In 1973 three crews lived in the weightless environment of the sky-lab Space Station. AAPT, with the support and assistance of NASA, has produced twelve single concept films from film footage taken during these missions. Each film demonstrates a concept in the world of zero-gravity physics. Each film is approximately 3 minutes long. The cost of each film is $14.75 to AAPT members and $21.00 to others.
- HUMAN MOMENTA -The astronauts float through the orbital workshop. Various initial conditions of motion are shown.
- ACROBATIC ASTRONAUTS -A complex series of spins, turns, and half-flips looks easy in zero gravity.
- GAMES ASTRONAUTS PLAY - Skylab recreation included darts, paper airplanes, weight lifting, and a balancing act.
- REFERENCE FRAMES - Scenes of moving astronauts taken with a still camera and a moving camera are contrasted.
- COLLISlONS - A sequence of colliding objects, from astronauts to water drops, is shown.
ASTRONAUTICS AND AERONAUTICS
1290 Ave. of the Americas
New York, NY 10019
Included with student dues; $28 per year to nonmembers of AIAA, issued 11 times a year; covers technical developments in aerospace.
AVlATlON WEEK AND SPACE TECHNOLOGY
1221 Ave. of the Americas
New York, NY 10020
$27 per year for qualified subscribers (involvement directly in aviation and space); $37 per year for nonqualified, issued weekly: hard news in the international aviation and space field
Colonies in Space Of the three Space Colony books around at this writing (Fall 1977 - the other two are O'Neill's and this one) Tom Heppenheimer's is the most focussed and out - of - doubt He writes knowledgeably, comfortably, with conviction, offering - to my mind - somewhat too clear a view of the future for the future ever to resemble. The book will date quickly as a result, but it'll feed aspirations in the meantime.
-SB
Colonies in Space
T.A. Heppenheimer
1977; 244 pp.
$12.95 postpaid
from
Stackpole Books
Harrisburg, PA. 17105 or Whole Earth
Suppose we want to get a ton of aluminum. The "recipe" would be:
"Take ten tons of anorthosite. Melt in a solar furnace at 3200 degrees. Add water and quench the melt to give a glassy solid. Allow to settle in a centrifuge; pipe off the steam from the quenching to a radiator to condense it to water. Remove the glassy material from the centrifuge, grind fine, and mix with sulfuric acid. Pipe to another centrifuge to separate off the aluminum-bearing liquid which has resulted. Mix with sodium sulfate and heat to 400 degrees; pipe to still another centrifuge to allow the resulting sodium aluminum sulfate to settle. Remove it after it has settled, and bake at 1470 degrees to produce a mixture of alumina and sodium sulfate; wash out the latter with water. Mix the alumina with carbon, and react the mixture with chlorine This gives aluminum chloride. Put the aluminum chloride through electrolysis. Result: one ton of molten aluminum."
Water fights will be great fun, carried out at long distances. A double handful or pailful of water will more or less hold together under its surface tension, forming a glistening blob which squirms and wiggles in its flight.
The assemblers will not be robots. They will be linked to small computers, programmed to guide the assemblers through repetitive operations on command. For instance, there will be a computer routine which will direct the assembler to make a weld in a given spot; the operator only has to specify the spot. Rather than looking like robots, the assemblers will be similar to numerically controlled machine tools. Such tools have been used for many years. Some of the largest are at the Boeing Company to rivet and assemble jetliner wings without the need for human riveters.
There is one science-fiction cliche which we can immediately dismiss. This is that the homes will use plastic perhaps even be built entirely of plastic. Plastics are made from hydrocarbons such as oil and these will be quite costly in the colony. The precious stores of carbon will cycle through the plants and food, not be locked up in the walls of a home unless there is a clear need (for example, as insulation for wiring). For the same reason, wood may be a rarity even if it is locally grown. The builders will rely on materials readily available. These include the metals aluminum, titanium, and iron or steel. Also there will be plenty of glass, including fiberglass for insulation or soundproofing. Other building materials will also be available from the lunar materials brought to the colony.
For instance, many lunar soils are chemically similar to clay. It should be possible to mix them with water, make bricks, and fire them in a solar furnace. The resulting bricks will usually be gray or chalky in color rather than being red or light brown. Bricks could also be made of cast basalt - a material used in France for tiles, plumbing pipes, and the like - from lunar basalt melted in the same solar furnace. Quicklime, obtained from lunar plagioclase and mixed with water and dry lunar soil, can be used for cement. It is quite common on the moon, nearly as abundant as aluminum. There would be concrete for sidewalks or walls, concrete blocks for foundations, and thin, watery cement to serve as stucco for houses.
