Part 33 (1/2)

axis and the ellipticity of the moon's...o...b..t, Earth from the same lunar vantage point migrated around a celestial box of about fifteen degrees by thirteen-movement the astronomers called libration. These weren't details any politician wanted or needed. ”As there has to be computing power somewhere giving very precise directions to the masers.” Any single maser was a physically rigid structure, the direction of whose output was fixed. By precisely controlling the emissions of sets of masers, however, those outputs could be aggregated into vast steerable beams. It worked just like a military phased-array radar.

”Not my specialty, Doctor, but it seems logical.”Kyle fancied he heard the sound of eyes glazing. Simplify! ”Our work involved altering test plots on the lunar surface. As expected, a cleared region did not radiate until the masers regrew. To our surprise, however, one experiment rendered inert an area much larger than had been temporarily cleansed. We had happened upon a sensor that gave steering guidance. When that sensor could no longer spot Earth, the masers that it controlled stopped firing.” Emissions from a blinded region would likely interfere with an adjacent well-aimed beam; suppressing an area whose sensor was for any reason targetless made sense.

”It sounds like we finally got lucky,” said the President.Now that the explorers could recognize the sensors, they knew how widely those sensors were dispersed. They had actually been unlucky, considering how much landscape had been tested, to go as long as they had before randomly encountering a sensor. ”We've been using our utility robots to blind sensors with opaque sc.r.a.ps.” While nanotech quickly regrew a destroyed sensor, an intact sensor could be covered. The nannies didn't distinguish shadow from nightfall.

”And the robots can spot sensors?”If only it were that easy. ”You might have heard of archeologists hunting for lost cities with s.p.a.ce-based, ground-penetrating radar. Major McNeilly”-he caught himself before calling her Windy-”used Endeavor's radar to map beneath her orbit. A subsurface view, and only using a narrow range of frequencies, reveals a non.o.bvious large-scale structure. The alien infestation repeats on the scale of a square kilometer. There's a sensor at the center of each region.

”This is what we do. Using the radar survey, we guide a robot to the center of a region. As the robot

trolls back and forth, we use its videocam to hunt for a small and subtle discontinuity in the artificial surface: the sensor. The robot then parks atop a suspected sensor until a satellite pa.s.sing overhead can confirm that the surrounding area has stopped emitting. The robot sets a sc.r.a.p of asbestos over the confirmed sensor, then heads off to the next region.” At a snail's pace.

”It sounds ingenious, Doctor. Is it too soon to say our problem is solved?”He suppressed an oath. The moon was big. ”I'm afraid, ma'am, that it is too soon. Disabling all the masers this way will take an armada of moon-orbiting satellites and myriads of moon-crawling robots. There are millions of sensors to be blinded, one by one.” And, perhaps, again and again. Kyle expected the nanotech to eventually, atom by atom, carry away the obscuring mats-as they had, on the day of The Big Dim, removed the last thin skin of lunar dust that had disguised the spreading infestation.”It sounds like an epic undertaking, Dr. Gustafson, but nonetheless something we can undertake. We have far greater cause for hope than before this expedition. I look forward to discussing it with you, and

to meeting with the whole crew, very soon.”

The President did not articulate the thought in everyone's mind. The four astronauts were returning to a remote quarantine, their exit from which was far from certain.

CHAPTER 39.

”Ready for another first, guys?”

McNeilly sounded altogether too chirpy, but it was probably just pilot bravado. The alternative

explanation, pilot exhaustion, didn't bear thinking about-nor could Kyle do anything about it. ”I say we get out and walk.”

The first to which Windy referred was a manned aerobrake maneuver. The heat tiles that insulated

Endeavor during its fiery reentry had been designed for near-Earth missions. Symmetry was a cruel mistress: just as the orbiter had had to add speed to reach the moon, it now had more speed to shed than any previous returning shuttle. That faster-than-spec reentry turned directly into unacceptable thermal stress on the tiles. Instead of reengineering yet another critical system, the mission had turned to a technique previously tried only with robotic interplanetary probes.

