Rosetta (spacecraft)
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This article is about the Rosetta spacecraft. For its lander, see Philae (spacecraft). For events, see Timeline of Rosetta spacecraft.
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, 8 months and 11 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 |
| Distance | 800 km (500 mi) |
| Flyby of 21 Lutetia | |
| Closest approach | 10 July 2010 |
| Distance | 3,162 km (1,965 mi) |
| 67P/Churyumov–Gerasimenko (67P) orbiter | |
| Orbital insertion | 6 August 2014, 09:06 UTC[2] |
| Orbit parameters | |
| Periapsis | 29 km (18 mi)[3] |
| Transponders | |
| Band | S band (low gain antenna) X band (high gain antenna) |
| Bandwidth | 7.8 bit/s (S band)[4] 28 kbit/s (X band)[5] |
| 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 comet67P/Churyumov–Gerasimenko (67P) with both an orbiter, and lander module Philae.[6][7]
Rosetta was launched on 2 March 2004 on an Ariane 5 rocket and reached the comet on 6 August 2014,[8] becoming the first spacecraft to orbit a comet.[9][10][11] (Previous missions had conducted successful flybys of seven other comets.[12]) It is part of the ESA Horizon 2000 cornerstone missions.[13] 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.[14] 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.[15]
The probe is named after the Rosetta Stone, a stele of Egyptian origin featuring a decree in three scripts. The lander is named after the Philae obelisk bearing a bilingual Greek and Egyptian inscription. A comparison of its hieroglyphs on the Rosetta Stone catalysed the deciphering of the Egyptian writing system. Similarly, it is hoped that these spacecraft will result in better understanding of comets and the early Solar System.[16][17] In a more direct analogy to its namesake, the Rosetta spacecraft also carries a micro-etched nickel alloy Rosetta disc donated by the Long Now Foundation inscribed with 13,000 pages of text in 1200 different languages.[18]
The spacecraft has already performed two asteroid flyby missions on its way to the comet.[19] In 2007, Rosetta also performed a Mars swing-by (flyby)[20] The craft completed its fly-by of asteroid 2867 Šteins in September 2008 and of 21 Lutetia in July 2010.[21] On 20 January 2014, Rosetta was taken out of a 31-month hibernation mode and continued towards the comet.[22][23]It has been estimated that in the decade preceding 2014, some 2,000 people had assisted in the mission in some capacity.[24]
Rosetta's Philae lander successfully made the first controlled touchdown on a comet nucleus, specifically Comet 67P, on November 12, 2014.[25][26][27]
Contents
[hide]Mission overview[edit]
Background[edit]
During the 1986 approach of Halley's Comet, 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 became obvious that follow-ons were needed that would shed more light on cometary composition and answer new 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 cancelled 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 and subsequently approved by the ESA,[24] 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. After the spacecraft launch, Gerhard Schwehm was named mission manager; he retired in March 2014.[24]
Mission firsts[edit]
The Rosetta mission will achieve many historic firsts.[28]
On its way to comet 67P, Rosetta passed through the main asteroid belt, and made the first European close encounter with several of these primitive objects. Rosetta was the first spacecraft to fly close to Jupiter's orbit using solar cells as its main power source.
Rosetta is the first spacecraft to orbit a comet nucleus,[29] and is the first spacecraft to fly alongside a comet as it heads towards the inner Solar System. It is planned to be the first spacecraft to examine at close proximity how a frozen comet is transformed by the warmth of the Sun. Shortly after its arrival at 67P, the Rosetta orbiter dispatched a robotic lander for the first controlled touchdown on a comet nucleus. The Philae lander's instruments obtained the first images from a comet's surface and will make the first in-situ analysis of its composition.
Construction and design[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 findprebiotic molecules, that is, molecules that are precursors of life, but not living microorganisms",[30] according to Gerhard Schwehm, Rosetta 's Project Scientist.
