Encounter With Tiber Page 10

  There was no way of simply constructing a radio telescope on the Moon as we would do on the Earth, however. Earthbound radio telescopes are gigantic dishes, like radar dishes or television satellite antennas, but much larger. The ones that are small enough to move, move on gigantic pieces of machinery; crews of dozens staff them. To build something on that scale on the Moon—let alone on the back side—was far beyond our capabilities in 2006, and we weren’t about to try.

  Rather, we took advantage of some naturally occurring phenomena. The Moon has plenty of craters of all sizes, even on the far side (though the very largest, for unknown reasons, are concentrated on the near side). The craters themselves are far from being perfectly parabolic, as an ideal radio dish would be, but they are certainly large and they make adequate reflectors. If they could be corrected to reflect waves from a particular point toward a central antenna, the radio telescope could even be aimed with a fair degree of precision. The natural lunar soil offered some radio reflectivity, a point fifty meters or so above the bottom of a half-kilometer-wide crater should have a fairly strong signal.

  The Far Side Radio Telescope was an ultrasensitive radio receiver with enough computer memory to store a very accurate digitized recording of whatever signal it received. It was to be mounted atop a small robot lander, which would fly to a preselected crater on the far side, land near its center, and then put up an antenna, a thin piece of aluminum pipe. Three small robot carts would depart automatically from the lander, crawling out about 100 meters from the landing site, at 120 degrees from each other; each would be dragging several long wires attached at various points to the antenna. When the carts were in position, a small tank of helium would be used to pressurize the inside of the telescoping antenna, causing it to extend upward very slowly; in radio communication with each other, the guy wire robots would continually adjust line tensions to keep the slender aluminum rod perfectly vertical. As the helium pressed each section into its final place, a snap lock would keep it there. At last, after a couple of hours, the aluminum pipe would reach fifty meters into the empty sky of the far side of the Moon, vertical and well-guyed, somewhere near where the crater would reflect radio waves. The computer on the FSRT would work out what were the “quiet times” when Earth, Jupiter, and Sun were all out of line-of-sight from the radio; two thousand kilometers of lunar rock would block and attenuate the radio signals from those strong noise sources—and the FSRT would be able to hear and record fainter signals, from more distant places, more accurately than any instrument ever before.

  Two additional features were needed to make it work. The first of these was the most urgent. Unfortunately, a robotic research station that is placed in an area where radio waves from Earth cannot penetrate also cannot receive orders telling it what to look at, nor can it send data back. A relay station was needed, and because the relay station itself was potentially a source of noise, it needed to be a very quiet one.

  The solution was the “halo satellite,” which took advantage of an odd phenomenon in orbital mechanics, one of those cases where the mathematics of physical equations predicted something that then turned out to be true in the real world. Prior to computers, most many-body problems in orbital mechanics—that is, problems that involved more than two bodies attracting each other gravitationally—were not soluble by any means available; the solutions had to be approximated by treating them as a set of separate two-body problems.

  Around the turn of the nineteenth century, Lagrange had pointed out that there were a few places in orbit around a two-body system (like the Earth and the Moon, Mars and Phobos, or the Sun and Jupiter—any system where you could ignore the other bodies temporarily) that did have solutions, stable places that would behave very much as if there were an attracting body there, even though they were just empty space. In those five spots, called “libration points” because they were places where the gravity and motion of the system balanced, a satellite could stay indefinitely, with no need for fuel or energy to “station keep”—i.e., to maintain its position.

  Those places were a midpoint where gravity balanced between the two bodies so that neither of them ever tugged the satellite one way or another; two places in line with the two bodies but on the outside, so that the satellite orbited the combined center of mass of both bodies with exactly the same period with which the two went around each other; and the places which formed an equilateral triangle with the two bodies, one ahead and the other behind the smaller body in orbit, where any motion toward one body would result in a stronger attraction by the other and pull the satellite back into place.

  Thus the Earth-Moon system (and any other case of one body orbiting around another) has five “Lagrange libration points”: places where a spacecraft can sit without expending fuel to keep itself in a constant relationship with the Earth and Moon. These are almost always referred to by L plus a digit. L1, L2, and L3 all lie in a line with the Moon and the Earth; L1 between them, L2 beyond the Moon, and L3 on the opposite side of the Earth from the Moon. L4 is 60 degrees ahead of the Moon in orbit; L5 is 60 degrees behind. The Lagrange libration points had been of great interest since the late 1960s, because they are the most energy-efficient places to put a space station, and when it cost $100,000 to move a pound of fuel into orbit, energy savings were vital.

  The Lagrange points have another odd feature. Because they are attractors (things near them tend to fall toward them), it is possible for a satellite to orbit them, even though they are just points in empty space.

  This was the birth of the idea of the halo satellite. A satellite orbiting L2, in about a two-week orbit, will always have both the entire far side of the Moon, and the facing side of the Earth, in direct line of sight. It was called a halo satellite because from the Earth it appeared to be making a circle around the orb of the Moon—and thus was never out of sight of either the Earth or the far side. The relay transceiver on the halo satellite, in turn, could be turned entirely off whenever the FSRT was working, so that the only thing running on board was a small clock set to turn the halo satellite back on at a prearranged time, then receive data from the FSRT and relay it back to Earth during the “noisy” periods. For technical reasons a pair of halo satellites worked slightly better, giving more complete coverage of the Moon’s back side. No one made much of a point of it, but a halo satellite in place would also mean that if humans ever ventured to the far side of the Moon, they would be able to radio home—a drastic improvement from the days of Apollo.

