International Space Station Solar Array Research Articles

Temperature response characteristics of the thermal control system of alpha magnetic spectrometer under the operations of international space station

Abstract The alpha magnetic spectrometer (AMS) in orbit is thermally affected by operations of the international space station (ISS). According to long-term monitoring data in orbit, three kinds of the most frequent ISS operations were determined, they were locking the ISS solar arrays by themselves, changing the ISS flying attitude with locking solar arrays and rotating the ISS starboard radiator with locking solar arrays. The β interval of ( − 75 ° , − 21 ° ) in which these three kinds of ISS operations have the most significant effect on the AMS thermal environment was calculated in reference to the ISS geometric model, and the calculation result was proved to agree well with the temperature records in orbit. The AMS radiator heat balance model was found under the different ISS operations. The numerical simulations were performed to provide quantitative analysis on external heat flux on AMS radiators. Based on those, the general temperature responses of the AMS radiators following the ISS β angle under the most frequent ISS operations were analyzed accordingly. We found that the ISS operations have varying degrees of the thermal influence on the AMS radiators under the same β angle. The suggestions of controlling the possible temperature anomalies caused by the ISS operations were given according to the temperature response characteristics of the AMS components under the most frequent ISS operations.

Correlation of IRTAM and FPMU data confirming the application of IRTAM to support ISS Program safety

A “Real-Time” plasma hazard assessment process was developed to support International Space Station (ISS) Program real-time decision-making providing solar array constraint relief information for Extravehicular Activities (EVAs) planning and operations. This process incorporates real-time ionospheric conditions, ISS solar arrays’ orientation, ISS flight attitude, and where the EVA will be performed on the ISS. This assessment requires real-time data that is presently provided by the Floating Potential Measurement Unit (FPMU) which measures the ISS floating potential (FP), along with ionospheric electron number density (Ne) and electron temperature (Te), in order to determine the present ISS environment. Once the present environment conditions are correlated with International Reference Ionosphere (IRI) values, IRI is used to forecast what the environment could become in the event of a severe geomagnetic storm. If the FPMU should fail, the Space Environments team needs another source of data which is utilized to support a short-term forecast for EVAs. The IRI Real-Time Assimilative Mapping (IRTAM) model is an ionospheric model that uses real-time measurements from a large network of digisondes to produce foF2 and hmF2 global maps in 15 min cadence. The Boeing Space Environments team has used the IRI coefficients produced in IRTAM to calculate the Ne along the ISS orbital track. The results of the IRTAM model have been compared to FPMU measurements and show excellent agreement. IRTAM has been identified as the FPMU back-up system that will be used to support the ISS Program if the FPMU should fail.

Preliminary Measurements of ESD Propagation on a Round Robin Coupon

The propagation dynamics of spacecraft electrostatic discharge (ESD) flashover plasmas have been a topic of increasing interest in the past few years. To investigate ESD propagation and possible contributions from facilities, methodology, and analysis, we performed inverted gradient ESD tests of an International Space Station solar array coupon as part of a U.S.-wide Round-Robin test campaign. Geosynchronous earth orbit charging environments were simulated and current transients were simultaneously measured on ten solar array strings. In addition, images of ESD events were collected by low- and high-speed cameras, and an array of eight Langmuir probes positioned above the coupon was monitored. Preliminary results will be discussed, with special attention given to the effect of different analysis techniques on derived propagation velocity. Comparisons will be made with the results from other labs, and implications for spacecraft ESD events will be discussed.

Zero-propellant maneuver guidance

Maintain its orbit and control its attitude, the International Space Station (ISS) is equipped with thrusters as well as four control moment gyroscopes (CMGs). The CMGs can be used only for attitude control, while the thrusters can be used for either attitude control or orbit corrections. For attitude control, thrusters can complete reorientations much more rapidly than the CMGs since the torque capability of the thrusters is at least an order of magnitude larger than the torque capability of the CMGs. However, using thrusters has signifi cant disadvantages, such as consumption of propellant, solar array contamination, and stressing of the ISS structure. CMGs can avoid these disadvantages as long as they operate within their angular momentum capacity because they are powered by electricity generated by the ISS solar arrays. If the CMG momentum becomes saturated, that is, the total angular momentum of the CMGs reaches its maximum value, the control authority of the CMGs is considered lost. For further information about CMGs and saturation, see "CMGs, Momentum Saturation, and Robotics Analogy." Even at a slow rate of rotation, large-angle ISS maneuvers performed with CMGs can result in momentum saturation because the CMGs must compensate for the environmental disturbance torques on the ISS along the fl ight-software-generated attitude trajectory. As a result, until 2006 all large-angle ISS rotations were performed using thrusters.

Mitigation of Thruster Plume Erosion of International Space Station Solar Array Coatings

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