Electrical power for the spacecraft comes from two solar arrays totalling 64 square metres (690 sq ft),[31] powering 1500 Watt (400 Watt in hibernation mode) controlled by a redundant Terma power module also used in the Mars Express.[32][33] Main propulsion consists of 24 bipropellant 10 N thrusters.[31] The spacecraft carried 1,670 kilograms (3,680 lb) of propellant at launch, composed of monomethylhydrazine fuel and dinitrogen tetroxide oxidiser, providing a maximum delta-v of 2,300 metres per second (7,500 ft/s). Four of the thrusters are used for delta-v burns.[34]
Launch[edit]
Rosetta was set to be launched on 12 January 2003 to rendezvous with the comet 46P/Wirtanen in 2011.
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.[35] After two scrubbed launch attempts, Rosetta was launched on 2 March 2004 at 7:17 GMT from the Guiana Space Centre in French Guiana. 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, Rosetta used gravity assist manoeuvres to accelerate throughout the inner Solar System. The comet'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 position of the comet 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. 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.[36] This Mars manoeuvre was therefore nicknamed "The Billion Euro Gamble".[37] The flyby was successful, with Rosetta even returning detailed images of the surface and atmosphere of the planet, and the mission continued as planned.[20][38]
The second Earth flyby occurred on 13 November 2007.[39][40] As it approached Earth, 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).[41]
Rosetta 's third and final flyby of Earth happened on 12 November 2009.[42]
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In May 2014, Rosetta began a series of eight deceleration burns. These reduced the relative velocity between the spacecraft and 67P from 775 m/s (2,540 ft/s) to 7.9 m/s (26 ft/s).[8]
Orbit around 67P[edit]
In August 2014, Rosetta rendezvoused with the comet 67P/Churyumov–Gerasimenko (67P) and commenced a series of manoeuvres that took it on two successive triangular paths, averaging 100 and 50 kilometres (62 and 31 mi) from the nucleus, whose segments arehyperbolic escape trajectories alternating with thruster burns.[9][10] After closing to within about 30 km (19 mi) from the comet on 10 September, the spacecraft entered actual orbit about it.[9][10][11][dated info]
The surface layout of 67P was unknown before Rosetta 's arrival. The orbiter mapped the comet in anticipation of detaching its lander.[43] By 25 August 2014, five potential landing sites had been determined.[44]
Philae lander[edit]
Main article: Philae (spacecraft)
The lander, named Philae, approached Churyumov–Gerasimenko at a relative speed of around 1 m/s (2.2 mph; 3.6 km/h) and on contact with the surface, two harpoons were to be fired into the comet to prevent the lander from bouncing off because the comet's escape velocity is only around 0.5 m/s (1.1 mph; 1.8 km/h).[45] However, the ESA announced that analysis of telemetry indicated that the landing was softer than expected and that the harpoons had not fired upon landing. After its attachment to the comet, the lander was scheduled to commence its science mission:
- Characterisation of the nucleus
- Determination of the chemical compounds present, including amino acid enantiomers[46]
- Study of comet activities and developments over time
With Rosetta in orbit 30 km (19 mi) above the comet's surface, ESA examined several potential landing sites for Philae. On 15 September 2014, ESA announced Site J, named Agilkia in honour of Agilkia Island by an ESA public contest,[47] located on the "head" of the comet as the lander's destination.[48]
Philae detached from Rosetta on 12 November 2014 at 08:35 UTC, with an estimated landing seven hours later.[49][50] Confirmation of landing on Comet 67P/Churyumov-Gerasimenko reached Earth on 12 November 2014 at 16:03 UTC.[51]
Social media coverage[edit]
The entire mission was featured heavily in social media, with a Facebook account for the mission and both the satellite and the lander having an official Twitter account portraying apersonification of both spacecrafts. The hashtag "#CometLanding" gained widespread traction. A livestream of the control centers was set up, as were multiple official and unofficial events around the world to follow Philae's landing on 67P. [52][53]
Instruments[edit]
Nucleus[edit]
The investigation of the nucleus is done by three spectroscopes, one microwave radio antenna and one radar:
