ESA Science & Technology - No. 2 - Activating Rosetta

Main Control Room at ESOC during the Rosetta Launch

Ground Stations

Spacecraft Activities

Initial activation of S-band transmission, using the 2.2 m large dish antenna, commenced at 23:16 on 3 March. Successful commissioning of the S-band up and downlinks on the low and high gain antennas took place throughout the night. Following on from this, configuration of the X-band, also using the high gain antenna, took place with a downlink signal received at both the Kourou and Madrid ground stations at 13:07 UT.

Termination of the S-band uplink occurred at 13:20 and X-band uplink established at 13:35. The X-band uplink was then terminated at 14:30 and uplink communications were re-established via the High Gain Antenna at S-band. By 7 March, tests of the X-band communications had been completed. These activities successfully demonstrated the nominal performance of the major communication systems, which will be critical for the mission. Due to the rapidly increasing distance between the spacecraft and the Earth, the possible data rate using the low gain antenna is already limited to 7.8 bits per second and this link will soon vanish. Using the High Gain Antenna the maximum data rate of 22 kbits per second is sustainable.

The attitude control system has undergone several characterization tests, such as gyroscope calibrations and determination of the friction in the reaction wheel system. This included, for the first time, switching on all four reaction wheels simultaneously. Substantial disturbance torques acted on the spacecraft during its first few days in orbit. Over the following days these torques gradually decreased to nominal levels. The phenomenon, attributed to the outgassing of the spacecraft, diminishes with time because the spacecraft is in the high vacuum of space.

Full configuration of the 25 Gbit solid-state mass memory took place on 4 March in order to support routine operations: creating data stores for all instruments and storing redundant files of application software. Activation of all memory modules for the mission is now complete.

Commissioning of the power subsystem took place at the end of the Madrid pass on 4 March. All checks were successful and the power subsystem behaved as expected.

The drive mechanisms of the solar array are being exercised during the early days of the flight in order to keep the solar cells perpendicular to the Sun as the spacecraft rotates. The azimuth and elevation drives, enabling the High Gain Antenna to track the Earth, have been extensively characterized. These mechanical functions are critical to the mission and they are working nominally.

Overview of Activities

Note all times are in Universal Time (UT)

LOS = Loss of Signal
AOS = Acquisition of Signal
EOT = End of Transmission

3 March 2004

4 March 2004

5 March 2004

Planned Instrument Activities

Planned Spacecraft Activities

Orbit Trajectory

At 12:00 on 8 March 2004 Rosetta was 1.988 million km from Earth. This placed it more than one million km outside its sphere of influence. Orbital elements are, therefore, quoted with respect to the Sun as Earth centric information is not so relevant at such a distance. The signal round-trip time was 13.26 seconds.