Interstellar

The slingshot effect was nothing new. Comets had been doing it since stars were formed. As for humans, it had been used almost as long as there had been interplanetary travel. Mariner 10 had been the first to employ it, sending the unmanned spacecraft past Venus to explore Mercury, followed by Voyager and Galileo.

You basically sent a spacecraft falling toward a much bigger body—say, a planet. The craft picked up speed as it “fell” toward the planet, whipped around it in a very tight pass, and then used the speed it had gained falling toward the planet to escape its gravitational pull, moving on a very different trajectory. And since the planet was in motion, the spacecraft could pick up the planet’s orbital speed, adding it to its own velocity. In this way you both changed course and increased speed toward another, final target without ever having burned an ounce of fuel.

That was what Cooper intended to do with Gargantua.

Of course, Gargantua wasn’t a planet, or even—in the conventional sense—a star. And if it hadn’t been—as Romilly put it—a “gentler” black hole, they would never have had a chance.

As Romilly had said—and as his twenty-odd years of notes had meticulously measured and elucidated—Gargantua rotated, which meant that it dragged space-time along for the ride. A slingshot was entirely plausible, but a bit more… complicated than zipping near a planet.

Cooper checked everything for the umpteenth time, hoping Romilly hadn’t gone more than a little looney while he was alone. Because Gargantua wasn’t going to grant him the slightest clemency for even the tiniest mistake.

* * *

Back in the Endurance, Amelia watched the lander come loose and shift orientation as Cooper and Tars prepared the maneuver.

Cooper’s voice came over the radio.

“Once we’ve gathered enough speed around Gargantua, we use Lander One and Ranger Two as rocket boosters to push us out of the black hole’s gravity,” he explained, as the lander reattached in the rear of the ring module, blocking her view of the Ranger and Cooper.

“The linkages between landers are destroyed,” Cooper said. “So we’ll control manually. When Lander One’s fuel is spent, Tars will detach—”

“—and get sucked into the black hole,” Tars finished.

Amelia thought they were joking at first. They did a lot of that, Tars and Cooper. Sometimes she wanted to change the humor settings on both of them. But it crept over her that this time there wasn’t any humor involved.

“Why does he have to detach?” she asked.

“We have to shed mass if we’re gonna escape that gravity,” Cooper explained.

“Newton’s third law,” Tars put in. “The only way humans have ever figured out of getting somewhere is to leave something behind.”

Doyle, Amelia thought, Romilly, Mann, her father—and now Tars? How much loss could she take?

“Cooper,” she said, feeling a little desperate, and even a little indignant. “You can’t ask Tars to do this for us—”

“He’s a robot, Amelia,” Cooper shot back. “I don’t have to ask him to do anything.”

“Cooper,” she snapped. “You asshole!”

“Sorry,” Cooper said. “You broke up a little over there.”

She was ready to launch into a full-blown tirade, but Tars interceded.

“It’s what we intended, Dr. Brand,” Tars said. “It’s our last chance to save people on Earth. If we can find some way to transmit the quantum data I’ll find in there, they might still make it.” The robot’s calm, reasonable tone checked her anger.

“If there’s someone still there to receive it,” she allowed, feeling emptier than ever.

Was it possible? Did it even make sense? It was hard to know anymore. But it was a better chance than nothing, and Cooper was probably right about shedding mass. Maddeningly, he was seldom wrong about such things.

But if there was a way to prove her father wrong, to redeem plan A, they had to take it. It just seemed so wrong that Tars had to be the one to make the sacrifice. It should be her, but it was too late for that—Cooper had seen to it, she realized. And—to be fair—neither the robots nor Cooper knew enough about the population bomb. If glitches developed, if improvisation was required, she had to be there. Seen logically, it should be Tars who did this, and not her.