A Step Farther Out

by Jerry Pournelle

  Finally: what makes the Sun shine? It does, you know. Some theorists now wish it didn't. (Sure: that would kill us all, but doggone it, it sure wrecks good theories.., .)

  Open any astrophysics or intermediate astronomy textbook, and you'll see confidently asserted a series of equations showing where the Sun gets its energy. Take four protons (hydrogen nuclei) and squeeze like mad; outcome four alpha particles (helium nuclei) plus two positrons plus two neutrinos. Adding the mass/energies of the input protons and subtracting out the masses of the output discloses some mass missing: enough to generate 25 million electron Volts, and thus the Sun shines.

  So, a number of years ago, theoretical astrophysicists devised an experiment which would confirm this so generally accepted theory. It wasn't supposed to be an exciting experiment; but after all, we know more about the Sun than any other star, most of our astrophysics theories are deduced from stellar observations and most of those are of the Sun, and it always helps to have confirming experiments of basic theory. Hans Bethe settled it theoretically back in 1939, but it couldn't hurt to do an experiment even if this was the best understood aspect of astrophysics.

  So, out in the old Homestake mine, was installed 100,000 gallons of perchloroethylene, C2C14, and a very elaborate system for counting what happened when neutrinos struck the chlorine. (That generates argon.)

  The 37Chlorine to 37Argon reaction expected from solar neutrinos was worked out by Dr. John Bahcall, Professor of Natural Sciences, Institute for Advanced Study about fifteen years ago. The unit is the "SNU" (pronounced "snoo"), about 10-36 captures per target atom per second: not very many, meaning that one needs a lot of 37Cl and a long time before you expect to see anything happen.

  Raymond Davis and John Evans of Brookhaven National Laboratory worked out the actual test equipment, which involves finding 15 argon atoms per month in that immense tank of cleaning fluid. They have also tested the procedure, injecting known numbers of argon atoms into the system and recovering them. To the best of everyone's knowledge that experiment ought to work, and the neutrino capture rate in the tank ought to be about 6 SNU.

  The observed result: a maximum of 1.3 SNU, and possibly none at all. This is astounding. Has the Sun gone out?

  Dr. Bahcall is a careful man. He wanted it clearly understood that he still believes the textbook proton-alpha reaction is the explanation for why the Sun shines. However, when pressed, he will discuss what he calls "cocktail party" theories: that is, theories that a scientist might put forth in a cocktail party, but which one has no business publishing in a serious journal.

  "Unfortunately," Dr. Bahcall told us, "a lot of cocktail party theories have been published. . ."

  There are three major classes of theories to explain why we have observed no solar neutrinos: those that horrify astronomers, those that horrify physicists, and those that drive both up the wall.

  The astronomers like to think something happens to the neutrinos on the way here: they're produced all right, but they're a lot less stable than physicists thought they were.

  After all, the only observations of neutrinos have been in paths from a few centimeters to a kilometer or so long; perhaps over longer distances they decay into something else. Most physicists don't care much for that theory.

  Physicists, meanwhile, have always felt that astronomers don't really understand stars as well as they think they do. Thus, Dr. Bahcall says, the failure of the standard theory just proves to physicists that they're right in being skeptical about what astronomers say. (Not that Bahcall himself has this attitude, but it is widespread.)

  The result, anyway, has been what Bahcall describes as a theoretical orgy, mostly of "cocktail party" theories. Item: the Sun has "gone out" and periodically does so, reigniting after a period of gravitational collapse. Item: there's a black hole of around 1% of the Sun's mass dead center in our star, and the Sun shines because matter falling into the hole gives off energy, there's no fusion in there at all. Item (a theory that really drives astronomers nuts): suppose all the heavy elements in the Sun are concentrated in the outer layers (for reasons no one can give); then the results would be consistent with neutrino observation.

