"Well—I mean—what specifically?" asked Tom softly.
"For instance, I've got to find the ratio for compression on the main firing tubes, using a given amount of fuel, heading for a given destination, and taking a given time for the passage."
"But that's control-deck operations—as well as astrogation and power!" exclaimed Tom.
"Yeah—I know," answered Astro, "but I've still got to be able to do it. If anything happened to you two guys and I didn't know how to get you home, then what?"
Tom hesitated. Astro was right. Each member of the unit had to depend on the other in any emergency. And if one of them failed ...? Tom saw why the ground manuals were so important now.
"Look," offered Tom. "Suppose we go over the whole thing again together. Maybe you're fouled up on the basic concept."
Tom grabbed a chair, hitched it close to the desk and pulled Astro down beside him. He opened the book and began studying the problem.
"Now look—you have twenty-two tons of fuel—and considering the position of your ship in space—"
As the two boys, their shoulders hunched over the table, began reviewing the table of ratios, across the quadrangle in the examination hall Roger Manning stood in a replica of a rocket ship's radar bridge and faced Captain Strong.
"Cadet Manning reporting for manual examination, sir." Roger brought up his arm in a crisp salute to Captain Strong, who returned it casually.