The problem of launching rockets to explore conditions in interplanetary space formed the subject matter of a previous note by the author. In this note further aspects of such exploration by probes are considered.

The orbits considered in the previous note were elliptic, and touched the orbit of the Earth at the conclusion of each journey around the Sun. For journeys within the Earth's orbit it is of interest to consider the situation in which the probe first enters one of these elliptic orbits and then, at the point of closest approach to the Sun, is placed in a circular orbit around the Sun.