 Why does Mary ask Phil to go to the rocket as soon as they can see it?
If anything could go wrong, they wouldn't be sending me; you know that. But I don't think I ever really believed it was possible—not until this morning when you said tonight was the take-off. It existed only because of the huge ship standing poised in the take-off zone five miles away in the desert. Its future as a town rested with the ship, and the town seemed to feel the uncertainty of its future, seemed ready to stop existing as a town and to give itself back to the desert, if such was its destiny. Phil turned the car off the highway onto the rutted dirt road that led across the sand to the field where the ship waited.
 She did not want to prolong the painful goodbye.
 She was not allowed to stay there, as a civilian, so she had to leave.  She did not want him to be late for his very important mission.  She needed to drop them off so she could leave.  She did not want to prolong the painful goodbye.