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KESSLER SLONGO ET AL. power point tracking (MPPT) techniques, high-efficiency solar cells, and energy-aware scheduling algorithms are some of the hot topics under research nowadays. Due to size restrictions and aiming low complexity in design, many nanosatellite designers adopt the direct energy transfer (DET) architecture. KySat-2 is an example of a successfully accomplished mission, based on this EPS topology. Designed by Morehead State University Space Science and Engineering group, KySat-2 EPS was powered by a set of gold-plated deployable solar panels with 26% of efficiency. It provided four high-power regulated rails (two 3.3 V and two 5 V) and a low-noise, low power 3.3V rail for noise-sensitive devices. The energy storage system was made of three 18650 lithium-ion cells connected in series, and the high-power rails reached efficiencies approaching 90%. 12,21 Aiming minimum space occupation and low power consumption, the EPS proposed for the AraMiS project has a boost regulator operating the solar panels close to their MPP. 16 In order to reduce the number of components, the designers opted by the constant voltage MPPT algorithm, using only analog devices. The EPS steps up solar panels voltage from 4.4 V to the distribution bus voltage level (14 ± 2 V). It provides power buses with 3.3 and 5 V voltage levels. The EPS efficiency analysis is demonstrated, calculating the main components power losses. Although this is a very detailed and well-described work, it does not compare the proposed solution with other EPS architectures. A 3U EPS efficiency analysis is presented by Gonzalez-Llorente et al. 22 The subsystem is based on a buck converter that steps down the solar panels voltage (15 or 7.5 V) to the litChium-ion battery range of 3.3 or 6.6 V. The authors define an optimum operation point for the DC-DC converter in order to achieve its maximum efficiency. The operation point is defined by the converter input voltage, output voltage, and output power. Therefore, the discussion is based on different solar cells connections configurations, and battery cells arrangement, that result in the most efficient EPS configuration. Different scenarios have been analyzed to achieve 98% of peak efficiency on the best configuration: input voltage of 7.4 V, output voltage of 3.3 V, and output current varying from 0.1 mA to 2.1 A. Only the buck converter topology is discussed in this paper, and it does not consider any MPPT technique. An interesting solution adopted for the ERPSAT-1 picosatellite uses fuzzy logic to obtain energy harvesting maximization. 23 The developed subsystem has three main blocks, which are the fuzzy maximum power point tracker, the power conditioner, and the hierarchical fuzzy subsystem controller. The fuzzy logic algorithm has been implemented in a dedicated microcontroller that controls a boost converter. Simulations have been performed to demonstrate the better efficiency of the proposed method when compared to the Perturb and Observe MPPT algorithm. Although a comparison is provided in this work,...

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This work presents a theoretical and experimental analysis of a copper mini heat pipe (MHP), fabricated from a sandwich formed between cylindrical wires and flat plates, which are welded by means of diffusion process. The edges formed between the wires and the plates provide the working fluid capillary pressure necessary to overcome all the pressure losses. Two different experimental set ups were developed: one for test in grav-ity (laboratory) and other for microgravity conditions (International Space Station—ISS). The main difference between them lies in the condenser section. In the laboratory, cool-ing water was used to remove heat from the mini heat pipe, while at the ISS, fins and air fan were employed. In gravity, three different working fluids were tested: water, acetone, and methanol, while, for the experiments at the ISS, just water was used. A model was developed to predict the maximum heat transfer capacity of the device. In comparison to the literature models, the main difference of the present model is the variation of contact angle to adjust the mathematical model. Therefore, the main contributions of the present work are development of wire plate mini heat pipe fabrication methodology using diffu-sion welding, improvement of the analytical model used to predict the maximum heat transfer capacity of the device, determination of the present technology optimum design parameters, and test data obtained under microgravity conditions. [DOI: 10.1115/1.4004526

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