A brand new and small space buff publication with appealing zeal. Its regular feature of bite-size reports on wide front of space news is handy.
-SB
Space Age Review
Steve Durst, Editor
378 Cambridge Ave.
Palo Alto, CA 943O6
Michelle Nichols (Lt. Uhura on "Star Trek"):
To black people I say, we'd better get in, sit in, fit in and grow in it as though your very lives depended on it - because they do. Humankind is going into space whether we like it or not. And when we colonize space, we don't want to be there as chauffeurs and tap dancers.
Edited by an enthusiast with libertarian bias, this newsletter is primarily interested in space industrialization, space capitalism, and political freedom in space.
-SB
Earth/Space News
Paul Siegler, Ed.
from:
Earth/Space News
2432 Whitney Dr.
Mountain View, CA 94043
These uses of Skylab are not restricted to the original owner (NASA), for under international law, Skylab is now recognized as a 'Space derelict'. This means the Space station is eligible for salvage claims by any person or organization which can board it first. The same holds true for the multitude of other derelict satellites now voiceless but retaining their high capacity for productive work.
If you want to get up to speed on the detailed progress of Space Colony design and speculation you'll need these books. Both are two years after the conferences they report, so many of the details have been superseded, but also many ideas that later became central doctrine first emerged here and have not been elaborated on since.
Space Settlements reports on the 1975 (the first of three) NASA-Ames Summer Study organized by NASA in California. The style here is group work toward specific design goals. O'Neill and his cohorts participate.
Space Manufacturing Facilities is the proceedings of the first two Princeton conferences organized by Gerard o'Neill, 1974 and 1975 (there have been two more since then). These are individual papers, many of them of considerable quality, on both technical and liberal-arts questions.
-SB
Space Settlements:
A Design Study
Richard D. Johnson
& Charles Holbrow, Eds.
1977; 185 pp.
$5.00 postpaid
from:
Supt. of Documents
U.S. Govt. Printing office
Washington, DC 20402
or Whole Earth
Space Manufacturing Facilities
Proceedings of the Princeton
AIAA/NASA Conference,
May 7-9, 1975
Jerry Grey, Ed. - 1977; 266pp
$19.50 postpaid
from:
American Institute of
Aeronautics & Astronautics
1290 Ave. of the Americas
New York, NY 10019
Christians have a seven-day week. On the other hand, the Balinese have several types of weeks running concurrently: 2-day week, 3-day week, 5-day week, 7-day week, etc. These different cycles "heterodyne" at regular intervals (though not at different frequencies, but at common multiple intervals), and you have a 105-day anniversary, 210-day anniversary, 420-day anniversary, etc.
Most Americans eat three times a day. There are cultures in which the number of meals per day is 1, 2, or 5. In France and Italy, the largest meal of the day is the noon meal, and the "lunch break" lasts 2 to 3 hours.
Heterogeneity between settlements not only increases the probability of the survival of the human species, but also increases the speed of the cultural evolution, as well as enrichment of human life. Furthermore, since we do not know which social systems work well and which do not until we have actually tried them out, we need to experiment with several different social systems.
Magoroh Marayama
Space Manufacturing Facilities
These two publications from the British Interplanetary Society (BIS) supply the very two things lacking in American Space journals - articulate English and disciplined grand speculation. For the Brits, space is an adventure, and their attitude is catching. And their perspective on American and Russian activities (bemused, delighted, appalled) can help prevent deadly ethnocentrism in our planetary endeavors. Loveable mags
-SB
Spaceflight
DR. A.R. Martin Ed.
$22.00/yr
from:
The British Interplanetary Society
12 Bessborough Gardens
London SW1 V 2JJ
England
This is a thoroughly professional book, yet fascinatingly readable and easy to understand. As its title indicates, it deals mainly with the people involved in the Spaceflight Movement, their backgrounds, hopes, aspirations and deeds, and the impact of the Movement on past, current and future history. However, the hardware receives attention adequate to the unfolding of the history of what is undoubtedly the greatest step forward since the Industrial Revolution, besides having far greater ultimate significance than anything since Man's discovery of the Genie of the Bottle - Fire.
