Rosetta (spacecraft)

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Rosetta
Rosetta probe
Computer model of Rosetta
Mission type Comet orbiter/lander
Operator European Space Agency
COSPAR ID 2004-006A
SATCAT № 28169
Website www.esa.int/rosetta
Mission duration 10 years, 5 months and 4 days elapsed
Spacecraft properties
Manufacturer Astrium
Launch mass Orbiter: 2,900 kg (6,400 lb)
Lander: 100 kg (220 lb)
Dry mass Orbiter: 1,230 kg (2,710 lb)
Payload mass Orbiter: 165 kg (364 lb)
Lander: 27 kg (60 lb)
Dimensions 2.8 × 2.1 × 2 m (9.2 × 6.9 × 6.6 ft)
Power 850 watts at 3.4 AU[1]
Start of mission
Launch date 2 March 2004, 07:17 UTC
Rocket Ariane 5G+ V-158
Launch site Kourou ELA-3
Contractor Arianespace
Flyby of Mars
Closest approach 25 February 2007
Distance 250 km (160 mi)
Flyby of 2867 Šteins
Closest approach 5 September 2008, 20:38 UTC
Distance 800 km (500 mi)
Flyby of 21 Lutetia
Closest approach 10 July 2010, 16:10 UTC
Distance 3,162 km (1,965 mi)
67P/Churyumov–Gerasimenko orbiter
Orbital insertion 6 August 2014, 09:06 UTC[2]
Orbit parameters
Periapsis 200 km (120 mi) planned
Transponders
Band S band (low gain antenna)
X band (high gain antenna)
Bandwidth 7.8 bit/s (S Band)
22 kbit/s (X Band)[3]
Instruments
ALICE: Ultraviolet Imaging Spectrometer
CONSERT: COmet Nucleus Sounding Experiment by Radio wave Transmission
COSIMA: COmetary Secondary Ion Mass Spectrometer
GIADA: Grain Impact Analyser and Dust Accumulator
MIDAS: Micro-Imaging Dust Analysis System
MIRO: Microwave Spectrometer 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

Rosetta is a robotic space probe built and launched by the European Space Agency to perform a detailed study of comet 67P/Churyumov–Gerasimenko.[4][5] On 6 August 2014 it entered into the orbit of 67P/Churyumov–Gerasimenko and became the first manmade spacecraft to orbit a comet.[6] It is part of the ESA Horizon 2000 cornerstone missions and is the first mission designed to both orbit and land on acomet.[7]

Rosetta was launched in March 2004 on an Ariane 5 rocket and was scheduled to reach the comet in August 2014.[8] The spacecraft consists of two main elements: the Rosetta space probe orbiter, which features 12 instruments, and the Philae robotic lander, with an additional nine instruments.[9] The Rosettamission will orbit 67P for 17 months and is designed to complete the most detailed study of a comet ever attempted. The mission is controlled from the European Space Operations Centre (ESOC), in Darmstadt, Germany.[10]

The probe is named after the Rosetta Stone, a basalt slab of Egyptian origin featuring a decree in three scripts. The lander is named after the Nile island Philae, where an obelisk was discovered with inscriptions. A comparison of the hieroglyphs on the Rosetta Stone and the obelisk led to greater understanding of the Egyptian writing system. Similarly, it is hoped that these spacecraft will result in better understanding of comets and the early Solar System.[11][12]

The spacecraft has already performed two successful asteroid flyby missions on its way to the comet.[13]In 2007, Rosetta also performed a Mars swing-by (flyby), and returned images.[14] The craft completed its fly-by of asteroid 2867 Šteins in September 2008 and of 21 Lutetia in July 2010.[15] On 20 January 2014,Rosetta was taken out of a 31-month hibernation mode and continued towards the comet.[16][17] Over the following months, a series of thruster burns slowed Rosetta relative to 67P, and Rosetta entered thruster-assisted orbit of the comet on 6 August 2014.[18]

 

 

Mission timeline[edit]

This is the planned timeline for the Rosetta mission:

  • Launch (2 March 2004)
  • First Earth flyby (4 March 2005)
  • Mars flyby (25 February 2007)
  • Second Earth flyby (13 November 2007)
  • Flyby of asteroid 2867 Šteins (5 September 2008)
  • Third Earth flyby (13 November 2009)
  • Flyby of asteroid 21 Lutetia (10 July 2010)
  • Deep-space hibernation (June 2011 – January 2014)
  • Comet approach (January–May 2014)
  • Deceleration burns (May-July 2014)
  • Orbital insertion (6 August 2014)
  • Comet mapping and characterisation (August 2014)
  • Landing on the comet (November 2014)
  • Escorting the comet around the Sun (November 2014 – December 2015)
  • End of mission (December 2015)

Rosetta's current location can be found on the ESA website.[19]

Mission overview[edit]

File:CHASING A COMET - The Rosetta Mission.webm
A 9 minute long video report by the DLR about the Rosetta mission. (Full HD; English)

Background[edit]

During the 1986 approach of Halley's Comet, a number of international space probes were sent to explore the comet, most prominent among them being ESA's Giotto. After the probes returned valuable scientific information, it was becoming obvious that follow-ons were needed that would shed more light on the cometary composition and answer newly opened questions.

