(Hans Van den Groenendal sal meer vertel by die klubvergadering op 17 Februarie 2018)
SA AMSAT embarked on the development and launching of a South African Amateur satellite. The satellite is based on the CubeSat principle.
Mission of Kletskous
While radio amateurs all over the world raved about SumbandilaSat, local radio amateurs missed out as the vast majority of Southern African passes were used to download images, the primary mission of SumbandilaSat. It can thus be argued that SumbandilaSat did not fulfil its secondary mission of education and creating an interest in science, technology, engineering, mathematics and space in Southern Africa.
The mission of Kletskous is to give radio amateurs (and educational institutions) in Southern Africa easy access to a Low Earth Orbit (LEO) satellite on as many of the available passes as possible and thus stimulate interest and activity in space, satellites and amateur radio. A secondary mission is to fly scientific payloads proposed and designed by educational institutions in South Africa. This will further increase the participation of the youth in the project, helping to create interest in Science, Technology, Engineering and Mathematics (STEM).
The name, KLETSKOUS reflects on the mission and functionality of the satellite: “Klets” is an Afrikaans word for talking a lot.
“We want the Southern African radio amateurs to talk and operate much more via satellite. “Kous” is the Afrikaans word for a sock. The transponder that is planned for the satellite can also be referred to as a “bent-pipe” transponder, aligning the idea to the “sock”.
While it is considered that a 2 m uplink and 70 cm downlink is desirable from a user perspective, the International Radio Union (IARU) advises that 2 metre uplinks are problematic as in many parts of the world there are too many illegal, non-amateur transmissions. The satellite may receive these transmissions and make matters worse by re-broadcasting these unwanted signals on 70 cm.
Given that most hand-held transceivers available today are both 70 cm and 2 m capable, the problem of non-availability of 70 cm transmitting equipment will fall away and KLETSKOUS should be as easy and convenient to work as what SumbandilaSat was.
For KLETSKOUS the uplink is on 70 cm, and the downlink on 2 m. A linear transponder with a bandwidth of 20 kHz is utilised for both FM and SSB. A sub-carrier for a telemetry downlink will be included. For command and control purposes a separate 70 cm frequency will be used. Currently frequencies in the 435.100 to 435.140 MHz range are considered for the uplink and 145.860 to 145.980 MHz for the downlink. The above architecture will
ensure that the transponder is accessible for general use while the satellite is being commanded and controlled by the ground station. Maximum access by Southern African radio amateurs to KLETSKOUS is thus ensured.
The development of the transponder has progressed to the point where the second prototype is now ready for on the air tests. The output power is at the required level (≥ 200 mWatt) and the gain of the RF path has also been increased to the amount required. The transponder will be integrated with the On Board Controller (OBC) after completion of the RF tests. The command link and telemetry downlink will then also be addressed. Lessons learned and updates that may be required will then be implemented on a next prototype.
KLETSKOUS will also carry scientific payloads designed and developed by education institutions (schools) Schools and other interest groups have been invited to submit proposals. The original closing date was 31 March but with school holidays it has been extended till 30 April 2016
KLETSKOUS will be a 1U CubeSat. The dimensions are 10 cm x 10 cm x 10 cm. The total volume of the satellite is 1 litre and the maximum weight 1.3 kg. This is indeed very compact.
Deon Coetzee, is achieving the unimaginable by crafting space frames in his home work shop. The first two prototypes were very impressive. The University of Stellenbosch has come on-board and the optimisation of the space frame is now a project addressed by post graduate mechanical engineering student, Francois Oberholser.
Deon is also developing the mounting and deployment mechanism for the antennas as well as investigating multiple solar panels on KLETSKOUS.
A Command Link will be required for housekeeping purposes and also maybe in-flight reprogramming of the on-board controller, although this is risky business as the satellite may be killed if the reprogramming is unsuccessful. The best option would be to launch the satellite with flawless software already loaded, if at all possible.
A Scheduler will switch the transponder on and off at pre-determined times that will correlate to certain areas being over flown by the satellite. It will be possible to set the on-board clock of the Controller to ensure that the Scheduler performs correctly.
A Telemetry Downlink will be required. Some of the parameters that must be monitored on the ground include battery voltage and temperatures, orientation of the satellite via the radiation sensors in the centres of the five solar panels and the output voltages of the solar panels. The first prototype On Board Controller (OBC) has been completed and the house keeping software is currently being developed and tested by Brian McKenzie. The second generation board is now being completed and software updated with the emphasis on the communication lines with the other units on the CubeSat
Johan Erasmus , ZR1BMD working for ISIS in the Netherlands gave the following information: A Typical 1U CubeSat will have 12 solar cells (2 each on the 6 facets of the cube). When stabilised by a passive magnetic system the solar panels will have a typical efficiency of about 28% at the start of their lives and for a typical orbit will have 2.7 W “orbit average” and 3.6 W “sunlit average” power available. After some time in space the efficiency will fall to about 21% and the available power budget will decrease to 2 W and 2.7 W respectively. (That is not much to play with!) The final values will be very dependent on the orbit selected.
We are very fortunate that Denel Dynamics have provided KLETSKOUS with three prototype solar panels on a long term loan agreement. These solar panels have been characterised and the data obtained is now being used by Fritz Sutherland jnr. to develop the power supply for KLETSKOUS. The EPP is an advanced design that ensures optimum utilisation of the power supplied by the solar panels. During flight all the electronics, especially the Transponder must be powered with any surplus power being used to charge the batteries. When the batteries eventually fail the satellite should be able to function when it is lit by sunlight
With this amount of power available the maximum RF output of the satellite cannot exceed 0.5 W. In general the output power will have to be reduced to 200 mW or less. Experience with other Low Earth Orbit (LEO) satellites; including SumbandilaSat have indicated that successful communications with a modest ground station is not a problem at this power level.
Although the initial decision around the battery type was that Li-Polymer batteries gave the best power-to-weight and power-to-energy ratio for a widely used battery, the fire hazards associated with the battery type prompted a second look at battery types. Since many Li-Polymer batteries have been used in space applications, the risk seemed acceptable, but there are other (newer) types with similar weight and performance with less risk of fire or explosion that are becoming widely available.
Hence the decision was made to move from a Li-Polymer battery to a LiFePo4 (Lithium iron Phosphate) battery. Since the nominal voltage and charge requirements differ slightly, the search for a new battery charge controller began. Eventually the LT3652 was chosen, which offers the additional bonus of having MPPT (maximum power point tracking) on the supply.
Once the new battery and charge controller had been integrated on the EPS circuit diagram, it was time to start the next version of the PCB. The goal of this version is three-fold:
1) To perform a functional test of the new battery and charge controller on the EPS.
2) To do a layout conforming to the specified PCB outlines to ensure the board will fit correctly into the space frame. This included specification of the PC104 inter-PCB connectors and the pin-functions to be used on this connector.
3) To use the board in the first system-wide test. All the PCBs that make up the satellite system will be connected together in order to test how the system works as a whole.
Currently the schematic and PCB layout have been completed and the boards are being assembled and tested.
It will be difficult to implement active stabilisation in a 1U package together with the transceivers required for the main payload.
For Kletskous we are planning to use passive magnet stabilisation. The first development board is shown below. The board is positioned in the space frame at the centre of gravity.
Frik Wolff ZS6FZ. Member of the AMSAT SA CubeSat project team