Rama-2

Rama continued

The superconductor is very heavy, about 6.3 million tons, and has a cross sectional area of just 0.01 meters. The cable is almost a meter wide but that's mostly layers of aerogel which weighs very little and layers of reinforcing C60 fullerene nanofiber fabric. A crude calc: 500m*pi=1570m
(3000)(1570)= 4,710,000m Since storage volume is 100m thick- 471,000,000 meters can be coiled, actually more.

The deflector coil consists of a single layer of similar cable. It deflects some particles and "inhales" other particles, pebble sized objects, etc. and sucks them through, depending on charge, so they don't hit the ship and damage it. The deflector field is not powerful enough to create signigicant drag in the thin interstellar medium.

                                                                        The mass beam

At 1G the roughly 25 megaton Star Carrier will travel 2E12 km. in 236 days. s= 0.5gt^2   That's 13,580 A.U. or about 350 times the distance of Pluto.

If the mag-sail loop is 40,000 km. in diameter the magnetic field surrounding it will be about 80,000 km. in diameter. The area of the field will be 5E15 square meters.   If the beam is 5E15m^2 in area and is as dense on the average as the solar wind at 1A.U. and it has a speed of 66%c or 200,000,000 m./sec. We find that in one second: (8.35E-21 kg./m^3)(2E8m/s)(5E15m^2)= 8,350 kg. of mass is ejected. In 236 days (20,390,400 seconds) a total of 1.7E11kg. or 1.7E8 metric tons of mass is ejected. That's about the mass of a small cometary body 700 meters in diameter with a density of 1.0g/cc. Since the propulsion beams will be firing in opposing directions to stay on station we will need at least 340 million metric tons and there will be inefficiencies due to beam dispersion, "slippage" past the mag-sail, and possibly other factors that increase requirements for beam mass. If we allow a factor of ten we need 1.7 billion tons of mass or a comet about 1.5 km. diameter with a density of 1.0g/cc. Seems feasible.

Earlier we calculated that 7.45E26j would be needed to propell the 25 megaton ship to 66%c. If the artificial minature black hole was 10% efficient ( it could be up to 40% efficient, but let's be conservative) at converting mass to energy we would need to "feed" it about 4 tons of matter per second or a total of about 80 million tons. Some mass would become energy as it spiraled into the "hole" and some would be absorbed. The object would become more massive and more powerful with time. Some mass would be ejected at relativistic velocities from the accretion disk of the spinning charged object.

To energize 1.7 billion tons of beam mass to 66%c we would need 5E28j. Due to relativity this mass would increase by about 50% and that would increase effectiveness of the beam. About 5.55E11 kg. or 5.55E8 tons of matter must be converted to energy. That's about 27.7 tons per second or 277 tons per second with a 10% efficient "hole" that we must "feed" for 236 days. That much matter could be gotten from a comet about 2.2 km. in diameter. If 27.7 tons of matter converts to energy every second and the other roughly 250 tons of mass is absorbed or spews out of the jets there will be plenty for the mass beam since we only need 8.35 tons/second or 83.5 tons per second due to inefficiencies( opposing beams, dispersion, "slippage" past mag-sail, etc.)

So it looks like we could feed small comets into giant driver beams with spinning aritificial minature black holes in them and generate high speed mass beams for propelling interstellar mag-sailers of great size. A better idea might be to build skyhooks around gas giants like Uranus or Neptune (Jupiter's gravity might be too high) and pump up hydrogen and helium gas to feed into the propulsion beams. Some very powerful turbo-pumps would be needed to raise gases up through thousands of miles of C60 fullerene pipeline to the orbiting Star Drivers. Immense energies from the mini-BHs radiated in the form of x-rays not absorbed by the plasma beam mass (Bremsstralung, synchrotorn) will be available to run pumps and other machines including flywheels perhaps that are used to adjust the attitude of the Star Drivers. These Star Drive machines would be rather fantastic achievments of mega-scale engineering.

Using gases from the atmospheres of Uranus or Neptune might be easier than capturing comets; however, in the Oort cloud we could make use of cometary material to feed beams for travel between distant cometary colonies and the inner solar system or between cometary colonies in interstellar space. These Oort cloud based beams might be used to apply mid-course corrrections to interstellar vehicles accurate interstellar navigation. If beam dispersion is a problem over great distances then a series of beams starting out at gas giant planets and more beams at comets might be built. Since some of these distant objects have orbits lasting millions of years they won't go very far in any reasonable span of time. An object at 10,000 A.U. travels in circular orbit at only 300 m/s and at 20,000 A.U. 210 m/s. A light year equals about 63,000 A.U. An object at 20,000 A.U requires 2.8 million years to circle the Sun once. So it takes almost 8000 years for an object at 20,000 A.U. to move through one degree of arc. Oort Cloud based beams won't go very far off station and they can fire beams of plasma over great distances to correct the courses of interstellar vehicles using mag-sails.

