| PHOTON DRIVE? A curious thing about black holes is that the smaller they are, the brighter and hotter they are with Hawking radiation. Perhaps a larger black hole combined with a larger ship would work better. Earlier, I envisioned Rama to amass 2.5 billion tons propelled by solar powered mass beams energized by the immense energies of the Sun collected with a partial Dyson shell that I dubbed RAVEN (Relativistically Accelerated Vehicle Energizing Node). I abandoned this because I thought it was too grandiose. Things may now turn full circle. If we build a 2.5 gigaton vessel and equip it with a black hole 100 times more massive than the one discussed earlier, or a BH of about 770 million tons mass, we have about 1.7 billion tons for the ship itself. Something this big would be more than a ship. We could call it an ark or a star carrier if you like that term. If it has four passenger spheres each 2 km. wide with 5 tons per square meter of radiation shielding, the shield mass will be about 250 million tons, and the rest of the ship would amass 1.45 billion tons, mostly structure, superconducting coils and fusion generators. The passenger volume will be 64 times larger so about 2.5 million people could travel in this vessel. Now we are looking at something more akin to Sir Clarke's Rama vessel. The black hole will have: lifetime = 3.8E19 seconds = 1.2 trillion years approx. Temp. = 1.59E11 deg. K. luminosity = 602 megawatts thus a 2 km. diameter magnetic containment will be illuminated by only 48 watts per square meter. A more massive hole won't fry our containment structures! Peak wavelength = 1.82E-14 meters or 1.82E-5 nm frequency of radiation = 1.65E22 hz energy of rays = 68 MeV So we are still dealing with hard gamma rays, most which will pass through structures and some ionization will occur Rs = 1.141E-13 cm A charged spinning black hole generates a twisted magnetic field and plasma jets originating from the accretion disk. Since even this object will be tiny it's gravity will not reach very far, thus matter from the ram scoop must be focused onto the hole with magnetic coils. As the particles spiral in they will collide with each other, endure friction, and heat up with 6% to 40% mass converted to energy depending on the rotation of the hole. If we can make such an object, probably by starting off with a small one and then feeding it with matter to increase its mass, we should be able to make it rotate also so we can get 40% mass to energy conversion. Radiation will be emitted and this will heat up ram scooped matter channeled by magnetic fields around the hole and into the exhaust. Some sophisticated engineering will be required to do all this as well as a highly advanced civilization that uses AI robotic mass production and has access to the resources of the solar system. We will need a civilization approaching the K2 level to build this might star ark or carrier and its black hole propulsion system. What about the energy emitted by the matter spiraling in? If we are to propell the giant ship up to 66% c in 20,400,000 seconds we need 5E28 j total at 100% eff. and we must generate 2.45E21 watts per second, thus we need to convert 27,233 kg. of matter to energy every second. At 40% eff. we need to feed 68,000 kg. or 68 tons of mass to the hole every second. We will need a huge ram scoop generating a magnetic field that can suck in ions from interstellar space perhaps a million km in diameter. Or we are going to need to use the hole to power a propulsion beam and sail the ship. As mass falls into the hole it will give off radiation that pushes back on the mass and regulate the infall to a steady state know as the Eddington limit.* L(watts) = E R c2 E = efficiency of mass to energy conversion R = rate at which mass is accreted by the hole c2 = s.o.l. Squared If E = 0.4 and R = 68,000 kg. per second we find that 2.45E21 watts are emitted The 2 km. diameter containment will be illuminated by 195 trillion watts per square meter of x-rays mostly. Mass flowing through the giant engine will probably not absorb all this energy and engine efficiency will be low. If ultra reflective materials could bounce the energy back at the hole this could serve to contain the hole. At the focal region of the x-rays temperatures would be immense. Perhaps we would be better off using this energy for a photon rocket drive instead of heating reaction mass up to super hot temps for thrust, presuming we could get the super reflectors and hold on to the black hole also! This is getting crazy! Anyhow, the Eddington limit would be L=6.39M (kg.) or 4.92E12 watts and we are trying to generate 2.45E21 watts. So the hole would push the infalling mass away. Perhaps we can operate the hole in pulsed mode, feeding it a little mass which it will rapidly consume with a burst of energy, then some more mass when the energy burst is over. We'd have to operate