The European Space Agency (ESA) and its Rosetta mission partners are working to juggle the spacecraft’s flight plan to help with renewed Philae lander science investigations on 67P/Churyumov-Gerasimenko.
By combining radio-wave data exchanged between Rosetta and Philae as part of the CONSERT experiment with trajectory data and the current model of the shape of Comet 67P/Churyumov-Gerasimenko, the location of the lander has been determined to lie within an ellipse measuring approximately 16 x 160 m. The CONSERT ellipse corresponds to the outer limits of the various solutions identified for the likely landing site of Philae, although this depends to some extent on the shape model assumed. Image credit: ESA / Rosetta / Philae / CONSERT / MPS for OSIRIS Team / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA.
ESA engineers have determined that Philae is already being exposed to sufficient sunlight to heat it to an acceptable operating temperature and to generate electricity.
“Power levels increase during the local ‘comet day’ – the part of the about 12 hour comet rotation when the lander is in sunlight – from 13 Watts at comet sunrise to above 24 Watts. It needs at least 19 Watts to switch on the transmitter,” explained Dr Patrick Martin, Rosetta Mission Manager.
The main task now for the mission partners is to determine how to optimize Rosetta’s orbit so as to facilitate contact and enable the science investigations.
Currently, the spacecraft experiences two possible communication slots per 24 hours. Until 7:35 p.m. EDT (04:35 p.m. PDT) on 16 June, Rosetta will be flying an orbit set by already-uploaded commands on the terminator – the plane between comet day and night – moving out from about 125 miles (200 km) to 146 miles (235 km) altitude. This orbit is not optimized for lander communication, so longer periods of contact may not be possible until the trajectory has been changed.
“With work done by the flight dynamics and operations team and based on intense planning being conducted with the mission partners today, a new orbit will be devised that ensures optimum lander communications beginning with the next command upload later tonight,” said Dr Paolo Ferri, ESA’s Head of Mission Operations.
This new orbit will include an already-planned reduction of distance from the comet’s nucleus, down to 110 miles (180 km) versus 125 miles (200 km), and ‘nadir pointing’ – continuously pointing Rosetta’s communications unit at the comet. The orbit will be flown by Rosetta starting after 7:35 p.m. EDT (04:35 p.m. PDT) on 16 June until 19 June, aiming to enable more and longer contacts with Philae, especially towards the end of this period.
Philae shut down on 15 November 2014 after completing its main science operations sequence on the comet when the primary battery expired as expected after about 60 hours.
On the evening of 13 June 2015, the lander came out of hibernation. A radio link between Rosetta and the lander was established for 85 seconds. More than 300 ‘packets’ – 663 kbits – of data were received.
A second, smaller burst of lander data was received on 14 June, lasting just a few seconds. These data were confirmed to give the current status, showing the lander’s internal temperature had already risen to 23 degrees Fahrenheit (minus 5 degrees Celsius).
The lander’s memory has stored over 8,000 packets of additional status data, but it is unclear from when in recent days they were recorded.