                                                          About Solar Wind Gas Harvesting

At 0.1 A.U. or 15 million kilometers from the Sun a 1000 km. wide magnetic scoop with an area of 7.85E11 square meters could harvest only a very small amount of matter. If the density of the wind is 100 times than at 1 A.U. or 8.35E-19 kg/m^3 and travels at 5E5 m/s then:

(7.85E11m^2)(5E5m/s)(8.35E-19kg/m^3)= 0.327 kg. per second! That's nothing!

With a scoop ten times wider we could only harvest 32.7 kg./second. Still nothing. However, a magnetic scoop may be able to accelerate solar wind ions into its clutches. If powerful enough it could suck lots of matter. It might even siphon 6,000 degree K. plasma from the surface of the Sun. This plasma would be contained within the intense magnetic fields of the beam device. Insulating the superconducting coils might be a problem but that could be solved with layers of reflective material and aerogel perhaps. Would the machine pull itself into the Sun with its magnetic suction scoop? Perhaps it could use mag-sails or solar sails to overcome this effect. Some grand engineering would be required for these machines.

                                                    Getting Around in a Solar System

If Star Terminals are located in close stellar orbit, about the same distance as Mercury from stars like our Sun, we might have a problem if propulsion beams cannot get enough mass from the star they orbit. Interplanetary ships could use solar sails and ride microwave beams from the Star Terminals out to the worlds of the system as well as mag-sails on the natural stellar winds. If our 25 megaton starship must ride out to Uranus on the natural solar wind it will reach a speed of:

At .316 A.U., roughly Mercruy's distance from the Sun, p=8.35E-20

D/M= 0.6 {(12.56E-7)[(8.35E-20)^2][(5E5)^4](20,000)/100,000}^0.333{2E6}=
0.0575 m/s^2

The weight factor was about 3 so actual acceleration would be only 0.019 m/s^2
in one hour the vessel accelerates by 69 m/s
in one day 1.66 kps
in ten days 16.6 kps

Even at this speed in addition to Mercury's orbital speed it will take years to reach Uranus. Perhaps the vessel could decelerate and dive around the Sun at low altitude, picking up a great deal of speed, and then use solar wind pressure to propel itself away from the Sun and acquire a high hyperbolic excess speed.

It may be possible to use a bigger mag-sail or attach light sails to the mag-sail loop to catch light from the Sun and laser or microwave beams from stations in near solar orbit. If propulsion beams can stay "tight" over a distance of several thousand A.U. then beams from other gas giants in the outer system may propell the craft. Other solar systems would need gas giants in the right place. So called "hot Jupiters" are in very convenient locations. Close to their parent star they would allow frequent launch windows from orbiting Terminals to other worlds in their systems by smaller ships and skyhooks could harvest their mass for propulsion beams of high power. In our solar system it might be possible to use skyhooks to harvest mass from the atmosphere of Venus to supply mass to the driver beams. Ions of carbon and oxygen might not acquire the high velocities of hydrogen and helium fed into the "holes" but they would be fast enough to propell our Star Carriers out to the more efficient beams of hydrogen and helium from Uranus or Neptune. Siphoning material from the Sun is still an interesting possibility for mega-scale engineers of the future, if it is even necessary with so many "hot Jupiters" having been detected and in our own system the planet Venus.

Using the Star Carrier's fusion thrusters might work. I pictured these thrusters for orbital maneuvering and docking at stations in space. They could also be used for obstacle avoidance perhaps and attitude control.    At high exhaust velocities reaction mass requirements are reduced but energy requirements go way up. If the ship has fusion engines with 18,000 kps exhaust velocity then to reach 1.6 million kph or 444 kps and get out to Uranus in about two months we need 624,000 tons of reaction mass; not too much for a 25 million ton vehicle to take on. We will need 1E23 joules to energize this mass. If we take ten days to accelerate we will need 1.2E17 watts of fusion drive power. If fusion engines with 3700 kw./kg power densities are used we need 31.6 million tons of engines! If we take 20 days to accelerate we are down to 15.8 million tons of engines but Rama amasses about 25 million tons! The only solution is to use a tug that has whopping fusion engines and tanks for LH2 to haul the mighty Rama out to Uranus or Neptune where the Drivers are. The tugs would be almost all engine and fuel tanks with some structural components and AI robotic brains. We could also take more time to accelerate and travel at a slower velocity also, but I am impatient! Propulsion beams in close stellar orbit harvesting gases from a star, hot Jupiters or the atmosphere of a planet like Venus will be used if and where they can. In their absence we will need tugs to haul Star Carrier's around. Star Drivers could also be built in orbit around Titan or within the rings of Saturn.

