the women unconscious and seemingly dead—but Valkerie has found Bob's hidden dose of sodium pentathol and uses that to put her and Lex into a coma once again—so that they survive, but Valkerie suffers multiple rib fractures when Bob attempts cardiopulmonary resuscitation. Finally, the astronauts realize the significance of the stainless-steel shrapnel with which Bob had been wounded in the initial explosion. None of the ship's systems was made of stainless steel—in fact, the lack of any material but plastic was a source of great frustration to Valkerie when she first attempted to seal the hull breach. Valkerie and Lex realize that the stainless steel must have come from a bacterial culture vial that Josh Bennett had received from a former girlfriend in Antarctica—and that the vial contained a radiation-resistant bacterium, the same one that in fact had contaminated some of the ship's systems after the explosion. Now the astronauts realize what has happened to them: Josh Bennett, fearing cancellation of Project Ares and the disbanding of NASA, sought to "seed" a radio-resistant bacterium on Mars for the astronauts to "discover." To accomplish this, he did plant a bomb on board, designed to detonate with the deployment of the aerobrakes. But the damage to the habitat on the rocky launch ultimately caused the bomb to detonate in transit. This also explains Josh's brittle emotional state—he realizes that his attempt to give the astronauts something to discover very nearly killed them instead. Bob ultimately tells Josh that Valkerie has figured it out, and that they all forgive him for what he did, knowing as they do that he never meant them any harm. The last scene is a set-up for the sequel (The Fifth Man): Bob, who is now enamored of Valkerie, proposes marriage to her before a worldwide six-billion-strong television audience that has tuned into watch "the first two astronauts to walk on Mars." Characters Astronaut Joshua "Josh" Bennett, original Mission Commander, afterwards CapCom. Astronaut Kennedy "The Hampster" Hampton, original Pilot Officer, afterwards Mission Commander. Astronaut Alexis "Lex" Ohta, original Mission Specialist (Geology), afterwards Pilot Officer. Astronaut Bob "Kaggo" Kaganovski, Mission Specialist (Engineering) Astronaut Candidate Valerie "Valkerie" Jansen, eventual Mission Specialist (Life Sciences and Crew Medicine) Nathan "Nate" Harrington, Mars Mission Director Steven Perez, Chief Administrator, NASA Robert Abrams, MD, senior psychiatrist, NASA Special Agent Crystal Yamaguchi, FBI Cathe Willison, engineer Major themes Space exploration, the importance of friendship, the