"The fuel was figured for this trip with very little margin, and we used some margin already because of that lovely instrument error on takeoff. I'd be a lot happier if we had a fusion system with fewer limitations, like the ones they're working on now."
"We agreed to this firing system and realized its risks—all because we'd rather not wait for the ones in development," Hiller reminded. "We're comfortably powered, anyway, provided we follow our original firing schedule. So, that means we enter the Inner Belt at our present velocity without changing course."
Merrick spoke up, ruffling the red hairs that partially covered his shiny scalp. "Back track here a minute, you boys went over that rapid. I think I get everything but the velocity business. We connect with the Belt at two m.p.s.? Sounds like optimistic but bad arithmetic to me." Screwing up his mouth, he squinted at Hollender.
Hiller found himself laughing, and it felt good. "Pardon our dynamics-centered minds," he said. He unsnapped his ballpoint from his pocket and placed it over the air blower grill.
"Say the horizontal braces on this grill running parallel are the clusters' paths at 12 m.p.s. My ballpoint's the ship at 15, traveling in the same direction as the clusters. In that case, we would collide with the particles, overtaking them at three m.p.s. right?"
Merrick nodded. "I see that, but—"
"Okay," Hiller went on. "Now suppose we crossed the Belt at right angles to the paths." He moved the ballpoint straight up the grill.
"They'd sock us at 12 m.p.s.," Merrick deduced. "So, what you're getting at is the angle—"
"The angle makes the difference," finished Hiller. "If we entered the belt at about this angle"—he inclined the ballpoint up slightly from the horizontal—"we'd sail through with the same velocity as the particles. If we hit any, it would be a nudge from our transit motion through the Belt or from their velocity or revolution, which is probably very low."
"I get it," Merrick slapped his forehead. "Our present course cuts the Belt at such an angle that we get bumped at two m.p.s. instead of 12." The others nodded. He reflected a moment, adding, "So, I get a bullet through the head at 1200 feet per second or 200 feet per second: I still get it in the end."