Delta-v, page 45
He glanced over to see Jin only now starting his switchover. Tighe assumed the engines must be burning at a slightly different rate. That was probably bad, but he was too exhausted to ponder the guidance implications. He instead focused on the tasks that he had practiced so many times he could even do them in his present state of exhaustion.
Tighe braced himself against the metal framework and grabbed the fuel-tank latch. Pulling hard, he unlocked it and watched as the gate for the 7-meter-diameter fuel tank opened. The enormous tank pulled from its hose and rolled along the ship, into the exhaust wake, which sent it spinning off into the cosmos. Moments later the nearly empty fuel tank exploded in a sphere of fire, kilometers behind them.
Jin’s tank soon joined it.
The two of them climbed forward on the spiral steps, against increasing acceleration.
A glance back and Tighe’s crystal display showed that Ryugu was almost a hundred kilometers behind them now, about the size of a grape at arm’s length. He could still make out the Konstantin’s silhouette to the left of it, in its shadow.
“J.T.! Keep moving!”
Tighe looked ahead to see that Jin was already in place at his next fuel lever. It took tremendous effort for Tighe to pull himself forward against the rapidly increasing g-forces. The ship had just shed 400 tons and the engines were starting to take command.
Tighe pulled himself into place.
“Fifty seconds to cutover!”
Tighe clipped his tether to the nearest eyebolt. Watching virtual gauges, he waited, and then opened the valve for Tank 3. Another glance showed the cutover was seamless—but by then, he needed to grip the metal rails with both hands to stop himself from sliding backward. Then he dropped down to kneel on a step instead. His crystal display showed he was already experiencing 2 g’s of acceleration.
Jin struggled to hold on to the valve handle. His cutover had not occurred yet, and the acceleration continued to increase.
Two point two g’s.
“Han! Do the cutover!”
“Not yet!”
Suddenly a plume of gas stabbed out from the piping aft of Tighe’s position. He looked back to see that one of the manifolds had failed and was venting pressurized fuel.
“Shit!”
Priya’s voice came over their local comm link. “Engine 1 is losing pressure. I’m shutting it down.”
“Do it!”
Two point five g’s.
At this acceleration Tighe weighed about 450 pounds.
Engine 1 stuttered, and the flame extinguished. The leaking plume of gas disappeared. Suddenly the g-forces of acceleration plummeted to 1.2.
Tighe got back to a leaning position and watched as Jin performed the cutover. Engine 2 continued burning as the ship accelerated more reasonably—at least for now.
Jin pointed. “We need to turn the crossfeed valve—to feed your third tank to Engine 2!”
Tighe nodded. Both he and Jin moved to the center of the pipe array, searching for a valve they knew was there.
“Hurry!”
Tighe found it and braced his feet as the g-forces built up again. Almost back to 2 g’s. “Hang on!”
Jin knifed his hand. “Now!”
Tighe turned the valve head until it stopped. He then slammed back into the nearest piping as the ship’s acceleration continued to increase.
Jin pressed his back against a vertical pipe and winced against the g-forces. “I think it worked!”
Tighe was unable to reply as their acceleration raced past 3 g’s. After what he knew must have been three minutes, he heard Chindarkar’s voice over the comm link.
“Shutting down Engine 2.”
In a few moments the almost unbearable g-force eased, and Jin cut away the last fuel tank. They both watched it roll away behind them as the exhaust plume shortened, then ceased. They were again in free fall. He and Jin embraced each other in relief.
Chindarkar said, “MECO.”
After he recovered his breath, Tighe looked back behind them.
Ryugu was now just a glowing white dot. Tighe’s crystal display indicated it was already 1,426 kilometers away, the distance increasing at a blistering 24.42 kilometers per second.
“Holy shit, we’re going fast.”
“J.T., Jin, are you guys okay?”
Jin answered, “Yes. How is our trajectory?”
