Set Of Thrusters Research Articles

A Comparative Analysis of Energy Consumption by Conventional and Anchor Based Dynamic Positioning of Ship

One of the requirements for ships equipped with dynamic positioning system is the ability to maintain a given position in various hydrometeorological conditions. At the same time, efforts at reducing electricity consumption are made in order to reduce operating costs and emissions of exhaust gases, such as sulfur oxides and greenhouse gases such as carbon dioxide (CO2). For this purpose, the ship designer at the design stage must predict both how much energy the ship will theoretically use during operation and how the expenditure can be reduced. The publication presents a comparison of energy consumption with two different approaches to ship positioning: the use of classic dynamic positioning utilizing a set of thrusters and by using a set of anchors. In order to determine the energy consumption during positioning, the matrix method was used, on the basis of which the analysis of the ability to hold the position of the ship (capability plot) was performed, in accordance with the recommendations of the classification society DNV GL. Thanks to this analysis, it was possible to find such a distribution of thrust vectors on propulsors that the ship would not lose its set position under the hydrometeorological conditions specified in the analysis. As a result of comparing the two positioning systems, it turned out that using anchor-based positioning uses 24% less energy than positioning based on a set of thrusters, which translates into 24% less CO2 emissions into the atmosphere.

A cutting edge 6U CubeSat ADCS design for Earth observation with sub-meter spatial resolution at 230\u2013380\xa0km altitude

A 6U CubeSat for Earth observation in 230–350 km orbits with sub-meter resolution is presented. The proposed Stable and Highly Accurate Pointing Earth-Imager (SHAPE) system’s attitude determination and control system (ADCS) is composed of a single momentum bias wheel with magnetic bearings at rotational speeds of 6000–7000 rpm and refined magnetorquers. Reaction wheels as instability source are absent. The ADCS stabilizes the spacecraft attitude by counteracting the torques from external disturbances in the thermosphere down to < 1° pointing accuracy and < 0.1° instability. The momentum wheel was sized to an angular momentum of 1 Nms based on the worst-case atmospheric density of the next solar cycle. The 0.5 Am2 magnetorquer dipole moment provides with low power consumption, mass and cost, high reliability and sufficient torque. The ADCS initialisation study revealed three stable start-up modes, while the all-spun state is achieved using a set of thrusters. De-tumbling analysis show that the magnetorquers reduce the tumbling rates with magnitudes of up to 35°/s to mean motion values in less than an orbit using a static gain B-dot controller. A 3U camera design capable of sub-meter spatial resolution at 230 km altitude is presented which complies with the SHAPE spacecraft system design. The instrument has a single deployable primary mirror enabled by a deployment hinge design with hysteresis < 0.5 μ. This payload combined with air-breathing electric propulsion technology at 230 km nominal altitude boosts the SHAPE system Earth observation potential down to sub-meter spatial resolution and enables tuning of the mission lifetime by orbit keeping.

Monte-Carlo Based Optimal Control Strategy Through State Estimator in Autonomous Space Systems

The present research relies on a control strategy to deal with the dynamics and its kinematics of the space systems, while a band of parameters uncertainties and disturbances in line with the variations of the thrust vector, center of mass, engine misalignment, moments of inertial and so on are taken into real consideration. To present the investigated outcomes in such a real situation, the process noise that are related to a set of thrusters and the measurement noise that are also related to a set of sensors are considered to be dealt with through optimal state estimator scheme. There are the double control loops including the inner loop and the outer loop, which are organized based upon a combination of low and high thrusts levels to handle three-axis rotational angles and its rates. The aforementioned thrusts levels in connection with the uncertainties and disturbances are handled through the Monte-Carlo based method to consider the proposed approach performance in a series of experiments. The acquired investigated results indicate that the performance of the proposed strategy is verified in which the well-known state-dependent Riccati equation based on the three-axis rotational angles and the corresponding angular rates is considered as the benchmark approach to be compared in the same conditions. DOI: http://dx.doi.org/10.5755/j01.itc.46.4.15391

Modular Testbed for Spinning Spacecraft

The ground verification of a spacecraft control algorithm is commonly done via air bearing facility. Air bearing testbeds are frequently developed for testing a three-axis stabilized spacecraft control algorithm but hardly for a spin-stabilized spacecraft. A modular testbed for testing a spinning spacecraft has been developed at Surrey Space Centre initially for the real-time verification of a prolate spinner slew control algorithm. This testbed is made from commercial off-the-shelf components with a modular system design approach through rapid control prototyping using Matlab xPC Target and is extendable to other rapid control prototyping techniques. It is equipped with a novel low-cost monocular vision system for attitude determination with accuracy of 0.06 deg and angular velocity accuracy of . For the current specification, a cold-gas propulsion system is fixed to the testbed with a two-degree-of-freedom thruster set that can deliver up to 0.25 N of thrust and an air bearing capability that gives three degrees of freedom with a maximum tilt angle of 30 deg. In this paper, the testbed implementation is described, and the test platform is verified.

