Help the Galactic Rangers is a mission in Up Your Arsenal, taking place in Outpost X12, Aridia. While Ratchet and Clank were exploring the crash site on Zeldrin, the Galactic Rangers sent a transmission about a tyhrranoid invasion of Aridia. Ratchet and Clank then led the assault against them.
To complete this mission, all five missions in Operation: DEATH VALLEY must be completed. These missions are all mandatory, though if you are struggling, consider returning to the Starship Phoenix to pick up some armor, as Aquatos or Annihilation Nation can provide a good source of bolts.