- ALICE (an ultraviolet imaging spectrograph). The ultraviolet spectrograph will search for and quantify the noble gas content in the comet nucleus, from which the temperature during the comet creation could be estimated. The detection is done by an array of potassium bromide and caesium iodide photocathodes. The 3.1 kg (6.8 lb) instrument uses 2.9 watts and was produced in the USA, and an improved version is used in the New Horizons spacecraft. It operates in the extreme and far ultraviolet spectrum, between 700 and 2,050 ångströms (70 and 205 nm).[54][55]
- OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System). The camera system has a narrow-angle lens (700 mm) and a wide-angle lens (140 mm), with a 2048×2048 pixel CCD chip. The instrument was constructed in Germany.[56]
- VIRTIS (Visible and Infrared Thermal Imaging Spectrometer). The Visible and IR spectrometer is able to make pictures of the nucleus in the IR and also search for IR spectra of molecules in the coma. The detection is done by a mercury cadmium telluride array for IR and with a CCD chip for the visible wavelength range. The instrument was produced in Italy, and improved versions were used for Dawn and Venus Express.[57]
- MIRO (Microwave Instrument for the Rosetta Orbiter). The abundance and temperature of volatile substances like water, ammonia and carbon dioxide can be detected by MIRO via their microwave emissions. The 30 cm (12 in) radio antenna was constructed in Germany, while the rest of the 18.5 kg (41 lb) instrument was provided by the USA.
- CONSERT (Comet Nucleus Sounding Experiment by Radiowave Transmission). The CONSERT experiment will provide information about the deep interior of the comet using aradar. The radar will perform tomography of the nucleus by measuring electromagnetic wave propagation between the Philae lander and the Rosetta orbiter through the comet nucleus. This allows it to determine the comet's internal structure and deduce information on its composition. The electronics were developed by France and both antennas were constructed in Germany.[58]
- RSI (Radio Science Investigation). RSI makes use of the probe's communication system for physical investigation of the nucleus and the inner coma of the comet.[59]
Gas and particles[edit]
- ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis). The instrument consists of a double-focus magnetic mass spectrometer DFMS and a reflectron type time of flight mass spectrometer RTOF. The DFMS has a high resolution (can resolve N2 from CO) for molecules up to 300 amu. The RTOF is highly sensitive for neutral molecules and for ions.[60] ROSINA was developed at the University of Bern in Switzerland.
- MIDAS (Micro-Imaging Dust Analysis System). The high-resolution atomic force microscope will investigate several physical aspects of the dust particles which are deposited on a silicon plate.[61]
- COSIMA (Cometary Secondary Ion Mass Analyser). COSIMA analyses the composition of dust particles by secondary ion mass spectrometry, after the surface is cleaned byindium ions. It can analyse ions up to a mass of 4000 amu.[62]
- GIADA (Grain Impact Analyser and Dust Accumulator). GIADA will analyse the dust environment of the comet coma measuring the optical cross section, momentum, speed and mass of each grain entering inside the instrument.[63][64]
Solar wind interaction[edit]
Search for organic compounds[edit]
Previous observations have shown that comets contain complex organic compounds.[67][68][69][70] These are molecules that are rich in carbon, hydrogen, oxygen, and nitrogen. These are the elements that make up nucleic acids and amino acids, essential ingredients for life as we know it. Comets are thought to have delivered a vast quantity of water to Earth, and they may have also seeded Earth with organic molecules.[71] Rosetta and Philae will also search for organic molecules, nucleic acids (the building blocks of DNA andRNA) and amino acids (the building blocks of proteins) by sampling and analysing the comet's nucleus and coma cloud of gas and dust,[71] helping assess the contribution comets made to the beginnings of life on Earth.[67]
- Amino acids
Upon landing on the comet, Philae will also test some hypotheses as to why essential amino acids are almost all "left-handed", which refers to how the atoms arrange in orientation in relation to the carbon core of the molecule.[72] Most asymmetrical molecules are oriented in approximately equal numbers of left- and right-handed configurations (chirality), and the primarily left-handed structure of essential amino acids used by living organisms is an anomaly. One hypothesis that will be tested was proposed in 1983 by William A. Bonner and Edward Rubenstein, Stanford University professors emeritus of chemistry and medicine respectively. They conjectured that when spiralling radiation is generated from a supernova, the circular polarization of that radiation could then destroy one type of "handed" molecules. The supernova could wipe out one type of molecules while also flinging the other surviving molecules into space, where they could eventually end up on a planet.[73]
