ESA’s Rosetta Mission
Astronomy in the contemporary world focuses on groundbreaking projects that aids in understanding the universe and its features. Such projects take a time to plan, design, and implement. Once implemented, monitoring can take years for the phenomena being measured to be realized. Understand the details of such projects are essential in appreciating information about the composition of the earth. At the same time, these projects provide firsthand facts about various objects in space. One object that has remained a mystery to the world is the comet. Comets contain primitive materials of the solar system and hold the key to understanding the formation of the solar system once these materials have been investigated. The information known about comets is derived from Earth-based instruments that measure through remote sensing. This means projects supposed to advance the study of comets will be a welcome to the information-hungry people. There are a number of such projects being undertaken, and one such project is the Rosetta Mission by the European Space Agency (ESA). This paper will explore the Rosetta Mission by ESA in details.
Rosetta is the name given to a space probe constructed by ESA. It was launched on March 2, 2004, with its lander module called Philae. It was directed to comet 67p also called Churyumov-Geresimenko, to carry out a series of studies on it. On August 6, 2014, about ten years after its launch, Rosetta arrived on comet 67P and started to conduct a series of studies in its orbit. It landed on the comet on 12 November after maneuvering through its orbit. The probe derives its name from Egyptian stele called Rosette Stone. The lander, on the other hand, derives its name from hierological inscription Philae obelisk.
In 1986, Halley’s Comet approached the earth, and this triggered interest in scientists on its composition among other features. Several international agencies sent space probes to study the comet, and one of them was Giotto probe sent by ESA. According to ESA (par. 2), the probe discovered valuable information, but more questions arose from the study thereby necessitating further studies. The follow-up mission was majorly required to iron out issues on the composition of the comet among other issues.
New studies on the comet needed special crafts to carry out the mission. As a result, NASA and ESA started developing a probe that could aid the mission. The project was done jointly, though each group was developing a different probe. The project undertaken by ESA was dubbed CNSR or Comet Nucleus Sample Return and it was a follow-on project. The project by NASA was dubbed the CRAF mission or Comet Rendezvous Asteroid Flyby. The two missions shared the spacecraft design of Marina Mark II as a way of cutting cost. However, in 1992, NASA canceled CRAF mission due to budgetary limitations. ESA was forced to develop CRAF project on its own. ESA made some preliminary preparations for the sample mission return but by 1993, little progress had been made. ESA was working with a limited budget, and thus was forced to redesign the project to fit the limited budget. ESA redesigned the mission based on the available budget, and it was approved. The flight mission resembled the CRAF mission that had been canceled. During a conference in November 1993, the Rosetta international mission was approved. The conference brought together the brightest minds in Europe and USA whereby they worked on a design for a lander and an orbiter for the Rosetta mission. These scientists were motivated by the quest to unravel the mysteries of the comet or mini ice world. Historical Achievements by Rosette
The plan and design of Rosette missions were meant to ensure ESA achieve some historic firsts. Rosette was designed to orbit the nucleus of the comet, and thus, it became the first spacecraft to orbit the comet. Its path included going towards the solar system and this meant flying alongside the comet. As a result, it became the first spacecraft to fly along a comet. Rosette further became the first rocket to fly close to the comet to examine the frozen status of the comet as well as how the sun warms the comet. On its path to comet 67P, Rosette maneuvered through the chief asteroid belt thereby making a close happenstance with some primitive objects. Rosetta was powered by solar cells and flew close to Jupiter thereby becoming the first spacecraft to achieve that fete. Upon arriving at 67P, the Rosetta orbiter sends off the lander Philae in a remote-controlled system to touch the comet. Subsequently, it becomes the first spacecraft to land on the comet. After landing on Comet 67P, Rosette instruments in the lander obtained the first images through robotic instruments on the comet. The in-situ analysis of the composition of the images was made by Rosetta and thus becoming the first spacecraft to undertake such achievements (Agle, Webster and Brown par. 2).
Rosetta was made from a large aluminum box measuring 2.8 by 2.1 by 2.0 meters. The box was made with payload support and bus support modules. The bus support module supported the subsystem and its base whereas the payload module support held the instruments for the survey. The orbiter had one of its side made to hold a communication dish measuring 2.2 meters in diameter. The communication dish was used as a high gain antenna. The opposite end had the lander attached. There were two large solar panels on either side (EUROPEAN SPACE AGENCY par. 3). Each solar panel measured 32 square meters with a total span of 32m. Each solar panel had consisted of five small panels and could be rotated through 180 degrees from either side to tap the maximum amount of sunlight.
According to the German Aerospace Center (par. 4), Rosette was designed such that once it landed on the comet, scientific instruments would point to the comet whereas solar arrays and antennae point to the sun and earth. The louvers and radiators were positioned at the back panels. This was an ideal position because the back panels receive a little amount of light when in orbit. At the same time, this location ensured that no damage is done on the radiators and louvers since they will be facing away from the comet dust.
