David inclined his head. “Kind of. Although if we don’t hit Serendipity, we might figure out a way to get back.”
Heidi gave a wry smile. “Correction. If we don’t die by burning up in Serendipity’s atmosphere we have a good chance of dying, anyway.”
David nodded in agreement. “That’s it.”
Heidi let out a breath and shook her head. “I think I liked it when my life was simpler. Back when we only had to worry about suffocating if our masks ran out of power. All these options for dying young, they are confusing.”
“Does that mean you don’t think we should do it?” David asked.
“Don’t be silly,” Heidi replied. “Of course we’ll do it.” She exchanged a glance with John and Ernie. “We have a lot to do, right guys? We need to get busy.”
They nodded their agreement and turned for the hatch, followed by Heidi.
David looked at Nathalie, one eyebrow raised, and she sighed. Three of her family were on board, counting Hope. John, she knew, always felt confident he could work his way out of a situation. She, however, could see failure on the horizon. She didn’t have John’s boundless optimism and feared her children could lose both of their parents. But what choice did she have?
“Of course we must do it,” she said, sending David a haunted look. “Of course.”
“Thank you. Hope? What do you think?”
“It would be less risky for you to ride back in Jack.”
“Are you saying you won’t help?”
“No, only I want you to live.”
David exchanged a look with Nathalie.
“Hope, ma fille, we will work together so we all survive,” Nathalie said. “D’accord?”
Hope threw in one of the pauses she’d learned that humans use for effect, then replied. “Oui, Maman. Together.”
Jack had a trick Hope hadn’t had. He could flatten his nose and shape it to fit the point where he contacted Opportunity. Then he almost emptied his fuel tanks, burning his engines for half an hour at low thrust to reduce the strain.
David commanded him to leave enough fuel to make it back to Hope. He didn’t need much. His best effort had added little delta-v to Opportunity at all, so the change in velocity to rejoin Hope required only a few percent of his fuel capacity.
By the time he arrived back at Hope, John, Heidi, and Ernie had a plan.
“It’s not pretty,” John said, “but it’s our best shot.”
“Let hear it,” David said.
“Well, we’ve sorted out the electrics, we think. All sorts of ugly stuff happened up front where the front two tanks got ripped off, but we’ve untangled that. What we need to do now is restart the reactor and get moving.”
“What about the hole in the aft tank?”
John grinned. “That’s the ugly part. Once we fixed Hope’s external sensors, we recalled the maintenance bot we left by Opportunity because I figured we’d need it to patch the hole. But the thing is, as Hope stopped spinning, the water in the tank froze in place and sealed the gap. It’s rough, but as long as we don’t accelerate too hard it should hold. It means we can get under way soon.”
David agreed with John – this was ugly. Patching a spaceship with ice didn’t seem like a bright idea. He frowned, a thought surfacing. “Wait, don’t we need to heat the tank to keep the water liquid? Won’t that melt the ice?”
John’s grin grew wider and David could tell the ugly wasn’t over yet.
“Tell him, Ernie, it’s your idea.”
Ernie cleared his throat. “Well, it’s like this. You’re right, we must keep the water liquid so we can pump it to the engines. That’s also one reason we keep an atmosphere of sorts in the tanks, although of course they’re also useful for storage purposes –”
“Ernie, mate, we’re a bit short on time,” John said, seeing Ernie was about to launch into a discussion on tank design.
“Ah, yes, well, the point is, it would be a problem long term, but not for a short-term fix. We can raise the temperature just above freezing and restore a low pressure atmosphere to help hold the integrity of the tank by exerting a positive outward pressure –”
“Ernie!”
A small chorus of voices cut him off this time.
“What Ernie means,” John said, “is the split in the tank is at the front. There are two ways the fuel feed works on Hope. One way is to spin the ship, meaning the fuel flows to the outlets on the outer side of the tanks. The other is to accelerate forward, in which case the fuel flows to the outlets at the back of the tank, follow?”