Reaction control system problems[edit]
In 2006, Rosetta suffered a leak in its reaction control system (RCS).[74] The system, which consists of 24 bipropellant 10-newton thrusters,[8] is responsible for fine tuning the trajectory of Rosetta throughout its journey. The RCS will operate at a lower pressure than designed due to the leak. This may cause the propellants to mix incompletely and so burn 'dirtier' and less efficiently, though ESA engineers are confident that they have sufficient fuel reserves to allow successful completion of the mission.[75]
Rosetta 's reaction wheels are showing higher than expected vibration, though testing revealed the system can be operated more efficiently resulting in less wear on the wheels. Before hibernation, two of the spacecraft's four reaction wheels began exhibiting "noise". Engineers turned on three of the wheels after the spacecraft awoke, including one of the bad wheels. The other improperly functioning wheel will be held in reserve. Additionally, new software was uploaded which would allow Rosetta to function with only two active reaction wheels if necessary.[74][76]
Misidentification[edit]
In November 2007, during its second flyby, the Rosetta spacecraft was mistaken for a near-Earth asteroid and given the designation 2007 VN84. Based upon images taken by a 0.68-metre telescope of the Catalina Sky Survey, an astronomer 'discovered' the spacecraft and misidentified it as an asteroid about 20 m (66 ft) in diameter, and performed a trajectory calculation showing that it would make its closest flyby of the Earth at a distance of 5,700 km (3,500 mi) on 13 November 2007. This extremely close approach (in astronomical terms) led to speculation that 2007 VN84 might be at risk of impacting the Earth.[77] However, astronomer Denis Denisenko recognised that the trajectory matched that of the Rosetta probe, which was performing a flyby of Earth en route to its rendezvous with a comet.[78] The Minor Planet Center later confirmed in an editorial release that2007 VN84 was actually the spacecraft.[79]
Timeline of major events and discoveries[edit]
Main article: Timeline of Rosetta spacecraft
- 2004
- 2 March – ESA's Rosetta mission was successfully launched at 07:17 UTC (04:17 local time) from Kourou, French Guiana. The upper stage and payload were successfully injected into an eccentric coast orbit of 200 km × 4,000 km (120 mi × 2,490 mi). At 09:14 UTC the upper stage engine fired to bring the spacecraft to escape velocity, leaving Earth and entering heliocentric orbit. Rosetta was released 18 minutes later. The ESOC in Darmstadt, Germany, established contact with the probe shortly after that.[80]
- 10 May – The first and most important deep space manoeuvre was successfully executed to adjust the course of the space craft, with a reported inaccuracy of 0.05%.
- 2005
- 4 March – Rosetta executed its first planned close swing-by (gravity assist passage) of Earth. The Moon and the Earth's magnetic field were used to test and calibrate the instruments on board of the spacecraft. The minimum altitude above the Earth's surface was 1,954.7 km (1,214.6 mi) at 22:09 UTC and images of the space probe passing by were captured by amateur astronomers.[81]
- 4 July – Imaging instruments on board observed the collision between the comet Tempel 1 and the impactor of the Deep Impact mission.[82]
- 2007
- 25 February – Mars swing-by. Philae 's ROMAP (Rosetta Lander Magnetometer and Plasma Monitor) instrument measures the complex Martian magnetic environment,[83] whileRosetta 's OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) took various images of the planet using different photographic filters.[20] While in Mars' shadow most of the instruments were turned off and the Philae lander was autonomously running on batteries. During this operation the ÇIVA instrument on the lander took pictures of Mars.[38] Among others, both actions were meant to test the spacecraft's instruments. The spacecraft used the gravity of Mars to change course towards its second Earth flyby in November.[84]
- 8 November – Misidentification of Rosetta spacecraft as an asteroid (see Misidentification).