Multi-Objective Optimization Applied to Real-Time Command Problem of Spacecraft Thrusters

A novel approach to solve the real-time command problem of spacecraft thrusters, called the thruster multi-objective command method, is proposed in this paper. The reaction control system technology uses a set of thrusters in a special setup to simultaneously provide force and torque to the spacecraft. The thruster management function calculates all the candidate solutions that solve the thruster coupling problem. Then, a discrete multi-objective optimization method selects at every control cycle the best combination of thrusters and their firing time duration, which simultaneously optimizes a group of four objectives: the force error, the torque error, the propellant mass consumption, and the total number of pulses. The proposed method is included in a coupled translational and attitude control system applied to the final approach rendezvous scenario. Furthermore, all elements of the guidance, navigation, and control loop are accurately designed and implemented in a simulation framework. Results indicate effectiveness, robustness, and a better performance when compared to the usual single-objective optimization case.

Geometric Controller for both FPWSO and Shuttle Tanker Dynamically Positioned

An integrated geometric control for an offloading operation from a FPWSO (Floating, Production, working, Storage and Offloading) to a shuttle tanker is proposed. The floating systems are in tandem configuration connected by a hawser. Both vessels maintain their position and heading by means of their sets of thrusters and propellers. The geometric theory is widely applied to control articulated multibody systems. The use of this theory for non-articulated vessels, with the control of the relative distance, results in a control law that commands both vessels integrally instead of commanding each vessel independently. Hence relative distance can be easily controlled, avoiding both an undesired proximity of the vessels, or excessive hawser tension. The control performance is assessed by means of numerical simulations and compared to a PD-like control with non-integrated controller. Relative distance is maintained very successfully as a result of this approach.

Application of SDRE technique to orbital and attitude control of spacecraft formation flying

This paper proposes the application of a nonlinear control technique for coupled orbital and attitude relative motion of formation flying. Recently, mission concepts based on the formations of spacecraft that require an increased performance level for in-space maneuvers and operations, have been proposed. In order to guarantee the required performance level, those missions will be characterized by very low inter-satellite distance and demanding relative pointing requirements. Therefore, an autonomous control with high accuracy will be required, both for the control of relative distance and relative attitude. The control system proposed in this work is based on the solution of the State-Dependent Riccati Equation (SDRE), which is one of the more promising nonlinear techniques for regulating nonlinear systems in all the major branches of engineering. The coupling of the relative orbital and attitude motion is obtained considering the same set of thrusters for the control of both orbital and attitude relative dynamics. In addition, the SDRE algorithm is implemented with a timing update strategy both for the controller and the proposed nonlinear filter. The proposed control system approach has been applied to the design of a nonlinear controller for an up-to-date formation mission, which is ESA Proba-3. Numerical simulations considering a tracking signal for both orbital and attitude relative maneuver during an operative orbit of the mission are presented.

인공위성 연료배관의 유압특성 연구

One of the way to derive design parameters of the fuel feeding system in satellite propulsion system is to analyze unsteady flow of liquid propellant (hydrazine). During steady thruster firing the flow rate is constant: if a thruster valve is abruptly shut down among a set of thrusters, pressure spikes much higher than the initial tank pressure occur. This renders the fuel flow unsteady, and the fluid pressure and flow rate to oscillate. If the pressure spikes are high enough, there are possibilities that propellant explosively decomposes, thruster valves we damaged, and adiabatic detonation of the hydrazine propellant is potentially incurred. Reflected shockwaves could also affect the calibration and operation of the pressure transducers. These necessitate the analysis of unsteady flow in the propulsion system design, and pressure behavior inside the propellant line obtained through some governing parameter variation is presented in this work.

On-orbit thruster calibration

Significant errors in force and moment output as well as large control coupling forces can result if the attitude and translation control thrusters of a spacecraft are not calibrated properly. Thruster calibration is also important for estimating fuel usage so that spacecraft life can be accurately predicted. A general procedure to accurately determine the true relationship between the commanded and the actual force output of a set of thrusters is presented. This relationship is determined from data generated by a spacecraft while it is in orbit. The calibration is based on the Kalman filter estimator and is verified by a digital computer simulation of the Gravity Probe B spacecraft dynamics. Gravity Probe-B is an Earth orbiting gravitational physics experiment, which will test several aspects of Einstein's general relativity theory. A set of 18 proportional thrusters generate attitude control moments around three axes and translation control forces along three axes for full six-degree-of-freedom control. A total of 108 parameters are needed to characterize both the force and moment outputs of all 18 thrusters. The ability to calibrate these parameters to an accuracy of better than 1 % rms is demonstrated.

