclude with an overview of the scientific <br>goals of the instrument team for the in-orbit mission phase.</p>

Modeling of Solar Electric Propulsion System for UAVs

UAVs are growing their importance in both civil and military applications. The endurance of UAVs are related to their on board fuel carrying capacity which is limited by the weight class of aircraft. There is a need for long endurance UAVs for persistent Intelligence, Surveillance, Target Acquisition, and Reconnaissance(ISTAR) missions. One of the solutions to overcome the endurance limitations for usage of UAV is the renewable energy. Among all renewable energy, solar energy is found more economical. Electrical powered aircraft/(UAV) propulsion system uses electrical energy to change the velocity of UAV. Electric propulsion system is now mature and widely used technology on spacecraft. In this work, UAV with solar cells on the surface of the wings as well as on board energy storage is discussed. This paper quantifies the requirement for perpetual endurance in solar-powered flight.