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Rosetta – A Milestone in Space Travel

Image: ESA/NASA – SOHO/LASCO Acknowledgment: The image of the comet was taken with the navigation camera on Rosetta (ESA/Rosetta/NavCam). Rosetta is the first space mission in history to rendezvous with a comet, escort it as it orbits the Sun, and deploy a lander to its surface. It is an ESA (European Space Agency) mission with…

Image: ESA/NASA – SOHO/LASCO Acknowledgment: The image of the comet was taken with the navigation camera on Rosetta (ESA/Rosetta/NavCam).

Rosetta is the first space mission in history to rendezvous with a comet, escort it as it orbits the Sun, and deploy a lander to its surface.

It is an ESA (European Space Agency) mission with contributions from its member states and NASA. The Philae lander is provided by a consortium led by DLR, MPS, CNES and ASI.

Complete details of the project can be found at

http://rosetta.esa.int/

Rosetta was launched on board an Ariane-5 rocket on 2 March 2004 and arrived at Comet 67P/Churyumov-Gerasimenko, around 675 million km from the Sun, on 6 August 2014. It actually travelled for a total of 6.4 billion km on a journey which included circling the Sun 4 times on wide loops in the inner Solar System and passing through the asteroid belt twice.

The spacecraft dimensions are 2.8 x 2.1 x 2.0 metres and there are two 14-metre-long solar panels with a total area of 64 square metres. From tip to tip, the spacecraft spans 32 metres. Rosetta’s total launch mass was 3,000 kilograms, the orbiter being 2,900 kg of which 1,670 kilograms was propellant. The lander weighs 100 kilograms.

Commands are sent periodically from Earth to readjust the spacecraft’s trajectory. At its furthest point from Earth, these take 50 minutes to reach the spacecraft. On reaching the comet, messages from Earth take about 28 minutes.

The comet is about 4km across and its shape has been likened to a “rubber duck”.

This image shows the comet from about 102km away on 11 Aug 2014.

Comet_on_11_August_2014_-_NavCam
Image: ESA/NASA – SOHO/LASCO

This image shows the comet from about 83km away on 20 Aug 2014.

Comet_on_20_August_2014_-_NavCam
Image: ESA/NASA – SOHO/LASCO

The 7 hour descent began on 12 Nov 2014. Touchdown takes place at walking speed which is less than one metre per second.

This image was taken by Philae’s down-looking descent ROLIS imager when it was about 40 m above the surface of Comet 67P/Churyumov-Gerasimenko. It shows that the surface of the comet is covered by dust and debris ranging from mm to metre sizes.

Comet_from_40_metres
Image: ESA/NASA – SOHO/LASCO

The large block in the top right corner is 5 m in size. In the same corner the structure of the Philae landing gear is visible.

The aim of the ROLIS experiment is to study the texture and microstructure of the comet’s surface. ROLIS (ROsetta Lander Imaging System) has been developed by the DLR Institute of Planetary Research, Berlin.

Philae completed a successful landing on the surface of the comet confirmed at 16:03 GMT on the 12th November 2014. Later analysis of data returned from the lander showed that it touched down 3 times having initially bounced off the surface a couple f times, the first time travelling for about 1km at a speed of 38 cm/s for about 1 hour 50 minutes and the second time travelling at about 3cm/s landing 7 minutes later.

Although the initial touch down appears to have been inside the predicted landing area, the final resting place of the lander is reported to be close to a rocky wall with one of its 3 feet in open space. Due to the location of the lander, it is also reported that the solar panels are only receiving 1.5 hours of sunlight per 12.4 hour comet day.

The battery lifetime of the lander is about 64 hours and with limited re-charging available it may not be possible to achieve results from all of the planned experiments.

On the 14th November 2014 Philae has managed to return all of its housekeeping data, as well as science data from the targeted instruments, including ROLIS, COSAC, Ptolemy, SD2 and CONSERT. This completed the measurements planned for the final block of experiments on the surface.

In an attempt to receive more solar energy, the lander’s body was lifted by about 4 cm and rotated about 35° but as the last science data fed back to Earth, Philae’s power rapidly depleted. Scientists hope that at a later stage of the mission, as the comet gets nearer to the Sun, there may be enough solar illumination to wake up the lander and re-establish communication.

The Rosetta orbiter will continue to orbit the comet and continue to capture data for further analysis.

Experiments on the mission consist of the following packages:

Orbiter science instrument packages:

  • ALICE Ultraviolet Imaging Spectrometer
  • CONSERT Comet Nucleus Sounding Experiment by Radio wave Transmission
  • COSIMA Cometary Secondary Ion Mass Analyser
  • GIADA Grain Impact Analyser and Dust Accumulator
  • MIDAS Micro-Imaging Dust Analysis System
  • MIRO Microwave Instrument for the Rosetta Orbiter
  • OSIRIS Optical, Spectroscopic, and Infrared Remote Imaging System
  • ROSINA Rosetta Orbiter Spectrometer for Ion and Neutral Analysis
  • RPC Rosetta Plasma Consortium
  • RSI Radio Science Investigation
  • VIRTIS Visible and Infrared Mapping Spectrometer

Philae lander science instrument packages:

  • APXS Alpha Proton X-ray Spectrometer
  • ÇIVA / ROLIS Panoramic and Microscopic Imaging System
  • CONSERT Comet Nucleus Sounding Experiment by Radio wave Transmission
  • COSAC Cometary Sampling and Composition experiment
  • PTOLEMY Evolved Gas Analyser
  • MUPUS Multi-Purpose Sensor for Surface and Subsurface Science
  • ROMAP Rosetta Lander Magnetometer and Plasma Monitor
  • SD2 Sample and Distribution Device
  • SESAME Surface Electrical Sounding and Acoustic Monitoring Experiment

Footnote:
Philae is the island in the river Nile on which an obelisk was found that had a bilingual inscription including the names of Cleopatra and Ptolemy in Egyptian hieroglyphs. This provided the French historian Jean-Francois Champollion with the final clues that enabled him to decipher the hieroglyphs of the Rosetta Stone and unlock the secrets of the civilisation of ancient Egypt.