 By that time Waverider was a serious contender to be the carrier vehicle for the NASA/JPL Parker Solar Probe mission to send an unmanned vehicle to within four solar radii (2.782 million kilometers) of the surface of the Sun.In theory, the mission could be accomplished by a Jupiter slingshot, but the radiation hazards and the very long flight time made such a method impractical.Aerogravity manoeuvres in the atmospheres of the inner planets could put the probe into a trajectory providing solar encounters every two to three months, but would require a carrier with a very high lift-to-drag ratio at high Mach numbers — for which Waverider seemed the best candidate, as Jim Randolph confirmed on his third visit to Scotland in April 1990.