Pulsed plasma thruster of the erosion type for a geostationary artificial Earth satellite

Analysis is made for the possibility of erosion pulsed plasma thruster (PPT) application while solving the task of maintaining the point sustaining a long-operating geostationary artificial Earth satellite. The concept of an erosion PPT with a pulse energy of 200–300 J, designed for holding the attitude of a satellite of 500 kg mass over 10 years is presented. The thruster, with a lifetime of 2–3 × 10 7 pulses, produces a total pulse of 2.5 × 10 5 Ns, consuming up to 13 kg of propellant (Teflon). Estimations have shown that the thruster total mass will not exceed 50–60 kg for the flying PPT. Even in the case of a two-fold redundancy the thruster set mass should comprise no more than 0.20-0.25 of the satellite mass. The prospect of a rail design for the PPT discharge chamber with lateral propellant feeding is experimentally examined.

Deployment and retrieval optimization of a tethered satellite system

This paper describes the optimization analysis results of deployment and retrieval of a tethered satellite system. The system is composed of two small satellites connected by a long tether. One of the satellites is equipped with a set of thrusters for purposes of control. The optimization analysis is based on the nonlinear equations of motion, and the optimized length law together with the optimized thrust histories are calculated. The optimization is performed with a MATLAB-based multicontroller algorithm. First, the algorithm is used to optimize the phases of deployment and retrieval for a simple model where the tether is represented by a massless rod. Then these results are used as a nominal path for a retrieval involving a more realistic model. When this model is used to simulate retrieval, the system is kept on the nominal path by means of a regulator. The optimization result, compared with results in previous papers, points to improved performance and a significant reduction in fuel consumption.

Temperature control of a liquid helium propulsion system

Two spacecraft, gravity probe B (GP-B) and the satellite test of the equivalence principle (STEP), incorporating onboard liquid helium cryogenic systems are scheduled to fly around the turn of the century. Effective propulsion systems can be implemented for these spacecraft by directing the helium gas which boils off from the cryogenic systems in specific directions through a set of thrusters. Due to extensive development and testing work, the ultra low flow rate helium thrusters for such a propulsion system are now considered proven technology. This article is concerned with implementing these thrusters into an effective overall propulsion system. A thermodynamic model relating the temperature, pressure, and flow rate of the propulsion system is derived. Based on this model a controller is developed which regulates the liquid helium supply temperature and pressure by varying the net heliqm mass flow rate through the thrusters. We show how the net mass flow rate can be controlled independently from the desired output thrust. The manifold pressure upstream of the thrusters is shown to remain remarkably stable even with fairly large flow rate variations. Using the GP-B spacecraft as an example we conclude that it is feasible to build a liquid helium based propulsion system with a very stable supply temperature and pressure.

On Orbit Thruster Calibration with Applications to Gravity Probe B

A general procedure to determine accurately the true relationship between the commanded and the actual force output of a set of thrusters is presented. This relationship is determined from data generated from a spacecraft while it is on orbit. On orbit thruster calibration measures the true outputs of the thrusters in the actual space environment in which they operate. The feasibility of the calibration technique is verified by a digital simulation of the Gravity Probe B (GP-B) spacecraft dynamics. GP-B is an Earth orbiting experiment which will test several aspects of general relativity. A set of 18 proportional thrusters generates forces and moments for three degree of freedom attitude and three degree of freedom drag free translation control of the GP-B spacecraft. A total of 108 parameters are needed to characterize the magnitude and direction of both the force and moment outputs of the 18 thrusters. The ability to calibrate these parameters to an accuracy of better than 1%is demonstrated.

Thruster-augmented active control of a tethered subsatellite system during its retrieval

The paper considers control of the rotational motion as well as longitudinal and transverse vibrations of a tethered subsatellite system during its retrieval to the shuttle. Control using a set of thrusters alone is studied first; then, a length rate control law augmented by thrusters is examined. The functional forms of the thrust components applicable to both cases are determined by analyzing simplified equations of motion. These are validated by computer simulation of the original equations. The schemes considered appear to be fairly effective in arresting the growth of rotations as well as vibrations while maintaining a nonzero tension in the tether. It is recommended that the exponential retrieval be replaced by uniform retrieval rate toward the end of retrieval.