The book is in every respect a penetrating and sensitive survey, and there is ample relevant meat therein to provide scores of thinking and talking points. Overall, the book tells how not the public will, but personal fanaticism drove men to the Moon. There are a number of interesting Tables and two Graphs, but no pictures. The inside histories of the great pioneers - Tsiolkovsky, Goddard, Oberth, Sanger, von Braun and others make absorbing reading, with new angles explored.
Space Flight
CONTENTS (MARCH 1977)
Journal of the British Interplanetary Society
Kenneth W Gatland, ED
$16.00/year
SPACEFLIGHT. COLONIZATlON AND INDEPENDENCE. A SYNTHESIS
COSMIC RAY SHIELDING FOR MANNED INTERSTELLAR ARKS AND MOBILE HABITATS
DETECTION OF STARSHIPS
FACTORS LIMITING THE INTERACTION BETWEEN TWENTIETH CENTURY MAN AND INTERSTELLAR CULTURES
MATERIALS IN INTERSTELLAR FLIGHT
SIGNALING OVER INTERSTELLAR DISTANCES WITH X-RAYS
. . . . space flight is, quite literally, the expansion of intelligence that it is one of the keys to the long-term survival and growth of the human species; and that it will change us irrevocably from what we are today.
-JBlS
It's more important to have a recent atlas of the universe than a recent atlas of the Earth-the Earth is pretty well known and politically stable compared to the constant change of information coming in from astronomy and space exploration. When you're very ignorant, as we are about the universe, a little information is a big change.
So, this is the most recent, comprehensive, and spectacular tome on what used to be called the heavens. I use it to cure confusion (where is the asteroid belt?), boredom ("Star Wars'' is only a movie), and egotism (there are only 30 galaxies in the local galaxy group - a small group).
LOCAL?!
-SB
The Rand McNally Concise Atlas of the Universe
Patrick Moore
1970, 1974, 1978; 190 pp.
$30.00 postpaid
from:
Rand McNally & Co.
PO Box7600
Chicago, Ill 60680
or Whole Earth
Local Group of Galaxies
Our Local Group is a small cluster, having less than 30 known members: the spirals M31, M.33 and our Galaxy; the Clouds of Magellan, and smaller elliptical and irregular systems. These galaxies are so close to us that their own peculiar motions mask the effect of the red shift/distance relation.
Our Galaxy contains 100,000 million stars. It has an overall diameter of 100,000 light-years; the maximum breadth is 20,000 light-years, and the Sun, with its planets, lies close to the main plane, 32,000 light-years from the galactic centre.
All good space cadets have first hand observational experience of the sun, moon, planets, and stars, and they use this magazine to keep up with new equipment, discoveries, and gimcrackery such as meteorite rings (''the only rings on Earth with stones from outerspace"), planet photos, etc.
-SB
Sky and Telescope
Joseph Ashbrook, Ed.
$10/yr (monthly)
$1/single copy
from:
Sky Publishing Corp.
49-50-51 Bay State Rd.
Cambridge, MA 02138
Lost for 41 years, the famous minor planet 1936 CA Adonis has been found again. This tiny, faint object is observable only when it makes a fairly close approach to Earth, as in 1936, when the minimum separation was about four times the moon's distance.
I'm afraid that this is going to sound like one of those bar bets, but if one was asked to name the best annual astronomy guide it would have to be Guy Ottewell's Astronomical Calendar.
It has only been around for three years so it hasn't yet received the attention that it should, but already it's replacing the Royal Astronomical Society of Canada's Observer's Handbook
The Calendar is published annually and contains all one wants to know and more about the coming events for the year. Guy himself does the cover illustration (l5'' x 11"), and produces, publishes and distributes the book himself. Somewhat like a Shakespearean play. It seems to work on all levels: the casual amateur or the serious astronomer can read through it and find something to appreciate on every page.
Guy has spent most of his life sleeping out of doors, and as a result the book lacks the cold detachment that turns one away from other similar books.
-Laurence Kent Sweeney
Astronomical Calendar
Guy Ottewell
55 pp.
$4.95 post paid
from:
Astronomical Calendar
Dept. of Physics
Furman University
Greenville, SC 29613
Astronomical Calendar is ready each October, a fine Christmas present.
