Encounter with Tiber [v1.0]

by By Buzz Aldrin

  “First one,” Chris agreed. “We’ve all had the training, but I’m sure that-”

  “I’m sure you’ll be fine, too,” Peter replied. “Tatiana, cut the floodlights please.”

  “Roger,” her voice crackled in their headsets.

  “Now, Chris,” Peter said, “I just wanted to suggest that you look up away from the Earth for a moment or two. It’s a view every astronomer should have.”

  I know what he saw, now, and can understand a little of how it must have struck him: when I was a kid and Dad would describe being outside in space for the first time, I didn’t understand why he was so excited about there being “so many stars” when after all he was an astronomer and he should have known how many of them there were anyway. Now I have a little more idea that when you have imagined something but never really seen it directly, for your whole life, just possibly the first time you see it may strike you dumb.

  They spent the ten minutes, while they waited to come around to the day side of the orbit, looking up into the stars, many times as many as you can see from Earth, the bright ones brighter by far than earthly eyes are used to. They had something pretty important to do, and no doubt they were strongly reminded of that by the brilliant beacon of Alpha Centauri—so close that even though it’s just a run-of-the-mill double star with a combined brightness only about one and a half times our own sun, it’s still the third brightest star in our sky.

  Chris waited, floating with one hand to hold him in place, till the Sun emerged over the Earth; in less than a minute, the glare on his visor erased the swarm of stars, leaving the sky black. The job was simple—or it would have been simple, on Earth. Nothing is simple in orbit, where the rules wired into your nerves by half a billion years of evolution stop working, and you’re encumbered by a thick, heavy pressure suit. The HT-based habitat was attached to the center node, aft of the truss (a long, thin structure on which the immense bank of solar panels that powered the station was mounted). The truss itself had a hexagonal cross section as wide as a hallway in an ordinary house; normally if one had to get to either end of it, one either climbed from strut to strut, along the structural members, inside the truss, or worked tethered to one of the structural members and crawled along the “bottom” (Earth-facing) side, when there were Earth-monitoring or space-science experiments to be conducted.

  As the Russians had pointed out, one of the many budget cuts the American Congress had imposed on the ISS had involved planning for a truss that was only “half useful,” in that there were no built-in places to attach experiments or equipment that faced out toward space. The United States, having successfully lured other nations into the cooperative enterprise, had almost at once begun to limit its capabilities, like a used car salesman who shows you something too good to be true and then tries to talk you into taking something grossly inferior for the same price. I can remember Dad growling to himself, after the mission was over, that a few hundred ex-lawyers in Washington had decided that everything interesting in the universe had to be in the same direction, the one that allowed orbiting astronauts to take photographs of their districts.

  As a result, Chris’s first EVA was an interesting exercise in improvisation. Station supplies had included a few dozen Clancy clamps, toothed clamps on a piece of pipe that tightened their grip when a small disk on the pipe was spun to the right, and a large roll of vacuum-proof silver bell wire. (To work in space, bell wire couldn’t have just an ordinary plastic jacket, because many plastics in a vacuum outgas the volatiles that keep them soft; hence, the insulation on the wire was a special fiberglass. And because the expense of getting the wire into orbit and the special insulation was already so high, it only added a small fraction to the cost to make the conductor out of extremely pure silver, which was both a better conductor and more flexible than copper or aluminum.) A small committee of experienced engineers and machinists had spent a long time figuring out what ought to be in the ISS’s tool and supply kits; so far their record was holding up.

  If the truss had been on the ground, it might have taken Chris alone only a few minutes to accomplish the basic job of putting a loop of bell wire onto its space-facing side with the Clancy clamps—he would only need to stretch a few meters of the wire along the girder, put a clamp over it, spin the disk, and move on to repeat the process.

  But on the 1SS, that required a whole set of other actions. First of all, attached to the structure itself by their tethers, Chris and Denisov were effectively coorbiting with the station—that is, they were bodies occupying their own separate orbits around the Earth that happened to coincide, mostly, with that of the station. Thus there was a tendency, because coorbiting is never perfect, for things to slowly drift to different positions. Everything, including Peter and Chris, had to be on a tether all the time, and tended to drift to the end of the tether, or to wrap around the girders.

  Then there was the matter of having something to push against. If you twist on the disk of a Clancy clamp on Earth, the disk turns easily and the clamp fastens, because the force of your hand turning the disk encounters very little resistance, and the equal and opposite force twisting the soles of your feet in the opposite direction is easily overcome by the friction of your shoes. But in space there’s nothing to control that opposite force; as you turn the disk, the disk turns you, unless you hold yourself in place with your other hand.

  Thus as Chris and Denisov worked their way out to one end of the truss, back to the other end, and then back to the habitat, they had to perform many more tasks than they would have had to do to accomplish the equivalent job on Earth. First, they would move forward to tether themselves, the bag of Clancy clamps, and the coil of bell wire into position. Then they would move back to detach the tethers from their previous positions, and then forward again so that finally after several minutes they were in position to accomplish any progress.

