... What if the Earth's axis were tilted 90њ to the ecliptic? ... I am no good judge of that, but also note that the abstract seems to refer to the solar wind above the Sun's poles, where field lines stick straight out and solar wind velocity is about double what it is near the ecliptic. ... If you launch parallel to the Earth's orbit you get the advantage of the Earth's orbital velocity of 30 km/s, but the distance is greater, so you need a greater average velocity to cover it in two weeks. ...