-SB
And I heard the learned astronomer
whose name was Heinrich Olbers
speaking to us across the centuries
about how he observed with naked eye
how in the sky there were
some few stars close up
and the further away he looked
the more of them there were
with infinite numbers of clusters of stars
in myriad Milky Ways & myriad nebulae
So that from this we can deduce
that in the infinite distances
there must be a place
there must be a place
where all is light
and that the light from that high place
Where all is light
simply hasn't got here yet
which is why we still have night
But when at last that light arrives
when at last it does get here
the part of day we now call Night
will have a white sky
little black dots in it
little black holes
where once were stars
And then in that symbolic
so poetic place
which will be ours
we'll be our own true shadows
and our own illumination
on a sunset earth
-Lawrence Ferlinghetti
Solor sails are a way of moving things around in space, from one orbit to another. After a year's work, they are beginning to look like the best means of space transportation for a wide range of uses: they may be both cheap and fast. Before discussing clipper ships vs. canoes, however, we should first discuss boats and the ocean.
Space is big It would take as many Earths to fill the solar system (500,000,000,000,000,000) as elephants to fill the sea (an unpleasant prospect). The Earth's orbit around the Sun is 23,000 times the Earth's circumference. Driving to the Moon (1/400 of the distance to the Sun) would take six months, at 55 mph of course. Driving to the nearest star would take 50,000,000 years, and so on. Space is Big. To get anywhere you have to go fast.
But, you say, since there is no air resistance in space, perhaps a patient traveler (or load of freight) could start out slowly and simply take whatever time was needed, drifting along. But, alas, gravity is in control. Objects in space don't really go anywhere, if left to themselves; they simply go around in orbits. Unless you kick something so hard that it stops completely (in which case it falls into whatever it was orbiting) or kick it so hard in the other direction that it can fly away despite gravity, never to return, the object will simply grunt at the kick, and shift its orbit somewhat. To get from one orbit to another generally takes at least two pushes: the first to put the object onto an orbit that crosses the orbit you're trying to reach, and another at the crossing point, to make the object start following the orbit you want, instead of the transfer orbit that the first push put it on. Another way to do the same thing is to push gently for a long time, and slowly twist and stretch the first orbit until it matches the second. Either way, you can add up the change in velocity that all the pushing would produce, in the absence of gravity, play around with different directions and times of push, and find that the total velocity change needed has a minimum that can't be beaten for a given trip. This requirement is usually measured in kilometers per second (1 km/sec is about 2,200 mph). One of the lowest requirements of any interest is 2.4 km/sec: the velocity needed to get off the moon.
Rockets have limits, because they must carry mass to throw away. A rocket can reach the same velocity as its exhaust fairly easily; not much fuel is needed to reach a few kilometers per second. The problem is that fuel has mass, just like the payload. Let's say you have a rocket with enough fuel to reach 1 km/sec, and to take a ton of payload with it. How much fuel would you need to reach 2 km/sec? Enough fuel to take the ton of payload to 1 km/sec, and enough fuel to take the fuel needed for the second km/sec to 1 km/sec. The total fuel mass needed turns out to increase exponentially with the velocity reached, just as population has been increasing exponentially with time. Both increases can gobble up more resources than you can afford to provide. Using the Saturn V moon rocket as a first stage, and piling up rockets from there, we could have reached 30 km/sec with enough payload to drop one haunch off an elephant into the Sun (an unpleasant prospect).
Rockets burning chemical fuels run out of ability fast when measured against the solar system, although they were decent for getting us as far as the Moon. The exponential curve that gets rockets into trouble can be made less steep, however, if more energy can be put in the exhaust. This is the principle of the electric rocket; by soaking up solar energy in space and using it to throw small amounts of mass away fast (a mass driver is particularly efficient and versatile at this job), payloads may be pushed around the solar system in a reasonable way. The main problem is the cost and mass of the solar power plant. To use it efficiently accelerations must be low and trips long. Costs are also low: freight rates from Earth orbit to Mars orbit might be as little as $.20 per pound.
Asteroid mining facility with moored sail. Top, right: solar sail(10 km diameter). Top, left; Bernal sphere colony (1/2 km diameter). Bottom, left; asteroid (1 km diameter). Bottom, center; industrial complex. Behind asteroid; mooring tower with shroud lines extending to sail in distance. The pit on the right side of the asteroid has supplied enough material to build this colony, the industrial complex, 50 power satellites and many, many sails like the one shown. The solar system contains thousands of similar asteroids. The sail shown is one of a fleet used for asteroid mining; when loaded (2,000 tons). It will depart for a two year trip to Earth.