                                                                           Braking

The interstellar medium only has a density of 1.67E-22 kg/m^3. A much larger mag-sail is needed to slow down. Since it is likely that replicating robotic colony ships will precede human travelers followed by smaller colony ships than Rama carrying humans who superivse the robots and solve problems that the machines cannot to build bases on asteroids, moons and planets, propulsion beams for return flight, terminals and interplanetary ships, there could be massive propulsion beams that are used to brake the ship as effectively as it was accelerated at 1G. The first ships would have to brake in the interstellar medium, but this is possible according to Dr. Zubrin.

                                                                 Who Builds All This?

I envision a time, centuries from today, when humans are freed from need and want by robotic factories and farm machines. At first humans will build the robots. Then we will program the robots to build robots. There will be more than enough for everybody and humans will devote themselves to art, education, recreation and other pursuits. Some will play with technology because it interests them. Being rich could get boring and there's a limit to how much one can party! The people who build the fantastic beam driver network will be people who are smart enough and motivated enough to program their personal robots to make more robots. Raw materials will be plentiful from the asteroids of the solar system and there will be no competition for these raw materials if we don't populate like fruit flys! People will learn to live for purposes other than breeding and genetic modification as well as advanced contraception will make that possible. If they don't the human race will go extinct in short notice due to over popluation. The people who build the beam driver network will multiply their robots and then use them to build the necessary machines. They will be amongst the more technologically intelligent of future people. Will they then sell tickets for interstellar voyages and form mega-corporations and get fabulously rich? Or will they do it all for the thrill of it? Or will governments take on the task of creating interstellar mass transit? Sounds like socialism and we don't like that (Who are "we?" Good question.).

comments on navigation: A friend says to me,"Dave, aren't half your Driver beams going to be on the opposite side of the Sun or the planet Uranus or Neptune? And what about those beams shooting through the solar system? Won't they hit other planets? See: Sky Mining

Well, my pal isn't thinking in 3D. Most of the nearby stars are out of the plane of the ecliptic. I can see this with my beloved star globe. The Alpha Centauri system is to the south. The propulsion beams will be firing at right angles, more or less, to the plane of the ecliptic, so they will not be eclipsed by the Sun or any planet they orbit and they will not blast any planets in the solar system.

As the Star Carriers leave the solar system precise aim will be needed by the beams. The Sun will cause their trajectories to curve somewhat as they leave space in the outer solar system. This problem would not be so great if the beams are in close solar orbit, but then Sol's gravity has to be fought also. At slow speeds the Carriers will be influenced by the gravity of Uranus or Neptune and Sol, so this complicates navigation. Once they are at high speeds they will travel away in nearly straight lines. If necessary, beams in the Oort Cloud could apply mid course corrections. A slight error in line of travel could add up to missing the target solar system by a vast distance. Fortunately, as the Carriers head towards Centauri or Sirius they will fall into their gravity wells and be pulled into comet like trajectories. There's another problem. At about 200,000 AU, approx. 3.17 light years, the gravity of the galactic core exceeds that of the Sun.* On our way to Centauri we will already be in the gravitational influence of that triple star system. On our way to Sirius, 8.6 ly distant, we will be affected by the galactic core. This will complicate interstellar navigation. Propulsion beams in the Oort cloud, stationed decades beforehand, using comets for beam mass, may be essential. We can adjust the outgoing trajectory of the Carriers also so that when they encounter the gravity of the core in interstellar space they are actually pulled into the correct line of direction for interception of the target star system. This will give mathematicians something to busy themselves with! Propulsion beams of the target solar system in orbital planes at right angles to the incoming path of the Carriers could guide the Carriers in. This would require that the Carriers be capable of adjusting their sail's attitude so that they can "bank sideways." Data on the Carrier's position and trajectory would have to be radioed well ahead of time to the beam stations. Beams at great distance from the target star in orbits at right angles to the starship's trajectory could push the Carrier into a trajectory that makes closer approach to the target star.

If the Sun was a foot in diameter, Uranus would be 2000 feet away. Alpha Centauri would be 5400 miles away. The line from Uranus to Centauri is about as straight as the line directly from the Sun, but lateral velocity along this line, even a little, could cause a miss. Sol's gravity might sort of "focus" the Carrier onto a line connecting it with Centauri. Navigator's of the future will allow for all these effects and aim the beams accrodingly.

