The Medusa Chronicles by Stephen Baxter Page B

President . . . ?”
    â€œLBJ asked Jim Webb,” the NASA Administrator, “to come up with options for NASA to respond to this. So Jim asked me to handle it, and now—
    Mo glanced at Seth. “And now he’s asking us, Tonto.”
    â€œAt noon tomorrow the President is going to address the nation from the press office, right here at Houston. Why here? Because this is where LBJ’s going to tell the world how this threat from space is going to be countered by the space agency he did so much to set up in the first place. Now, since I got handed this hot potato I already got everybody from MIT college kids to the Mercury Seven working on this. But right now it’s you two I need to rely on, and I picked you because Deke Slayton tells me you’re the best of the best . . .”
    Or, more likely, Seth thought sourly, nobody else was around this Sunday morning.
    â€œSo tell me. How do we use Apollo-Saturn technology to deflect an asteroid?”
    Mo got up and paced. “We’re a nuclear power,” he said simply. “We nuke it.”
    Seth said, “But how do you blow up an asteroid? I guess, in theory, you’d want a bomb big enough to dig a crater the size of the rock itself—in this case a mile. Which is maybe ten times as deep as Meteor Crater.” He got to his feet, walked over Bob Gilruth’s thick pile carpet to a blackboard, wiped it clean of what looked like notes on the Apollo fire, and began to scribble. “As I recall the depth of Meteor Crater is five hundred feet. Mr. Sheridan, do you have the megaton equivalent of the strike that created that?”
    Sheridan looked through his papers. “Ten megatons.”
    â€œOkay.” Seth scribbled numbers. “So we’re going to need a lot more than that. Somebody in the weapons business must have done studies of energy expended against crater depth—”
    Mo nodded. “So ten megatons bought a five-hundred-foot hole. Shit. Even if it scaled as simple linear, we’d need a hundred megatons: ten times the depth, ten times the power. If it was inverse square, we’d need, umm—” Out came Mo’s slide rule, which he never travelled without. “A gigaton. And if it’s inverse cube—”
    Seth eyed Sheridan frankly. “I think we need a rule, sir. No secrets between us.”
    â€œGo on,” Sheridan said cautiously.
    â€œChances are even a single hundred-megaton bomb wouldn’t be big enough for the job. Now, I’m in the USAF. I know we have fifty-megaton nukes in the arsenal, in development anyhow . . .”
    â€œI could get you hundred-megs.” Sheridan sighed. “There are programmes that could be accelerated.”
    Mo said, “But not gigatons.”
    â€œWe’ll have more than one bomb. But you’re the spacemen—if you need a gigaton, why not just deliver ten of these things to rendezvous at the asteroid, the way you had your Gemini craft link up in space? Set them off together.”
    Seth was doubtful. “The timing would be critical—one nuke going upa microsecond early would destroy its brothers before they had a chance to detonate.”
    â€œIt’s not just that,” Mo said, his voice abstracted, his slide rule a blur in his hands. “We couldn’t deliver the nukes to the rock in the first place. Not if we’re to decelerate and drop them off. The only rocket we’ve got that could throw a bomb weighing tons across interplanetary space is the Saturn V.”
    â€œWhich hasn’t actually flown yet,” Seth pointed out.
    â€œRight,” Mo said. “And even with a Saturn V, even with just a single bomb, we can’t slow down. All we could manage is a flyby—a fast intercept.”
    Sheridan rubbed his chin. “Well, that could still work, if you hit the thing with ten nukes at once, fire off ten Saturn Vs. Couldn’t