No. 143 - Deep-space telecommand testing
03 September 2010 15:05
Report for the period 31 July to 27 August 2010.
This report covers 28 days of Rosetta operations. During the reporting period the spacecraft remained configured in active cruise mode in preparation for the new test and validation campaign required for the deep space phase of the mission. The main activities were the high-gain antenna (HGA) strobing test and the low-gain antenna (LGA) telecommand link test performed on 20 August.
During the reporting period mission operations were conducted using the ESA New Norcia (NNO) ground station and DSS-43 (Canberra, 70 m) NASA Deep Space Network (DSN) antenna.
At the end of the reporting period on 27 August, Rosetta was 576 million km from Earth (3.85 AU); the one-way signal travel time was 32 min 02 sec (1922 sec). The spacecraft's distance from the Sun was 456.5 million km (3.05 AU).
High-gain antenna strobing test; low-gain antenna telecommand test
During the hibernation entry window next year, Rosetta will be between 3.7 and 4.4 AU from Earth. At those distances and once Rosetta is spinning, it will be necessary to be able to command Rosetta using the LGA and to detect the strobing signal coming from the HGA.
On 20 August, a test was conducted to characterise the telecommand link to the LGA and detection of the HGA strobing signal at 3.75 AU from Earth. It was possible to command the spacecraft using the LGA at 7.8 bps from the New Norcia and DSS-43 ground stations. Both stations detected the HGA strobing signal; this signal was obtained by commanding the HGA to sweep the Earth several times, simulating a strobing signal.
The reporting period was a bridging phase between the last science phase of the mission before hibernation and the real deep-space mission. The spacecraft has now crossed the boundary of 3 AU heliocentric distance and is entering the real deep-space phase. Activities are now focused on hibernation entry and a successful comet rendezvous; as part of this, a first solar array performance test is planned before the conjunction phase.