”Hold on to your helmets, folks.” The orbiter shuddered as it bludgeoned its way through the Earth's upper atmosphere. The angle of attack was by intent shallower than any previous reentry. ”Getting toasty up here.” The ”up here” was because Windy, for her own protection, was alone on the flight deck. Those who had been to the lunar surface remained sealed in Resolute's claustrophobic ascent stage, inside Endeavor's cargo bay. Darkroom-style red bulbs provided their only, and decidedly dim, lighting.

”Nearing fourteen hundred degrees C.” Carlisle meant the tiles, not the flight deck. He was studying telemetry from the c.o.c.kpit. His remoted instruments reproduced everything he would have seen in his now-empty command seat beside the pilot. ”I'd say that qualifies as warm.”

”And back out we go.”Kyle clutched the arms of his acceleration seat as the cabin vibrated like mad. Aerobraking was such an antiseptic term. In reality, the Endeavor had hit the atmosphere at almost seven miles a second. The Earth's skin of air was softer than, say, a brick wall . . . but at these speeds, not by much. The trick was to strike a glancing blow. Each dip into the atmosphere removed a bit of velocity, followed by a return to s.p.a.ce to shed the friction-induced heat. If they entered at the wrong angle, the Endeavor would bounce like a stone skipping off a lake, or heat up past the thermal tiles' capacity to protect them.”Whee!” Gonzalez was either having a great time or had forgotten their thin margin of safety. Maybe both. ”Once more, Windy.”

”Anything for you, Speedy.”

A few tooth-rattling repet.i.tions slowed them enough for a sedate, five-mile-per-second low Earth orbit,

circularized at an alt.i.tude of two hundred miles. Landing from LEO should be a piece of cake-if all the aerobraking shocks hadn't dislodged too many tiles.”Great job, Endeavor.”

”Copy that, Houston. Quite a ride, actually.”

”Sorry to be the bearer of bad tidings, but you'll have to wait a bit longer. Storm in the Marshalls.” That put off until the weather cleared another item for the record books: the first shuttle landing at a remote Pacific atoll.

Quarantine Central.

Endeavor smacked the isolated runway, bounced, and settled into a fast roll. The landing strip had been lengthened for them, but the curve of the atoll limited what could be done. They shook with relief when the orbiter coasted to rest with only a few hundred feet to spare.

”You make it look easy, Windy. Whenever you're ready.”

”Thanks, Houston.” Over the in-s.h.i.+p radio Kyle heard flung metal buckles striking whatever-and a meaty thud. ”Head rush.”

It was a wonder, thought Kyle, the shuttle pilot could stand at all. Except for a few minutes acceleration

and deceleration, she had been weightless for almost a month. By rights, someone should have helped

her from her seat. That was a risk no sane person would take.

”Tricky, Speedy . . . Doc.” The pilot was breathless merely from struggling back to her feet. ”It's been . . . fun. See you . . . in a few weeks.”

They watched by close-circuit TV as their s.h.i.+pmate stumbled to the middeck. Braced against a bulkhead, Windy waved at the videocam. ”Stay out of trouble, guys.” She struggled briefly with the hatch's release. As the door slid aside, TV showed the three (still sealed in the Resolute's ascent stage) an approaching, teleoperated motorized staircase. Windy would be taken, entirely by remote-controlled vehicle, to the farthest part of the atoll. They, once she was safely away, would go to their own, separate quarantine.

They had one final task to perform first.Kyle and Craig Carlisle struggled with the suddenly heavy cooler-sized chest, in which nested smaller vacuum-sealed vessels. Each inner container held lunar-dust samples, harvested by abandoned robots. Gonzalez, meanwhile, opened the hatch into the Endeavor's payload bay. Two weeks in one-sixth G, Kyle decided, were little better than free-fall the entire time as McNeilly had experienced. All three were panting before they'd wrestled the chest from the ascent vehicle, through the orbiter, and down mobile stairs to the concrete runway. It was the middle of the night, as per plan, and the electric lighting on the stairs was decidedly dim.

Out of breath, Kyle awaited another remote-controlled vehicle. Out to sea, wars.h.i.+ps were discernible