  The other device was a simple, incremental improvement that would allow the FSRT to become a steadily better tool for decades to come. Weighing just forty pounds, the Self-Propelled Ultralight Microantenna (SPUM) was designed to be launched to the Moon using any convenient system; it would find the FSRT by radio beacon during a noisy time and descend into the crater, avoiding the guy wire robots and the previously arrived SPUMs by receiving information from the FSRT computer. Once down, it would unfold a simple wire-frame antenna, not much different from an old-fashioned umbrella, about fifteen meters across—an easy enough size to handle in the light lunar gravity.

  Coordinated by the FSRT, the SPUM would run a series of test radio beeps so that the FSRT would know its exact location, plus how to translate what the SPUM said about its position into the FSRT’s more general coordinate system. Each added SPUM would increase both the signal strength and the ability of the FSRT to focus; a few hundred of them would make the FSRT into an extraordinarily powerful and effective instrument.

  The FSRT, halo satellite, and SPUMs were all to be powered by batteries recharged by solar cells. Since by definition when there was sunlight it was a noisy period, the charging process should create little interference with the work of the FSRT.

  The system was elegant and cheap; it took advantage of enormous improvements in computers to minimize expensive mass being sent to such a difficult location.

  But everyone had learned the bitter lesson of the Hubble Telescope, which had originally gone up with a wa
rped mirror, unable to focus properly. Though it had been successfully repaired, the damage it had done to NASA’s public image had been incalculable. The University Space Research Associates, with a far smaller budget and much less public visibility than NASA, needed this first bold mission to be a complete success, and so they had determined that they would thoroughly test each component before sending it on its way. In late 2005, the halo satellite had checked out perfectly, and a Centurion/Starbooster combination had carried it into halo orbit, from which it was reporting that results thus far were perfect.

  Next would come testing the FSRT’s receiver in Earth orbit, to make sure that it would work properly in vacuum and in the alternating tremendous heat and cold of sunshine and shadow in space. Chris had been assigned to do the full checkout of the FSRT at the ISS, following which, if time permitted, he could use extra time on the ISS for astronomical observations for his own projects and assist the rest of the crew with assignments coming up from the ground.

  This was the seventh American flight of an Apollo II on top of a Centurion/Starbooster combination, the temporary configuration to augment the three remaining shuttles until Starbird would replace them later in the decade.

  Lori Kirsten was to be the pilot for the mission that would take them up; she had trained with the astro-Fs in France and knew Apollo IIs thoroughly, but she hadn’t actually flown one before. The mission’s principal functions were Chris’s FSRT mission, and getting another escape module (and better still, one that was neither Russian nor French) up to the ISS.

  It was really a good thing that Chris and Lori were the only crew; the FSRT took up a great deal of room in the Apollo II so the other four crew seats had been removed.

  “Ever feel like a museum reenactment?” Chris muttered to Lori as they strapped in for launch.

  “Don’t you like the Pigeon?”

  “The what?”

  “When I went down and trained with the astro-Fs, we started calling it that to annoy the French. It’s called a Pigeon because it goes somewhere and roosts for a while, but it’s always supposed to come back home.”

  “Well, it’s a better name than Apollo II. Less of a phony sound to it. And these things don’t look much like Apollos to me, anyway—too steep-sided and too big.”

  “Yep, I’ve seen the original Apollos in the Smithsonian. They’re really tiny. By comparison a Pigeon is huge.” She wriggled and stretched as much as she could, confined to the acceleration Couch. “Geez, first mission since we lost Endeavour. I hope we have better luck with this one—I don’t think it’ll glide real far.”

  “Yeah, but these, uh, Pigeons are designed to float.”

  “Apollo II, this is Control,” a voice said through their earphones.

  “Roger, Launch Control, Pigeon is here and ready,” Lori said.

  “Excellent, Apollo II, we anticipate no delays, and we’ll be commencing countdown shortly. Please confirm the following checklist—”

  They did—everything was perfectly normal—and then watched and listened as the countdown proceeded. Aunt Lori always said the Pigeons were the beginning of the end for the “real” pilots because they were the first ships really designed to do everything either by remote control or by robotics; not even docking was to be manual. She grumbled that from the Pigeon forward, American astronauts were “passengers more than pilots.”

  Years later, when I began flying Pigeons, I disliked them intensely because it seemed to me that their computer system needed manual overriding much too often. No doubt someday the captains of later star-ships will wonder how anyone could put up with the living human pilots of the earlier starships.

  Chris and Lori endured the high-acceleration ride as first the Starbooster engine plus the upper stage carried them aloft, then the Starbooster peeled off to fly back to the Cape. A while later, they shut down the upper stage.

  “Made it to orbit this time,” Lori said. “That’s a bit more dignified.”

