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Rosetta / Philae

Rosetta [ESA]

Philae (Rosetta Lander) [ESA]

ESA's Rosetta is a mission to study the nucleus of comet 67P/Churyumov-Gerasimenko. It also released a small lander Philae to the surface of the comet.

The original plan for the Rosetta comet orbiter (planned launch January 2003) was to use a Mars gravity assist (26.08.2005), and two Earth gravity assist maneuvers (21.11.2005 and 28.11.2007) to reach comet 46P/Wirtanen orbit (29.11.2011). On the way, there were to be two asteroid flybys (4979 Otawara, 11.07.2006; 140 Siwa, 24.07.2008). It was to study comet 46P/Wirtanen and its environment in great detail for a period of nearly two years, the near-nucleus phase starting at a heliocentric distance of about 3.25 AU.

After delays due to an Ariane-5 launch failure, Rosetta missed the launch window (cancelled 15.01.2003), which is required to reach the original target.

Only minor adjustments were needed to be made to Rosetta. The short time to the new launch window prohibits radical changes to the probe. Like its original mission plan, Rosetta will get to Churyumov-Gerasimenko via a series of complex space manoeuvres. including a Mars flyby to catch the comet out near Jupiter and then follow the target comet in towards the Sun. The time scales involved are similar with the rendezvous planned for August 2014.

The larger size of 67P/Churyumov-Gerasimenko (3 km) 46P/Wirtanen might cause some problems for the lander. There is concern, that the higher gravity will cause the lander to hit the surface at higher speed than the speed it was built for. Possibly the legs will be redesigned to cushion the impact.

The Rosetta probe headed for 67P/Churyumov-Gerasimenko on 2 March, 2004, still launched on an Ariane-5G+ launch vehicle.

During the cruise phase, the mission performed following milestones. A first Earth gravity assist on 4 March 2005, a Mars gravity assist on 25 February 2007, then a second Earth gravity assist on 13 November 2007. On route also a flyby with asteroid Steins was made on 5 September 2008, followed by the third Earth gravity assist on 13 November 2009 and a flyby with asteroid Lutetia on 10 July 2010. Then the probe spent te time from 8 June 2011 until 20 January 2014 in deep space hibernation.

The actual comet rendezvous manoeuvre began in May 2014 with arrival at the comet on 6 August 2014. The mapping mission starts in August 2014. The Philae lander will be deployed in November 2014. Rosetta's mission will continue through the comet's perihelion passage on 13 August 2015 until a nominal mission end on 31 December 2015.

Rosetta Orbiter

The 11 instruments on the Rosetta Orbiter can be grouped according to the types of measurements they will carry out.

Remote Sensing

  • OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System):
    A wide-angle camera and a narrow-angle camera to obtain high resolution images of the comet's nucleus and asteroids Siwa and Otawara. The images will be used to determine the volume, shape, bulk density and surface properties of the comet's nucleus.
  • ALICE (Ultraviolet Imaging Spectrometer)
    Analyses gases in the coma and tail and measures the comet's production rates of water and carbon monoxide / dioxide. Also provides information on the surface composition of the nucleus.
  • VIRTIS (Visible and Infrared Thermal Imaging Spectrometer)
    Maps and studies the nature of the solids and the temperature on the surface of the nucleus. Also identifies comet gases, characterizes the physical conditions of the coma and helps to identify the best landing sites.
  • MIRO (Microwave Instrument for the Rosetta Orbiter)
    Used to determine the abundances of major gases, the surface outgassing rate and the nucleus sub-surface temperature. It will also measure the sub-surface temperatures of Siwa and Otawara, and search for gas around them.

Composition analysis

  • ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis)
    Two sensors will determine the composition of the comet's atmosphere and ionosphere; the velocities of electrified gas particles, and reactions in which they take part. It will also investigate possible asteroid outgassing.
  • COSIMA (Cometary Secondary Ion Mass Analyser)
    Will analyse the characteristics of dust grains emitted by the comet, including their composition and whether they are organic or inorganic.
  • MIDAS (Micro-Imaging Dust Analysis System)
    Studies the dust environment around the asteroids and comet. It provides information on particle population, size, volume and shape.

Nucleus large-scale structure

  • CONSERT (Comet Nucleus Sounding Experiment by Radiowave Transmission)
    Probes the comet's interior by measuring radio waves that are reflected and scattered by the nucleus.
  • GIADA (Grain Impact Analyser and Dust Accumulator)
    Measures the number, mass, momentum and velocity distribution of dust grains coming from the nucleus and from other directions (reflected by solar radiation pressure).

Comet plasma environment and solar wind interaction

  • RPC (Rosetta Plasma Consortium)
    Five sensors measure the physical properties of the nucleus; examine the structure of the inner coma; monitor cometary activity; and study the comet's interaction with the solar wind.
  • RSI (Radio Science Investigation)
    Shifts in the spacecraft's radio signals are used to measure the mass, density and gravity of the nucleus; define the comet's orbit; and study the inner coma. Also used to measure the mass and density of asteroid Siwa, and to study the solar corona during the periods when the spacecraft, as seen from Earth, is passing behind the Sun.

The spacecraft entered an orbit around comet 67P/Churyumov-Gerasimenko in August 2014 and operated successfully unti 30 September 2016, when it made a controlled landing on the surface, with the last signal from the spacecraft arriving at 11:19 a.m. UTC. The project decided to land Rosetta to collect some final data close to the comet as it heads away from the sun, depriving the spacecraft of solar power.

The Rosetta Lander (Philae)

The 100 kg Philae lander, which was originally named RoLand (Rosetta Lander), carries nine experiments, with a total mass of about 21 kg. It also carries a drilling system to take samples of sub-surface material. The Lander instruments are designed to study in great detail the composition and structure of the nucleus material.

The instrument on board are:

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

Philae was released on 12 November 2014 to land on the surface of the comet about seven hours later. It successfully landed on the surface, but the cold gas thruster did not fire nor did the harpoons anchor it on the surface.

Philae completed its prime mission but went into hibernation after 60 hours on the comet's surface as it was not being able to recharge the batteries due to unsufficient lighting conditions. Philae has woken up in June 2015 after seven months in hibernation on the surface of Comet 67P/Churyumov-Gerasimenko.

Nation: International
Type / Application: Comet orbiter and lander (Mars and Asteroid fly-by)
Operator: ESA
Contractors: Astrium
Configuration: Eurostar-2000 based
Propulsion: S400, 24 × 10 N Thrusters
Power: 2 deployable solar arrays, batteries
Lifetime: 12 years
Mass: 2900 kg
Orbit: Interplanetary
Satellite COSPAR Date LS Launch Vehicle Remarks
Rosetta 2004-006A 02.03.2004 Ko ELA-3 Ariane-5G+ with Rosetta Lander
Philae (ex RoLand) 2004-006# 02.03.2004 Ko ELA-3 Ariane-5G+ with Rosetta


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