________________________________________ GURPS Vehicles 2nd Edition Additions MA Lloyd (malloy00@io.com) 9 August 1998 Modifications and Additions to Chapter 2: Propulsion and Lift ________________________________________ This chapter should have followed the Equipment and Armaments chapters. ________________________________________ p29* Harnessed Animal Propulsion. Motive Thrust. Multiply motive power by 2 to get pounds of aerial motive thrust, by 20 for aquatic motive thrust. p32* Example. 200 kW is 268 horsepower. p32 Powered Aquatic Propulsion. Late TL5 paddlewheels can be feathered for quadruple cost. This increases Motive Thrust to 10. p32 Powered Aquatic Propulsion Table. TL8 Hydrojets should not outperform propellers. Drop Aquatic Motive Thrust to 15. p32 Hydrojets. Drop the magnetohydrodynamic reference. p33 Aerial Propellers and Ducted Fans. Motive Power. Single propellers with higher thrusts have been built. Add 'For triple cost a single propeller may have a motive power as high as 2000kW x (TL-4). p33 Airscrew Table. Motive thrust is quite sensitive to operating speed. The realism of very low or very high speed designs is improved if the thrust factor is multiplied by (125/Top Speed). Of course this adds a loop to the design process. p35 Jet Engines. Afterburners. Change statistics to 'for every 10% added to thrust, up to 100%, an afterburner adds 2% to engine weight, 5% to cost and 30% to fuel consumption when lit'. Use the same multipliers for any engine type. p36* Rocket Engine Cost. Multiply by $100 if fusion. p37 Fuel Consumption. Multiply Antimatter Pion fuel usage by 10. p37* Solid Rocket Table. Gunpowder propellants improve from TL3 to TL4, use: TL3 2.2 $0.5 TL4 1.0 $0.5 p37 Thrust Bomb Table. Realistic thrust bombs may not be lighter than 2 lb/kT, not because nuclear explosives can't be smaller, but because otherwise there isn't enough mass to transfer the momentum necessary to obtain the stated thrust. p38* Magnetic Levitation. Cost per pound of lift is $50(TL7) $8(TL8) or $2(TL9). p39* Stardrive Table. Power requirement. The units for the energy required to enter hyperspace or open a jump point should be kWs (kilowatt-seconds). The other units are correctly kW (kilowatts). p40* Teleportation Drives. In paragraph 3, change 100 times the cost and power to 10 times. p40 Teleportation Drives. The relevant skill is Electronic Operation (Teleport Drive), not Piloting(Teleportation). p40 Parachronic Conveyers. The largest projectors are city-block sized, not city-sized, and projector size depends on mass projected not quantum difference (see pTT90). p40 Lifting Gas. Cost. A day's flight, a takeoff or landing uses about 10% of the ballast or gasbag gas volume. p41 Levitation. Antigravity Coating. Neutralizing all of a vehicle's weight is likely to cause more trouble than is immediately obvious. It is much safer to either set a maximum lift (say 100lb/sq ft of coating) or a lift per unit of coating weight (see Liftwood p40a for an example). ________________________________________ Propulsion and Lift p29a Harnessed Animals ________________________________________ Harnessed humans use the same rules as any other harnessed animals, but a proper load distributing harnesses (efficiency 0.02) is available at TL1. ________________________________________ Propulsion and Lift p30a Sails ________________________________________ See Incanus' excellent expansions to the sails rules at http://www.bakal.hr/incanus/gurps/sailing.html Wingsails (TL7) are rigid airfoil designs, ranging from giant upright wings to forests of inch wide slats. The major advantages are simplified handling - no sailing crew is necessary; easier match to the wind direction - wingsails travel at full speed in any wind but Wind on the Bow, against which they tack at 50% speed; and higher thrust - wingsails develop 0.9 lb x sail area x Beaufort number. Wingsail assemblies have the same height and number restrictions as masts. They may have areas up to 0.5 x height^2, built as structural frame of that area. Some versions will also have DR over the frame, but others use fabric covers with DR0 (use the statistics for sails of the same area). ________________________________________ Propulsion and Lift p30a Powered Sails ________________________________________ The idea of a sailboat that requires a motor seems insane on the surface, but powered sails often generate more thrust from a given amount of fuel than a conventional aquatic propulsion system. A TL earlier, when ships couldn't carry enough coal to make an Atlantic crossing under power, Flettner rotors might have been a success; but when actually introduced in the 1920s fuel oil was cheap. There was some revival of interest in the late 1970s, but oil prices fell again about the time construction finished on the prototypes. Flettner rotors (TL6): are a