Space station orbit design missions are characterized by a long-duration and multi-step decision process, which makes its optimization design very complicated. An integrated nonlinear programming (NLP) model is developed by considering the interaction effects of different flight segments of a space station. A two-level optimization approach is proposed to optimize the total propellant consumption while satisfying different constraints. The up-level problem employs the orbital altitudes of each flight segment as design variables, and adopts the simplex method to search for the optimal solutions; the low-level problem employs the maneuver impulses and times within each flight segment as design variables, and the objective function is calculated by combining approximate an analytical method and a shooting iteration method. The proposed approach is evaluated in two test cases of a six-month orbit mission and a nine-month orbit mission. The results show that the proposed approach can effectively optimize the space station long-duration orbit design problem, and can save considerable propellant by 60–70% compared with previously proposed space station orbital strategies.
Responsive communications or Earth surveillance missions typically require frequent revisits to any point on the Earth's surface and employ a constellation with two satellites to improve coverage performance. As a new approach to constellation design, in this paper, a novel constellation is presented by fixing the interval between successive revisits at all latitudes. Analytic and numerical simulations are implemented to illustrate the existence of such a revisiting constellation in a large region parameterized by the relative values of right ascension of ascending node and argument of latitude. We also present a global investigation to address the existence region of the PTR constellation, associated with the relationship between the characteristic parameters and the orbital elements (for example, semi-major axis and inclination). In order to design the stationkeeping strategy for PTR constellation, a new concept of J2 invariant PTR constellation is introduced. Compared to a single-burn strategy tracking a specified PTR constellation, the improved strategy has a clear competitive advantage of reducing the control frequencies or costs down to one fifth.
This study explores a multidisciplinary design optimization method for the conceptual design of hypersonic aircraft. By integrating analysis methods into the optimization problem, the design of the aircraft and its flight trajectory are successfully optimized. In addition, the use of approximation models to accelerate time-consuming analyses without losing accuracy is proposed. Moreover, because aerodynamic heating is expected to be significantly higher during high-speed flights, the heating effects of the hypersonic aircraft are evaluated. Finally, the characteristics of the optimal solution are investigated, and the effectiveness of the proposed multidisciplinary optimization is confirmed.
In recent years, the power generation requirement of spacecrafts has increased in order to load them with many mission devices and to extend their lifetime, hence, high voltages are used. However, such high voltages can cause electrostatic discharges on solar arrays, resulting in damage to the solar arrays. Therefore, we use an antistatic coating, which mitigates the surface charging on solar cells, in order to prevent the discharge. It is considered that an antistatic coating can mitigate surface charging and can prevent discharges on solar cells. The purpose of this research is to develop a coating to mitigate the surface charging applicable to geostationary Earth orbit satellites. We selected a candidate coating with the required surface resistivity and vacuum resistance. Furthermore, we selected a commercial-off-the-shelf antistatic coating after considering the experimental results of charging mitigation performance when simulating the charging condition in space. The candidate agent was coated on a conventional solar array coupon panel, and the charging mitigation performance of the latter was evaluated. We have confirmed a dramatic improvement in charging mitigation performance with this coated conventional solar array coupon.
This paper presents two techniques in iterative learning identification (ILI) when the zero initial state condition is not achieved. One is to obtain acceptable impulse responses. The other is to measure the response error to the exclusion of non-zero initial state factor. This paper proposes an estimation technique using the least-squares (LS) method for the former and introduces discarded data in measurement of the response error for the latter. The ILI with the proposed techniques is applied to estimation of the aerodynamic derivatives in a lateral linear model of aircraft. The effectiveness of the proposed techniques is demonstrated in numerical simulations.
Cycle-slip detection is mandatory prior to estimating positions based on carrier-phase observations. Recently, inertial sensors are integrated to detect cycle-slips regardless of sizes and combinations of cycle-slips in different frequencies. However, since inertial sensors contain errors such as random noise and bias, performance of the cycle-slip detection depends on the sensor performance. In general, there is a trade-off relationship between cost and performance of sensors, and we need to select appropriate sensors to achieve required cycle-slip detection performance. Therefore, we need a standard to select appropriate sensors. This paper introduces a procedure to predict allowable sensor error limit for gyroscope and odometer aided cycle-slip detection using theoretical formulation. By using error models of sensors, an error equation is set to predict error contributions from the sensors contained in the monitoring value that is used for cycle-slip detection. Simulation data is used to evaluate derived error equation and predict the error limit of sensors achieving objective performance. As a result, allowable sensor error region is predicted to detect 1 cycle-slip as a minimum detectable cycle-slip. This approach can be extended to accelerometers, and then it can be applied not only to vehicles on land, but also to those in aerospace.
A fundamental algorithm using the relative position and velocity vector and flight intent for the aircraft self-separation operation in a high density air corridor is presented. A high density air corridor is expected to be an air space where aircraft capable of airborne self-separation are allowed to fly in the same direction. An appropriate self-separation algorithm is indispensable to operate it safely and efficiently. In this study, a typical free-flight algorithm is examined to investigate its suitability for the corridor operation. Through a series of traffic simulations, we clarify that the free-flight based algorithm causes many aircraft to perform excessive heading change maneuvers, and frequent conflict occur against pilots' intent. To avoid any conflict, the self-separation algorithm is improved by introducing the flight intent in the corridor that all aircraft intend to fly in the same direction. Through the numerical simulation, the improved algorithm facilitates a more intuitive aircraft maneuver to achieve the conflict-free operation with much fewer maneuvers. It is concluded that the flight intent has a significant role to develop a self-separation algorithm capable of the safe and efficient high density corridor operation.