TanDEM-X Blog | 24. June 2010

Commissioning of the radar instrument – everything still ‘green’

The commissioning of the satellite went smoothly. Now, the radar instrument team must start their work. Each of the electronic units that make up the radar must be turned on one by one and tested. The instrument telemetry, received at the ground stations in Weilheim (Germany), O'Higgins (Antarctica), Svalbard (Spitsbergen, Norway), and St. Hubert and Saskatoon (Canada), will be sent to the control room in Oberpfaffenhofen for evaluation.

Here we compare operating currents, voltages, temperatures and many other parameters with the reference values, which were measured before on the ground before launch. Only then can the power-on sequence of the radar be continued. Testing must cover the solid-state memory for the radar data, the main radar electronics, the antenna control electronics and the active antenna itself. Special attention is always paid to currents, voltages or temperatures that are too high or too low – that is, deviations from the norm – which we have so far been spared.

All measurements were in the safe area, so the test depth could be increased. The digital components were verified with long sequences of test patterns and checksums. Here again, everything was flawless. The power-on test of the active radar antenna is the final step in this test sequence. An active antenna means that there is no large power amplifier and antenna radiator, but instead an array of 384 small transmit/receive amplifiers, with the same number of radiating elements. The power consumption of all 384 modules adds up to an impressive 4500 watts and an error could lead to overheating and discharge of the satellite’s battery. Therefore, these measurements are performed with great care.

Also in these tests, everything was as it was before launch. The subsequent analysis of telemetry from each individual module gave us the added assurance that there is no externally measureable change in any of the modules. Finally, it is clear that the reported values correspond in all respects with the specification and the radar can be cleared for more detailed tests. So far, everything is ‘green’!

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