sail technology in which a rotating cylinder replace masts, producing thrust from the wind through the Magnus effect. The rotors have the same number and height restrictions as masts. They can have a surface area of up to 0.63 x height^2, and should be built with that much structural area and a rigid skin of DR1 or more. Add a Magnus effect drivetrain (p34a) to turn them. Thrust is 5.4 lb x the square root of (rotor area x kW) x Beaufort number. Flettner rotors travel at full speed in any wind but Wind on the Bow, against which they tack at 50% speed. Rotors also work fine in very high winds, and do not reduce wSR. Turbosails (TL7): are hollow, slightly streamlined cylinders with valved holes on each side and a fan at the top. They look like Flettner rotors, but do not rotate, and generate lift quite differently. The fan pulls air through the opened holes on the leeward side to maintain a low pressure region that induces the necessary vortices in the passing wind. Thrust is 1.8 x turbosail area x Beaufort number. Turbosail subassemblies have the same number and height restriction as masts. They can have an area up to 0.2 x height^2 sf, designed as a structural frame with a rigid DR1 or better skin. To power them add an upward pointing ducted fan at the top of each column, with a thrust equal to 2 lb x sail area. ________________________________________ Propulsion and Lift p31a Beamed Power Lightsails ________________________________________ It is possible to push a lightsail using an artificial photon source (a laser, microwave beamed power transmitter etc.) but the thrust is so low [beam power (in kW)/700,000 lbs] it is usually only used for extremely light spacecraft or by extremely high tech civilizations. Sails are so fragile they must be at least 100 times beyond the maximum range the source can inflict damage. Beam divergence is a problem, the normal spot size is 400 square miles times (distance in AU)^2, divided by beam focusing array diameter in yards. If the sail is smaller than the spot, reduce thrust in proportion to the ratio. Purpose built launching lasers will need arrays thousands or millions of miles across to keep the beam usefully small at interstellar ranges. At TL8+ perforated sails with 1/10 the weight of normal lightsails are available. They generate 1/10 the thrust from visible light, but still completely reflect microwaves and get full thrust from microwave beamed power. ________________________________________ Propulsion and Lift p31a Radioactive Sail ________________________________________ *Radioisotope Sails* (TL6) are an idea from the early years of space flight and nuclear power. A thin layer of radioactive material is spread on one side of a foil thick enough to stop the decay products. In the other direction particles escape to space, producing thrust. Radioactive sails resemble lightsails, and can even be polished to work as lightsails for extra thrust, but must be much heavier to stop the emitted particles. They have the same approach limits and furling times as lightsails. The radiation hazard varies but generally any radiation shielding protects against it completely (isotopes *are* selected for the ability of a thin foil to stop most of the momentum...). A radioactive sail weighs 300,000 lb. per square mile. The thrust is initially 20,000 lb. divided by the isotope half-life in days, and falls by 50% every half-life. ________________________________________ Propulsion and Lift p32a Active Flotation ________________________________________ Any powered aquatic propulsion system can be installed to point downward, so its thrust offsets part of the vehicle's weight. When determining if the vehicle can float or computing its hydrodynamic drag subtract the active flotation thrust from the vehicle's loaded weight. An active flotation system can also be installed to add to loaded weight, to enable a light vehicle to submerge for example. Or at 1.5 times the weight, volume and cost it can be installed as a vectored thrust system (cf p.41) able to do both, and propel the vehicle. It is advisable to compute statistics with and without the active flotation system. A vehicle that only floats while the system is operating will be in serious trouble if the power fails. ________________________________________ Propulsion and Lift p32a Aquatic Flexibody ________________________________________ The vehicle uses movable fins, a tail or whole body undulations to swim like a fish. Use the standard flexibody statistics (p31), but the drivetrain provides no ground propulsion, instead it produces 25 lb/kW (TL8) or 35 lb/kW (TL9+) aquatic motive thrust. ________________________________________ Propulsion and Lift p32a Aquatic Propulsion ________________________________________ MHD Propulsion (TL7): magnetically accelerates a conductive fluid (such a salt water) to produce thrust. Realistic performance is barely 1 percent of hydrojets, and the gigantic magnetic signature and huge power requirement more than negates any advantage of silent operation. Still it keeps cropping up in experimental ships and cold war fiction. 