Solar sails don't work on the rocket principle, but on light pressure. Like stage magic, this trick is all done with mirrors. Because E = mc2, energy, including light, has mass. For light in particular, that little bit of mass moves very fast through space; when it is bounced off a mirror it exerts a force, just like fast ping-pong balls bouncing off a wall. If you wanted that wall to move quickly, even without friction, you'd want it to have little mass and be hit by many ping-pong balls. Similarly, the mirror that makes up a solar sail should be very thin and lightweight, and have a large area - a square mile of reflected sunlight exerts enough force to support the weight, not of a building, not of a car, a person, or a large dog, but of a medium-sized cat. The name of the game, then, is to maximize acceleration by minimizing the mass per unit area of the mirror.
People have looked at this problem, off and on, for about 20 years. They set themselves the problem of stuffing about a square mile of folded reflecting surface into the nose of a rocket, of launching it, and of making it unfold and stretch into a reasonably flat surface in space. A design for a kite-like sail, with thin, aluminized plastic film for the reflecting surface, has finally reached an advanced planning stage at the Jet Propulsion Laboratory in Pasadena, California. (See illustration on inside back cover.) Their design can accelerate at about 1/7,000 of a gravity, which is actually fairly good: the sail can reach 1 km/sec in about eight days. This lets you get around, and because it needs no fuel, and no fuel to help carry fuel, and so on, it doesn't peter out at high velocities like a rocket does. They want to use it to reach Halley's comet (an object which is going around the sun the wrong way compared to the Earth; a huge velocity is needed): the flight would take four years. They may not get to do it, because solar electric rockets, mentioned above, still look good by comparison (1/7000 of Earth's gravity isn't spectacular) and because these rockets have been sitting in everybody's "come on, let's do it" file for many years. They have seniority.
Can solar sails be made better? The answer seems to be yes, if you forget about folding them up and launching them from the ground. I came to suspect this in the summer of 1976, and now, a year later, it looks as if it may be true: solar sails can be made in space, not as aluminized plastic sheet, but as aluminized nothing, which weighs far less. Designs now worked out on paper use aluminum foil as the reflecting surface, but foil 1/1000 the thickness of the kitchen kind. These sails are over 40 times as light, and therefore over 40 times as fast, as previous designs. This is spectacular.
If I had to draw a sail today, it would be a hexagon about six miles across, and weighing 20 tons. This is somewhere between the size of Manhattan and San Francisco, but the metal of the sail could be wadded up to the size of a Volkswagen bug. They could be made both much larger and much smaller. The sail itself would be a spinning (to keep it taut) metal mesh with long, parallel strips of very thin metal foil glued to it. At regular intervals across the front, wires would come up, and be bundled to form groups, with each group having a wire coming from it, with these wires, in turn, bundled to form groups still farther in front of the sail. After this bundling and re-bundling has concentrated the load of light pressure on the sail enough (that's what the wires are for), shroud lines take the concentrated force to the payload (see drawing).
The sail would be made on a large, lightweight framework, like a loom. Wires would be laid down, and fastened to each other where they crossed. As the wires go down, a device would travel back and forth, producing thin metal foil by vapor deposition on wax, vaporizing the wax for recycling, and laying the foil on the wire mesh. The whole process would take about six months; building the "loom" would require several flights of the Space Shuttle. Additional sails require about one flight apiece to provide needed raw materials. Eventually, sails would be built from extraterrestrial materials.
What can you do with a solar sail? First, how can you "tack"? Boats can go in any direction by using both wind and water; solar sailing vessels can go in any direction by using both light pressure and the Sun's gravity. Light pressure on a mirror is always at right angles to the mirror's surface, even when the mirror tilts and bounces the light at an angle. As the mirror tilts towards being edge-on to the light, the force becomes smaller and approaches zero. This means that the mirror can collect some force in any direction that would take it farther from the light source, in this case the Sun. So how can a solar sail reach, say, Venus, which is closer to the Sun than Earth? By using light pressure to slow down in its orbit, then letting the Sun's gravity pull it in. Solar sails can go anywhere in the solar system, and, in the inner solar system (where we are), they can get there faster than almost anything proposed.
