Rosetta

Rosetta will study the nucleus of a comet, which has to be determined. It will also release a small lander RoLand (Rosetta Lander) to the surface of the comet.

The Rosetta comet orbiter (planned launch January 2003) was to use a Mars gravity assisst (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.

The Rosetta probe will now head for 67P/Churyumov-Gerasimenko in February, 2004, still launched on an Ariane-5G+ launch vehicle.

Probably only minor adjustments need to be made to Rosetta, if any. 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 timescales involved are similar with the rendezvous planned for 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.

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, characterises 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 Rosetta Lander (Philae)

The 100 kg 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.

Last update: 27.09.2009
Contact: gunter.krebs@skyrocket.de
© Gunter Dirk Krebs