Final day is coming – Rosetta controlled descent planned on 30 September 2016

One of the most recognizable space probes sent by European Space Agency in recent years will finish its mission on 30 September 2016 in controlled descent on Comet 67P/Churyumov-Gerasimenko.

ESA announced on June 30, that Rosetta space probe will finish its lasting for last twelve years mission on 30th September 2016. Probe is now on orbit of Comet 67P, 525 million kilometers from Earth and is increasing distance from the Sun. It causes that onboard solar arrays of Rosetta are starting to provide less power, which is necessary for temperature control system, which keeps onboard systems operating. Probe is flying to cross Jupiter’s orbit and after reaching specified point, it will not be able to use solar arrays efficiently enough; also communication system will probably stop operating due the distance and lower power. After 12 years of space flight Rosetta is also reaching naturally its end of operational life due the progressing degradation caused by radiation, cold and contact with dust emitted by comet. ESA made decision to wait until 30th September and then perform controlled descent and rather harsh touchdown on the surface of comet 67P/Churyumov-Gerasimenko. Before crash Rosetta will be able to provide most detailed pictures of comet 67P, gather precision data from onboard microwave detectors, spectrometers and radars. It will be possible due the slow decreasing distance to 67P surface from present 13.5 km to 0 km. Descent maneuver will be performed under control of European Space Operations Centre (ESOC), in Darmstadt, Germany and will start in August. Probe will be put into lower elliptical orbits around comet until it will crash on its surface. Controlled descent is particularly hard in this case, due the changes of gravitation force which is generated by Comet 67P, but performing successful contact with comet and data, which will be gathered, are undisputable worth of increased effort of ESOC.

Rosetta was launched on March 2, 2004 on atop of Ariane 5 rocket from Guiana Space Center. Mission objective was to reach comet 67P/Churyumov-Gerasimenko with Philae lander onboard, perform orbit insertion to comet 67P orbit, deploy lander and gather as much data as possible until comet will fly from the sun at such a distance that onboard solar arrays of Rosetta and Philae will not be able to provide enough power for internal heaters to keep them operational.

Rosetta journey history is filled with multiple gravity assist maneuvers; first was performed on March 4, 2005, when probe passed Earth in distance of 1954.7 km and after calibrating onboard instruments increased its speed. After almost two years on February 25, 2007, probe reached Mars orbit. Next it returned to Earth and performed third gravity assist maneuver using Earth's gravity on altitude of 5295 km on November 13, 2007. Probe was already flying with speed of 45000 km/h. In 2008 Rosetta was flying close to 2867 Šteins asteroid and main-belt asteroid (with distance of 800 km). Rosetta reached Earth again in 2009 on November 13, 2008 flying with speed at 48024 km/h. It was last time when Rosetta was close to Earth and after that, it started its deep space journey to 67P. In 2010 probe performed additional observation tasks: it send to Earth pictures of asteroid P/20110 A2 and pictures of 21 Luteria asteroid. On July 8, 2011, Rosetta was switched into hibernation mode and continued its flight in controlled spinning (main computer was operating). On January 20, 2014, Rosetta switched to normal mode and communicated via NASA DSN Goldstone facility with ESOC. Next days passed on updating software of probe to increase communication speed ratio and general self-tests. On May 2014, probe was 1900000 km from 67P and ESOC started to send commands to start burns of Rosetta's propulsion to align trajectory of probe and 67P. First of eight burn was performed on May 7 and after last on July 23 distance from 67P was only 4100 km. On August 6, 2014, Rosetta finally reached comet 67P and on September 4 ESOC received first data on 67P gathered by Rosetta. Probe started to orbit around 67P on altitude of 29 km and deployed Philae lander on November 12, 2014. Unfortunately after landing Philae was placed in the shadow of edge of the crater and was not able to use its solar arrays with assumed efficiency. This caused problems in communication with Rosetta after only two days on 67P surface. In 2015 and 2016 Rosetta performed various research tasks from orbit of 67P and performed short mission flying for 1500 km away from comet to perform research of comet's environment. During this year Rosetta sent data to Earth which confirmed presence of water ice and molecular oxygen on 67P.

Rosetta was result of research and development of ESA and European Aeronautic Defence and Space Company. Probe was manufactured by Astrium, subsidiary of EADS. It weighs 2900 kg (Philae weigh was 100 kg and additional instruments for science experiments and research weighed 165 kg) and its structure is based on light honeycomb aluminum structure. Its dimensions are 2.8 m × 2.1 m × 2.0 m with span of two solar arrays of 14 m; arrays are providing from 400 w to 1500 w depending on distance from the Sun and charging four 10 AH Ni-Cd batteries. Communication antennas are dish type with diameter of 2.2 m (X band), 0.8 m long low gain antenna (S band) and two small additional omnidirectional antennas. Propulsion is based on 12 pairs of thrusters fueled with MMH/N2O4. Load of propellant is stored in two tanks with capacity of 1108 l each. Scientific payload is installed in upper module which is mounted on atop of service module which contains avionics and probe subsystems. Scientific instruments are: ultraviolet spectrograph (ALICE for detecting noble gas inside nucleus of 67P), OSIRIS (combination of spectroscope and IR and optical camera), VIRTIS (spectrometer for thermal and optical imaging), microwave device for detecting water, ammonia and CO2 (MIRO), radar for analysis of nucleus of 67P (CONSERT), and RSI which uses communication system for analysis of 67P nucleus using radio waves. Additional instruments are spectrometer for ion and neutral analysis (ROSINA), hi resolution microscope for analysis of comet dust (MIDAS), COSIMA which is ion mass analyzing device, GIADA (for analyzing speed and mass of dust particles) and RPC for analyzing of 67P nucleus.

On picture above: Rosetta selfie.