After a triple landing, positioning it in a new, unplanned location, conditions were not optimal, but Philae was able to work for more than 60 hours sniffing the atmosphere, drilling and hammering to send the resulting data back to Earth.
The team responsible for the MUPUS (Multi-Purpose Sensors for Surface and Sub-Surface Science) instrument, which hammered a probe into the comet, estimates that Comet 67P is hard as ice:
Although the power of the hammer was gradually increased, we were not able to go deep into the surface,
explains Tilman Spohn from the DLR Institute of Planetary Research, who is leading the research team. Shortly after the triple landing, the scientists could only hope that Philae would be in a position that would allow the probe to be hammered into the surface. However, with MUPUS it has been possible to directly study the strength of a comet’s surface for the first time – and 67P/Churyumov-Gerasimenko proved to be a ‘tough nut to crack’.
We have acquired a wealth of data, which we must now analyse,
says comet researcher Spohn. Only the thermal sensors and accelerometers in the anchors that should have fixed Philae to the comet’s surface were not used, because they were not deployed during the touchdown.
Listening to the comet
The team of the SESAME experiment (Surface Electrical, Seismic and Acoustic Monitoring Experiment) can confirm that Churyumov-Gerasimenko is not nearly as soft and fluffy as it was believed to be.
The strength of the ice found under a layer of dust on the first landing site is surprisingly high,
says Klaus Seidensticker from the DLR Institute of Planetary Research. The instrument CASSE, which sits in the feet of the lander, was turned on during the descent and clearly registered the first landing as Philae came into contact with the comet. From additional data, the mechanical properties of 67P will be derived. SESAME’s two other instruments suggest that cometary activity at this landing site is low, as well as revealing the presence of a large amount of water ice under the lander.
Images and radio waves before hibernation
One of the big ‘winners’ of the Philae landing is Stefano Mottola from the DLR Institute of Planetary Research, who is responsible for the ROLIS (ROsetta Lander Imaging System) camera. The instrument, mounted on the bottom of the lander, acquired images during the first descent showing the planned landing site, Agilkia. Even after the third landing, it proved possible to reactivate ROLIS and acquire images of the comet’s surface at close range. Thus, the team has data for two different locations on the comet.
A wealth of data was also obtained with the CONSERT (COmet Nucleus Sounding Experiment by Radio wave Transmission) instrument. To achieve this, the lander and orbiter were on different sides of the comet and worked together to analyse the comet nucleus by passing radio signals through it and creating a three-dimensional profile of the core. During the CONSERT measurements, Philae went into hibernation after the power from its primary battery was exhausted. This battery was flown through space already charged to ensure the completion of the first scientific work phase.
Sniffing for organic molecules
The last of the 10 instruments on board the Philae lander to be activated was the Sampling, Drilling and Distribution (SD2) subsystem, which was designed to provide soil samples for the COSAC and PTOLEMY instruments. It is certain that the drill was activated, as were all the steps to transport the sample to the appropriate oven. COSAC also worked as planned and was able to ‘sniff’ the atmosphere and detect the first organic molecules after landing. Now scientists need to analyse whether a soil sample was actually examined in the gas chromatograph. This will be done in collaboration with several instrument teams.
Waiting for news of Philae
I’m very confident that Philae will resume contact with us and that we will be able to operate the instruments again,
says DLR Lander Project Manager Stephan Ulamec. Once the rechargeable secondary battery has been warmed by sunlight again, Philae will restart and the DLR LCC team will take their places at the control consoles again.
At the first landing site, we would, of course, have had better solar illumination conditions, says Ulamec.
Now we are somewhat in shadow, we will need more time to charge.
One advantage of the shadier landing site in a crater is that the Philae lander will not overheat as quickly as the comet approaches the Sun, but will benefit from the stronger sunlight. The team managed to rotate the lander during the night of 14/15 November 2014, so that the largest solar panel is now aligned towards the Sun.
Stephan Ulamec believes it is probable that in the spring of 2015, the DLR LCC will once again communicate with Philae and receive data about how the lander is faring on Comet 67P/Churyumov-Gerasimenko. In the summer of 2015, it might be possible that temperatures on the comet will allow Philae’s battery to be recharged.
The orbiter will continue with its overflights to receive any signals from the lander once Philae wakes up from hibernation.
Rosetta and the UK
With funding from the UK Space Agency and the Science and Technology Facilities Council (STFC), Rosetta is a mission with significant UK involvement from industry and science.
One of the main challenges for all the companies designing instruments for Rosetta has been to ensure the components remain intact for ten years, while the spacecraft makes its way to the comet, and then work perfectly when it gets there. Not an easy task!
- Airbus Defence and Space, based in Stevenage, was the major subcontractor for the Rosetta platform
- e2v, based in Chelmsford, designed and supplied the high performance imaging devices used in the Navigation Camera, OSIRIS narrow field and wide field cameras and VITRIS-M instruments on the orbiter and ROLIS and CIVA instruments on the lander
- ABSL Space Products provided innovative batteries for the spacecraft and lander
- These are smaller, lighter and much more reliable than the traditional nickel-cadmium batteries
- ERS Technology supported the development of many subsystems including the reactions wheels, solar array drive motors, Philae harpoon motors and developed the lubricant for the atomic force microscope on the Micro-Imaging Dust Analysis System (MIDAS)
- Technology created by CGI Group helped to explore some of the issues involved in such a long mission
- The company was also involved in the development of the Rosetta on board software.
- Moog provided tanks to store the helium used by the lander
- STFC’s RAL Space co-developed the Ptolemy instrument with the Open University and designed the thermal insulation for the GIADA and VIRTIS instruments as well as the Philae lander itself
- SciSys UK Ltd is responsible for the spacecraft Mission Control System development and maintenance
- In recognition of this work on the Rosetta and the Beagle 2 missions, SciSys were awarded the title of “Innovator of the Year” by the UK Computing Awards for Excellence 2004
- Surrey Satellite Technology Limited (SSTL) designed a wheel that will stabilise the probe as it descends and lands on the comet
- Telespazio VEGA was involved in many aspects of the Rosetta mission, from the overall design of the spacecraft to the on-board software
UK scientists are involved in ten of the 21 experiments that Rosetta will carry out during its mission:
- The Open University in collaboration with STFC RAL Space designed and built the Ptolemy instrument on the lander and is contributing scientific expertise to the GIADA, MUPUS and SESAME instrument teams
- The University of Kent will be helping to analyse the results from the OSIRIS instrument and have been involved in observing Rosetta’s target comet from ground-based telescopes to aid mission planning
- Imperial College London and University College London’s Mullard Space Science Laboratory (MSSL) supply the team studying the comet’s plasma.
- Scientists at Oxford University are part of the science team for VIRTIS
- Queen Mary College at the University of London will be investigating the results of the CONSERT instrument
- Researchers from Queen’s University Belfast are part of the team observing Rosetta’s target comet using ground-based telescopes