The Peacekeepers. Book 20 The Guardian

Five years into their mission, the peacekeepers are preparing to launch the largest and most advanced space station in history to safeguard the United States, but threats from China and Russia loom large. When Beth persuades Gabe to undertake a daring stolen trip to the moon, they face a series of intense emergencies that test their survival skills. Meanwhile, scientists race to find solutions as the young stars navigate dangers with limited supplies on their perilous journey.