“He’s quite right.” Rob rubbed thoughtfully at his forehead. “I’d forgotten that it was a Mischener Drive. They’re controlled to half a gee or less. You could never modify one to get more than a couple of gees out of it — the whole thing would blow up.”
“I couldn’t modify any drive to do anything, but I know what you mean. I checked out that information on the Mischener Drive myself. I’ll get to that in a minute. Here’s something else for you. Atlantis is just about out in the Belt now, but I’ve been tracking its position as it moved. Take a look at this.”
Howard Anson held another sheet up to the camera. “Forty-five days old. A tracking station near the inner edge of the Belt recorded an unauthorized launch of a life-support pod from a point very close to Atlantis. Nobody sent out a Mayday, so the pod didn’t get tracked by Search and Rescue. All that happened was a violations report to Central Records. See how that would fit with what Pascal said about the pod’s log? The pod computer shared reference readings that say it started out in the Belt, thirty days before it drifted past the antenna farm. The time would fit perfectly. If the Goblins had started out from Atlantis in that pod, thirty days before Pascal sighted it, they’d have been just right to match that unauthorized launch. It would all be consistent, except” — he shrugged, a bewildered expression on his tanned face — “I don’t see how the Mischener Drive could do it.”
“It couldn’t.” Rob was shaking his head firmly. “Your argument won’t fly, Howard. I’ll do the detailed calculations for you if you like, but I already know the answer. There is no way you could fly from out near the Belt, where Atlantis was a month and a half ago, and get to the Moon on a Mischener Drive in thirty days. The orbit geometry is wrong. Anyway, the Mischeners don’t have the capacity for a continuous impulse trajectory, even at a fraction of a gee. They were designed for free-flight Hohmann transfer orbits, with a little bit of thrust at the beginning and a little bit more at the end.”
“So you’re saying the Goblins would have to have come in some other ship?”
“Must have, if they were going to get to the Moon in thirty days. If you want to do a fast transit from the Belt to the Earth-Moon system, you have two ways to go. You can ride a continuous-impulse ship, like the best medical vessels — and you’d still be limited to three gees, unless you could prove to the USF controllers that you had a real emergency on your hands. Did you know that the flight computers on every ship and every pod are sealed, and they keep a log of every time that the drives go on and off? I don’t know of any way to trick them. And you’d somehow have to fake the reaction mass you used, as well. I don’t think that’s feasible. The only other way you can get a really fast transit is to use a monster short-duration acceleration in place of a small continuous thrust. You’d do it twice, once at the beginning of the flight and again at the end. That would speed it up a lot at the beginning. You’d fly in fast, then slow down fast when you were close to Earth. People have talked about ships with that much acceleration for years, but nobody has ever built one. Not even for medical ships.”
“All right.” Howard Anson held up a protesting hand. “I’ll believe you, no need for the lecture. Ask you a simple question and you throw a book at me. So the Mischener Drive won’t do it, and the other drives can’t do it secretly. Doesn’t it seem too much of a coincidence, though, to have the Goblins arrive here with just the right timing for a pod launch from Atlantis? Aren’t you convinced that the Goblins live on Atlantis?”
“You know I am.”
“So if you won’t take my explanation, what’s yours?”
“I don’t have one.” Rob’s irritation was clear in his expression. “I’m with you, the Goblins started out from Atlantis. I believe there are some on Atlantis right now. But we can’t use magic to get them here. There’s some rational explanation to what Lenny Pascal saw and to what your Information Service dug up. I just can’t see it yet.”
Anson leaned forward to the camera. “You know I’m not a scientist, but I’ve got one other idea you haven’t mentioned. What about gravitational swing-by? The way I’ve heard about it, you can put a ship past a big mass, and if the positions are right you can pick up speed doing it. They used to use it to get ships past Jupiter and Saturn to the Outer System, when they didn’t have reaction mass available. Wouldn’t that be the way to speed up a passage in to Earth?”
“Yes — but no.” Rob saw Anson’s frustration. “Don’t blow yet, Howard. I’m giving you a serious answer, and I know you want to sort this thing out as much as I do. You are right in a way. Gravitational swing-bys are a good method of picking up free momentum, if you happen to be going past a big mass. But when I say a big mass, I mean a big mass. There’s nothing between here and Atlantis that could possibly do it.”
“You mean nothing that we know about. But what about the possibility of a black hole? That could do it. It would be very small, and we couldn’t see it. And Morton says that the Halo—”
He stopped. Rob was shaking his head again.
“Sorry to spoil your idea, Howard, but if there were a decent-sized black hole — one with significant mass — anywhere in the System, we’d have found it long ago. Its gravitational effects would perturb all the other bodies. Same applies to an unknown planet. There just can’t be an undiscovered mass in the Inner System. Not one big enough to have an appreciable gravitational field.” He shook his head. “Sorry, Howard, but we won’t find an explanation so easily. Anyway, your idea wouldn’t fit with what Pascal said about the way that the Goblins died.”
Rob noted again the way in which Anson’s eyes lost all expression when he was receiving new information of a factual nature. It was as though he became an object without feelings or personality, a blank tablet on which the facts would be permanently stored. As soon as the storage was finished, the other Howard Anson turned back on, the pleasant and sympathetic gentleman with his own strong personality. That Howard was again in control, and frowning at Rob’s last comment.
“What do you mean, wouldn’t fit with what Pascal said? You’d get big forces if you swing by a black hole — the acceleration ought to be fierce.”
“It would be.” Rob nodded. “But you wouldn’t feel a thing. The gravitational and dynamic accelerations would balance exactly. You’d feel tidal forces if you were near enough, but they fall off very fast with distance. Before they were a factor you’d have to get really close. For most swing-bys, you’d feel as though you were in free fall all the way. It’s no good, Howard, you might as well forget about gravitational forces. They can’t explain what Pascal told you.”
“That’s it then.” Anson shrugged. “That was my last arrow. You’re the expert, so you tell me. What did happen to the Goblins, and where did they come from? You’ve ruled out the only things I can think of.”
“It’s worse than you realize.” Rob smiled ruefully. “I’ve ruled out the only things I can think of, too. Let me stew on it for a while. At the moment I’ve got my head so full of beanstalk movement and new mining methods, there’s not room for anything else.”
“Do you have to go out to Atlantis to observe the mining of Letitia?”
“It uses my Spider. And I promised Regulo that I would.”
“Maybe. But is either of those the reason why you’re going? Are you sure it’s not obsession with the Goblins, and learning more about them?”
Rob did not answer. After a few moments Anson shook his head and said, “I don’t know why I bothered to ask. All right, you’re going. Be careful, and come back quickly.”
“No question of that. Regulo won’t delay me — he’s as keen to see the beanstalk landing and tether as I am.”