  Then Denisov would take the coil of bell wire and stretch about five meters of wire along the girder, using the previously attached clamps to anchor it behind him and holding onto the girder with his outspread arms wrapping around up toward his shoulders, putting his hands on the “top” so that the wire was held in place where it could be clamped. Then Chris would tow the bag of clamps over, fish out one (with one hand, while hanging on with the other), clip the clamp to his own suit for a moment, close the bag and release it, take the clamp off its clip, fit it over the wire Denisov was holding, brace himself with his other hand, and spin the disk to tighten the clamp.

  After that they would repeat the process again. It took them about six hours in all—plus an extra twenty minutes or so spent in fetching more supplies.

  When Chris climbed back in, he ached in an amazing array of places from the use of so many muscles in such unfamiliar ways, and his coverall under his pressure suit was drenched with sweat. By universal agreement, Chris and Peter got an extra shower that day; theoretically they should then have napped, but within minutes of getting into a fresh coverall, Chris had swallowed some freeze-dried coffee and aspirin, and was on the job of getting the FSRT plugged into the external contact system that Tatiana Haldin and Lori had set up to use the big-loop antenna. In less than an hour, fiddling and scanning, François and Chris had managed to bring in the signal from Alpha Centauri.

  When they were sure that the signal was coming in clear, the data were being recorded, the datalink to groundside was working, and that the FSRT was behaving as it should, Chris stretched and said, “Well, now, finally, I’m going to use some of that flexibility they say we have, and take that nap.”

  By the time Chris arose, the hypothesis that it was an alien signal had gone from the least likely (at least to the well-informed and scientifically literate) to the most likely. François briefed him as he gobbled a quick breakfast.

  “They say it is coming in in a high tone/low tone/blank pattern; if we assume the blanks are spaces, then since it is coming as triple beeps, it looks very much like a transmission in base eight.”

&nb
sp; Base eight, Chris thought; there’s the first clear evidence that it’s really aliens—or at least that if it’s a hoax, someone has really thought the hoax through. The most common numbering system on Earth is base ten. That is we have ten digits, zero through nine, and each place in a number (counting left from the decimal point) represents a power of ten—5280 is 5 x 103 + 2 x 102 + 8 x 101 + 0 x 100, or as we say it out loud, “Five thousand two hundred eighty”—so casually that we don’t tend to remember there’s multiplication and addition in there, five thousands plus two hundreds plus eighty (which is the swallowed English pronunciation of the original “eight tens”). More recently the computer industry has taught many people to work in “hexadecimal”—base sixteen, in which there are sixteen digits (1-9 plus A-E, representing 10-15 respectively), or in bytes, which are base 256 numbers for practical purposes. (16 and 256 are both powers of two, and because the basic machinery of computers, down at the microscopic level, works on binary [base 2] numbers, this makes for compact information storage; if they were not powers of two, some combinations of symbols would have to be meaningless within the system, thus “wasting” some of the potential information it could carry.)

  Almost every schoolchild has used the simple code in which A = 1, B = 2, and so forth, and most people know that newspaper and computer pictures are transmitted in pixels: two numbers to specify a position on the screen or in the picture, and another number to specify brightness (or for a color picture, three numbers to specify the brightness of the red, blue, and green components that mix to produce color). Indeed, in the 1930s Kurt Gödel and Alan Turing demonstrated that any information we can understand can be sent as a string of numbers. Thus, a message from another civilization—if that was what this was—ought to arrive in a string of numbers. But since the base of a number system is arbitrary (there’s no particular reason why it should be ten rather than twelve or five), it would be extremely unlikely that such a message would arrive in base ten numbers.

  Apparently what was coming in was groups of three high and low tones, or, as the Earth-based scientists were shortly to call them, beeps and honks. A group of three beep-or-honk choices could have eight different arrangements:

  beep beep beep

  beep beep honk

  beep honk beep

  beep honk honk

  honk beep beep

  honk beep honk

  honk honk beep

  honk honk honk

  And on some system or other, those probably represented the digits 0-7, which were the digits for a base eight system. The strings of digits would represent pictures or text.

  “Base eight,” Chris said. “So maybe they’ve only got a thumb and three fingers?”

  “Or eight tentacles,” François said. “Or one thumb and one finger on each of their four arms, or they’re all Buddhists and it’s terribly important to them to express things in terms of the Eightfold Way. Or they have three heads and those are all the combinations of nodding and shaking that are possible. It seems to me that for a while here we will be theorizing in advance of data.”

  “Just because it doesn’t have much foundation in fact doesn’t mean we can’t enjoy it,” Chris said. “I wonder if the USRA has anything they can tell me. I can get them by voice relay through the Internet.”

