Alim Rüstem Aslan

TURKSAT-3USAT: A 3U communication CubeSat with passive magnetic stabilization

TURKSAT-3USAT is a three unit CubeSat developed for voice communication at low earth orbit. The payload is a VHF/UHF transponder operating at amateur bands. The transponder and all other subsystems, except the stabilization, are doubled for redundancy. Where possible, both COTS systems and in-house development is employed. The energy is provided using lithium polymer batteries together with super capacitors. Satellite stabilization is accomplished using passive magnetic attitude control system with hysteresis rods. Based on the recent United Nations regulations and CubeSat standard, the satellite is to include a de-orbiting system which will make it reenter the atmosphere following completion of its life time. The 3USAT is foreseen to be ready for launch, early 2012.

Micro synthetic jets and their interaction with a cross flow in slip regime

The flow field generated in and around a micro synthetic jet actuator is analyzed using the an existing Navier-Stokes solver. The solver is modified to accommodate slip wall boundary condition proposed in literature for micro scale flow problems. Two actuator cavity shapes, rectangular and triangular, are investigated for quiescent and cross-flow external domain conditions. Results are presented and compared for slip and no-slip conditions. Cavity shape is found to affect the orifice expulsion velocity profile. Cross-flow affects the orifice velocity distribution as well as the flow field inside the cavity.

Computing Separated Flows in MEMS Devices

Fluid flows in micro devices span the entire Knudsen (Kn) number regime. Depending on the Kn range, a full continuum or a full free-molecular analysis may be applicable. In the present study, flows in the Kn range of 10−3 to 10−1 are considered and they are modeled using a conventional Navier-Stokes solver. Its boundary conditions, however, have been modified to account for the slip velocity and the temperature jump conditions encountered in these micro-sized geometries. The computations have been performed for straight micro channels, a micro backward facing step, and a micro filter. The present results are then compared with analytical formulae and other computations available in the literature. The results indicate that the rarefaction and compressibility effects present in these micro devices have been accurately predicted. In the case of slip flow, the separation is found to occur at a higher Reynolds number compared to the corresponding no-slip flow case. As the next step of the study, micro synthetic jets will be computed and the optimal cavity actuator geometries will be sought for desired flow deflections.Copyright

Reliability Based Design Optimization of a CubeSat De-Orbiting Mechanism

We optimize de-orbiting mechanism of a 3-Unit satellite structure to enable a reliable and efficient orbit decay process through enhancement of aerodynamic drag with a probabilistic design approach. The system consists of spiral springs as energy producing mechanisms needed for deployment and thin membranes needed as aero-brake structures. A multi-objective optimization problem is formulated to maximize both aerodynamic drag force and also moment produced by spiral springs for a carefree and fast orbit decay. Mass of membranes and stresses acting on spiral springs are subjected to constraints for lightweight and durability. An in-house code is developed to evaluate the deterministic optimization criteria in terms of the optimization variables which are attributes of thin membranes and spiral springs. In space environment, atmospheric density is highly affected by solar radiation and also the system components are strictly related to manufacturing quality, so uncertainties in design parameters are incoorperated into optimization and a reliability based design optimization of the de-orbiting mechanism is performed. Dimensions of membrane structures, outside diameter of spiral springs and atmospheric density are considered to be uncertain parameters. These uncertainties are propagated by Monte Carlo Simulation method which is integrated into reliability evaluation loop in the optimization framework. Finally, de-orbiting duration values of pareto optimal designs are computed using Satellite Tool Kit where it is shown that the selected optimum design is expected to satisfy the specified maximum life-time criterion.

PETRI-NET MODELING AND PROTOTYPE OF A MULTIMICROSTRIP ANTENNAE NETWORK FUZZY CONTROLLED SYSTEM FOR PICOSATELLITES

This article focuses on antenna array management on board picosatellites. The fuzzy controlled multimicrostrip antennas network is introduced for selecting among four antennas, the choice of which is most important in terms of received signal power. Because the values are approximate and imprecise, the integration of a fuzzy controller based on selection rules by an expert is adequate. System design through the steps necessary to validate its behavior before implementation include Petri-net modeling, simulation, and integration of optimized algorithms to minimize computation time and avoid possible system blockages.

Contribution of UNISEC-global to capacity building in space engineering

Capacity building in space engineering is vital process to space development at both the national and international levels. Long term sustainability is also vital to the future space activities. This is a key theme of the discussions in global space forums such as UNCOPUOS. The issue of increasing density of debris in orbit is very relevant to nano-satellite activities at university level. The University Space Engineering Consortium (UNISEC) in Japan was established to support and promote practical space project development activities, such as nano-satellites and hybrid rockets at university level. The UNISEC concept in Japan is to facilitate activities by providing a platform where members can show and exchange the progress and lessons learned from each other. Sharing UNISEC experience and know-how with non-space faring nations was one of the main motivation to establish the UNISEC-Global in 2013 as well as fostering the international cooperation. This present paper presents the concept of UNISEC, establishment of UNISEC-Global and its contribution to the long term space sustainability and development.

HAVELSAT: A software defined radio experimentation CubeSat

Despite the small amount of available volume, CubeSat missions have proven to be quite useful, especially for scientific data gathering, educational purposes and small scale industrial equipment testing. The aim of this article is to discuss the design principles and project goals of a CubeSat that is part of the QB50 project. HAVELSAT is a double-unit CubeSat with one functional and one scientific unit. The scientific payload of HAVELSAT is a Software Defined Radio for communication. The satellite also performs a small scale onboard image processing.

Thermal vacuum chamber test of a DC-DC converter

A voltage multiplier (DC-DC converter) is tested in simulated space environment to establish a benchmark result for further studies. The literature includes a variety of methods to design such systems; however, test results are very rare.