  Whatever is the explanation, there's probably a Nobel Prize in it, which may explain why the Soviets are spending enormous sums, really a lot of money, on solar neutrino experiments. They're scaling up the Davis experiment by a factor of 10 in a tunnel under a mountain (these things need to be down deep to keep the cosmic ray counts low enough so that the solar neutrinos won't be hidden in a fog of interactions).

  There's one final possibility, strange, but not out of sight: that the Sun operates, not on the

  4P—>4α+2e++2νe+25 meV

  reaction I described earlier, but through the PeP reaction: a proton plus an electron plus another proton yields deuterium (heavy hydrogen) plus one neutrino i.e.,

  P+e-+P—> 2D1+νe

  which as you can see produces just half the number of neutrinos, and they're at a lower energy level too, so that the expected SNU should be about 0.3—and that's just consistent with the observed data. (NOTE: there's no proof that we have found any solar neutrinos; but the likely level is in the order of 1 SNU.)

  Now the astronomers will not like it if the Sun turns out to run on PeP; but their unhappiness is as nothing compared to what will result if experiment shows no solar neutrinos at all. Lower than 0.3 SNU requires something really far-out, strange, new, different, a theoretical restructuring along the lines of Einstein's work.

  All of which proves we don't understand our universe quite as well as some of us think we do, and that shouldn't be any surprise. Stand by. In anthropology, immunology, energy technology; astrophysics; in these and many more fields, exciting things are happening. Like it or not, the Age of Marvels is not over, and I confidently expect that about half the things I think I know will be obsolete in five years.

  We don't even know what makes the Sun shine!

  * * *

  It's 1979 and we still don't know. I thought when I wrote the above that before it could be published in book form we'd have new data. We do not, and the unfinished story is still the best we have.

  Unfortunately the same is more or less true in fusion research. President Carter has given the program something less than enthusiastic support. His predecessor cut the budget, but Carter cut it again. One wonders if the US government wants fusion.

  In 1976 a Soviet expert named Rudikov came to the United States. The Soviets are very interested in fusion; they need the energy, to help them develop the vast regions of Siberia and Turkestan and Soviet Asia. They are also quite aware that US science and technology is generally more advanced than their own, although in some areas of fusion research they lead us. Rudikov went to great pains to get the Soviet authorities to declassify his work; he came to the US to propose a cooperative effort, and gave a briefing at which he showed the work he had been doing and the results he obtained.

  The US authorities immediately classified his talk They quite literally hung a blanket over the blackboard Rudikov used in his lecture! If you wonder from whom they were keeping this secret, join the club. I wonder too.

  Then in November 1977 Nikolai Bassov, the Soviet laser expert and Nobel Prize winner, came to the US and at a meeting in Fort Lauderdale, Florida, presented his results—including the announcement that his laser fusion experiments have exceeded the Lawson Criterion by a factor of five: i.e., he has reached scientific breakeven.

  Once again the US authorities classified the information. Meanwhile Carter has cut the fusion budget to the bone, and as I write this they're laying off people in the fusion labs. Carter declares war on the energy crisis and as his first marching order disbands the armored divisions; in his address to the nation he used the word "research" precisely once, and that in passing; he mentioned fusion not at all.

  —JEP, Hollywood, Spring 1978

  Highways to Space

  Some readers will recall that in my science fiction stories I often po
stulate laser-launching systems: that is, a very large laser that stays on the ground provides the energy to put spacecraft into orbit. It wasn't my invention: I took the concept wholesale from a paper by A N. Pirri and R, F. Weiss of Avco-Everett Research Center, and they got the concept from an earlier paper by A. R. Kantrowitz. It's not only feasible, it seems inevitable.

  The concept is rather simple. Take a number of lasers, and shine the output of each into a mirror. Use the mirrors to direct all that laser energy into one big steerable mirror.

  The spacecraft look normal enough, and can mass up to about a metric ton (2200 pounds). They have a bell-shaped rocket chamber at the bottom. The laser energy is directed into that chamber. It heats the air in there; the air, being heated, comes out through the nozzle—exactly as does the heated gas from a conventional rocket.