at about 500 million pulses per second at least. Let's try a photon rocket with a ram scoop that only harvests enough mass to create energy that will be reflected from a 20 km. diameter hemispherical near perfect x-ray reflector. Since the photon force will be: F= 2(P*A)/c P= 1.95E12 watts/sq. meter A= 628,000,000 sq. meters c=3E8 m/s F = 8.164E12 N or 815 million metric tons Thus our 2.5 GT ark will accelerate at 0.326 G or 3.2 m/s/s It will take about two years to reach 66% c Since we are scooping up hydrogen ions in the interstellar medium we could continue to accelerate to higher speeds. Acceleration would be slower at first and increase with speed as the scoop collects more ions as it moves faster. The photon exhaust intensity would also increase with speed. So the picture is actually more complex than this. In the thicker "soup" of ions in the solar system from the solar wind and within the heliosphere we could get more mass to feed to the BH at lower speeds compared to what we'll get at higher speeds in the interstellar medium so that we could run up to high speed upon entering the thin IM and make the scoop more efficient. As long as the whole thing doesn't incinerate itself in a flood of x-rays and gamma rays or the charged black hole doesn't escape from the magnetic fields that hold on to it! As for gravity waves and such, it seems that this machine is going to involve every last bit of science we know of from black holes to exotic materials to biological life support and mega-scale engineering of the future. Will gravity waves affect the vacuum somehow to reduce inertia and energy requirements to accelerate this thing? Who knows? Since: (200,000,000 m/s)/ 3.2 m/s/s = 62,500,000 seconds and s=0.5at2 we will cover about 6.25E12 km or about 0.65 light years until reaching cruise velocity If we want to collect 68,000 kg. per second on the average to generate 2.45E21 watts per second and there is one hydrogen ion per cc of the IM our scoop must be: 62,500,000 seconds X 68 tons = 4.25 billion tons or 4.25E15 grams (6.25E17cm)( area in cm2)/ (6.02E23 particles per gram of hydrogen) = 4.25E15 grams area = 4E21 square centimeters or a circular area with a radius of 361,000 km. The scoop won't be that big physically but it's magnetic field must be of these proportions. The field area and strength could be adjusted depending on particle density in space to reduce drag. So there are more complexities to this. Through a glass, darkly. The vessel could use its scoop to control a plasma bubble for braking. What if by some terrible accident of Fate the vessel crashed into the Sun or another star? Would it cause a nova? If the Eddington limit for the 770 megaton mass BH is 4.92E12 watts and the Sun emitts 3.8E26 watts we are talking about a drop of water in a bucket-just 1.29E-14 the Sun's energy. In the interior of the Sun where pressures are intense it seems more matter could be forced into the hole against its own luminosity. If a million times as much matter could be rammed into the hole fallen into the Sun, it would still only add 1.29E-8 of the Sun's energy to the output of the Sun, so this seems to be something we don't have to worry about. We can locate our star terminals in close stellar orbit without anxiety about causing man made novas to take advantage of frequent launch windows to planets of other star systems. However, what if the black hole grew and grew to enormous size? How many years or millions of years would elapse before the thing blew the Sun apart? I can't answer this question. We would take every imaginable precaution to prevent a star ark, carrier, whatever you want to call it from falling into a star. If its limit is 4.92E12 watts then at 40% efficiency it converts merely 5.46E-5 kg mass per second and absorbs about 8.2E-5 kg/second, therefore it would take about 12 trillion years to absorb one million tons of mass and by then the Sun would be dead. Let's hope this is correct. If not, perhaps a massive sunspot and solar flare would eject the black hole infection and throw it into space forever. Perhaps it would be repulsed due its static charge by solar magnetic fields. So all this seems very pseudo-scientific. I have no doubt that AI robotic mass production and mining of the asteroids and moons of the solar system will be possible someday, but we have yet to invent magical processes for making miniature black holes, superconducting magnetic ram scoops that can harvest hydrogen ions from swaths of space wider than the distance of the Moon from the Earth, superconducting magnetic containment systems for charged black holes, carbon 60 materials in huge masses, and super reflectors that bounce 99% to 99.9% of radiations falling on them away and transmit the remainder so that little or no absorption and heating results. Dielectric mirrors composed of layers of tellurium and polymers have been made at MIT