MESSENGER
MESSENGER ( Mercury Surface english, Space Environment, Geochemistry and Ranging; approximately, Mercury Surface, Environment, Geochemistry and distance measurement ') is a NASA space probe of the Discovery program, which explores the sun next planet Mercury. The abbreviation gives the English word for ' messenger ' and refers as well to the Roman god Mercury, messenger of the gods. The probe was launched on August 3, 2004 On their way into the inner part of the solar system they were in several flyby maneuvers at Earth, Venus and Mercury as much kinetic energy from that on March 18, 2011 at the fourth flyby of Mercury with a 15. - minute braking maneuver einschwenkte into orbit around the planet. MESSENGER is by Mariner 10, the second spacecraft to visit Mercury, and the first which surrounds him as orbiter.
The mission is led by the Johns Hopkins University Applied Physics Laboratory (APL ), which also built the spacecraft. The instruments were supplied by both the APL, as well as from the Goddard Space Flight Center of NASA, from the University of Michigan and the University of Colorado. The cost of the mission, including the spacecraft and its instruments, the launch vehicle and mission execution and data analysis to the end of the primary mission in March 2012 amounted to about 427 million U.S. dollars.
- 4.1 functioning of the mission
Mission Objectives
Mercury is one of the least explored planets of the solar system. This is mainly due to the very harsh conditions of space probes in the vicinity of the sun, such as the high temperature and intense radiation, as well as numerous technical difficulties that need to be taken on a flight to Mercury in purchasing. Even from orbit from the observation conditions are too unfavorable to watch him with telescopes. For example, the mirror of the Hubble Space Telescope would take by the particles of the solar wind a lot of damage if you would point it at a region close to the sun so much.
Mercury was up to the first flyby of MESSENGER's visited by only one spacecraft, the U.S. Mariner 10, which happened three times until 1975 the planet by 1974. However, only 45 percent of its surface could be mapped. Additionally examined Mariner 10 Mercury in the infrared, UV - light and adopted prior to measurements of the magnetic field and the charged particles.
In contrast to the Mariner 10 probe, which could only perform flybys of Mercury, MESSENGER can explore the planet with its numerous instruments far more accurate from an orbit out.
The primary mission of the probe in the Mercury orbit was designed for exactly one year. MESSENGER first time was able to completely map the planet and devoted himself especially to the study of geological and tectonic history of Mercury as well as its composition. Furthermore, the probe should search for the origin of the magnetic field, determine the size and condition of the planet core, examine the polar caps of the planet and explore the exosphere and magnetosphere. On 18 March 2012, a first extended mission, which ended on March 18, 2013 began. Since then, measurements continue to be performed. Whether an additional mission follows, was not decided in August 2013. [ Deprecated]
Construction
MESSENGER consists of a 1.27 m × 1.42 m × 1.85 m ( = 3.3 m3) great body and is protected by a semi-cylindrical, about 2.5 m high and 2 m wide shield against sunlight. Only two solar panels on opposite sides of the body, and a 3.6 m long magnetometer boom are mounted on the outside of the protective shield. The total launch mass of the spacecraft is 1093 kg; with a weight of 485.2 kg, the probe itself, the remaining 607.8 kilograms attributable to the carried fuel ( hydrazine and nitrogen tetroxide ) and helium gas pressure.
Instruments
MESSENGER carries seven scientific instruments, also the communication system of the spacecraft is used to determine the gravity field of Mercury used (Radio Science). Five of the instruments are mounted in the lower part of the probe, one ( EPPS ) at the top and on the side and the MAG on a 3.6 m boom.
Mercury Dual Imaging System ( MDIS )
MDIS consists of a wide-angle camera with a field of view of 10.5 ° and a narrow-angle camera with a field of view of 1.5 °. , The light enters into the instrument through a 12 cm x 12 cm box, which only allows the visible and near-infrared light up to a wavelength of 1.1 microns. The main tasks of MDIS are: color photographs of Mercury during the flyby, high-resolution images of selected areas and stereo images for high-resolution topography. A global monochrome mosaic of Mercury with an average resolution of 250 meters per pixel is to be created during the first six months of the mission. During the next six months, the receiving of the mosaic from a different angle to be repeated in order to produce as stereo images. Wide color photos with all ten color filters to be created for about 40 % of the surface.
The wide-angle camera has an achromatic Cooke triplet lens with a diameter of 30 mm and a focal length of 79 mm. The camera is equipped with a 12 - position filter wheel. Two of the filters are bandpass filters with a bandwidth of 100 nm, each centered at 600 nm and 750 nm further ten filters are color filters, centered at 415 nm (40 nm bandwidth), 480 (30), 560 (10), 650 (10 ), 750 ( 10), 830 (10), 900 (10), 950 (20) 1000 ( 30) and 1020 (40). The incident light is absorbed by a frame-transfer CCD with 1024 × 1024 pixels ( pixel). Each pixel is 14 square microns in size. Images at full pixel size can every four seconds, partial images (512 × 512 or smaller) are obtained every second. The resolution of the camera is 72 m at a distance of 200 km and 5.4 km at 15,000 km.