“Ade helped me make several corrections.” Her voice strained with emotion. “He says we look good. That we’re on course for an Earth encounter. Would you both please come inside?”
CHAPTER 48
Chasing Earth
Inside the crew module, Tighe fell asleep almost immediately—and in free fall that was a first for him. He woke up more than six hours later and thrashed about for a moment in a panic, forgetting that he was in microgravity. The familiar sensation of stuffed sinuses had returned.
Tighe floated over to see Chindarkar and Jin staring into a holographic display of their trajectory. “How’s it look?”
She turned tired eyes on him.
Jin said, “We are going very fast—which is necessary to have any chance to catch up to Earth. But I am concerned about the aerocapture maneuver.”
Chindarkar pointed and said, “Han thinks we might skim straight through Earth’s atmosphere without slowing down enough and then hurtle off into deep space.”
Jin adjusted values in the diagram. “Earth gravity will accelerate us even more as we approach.”
Tighe looked from one to the other. “Didn’t mission control calculate all this?”
“They wrote the autopilot software for an 18-kilometer-per-second aerocapture—not 25. In fact, it might be higher than 25. I don’t know yet. If we dive deeper into the atmosphere, we could burn up—or die from the g-forces necessary for capture.” Jin stared at the diagram. “I need to calculate whether it’s even possible.”
* * *
—
The James Caird was designed to spin lengthwise, creating one-sixth gravity in the crew module. However, because it lacked the Konstantin’s spin radius, the crew had to lie on the floor to keep the Coriolis effect from sickening them. Sleeping in low gravity, however, was much easier for Tighe than sleeping in free fall.
On the second day of the transfer, Tighe awoke to see Jin and Chindarkar eating in a reclined position.
Jin motioned for caution. “Do not sit up. And do not try standing.”
Tighe rose slowly to his elbows.
Chindarkar tossed him a water pouch.
He took a long sip from it. “Forty days of crawling? Maybe space is like caving.” He looked around at the confined cabin. “Is the ship holding up?”
Chindarkar ate rehydrated oatmeal out of the package. “Life support is sketchy. We’ve got overheating problems. There’s almost no radiation shielding. We could all die any second.”
Tighe nodded. “So the usual shit.” He finished the water. “Any word from Isabel and Ade?”
Chindarkar grew somber. “They’re monitoring our progress. Still giving us slight course corrections.”
“When’s the earliest we can return for them?”
Jin considered the question. “Not until Ryugu’s next close approach in 2042.”
“Twenty forty-two! That means over eight years in space for them both.”
“It is a lot of rads.”
Tighe crawled forward and reached for a food packet. “So let’s say we survive and get Earth capture—what then?”
Jin said, “Assuming Earth capture, Ade’s plan was to then swing around again to circularize into a low Earth orbit.”
“How do we get back to the surface? Fly a reentry?”
Jin shook his head. “We’ll have almost no delta-v to select a glide path. We’d most likely land in an ocean—and sink.”
Chindarkar added, “It’s 2038. There are more people in LEO now. Someone should be able to rescue us in orbit.”
* * *
—
Two weeks into their transfer orbit, they lost the Ka-band link to the Konstantin. The connection did not return. They were now on their own, with no communication with either Earth or their crewmates back at Ryugu. Tighe wondered what it meant. Was it an equipment failure or had something happened to Abarca and Adisa?
With no physical windows, Tighe instantiated a virtual window in the hull using imagery from cameras on the nose of the ship. Exposed to the Sun as they were, space appeared as a featureless black void. Only the planets were bright enough to be visible in the glare.
Tighe watched as day by day, the bright white disk of the Earth continued to glide in from the left edge of the screen. It eventually resolved into two dots of light: the Earth and the Moon. The bright dot of Mars appeared just above Earth. Jupiter, dead ahead.
Tighe found it impossible to wrap his head around the enormous distances. They’d been traveling at 87,000 kilometers per hour—more than 2 million kilometers per day—for weeks, and the Earth looked the same. The only thing that changed was that it had edged rightward, moving toward the place the James Caird was headed.
