MESSENGER is a scientific mission intended to explore Mercury (the least explored of the terrestrial rocky planets). Understanding Mercury is crucial to understanding the formation and evolution of the inner planets. Before MESSENGER, Mercury had been the only inner rocky planet never to have been orbited by a spacecraft. To obtain the desired data from Mercury, MESSENGER carries scientific instruments and a radio science experiment designed to work in extreme high temperatures. Determining Mercury´s surface composition is one of the major goals of the mission.
Mercury is the rocky planet nearest to the Sun. It has a diameter of about 3,032 miles (4,879 km), making it slightly larger than the Earth´s Moon. It has the most eccentric orbit of any planet, with a distance ranging from 29-44 million miles (47-71million km) from the Sun. mercury´s year, which is the shortest of any planet, takes approximately 88 days, and it rotates on its own axis once every 59 days. Mercury´s day and year are interrelated in a 3/2 spin-orbit resonance, meaning that while the planet spins on its own axis three times, it circles the Sun twice. Its surface temperature varies from 800 °F (427 °C) to about -300 °F (-184 °C) with the higher temperature present in the sunlit side and the lower temperatures in the shaded side near the poles.
Scientists believe that gaining a deeper understanding at the composition, formation, and evolution of Mercury will give them a better understanding at how the planets in the solar system have evolved. The MESSENGER spacecraft and instruments were designed with this purpose in mind. The object of the mission focuses on finding the answer to six important questions regarding Mercury´s density, geologic history, Mercury´s magnetic field, Mercury´s core structure, composition of materials at the poles, and composition of Mercury´s exosphere.
MESSENGER was launched from Cape Canaveral, Florida on August 3, 2004. On its way to Mercury, MESENGER returned to Earth for a gravity assist on August 2005. It used Venus ‘gravity to correct its trajectory into Mercury´s orbit. Three Mercury flybys put Messenger into the right position to enter Mercury´s orbit which occurred on March 2011. During the flybys, MESSENGER sent the first new data from Mercury in more than 30 years. Before MESSENGER, the only images from Mercury had come from NASA´s Mariner 10 spacecraft which flew by Mercury three times in 1974 and 1975.
MESSENGER´s instruments, electronics, wiring, and instruments are contained into a small frame no bigger than the one that could fit inside a sport utility vehicle. A sunshade made of ceramic, along with heat radiators, protects MESSENGER from the extreme hot temperatures that are encountered at closer distances to the Sun. all this equipment is integrated with a low-mass propulsion system that distributes efficiently approximately 600 kg (1,320 pounds) of propellant which account for approximately 54% of MESSENGER´s total payload.
To answer the six scientific questions, MESSENGER payload comprises a Mercury Dual Imaging System (MDIS) which includes two cameras and a scanning mirror; a Gamma-ray and Neutron Spectrometer (GRNS) which can detect neutrons and gamma-rays; a Magnetometer (MAG) which will be used to map Mercury´s magnetic field; a Mercury Laser Altimeter (MLA) which contains a laser that will be used to produce accurate descriptions of Mercury´s topography; a Mercury Atmospheric and Surface Composition Spectrometer (MASCS) which measures the abundances of minerals and atmospheric gases on Mercury´s surface.
An Energetic Particle and Plasma Spectrometer (EPPS) which measures the energy and composition of charged particles in Mercury´s magnetosphere; an X-Ray Spectrometer (XRS) which can detect low-energy x-rays emitted by surface elements on Mercury´s crust; and a Radio Science (RS) experiment which can measure the spacecraft´s velocity variations along Mercury´s orbit. This will reveal mass distribution, including variations in the thickness of Mercury´s crust.
During its 6.5 year journey, MESSENGER made more than 15 trips around the Sun, encompassing 4.9 billion miles (7.9 billion km), flew close to Earth´s orbit once; close to Venus ‘orbit twice and finally used Mercury´s gravity to enter its orbit. After each of the first two Mercury flybys, MESSENGER approached the record speed for all spacecraft by reaching speeds of more than 140,000 miles/hr. (225,300 km/hr.) which is about eight times faster than the speed reached by NASA´s Space Shuttle in low-Earth orbit.