Some eleven months ago we were able to announce that the planned SSETI ESEO GTO satellite would include a linear transponder which would be developed by a team from AMSAT-UK.

Since then we have been very busy developing all the various parts of the satellite sub-system and apologise for not having provided many updates on the progress made.

This report will hopefully help to correct this omission!

Firstly the launch is still planned for Nov 2008 from Kourou, indeed the www.sseti.net website already has a countdown clock running. This website also has lots of detail about the ESEO mission and includes a page under the ESEO, mission, teams tags which shows our input under the “COMM_AMSAT” heading.

Updates on the transponder project in general and the novel DSP based transponder system have been provided at both the AMSAT-UK and the AMSAT_NA meetings during the past few months. The relevant “Proceedings” give in depth information and are available from the respective organisations.

In outline there will be a U/S linear transponder with selectable DSP or analogue system providing at least 50kHz bandwidth. The transponder will have approx 10 watts of RF power which will be fed to two simple 0dB linear antennas. This configuration is required as the attitude control of the spacecraft may not be under control after the initial 28-day mission period. Work on the final link budgets is still underway but initial results confirm that a larger S band antenna will be needed by users than was required for satisfactory operation through AO40.

The 70cms receiver will also use a pair of linear antennas so circular polarisation of the groundstation antennas will be required.

The AMSAT sub-system is an additional back-up facility for the satellite and will operate alternately with the main S-band (2.0-2.2GHz) communication sub-system that is being provided by the COMM_PL team at the University of Wroclaw. We will also be providing the usual 400bps telemetry and the ability for command stations to send telecommands to the satellite and to receive downlink mission data via the “A” blocks in the 400bps data stream.

A full day meeting of the team was held in London on Saturday 18th November 2006 to further progress the work and here are some of the “headlines”

PRESENT: G3WDG, G3VZV, G0MRF, G4DDK, G7OCD, G6LVB, W3GEY (ON6UG was on holiday and apologised)

It was agreed to construct, before the end of the year, a full size aluminium model of the satellite structure to enable verification of antenna radiation from different attitudes.

The satellite has a CAN bus and we noted that we need to find out lots more about the full details of the specific CAN implementation, also what has happened about the planned Internet based CAN simulation development system.

It was agreed that we should check if any other subsystems and payloads will be especially sensitive to low level radiation at any particular frequencies. (Radiation from switch mode power supplies could give them problems – also we need to verify that our IFs do not clash with the COMM_PL system)

We need to check that the COMM_PL transmissions will not block our 435MHz receiver; therefore we need to identify the locations of their transmitter antennas and obtain their wideband output spectrum plots. Equally we must also ensure that our 2.4GHz TX will not radiate noise at 435MHz. Additional filtering may be required.

G4DDK discussed the choice still available between having a PLL or crystal local oscillator for the sub-system. For noise and other reasons it is likely that we will develop a crystal oscillator and multiplier configuration.

A simple hardware beacon is required for safe mode operation in the event of major OBC failure. G6LVB showed a circuit of a simple “ESEO” CW beacon where the speed of the CW could be temperature dependent!

G6LVB provided an update on the DSP system and noted that it will have a 3-day watchdog timer that will perform a hard reboot to the system.

We noted that the other teams need to be aware of risk of the solar panel wiring acting as antennas and bringing S-Band signals back inside the structure.

G0MRF described the switch mode power supply system and requested updates on the precise voltages and currents that would be need by each board.

G3WDG presented the results that he has achieved with 2 Engineering Model PA units, circulators, power splitters and dividers. The results show high efficiency, good linearity and full stability.

It was agreed that we should try to obtain some of the honeycomb structure panel material to perform some thermal tests with it.

Frequencies were agreed for completion of the IARU coordination form.

The proposed frequencies are as follows: The centre of the transponder on the S-Band downlink would be 2400.100MHz with a bandwidth of either +/-25kHz (analogue or DSP) or up to +/- 50kHz (DSP transponder only) The analogue beacon would be on 2401.150MHz (ie 25 kHz above nominal edge of transponder passband). The DSP beacon would be at 2400.100MHz

UHF uplink would be 435.900 centre of RX passband with nominal bandwidth of +/-25kHz if analogue or up to +/-50kHz if DSP. The transverter would invert.

We hope to finalise these frequencies within the next two months.

It was agreed to produce a “Flatsat”, with the hardware completed by end of March 2007 for delivery and demonstration to ESTEC. It was noted that the software would not be complete by then as considerable interface with the other teams will be needed to achieve “fully operational status”!