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Rosetta

ESA/NASA Solar Probe
ESA Comet Rendevous/Landing
Courtesy of NASA's National Space Science Data Center

Launch Date/Time: 2004-03-02 at 7:17 UTC`
On-orbit dry mass: 1200 kg
Nominal Power Output: 850 W


Description

Rosetta is European Space Agency (ESA) Horizon 2000 cornerstone mission number 3 designed to rendezvous with Comet 67 P/Churyumov-Gerasimenko, drop a probe on the surface, study the comet from orbit, and fly by at least one asteroid en route. The principal goals are to study the origin of comets, the relationship between cometary and interstellar material and its implications with regard to the origin of the solar system. Its scientific objectives to achieve these goals are: global characterization of the nucleus, determination of dynamic properties, surface morphology and composition; determination of the chemical, mineralogical and isotopic compositions of volatiles and refractories in a cometary nucleus; determination of the physical properties and interrelation of volatiles and refractories in a cometary nucleus; study of the development of cometary activity and the processes in the surface layer of the nucleus and the inner coma (dust/gas interaction); global characterisation of asteroids, including determination of dynamic properties, surface morphology and composition.

Spacecraft and Subsystems

Rosetta's design is based on a box-shaped central frame, 2.8 m x 2.1 m x 2.0 m with an aluminum honeycomb main platform. Total launch mass is 3000 kg including the 100 kg lander and 165 kg of scientific instruments. Two solar panels, 32 square meters each, extend outward from opposite sides of the box, spanning 32 m tip-to-tip. The spacecraft consists of two primary modules, the Payload Support Module (PSM), which holds the scientific instrumentation and two payload boom deployment mechanisms in the top part of the frame, and the Bus Support Module (BSM), which holds the spacecraft subsystems in the lower part. A steerable 2.2 m diameter high-gain parabolic dish antenna is attached to one side, and the lander will be mounted on the opposite side. The science instrument panel is mounted on the top and designed to be facing the comet continuously during orbit while the antenna and solar panels face the Earth and Sun. Radiators and louvers are mounted on the back and side panels which face away from the Sun and comet. In the center of the spacecraft protruding from the bottom is a vertical thrust tube made of corrugated aluminum with strengthening rings.

The thrust tube provides the propulsion for primary maneuvers and contains two 1106-liter propellant tanks, the upper one containing propellant and the lower one oxidizer. A total of 660 kg of propellant (bipropellant monomethyl hydrazine) and 1060 kg of oxidizer (nitrogen tetroxide) is necessary to provide 2200 m/s delta-V over the course of the mission. The launch mass of the craft including fuel is 2900 kg. There are also four 35-liter pressurant tanks. The spacecraft will be three-axis stabilized and the orientation controlled by 24 10-N thrusters. Attitude is maintained using two star trackers, a Sun sensor, navigation cameras, and three laser gyro packages. Power is supplied by the solar arrays, which will be composed of low intensity, low temperature Si or GaAs solar cells. These will provide 400 W at 5.2 AU and 850 W at 3.4 AU, when comet operations begin. Power will be stored in four 10 Ahr NiCd batteries which will supply the 28 V bus power. Communications will be via the high-gain antenna, a fixed 0.8 meter medium-gain antenna, and two omnidirectional low gain antennas. Rosetta will utilize an S-band telecommand uplink and S- and X-band telemetry and science-data downlinks, with data transmission rates from 5 to 20 kbits/s. Communication equipment includes a 28 W RF X-band TWTA and a dual 5 watt RF S/X band transponder. On-board heaters will keep the instrumentation from freezing during the period the spacecraft is far from the Sun. Total scientific payload mass is roughly 150 kg.

Philae Lander

The Rosetta lander, Philae, will be attached to the side of the Rosetta spacecraft and released some time after Rosetta achieves orbit around the comet.

Mission Profile

Rosetta was launched at 7:17 UT on 2 March 2004 on an Ariane 5 G+ from Kourou, French Guiana. The spacecraft entered heliocentric orbit and will have an Earth flyby and gravity assist in March, 2005. A Mars flyby/gravity assist will follow in March 2007, and two more Earth gravity assists are scheduled for November 2007 and November 2009. In between these Earth flybys, on 5 September 2008, Rosetta will fly within 1700 km of asteroid 2867 Steins at a relative velocity of 9 km/s. Steins is a main belt asteroid a few km in diameter. After the second Earth flyby the spacecraft will enter the main asteroid belt for the second time and fly by asteroid 21 Lutetia at a distance of 3000 km and a speed of 15 km/s on 10 July 2010. Lutetia is a large asteroid, about 100 km in diameter. The spacecraft will enter a hibernation phase in July of 2011. In January 2014 Rosetta will come out of hibernation and begin its rendezvous manuever for Comet Churyumov-Gerasimenko in May 2014.

The rendezvous maneuver will lower the spacecraft velocity relative to that of the comet to roughly 25 m/s and put it into the near comet drift phase. Some time after this observations of the comet and the far approach trajectory phase will start. At the end of this ~90 day phase, the relative velocity between Rosetta and the comet will have been reduced to 2 m/s, at a distance of about 300 comet nucleus radii. At this point landmarks and radiometric measurements are used to make a precise determination of spacecraft and comet relative positions and velocities and the rotation and gravity of the comet nucleus to fine-tune the approach. This information is used to start orbit insertion at about 60 comet radii distance at a few cm/s. At about 25 comet radii a capture maneuver will close the orbit. Polar orbits at 5 to 25 comet nucleus radii will be used for mapping the nucleus beginning in August 2014. After global studies of the nucleus are completed, about five areas (500 x 500 m) will be selected for close observation at a distance down to 1 nucleus radius.

Using the information gathered from orbit, a landing site will be chosen for the Philae lander. The spacecraft will go into an eccentric orbit with a pericenter as low as 1 km over the landing site and an ejection mechanism will separate Philae from the spacecraft with a maximum relative velocity up to 1.5 m/s in November 2014. The lander will touch down on the surface at a relative velocity of less than 1 m/s and will transmit data from the surface to the spacecraft, which will relay it to Earth. Rosetta will remain in orbit about the comet past perihelion passage in August 2015 until the nominal end of mission in December 2015.

Rosetta is funded by the European Space Agency. The total cost of the mission, including launch and operation was about $900 million before the launch delay. The mission was originally to rendezvous with Comet 46 P/Wirtanen. Flybys of two asteroids, 4979 Otawara and 140 Siwa, on the way to the comet were also planned. The mission was delayed due to problems with the Ariane booster. The delay has reportedly cost an extra $70 to $80 million.

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