Corley raised his voice. “Please! Everybody! I — didn’t say we weren’t going to get back. I said — ”
“But you — ”
“Shut up, Red! I said this orbit is no good. We’ve got to vector west, toward the Moon. And we’ve got to do it at — ” He glanced at a clock. “Good grief! Seven minutes from now.”
Barnes jerked his head ar~ind. “Acceleration stations, everybody! Stand by to maneuver!”
VII
The most treacherous maneuver known to space flight is a jet landing on an airless planet. Even today, it commands the highest pay, the most skilled pilots — Farquharson, Ibid., III: 418
For forty hours they fell toward the Moon. The maneuver had worked; one could see, even with naked eye, that they were closing with the Moon. The four took turns at the radio, ate and slept and talked and stared out at the glittering sky. Bciwles and Traub discovered a common passion for chess and played off the “First Annual Interplanetary Championship” — so dubbed by the Admiral — using pencil marks on paper. Traub won, four out of seven.
Some two hundred thousand miles out the Luna slid past the,null point between Earth and Moon, and began to shape her final orbit. It became evident that the correction vector had somewhat overcompensated and that they were swinging toward the Moon’s western limb — “western” as seen from Earth: the Luna’s orbit would intersect her namesake somewhere on the neveryet-seen far side-or it was possible that the ship would skim the far side at high speed, come around sharply and head back toward Earth.
Two principal styles of landing were possible-Type A, in which a ship heads in vertically, braking on her jets to a landing in one maneuver, and Type B, in which a ship is first slowed to a circular orbit, then stopped dead, then backed to a landing when she drops from the point of rest. —
“Type A, Jim-it’s simplest.”
Barnes shook his head. “No, Doc. Simple on paper only. Too risky.” If they corrected course to head straight in (Type A), their speed at instant of braking would be a mile and a half a second and an error of one second would land them 8000 feet above-or below! — the surface. —
Barnes went on, “How about a modified ‘A’?” Modified Type A called for intentionally blasting too soon, then cutting the jets when the radar track showed that the ship hovered, allowing it to fall from rest, then blasting again as necessary, perhaps two or three times.
“Confound it, Jim, a modified ‘A’ is so damned wasteful.”
“I’d like to get us down without wrecking us.”
“And I would like us to get home, too. This ship was’ figured for a total change of twelve and a half miles per second. Our margin is paper thin.”
“Just the same, I’d like to set the autopilot to kick her a couple of seconds early.”
“We can’t afford it and that’s that.”
“Land her yourself, then. I’m not Superman.”
“Now, Jim — ”
“Sorry.” Barnes looked at the calculations. “But why Type A? Why not Type B?”
“But Jim, Type B is probably ruled out. It calls for decelerating at point of closest approach and, as things stand now, ‘closest approach’ may be contact.”
“Crash, you mean. But don’t be so damned conventional; you can vector into a circular orbit from any position.”
“But that wastes reaction — mass, too.”
“Crashing from a sloppy Type A wastes more than reaction mass,” Barnes retorted. “Get to work on a ‘B’; I won’t risk an ‘A.”
Corley looked stubborn. Barnes went on, “There’s a bonus with Type B, Doe-two bonuses.”
“Don’t be silly. Done perfectly, it takes as much reaction mass as Type A; done sloppily, it takes more.”
“I won’t be sloppy. Here’s your bonus: Type A lands us on this face, but Type B lets us swing around the Moon and photograph the back side before we land. How does that appeal to your scientific soul?”
Corley looked tempted. “I thought about that, but we’ve got too little margin. It takes a mile and a half of motion to get down to the Moon, the same to get up-three miles. For the trip back I have to save enough mass to slow from seven miles a second to five before we dip into the atmosphere. We used up seven to blast off-it all adds up to twelve. Look at the figures; what’s left?”