Both ESA and NASA started cooperatively developing new probes. The NASA project was the Comet Rendezvous Asteroid Flyby (CRAF) mission. The ESA project was the follow-on Comet Nucleus Sample Return (CNSR) mission. Both missions were to share the Mariner Mark II spacecraft design, thus minimising costs. In 1992, after NASA canceled CRAF due to budgetary limitations, ESA decided to develop a CRAF-style project on its own. By 1993 it was evident that the ambitious sample return mission was unfeasible with the existing ESA budget, so the mission was redesigned, with the final flight plan resembling the cancelled CRAF mission, an asteroid flyby followed by a comet rendezvous with in-situ examination, including a lander.

Mission firsts[edit]

The Rosetta mission will achieve many historic firsts:[20] Rosetta will be the first spacecraft to orbit a comet nucleus. It will be the first spacecraft to fly alongside a comet as it heads towards the Inner Solar System. Rosetta will be the first spacecraft to examine from close proximity how a frozen comet is transformed by the warmth of the Sun. Shortly after its arrival at comet 67P/Churyumov-Gerasimenko, the Rosetta orbiter will dispatch a robotic lander for the first controlled touchdown on a comet nucleus. The Rosetta lander’s instruments will obtain the first images from a comet’s surface and make the first in situ analysis to find out what it is made of. On its way to comet 67P/Churyumov-Gerasimenko, Rosetta passed through the main asteroid belt, and made the firstEuropean close encounter with several of these primitive objects. Rosetta was the first spacecraft ever to fly close to Jupiter’s orbit using solar cells as its main power source.

Construction[edit]

Rosetta was built in a clean room according to COSPAR rules, but "sterilisation [was] generally not crucial since comets are usually regarded as objects where you can find prebiotic molecules, that is, molecules that are precursors of life, but not living microorganisms",[21] according to Gerhard Schwehm,Rosetta's Project Scientist.

Launch[edit]

Rosetta was set to be launched on 12 January 2003 to rendezvous with the comet 46P/Wirtanen in 2011.

Trajectory of the Rosetta space probe

However, this plan was abandoned after a failure of the Ariane 5 carrier rocket during a communications satellite launch on 11 December 2002, grounding it until the cause of the failure could be determined. A new plan was formed to target the comet Churyumov–Gerasimenko, with a revised launch date of 26 February 2004 and comet rendezvous in 2014. The larger mass and the resulting increased impact velocity made modification of the landing gear necessary.[22] After two scrubbed launch attempts,Rosetta was launched on 2 March 2004 at 7:17 GMT. Aside from the changes made to launch time and target, the mission profile remains almost identical.

Deep space manoeuvres[edit]

To achieve the required velocity to rendezvous with 67P/C-G, Rosettaused gravity assist manoeuvres to accelerate throughout the inner Solar System. The asteroid's orbit was known before Rosetta's launch, from ground-based measurements, to an accuracy of approximately 100 km (62 mi). Information gathered by the onboard cameras beginning at a distance of 24 million kilometres (15,000,000 mi) were processed at ESA's Operation Centre to refine the asteroid's position in its orbit to a few kilometres. The first flyby of Earth occurred on 4 March 2005.

On 25 February 2007, the craft was scheduled for a low-altitude bypass of Mars, to correct the trajectory after the first launch attempt in 2003 was delayed by one year. This was not without risk, as the estimated altitude of the flyover manoeuvre was a mere 250 kilometres (160 mi). During that encounter the solar panels could not be used since the craft was in the planet's shadow, where it would not receive any solar light for 15 minutes, causing a dangerous shortage of power. The craft was therefore put into standby mode, with no possibility to communicate, flying on batteries that were originally not designed for this task.[23] This Mars manoeuvre was therefore nicknamed "The Billion Euro Gamble".[24] Fortunately, the flyby was successful and the mission continued as planned.[25]

The second Earth flyby occurred on 13 November 2007.[26][27] In 2007, as it approached Earth for a fly-by, the spacecraft was briefly designated as minor planet 2007 VN84 due to it being misidentified as an asteroid.

The spacecraft performed a close flyby of asteroid 2867 Šteins on 5 September 2008. Its onboard cameras were used to fine-tune the trajectory, achieving a minimum separation of less than 800 km (500 mi). Onboard instruments measured the asteroid from 4 August to 10 September. Maximum relative speed between the two objects during the flyby was 8.6 km/s (19,000 mph; 31,000 km/h).[28]

Rosetta's third and final flyby of Earth happened on 12 November 2009.[29]

Reconstruction of the comet's shape

In May 2014, Rosetta began a series of eight deceleration burns. These reduced the relative velocity between the spacecraft and 67P/C-G from 775 m/s (2,540 ft/s) to 7.9 m/s (26 ft/s).[8]

Orbit around 67P/C-G[edit]

In August 2014, Rosetta entered a slow thruster-assisted orbit around the comet[18] and will gradually slow down in preparation for releasing a lander that will make contact with the comet itself. The exact surface layout of the comet is currently unknown and the orbiter has been built to map this before detaching the lander. It is anticipated that a suitable landing site can be found, although few specific details exist regarding the surface.[30]

Philae lander[edit]

The lander, named Philae, will approach Churyumov–Gerasimenko at relative speed around 1 m/s (2.2 mph; 3.6 km/h) and on contact with the surface, two harpoons will be fired into the comet to prevent the lander from bouncing off. Additional drills are used to further secure the lander on the comet.

Once attached to the comet, expected to take place in November 2014, the lander will begin its science mission:

  • Characterisation of the nucleus
  • Determination of the chemical compounds present, including enantiomers[31]
  • Study of comet activities and developments over time