An analysis of the ZACube-2 mission operations

Abstract

This research entails a comprehensive analysis of ZACube-2 operational mission data that addresses on-orbit operations. Mission operations evaluation criteria will be investigated, including all available telemetry, tracking, and command data sets at system and subsystem levels, the orbital dynamics of the system, and the ground segment operations. An auxiliary analysis will investigate space weather and its effects on the mission, pertaining to how the system reacts in the presence of solar activity over specific areas of the Earth; therefore, giving an overall assessment of system robustness. From the data analysis that was completed on the various telemetry channels and subsequently the various resource budgets, there was no instance found in which any of the subsystems acted abnormally to an extent where the satellite was at risk for complete failure. A comparison of the various calculated resource budgets such as the link, power and thermal in relation to the designed resource budgets proved, that the resource budgets the engineering team used to design ZACube-2 were more conservative in nature than the respective resource budgets that were calculated using the provided telemetry values. The method in which the link budget was shown to be conservative was in comparing the UHF RSSI values for both ZACube-2 and the ground station. The UTRXC RSSI values aboard the satellite were compiled in a CDF graph which was then compared RSSI to the received power values conversion table found in the user manual. The downlink UHF RSSI values of the ground station were compared to downlink values stated in the link budget to validate the link margin. This method proved that the link budget was conservative, however, while the received power values were larger than the link margin the disparity was far too large for it to be realistic. It was found that there was an inherent offset, in the range of 50 dB to 60 dB, due to the RSSI values recorded by the mission control software are not absolute but rather, comparative, or relative to the ADC’s full scale. To standardize to an absolute value, calibration of the ground station's UHF receiver with a signal generator both at the receiver and along the downlink path to the antenna would be required. The power budget like the link budget was demonstrated to be conservative in addition to the calculation of the various power profiles, orbital parameters such as sunlit minimum, eclipse maximum, average power generated by the solar panels and orbital duration which was described in the said budget were calculated.

To calculate the orbital parameters, the battery charging and discharging telemetry was used to check when the satellite was in either sunlit minimum or eclipse maximum, respectively. This process was completed over a span of a day with the respective times averaged, the output of this process showed that the largest variance was approximately 2.613 minutes, which is within the margin of error of 3 minutes as this was the interval at which telemetry data was recorded. With the confirmation of the orbital parameters, the various solar panel configurations had to be verified of which each configuration yields a different total power generated, which is dependent on the number of solar panels generating power. For ZACube-2 the minimum required power generated is 6.4717 Wh. This value is achieved when a single 3U solar panel is in view of the Sun. Two separate telemetry-based samples were calculated and both sample power calculations did not meet the minimum power requirement. However, this deficiency was attributed to several factors such as the interval at which the telemetry was recorded, the incorrect combination of current and/or voltage readings belonging to a specific pair of solar panels, if the telemetry recorded was during solar declination and if the Sun was in a state of solar maximum or solar minimum. In total there are four power consumption profiles with each profile having a sun and eclipse variant specifying the minimum required power generated to satisfy the optimal operation of the satellite. The resultant power consumption profile calculations showed that the values described in the power budget were greater than the telemetry-based profiles with the smallest and largest discrepancy for the profiles “Downlink Eclipse” and “Payload Sun” being 1.6% and 53.8% respectively. Additionally, on average profiles that were reserved for when ZACube-2 was in sunlit minimum conditions used less power, with the smallest variation being 3.1%, than the profiles operated in eclipse maximum conditions, with the smallest variation being 1.6%. Lastly, while it may not be a resource budget in comparison to the budget used to calculate the required link and power needed, the thermal aspect of the satellite proved to be within manufacturers and design constraints. While no formal thermal simulation was finalized for the satellite, using a combination of telemetry and thermal calculations based on techniques described by Fortescue, Swinerd and Stark (2011) and Gilmore (2002), the thermal environment was characterised In regard to the thermal-related telemetry the various subsystems operated well within the respective thermal limits described by both the subsystems user manuals and aforementioned techniques manufacturer, implying that the passive thermal management techniques employed on ZACube-2 worked as desired. The hottest and coldest subsystems were the HSTXC of 37.2°C and K-line imager of -15.1°C, respectively, with the imager having the largest thermal difference when comparing the maximum and minimum temperatures experienced. Comparing these values to the maximum and minimum temperature limits from both methods resulted in the telemetry values demonstrating that the technique by Fortescue, Swinerd and Stark (2011) is more conservative than that described by Gilmore (2002), with the thermal range between the maximum and minimum temperature variation being smaller in the latter technique. The budgets being conservative is a positive, demonstrating that the techniques used by the engineering team when designing the satellite and future satellites are viable, with some areas to improve. There were multiple occasions in which telemetry channels shared the same period in which no data was recorded, or outliers were present in the data set with these instances not being mutually exclusive with documented space weather events leading to the causes for lapses in the recorded telemetry data. Overall, these lapses were attributed to system issues rather than an external environmental matter. In closing, while there is an opportunity to further improve and increase operational efficiency, ZACube-2 operated as intended without any major incident that resulted in the satellite being temporarily inoperable. The output of the research will provide an objective assessment of the operational performance of the system comprising space and ground segments against the mission design specifications and will compare as-designed features of the satellite with actual system performance. Design improvements will be recommended for incorporation in the design cycle of future missions further improving the forthcoming satellites operational functionality as well as the engineering team design methodology.