SPORT Spacecraft

Investigate the state of the ionosphere that leads to the growth of plasma bubbles.

Study the formation of ionospheric plasma bubbles, which are the main sources of radar reflections in the equatorial region. Investigate the state of the ionosphere that leads to the growth of plasma bubbles. The relationships between plasma irregularities in satellite altitude and the radio scintillations observed in the equatorial region of the ionosphere will also be studied.

During the AIT process, one of the major issues that occurred was the failure of the battery during the spacecraft proto flight model environmental test. The main issue was that the pouch cells of the battery swelled during the thermal vacuum test, and this caused a deflection on the PCB consequently the malfunction of the EPS system. As a project philosophy, the engineering unit of the EPS of the spacecraft was a spare unit, so the team decided to run an environmental test on the spare units of the battery. Unfortunately, the same problem occurred in this spare unit at a lower temperature and in a short period of time. After some time in ambient conditions, the battery was still functional but not reliable for flight or for handling on ground, so it was stored in a safe condition but discarded for use. At this late stage of the development, changing the battery configuration was not an easy task. The supplier was contacted but, unfortunately, they could not provide us with the same set of battery packs in terms of capacity, since the cells themselves were not available on the market anymore. The team searched for solutions that minimize rework or changes in this late stage and we could find a battery pack that could replace the damaged one, and the delivery time could be accommodated by the project schedule. 

SPORT encountered an issue during transportation, and determining the exact cause or location of the problem has proven challenging. The first visual inspection showed that the spacecraft had moved from its fixed position, and it was damaged. Finalized the unpacking, the team could see the broken piece of the probe. Further inspection showed that no damage occurred to the solar panels. The springs of the hinges of the booms were damaged but spare parts were available for exchange. Functional tests, as far as they could be tested, showed expected behavior, so it was determined that only the E-field probe was broken.  

Describe challenges of getting the first signals after SPORT’s placement in orbit, ground station problems, and spacecraft anomalies.

On December 29, 2022, within less than ten orbits, the SPORT team saw the first window of opportunity to communicate with the satellite over Brazilian territory. In that opportunity, INPE's ground station in Cuiabá received the first beacons from the spacecraft. 
With the first data samples from orbit, the team observed the spacecraft in a satisfactory general state. The spacecraft was in its SAFE operating mode and with the expected energy consumption. The battery was fully charged, and all temperature sensors were in the nominal ranges. 

Communications in the next few days became a challenge because of uncertainties in satellite tracking. The first orbits fit well into the initial pass predictions, which were based on the nominal state vectors provided by the launch provider. However, for the next days the team did not have access to SPORT's precise Two-Line Element (TLE) sets. Therefore, for several days the team struggled to track the satellite correctly and did not get much, or even any, telemetry. 

Not only during the period of TLE problems, but also afterwards, the SPORT team received invaluable assistance from the amateur radio community. Whereas INPE's ground stations were more specialized, and therefore had narrower line-of-sight, radio amateurs were able to receive and demodulate beacons, with which the SPORT team was able to determine that the spacecraft continued to be generally healthy. 

Although the spacecraft was generally healthy, an issue arose that continues to the day this text is written. The EPS has a watchdog mechanism that reacts to the lack of communication from the onboard computer (OBC) if it is over a certain time threshold - four minutes by default. This watchdog mechanism is triggered frequently, resetting the spacecraft at an average of about 26 hours. Much longer and shorter periods have been observed (from one orbit to five days). The SPORT team was not able to determine the cause of the problem, although some possibilities have been identified. Those include a software defect or malfunction in any of the nodes connected to the I2C bus. An analysis of the moments of reboots over approximately 100 occurrences (in three months) suggest there is no relation between the reboots and positions on the globe. 

The status check revealed that five out of the seven elements that should have been deployed were successfully deployed. One boom was not, and therefore also its respective array. This demanded manual deployment tries over the course of some days, with different parameters, including the deployment of the array to force the deployment of the boom above it. The tries were unsuccessful, and the elements remain stowed. 

The stowed solar panel array results in reduced power availability, which however has not caused problems or concerns during the mission so far. Eventually the decision was made to leave the booms stowed and proceed with the commissioning phase. At this point, the LEOP phase was considered over.

The EPS meets expectations, with adequate power conditioning and distribution. All power buses and switchable lines operate within their nominal operating ranges. Energy consumption levels are very close to what has been characterized during AIT. The only situations in which the battery was not fully charged or close to that were in tests involving the payloads, with a significant energy consumption. To this date, the battery has not undergone a significant depth of discharge, except in a handful of situations. 

Evaluation of the spacecraft housekeeping data, along with simulations on ground, led to the conclusion that there was a mismatch between the actual orientation axes of reaction wheels and the reference matrix embedded in the ADCS onboard software. Fortunately, we could change the elements of the reference matrix via telecommand (TC) and validate the correction through an open-loop flight test procedure.

The respective procedures to perform AAM and NM presented challenges because they rely on precise attitude determination by ADCS sensors, and it has been difficult to obtain valid attitude readings from the star tracker - the most precise sensor. Even when the star tracker achieves a valid attitude and despite control modes stabilizing the spacecraft in the inertial reference frame a few times, in most of the attempted cases the control system does not converge, and we do not observe a station-keep behavior. For that reason, obtaining nominal pointing for the science payloads is still an ongoing challenge. 

First, due to an undetermined reason, the uplink is intermittent even in good passes, causing the operators to sometimes need to resend TCs multiple times until the spacecraft receives and executes them. Sometimes the spacecraft does receive TCs, but the downlink fails, causing the response to a TC to be lost and sacrificing precious pass time. There are also infrastructure issues that happen sporadically that cause passes to be lost, such as network connectivity problems between the control room and the ground station antennas. Also, some procedures such as scheduling an X-band downlink pass take several TCs that could have been synthesized into fewer during software development, by means of an automated procedure.

The superset of all data generated by the bus and by the payloads is downloaded via X-band. The downlink has been successfully demonstrated several times, which validates the end-to-end chain (data collection to data analysis on the ground by the science teams). However, the X-band downlink also presents a difficulty, which is the fact that the onboard X-band antenna is directional. Coupled to the lack of nominal pointing, and with a low (but not null) angular momentum, it makes the success of any given X-band transmission an uncertainty. 

Spacecraft and operations by Brazil, coordination and funding by NASA.

They are public about their problems, challenges and lessons learned, which is great to see.

• BATTERY - Clyde Space

• DANTESat
• HSKSAT
• LORIS
• NutSat
• OPTIMAL-1
• ORCA2Sat
• SS-1
• MARIO
• PetitSat
• SPORT
• TJREVERB
• Astrocast 17
• Astrocast 18
• Astrocast 19
• Astrocast 20
• Thybolt-1
• Thybolt-2