| The Tug If tapping mass directly from a star or its corona and solar wind is not possible, if the star has no "hot Jupiter" (a gas giant planet in orbit about as distant as Mercury or Venus) although many have been detected from which to obtain mass with skyhook pipelines and pumps, or there are no inner planets like Venus with an atmosphere that can be tapped for mass, we will need a tug to push the Rama class Star Carrier to greater distances from the star where hopefully a gas giant or world like Titan with a methane atmosphere exists. Or, we will capture comets and use them to supply mass to propulsion beams. The tug has a large protrusion tht fits in the aft end of the Carrier's keel tube. Looks silly, but we wouldn't want to drag the Carrier with cables and douse it with highly radioactive exhaust from the tug's fusion engines. It has four 750 meter diameter LH2 tnks holding 61.5 million tons of liquid hydrogen. The Carrier amasses 25 million tons and the tug about 5 million tons empty. The ships will not go that fast. Instead they will rocket away from the terminal in near stellar orbit at 200 kps and reach the distance of Uranus in about 160 days not considering accel and decel times. It may be possible to brake in the solar wind with mag-sails upon reaching Uranus, but if the wind is still moving at high speed in the outer system it won't be possible to do this anymore than one can slow down when going upstream in the same direction as the river current. So the tug will have to use retros. The tug must have enough LH2 to exit Uranus or some similar gas giant in orbit around another star, brake with mag-sails into near stellar orbit going against the solar wind of course, and have enough propellant to rocket out to Uranus and retro-rocket into the planet's orbit with a Star Carrier "in tow" so it will perform three maneuvers. When returning to the inner system without a "ship in tow" it will be lighter but it's tanks will be fully loaded with LH2. The tug as drawn has 130 engines. If each one amasses 15,000 tons and produces 3700 kilowatts per kilogram (see: Fusion Revisited) there are 1,950,000 tons of them generating 7.215E15 watts. 30 days acceleration ( approx. three 10 day "burns") 7.215E15*( 30*24*3600) = 1.87E22j total We will need about 30,000 tons of helium 3 fusion fuel! 0.5(61,500,000,000 kg.) (780,000 ^2) = 1.87E22j exV= 780 kps Tug mass is about 5 million tons total. That's 1.95 million tons of engine and another three million tons of thick insulated LH2 tanks, structure, radiators, pumps, etc. It's bulky though. If it is pushing a Carrier and uses all its propellant it can reach: 25+5+61.5/30=3.05 ln=1.115 dV= 870 kps If it loads up at Uranus with a full 61.5 megatons LH2 5+61.5/5= 13.3 ln is 2.5877 dV without a Carrier with an exhaust V of 780 kps = 2250 kps but lets just go 125 kps and let solar gravity pull us in up to 30-50 kps like a comet and brake with mag-sails to return to inner system in about 6 months. If we only had to go as far as Jupiter we could get things done faster but Jupiter has high gravity and a high escape velocity, is surrounded by intense radiation belts, and is very stormy; however a clear layer of hydrogen and helium floats above the cloud tops. We might mine Callisto or Europa for mass. That might entail electrolysis of water to get pure hydrogen but gravity would not have to be fought as much. I don't like oxygen ions in the mass beam. They could oxidize things if they penetrate magnetic fields. That's one of the problems with Venus. If we could decompose the CO2 to C and O2, dump the O2 and just use the C ions...perhaps when the CO2 is devoured by the mini N star the molecules will be ripped apart and given the positive charge of C and negative charge of O ions they would jet out from opposing poles and we could ride the carbon ion beam out to Jupiter or Uranus or Titan to catch a bigger beam to another star. The same would occur with H2O if we mined water from an ice moon or comet. A beam of H ions and a beam of O ion opposing ions each other would form. Since the energy provided would be the same the H beam would move faster and be lighter but the O beam would be heavier and slower, so the opposing beams of the Drivers will balance out and the Driver will stay on station. Getting back to the math: e^(125/780)=1.174 (5+61.5)/(5+x)= 1.174 x= 51.64 61.5- 51.64 = 9.86 9.86 million tons LH2 used for return. Now we have when attached to the Carrier MR= (5+25+51.64)/(25+5) = 2.721 ln 2.721 = 1.0001 thus we can reach 1.0001(780)= 780.8 or just 780 kps! we can make two ten day burns of about 390 kps each to reach Uranus in (10+10+80) about 100 days. 2.7E9 km./390 kps = 80 days If we only went to Callisto we'd need only 45 days and to Titan to use its atmopsheric methane which would give us a mass beam consisting of H and C ions we'd need only 83 days, so going all the way to Uranus or Neptune might not be necessary. The tug could shuttle back and forth with several Ramas every year if we can tap resources less distant than Uranus. We will have mapped other star systems in great detail with space telescopes and robotic probes before we travel by Rama to those systems. The systems will be colonized many decades, even centuries in advance by men and women who travel by smaller but equally fast ships of various designs. Replicating robots (see: Robots) will use asteroidal and planetary materials to build large structures in space and on planets. Today man and woman cultivate crops and children. Tomorrow man and woman will cultivate AI robots and the vast wealth of material things they produce. We will know where various planets and moons are and make plans to utilize their resources. If there are hot Jupiters, Venuses or Titans available we will use them. If there are only distant Uranus and Neptune like planets we will plan to use tugs to move Star Carriers from the inner system to those worlds where we build Star Drivers in orbit. Some may object to my insistence on building Star Terminals in near stellar orbit, but when hundreds of thousands of travelers enter a system and want to spread out by smaller ships to many different locations near stellar orbit will be the only logical place to base the terminals for the sake of scheduling hundreds of flights to worlds, natural and artificial, of that system. Too bad we can't just mine a star, or can we? |
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| The Fly-By Strategy If you have read other pages of this web site you may know that it might be far better to let the mighty star ships just fly-by stars and have passengers in low mass pods decelerate into a system and ride pods to catch up with and board the star ships as they head out towards another star system and that this will be far more efficient than braking and propelling the big ship back up to speed at every star it visits. So what good is the tug after all this? At NODEs where star ships are built and propelled up to speed on courses that fly-by many stars, with course corrections from mass beams at fly-by stars of course, the tug might be useful for moving the great vessels from the ship yards in space to the vincinity of the propulsion beams that give them their intial velocity. As the star ships of various designs and sizes on up to Rama class Star Carriers follow their winding courses through the galaxy past many red dwarfs, orange K type stars, yellow G type stars and yellow-white F-type stars, and a few white A-type stars they will eventually arrive at the end of the line-terminus. Here they will brake, perhaps "for free" in the interstellar medium rather than on an energy intensive mass beam, at a major NODE where they will be refurbished or even torn down, cannibalized and new ships built. That depends on how long they are in space and how far they travel. A tug at a major NODE at the end of the line will be useful for moving Rama class Star Carriers around in the system to the ship yards and out into position to catch a propulsion beam that propells the star ships back up to speed and back the way they came so that two way travel on various routes is possible when lots of starships are in the circuit. The NODE of origination will probably be a hot, bright A-type star like Sirius, Vega, Altair or Fomalhaut that has lots of energy available for stellar energy powered propulsion beams. The terminus NODE will probably also be a bright star like one of these. Yellow G-type stars can also supply plenty of energy although stellar energy complexes might be larger than the ones at A-type stars. If black holes are used to power propulsion beams, NODEs of origination and terminus NODEs ( which can be seen as both depending on which way you are going on the route) could be located at any kind of star as long as there were planetary atmospheres to harvest or comets to capture to supply mass to the mini-black hole powered propulsion beams. That would make route design much more flexible. |