Station Info :: Nine Planet Solar System ::
Space Mercury :: Mercury Exploration
Reaching Mercury from Earth poses significant technical challenges. Mercury orbits three times closer to the Sun than does Earth, so a Mercury-bound spacecraft launched from Earth must travel over 91 million kilometers down into the Sun's gravitational potential well. From a stationary start, a spacecraft would require no delta-v or energy to fall towards the Sun; however, starting from the Earth, with an orbital speed of 30 km/s, the spacecraft's significant angular momentum resists sunward motion, so the spacecraft must change its velocity considerably to enter into a Hohmann transfer orbit that passes near Mercury.
In addition, the potential energy liberated by moving down the Sun's potential well becomes kinetic energy, increasing the velocity of the spacecraft. Without correcting for this, the spacecraft would be moving too quickly by the time it reached the vicinity of Mercury to land safely or enter a stable orbit. The approaching spacecraft cannot use aerobraking to help enter orbit around Mercury since it has no atmosphere and must rely on rocket boosters. Because of this, a trip to Mercury requires even more rocket fuel than to escape the solar system completely. As a result of these problems, there have not been many missions to Mercury to date.
Also see the
Physical Characteristics of Mercury
Understanding Of Mercury
Exploration Of Mercury