The narrow-angle camera uses a Ritchey -Chretien telescope with a focal length of 550 mm. Only one filter is of the camera. One with the Wide Field Camera CCD identical, creating the recordings used. The resolution is 5.2 m at a distance of 200 km and 390 m at 15,000 km.
MDIS weighs 7.9 kg and requires an average of 10 watts of power. A total of 12 Gb of data MDIS expected by the end of the primary mission. The instrument was developed by the Applied Physics Laboratory of Johns Hopkins University.
Gamma - Ray and Neutron Spectrometer ( GRNS )
GRNS with the composition of Mercury is explored, in particular to the presence of such elements, such as oxygen (O), silicon ( Si), sulfur (S ), iron ( Fe), hydrogen (H), potassium ( K), thorium (Th ) and uranium (U) to be examined. With GRNS especially the geological history of the planet to be studied and searched for ice at the polar caps. The experiment consists of two instruments: the Gamma - Ray Spectrometer and Neutron Spectrometer.
The Gamma Ray Spectrometer measures gamma radiation, either by the bombardment of galactic cosmic rays (O, S, Si, Fe, and H) or by natural radioactive decay (K, Th and U) occurs up to a soil depth of about 10 cm. The Gamma Ray Spectrometer is a 31 cm high cylinder which contains the actively shielded scintillator. This is protected by a 9 cm × 9.5 cm, 1.25 cm thick shield made of bismuth germanate ( BGO), behind which is a photomultiplier. The shield allows a field of view of 45 °. The detector is a germanium -type semiconductor crystal, which is cooled to a temperature of -183 ° C. The measurable energy range is 0.3 to 10 MeV, the integration length is 5 min in the periapsis and apoapsis in 30 min.
The Neutron Spectrometer detected low-energy neutrons, which are formed in the upper 40 cm of the planet's surface by the bombardment of cosmic rays and subsequent collisions with hydrogen-rich material. The spectrometer consists of two paddle-shaped GS20 - glass scintillators (6.6% lithium) with an area of 80 cm ² and a thickness of 6.5 cm, separated by two neutron -absorbing BC454 scintillators ( borated plastic) with a total of 80 cm ². The GS20 scintillators measure thermal, BC454 scintillators epithermal and fast neutrons.
GRNS weighs 13.1 kg and requires an average of 4.5 watts (maximum 23.6 watts) power. A total of 3.9 Gb of data GRNS expected by the end of the primary mission. The instrument was developed by the Applied Physics Laboratory of Johns Hopkins University.
Magnetometer ( MAG)
The magnetometer measures the magnetic field of Mercury. Based on the data provided a three-dimensional model of the magnetosphere of the planet was created. To avoid interference by the on-board magnetic field, the instrument is mounted on a 3.6 m boom, which in the sun facing the opposite direction. MAG measures the magnetic flux density in the range of -1024 to 1024 nT. For the quantization of the measured values are 16 bits available, thus achievable measurement resolution is 0.03 nT. The sampling rate of the detector is 40 Hz, the measured values can be read in adjustable time intervals of 25 ms to 1 s.
MAG weighs along with the boom 4.4 kg and requires an average of 2 watts (maximum 4.2 watts) power. As at the end of the primary mission about 440 MByte data were expected by the magnetometer. The instrument was developed by the Goddard Space Flight Center of NASA.
Mercury Laser Altimeter (MLA )
By means of laser pulses whose duration is measured from the probe to Mars and back, MLA can win topographic findings about Mercury. Measurements can be made as soon as the height of the orbit of the probe is less than 1000 km above the surface of the planet. As MESSENGER moves on a highly elliptical orbit whose lowest point is at 60 ° north latitude, MLA can detect only the northern hemisphere planet.
MLA is based on the instruments MOLA (Mars Orbiter Laser Altimeter ) of the spacecraft Mars Global Surveyor and GLAS ( Geoscience Laser Altimeter System) of the ICESat satellite. The instrument uses a Cr: Nd: YAG laser having a wavelength of 1064 nm, the laser operates at a frequency of 5 Hz, and sends light pulses with an energy of 20 mJ and a duration of 5 ns. The reflected pulses are from the planet by a receiver, consisting of four sapphire lenses collected. The transit time of a light pulse is measured with an accuracy of 3.3 ns, this gives a measurement resolution of 0.5 m.
MLA weighs 7.4 kg and requires an average of 20 watts (maximum 38.6 watts) power. As at the end of the primary mission about 1.5 Gb of data were MLA expected. The instrument was developed by the Goddard Space Flight Center of NASA.
Mercury Atmospheric and Surface Composition Spectrometer ( MASCs )
This spectrometer explores the composition of the atmosphere of Mercury. MASCs weighs 3.1 kg and requires an average of 3 watts (maximum 8.2 watts) power. The instrument has been developed by the University of Colorado.
