SwissCube is still doing well and alive. Over the last weeks, we have had several passes with lots of data and several passes with no data at all (besides the beacon). The satellite has experienced a few resets (5 since launch), which can be expected. That did not impact its functioning.
One newly involved student, Angelo, has been performing radiation tests at the Paul Scherrer Institute, in Villigen Switzerland, on the MSP 430 microcontroller. He could characterize its performance compared to ARM type controllers. Quite interesting... we are impatiently waiting for his report. We will post it as soon as possible.
Coming back to Swisscube, it is still rotating very fast, which prevents us from taking pictures. Leaving it alone, its rotation is actually decreasing, as can be seen in the attachment (thanks Anton!). The data seen in the graph comes from the analysis of the RF signal. If SwissCube keeps the same slowing rate, we should be able to start the bdot controller onboard by the end of January.
For those interested in the daily activities, you can check the live data received from the satellite on: swisscube-live.ch
Over the week-end of Oct. 24-25, the satellite's attitude control system experienced a "reset" of the microcontroller. The satellite has one microcontroller per subsystem (power, communication, payload...), but only the attitude control one was reset, which leads to think that some external event happened. That behavior had never been seen during the tests.
The satellite's communication still works well, as all its subsystems. We experienced communication difficulties due to some software anomalies on the ground and also due to the spinning of the satellite. We are currently resolving the ground software anomalies (related to the uplink TNC). Both the EPFL and the Fribourg ground stations are used for uplink and downlink of the data. We are also seeing perturbations on the I2C data bus aboard the satellite, also never seen during tests. But they do not prevent us from talking to the satellite. We are investigating the reasons.
Our efforts to understand the rotation rates of the satellite are making progress. The new students working on it are improving models and getting close to making predictions. One of the students made an Antenna Deployment Test in air, which shows that we do have a residual rotation after deployment. Further testing will be done in vacuum next semester at the EPFL LCSM laboratory. You will be able to see one video of the deployment tests on the SwissCube main website. (See here) Although this does not totally explain the initial high rotation rates, and although it is very counter-physical, it is one potential explanation . We will be investigating another reason with additional tests at DTU (Denmark Technical University) with measurements of the residual magnetic dipole of the satellite.
We also had a discussion with the Radio Amateurs of Vaud to share our understanding and findings about the high rotation rates. Quite a few radio-amateurs are proposing very good explanations and solutions to this high rotation. Work is still in progress and we still have a few weeks of work before implementing a detumbling (de-spinning) procedure.
We really want to thank all the Radio-Amateurs in the world sending us very valuable data every day. They allow us to check that the satellite is still in good health, and also participate in our understanding of the behavior of the satellite when it is far away from Switzerland.
The satellite is still in very good health, all subsystems send green housekeeping data. The operations still concentrate on explaining the high rotation rates seen after launch and the strategy for slowing it down (call detumbling). Most of the new students in the operations team are now analyzing the data and trying to understand the rotation from the RF signature and other housekeeping parameters (like temperatures, current in the solar cells). But this task is not easy as the rotation rates (200-400 deg/s) are higher than the sampling rates for the sensors on-board. It is a tricky problem, but this makes it even more motivating! In this matter, we are getting help from the Radio-Amateurs around the world and from other universities in Europe. As soon as the satellite is more stable, we will start taking pictures.
One student performed antenna deployment tests, which tend to confirm that it could be the cause of the high rates in the Y-axis, but we are still investigating why we experienced high rates in the X-axis as well.The ground stations are now being used daily and we are trying to improve them as we go along. Commanding and reception on satellite data is done from both ground station (HES-Fribourg and EPFL).
We're still waiting on positive ADCS simulation results before engaging new operations with ADCS. All the housekeeping data from a very good pass today indicate that the spacecraft is still very well except for its high rotation. Both ground stations are now completely operational for individual or parallel usage.
Analysis of the audio signals shows that the spacecraft rotation slowed down a little. But this decrease is still nowhere near the maximum value that the gyroscopes can measure. The ADCS simulations are still being done and we are still looking for a solution. Both ground stations are now in operation and this increases the amount of data we can receive. We are still in the process of getting the maximum data we can from the spacecraft, but the communication was difficult these past two days. This was observed at both ground stations.
The spacecraft is not reporting changes on the attitude; simulations are being done to decide what we will do next week and to be sure that we won't make the problem worse. All the data downlinked during the last two days indicate that otherwise the spacecraft is in good health. Solar cells current production and batteries level are still higher than expected and we are able to do FSK communication for the complete duration of all the sunlight passes. On the ground, we tested for the first time both ground stations (EPFL and HE-FR) at the same time. But due to a problem with the azimuth controller of one our antennas, test will resume on Monday after repairs are made.
