... It was designed to observe the solar wind approaching Earth, from a position near the Lagrangian point L1, and it is part of the International Solar-Terrestrial Physics (ISTP) Initiative . ... The original plan called for "Wind" to approach its final station over two years, undergoing two close encounters with the Moon to boost its speed. ... If however the object is moving , the encounter is not symmetric, and in the end the spacecraft may have gained or lost speed, depending on its trajectory. ...