Constructing all these things will require some fantastically intelligent robots, and humans of equal intelligence to design the robots. Space supplies plenty of raw material from asteroids, moons, comets and planetary atmospheres.

What decides who gets to travel to other star systems and who stays home? Merit? Volunteering to work on the project? A lottery? The communist party? Nope. That magic decision maker is going to be the very foundation of civilization, law and government-money. I think we will just never get away from the stuff even in the replicating AI robotic mass production future. It's too useful. If you want to travel to another star system you have to earn the coin to get the priviledge of doing it. If you aren't motivated to make the do re me and are happy living on Earth or Mars or in a space colony doing something that doesn't bring in the big bucks, then it won't matter to you if some thrill seekers get you to buy their cars, boats, airplanes, software, CDs, VR productions (cyber entertainers and cyber you know whats), old fashioned books, paintings, sculptures, legal advice, medical treatment, life extension and rejuvenation treatments, reproductive and genetic engineering services, college educations, gourmet meals, whacky inventions, houses, clothes, shoes, jewlry, perfumes, tatoos, hair styles, suits, electronic gizmos, stay in their hotels, visit their casinos, go to their sports events, drink their beer responsibly, subscribe to their magazines, etc. Since possession is 9/10s of the law we can be certain private property and money will last as long as civilization does. Stock brokers and accountants will be happy to read that prophesy. What if you are one of the poor (by tomorrow's standards) welfare recipients of tomorrow that society can't come up with a job for and the robots make it possible for you to have nutritious food, medical care, a car, home, and most of the good things in life that middle class people today want or you live in a simple dome home in a rural commune of spiritual types somewhere who shun the glitz and glamour of the big cities but you want to travel to another star system anyway? Well, there are contests, game shows, and you might have a rich relative who wants an interstellar family reunion who will find you and pay your way. Maybe I'm being superstitious again, but if you really want something, somehow you will get it, and I don't mean by stealing or stowing away!!

ABOVE) Presuming it is impossible to mine enough mass for particle beams from stars, in star systems where there are no hot Jupiters near the star or other planets near the star with atmospheres that can be mined for mass beams, a fusion powered tug as mighty as Rama itself pushes the Star Carriers with great speed (250 to 500 kps) out to distant gas giant planets where propulsion beams and atmosphere mining skyhooks are located so that Rama can catch a beam back to our solar system or to another star system. Liquid hydrogen for the tug comes from ice moons and the atmospheres of gas giants. Rama and the Tug use mag-sails to brake in outer stellar systems as they encounter the solar wind perpendicularly. The Tug reloads with LH2 at the gas giant planet and returns to inner system Star Terminals and mag-sail brakes into near stellar orbit with enough LH2 left to propell another Rama out to the propulsion beams.

ABOVE) Rama class Star Carrier, 40,000 passengers, compared to Island 3, a 20 mile long space colony home to millions of people.

Another Strategy Entirely

Why brake Rama into a star system and reaccelerate the vessel to 0.66c? That will require a tremendous amount of energy. And why haul the vessel around with a huge tug? Let Rama fly-by the destination star system and just have small pods of comparatively tiny mass, carry the passengers into the destination star system. It will take far less energy to brake the pods. Travelers wishing to venture farther out into the galaxy could ride in mag-sailing pods propelled by mass beams to rendesvouz with Rama and get on board! If each pod carries 400 passengers like a big wide bodied jet then we need 100 pods to convey all 40,000 passengers. Some could ride in the pods to the near-star Terminal and others could ride the pods directly to worlds in the star system they want to visit. If each pod amasses 1000 tons then 100 pods only amass 0.4% of Rama's mass. We only need 1/250th as much energy to brake the pods as we would need to brake Rama on a mass beam, and we only need 1/250th as much energy to accelerate pods to dock with Rama as we would need to reaccelerate Rama. That's an incredible saving and mass beam projectors could be reduced by a corresponding degree. So we only need 1/125th as much energy and mass beam projector capacity to deal with pods to and from Rama. We don't need the tug at all. We will need energy to power mass beams to deflect Rama as it flys by on to a course that takes it to a star system further out. Even so, the energy required to deflect Rama will be far less than that required to brake the vessel and propell it up to speed again. See: Interstellar Shuttles

* data from Richard P. Terra, "Islands in the Sky, Human Exploration and Settlement of the Oort Cloud." pg. 97. Islands in the Sky. ed. Stanley Schmidt and R. Zubrin. Wiley:1996.