"But you said that this man Anders had seen to it that they were all aboard before takeoff."
"Which I have no doubt he did. But the civilian mind skips a few details when it thinks over his report. They see him look at the boys, nod, then go up front and press the starter button. It doesn't happen quite that simply. There are a lot of other things to be done. Anders had to go into the pilot's cabin, strap himself in place, check the guages which showed his course, mass, fuel supply, thrust control, oxygen-nitrogen mixture, and a million and one other things. He had to check the last and most important dial examined before takeoff; the one which told him that each of the fifteen takeoff racks in the ship were occupied."
"But—" Snow cut in, bewildered, leaning forward.
"Let me finish." She set her mouth and sat back again. "He had to know that, because takeoff thrust on a human being not snugly in his padded rack would probably squash him to pieces against a bulkhead. So there had to be something in those racks in order to fool Anders into thinking that the scouts were still aboard; something which, by the time Anders had maneuvered the ship into its flight vector, would be gone without leaving a trace, or not much of a trace, unless one were actually looking for it."
"What?" asked Snow, fascinated.
"Ice," I said. "Hunks of ice in every one of the fifteen bunks. Ice which the temperature control unit would commence to melt immediately."
"But that would mean ice blocks of hundred-pound weights! They couldn't melt so fast. Wouldn't Anders be likely to come back to the racks and find them still there?"
"Not," I said, "with the efficiency of the temperature control system. Sharp deviations from comfortable levels in a spaceship can be disastrous. So the thermostat in the ship is set for a rigid fifty-five degrees, and it's built to keep the interior heat at that level. Put fifteen-hundred pounds of ice on board, and the heat in the rack cabin goes up, trying to get the temperature back to its correct level. The ice, lying there melting, absorbs the heat swiftly. So more heat is pumped into the room. Well, figure fifteen minutes before all the ice was liquified. More than enough of a margin of safety."
"Safety for whom?" Snow asked.
"For whoever didn't want Anders finding any evidence of how the disappearance was accomplished. About an hour passed between takeoff and the time he checked the cabin. You must remember that Anders had to maneuver the ship free of Mars' gravity, set his course for Earth, and then make a final check of all his equipment before going back into the ship proper. That takes plenty of time."