that can reflect 99% of light falling on them so super reflectors for photon rockets may be possible. Where do we find all the tellurium for giant reflectors becomes a question. Starships will not spring out of the head of one man or woman like Athena from the head of Zeus or Siva from the forehead of Brahma. Nobody could be smart enough to work out all the details. Small armies of scientists, engineers and technicians will be needed in the future. Even so, spaceships will evolve gradually just as canoes led to bigger canoes, small wooden ships propelled by sail and oar, huge Spanish galleons, steamboats (many which blew up before the invention of steam pressure gauges and relief valves), iron ships propelled by coal and steam, steel ships propelled by turbines and diesels, nuclear powered ships and submarines, super tankers, and perhaps even mightier ships someday made of titanium with fusion reactors on board to power turbines and propellors or pump jets. We will see small rocketships powered by various chemical fuels and nuclear thermal motors to the Moon and Mars in this century and these will lead to larger ships powered by NEP or hybrid NTR/NEP. Cycling stations will emerge. Fusion rocketships might open up the entire solar system in the late 21st or sometime in the 22nd century, depending on progress in controlled fusion. There's also that matter of what we want to put resources into. Solar power satellites and helium 3 fusion could motivate us to return to the Moon. Scientific curiousity may motivate missions to Mars. Orbital manufacturing might lead to lasers that make the fusion breakthrough possible and the creation of exotic alloys and other materials, even super reflectors and C60 super fibers of immense length. It's all going to depend on money and economic conditions around the world. Robotic mass production may push away financial limitations. Research in deep space with thermonuclear explosions to compress matter might be conducted. Solar powered beam riding probes will probably reach the nearby stars before we get there with black hole powered arks. We might even find that it is possible to compress magnetized matter to make minature magnetars that don't have a lot of gravity but have magnetic fields strong enough to accelerate ions up to impact speeds that cause them to give up much of their energy. These might be easier to deal with than miniature black holes. The careful reader will notice that I did not discuss the increase in mass by the black hole with each flight. It will increase by several billion tons! That's going to be a lot of parasitic mass. What do we do about it? Discard the hole after each journey and get a new one? We'd have to be capable of producing lots of these objects. If the hole is part of a "stationary" propulsion beam driver this won't matter. Perhaps the sail concept is the best. When holes get very large we might use them to ignite brown dwarfs. Perhaps black hole power could be used to generate antimatter for starships. |
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| ABOVE) A really gigantic starship with 2 km. wide passenger hulls for 2 million passengers and a 20 km. diameter reflector for photon drive. But will this crazy thing really work? How is the black hole contained? If you can figure out how to make this design more plausible, I'd sure like to know how you did it! |
| * from Robert Zubrin. Entering Space. chp. 10, pg. 244. Tarcher-Putnam: 1999. |
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| Ramjet starships remind me of trumpets. When these ships appear, if they ever do because future science may allow far better technology, in a future time when technology has provided for all people's material needs and wants, these ships will be like Gabriel's horn sounding and one world will end and a new world of interstellar travel and colonization will begin. Perhaps there are even natural "wormholes" in space that will allow travel to the far edge of our galaxy and even to other galaxies. These ships would use mag-sails or magnetoplasmic sails for braking. The sails could also ride propulsion mass beams up to 1% to 2% light speed at which the ramscoop starts collecting enough interstellar plasma to get the ramjet drive working. The ship might just fly by some stars and launch small pods containing cargo or hibernating humans that brake into the star system while the mother ship carrying the major load of cargo and humans goes on to another star system where it brakes into stellar orbit. It could catch beams from the flyby star system to alter its course. See: Interstellar Shuttles |
| URLs for some excellent interstellar ramjet pages: http://en.wikipedia.org/wiki/Bussard_ramjet http://homepage.ntlworld.com/andy-nimmo/Webpage2b.htm http://homepage.ntlworld.com/andy-nimmo/Webpage2c.htm http://www.bisbos.com/rocketscience/spacecraft/bussardramjet/bussard.html |