Energetic Particle and Plasma Spectrometer ( EPPS )
EPPS measures the composition and distribution of charged particles such as electrons and various ions in Mercury's magnetic field. EPPS weighs 3.1 kg and requires an average of 2 watts (maximum 7.8 watts) power. The instrument was developed by the University of Michigan and by the Applied Physics Laboratory of Johns Hopkins University.
X - Ray Spectrometer ( XRS )
Gamma and X-ray radiation from the sun can cause on Mercury's surface elements to emit X-ray radiation of low energy. XRS can detect this and thus allow conclusions on the composition of Mercury. Thereby be detected by the XRS elements magnesium (Mg), aluminum (Al), sulfur (S ), calcium (Ca ), titanium ( Ti), and iron (Fe) from the upper surface layer of 1 mm thick.
XRS is a modified version of the instrument XGRS the NEAR Shoemaker spacecraft. XRS includes three cylindrical, gas-filled proportional counter, which is mounted behind a 25 micron thick beryllium window. XRS weighs 3.4 kg, and requires an average of 8 watts (maximum 11.4 watts) power. As at the end of the primary mission about 1.5 GB of data XRS were expected. The instrument was developed by the Applied Physics Laboratory of Johns Hopkins University.
Radio Science (RS)
In the context of RS small variations in the speed of the probe can be measured by the on-board communication system by means of the Doppler effect. From these data it can be concluded on the mass distribution of Mercury. Through Radio Occultation also the exact dimensions of the planet and the amplitude of its libration are measured. RS is managed by the Goddard Space Flight Center of NASA.
Mission History
The project of a space probe to Mercury named MESSENGER was in 1997 among the finalists of the Discovery program selection, but could not prevail against other missions. In March 1998, MESSENGER was included again by NASA in the selection for a mission within the Discovery program, in November 1998, MESSENGER was one of five finalists with the best scientific yield from a total of 26 proposals. Finally, it was approved along with Deep Impact for funding under the Discovery program on 7 July 1999 MESSENGER. The cost of the spacecraft were then estimated at 286 million U.S. dollars.
The initially planned 19-day launch window in March 2004 and also the second, 12-day mid- May 2004 could not be met due to technical reasons. On July 30, 2004, opened again a 15 -day window. A start on August 2, but was canceled due to dense cloud cover over the spaceport Cape Canaveral. On August 3, 2004 at 02:15:56 local time ( EDT), the probe was launched finally on a rocket from the Delta II 7925H type. The new launch window had a different trajectory to select which postponed the originally planned for 2009 arrival two years back.
The spacecraft is about eight billion miles flown through the solar system when it became the first einschwenkte into orbit around Mercury in March 2011. For the sake of fuel economy multiple swing-by maneuver at Earth, Venus and Mercury had to be carried out. The probe lost due to asymmetric approach to the planet some of their orbital energy and has been slowed down.
The only swing-by on the earth took place on 2 August 2005. On 24 October 2006 and on 5 June 2007 it passed by Venus in the swing-by. On these occasions, some on-board instruments are activated to carry out measurements on the two planet.
The first of three swing-by maneuvers at Mercury took place January 14, 2008, the second on 6 October 2008 and the last on 29 September 2009. Overall, the three maneuvers built about 33 % of the energy. In these maneuvers MESSENGER flew each in about 200 km above the planet's surface, carried out measurements and mapped regions that could not be detected during the flybys of Mariner 10. Only the third swing-by no observation data were acquired during the shortest distance to Mercury, because the probe was switching four minutes before unexpectedly for several hours in the safe mode.
On 18 March 2011, the probe swung with a braking maneuver ( change in velocity 862.4 m / s) in an orbit around Mercury.
The probe orbiting Mercury in altitude of 200 to 15,000 km. Due to the slow rotation of Mercury, the planned orbit of MESSENGER has a special shape in order to observe the planet each in the sunlight, and the probe can not be too long exposure to the sun's heat reflected from the surface.
Functioning of the mission
The following table gives an overview of the previous flight history and the most important planned way stations.
* Trajectory Correction Maneuver TCM = ( trajectory correction maneuver) DSM = ** Deep Space Maneuver (lane change maneuver)
Description of the course
The first mission began as planned on April 4, 2011. The spacecraft flew around the planet once every 12 hours for the duration of one year on Earth (equivalent to two Mercury days ). On 5 October 2011, the researchers published their results for the first six months of the mission at the European Planetary Science Congress in Nantes.
The data showed unexpectedly high concentrations of magnesium and calcium on the night side of Mercury. In addition, the magnetic field of the planet is not in the center but is far to the north.
On March 17, 2012 launched the extension of the mission in order to observe the maximum of the sunspot cycle can. In November 2012, NASA reported that the spacecraft has found both at the North Pole frozen water and organic materials in craters on Mercury's surface, in the sunlight never falls. In February 2013, NASA published a recent and most detailed 3D map of Mercury's surface. It consists of thousands of images that MESSENGER has taken during the mission.
On March 17, 2013 MESSENGER also finished this expanded mission and further funding is still open.