David nodded. He knew all this already. In training, they’d all had enough ship theory and practice stuffed into their heads to last a lifetime.
“So if we accelerate forward, the fuel flows aft and away from the split. If the temperature is kept just above freezing, then the ice seal should stay solid long enough to get away from danger.”
“And you don’t think the acceleration will cause it to break loose?”
John, Ernie, and Heidi shared a look. “We don’t think so. There’s not a lot of reference material on ice seals on starship fuel tanks to draw on, though.”
Nathalie shook her head. “Does that mean we can’t do it?”
David snorted. “This whole mission has been a sequence of crap shoots. Why stop now?”
John grinned. “I knew you’d say yes. Now, just one more thing.”
David rolled his eyes in mock disbelief. “Of course.”
“Restarting the reactor might be a bit dicey.”
Chills ran down David’s spine as he remembered Hope’s birthday, the day they almost couldn’t restart their sole remaining reactor. “Why?”
“Because of the connection between the fuel tanks and the reactor. The reactor generates a lot of waste heat, so we pump water from the fuel tanks to cool it. This keeps the tank water liquid.”
David nodded, a stab of sorrow as Grace came to mind again. He remembered unauthorized frolicking in the mid tank during their unscheduled awakenings. It had been easy enough to raise the temperature of the tank water to a comfortable swimming warmth when they wanted to. He rubbed his forehead, trying to push those memories away. “Yes, yes, and the tanks are used to radiate waste heat. That’s one reason we don’t run them dry.”
He noticed John, Ernie, and Heidi looking at him. “Is there a problem?”
Heidi nodded. “The whole system is set up so the reactor never shuts down, so the fuel is kept liquid.”
David frowned. “But it can be, can’t it? We have procedures to restart even if the tanks freeze over.”
“True,” Heidi replied, “but they take time. A lot of time. And they don’t allow for the fuel floating around in little lumps of ice, they work with it being frozen to the sides or back of the tank.”
“How much time?” David asked. He had a bad feeling about this.
Heidi shrugged. “In ideal conditions, ten hours. These aren’t ideal conditions.”
David looked at Nathalie. “How long until we reach Serendipity?”
Nathalie bit her top lip and ran a hand through her hair. “One hour, twenty-six minutes.”
“Look, you can’t rush these things. Ice needs to melt. It takes time.” John’s cheeks reddened.
“How does it work?” David asked, keeping his voice even. He knew he was pushing John, but when the alternative meant certain death, he had no choice.
“Hope has heating elements around the perimeter of the tank,” John replied. “It’s as simple as that. Of course, the fuel isn’t around the perimeter, it’s floating around in chunks of ice.”
“What can we do about that?”
John shrugged. “The best we can do is use chemical thrusters for ullage, to accelerate the ship so they fall to the back. Then we can heat them up ... although if they’re loosely packed it’ll take longer, and we don’t have unlimited fuel for the thrusters.”
“And there’s no other way?” David asked, then hastened to mollify John when he noticed his expr
ession. “John, I know things aren’t ideal, but unless the thrusters can boost us clear, we need something else. Anything else.”
John exchanged a glance with Heidi and she shook her head. “Those thrusters are for maneuvering,” he said. “They can’t shift Hope far.”
“There is one other option, Papa,” Hope said.
John looked thoughtful for a moment, then his eyes widened. “Oh, no. No. If you’re thinking of –”
“– the emergency standby tank,” Heidi finished. “That’s it, isn’t it, Hope?”
“Yes,” Hope replied. “I can reroute the outflow into the aft tank.”
David looked up. “What does she mean?”
John turned pale. “The standby tank. The water doesn’t go straight from the fuel tank to the reactor. First it goes through a smaller buffer tank. If there’s an interruption to the fuel flow from the tank, it can be used as an emergency supply of coolant while the reactor is shut down.”
David nodded. “OK. How does it help us now?”