  Now pulse the laser beam; about 250 times a second seems to work. Enough air gets into the rocket chamber to provide reaction mass; the capsule rises, with the laser beam tracking it as the mirror is steered. When the capsule gets high enough so that the air is too thin to work as reaction mass, fuel from on-board tanks is pushed into the rocket chamber; the laser still provides the energy (and because it does there's no need for heavy pumps and compressors and such).

  Eventually the capsule gets to space: the laser cuts off and a very small solid rocket is lit off to provide the last few pounds of thrust to put the capsule in orbit.

  That's the concept, and I think I was first to use it in a science fiction story. Imagine my surprise, then when at an AAAS meeting I heard Freeman Dyson give a lecture on laser-launched systems as "highways to space."

  Dyson is, of course, one of the geniuses of this culture. His Dyson spheres have been used by countless science fiction writers (Larry Niven cheerfully admits that he stole the Ringworld from Dyson), One should never be surprised that Freeman Dyson—perhaps I should rephrase that. One is always surprised by Freeman Dyson. It's just that you shouldn't be surprised to find you've been surprised, so to speak.

  Dyson wants the US to build a laser-launching system. It is, he says, far better than the shuttle, because it will give access to space—not merely for government and big corporations, but for a lot of people.

  Dyson envisions a time when you can buy, for about the cost of a present-day house and car, a space capsule. The people collectively own the laser-launch system, and you pay a small fee to use it. Your capsule goes into orbit. As I have proved elsewhere (in the first Galaxy column I ever wrote, entitled "Halfway to Anywhere," April, 1974), once you're in orbit you're halfway to anyplace in the solar system. Specifically, you're halfway to the L-5 points, if you want to go help build O'Neill colonies. You're halfway to the asteroid Belt if you'd like to try your hand at prospering. You're halfway to Mars orbit if that's your desire.

  America, Dyson points out, wasn't settled by big government projects. The Great Plains and California were settled by thousands of free people moving across the plains in their own wagons. There is absolutely no reason why space cannot be settled the same way. All that's required is access.

  Dangerous? Of course. Many families will be killed. A lot of pioneers didn't survive the Oregon Trail, either. The Mormon's stirring song "Come Come Ye Saints" is explicit about it: the greatest rewards go to those who dare and whose way is hard. And if we've such a horrendous surplus of people on this planet, why is it that the same people who are so enamored of Zero-Growth also want to protect everyone from every conceivable risk? Dyson's vision is different Perhaps his first name has something to do with it? Because he's right, you know. That kind of Highway To Space would generate more true freedom than nearly anything else we could do; and if the historians who think one of the best, features of America was caused by our open frontiers, and that we've lost much of our freedom through loss of the frontier—if they're right, we can in a stroke bring back a lot of what's right with the country.

  Why don't we get at it?

  "Come Fly with Me"

  Hot Diggity Dawg! I am so excited I can hardly stay in my seat.

  Which, when you come to think of it, is a pretty strange reaction to my having been to a scientific/engineering conference, namely the 'Third NASA Conference on Radiation Energy Conversion;" or is it? Before I'm through with this chapter, I hope to have you jumping out of your chairs too.

  The conference title doesn't tell much; but look at the session titles, and maybe it will begin to dawn. Laser Energy Conversion; Space Solar Power; Radiation Enhanced Chemistry, Solar Pumped Lasers. No? Well, I admit that the bare titles didn't exactly turn me on, either. I did have to attend: so far as I know I published the first science fiction story in which spacecraft are launched by ground-based lasers ("High Justice," which is included in the book by the same name, available from Pocket Books if you haven't bought it yet) and one paper was to be on laser-powered spaceflight. If that wasn't enough, there were also papers on solar-power satellites, and given my interest in both energy and space that's impossible to pass up.

