Signals from the comet mission Rosetta

ESA launched from Kourou on 2 march 2004 with an Ariane 5 launcher the spacecraft Rosetta. The aim is to land on a comet for the first time ever. To do this, the spacecraft needed to be put in the same orbit at the comet. This was achived by several gravity-assist encounters with Earth and Mars. All changes of the trajectory can be followed by Doppler recordings of the frequency, like in the plots below from our station in Kiel-Rönne. On this day, Rosetta was in about 11 million km distance from Earth.

This shows the main signal of Rosetta's transmitter. Apart from the strong main carrier one notes several weak signals. Their presence indicates that the craft was transitting data. In the lower part of the image the signal strength is displayed like in a pen recorder. The colour is a measure of the signal strength. The times are indicated at the left edge.

This shows the modulation 16 kHz above the carrier.

Modulation 800 kHz off the main carrier.

The entire spectrum of the signals is composed of the main carrier and subcarriers at 16, 220, and 800 kHz on either side of the main carrier