Rosetta

Rosetta

Rosetta's Earth-Flyby Quelle: ESA

Rosettas Earth-Flyby
Source: ESA

Rosetta is the first mission with the aim to accompany a comet over a longer time period and to investigate its nature.
On the 2nd of March 2004 the ESA spacecraft started its decennial journey to the comet Churyumov-Gerasimenko with an Ariane-5 rocket from Kourou, French-Guayana. Until its arrival on the comet in 2014, Rosetta will use several flybys on Earth and Mars (“swing-bys”) to get enough swing to reach the comet. The goal is to investigate the comet Churyumov-Gerasimenko at close quarters, to orbit around it for several months and finally to send a lander to the comets surface. Since the comet moves all along towards the Sun, it will the possible for the first time to investigate the changes of a comet during its journey about several million kilometers through the universe.  In addition Rosetta will pass two asteroids, Steins and Lutetia, on its way towards the outer Solar System, which can be investigated during this flybys.

Why fly to a comet?

The origin of the Solar System is unresolved in many respects. Thus the origins of comets and the relationships between comets and interstellar matter are investigated in order to draw conclusions for the origin of the Solar System. Because the cores of the comets are just a few kilometers big in size and consist mostly of ice and dust, they are often called “dirty snowballs”.
The origin of the long periodic comets is the so called Oort cloud, which is arranged spherical in a distance of approx one light year around the sun. The short periodic comets (which orbit faster and with shorter periods around the sun) presumably originate from the Kuiper belt, which is a flat and discoidal region beyond Pluto. There they reside to some extend in a manner of cosmic freezer due to the large distance to the sun and hence consist of the primary material from which our Solar System developed some 4,6 billion years ago.

Diameter of nucleus – estimated (km) 3 x 5
Rotation period (hours) ~ 12.7
Orbital period (years) 6.45
Perihelion distance from Sun (million km) 186.0 (1.243 AU)
Aphelion distance from Sun (million km) 849.7 (5.68 AU)
Orbital eccentricity 0.64
Orbital inclination (degrees) 7.04
Year of discovery 1969
Discoverers Klim Churyumov &
Svetlana Gerasimenko

 

Steins and Lutetia

After the successful launching of Rosetta the decision of the flybys past the asteroids Steins and Lutetia was finally fixed on the 11th of March 2004. The asteroids reside in the asteroid belt between the orbits of Mars and Jupiter. The visit of an asteroid or more is part of the scientific aims of the mission since its beginning.
Asteroids are primitive bricks of the Solar System from the time when it formed some 4,6 billion years ago. They vary in size (some to 100 km) and composition and until now only a few could be investigated at close range.
The chosen asteroids Steins and Lutetia have quite different properties. Steins is a rather small object, with a diameter of about a few kilometers.  Steins, mit einem Durchmesser von nur wenigen Kilometern ein vergleichsweise kleines Objekt, soll von Rosetta am 5. September 2008 aus etwa 1700 km Entfernung beobachtet werden. Diese “Begegnung” wird bei der relativ geringen Geschwindigkeit von etwa 9 km/s während Rosettas ersten Ausflugs in den Asteroidengürtel stattfinden.
Der zweite Asteroid, Lutetia, ist weitaus größer: Er hat einen Durchmesser von rund 100 km. Ihn wird Rosetta am 10. Juli 2010 während ihres zweiten Flugs durch den Asteroidengürtel mit einer Vorbeifluggeschwindigkeit von 15 km/s aus rund 3000 km Entfernung beobachten.
Die Sonde dürfte bei ihren Vorbeiflügen an diesen Urzeit-Felsen spektakuläre Bilder aufnehmen. Ihre Bordinstrumente werden Aufschluss über Masse und Dichte der beiden Asteroiden geben und uns somit mehr über ihre Zusammensetzung verraten. Rosetta soll außerdem die Temperatur unter ihrer Oberfläche messen und nach Gas und Staub in ihrer Umgebung Ausschau halten.

Scientific aims of the Radio Science Investigations Experiment (RSI) at the comet Churyumov – Gerasimenko

‘Gravity field measurements for a comet’

  • Determination of mass and mean density
  • Moments of inertia of the comet
  • Precise determination of the comets orbit

‘Investigation of the comet coma’

  • Electron content
  • Gas and dust production rates
  • Amount of dust with grain size cm – dm
  • Mass flow to the spacecraft

‘Investigations of the comet nucleus (bistatic radar)’

  • Size and shape
  • Structure and roughness of the surface
  • Rotation, precession and nutation rates of the comet nucleus

