Engineers are struggling to find a suitable landing spot on the rugged surface of comet 67P for the lander aboard comet-chasing spacecraft Rosetta.
With the first ever attempt to land a man-made object on the surface of a comet scheduled for 11 November, the team supporting Rosetta’s Philae lander is under pressure to propose suitable landing sites. The landing spot needs to be level, have sufficient Sun exposure to power the lander’s solar cells, but also has to give the spacecraft the chance to maximise its scientific potential.
"In selecting the landing site, we have to take many criteria into consideration and weigh them up against each other," said Stephan Ulamec from the German Aerospace Centre, Project Manager for the Philae lander.
"As we do so, it is certain that there will not be a perfect landing site – in reality, we will never find one. It just needs to be the best landing site that the comet has to offer."
The time for scanning the surface of the comet is running out as the shortlist of five prospective landing spots has to be finalised by 24 August.
The German Aerospace (DLR) centre is now working with French space agency (CNES) to evaluate the technical needs of the lander and its scientific instruments to make the best trade-off.
The teams are using data from instruments aboard the Rosetta spacecraft to assess conditions on the surface of 67P/Churyumov-Gerasimenko, including temperature fluctuations and surface shape and texture.
As a control signal from Earth takes over 30 minutes to reach the lander, Philae must take care of the landing by itself, automatically, using a procedure pre-programmed by DLR and with no real-time corrective actions from the control centre. Therefore, the lander team wants to avoid regions with large boulders, rock or fissures, to reduce the risk of damage during the landing.
Philae is expected to attach itself to the comet’s surface using two harpoons, which means a slope steeper than 45 degrees may be too much for the task to be carried out successfully.
"Also, we do not want to land in a site that has either constant daylight or night-time," Ulamec said, explaining such situation would be unfavourable for the energy supply and temperature of the lander. After an initial phase in which all ten instruments on board Philae are turned on and tested, the lander needs to be supplied with solar energy for as long as possible to allow thorough scientific investigation of the environment.
The final landing site will be announced by mid-October.