NASA’s MESSENGER spacecraft was launched into space onboard a Delta II 7925 rocket on 3 August 2004 at 06:15:56 UTC from Space Launch Complex 17B at the Cape Canaveral Air Force Station in Florida
Getting to Mercury from the Earth requires a large velocity change because the closeness of Mercury to the Sun places the planet deep within the Sun’s gravitational potential well. Furthermore, Mercury’s extremely tenuous atmosphere makes it impossible for an aerobraking manoeuvre to be employed to sufficiently slow an incoming spacecraft for capture into orbit around Mercury. To solve this issue, MESSENGER extensively used gravity assist manoeuvres by making flybys of the inner planets to gradually decelerate the spacecraft such that the amount of propellant required to slow the spacecraft into orbit around Mercury is greatly reduced. However, this comes at the cost of prolonging the trip to Mercury by a few years. The trajectory that MESSENGER took through the inner solar system to get to Mercury included one flyby of Earth, two flybys of Venus and three flybys of Mercury itself.
On 18 March 2011 at 12:45 a.m. UTC, the orbital insertion manoeuvre brought MESSENGER into a highly elliptical orbit around Mercury whose lowest point is 200 kilometres above the planet’s surface while the highest point is over 15000 kilometres above the planet’s surface. The three previous flybys of Mercury by MESSENGER have already generated an astonishing amount of interesting science that has changed our understanding of the enigmatic innermost planet of the solar system. However, these flybys are merely a sneak preview of the discoveries that are expected to come as MESSENGER is now the first spacecraft ever to orbit Mercury for long-term observations. Visit http://messenger.jhuapl.edu/index.php to learn more about MESSENGER and its mission around Mercury.