Rosetta – Data

Mission
Start 2nd March 2004, 08:17 am MEZ
Start position Kourou, French Guayana
Carrier rocket ARIANE 5 G
Duration of the mission In total 12 years, until December 2015
Mission Control Center European Space Operations Center (ESOC), Darmstadt
Philae Lander Control Center DLR MUSC, Cologne
Ground stations Perth (Australia), Kourou (French Guayana)
Start weight 3.000 kg
Fuel 1.670 kg
Scientific actual load 165 kg
Orbiter
Dimensions orbiter 2,8 x 2,1 x 2,0 m
Dimensions solar cell 2 pieces, each with 14 m length, with a total plain of 64 sqm
Energy supply / Energy production of the solar cells 850 W at 3,4 AU*, 395 W at 5,25 AU*
Communication antenna High gain antenna, 2,2 m diameter, rotatable
*AU = astronomical unit (mean distance between Earth and Sun, approx. 150 million km)
Philae-Lander
Weight 100 kg
Data transfer 16 kilobytes per second via orbiter
Energy supply Solar generator, 4 W, primary (for the first 60 hours after landing on the comet) and secondary (rechargeable) batteries
Time schedule
Start March 2004
1st Earth flyby March 2005
Mars flyby March 2007
2nd Earth flyby November 2007
3rd Earth flyby November 2009
Rendezvous maneuver May 2014
Global mapping of the comet August 2014
Landing on the comet November 2014
Orbit flight August 2015
End of the mission December 2015

Meeting with the comet

Aufnahme der Rosetta-Kamera während des ersten 'swing-by-Manövers' von Erde und Mond Quelle: ESA

Recording from the Rosetta camera during the 1st ‘swing-by’ maneuver of Earth and Moon
Source: ESA

The most difficult phase will be the meeting with the fast moving comet Churyumov-Gerasimenko. In May 2014 Rosetta should reach an orbit around the planet. Churyumov-Gerasimenko is a short periodic comet which recurs every 6,57 years. It was discovered in 1969 by Klim Churyumov (University of Kiev, Ukraine) and Svetlana Gerasimenko (Insitute of Astophysics Dushanbe, Tajikistan). Two approaches to Jupiter in 1840 and 1959 changed the comets orbit from initially 4,0 AU perihelion distance to 1,28 AU. It belongs to comets of the so called Jupiter family (with the aphelion, i.e. the most distant point, at the Jupiter orbit) which is a group of short periodic comets in the Solar System.

Rosetta will follow Churyumov-Gerasimenko on its orbit and meet it in 2014. The rendezvous shall happen in a distance of 4.8 AU from the Sun and in May 2014 Rosetta will take to an orbit around the comet and go along with it for 17 months. Because there is only few knowledge about Churyumov-Gerasimenko and neither its size nor shape nor mass are well known, the approach will be quite difficult. After choice of a suitable landing place, one month after starting mapping the comet in approx. 3.25 AU distance to the Sun, the orbiter will send a lander (Philae lander) of 100 kg weight to the comets surface. Due to the very low gravity, the landing speed must be very slow (1 m/s), otherwise the lander would bounce from the comets surface and vanish into space. Simultaneously the spacecraft will carry on orbiting the comet and follow its changes for more than 14 months. In this time Sun will have started to evaporate parts of the comet nucleus and the surface of the comet will outgas. Here one can investigate the behavior of a comet during approach and department (perihelion passage) and at its closest distance to the Sun for the first time.

Primary aims of the Rosetta mission:

  • Investigation of the origin of the Solar System through the investigation of the composition of a comet
  • Investigation of the interaction between comet material and interstellar material
  • Global characterization of the comet nucleus (dynamical properties, surface morphology, composition)
  • Chemical, mineralogical and isotopical composition of the volatile and solid substance of the comet nucleus
  • Physical properties and correlation between the volatile and solid substance of the comet nucleus
  • Investigation of the development of the comet activity and the processes in the cover of the core and the interior coma (dust/gas interaction)
  • Investigation of the general characteristics of the asteroids including the investigation of their dynamical properties, surface morphology and composition

The orbiter actual load consists of twelve experiments to investigate the comet nucleus and the gas and dust cloud surrounding the comet. Beyond that the lander actual load provides the possibility to analyze the core surface and the structures below at close range. The following tables show the experiments of the Rosetta orbiter and the actual load of the lander.

Experiments

Radio Science
RSI Radio Science uses the telecommunication system of the spacecraft, and an ultra stable oscillator (USO) in two frequencies (S band downlink, 2.3 GHz; X band up- and downlink, 8.4 GHz) to investigate the comet nucleus, the coma and the asteroids
Remote sensing
OSIRIS High resolution camera (250 – 1000 nm)
ALICE UV-spectrometer (0,7 – 205 nm)
VIRTIS Spectrometer in visible and infrared wavelength regime
MIRO Microwave spectrometer (1,3 mm and 0,5 mm)
Analysis of the composition
ROSINA Neutral gas and ion mass spectrometer
COSIMA Dust mass spectrometer
MIDAS Dust microscope
Großskalige Struktur des Kometenkerns
CONSERT Kern Tomographie
Dust-mass distribution and mass flow
GIADA Dust detector
Comet plasma environment and interaction with solar winds
RPC Plasma analysis

Rosetta Lander Philae Actual Load

Rosetta lander – Philae
APX α-particles and X-ray detector
Probe-
drawing
-
COSAC Gas analysis and elementary, molecular composition, respectively
MODULUS
Ptolemy
Gas analysis and isotope composition
ÇIVA
ROLIS
Rosetta lander cameras
SESAME Material analysis
MUPUS Material analysis
ROMAP Magnetometer and plasma analysis
CONSERT Tomography of the core

Further information on the ESA-website