MESSENGER MISSION TO MERCURY
The only spacecraft to date to visit Mercury was Mariner 10 launched on 3rd November 1973. It flew by Venus to use the gravity of the second planet to boost its trajectory and place it on course for Mercury. It passed Venus on 5th February 1974 taking the first close up photos of the planet and acquiring scientific data.
Its first flyby of Mercury was on 29th March 1974, the second on 21 September 1974 and the third and final on 16th March 1975.
Unfortunately Mariner 10 was only able to photograph about 45% of the surface of Mercury so our knowledge of the surface is somewhat limited. Most of the detailed but incomplete knowledge we have of Mercury comes from the Mariner 10 mission.
Getting to Mercury is not as easy as it sounds. The main problem is that because Mercury is closer to the Sun it moves much faster in its orbit than Earth does. The Earth moves at 29.8 km/second around the Sun whereas Mercury moves at 47.9 km/second. Any spacecraft hoping to go into orbit around Mercury must first match speed with the planet.
It is not possible with present technology to send a spacecraft directly from Earth to Mercury. Additional energy is gained by carefully planned flybys of Earth, Venus and Mercury. As the spacecraft approaches the planet it can pick up energy from the movement of the planet in its orbit. This is called a gravity assist. Each gravity assist changes the trajectory of the spacecraft so that it is in a position to go into orbit around Mercury without having to use too much of the on-board fuel supply. As it is a third of the fuel will be needed to achieve orbit. Without gravity assist placing Messenger in orbit around Mercury would be impossible.
Messenger was launched from Cape Canaveral, Florida, on 3rd August 2004. It returned to Earth on 2nd August 2005 for a gravity assist. It will fly by Venus in October 2006 and again in June 2007. It will then fly by Mercury three times, January 2008, October 2008 and September 2009 finally entering Mercury orbit in March 2011.
The spacecraft is made of a graphite epoxy material providing relatively low mass with considerable strength. It is controlled by a number of computer processors. Communication with Earth is by a phased array X-Band antenna and back up low gain antennas. The spacecraft is protected from the Sun's heat by a sunshade of ceramic cloth. In the vicinity of Mercury the Sun is 11 times brighter than on Earth and the temperatures can reach 450º C. Behind the sunshade though the interior of Messenger remains close to room temperature.
Messenger's 12 month orbital mission will map the planet in colour, photograph areas unseen by Mariner 10 and return the first new data from Mercury in 30 years.
