As soon as you got used to Wenig’s accent, he was easy to follow — I doubt if anybody could get into the Institute unless he was more than bright enough to explain concepts in easy terms.

I nodded. “I can understand that easily enough. But you’ve just replaced one problem with a worse one. You can’t find any drive in the Universe that could accelerate Jupiter at two and a half gee.”

“We cannot — not yet, at any rate. Luckily, we don’t need to use Jupiter. We can do it with something a lot smaller, and a lot closer. Let’s look at the Dotterel and the Merganser. At McAndrew’s request I designed the mass element for both of them.”

He went across to the window that looked out from the inside of the Institute to raw space. The Dotterel was floating about ten kilometers away, close enough to see the main components.

“See the plate on the bottom? It’s a hundred meter diameter disk of compressed matter, electromagnetically stabilized and one meter thick. Density’s about eleven hundred and seventy tons per cubic centimeter — pretty high, but nothing near as high as we’ve worked with here at the Institute. Less than you get in anything but the top couple of centimeters of a neutron star, and nowhere near approaching kernel densities. Now, if you were sitting right at the center of that disk, you’d experience a gravitational acceleration of fifty gee pulling you down to the disk. Tidal forces on you would be one gee per meter — not enough to trouble you. If you stayed on the axis of the disk, and moved away from it, you’d feel an attractive force of one gee when you were two hundred and forty-six meters from the center of the disk. See the column growing out from the disk? It’s four meters across and two hundred and fifty meters long.”

I looked at it through the scope. The long central spike seemed to be completely featureless, a slim column of grey metal.

“What’s inside it?”

“Mostly nothing.” Wenig picked up a model of the Dotterel and cracked it open lengthwise, so that I could see the interior structure. “When the drives are off, the living-capsule is out here at the far end, two hundred and fifty meters from the dense disk. Gravity feels like one gee, toward the center of the disk. See the drives here, on the disk itself? They accelerate the whole thing away from the center column, so the disk stays flat and perpendicular to the motion. The bigger the acceleration that the drives produce, the closer to the disk we move the living-capsule up the central column here. We keep it so the total force in the capsule, gravity less acceleration, is always one gee, toward the disk.”

He slid the capsule along an electromechanical ladder closer to the disk. “It’s easy to compute the right distance for any acceleration — the computer has it built-in, but you could do it by hand in a few minutes. When the drives are accelerating the whole thing at fourteen gee, the capsule is held a little less than fifty meters from the disk. I’ve been on a test run in the Merganser where we got up to almost twenty gee. Professor McAndrew intended to take it up to higher accelerations on this test. To accelerate at thirty-two gee, the capsule must be about twenty meters from the disk to keep effective gravity inside to one gee. The plan was to take the system all the way up to design maximum — fifty gee thrust acceleration, so that the passengers in the capsule would be right up against the disk, and feel as though they were in free fall. Gravity and thrust accelerations will exactly balance.”

I was getting goose bumps along the back of my neck. I knew the performance of the unmanned med ships. They would zip you from inside the orbit of Mercury out to Pluto in a couple of days, standing start to standing finish. Once in a while you’d get a passenger on them — accident or suicide. The flattened thing that they unpacked at the other end showed what the human body thought of a hundred gee.

“What would happen if the drives went off suddenly?” I said.

“You mean when the capsule is up against the disk — at maximum thrust?” Wenig shook his head. “We designed a safeguard system to prevent that, even on the prototypes. If there were a sign of the drive cutting off, the capsule would be moved back up the column, away from the disk. The system for that is built-in.”

“Yeah. But McAndrew hasn’t come back.” I had the urge to get on our way. “I’ve seen built-in-safe systems before. The more foolproof you think something is, the worse the failure when it happens. Can’t we get moving?”

“Come on.” Wenig stood up. “Any teacher will tell you, you can’t get much into an impatient learner. I’ll give you the rest of the story as we go. We’ll head out along the same path as McAndrew did — that’s plotted out in the records back here.”

“You think McAndrew went along with the nominal flight plan?”

“We know he didn’t.” Wenig looked a lot less sure of himself. “You see, when the drives are on maximum the plasma round the living-capsule column interferes with radio signals. Fifty hours after they left the Institute, the Merganser was tracked from Triton Station. McAndrew came back into the Solar System, decelerating at fifty gee. He didn’t cut the drive at all — just went right through the System and accelerated out again in a slightly different direction. We got the log, but we have no idea what he was doing. There was no way to get a signal to him or from him with the drive on.”

“So they got all the way up to the maximum drive! And they came back here. God, why didn’t Limperis tell me that when we were in the first meeting?” I went to the locker and pulled out a suit. “He took it up all the way, fifty gee or better. Let’s get after him. If he kept that up, he’ll be halfway to Alpha Centauri by now.”

The living-capsule was about three meters across and simply furnished. I was surprised at the amount of room, until Wenig pointed out to me how equipment and supplies that could take higher accelerations were situated on the outside of the capsule, on the side away from the gravity disk.

We had started with McAndrew’s flight plan for only a few minutes when I took Limperis at his word that I’d be boss and changed the procedure. If we were to reach McAndrew, the less time we spent shooting off in the wrong direction, the better. He had come right through the System, and we ought to head in the direction that he was last seen to be heading.

“I’ll take us up to fifty gee,” said Wenig. “That way, we’ll experience the same perturbing forces as the Merganser did. All right?”

“Christ, no.” My stomach turned over. “Not all right. Look, we don’t know what happened to Mac, but chances are it was some problem with the ship. If we do just what he did, we may finish up with the same trouble.”

Wenig took his hands off the controls and turned to me, palms spread. “But then what can we do? We don’t know where they were going, all we can do is try and follow the same track.”

“I’m not sure. All I know is what we’re not going to do — and we’re not trying for top acceleration. Didn’t you say you’d flown Merganser at twenty gee?”

“Several times.”

“Then take us out along Mac’s trajectory at twenty gee until we’re outside the System. Then cut the drive. I want to use our sensors, and we won’t be able to do that from the middle of a ball of plasma.”

Wenig looked at me. I know he was mentally accusing me of cowardice. “Captain Roker,” he said quietly. “I thought we were in a hurry. We may be weeks following Merganser the way you are proposing.”

“Yeah. But we’ll get there. Can Mac’s support system last that long?”

“Easily.”

“Then don’t let’s kick it around any more. Let’s do it. Twenty gee, as soon as you can give it to us.”