“Hope is suggesting we restart the reactor using the emergency standby tank,” Heidi said. “Right, Hope?”
“Yes.”
“And this will give us enough thrust?” David asked, frowning. “It doesn’t seem like it would.”
“It won’t,” John said. “Tell him what you’re planning Hope.”
“David, once we restart the reactor, the emergency standby tank will superheat in minutes and I can redirect the hot water into the fuel tank. At high temperature and pressure it will melt the ice near the inlet rapidly, and we can pump the water back into the reactor to keep it cool.”
John shook his head.
“What?” David asked.
“Mate, that’s the good news. The bad news is, if this works, there’ll be a delay between the ice melting and the water coming through from the tank. A delay plenty long enough for the reactor to overheat.”
David pursed his lips, thinking. It wasn’t a hard decision – a choice of a slim chance or no chance. He looked at John, knuckles whitening where he gripped a handhold.
“Do it.”
“OK, I guess this is the moment of truth,” David said. “Hope, prepare the startup sequence for reactor one.”
“Sequence prepared, confirm for initiation,” Hope replied.
“Confirmed. Initiate.”
Had there been gravity and a pin, they could have heard it drop.
Hope relayed a commentary of the reactor startup progress. “Reactor one diagnostics confirmed … Coolant flow rates nominal … Containment fields initiated … Containment fields stable … Commencing fuel injection … Initiation pulse triggered … Fusion confirmed. Reactor one is now operating at ten per cent capacity, all systems nominal.”
David sighed. One demon exorcised – the reactor had started. “Hope, engage thrusters and direct all available power to the tank heaters.”
“Yes, David, engaging thrusters now.”
They detected a slight but distinctive pull toward the rear of the cargo hold. David let himself drift and the others followed suit. David tried to imagine the icy globules floating in the fuel tank coalescing at the rear near the outlet. He hoped they would melt fast enough. He hoped they had enough time to boost clear of Serendipity. He hoped they had enough fuel.
“Hope, how long until the emergency tank is hot enough?”
“Three minutes.”
John blew out his cheeks. Not long now. The tank, although small relative to Hope’s enormous fuel tanks, measured three times the size of Jack. But even at its lowest power setting, their little captive star threw out a lot of heat.
“Nathalie, time to the latest boost point?” David asked, meaning the latest time they could start accelerating away from Serendipity at maximum thrust and still make it to safety.
“Twelve minutes.”
David stroked his chin, then gave a mental shrug. He could do nothing to improve their odds, all they could do was wait, and hope.
Still rotating, Opportunity plunged through the void, trailing a hazy mist of sublimated ices, rushing toward its encounter with the blue planet now so near.
A combination of Jack’s efforts and Hope’s maneuvers had allowed Opportunity to pull ahead of Hope. It would arrive at Serendipity first. To the naked eye, it seemed inevitable Opportunity and Serendipity would collide.
Below and behind, Hope followed, faint wisps of exhaust from her thrusters just visible as she continued to push the ice in her remaining fuel tank to the rear.
Her main drive remained silent. No plume of ice crystals marked an attempt to escape the gravity well of the planet she rushed toward.
In less than ten minutes they had an answer to Serendipity’s fate.
Cameras on the ground caught a white scar drawn across the sky as Opportunity kissed the outer fringes of the atmosphere. It traveled so fast only a few seconds were needed to tear the ice and snow from one side of the little asteroid. Then it passed and headed away on a trajectory that would take it out to the far reaches of the star system.
High above the surface, Elizabeth and the others watched it come. They would have missed it, had it not been for Jill tracking and recording it.
Elizabeth pushed away feelings of mingled relief and joy. It wasn’t over, yet.
“Jill, show us Hope.”
Jill brought up a view of Hope on screen for all of them to see. Hope had oriented herself to thrust perpendicular to her approach, to push her wide of Serendipity. But her main drive still did not fire.