Rosetta contained instrument as part of its payload to aid in the investigation. There were 11 instruments on the payload. The instruments were made using the state of the art technology and were oriented to ensure they always face the comet during the entire journey. Each instrument was adapted to a particular phenomenon being observed. Major instruments were in the lander. The lander had a shape of a box and was ejected from the spacecraft to land on the comet. The lander has a platform for instruments and an antenna for data transmission via the orbiter. Among the instruments in the lander include the APXS spectrometer, CIVA imaging system, COSAC gas analyzer, and Ptolemy gas isotopic composition analyzer. Microwave radio antennae, spectrometers, and radar were used to observe the nucleus. An instrument abbreviated as CONSERT to imply Radio wave transmission comet nucleus sounding was also placed in the lander. The CONCERT was used for tomography. Also, the lander contained SESAME acoustic monitoring probe, SESAME dust impact monitor, and SD2 drilling sample retrieval. The main purpose of the Lander payload was to study the structure and composition of comet 67P. Each instrument had a specific location in the lander to avoid interference during the data collection process. Fig 1 indicates the lander and the position of each instrument.
Figure 1: Lander with Instruments ( EUROPEAN SPACE AGENCY)
The Obiter had 11 instruments that combined remote sensing techniques to capture data from the lander and universe and relay them to the earth. The combination of technologies such as direct sensing, radio, and camera science, and dust particle analysis were used singly or together to bring about the desired results. Among the instruments in the orbiter includes Alice UV imaging spectrometer, COSIMA Iron mass analyzer, GIADA grain and dust analyzer, and MIDAS micro dust analyzer. The orbiter also contained MIRO microwave, ORIS Infrared system for imaging, ROSINA Neutral analyzer, Plasma Consortium for Rosetta, RSI investigator, and VIRTIS spectrometer. Each instrument had a special position in the orbiter to ensure maximum utilization of its capability. Figure 2 indicates the orbiter with the position of each instrument.
Figure 2: Obiter with instruments (ESA)
The propulsion system was located at the heart of the Orbiter. The propellant consisted of two large tanks mounted around a vertical thrust tube. The lower tube contained the oxidizer whereas the upper tube contained fuel. The orbiter further carried 24 thrusters for attitude and trajectory control. Each thruster had a force of 10N. The propellant takes about half of the weight of launch. Gibney (16) claims that the Rosetta was constructed based on COSPAR rules whereby the entire process took place in a clean room. However, less emphasis was placed on sterilization because a comet is not a microorganism. The Rosetta project cost was estimated at 1.3 billion sterling pounds.
After years of design and preparations, Rosetta mission was scheduled to be launched in January 2003. However, the Arianne Rocket failed to launch forcing the engineers to modify and consequently postpone the launch date. The ESA team came up with a new plan of targeting the comet Churyumov-Gerasimenko at a new date. The landing gear was modified to ensure it accommodates the large mass of the lander and the resultant impact velocity. After some modifications, the Rosette was launched on March 2, 2004, at about 0717hrs GMT. The launch took place at the Space Center in Guiana, France (Gibney 16). Apart from the modifications made to the target and launch date, the profile of the mission remained as planned.
Rosetta required a steady and sufficient velocity to navigate through the inner solar system. As a result, the ESA team used gravity assist maneuvers to assist it. The scientists working on the project ascertained the orbit of the comet 67P to a fair accuracy while on the ground. According to the German Aerospace Center (par. 3), the accuracy was about 100km. However, the position of the comet in the orbit was refined based on the information relayed by cameras from a distance of about 24 million km. ESA had set up an operation center on the ground to process information from the cameras and guided the Rosetta. After the launch, the Rosette began its 10-year expedition to comet 67P. It was initially put into a parking orbit before being sent into the solar system outwards its parking orbit.
According to the German Aerospace Center (par. 5), there is no rocket with the ability to send a spacecraft into the orbit of comet 67 directly. As a result, Rosetta was designed to rebound around the inner section of the solar system like a cosmic billiard ball. In this case, the Rosetta circled the sun four times on its way to comet 67P. Taking the roundabout route ensured the Rosette enter the asteroid belt two times thereby gaining high velocity from gravitational kicks. The gravitational kicks were achieved through fly-bys close to the Earth and Mars.
The Rosetta flew from the earth and a later encountered the Earth in 2005 in its first flyby. During its time of cruise back to the Earth, it remained active and relayed some images. The flyby distance was 250km and was meant to correct its trajectory. Following the success of the first flyby, a second flyby was planned and took place on November 13 007 at a distance of about 5700km. During the flybys, the focus was on tracking and determining the orbit of the Rosetta and performing a payload check. Also, orbit correction was done during and after each flyby. Following its first flyby on earth in 2005, Rosetta flew to Mars and later came back to earth in November 2007 for the second flyby and November 2009 for the third flyby (Agle, Webster, and Brown par 10).
The Rosetta performed a flyby on Mars in February 2007 thereby making an important observation through its payload instruments. During the flyby, there was an earth eclipse by Mars, which lasted for about 37 minutes. This eclipse caused communication blackout for 37 minutes.
The Rosette flew by the asteroids belt. The journey to the asteroid was passive because the solar panels were not directly overhead the spacecraft thereby causing some power shortage for about 15 minutes. Thus, passive mode ensured power was saved. After the flybys, the data recorded were transmitted to the earth.
