Noboru Takeichi

Practical Operation Strategy for Deorbit of an Electrodynamic Tethered System

This paper presents an operation strategy employing electric current switching for deorbit of an electrodynamic tethered system. The electric current in the tether experiences some unexpected changes due to its plasma environment and thermal conditions. Libration control through current switching, in which only the on/off status of the current is determined, can avoid such changes and unexpected instability. A simple control law to determine current switching to stabilize both in-plane and out-of-plane libration is presented. A new stability function is also presented to facilitate evaluating the stability of a tethered system on an elliptic orbit. The effectiveness of the libration control strategy and the stability function is demonstrated through several numerical simulations. It is clearly indicated that the stability function and a switching control toward a periodic solution facilitate an appropriate stability evaluation and an efficient libration control. The control strategy is considered to be easily materialized in actual electrodynamic tethered systems, and enables a more rapid and secure deorbit.

Fundamental Strategies for Control of a Tethered System in Elliptical Orbits

Fundamental strategies for libration control and deployment of a tethered system in elliptical orbits are presented. Through the physical interpretations of the dynamic behavior of tethered systems in elliptical orbits, it is shown that the periodic solution is proper as a control objective. An on ‐off control strategy using a thruster installed to the subsatellite is examined in elliptical orbits, and the periodic on ‐off control, which acts at certain true anomalies in the orbit, is presented as the fundamental strategy. For tether deployment, uniform rate deployment is examined in elliptical orbits through physical interpretations of the equations of motion and numerical simulations, and it is shown that the slower deployment is preferable to deploy a tether closer to the periodic solution at the end of the deployment. It is considered that the strategies presented in this study can be applied to tethered systems in orbits of an arbitrary eccentricity, as far as the libration is possible.

Dynamic Behavior of a Tethered System with Multiple Subsatellites in Elliptic Orbits

Dynamic behavior of a tethered system with multiple subsatellites subjected to both atmospheric drag and changes of gravity gradient in elliptic orbits is investigated. The tethered system is modeled as a combination of rigid-body subsatellites and lumped tether masses, and flexibility of the tether is considered. The results of the numerical experiments show that the libration of the total system can diverge due to the atmospheric drag, and the total system begins tumbling motion later. The physical interpretation is clearly presented by focusing on the deviation from the periodic motion. Effects of the atmospheric drag on the attitude motions of the subsatellites and the tension states of the tether are also investigated. It is shown that the large perturbations can cause partial slack states of the tether, which causes unstable attitude motions of some of the subsatellites.

Periodic Solutions and Controls of Tethered Systems in Elliptic Orbits

In this paper we study the periodic solution of the librational motion of a tethered system in elliptic orbit and clarify its mechanical characteristics. Basic libration control toward the periodic solution is also presented. A tethered system is modeled as a rigid body, and a set of nonlinear equations of motion about the librational and the orbital motions is formulated. An approximated analytical solution is obtained through the Lindstedt perturbation method. The total mechanical energy is formulated, and it is shown that it has the minimum value when the librational and orbital motions coincide with the periodic solution. This means that the periodic solution is the minimum energy solution, and that the periodic solution in an elliptic orbit has the same significance as the equilibrium state in a circular orbit from the mechanical point of view. A libration control toward the periodic solution is also investigated, and the effectiveness of this control strategy is demonstrated by using the periodic on-off control through a thruster installed on the subsatellite.

Validation Study on Descent Trajectory Optimization and Scheduling Improvement using Actual Operation Data

The effectiveness of the four-dimensional descent trajectory application and the scheduling algorithms in the arrival management are discussed. A descent trajectory configuration that is capable of arrival time control with possible minimum fuel consumption is proposed. Through the fuel consumption comparison between the current actual operation data and the four-dimensional descent trajectory, it is revealed that the application of the proposed descent trajectory reduces the fuel consumption more than 30% from the current operation on average. In addition, a scheduling algorithm is proposed that uses the time advance to minimize the operation cost. Through the arrival management simulation using the actual traffic data for its initial condition, the advantages of the proposed scheduling algorithm compared to a conventional one, that delays the following aircraft to create the safe separation, are investigated. It is clarified that the proposed algorithm including the time advance is able to reduce both the operation cost and the delay accumulation. The cruise traffic streams in the current operation are usually subject to large disturbances on cruise routes. The analyses in this study clearly demonstrated the effectiveness of the scheduling algorithm including the time advance even for such a largely disordered traffic stream. When some four-dimensional management are introduced into the cruise route, the effectiveness of the scheduling including the time advance is expected to be enhanced further.

A Self-Separation Algorithm for High-Density Air Corridor Allocated to Optimal Flight Trajectories

Algorithms for air corridor operation are discussed. The air corridor is considered to be segregated airspace that connects congested areas. In the air corridor, only aircraft capable of self-separation may operate and all the aircraft fly in the same direction while maintaining safety without instructions of air traffic controllers. To realize efficient operations, the optimal allocation of the corridor and appropriate self-separation procedures are indispensable. In this paper, the self-separation algorithms in the air corridor allocated along the optimal trajectory are discussed. Particularly, the effectiveness of conflict avoidance maneuvers is focused on. Through the numerical simulation using the vertical self-separation maneuver, it is demonstrated that the average fuel-burn increases since some aircraft need to change its altitude for operational safety. On the other hand, it is demonstrated that the horizontal maneuver is able to resolve conflict while minimizing extra fuel-burn with punctuality.