  Two more burns put them on course for the ISS. As they approached it, Chris whistled. “They’ve done a lot with the old joint since I was up here six years ago. The truss is done, the solar collectors are deployed … and so that’s the Big Can.”

  “We’re supposed to call it an HT.”

  “I bet you’re supposed to call this Pigeon an Apollo II, too.”

  “Maybe so, but if you were a woman you’d get tired of the number of male ground controllers who want to tell you that your Big Can is moving strangely, or that a couple of guys will be docking with your Big Can shortly, or to make sure I put my Big Can up high where people can see it.”

  Chris snorted. “I imagine those jokes do get old.”

  “Unh-hunh. Anyway, rumor has it that it’s pretty nice in there.”

  The Pigeon nosed gently into the docking module without Lori’s having to touch the controls. “Great system, but I’m not sure the union’s gonna like it,” she muttered. “Well, let’s get inside.”

  They had unshipped the FSRT and were just in process of getting to know the rest of the crew—two cosmonauts, a Japanese astronaut, and an astro-F—when the chime that indicated a high-priority message sounded.

  “Probably something that will prevent dinner,” Peter Denisov grumbled, going to the radio. “Preventing dinner seems to be their highest priority down there.” Between Mir and ISS, Denisov had almost four years in space; doctors were constantly poking at the pudgy red-haired man to see how many things differed between him and the rest of the human race.

  He talked with them for a long time, earphone clapped to his ear. Mostly what he said was “No,” and “It can’t be,” and “I don’t believe it.” Once he asked if this was some kind of prank. Finally he hung up, still denying everything—whatever everything was.

  By that time the room had fallen silent. Tatiana Haldin, the ranking officer on board, finally asked, “Peter Mikhailovich, what are they telling you on the radio?”

  “It’s a prank. It must be a prank.”

  She shrugged. “Unless they ordered us to do something dangerous, I think we should comply.”

  He wouldn’t respond at all, staring at the wall, just floating there; afterwards Chris learned that no one had ever really seen him upset before.

  Jiro said, quietly, “You should let the rest of us in on it. It won’t be a prank on you personally, anyway, even if that’s what it is.”

  Peter Denisov looked up and saw everyone—Chris, Lori, Jiro, Tatiana, and François—nodding. Finally, he blurted out, “They claim that they are getting radio messages from Alpha Centauri.”

  5

  WHAT DAD TOLD ME later was that what Denisov had said produced an “astonishing silence.” Finally, after a long time, Haldin, floating at the other end of the Big Can, pulled her pale blonde hair back and smoothed her stubby ponytail. Visibly, she composed herself and said, “Peter Mikhailovich, you will embarrass us. If the message is real we need to acknowledge it; if it is a prank we need to report it.”

  Denisov nodded, very unhappily. François said, “If you like, I can call CNRS directly—we are line-of-sight from France—and see what they know about it. A back channel approach, so that if it is a joke no one needs to know that we took it seriously.”

  “What’s CNRS?” Chris said, feeling a little dumb.

  “Centre nationale pour le recherche scientifique,” François explained. “It’s our umbrella science organization; any unclassified problem will go there first. And this is about as unclassified a problem as anyone has ever seen, so I’m sure my friend there will know as much as anyone. Shall I call him?”

  “Do it,” Haldin agreed. She turned to Chris and Lori. “Well, this is going to be a memorable first day at the station for you. How did the flight up go? An American crew riding a French capsule on a Russian rocket must be a complex job.”

  “Well, Starbooster engines have been built in the U.S.A. for three years now, and thank heaven the software and control systems are American,” Lori said, “and that’s all I nee
d to talk to.” She had recognized Haldin’s dig at them, but her orders were to not escalate any arguments; as much as Americans might resent their temporary junior status at ISS and in space, after all it was of their own making, and given that the ugly situation with China seemed to be getting worse, and we needed our traditional Russian, Japanese, and French alliances in the event of trouble, it paid Americans to be nice even when others weren’t.

  Haldin nodded and said, “An uneventful flight is always to be hoped for.”

  By that time François had gotten through to a ground station and was contacting his old friend at CNRS by voice Internet. The small, muscular astro-F gestured for silence, muttering, “It’s a terrible connection, it always is—Allo, Michel?”

  Chris had only a little bit of French, enough to get him around town at conferences; it had only been very recently that American astronauts had had much reason to learn the language, and Russian was still by far the most common second language in the astronaut corps.

  But Lori had spent part of last year training with the astro-Fs in Toulouse, and she had a knack for languages anyway. Chris watched her reactions closely to gauge what was going on. At first she listened patiently; clearly François was making small talk with his friend for a minute, laughing politely and working his way around to the question. Then suddenly François fell silent, and when he spoke again it was fast, loud, and very excited. Then he put the conversation up on the speakers so that everyone could hear both sides. Lori leaned forward eagerly, and slowly, as she listened, her mouth fell open and she breathed in great sighs. By the time the call was over, everyone in the Big Can knew, whether they spoke French or not, from the excitement in the voices.

  “It’s not a prank,” Jiro said, very quietly. “At least for the moment it looks real.”