The 20 ton solar sail mentioned above could take 180 tons of payload to any place in the solar system, stop (not orbit, but stop) and hang there on light pressure. With 800 tons of payload to slow it down, it would finally have the same acceleration as a plastic film sail with no load at all. With 6 tons of payload, it could fly to Pluto in one and a half years. Pioneer 11, launched over four years ago, won't reach Saturn until two years from now, and Saturn is only 1/3 the distance of Pluto.
Rough cost estimates suggest that solar sails will cost between $.03 and 1/3 cent a square foot. Kitchen wrap costs about $ .01 a square foot. If nobody throws them out of the solar system, toasts them too close to the sun, or crashes them into something, they should last for thirty to three hundred years. Maintenance costs should be about nil (you don't fix the sail at all, and there are only about two dozen reels for the shroud lines to keep track of). Each sail, without fuel expenses, can cruise around the solar system almost indefinitely. While a rocket must be built differently for almost every mission, the same sail that flies from low Earth orbit to geosynchronous orbit and back can do a perfectly good job of flying twenty times the freight to the asteroid belt, out beyond Mars. Not only that, but the sail costs above, with 10% real rate of interest on capital, can give costs like $.10/lb for transportation around the solar system. And sailboats have always had little environmental impact....
How do (apparently) good ideas like this arise? Well, they never seem to be new. Solar sails are an old idea The literature even contains references to metal film solar sails, although not of the high performance discussed here. It even contains a reference to the idea of making the material in space. When I first had the idea, my reasons were not to seek high performance, but to try to make a sail out of metals, which are readily available in space. My background was oriented towards manufacture in space, towards materials properties, and towards vapor deposition.
Previous workers concentrated on hauling sails up from the ground, but metal film sails are too delicate for that, so they were never studied. The few who considered making the films in space considered inappropriate manufacturing techniques, which either didn't work or produced films about 500 times as thick as optimum.
Many questions come up about the new design:
- Can films be made that thin (thinner than a soap bubble )? Yes.
- Do they have decent strength? Yes, I've made some, and taken them from coast to coast in. my luggage.
- Are the films still reflective when so thin? Yes.
- Will fast moving atoms from the sun knock enough atoms from the film to destroy them quickly? No.
- Will this stream of atoms exert destructive forces on the sail during solar storms? No.
- Will electric charging or magnetic fields cause problems? No.
- Will the films be able to stand the temperatures they reach in the inner solar system? Yes.
- Will meteoroids destroy the films quickly enough to matter? No.
- Will they destroy the wire mesh that is the structure of the sail? No.
- Can the films be mass-produced in space at low cost? Yes
- How much does the device for making the films weigh ? It's manageable.
- What trajectories can the sails fly on? Name it.
- Could the sails possibly find use for near Earth transportation, as well as deep space? Maybe.
- Will the sails ripple under light pressure and gradually tear themselves apart? No.
- How well can the sails be turned to point where you want them to? Well enough.
- Will stresses from changing temperatures cause problems? No.
And so on. Work of this kind never really stops until something has been built and running for a while and people take it for granted. Solar sails of this design have two things going for them: they have passed many tests, and no one has examined the idea and rejected it in the past. At the time of this writing, formal publication and widespread examination and criticism are about to take place. Time will tell, but the chances seem good that we're on to something interesting.
How interesting? As interesting as cheap space transportation, free of fuels and complex maintenance. As interesting as moving Earth's industry into deep space and scattering her life to the Sun's light. Arthur Clarke said: "If man survives for as long as the least successful of the dinosaurs - those creatures whom we often deride as nature's failures - then we may be certain of this: For all but a vanishing instant near the dawn of history, the word 'ship' will mean - 'spaceship.' " And, those ships may yet have sails.
The Jet Propulsion Laboratory in Pasadena, California, has proposed a spinning solar sail where centrifugal force keeps the twelve 4-mile-long sail blades flat. The blades would be 1 mil thick aluminized plastic 25 feet wide for a total area of 600,000 square yards and a payload capability of 1100 pounds. The blades would be variable pitch so that sunlight would spin the vehicle and allow you to control attitude and acceleration and deceleration. Such a vessel could rendezvous with Halley's Comet in 1986.
-SB
(sent by Mike Liebold)