Part two were the gravity coils, which actually originated and directed

the gravity. They were simple and very nearly indestructible. They could be destroyed but they couldn't be altered and still produce the field.

The third part was the control unit, the real heart of the gravity generating system. It calculated the relationship between the power flowing through the coils and the created field in any one microsecond. It used the computed relationship to alter the power flowing in the next microsecond to get the same gravity. If the power didn't change the field died instantly. The control unit was thus actually a computer, one of the best made, accurate and fast beyond belief.

The engineer rubbed his chin. "Now I guess you can see why it doesn't always behave as we want it to."

He looked questioningly at Cameron, expecting a reply. "I'm afraid I can't," said the doctor.

"If it was one of your patients you'd understand," said Vogel. "Fatigue. The gravity control unit is an intricate computer and it gets tired. It has to rest an hour and a half to do forty-five minutes work. It can't keep running all the time any more than any delicate machine can. It has to be shut down to clear the circuits.

"Naturally they don't want anyone tinkering with it. It's sealed and non-repairable. Crack the case open and it disintegrates. But first you've got to open it. Now I know that it can be done, but not without a lot of high-powered equipment that I could detect if it was anywhere on the asteroid."

In spite of the engineer's attitude it didn't seem completely foolproof. But Cameron had to admit that it was probable none of the accidentals could tamper with it. "I'll forget about gravity," he said. "Next, what about hand weapons? What's available?"

"Nothing. No knives even. Maybe a stray bar or so of metal." Vogel scratched his head. "There is something that's dangerous though. I dunno whether you could classify it as a weapon."

Cameron was instantly alert. "If it's dangerous someone can find a way to use it. What is it?"

"The asteroid itself. Nobody can physically touch any part of the gravity system. But I've often wondered if an impulse couldn't be squeezed into the computer. If anybody can do that he can change direction of the field." Vogel's voice was grave. "Somebody could pick up Handicap Haven and throw it anywhere he wanted. At Earth, say. Thirty miles in diameter is a big hunk of rock."

This was the kind of information Cameron had been looking for, though the big engineer seemed to regard the occasion as merely a long overdue social call. "What's the possibility?"

Vogel grinned. "Thought I'd scare you. Used to wake up sweating myself. Got so bad I had to find out about it."

"Can or can't it be done?" demanded the doctor.

"Naw. It's too big to take a chance with. They got monitors set up all over, moons of Jupiter, Mars, Earth, Venus. This or any other gravity computer gets dizzy, the monitor overrides it. If that fails they send a jammer impulse and freeze it up tight. It can't get away until the monitor lets loose."

Cameron's mind was already busy elsewhere. Vogel was loquacious and would talk all night if encouraged. It wasn't that he lacked information but he had no sense of what was important. "You don't know how you've helped me," the doctor said, standing up. "We'll have to get together again."

He watched the engineer depart for the gravity generating chamber below the surface of the asteroid. The day had started badly and wasn't getting better. Docchi to Thorton to Vogel. All the shades of shortsightedness, the convalescent's, authority's, and finally the technician who refused to see beyond his dials. A fine progression, but somewhere the curve ought to turn upward.

The post on Handicap Haven wasn't pleasant but there were advantages--advancement was proportional to the disagreeableness of the place. After shepherding accidentals for a year any other assignment would be a snap. Ten months to go before the year was over and if Cameron could survive with nothing to mar his administration he was in line for something better, definitely better. This was where the Medicouncil sent promising young doctors.

Cameron flipped on the telecom. "Connect me with the rocket dome. Get the pilot."

When the robot answered it wasn't encouraging. "There's no answer. I'm sorry. I'll notify you when he comes in."

"Trace him," he snapped. "If he's not near the rocket he's somewhere in the main dome. I don't care how you do it, get him."

A few seconds of silence followed. The answer was puzzling. "There's no record that the pilot has left the rocket dome."

His heart skipped and his breathing was constricted. He spoke carefully. "Scan the whole area. Look every place, even if you think he can't be there. I've got to have the pilot."

"Scanning isn't possible. The system is out of operation in that area. I'm trying to check why."

That was bad. He could feel muscles tighten that he didn't know he had. "All right. Send out repair robots." They'd get the job done--they always did. But they were intolerably slow and just now he needed speed.

"Mobile repair units were dispatched as soon as scanning failed to work. Is this an emergency? If so I can alert the staff."

He thought about it. He needed help, plenty of it. But was there any one he could depend on? Vogel? He'd probably be ready for action. But to call on him would leave the gravity generating plant unprotected. And if he told the engineer what he suspected, Vogel would insist on mixing in with it. He was too vital where he was.

Who else? The sour middle-aged nurse who'd signed up because she wanted quick credits toward retirement? She slept through most of her shift and considering her efficiency perhaps it was just as well she