|
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.
|
