The international Rosetta mission was approved in November 1993 as the Planetary Cornerstone Mission in ESA’s long-term space science programme. The mission goal was initially set for a rendezvous with Comet 46 P/Wirtanen. After postponement of the initial launch, a new target was set: Comet 67 P/Churyumov-Gerasimenko. On its 10-year journey to the comet, the spacecraft will also pass by two asteroids.
Rosetta’s main objective is to rendezvous with, and enter orbit around, Comet 67P/Churyumov-Gerasimenko, performing observations of the comet’s nucleus and coma. During the period that Rosetta orbits the comet, 67P/Churyumov-Gerasimenko will reach the closest point to the Sun in its orbit. A lander, named Philae, will be deployed and it will attempt to make the first-ever controlled landing on a comet.
The Rosetta Mission Operations Centre (MOC) is located at ESOC, Darmstadt, Germany.
|LAUNCH DATE||2 Mar 2004|
|LAUNCHER/LOCATION||Ariane 5/Kourou, French Guiana|
|LAUNCH MASS||3000 kg|
|ORBIT||Highly complex, with 3 Earth & 1 Mars gravity assists en route; On arrival at Comet 67P, Rosetta will orbit the comet, tracking with it toward the Sun|
|NOMINAL MISSION||to 2015|
|+ Rosetta will track a comet as it arcs toward the Sun and its lander Philae will make the first-ever controlled landing on a comet +|
The Flight Control Team
The Flight Control Team (FCT) at ESOC operates from the same Dedicated Control Room (DCR) as Mars Express and Venus Express. Spacecraft Operations Manager (SOM) Andrea Accomazzo, from Italy, oversees a team of four flight control engineers working full-time on Rosetta. The team is further composed by analysts and SPACONs (spacecraft controllers), who support all three ESA interplanetary missions via integrated ground software and daily operations.
Other ESOC teams provide additional support in the areas of Flight Dynamics, Ground Facilities and Software Support.
Mission operations overview
During its 10-year journey to Comet 67P/Churyumov-Gerasimenko, Rosetta will circle the Sun almost four times. It will also cross the asteroid belt twice and gain velocity from gravitational ‘kicks’ provided by close swing-bys of Mars (2007) and Earth (2005, 2007 and 2009).
The launch and early orbit phase (LEOP)
The planned launch date for Rosetta was 07:36:49 UT on 26 February 2004. However, an initial delay due to adverse weather, and a subsequent delay due to a technical issue with the launch vehicle, pushed the launch date back by five days, to 2 March 2004.
After burn-out of the lower stage, the spacecraft and upper stage remained in Earth parking orbit (4000 x 200 km) for about two hours. Ariane’s upper stage then ignited to boost Rosetta into its interplanetary trajectory, before separating from the spacecraft.
Rosetta first travelled away from its home planet, before returning a year after launch, in March 2005. Rosetta then headed to Mars and returned to Earth in November 2007 for its second swing-by of our planet. In November 2009 Rosetta will fly past the Earth for the third and last time to receive the final boost required to reach its final target.
Rosetta alternates periods of active and passive phases during the cruise to Earth. The distance at closest approach is between 300 and 5300 km. Operations are mainly focused on orbit determination for the fundamental swing-by manoeuvres; however payload check-out, calibrations and scientific observations are also performed. If required, orbit correction manoeuvres take place before and after each swing-by.
Rosetta flew past Mars in February 2007 at a distance of about 250 km, phasing its trajectory for the next Earth swing-by and, as a spin-off, obtaining some science observations. During the swing-by, Rosetta had to survive an eclipse for which, due to the mission target change, the spacecraft was not specifically designed to handle. This operation required a significant effort by the FCT, but was entirely successful; during the swing-by itself, a communications black-out was also caused by an occultation as the spacecraft passed behind Mars with respect to the Earth.
During the cruise phase, Rosetta alternates between phases of passive and active operation, depending on mission needs. As a secondary scientific objective, Rosetta has observed asteroid Steins in 2008 from a distance of 800 km. In July 2010 only 3160 km will separate Rosetta from asteroid Lutetia when it will fly past. Science data recorded onboard will be transmitted to Earth afterwards.
Following a planned deep-space manoeuvre using the engine to achieve a change in speed of approximately 800 m/s, the spacecraft goes into hibernation between June 2011 and January 2014, due to the very limited power that will be available – which would not allow safe spacecraft operations. Almost all electrical systems are switched off, except for the thermal subsystem, on-board computer, radio receivers, command decoders and power supply.
During this period, Rosetta should record its maximum distance from the Sun, about 800 000 000 km, and Earth, about 1000 000 000 km.
