RCS Thruster Research Articles

Mass property estimation on TSE(3) via unscented Kalman filter using RCS thrusters

Estimation of spacecraft mass properties in the presence of noise is a nontrivial problem that, when properly addressed, can substantially reduce the crew time devoted to cargo management, control effort expended to manage fuel mass, or both. The estimation of such properties is treated here using a dual unscented Kalman filter (UKF) where the dynamics of the rigid-body spacecraft are formulated on the special Euclidean group SE(3) and its tangent bundle TSE(3) to avoid singularity and nonuniqueness issues found in attitude parameterization sets. The dual UKF on TSE(3) is developed, and a specific methodology is proposed for the estimation of the constant mass properties. An excitation approach is employed in the mass property estimation scheme. Arbitrary sensor suite placements are considered and implemented in the measurement model to capture real-world spacecraft behavior. Furthermore, a reaction control system with duty cycle constraints and noisy thrust values is implemented to account for uncertainty in the excitation inputs. With these features, the methods contained herein are found to be effective at estimating mass properties.

Recent Advances in LOX / LH2 Propulsion System for Reusable Vehicle Testing

The third-generation vehicle RVT#3 equipped with a pressure-fed engine, which had upgraded in terms of durability enhancement and a LH2 tank of composite material, successfully performed in repeated flight operation tests; and the vehicle reached its maximum flying altitude of 42m in October 2003. The next step for demonstrating entire sequence of full-scale operation is to put a turbopump-fed system into propulsion system. From a result of primary system analysis, we decided to build an expander-cycle engine by diverting a pair of turbopumps, which had built for another research program, to the present study. A combustion chamber with long cylindrical portion adapted to the engine cycle was also newly made. Two captive firing tests have been conducted with two different thrust control methods, following the component tests of combustor and turbopumps separately conducted. A considerable technical issues recognized in the tests were the robustness enhancement of shaft seal design, the adjustment of shaft stiffness, and start-up operation adapted to the specific engine system. Experimental study of GOX/GH2 RCS thrusters have also been started as a part of a conceptual study of the integration of the propulsion system associated with simplification and reliability improvement of the vehicle system.

Laser Ignition Condition for a New RCS Thruster Using Green Propellant

Laser ignition condition was studied for a new reaction control system using green propellant of GH2/GO2 by the use of laser-produced ablation plasma. Dependence of the laser pulse width on the minimum ignition laser energy was measured experimentally. Temporal behavior of the laser pulse gave an explanation of the dependence in 10 to 22 ns regime. Heating slope threshold consisting of slope threshold and duration threshold was newly introduced for the interpretation. This new concept could describe not only the explanation of the dependence but also a possibility of more efficient ignition condition.

非対称柔軟構造を有する宇宙機のトルクアーム摂動を考慮したスラスタ制御系設計

Spacecraft, Attitude Control, Flexible Structure, Unsymmetric Structure, Torque Arm Abstract: Unsymmetric flexible spacecrafts have particular dynamic characteristics; when the attitude control actuator such as RCS thruster is used, the imbalance between negative torque and positive torque is caused. And even worse, an inertia matrix and a coupling matrix are changed depending on the displacement of the rotational paddle and the mobile sensor. In this paper, an attitude control system with consideration of these characteristics is proposed. Location of thrusters is designed to satisfy that the nominal control torque is larger than the imbalance torque. And control method includes PD, filter and variable gain, which maintain high quality of closed loop system. The validity of the proposed method is verified through the numerical simulation results.

非対称柔軟構造を有する宇宙機のダイナミクス解析

Most of earth observation satellites have a single solar array due to the requirement imposed by the optical sensor visibility. This requirement makes spacecraft configuration highly unsymmetric, which produces particular dynamic characteristics. When the actuator such as RCS thruster is used, sensitivity from the displacement force to the attitude varies depending on the control frequency. This causes the imbalance between negative torque and positive torque on the main body, in other words, rotational center shifts from the mass center of the spacecraft. In this paper, this unsymmetric characteristic is formulated, and even more bending moment and shearing force acting on the root of the solar array are formulated. And then notations for designing a structure and a controller are indicated. Given a numerical model, formulated characteristics are also shown quantitatively.