“Why aren’t they moving?” Elizabeth asked. “They have to move!”
“Emergency tank temperature approaching maximum safe level,” Hope said.
David looked at John. “It’s now or never,” he said. “Release the emergency tank water into the main tank.”
“Releasing now,” Hope replied.
Hope’s chemical thrusters still fired, generating negligible effective gravity, but enough to encourage the remaining ice to cover the rear outlet. Some ice had already melted from the heating elements embedded into the tank wall. Now, superheated water gushed in, turning the ice into slushy water and boiling off as steam. Within seconds the tank contents changed from ice to a roiling, steaming pool of slushy water.
The following minute seemed the longest in David’s life. “Hope, what’s happening?”
“My tank cameras show a significant body of liquid water in the aft tank,” she replied. “Reactor core temperature is rising.”
“Hope, circulate fuel tank water to the reactor,” John said. “Now!”
“Acknowledged.”
More waiting.
“Five minutes to cutoff point,” Nathalie said, cutting through the silence.
David nodded. “Hope?”
“Core temperature remains stable, David. It hasn’t dropped, but it isn’t rising anymore. The water from the aft tank is having an effect.”
David looked at John. “We need to start the main engines.”
“We should let the core cool first,” John said. “That would be safest.”
David shook his head. “Safest is getting the hell away from Serendipity.” But he respected John’s opinion too much to override him yet. “Let’s start a pre-burn sequence,” he suggested.
John nodded. A pre-burn would pump a low volume of water through the drive unit without accelerating it, to check all was well with the drive before engaging.
“OK, but be aware we need to keep the tank liquid. If we drain it down to ice, it all turns off.”
“Hope, tank status?” Heidi asked.
“I estimate current fuel levels at eight percent. I estimate fuel at fifty percent liquid.”
“Three minutes to cutoff,” Nathalie said.
“Hope, start pre-burn sequence,” David said.
“Acknowledged. Starting pre-burn sequence.”
They detected a vibration through the hull as the pumps started. “On screen please Hope,” Heidi said. They saw a shower of ice crystals exit t
he drive tubes.
“Two minutes to cutoff.”
David looked at John. “It’s gotta be soon.”
John nodded. “OK. Now.”
“Hope,” David said, “engage main drive, minimum thrust.”
“Engaging main drive, minimum thrust,” Hope replied.
They felt, rather than heard the familiar background hum of the drives engaging. On screen, the shower of ice crystals disappeared beyond the range of the cameras. The gentle pressure of gravity returning confirmed the ship acceleration.
“We’re moving,” Nathalie said, smiling. “I can feel it!”
John exchanged a glance with Heidi and Ernie and pressed his lips together. “We’re not there yet.”
“Hope, increase thrust to maximum,” David said. John looked dubious but Hope complied.
“Thrust increased to zero-point-two-five gravities,” she said. They could all sense the gravity-like sensation of the ship acceleration increasing beneath their feet, now greater than ever thanks to Hope’s lighter mass. Ten minutes of this and they would be out of immediate danger.
“Opportunity’s passed Serendipity!” Nathalie said. She looked up from her data pad, her face lit with a wide smile. “It missed! It missed!”
David closed his eyes for a moment, allowing himself the luxury of relief. His family was safe. The colony was safe.
He opened his eyes when John clapped him on his back. “See? I told you it would be alright!” David snorted and John laughed, both of them knowing full well that only a few minutes before, they’d both thought the exact opposite.
The shrill peal of an alarm interrupted their celebration.
“Reactor one temperature alert! Reactor one temperature alert!”
David’s head snapped around to look at their status screen. They had tempted fate by celebrating early, and here was the proof.
“Hope! Report!”
“There’s been a sharp drop in fuel flow from the main tank,” Hope replied. “At current power levels the standby tank can only sustain another sixty seconds before the core goes critical.”
“We have to cut power,” John said. “If we don’t do something, it’s all over.”
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