  Those papers were excellent, and I'll tell you about them in due time; but the real kicker was presented by Kenneth Sun, a graduate student at the University of Washington, the paper itself co-authored with his professor, Dr. Abraham Hertzberg. It was called "Laser Aircraft Propulsion" and who'd have thought it would be the liveliest thing I've heard all year?

  But it was. One of the problems with advocating space exploration is answering the question "Yes, but how can we make any money out of it? How can investments be paid off? Don't tell me about new knowledge and all that, or about pie-in-the-sky fifty years from now; what I want to know is, how can we profit in a reasonable time?"

  And the answer to that one is hard to come up with. As I discussed in the column on space industries, we have a number of concepts that look good to make money: manufacture of exotic materials such as high-coercive-strength magnets, which is easy in zero-gravity and very costly here on Earth; biochemical research; and of course space power beamed down to Earth; but every one of those is a "maybe" because of the unknown costs and unpredictable market for the products. (Energy will have a predictable market, but the cost of space power satellites is so very large compared to the same costs for kilowatts here on Earth that you need faith to invest in SPS.)

  Comes now Sun and Hertzberg to give an answer to that question.

  We'll pay for space satellites by using them to power airplanes; and the savings will come in money we don't have to pay the Arabs for kerosene (otherwise known as jet fuel).

  Sun and Hertzberg are quite serious—and their concept uses nothing but off-the-shelf technology. The airplane is a present-day machine; by a coincidence that hardly surprises you, the Seattle team studied a Boeing airplane. The aircraft is just barely modified: the regular engines and fuel tanks are left intact. The tail (vertical stabilizer) is twinned for reasons which will be obvious in a moment; otherwise the only modification is the addition of a new engine on top of the fuselage.

  The engine looks like a regular turbofan jet engine, except that in the middle, where the combustion chamber would be if it ran on kerosene, they've placed a big box-like heat exchanger. The top of the heat exchanger is a laser target. Laser energy shines onto the target; heat goes into the system; air comes in from the front through a compressor, and is heated, just like in a regular jet engine, except that instead of getting the heat from burning kerosene it gets it from the heat exchanger; and lo, the airplane flies.

  It takes off under normal kerosene power. It carries aboard enough fuel to go some 900 kilometers if it loses the laser power. It lands with its usual engines. True, there's a bit of drag from the additional engine up on top, but the reduced fuel load more than compensates. Understand, Sun and Hertzberg have made no attempt to optimize the system. They have taken an existing aircraft and (on paper—no working model yet) modified it. Everything is to be kept simple.

  Kerosene at present sells for about $1.00 a gallon. It is hardly unrealistic to assume that within a few years
the price will be $1.00 a liter, or about $4.00/gallon. Thus the saving is significant, given what a jet plane consumes while flying.

  The effect on the upper atmosphere is all to the good, too. There's no contrail from the exhaust. No exhaust. No water vapor to form clouds. No oxides of nitrogen. Nothing but hot air.

  Fine. Where are they getting the laser power?

  From a satellite. A very dumb satellite. The power plant is nothing but a vast grid, something like 3 kilometers by 1 kilometer, covered with presently-available solar cells operating at present efficiencies of such. At each end of the satellite is a very large CO2 laser with mirror for steering so that it can track the aircraft. The airplane has a small laser for "handshaking" communication with the satellite, thus aiding the satellite in tracking its target.

  And that's the system. Everything, including the laser, is off-the-shelf. This being an unclassified conference there wasn't and couldn't be much discussion of the big military lasers we all know exist; but nobody seriously doubts that a laser of the proper power could be built.

  The satellite is a grid of carbon-filament structure, nothing difficult to build. It can be rolled or folded up in segments and carried in the Shuttle. The grid, partly assembled on Earth, can be unrolled—if you've never seen some of the new carbon-filament stuff, you'd be amazed at how strong it can be and yet roll up like whalebone—once it's up to low earth orbit (LEO), after which it is covered with solar cells. The electricity generated by the cells is used to drive an ion engine—also off-the-shelf—which takes the satellite up to geosynchronous earth orbit (GEO).