Behind them, Ryugu had long since disappeared in the vastness of space. Thinking of their lost friends and crewmates only added to the misery of living inside the Caird.
* * *
—
By March 28 they were 6 million kilometers and three days away from Earth rendezvous. The Earth and Moon still appeared only as points of light—albeit now a thumbnail’s width apart—moving ever into the path of the James Caird.
It wasn’t until twenty-four hours before their encounter with Earth that Tighe, gazing forward through the virtual viewscreen alongside Jin and Chindarkar, finally could discern the Earth’s blue, sunlit side. Chindarkar gripped Tighe’s shoulder. It was no longer just a white dot. Now 2.3 million kilometers away, the Earth was finally a crescent. However, the Moon, two finger’s widths to the left, was still just a point in space.
Jin used the positions of the Earth and Moon to rerun calculations on their trajectory. Since they lost contact with the Konstantin, they’d been using star-tracking software for astrogation. However, it was apparent that Adisa’s accuracy early on had saved them. They would indeed encounter Earth.
Tighe stared unblinking as, hour by hour, his home world approached.
At 1.1 million kilometers’ distance, the Earth was now a sphere, the size of a pebble held at arm’s length. The Moon, still only a white light, was now a hand’s width to the left. Glancing at his crystal, Tighe could see they were twelve hours from the aerocapture maneuver. After forty days in transit, it hardly seemed possible the final phase would happen so fast.
While Jin reran the aerocapture simulation in his crystal, Tighe and Chindarkar popped thrusters to halt the spin of the James Caird and pointed the ship forward.
Now in microgravity again, Jin looked grim as he called Tighe and Chindarkar over. He projected a virtual diagram of the Earth onto their crystal displays. It showed their trajectory, coming in at a nearly flat angle across Earth’s atmosphere.
He pointed. “We are gaining more velocity due to the Earth’s gravitational pull. My calculations show we will be going 26.8 kilometers per second when we attempt aerocapture.”
“Jesus.”
Chindarkar did some calculations of her own. “That’s about 60,000 miles per hour.”
“We must lose at least 14 kilometers per second to achieve Earth capture, and we will only have about 4,000 kilometers of atmosphere to do it in—roughly three minutes in deceleration that could peak at 9 g’s—maybe higher. Possibly much more. I cannot say precisely. Earth’s atmosphere is too variable.”
“Oh my god . . .”
“If we do not burn up and we manage to achieve Earth capture, then we can orbit around and perform more aerobraking maneuvers at perigee to bring our velocity down further.” His diagram showed another low swing through Earth’s atmosphere. “Then we fire cold-gas thrusters to circularize our orbit.” He looked up. “Right now we are 750,000 kilometers out. We should strap in to our seats at 250,000 kilometers. Do you both understand?”
They nodded.
Tighe turned to look out the virtual windows. The Moon was now visible as a tiny sphere, with a nightside and dayside. The Earth lay dead ahead, pea-sized.
In the following hours it grew.
At 500,000 kilometers from Earth, the Moon passed left beyond the edge of the forward screen. They were now six hours out.
Three hours later they pulled on their blue flight suits.
Chindarkar hugged Tighe. “Good luck, J.T.”
“You, too.”
She then hugged Jin. “Let’s hope the Caird can take it.”
Tighe gripped Jin’s shoulder. “I know if it’s possible, you can do it, Han.”
Jin nodded grimly.
They then entered the aerocapture vehicle through its aft hatch, sealing it behind them. During the transfer from Ryugu, they had removed two of the five seats and remounted the remaining three to face rearward in order to help them withstand g-forces of deceleration. Tighe took a seat near the rear hatch, while Jin and Chindarkar strapped in alongside each other in middle seats and busied themselves preparing the ship.
Jin instantiated a virtual viewscreen on the stern bulkhead, creating the illusion that they were all still facing forward.
