He must use it to rendezvous with the Hermes

Film: The Martian (2015) Movie Scene
Starring: Matt Damon, Jessica Chastain, Kristen Wiig, Jeff Daniels, Michael Peña, Sean Bean, Kate Mara, Sebastian Stan, Aksel Hennie, Mackenzie Davis, Benedict Wong, Donald Glover, Chen Shu, Eddy Ko, Chiwetel Ejiofor.