Takanobu Shimada

Durability evaluation of InGaP/GaAs/Ge triple-junction solar cells in HIHT environments for Mercury exploration mission

The Japan Aerospace Exploration Agency has been developing the Mercury Magnetospheric Orbiter (MMO), which is Japanese part of the BepiColombo mission. During its mission around Mercury, the spacecraft will be exposed to high solar irradiance of up to 11 suns, with an estimated maximum solar panel temperature of 230°C. In such an environment, solar cells are required to operate under high intensity and high temperature (HIHT) conditions. Therefore, it is necessary to evaluate the durability of solar cells to meet the power requirements throughout the mission life. We conducted a continuous operation test under HIHT conditions to examine the validity of the solar array configuration, using the interior planetary thermal vacuum chamber. Our HIHT tests clarified the following facts: (i) Transparency of the coverglass and the performance of the solar cells do not degrade and (ii) transparency of the DC93-500 adhesive in the top cell response region degrades mainly due to ultraviolet exposure at high temperatures. We decided to use AR0213 coverglass (from JDSU) with a thickness of 300 µm, which have a longer cut-on wavelength in ultraviolet region. With this configuration, the predicted decrease in Pmax due to the HIHT environment is 17.3% and that due to radiation effects is 11.0% Our new design will offer the available power at EOL of 394.2 W, which is 46.7 W greater than the required power.

Degradation analysis of InGaP/GaAs/Ge triple-junction solar cells in high-temperature and high-light-intensity environments by luminescence techniques

This paper demonstrates results of durability tests and photoluminescence spectroscopy of InGaP/GaAs/Ge triple-junction solar cells for Japans inner planetary missions. Degradation of the solar cells under high-light intensity and high temperature environments was evaluated by a forward current injection test and a continuous operation test. These tests revealed that the forward current application possibly causes more degradation than the actual solar cell operation. We diagnosed the solar cells in more detail by photoluminescence spectroscopy. The intensity of the band-edge emission decreased excessively after the forward current injection test, but did not decrease after the continuous operation test. This result agreed well with the change in the electrical property. No new deep level emissions were detected after the tests.

Reactant Recirculation Technique Utilizing Pressure Swing for Proton Exchange Membrane Fuel Cell System

Fuel cell systems aiming for high energy utilization require a reactant recirculation system in which unreacted reactants discharged from the outlet of the fuel cell are recirculated back to the inlet to minimize wastage of the reactants. Conventional recirculation systems using mechanical pumps have major drawbacks in terms of efficiency, vibration, and reliability. This paper proposes a novel reactant recirculation technique that utilizes pressure swings produced by the reactant supplies and consumptions. The pressure swing recirculation system requires only two check valves and a fluid control device. It, therefore, offers a simple, efficient, and highly reliable system. The pressure swing recirculation was applied for both anode and cathode systems. Experimental performance tests demonstrated that the fuel cell could operate for long hours with the pressure swing recirculation, whereas the cell voltage declined rapidly in dead-end mode operation.

On-orbit performance analysis on solar array paddle of X-ray astronomy satellite “Suzaku”

This paper presents analysis results for the on-orbit performance of a solar array paddle of the X-ray astronomy satellite Suzaku. The current generated by the solar array was decreasing significantly for approximate one year after mid-2011. We estimated the degradation of the output by simulating the on-orbit environment according to the JPL prediction method. The analysis results indicate that the on-orbit degradation of the solar array paddle is greater than the predicted performance degradation in a space environment. We determined that the difference between the on-orbit data and the analysis results could be attributed to either an increase in cell temperature or radiation degradation due to solar flares.