In May 2014, Rosetta’s thrusters will brake the spacecraft so that it can match Comet 67P/Churyumov-Gerasimenko’s orbit. The spacecraft will arrive in the comet’s vicinity a few weeks later.
Over the following six months, it will edge closer to the black, dormant nucleus until it is only a few kilometres away. The way will then be clear for the exciting transition to global mapping, lander deployment and the continuing ‘comet chase’ toward the Sun.
The ground station – New Norcia
Since launch, the Rosetta mission has been controlled from a single control centre, the Rosetta Mission Operations Centre (MOC) at ESOC, Darmstadt, using ESA’s DSA 1 deep-space ground station at New Norcia.
During critical mission phases (launch, planet swing-bys, etc.) it is supported for tracking, telemetry and command by other ESA ground stations at Kourou and Cebreros, and by the NASA Deep Space Network (DSN) stations at Madrid, Spain, and Goldstone, USA.
Ground segment & mission control system
The Rosetta ground segment is designed to meet both the scientific objectives and the challenges imposed by a deep-space mission. These challenges include long turnaround times for signals (up to 100 minutes), low bit rates for data (8 bps), low power availability (it is the first spacecraft ever to fly with solar power generators beyond 3.1 AU from the Sun) and very precise navigation during planetary swing-bys (Rosetta made use of gravity-assist manoeuvres with Mars and Earth to achieve its final orbit around the Sun).
ESOC must cope with the long mission duration and the related problems in scheduling expertise and experienced FCT personnel, while minimising overall cost. The central element of the Rosetta ground segment, the Mission Control System, is based on SCOS-2000.
The Rosetta Science Operations Centre (SOC) will produce detailed scientific mission planning requests, which are submitted to the MOC in the form of operation requests. The SOC will make pre-processed scientific data and the scientific data archive available to the scientific community.
A Rosetta Lander Ground Segment (RLGS) will control the Philae lander, in particular before and after completion of the landing and relay phase. These will be coordinated through the Lander Control Center at the German Aerospace Research Centre (DLR), Cologne, Germany, and the scientific control centre of CNES, France’s space agency, in Toulouse.
The platform and payload
The platformRosetta is a large aluminium box, 2.8 x 2.1 x 2.0 metres in size. The scientific instruments are mounted on the ‘top’ of the box (the Payload Support Module) while the subsystems are on the ‘base’ (Bus Support Module).
On one side of the orbiter is a 2.2m-diameter communications dish antenna – the steerable high-gain antenna; the lander is attached to the opposite face. Two enormous solar panels extend from the other sides. These ‘wings’, each 32 square metres in area, have a total span of about 32m tip-to-tip. Each comprises five panels, and both may be rotated through +/-180° to track the Sun in every attitude assumed by the spacecraft.
In order to investigate the comet nucleus and the gas and dust ejected from the nucleus as the comet approaches the Sun, Rosetta carries a suite of eleven instruments on-board the orbiter; the lander, Philae, is equipped with a further ten instruments to perform surface measurements.
The orbiter instruments combine remote sensing techniques, such as cameras and radio science measurements, with direct sensing systems such as dust and particle analysers. The instruments are provided by collaborative efforts between scientific institutes in ESA member states and the USA. Principal investigators in several European countries and America lead the nationally funded science teams.
|ALICE||Ultraviolet Imaging Spectrometer|
|CONSERT||Comet Nucleus Sounding Experiment by Radiowave 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 Thermal Imaging Spectrometer|
Lander instrumentsThe ~100-kg Philae lander will be the first spacecraft ever to make a soft landing on the surface of a comet nucleus. The lander is provided by a European consortium under the leadership of the German Aerospace Centre (DLR); other members include ESA, CNES and institutes from Austria, Finland, France, Hungary, Ireland, Italy and the UK. The Philae Lander Control Centre is located at the DLR facility in Cologne, Germany.
The lander structure consists of a baseplate and an instrument platform made in a polygonal sandwich construction, all made of carbon fibre. Some of the instruments and subsystems are beneath a hood that is covered with solar cells.
The lander experiments will study the composition and structure of Comet 67P/Churyumov-Gerasimenko’s nucleus.
|CIVA||Panoramic and microscopic imaging system|
|CONSERT||Radio sounding, nucleus tomography|
|COSAC||Evolved gas analyser – elemental and molecular composition|
|MODULUS Ptolemy||Evolved gas analyser – isotopic composition|
|MUPUS||Measurements of surface and subsurface properties|
|ROMAP||Magnetometer and plasma monitor|
|Sampling, Drilling and Distribution Subsystem (SD2)||Drilling and sample retrieval|
|SESAME||Surface electrical, acoustic and dust impact monitoring|