At 250,000 kilometers, the Earth was the size of a grape held in one’s outstretched hand. Tighe could hardly believe the sight—a brilliant swirl of blue, white, green, and brown. He half convinced himself he was watching a training simulation.
Jin called out, “Undocking crew module and booster.” After a brief pause. “Now.”
There was a mild clunk sound as bolts disengaged. The ungainly booster stage of the ship was intended to pull away before they entered the atmosphere, and burn up on reentry.
“Let’s start our prebreathe.”
They all pulled on oxygen masks.
An hour and a half later they were 100,000 kilometers away from the Earth, which appeared the size of a lemon. They all marveled at the lights of Earth’s cities glittering on the nightside. They’d been out in deep space for so long that the beauty of their home world brought them to tears. That, and the memory of those who would never witness this sight again.
But now it was becoming clear just how fast they were going. The Earth was visibly increasing in size as they screamed in at a flat angle across its darkened right hemisphere. “We are really moving.”
Chindarkar said nervously, “How are we doing, Han?”
Jin worked invisible controls. “Five by five.”
At 50,000 kilometers out Tighe finally recognized the continents. They were coming in from a shallow angle he hadn’t expected—low above darkened Antarctica, streaking north toward Africa—Johannesburg a recognizable cluster of lights.
Jin called out, “Pressurize your suits and stow oxygen masks.”
They all did so, zipping up their helmets and going on radio comms.
“Evacuating ship atmosphere.”
The air swirled around them as it vented. It was a hundred pounds less mass to decelerate and its absence would help prevent heat from radiating into the cabin.
As they closed on 25,000 kilometers, things started to happen fast. The surface of the Earth expanded beyond the edges of the viewscreen.
Jin called out, “I will try to remain conscious for as long as possible. Due to variability in the atmosphere, I might need to make last-minute adjustments.”
Tighe said, “I wish we could help, but you’re the only one of us qualified to do this, Han.”
“I will do my best.” Jin busied himself checking and rechecking systems.
Ten minutes later the Earth started to roll past beneath them. Their speed looked downright alarming at a distance of only 5,000 kilometers.
Jin looked up in surprise. “The crew module—it failed to detach!”
The James Caird began to yaw slightly from side to side.
Jin grabbed at virtual controls while the Earth loomed. “The aerocapture software cannot pilot this ship with 15 tons of deadweight on our tail. We will go straight in!”
Tighe unbuckled his straps and pulled himself toward the rear hatch.
Jin shot a look at him. “In less than three minutes we will be in the atmosphere.”
“Then don’t wait for me!”
Chindarkar looked to Tighe but was immediately forced to turn her attention to the bucking ship.
With the ship depressurized, Tighe pulled himself through the rear hatchway and back into the crew module. The whole cabin shook. The seal between the compartments shifted slightly up, then slightly right, then left. In the gap between the sections, Tighe caught glimpses of the Earth’s surface. Even without atmosphere, he could feel the metal twisting and vibrating.
He grabbed a meter-long socket wrench from a bracket on the wall and then pulled himself to the upper crew module hatch. After opening the hatchway he felt something like a strong breeze whipping past the ship. They were going so fast that even the sparse molecules out here produced noticeable drag.
Tighe struggled out on top of the crew module, entering what seemed like a 30-kilometer-per-hour wind. For a moment he felt vertigo as the span of all of Earth stretched out and away below the ship—the surface closing fast. His crystal indicated they were nearing 3,000 kilometers’ altitude, and he pulled himself forward toward the link between the stages. He strained against the force of a rarified slipstream.
The crew module bucked as he climbed forward and on top of the James Caird’s aerodynamic surface. The sleek skin of the craft was difficult to hold on to, so Tighe reached down into the gap between the sections and quickly clipped his tether into a stern eyebolt. He withdrew his gloved hand before it could be crushed by the writhing crew module—and then he spotted what was holding the sections together.
