FAILURE MODE
“Died?” Grant mumbled, still thick-headed with sleep.
“Motor just crapped out, pooey, just like that.”
Grant couldn’t see Phillips’s face inside his helmet but the tone of his voice had an edge of fear in it.
“Is it the motor or the generator?” Grant asked.
The tractor’s electric motor drew its power from a miniaturized nuclear generator, buried inside heavy lead shielding in the belly of the vehicle.
“How the hell should I know?” Phillips snapped. “It just happened.”
“Check the diagnostics.”
Together they ran through the diagnostics program.
“Engineer’s hell,” Phillips muttered as they stared at the display screens. “Everything checks but nothing works.”
“Life support’s still working,” Grant muttered. “Radio’s still powered up. The batteries aren’t discharging.”
“So the generator’s still putting out kilowatts. It’s not the generator.”
“Must be the motor.”
“Better call Farside, get ’em to send a hopper out for us.”
“Not yet,” said Grant. “I’ll go out and open her up, see what’s going on.”
“We’re gonna need a hopper,” Phillips insisted.
“Just tell Farside we’ve got a problem and we’re trying to fix it.”
“But—”
“Keep cool, Sherry. No need to panic.” But Grant added silently, Not yet.
As his partner sent a message to the excursion monitor, Grant opened the hatch on his side of the cab and jumped down in lunar slow motion to the ground. Like most of the Moon’s surface, it was covered with several centimeters of soft, talc-like dust. Almost like a sandy beach, back Earthside. Grant walked to the rear of the tractor and as he opened the motor’s hatch he glanced back at the bootprints he’d left in the dust. They were bright and new-looking compared to the dust-gray surface of the ground.
The motor looked all right to his eyes. But it wasn’t working. Grant couldn’t see any obvious damage. We haven’t been hit by a micrometeor, he thought, remembering that last year a hopper had been crippled while sitting at the edge of Farside’s spaceport by a chip-sized meteor that had hit its control computer as accurately as a sniper’s bullet.
It’s got to be something, Grant said to himself as he bent over in his unwieldy space suit to examine the motor’s magnet coils more closely. They were superconductors, encased in metal dewars that held liquid nitrogen.
The pressure gage on the stator coil’s dewar read zero. Grant blinked with surprise. All the nitrogen’s gone? How could that happen? He could see no obvious damage to the dewar, no puncture or leaking seal.
Without the nitrogen coolant the magnet loses its superconductivity. Then it shuts down. Either that or it dumps all its energy into an explosion. We’re damned lucky the magnet didn’t blow up.
The nuke was still generating electricity, that’s why the life-support equipment and the radio were still working.
Okay, Grant said to himself as he plodded back to the cab. We know what’s wrong. Now we’ve got to fix it. And then figure out why it went wrong.
Phillips was still on the radio, chattering nervously with the excursion monitor back at Farside, when Grant climbed back into the cabin.
“Yeah, the motor’s dead,” Phillips was saying. “How many times do I have to tell you guys?”
Sherry sounds scared, Grant thought. Normal reaction. I guess I am too, a little.
“This is Grant,” he said as he settled into his seat. “Nitrogen coolant on the motor’s main coil is gone. We’ll need a replacement dewar.”
He sensed Phillips staring at him from inside his bubble helmet.
“Replacement dewar, yes,” the monitor’s voice replied. Grant recognized Rava Sudarthee, the Hindu computer analyst, taking her turn at the excursion center. “We’ll send it out on a hopper. It should get to you in one hour or less.”
“Send a replacement crew with it,” said Phillips.
“Negative,” Grant snapped. “Once we get the motor running we can drive this buggy back home.”
Phillips said nothing, but Grant could feel the fear-driven anger radiating from him.
Once he cut the connection to Rava, Grant said, “There’s no need for a replacement crew, Sherry. We can drive back home once we get the dewar replaced.”
“Says you,” Phillips muttered.
Grant drew in a breath and thought it over. Sherry’s scared. He wants out. Maybe I should be scared too, but it’s my responsibility. I can’t leave this to somebody else. It’s my responsibility.
“Tell you what, Sherry,” he said. “You go back with the hopper. I’ll drive back to Farside.”
“You know damned well you can’t go alone; the safety regs require two people.”
Pursing his lips before replying, Grant said, “Okay, tell Rava to send Harvey along on the hopper. You can go back and Harvey’ll keep me company on the drive home.”
Phillips hesitated only a heartbeat. “Okay, fine.” Then he added, “Uh … thanks, Grant.”
* * *
McClintock was waiting for Grant at the airlock. The instant Grant stepped through the inner hatch and began unfastening his helmet McClintock demanded, “What the hell happened out there?”
Before Grant could begin to explain, McClintock’s expression went to disgust. “Good god! Go take a shower, for pity’s sake.”
Grant saw that even though McClintock was wearing ordinary gray coveralls, like almost everyone at Farside, on him the coveralls looked somehow a cut above anyone else’s: crisper, newer, finer.
Tightly, Grant replied, “Shower. Right.”
“Then come straight to my office,” McClintock said to Grant’s retreating back.
He’s just as bad as the Ulcer, Grant thought. Another pain in the ass.
After showering and changing, though, Grant went not to McClintock’s office but to the maintenance center. It was little more than a scruffy workshop where technicians labored over various pieces of equipment, trying to keep them all in working order. Most of them knew that their work meant the difference between life and death outside on the Moon’s harsh surface.
Grant went to the workbench where two of the technicians were bending over the dewar from his tractor’s motor.
“So why’d it go dry?” he asked.
Toshio Aichi looked up from the dewar. He was the best maintenance tech among Grant’s people, unsmilingly serious. His face was lean, sallow, with hollow cheeks and an unruly mop of straight black hair going every which way. Despite his scarecrow frame, Toshio could out-eat any of the technicians, and often won bets against newcomers about who could stow away the most chow in the least time.
The dewar rested on the workbench, its cylindrical body split down its middle, its inner layers of insulation open to inspection.
“Pinhole leak,” Toshio said. “Microscopic.”
Grant looked down at the dewar.
“You can’t see it with the naked eye,” Toshio told him. “We had to scan it with the laser probe to find the sucker.”
“That small?”
“Nanometer sized,” said the other technician, Delos Zacharias. He was physically Toshio’s opposite: a chubby, apple-cheeked kid, with an eternally sunny disposition.
“That small,” Grant repeated.
“Plenty big enough for nitrogen molecules to sneak through,” said Toshio. “The pinhole must have looked like the main gate of the Imperial Palace, to them.”
“How come the coil didn’t explode?” Grant asked.
Zacharias jumped in. “The enn-two escaped slowly enough so that the coil shut down. It wasn’t a rapid loss. The coil didn’t develop a hot spot. The whole assembly warmed up gradually and once it passed its critical temperature it stopped being superconducting and just shut itself down.”
Grant looked from the empty dewar to the two technicians. “I guess we were pretty lucky, then.”
Almost cheerfully, Zacharias said, “Actually, the system worked the way it was designed to, even in failure mode.”
Toshio was more restrained. “You were indeed pretty damned lucky, Grant. A slightly bigger leak, a more rapid loss of coolant, and the coil could have gone off like a bomb.”
Zacharias disagreed. “There’s not that much energy in the coil—”
“There’s enough to blow off the rear end of the tractor, rupture the cab, and shred the drivers with shrapnel,” Toshio insisted.
Zacharias’s round face looked more like a disappointed little boy’s than a serious technician’s. “Oh, well, yeah,” he admitted. “Maybe so.”