  But he wasn’t able to look into that possibility for three full days. Time in space is terribly precious, cannot be wasted, and if lost, must be replaced. Thus time is planned to the utmost and only the bare minimum needed for rest is left to individual initiative. Normally, because the hardware is expensive, and the equipment needed for making decisions is bulky, heavy, and better located on the ground, people on space missions don’t so much make decisions as execute them. Even (or especially) in emergencies, what ought to happen next is worked out on the ground, right down to how many times to turn a bolt, and the crew in space then carry out the directions with constant monitoring by radio. That doesn’t mean that no one ever does anything on their own initiative, but it’s rare, it’s not supposed to happen, and most of the time when it does happen it’s something brief.

  One reason why this is so is that time in orbit is unspeakably expensive. Just to get an astronaut, cosmonaut, or astro-F into orbit is expensive enough, but after that everything needed to keep him or her alive, for as long as the mission lasts, has to be gotten up to orbit as well. This is true whether the crew is working on an assigned project, resting, eating, or playing cards. The maximum possible work has to be squeezed out of a space crew, and it’s more likely that careful planning from the ground will result in more efficiency than the astronaut’s mere following of whim.

  But this was different; the mystery signal from Alpha Centauri had been a crisis, because no one knew what it was or how long it might last at the start. Now that the FSRT was running automatically, however, no matter how interesting the crew of the ISS might find the signal to be, they had to make up for dozens of lost person-hours on dozens of other important experiments, and everyone had to pitch in and get that work done before there would be any leisure to look at the serendipitous discovery.

  Lori had volunteered to stay an extra week to take up the slack, and even then they did not really have enough hands. Still, NASA understands that people must have rest, and after three days Chris found himself with a blessed four hours, not allocated to sleep, all his own.

  He promptly used it to do more work. “Jiro,” he asked, “I don’t suppose that there’s any way I can access the recorded data from the Alpha Centauri transmission?”

  “Of course there is,” Jiro said, grinning at him. “Join the club. We all spend our recreation time analyzing it. What’s your project?”

  “Well,” Chris said, “I have this idea that the source probably isn’t on either of the stars. That would be insanely unlikely. So I think it’s in orbit around them; and since I have several days’ worth of data now, I bet if I analyze it for Doppler shift, I can at least figure out which of the two stars it’s orbiting, and maybe even plot a rough orbit for it.”

  The Doppler shift is the change in frequency that occurs for waves originating from a moving object; the familiar example is the way that the sound of a car’s engine, as the car passes you, sounds at first like it’s rising in pitch, then like it’s falling. It happens because when the waves are coming from an object approaching you, each successive wave starts out a little closer to you, and thus has a shorter distance to travel and gets there sooner. And as the waves seem to “pile up” on top of each other, more of them arrive in a given time—and the number of waves arriving in a given time is the frequency.

  Similarly, if the object emitting the waves is moving away, each wave starts further away than its predecessor and takes longer to reach you; thus fewer and fewer of them arrive per second, and the frequency seems to decrease. High frequency sound is high pitched; low frequency sound is low pitched; and thus as the car passes you the sound seems first to rise and then to fall in pitch.

  The same phenomenon also happens with light, radio, X-rays, or any other form of electromagnetic radiation; high frequency light is violet, low frequency light is red. Thus by measuring changes in the apparent frequency of radio or light emitted by an object, you can measure whether an object is moving toward you or away from you, and how fast.

  For an orbiting body, this is enough, usually, to figure out a great deal about its orbit. The frequency will rise while the object is on the side of its orbit that has it approaching you; it will fall on the other side. If you know its speed at any point in the orbit, or better still over some part of the orbit, then since the speed with which a body moves in an orbit depends only on the shape of the orbit and the distance from the body it orbits around, the exact pattern of variation of frequency will give you an idea of the orbit’s shape, and from that you have a good guess at its distance. (Because Alpha Centauri is a double star, furthermore, Chris was able to know which of the two stars the body must be orbiting; the orbit of the two stars around e
ach other revealed their masses, and the relation between orbital speed, shape, and distance depends on the mass of the star; the calculated orbit could only be consistent with one of the two stars.)

  The problem was complex and tricky in a way Chris liked, because before he could study Doppler effects in the frequency of the 0.96 mm radio signals from Alpha Centauri, he first had to factor out several known sources of Doppler effects: the motion of the ISS around the Earth (which created a 90-minute cycle), the motion of the Earth around the Sun, and the motion of Alpha Centauri A and Alpha Centauri B with respect to the Sun. His four hours of recreation were almost up before he finally began to see satisfactory results.

  Meanwhile he caught up on his reading about the mysterious signal. The message was repeating, starting over again about every eleven hours and twenty minutes. Each group of 16,769,021 base-eight numbers was taking about two and a half seconds to come in, so that there were 16,384 such groups in all. That was as much as anyone was saying in public.