Consider the following pairs regarding planetary exploration missions and the techniques/features associated with them:

Pairs

1. Gravity-assist manoeuvre — Using the gravitational field of a planet to alter a spacecraft's speed and trajectory without expending additional fuel
2. Main asteroid belt — Region between the orbits of Mars and Jupiter where most of the solar system's asteroids are concentrated
3. Elliptical orbit — An orbit with two focal points, allowing a spacecraft to sweep across a wider range of altitudes and cover more of a planet's atmosphere