Between May 2011 and January 2014, Rosette flew into deep space on its way to comet 67P after a series of flybys. At the deep space, Rosette went into hibernation mode. During this time, the maximum distance recorded from the earth was approximately 1000 million km whereas the distance recorded from the sun was about 800 million km. Rosetta woke up from its hibernation mode on January 20, 2014.
During May 2014, the thrusters of Rosette began to brake the spacecraft to ensure its speed matches that of comet 67P. On August 2014, Rosetta arrived on comet 67P. It started collecting information from the comet. ESA (par 1) states that data collection is still ongoing as it orbits comet 67P.
Rosetta performed two triangle maneuvers on the comet after aligning its speed to match the speed of comet 67P. The path created was about 100km during the first maneuver and 50km during the second maneuvers. On September 10, 2014, the spacecraft had closed the gap with comet 67p to about 30km. As a result, it entered the orbit of 67P. Upon arriving on 67P, it was not possible to land because the layout of 67P was not known. Rosette thus preformed some mapping and identified five landing sites. On 15 September 2014, one landing site named Agiika was identified (Agle, Webster, and Brown par 11).
Rosetta detached from its lander on 12 November 2014. It landed on comet 67P but bounced two times due to its high speed. The science mission began. The mission of the Lander was mainly to determine the characterization of the nucleus, ascertain its chemical composition, and confirm whether a type of amino acids enantiomers was present or not. The mission further involved studying the activities of comet 67P, and ascertaining how the comet has developed with time.
According to Gibney (16), Philae landed oddly on comet 67P. Gibney (16) further claims that the lander might have landed in a shadow of a crater wall or a cliff because it landed at an angle of about 30 degrees. Landing on a shadow made it impossible for Rosetta to maintain contact on earth because its batteries run out and could not be charged. The contact was lost just two days after landing and, this time was not adequate for the ESA scientists to achieve their intended objectives. Between 13 June and July 9, 2014, intermittent communication with Rosetta was established after a few months of losing contacts. Some information was received from Rosetta during this time before the contact was lost again. Gibney (17) anticipates that there will be no further communication from Rosetta.
The initial findings by Rosetta indicated that Comet 67P had a magnetic field with an oscillation of about 40 to 50 millihertz. This signal was amplified more than 10000 times to make it visible. However, information from Philae lander indicated that Comet 67P had no magnetic field in its nucleus. ESA scientists concluded that the magnetic field originally detected from Rosetta might have been caused by the solar winds influence.
ESA discovered that the composition of water vapor on comet 67P was different from the composition of the water vapor on earth. The isotopic signature of the water vapor found on comet 67P different with that found on the Earth. The difference comes from the ratio of deuterium to hydrogen whereby the ratio was three times more than water vapor found on the Earth. The difference implies that earth’s water vapor does not come from comets with same features as comet 67P. It was further observed that water vapor on comet 67p increased tenfold between June and August 2014.
NASA (par. 1-4), working on the data from ESA’s Rosetta, reported that the degradation of carbon dioxide and water molecules were because of electrons held within a kilometer distance from the nucleus of the comet. These molecules are freed from the nucleus of the comet to its coma. The electrons, on the other hand, were produced by photoionization of molecules of water by solar radiations. Earlier postulations had indicated that photons from the sun were responsible for photoionization, but this study proved otherwise.
Previous observations had indicated that the composition of comets was complex and contain the organic compound. The organic components include amino and nucleic acids that make up life. It was assumed that comets delivered large quantities of water on earth and thus might have brought along the organic components that triggered life on the Earth. Rosetta managed to detect molecules in the atmosphere of the comet before its power went off. Further information will be discovered if contact is established.
Rosette will further establish the rationale behind the left-handedness of essential amino acids. Atoms orient on the left side of the molecules and living things have a unique left-handed structure. The study will aim to establish the theory behind this arrangement and confirm or dispute some of the hypotheses suggested to explain the phenomena.
Preliminary results indicate that there are organic macromolecule compounds on comet 67P. These organic compounds are nonvolatile. The study further established that water ice was not available on comet 67P. Further discoveries indicated that material near the comet has carbon molecules. However, further analysis of the studies near the nucleus and coma of comet 67P does not indicate the presence of carbon compounds.
ESA has made a groundbreaking project by sending Rosetta to Comet 67P. Pioneering projects aid in understanding the universe and its features. Rosetta mission was initiated with an aim of ascertaining known features about comets and finding out an unknown information about its material composition. The information discovered could further aid in understanding information about the formation of the earth because comet has materials that resemble earth’s primitive material. This paper has discovered that Rosetta mission was launched successively in 2004. Rosetta spent ten years in space and passed by the earth three times before reaching comet 67P in 2004. ESA scientists have discovered essential information about comet 67P and more information is being discovered because the mission has not yet concluded.
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ESA. “Lander Instruments.” Dec 2015. Web. 2 Apr 2016 <http://sci.esa.int/rosetta/31445-instruments/>.
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