Unfortunately the ADCS could not reduce the (too) high rotation we had since the start of the mission. In fact it increased the rotation of the satellite.Yesterday after finding that out we downlinked as much housekeeping as possible and we powered down the ADCS.We also tested the payload board by powering it up and getting its housekeeping. It seems fine (we tried to downlink to image but the communication link was not good, so no image yet!). Today we decided to power up ADCS, disable the stabilization algorithm and set a fixed current output on one magnetotorquer (use it as a permanent magnet). It should help the spacecraft stabilizes around this axis but it will not reduce its high rotation speed.
We could do everything on the first pass and, thank to a very good link with the spacecraft, also get a lot of housekeeping data that should help us have a better understanding of the rotation. The second pass was also only for housekeeping data to check that everything is still ok onboard (it is). On the third and last pass we could only start the downlink at the end of the pass and could not get any useful data.
28 Sept: Here are the news for the week-end and today:
SwissCube did catch "a cold" in the night between Friday and Saturday. Nothing to serious, but the beacon sound was a bit distorted. Messages could be still decoded by the amateur radio community, but it was a bit harder. Signal got back to normal Saturday evening. The behaviour of some components of the beacon must have changed due to the low temperature. This already happened during the thermal tests and the signal always got back to normal.
Today we started the ADCS on the first (low elevation) pass and retrieved housekeeping for our three powered up subsystems (COM, EPS and ADCS). We spent the next (long) pass retrieving as much housekeeping as possible. Thank to an amateur radio in Germany (DK3WN), we are now able to recover packets that we couldn't receive properly by replaying data that he received. It's very useful as we really need practice with the ground station to operate it properly. We couldn't send any telecommand to the spacecraft during the third pass. We tried to do some tweaking of the uplink transceiver before and apparently made things worse. After that we also recalibrated the pointing of the antenna as it seemed a bit off.
All the housekeeping is in the green; the spacecraft is ok but is rotating fast. The current estimation is of 37rpm (a bit more than half a rotation per second). Tomorrow(29.09.09) we'll see if the ADCS could stabilize it a bit.
25 Sept: Here is today's report on the operations.
The first pass at 11h32 was too low and too short to receive anything. But we received this morning beacon data from a radio amateur in Japan telling us than the spacecraft was OK with good battery levels.
We then had a great pass with a lot of data downlinked on the FSK link. We could receive the minimum and maximum values for the temperatures, voltages and current of the EPS since the start of the mission (we were really looking forward to these values). We could also get the three onboard archives (temperatures, voltages and solar cells currents) containing a full orbit worth of values. Things were working so great that we decided to turn on the ADCS for a few minutes to get its first measurements and that was also a success. On the third pass we had less success and could only downlink a few housekeeping measurements of EPS and COM and one for the ADCS. We're still having some troubles getting our telecommands up to the spacecraft.
25 Sept: Passes are expected at:
- 11h32: low and short pass, beacon only;
- 13h07: nice high and long pass (13 min), uplink and downlink again of HK parameters
- 14h45: low elevation but long pass, will perform high data rate uplink and downlink again.
24 Sept After a first pass over Switzerland at 12h19 with a very good beacon signal (bip-bip), the team tried the "high data rate" communication link (1200 bauds, FSK) at the 13h56 pass and then 15h35 pass. The uplink had difficulty to be heard by the satellite at first, it is probably rotating fast. We are still evaluating its rotation rates. But at the second pass, the uplink went through and housekeeping data was downlinked. This housekeeping data shows that the satellite is doing great!
24 Sept The first pass of the day went very well, with a very clear beacon signal. All systems (turned-on) work great!
23 Sept 14:47 (Swiss time) On the second pass over Switzerland, we could decode telemetry thanks to Fribourg ground station:
the batteries are fully charged (4.1 V), were around at -4o Celsius, and the power and communication systems are working fine. The solar cells are
also producing between 350 mA and 500 mA.
23 Sept 13:20 (Swiss time) We have recognized the call sign and the thirty seconds of silence between two beacon messages. This means that the message emitted by the satellite is generated by the software and thus the satellite communication system is working great.
23 Sept 12:20 (Swiss time) The satellite has been heard from California and the Netherlands.Listen to it
23 Sept 8:51 (Swiss time) Contact with OceanSat-2 has already been established. We're now waiting for contacts with cubesats. We expect first contact with SwissCube between 13:10 and 13:22 (Swiss Time).
23 Sept 8:41 (Swiss time) SwissCube has been deployed!!!!!
23 Sept 8:30 (Swiss time) Waiting for cubesat separation in about 10 minutes.
23 Sept 8:30 (Swiss time) Vehicle performance is perfect.
23 Sept 8:24 (Swiss time) Fairing separation. Vehicle performance nominal
23 Sept 8:21 (Swiss time) Successful take off
23 Sept 8:09 (Swiss time) Final readiness polls should now be conducted
23 Sept 8:02 (Swiss time) All the system on the launch vehicle have been powered on and everything is ready to go.
16 Sept 2009 : SwissCube has been integrated on the upper stage of the PSLV launch vehicle. All the signals are now positive for a launch on Wednesday 23 September at 8:21.