Heliocentric orbit

Representation of the heliocentric orbits that follow the planets of the solar system.

A heliocentric orbit (also known as a circumsolar orbit) is one that takes place around the Sun. In our solar system, all the planets, asteroids and comets have orbits like this one, as well as some space probes and space junk. In contrast, for example, the Moon has a geocentric orbit, that is, around the planet Earth.

The prefix helium- comes from the ancient Greek word helios (ἥλιος), meaning sun, and also of Helios, the personification of the Sun in Greek mythology.

Trans-Mars Injection

Trans-Marte injection diagram. A = Hohmann transfer orbit. B = conjunction mission. C = Opposition Mission.

A Trans-Mars Injection (TMI) (or Trans-Martian) is a heliocentric orbit in which a propulsive maneuver is used to set a spacecraft on a trajectory, also known as a Mars Transfer Orbit, that will cause the spacecraft to get to orbit Mars.

Every two years, low-energy transfer windows open that allow movement between planets with the lowest possible delta-v conditions. Transfer injections can place a spacecraft into a Hohmann transfer orbit or a bi-elliptic transfer orbit. Trans-Mars injections can be a single thrust maneuver, such as used by NASA's MAVEN orbiter, or a series of repeated perigee thrusts, such as used by the ISRO Mars Orbiter Mission.