Watney plans to drive to Schiaparelli crater where the next mission, Ares 4, will land in four years.
However, astrodynamicist Rich Purnell devises a "slingshot" trajectory around Earth for a gravity assist[REF] that could get Hermes back to Mars on a much-extended mission to save Watney, using the Chinese rocket to send a simpler resupply probe to Hermes as it passes Earth.