- 13 November – Rosetta performed its second Earth swing-by at a minimum altitude of 5,295 km (3,290 mi) at 20:57 UTC, travelling 45,000 km/h (28,000 mph).[85]
- 2008
- 5 September – Flyby of asteroid 2867 Šteins. The spacecraft passed the main-belt asteroid at a distance of 800 km (500 mi) and the relatively slow speed of 8.6 km/s (19,000 mph; 31,000 km/h).[86]
- 2009
- 13 November – Third and final swing-by of Earth. Rosetta made its closest approach at 2,481 km (1,542 mi) altitude over 109°E and 8°S – just off the coast of the Indonesian island of Java, at 07:45 UTC. The spacecraft was travelling at 48,024 km/h (29,841 mph).[87][88]
- 2010
- 16 March – Observation of the dust tail of asteroid P/2010 A2. Together with observations by Hubble Space Telescope it could be confirmed that P/2010 A2 is not a comet but an asteroid and that the tail most likely consists of particles from an impact by a smaller asteroid.[89]
- 10 July – Flew by and photographed the asteroid 21 Lutetia.[90]
- 2011
- 8 June – The spacecraft was commanded into a spin stabilised mode and all electronics except the on-board computer and the hibernation heaters were switched off.[91]
- 2014
- 20 January – At 10:00 UTC a pre-programmed timer interrupted the hibernation mode and started post-hibernation procedures. Rosettarestored communications with ESOC through NASA's Goldstone ground station at 18:18 UTC.[92][93]
- May to July – Starting on 7 May, Rosetta began orbital correction manoeuvres to bring itself into orbit around 67P. At the time of the first deceleration burn Rosetta was approximately 2,000,000 km (1,200,000 mi) away from 67P and had a relative velocity of +775 m/s (2,540 ft/s); by the end of the last burn, which occurred on 23 July, the distance had been reduced to just over 4,000 km (2,500 mi) with a relative velocity of +7.9 m/s (26 ft/s).[8][94] In total eight burns were used to align the trajectories of Rosetta67P with the majority of the deceleration occurring during three burns: Delta-v 's of 291 m/s (950 ft/s) on 21 May, 271 m/s (890 ft/s) on 4 June, and 91 m/s (300 ft/s) on 18 June.[8]
- 14 July – The OSIRIS on-board imaging system returned images of Comet 67P which confirmed the irregular shape of the comet.[95][96]
- 6 August – Rosetta arrives at 67P, approaching to 100 km (62 mi) and carrying out a thruster burn that reduces its relative velocity to 1 m/s (3.3 ft/s).[97][98][99] Commences comet mapping and characterisation to determine a stable orbit and viable landing location for Philae.[100]
- 4 September - The first science data from Rosetta 's ALICE instrument was reported, showing that the comet is unusually dark in ultraviolet wavelengths, hydrogen and oxygenare present in the coma, and no significant areas of water-ice have been found on the comet's surface. Water-ice was expected to be found as the comet is too far from the Sun to turn water into vapor.[101]
- 10 September 2014 – Rosetta enters the Global Mapping Phase, orbiting 67P at an altitude of 29 km (18 mi).[3]
- 12 November 2014 – Philae landed on the surface of 67P. Touchdown 16:08 GMT.
- Future milestones
- November 2014 to December 2015 – Rosetta escorts the comet around the Sun.
- December 2015 – End of mission.
See also[edit]
- Deep Impact (spacecraft)
- Halley Armada
- Hayabusa - successful sample-return mission to an asteroid
- 67P/Churyumov–Gerasimenko
- Stardust (spacecraft)
- Timeline of Solar System exploration
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