Numerical simulation of the flow around an air data sensor (ADS), which measures flow angles and Mach numbers using surface pressures on a nose cone, was conducted in this study. Effects of the half-cone angle on the flow angle and Mach number measurements were investigated. Results show that a large half-cone angle achieves high sensitivity of flow angle measurements. Results further demonstrated that a small half-cone angle achieves high-sensitivity of Mach number measurements. To satisfy these conflicting requests, we proposed the use of bi-conic nose cones with two gradients. High sensitivity was achieved for both flow angle measurements and Mach number measurements using this bi-conic nose cone.
Noise failure, particularly due to random walk error (RWE) degradation behavior, is one of the critical failure modes for fiber-optic gyroscopes (FOGs) in space applications. In this paper, firstly, the analytical model of RWE is presented and the affected parameters are listed according to the gamma irradiation damage mechanism. In addition, the influence of temperature is also included. The deterioration of affected parameters is determined through a 60Co radiation experiment on optic and optoelectronic components. Based on the parameters’ deterioration range and assumed distribution properties, their importance to the noise failure is calculated through the Sobol method, a global sensitivity analysis method. In the computation steps, the Latin Hyper Sampling (LHS) based Monte-Carlo numerical simulation technique is adopted. It is determined from calculation results that the detected light power (DLP) is the noise failure characteristic which is the most sensitive parameter in the space environment. Finally, another 60Co radiation experiment with the same conditions is performed on a superluminescent diode (SLD) FOG. The original noise degradation behavior is compared to the simulated RWE, calculated according to DLP, and the result shows that they follow trend almost identical. This supports the conclusion that DLP is the most sensitive noise failure characteristic for SLD-based FOGs.
A sliding mode controller with an optimized sliding surface is proposed for an aircraft control system. The quadratic type of performance index for minimizing the angle of attack and the angular rate of the aircraft in the longitudinal motion is used to design the sliding surface. For optimization of the sliding surface, a Hamilton-Jacobi-Bellman (HJB) equation is formulated and it is solved through a numerical algorithm using a Generalized HJB (GHJB) equation and the Galerkin spectral method. The solution of this equation denotes a nonlinear sliding surface, on which the trajectory of the system approximately satisfies the optimality condition. Numerical simulation is performed for a nonlinear aircraft model with an optimized sliding surface and a simple linear sliding surface. The simulation result demonstrates that the proposed controller can be effectively applied to the longitudinal maneuver of an aircraft.
On-orbit servicing is of interest for long duration missions due to potential benefits such as increasing the mission lifetime. In order to realize on-orbit servicing Coulomb, formation satellite systems lend themselves as one possible approach. This paper discusses such a system. A method is proposed for deploying a small deputy satellite from a docked condition on a main satellite to a Clohessy-Wiltshire bounded solution. A series of elliptical guidance paths are used for this purpose. Additionally, a method of changing the relative plane of motion of the deputy satellite is presented. This method requires the reorientation of the main satellite. Numerical simulations indicate that such maneuvers are possible within the given assumptions. It is observed that even in the worst-case scenario, positional errors can be kept within several centimeters.
The establishment of exact two-dimensional flow conditions in wind tunnels is a very difficult problem. This has been evident for wind tunnels of all types and scales. In this paper, the principal factors that influence the accuracy of two-dimensional wind tunnel test results are analyzed. The influences of the Reynolds number, Mach number and wall interference with reference to solid and flow blockage (blockage of wake) as well as the influence of side-wall boundary layer control are analyzed. Interesting results are brought to light regarding the Reynolds number effects of the test model versus the Reynolds number effects of the facility in subsonic and transonic flow.
This paper describes the performance of an arcjet thruster using dimethyl ether (DME) as a propellant. DME, an ether compound, has adequate characteristics for space propulsion systems; DME is storable in a liquid state without a high pressure or cryogenic device and requires no sophisticated temperature management. DME is gasified and liquefied simply by adjusting temperature, whereas hydrazine, a conventional propellant, requires an iridium-based particulate catalyst for its gasification. In this study, thrust of the designed kW-class DME arcjet thruster is measured with a torsional thrust stand. Thrust measurements show that thrust is increased with propellant mass flow rate, and that thrust using DME propellant is higher than when using nitrogen. The prototype DME arcjet thruster yields a specific impulse of 330 s, a thruster efficiency of 0.14, and a thrust of 0.19 N at 60-mg/s DME mass flow rate at 25-A discharge current. The corresponding discharge power and specific power are 2.3 kW and 39 MJ/kg.
This paper presents a system identification technique, called iterative learning identification for multi-variable continuous-time state-space (SS) systems using iterative learning control. The transfer function (TF) parameters are regarded as functions with respect to the SS parameters that are to be identified. The relationship between the SS parameters and the response error is explicitly derived. An updated law of the SS parameters is given so as to reduce the response error. The proposed technique is applied to estimation of aerodynamic derivatives in a lateral linear model of aircraft. The effectiveness is demonstrated in numerical simulations.
The analytical and numerical methods for estimating power and efficiency of a multi-wing cascade configuration of an elastically supported flapping wing power generator are presented. The analytical method is based on the 2D linear potential aerodynamic theory and the numerical method is based on 2D Navier-Stokes equations. Both methods are applied to the two- and three-wing configurations of a hydroelectric power generator oscillating in in-phase and anti-phase modes of oscillation, and the effects of the oscillation mode and wing distance on the power and efficiency of the system are clarified. The power increment expected by introducing the ten-wing configuration is estimated to be approximately 25–33% for the anti-phase mode of oscillation with the adjacent wing distance of 2.0–2.5 chord lengths compared with the simple sum of power generated by a single wing.