7+ MHD Propulsion 100xkW (60xkW)+200 0.2 ________________________________________ Propulsion and Lift p32a Underwater Rockets ________________________________________ Any chemical, fission, non-optimized fusion or antimatter thermal rocket can be modified to function underwater. The engine is built normally, but the final thrust is halved - by inappropriate design in air or vacuum, back pressure underwater. ________________________________________ Propulsion and Lift p34a Magnus Effect Drivetrains ________________________________________ The Magnus effect generates lift from an airflow over a surface rotating perpendicular to the flow. The usual Magnus effect rotor is a spherical or cylindrical gasbag; though a dedicated rotor subassembly containing no lifting gas is possible, some experimental aircraft designs use rotating cylinders instead of wings. A vehicle with a Magnus effect drivetrain has a stall speed of 1.5 mph x (Lwt-Static Lift)^2/(rotor area x kW), divided by the relative air density. Magnus Effect Drive Table under 5 kW 5 kW or more 6 ME Drivetrain 10 x kW (2 x kW) +40 7 ME Drivetrain 7 x kW (1 x kW) +30 8+ ME Drivetrain 5 x kW (1 x kW) +20 Volume is weight/50, cost is $25 x weight. ________________________________________ Propulsion and Lift p34a Unconventional Rotorcraft ________________________________________ Tiltrotors and tiltwings use the Tilt-Rotor rules (p34). Folding Tiltrotors also use the Tilt-Rotor rules, but double cost. Require this option for a tilt-rotor that flies between 450 and 600 mph. Rotor in Wing designs are built as Ducted Fans. Deflected slipstream designs are built as vectored thrust Ducted Fans. Autogyros are built as TTR or MMR rotors; they lack an anti-torque system but this has no effect on rotor statistics. Rotor area counts as lift area for determining stall speed, but without a helicopter drivetrain provides no static lift or thrust. Stopped rotor designs can lock the rotors and convert them into wings. This requires less efficient rotor shapes (multiply thrusts by 0.8) and a modified helicopter drivetrain (multiply weight and volume by 1.25 and cost by 3). When locked the rotors behave exactly as wings of the same surface area. They can only be unlocked if the vehicle is travelling below 300 mph. ________________________________________ Propulsion and Lift p35a Jet Engines ________________________________________ All jet engines work by pulling in the surrounding air and expelling it to produce thrust; most generate the necessary increase in pressure by heating the air. They only work in atmospheres of greater than trace density. *Super Turbofans* (TL9): are turbofans built with hyperfan technology, but burning conventional hydrocarbon fuels. *Electric Turbofans* (TL8): are turbofans using electric power to heat the air. They are much less efficient than Ducted Fans, but can reach higher speeds. *Laser Turbofans* (TL8): are turbofans powered directly by beamed power (p87). The beam from the remote transmitter heats the air directly, no separate receiver is required. *Fission Air Rams* (TL7): use a fission reactor to heat the air. They operate for 2 years on an internal nuclear fuel supply. The exhaust from a properly designed fission air ram is only slightly radioactive, though there were early TL7 proposals to build an unshielded version (see p86a) *Fusion Air-Rams* are (TL9), not (TL10). The Mecha version is a cinematic system from GURPS Mecha which outperforms TL9 Fusion reactors. *Fusion Ram Rockets* (TL10): are fusion air rams that can somehow reconfigure to operate at fantastically higher temperatures and lower flow rates and function as Fusion Rockets in vacuum. Jet Engine Table 9+ Super Turbofan (0.08 x thrust) + 3.3 0.03J 8+ Electric Turbofans (0.5 x thrust) + 100 4kW/lbf 8+ Laser Turbofans (1.0 x thrust) + 500 4kW/lbf 7 Fission Air-Ram (0.5 x thrust) +4000 2yr 8+ Fission Air-Ram (0.2 x thrust) +1000 2yr 9 Fusion Air-Ram (0.5 x thrust) + 500 2.5yr 9 Mecha Fusion Air Ram (0.1 x thrust) + 100 1yr 10+ Fusion Ram-Rocket (0.06 x thrust) + 60 2.5yr (0.02W) ________________________________________ Propulsion and Lift p36a Rocket Engines and Spacedrives ________________________________________ *Cold Gas Thrusters* (late TL5): are extremely simple reaction engines, little more than a valve and a nozzle on a tank of compressed gas. Performance is unimpressive, but they are very reliable (one moving part) and very safe (cool, nonflammable, non-radioactive, chemically inert, non-toxic exhaust). They are used where safety and reliability are critical, such as space suit thrusters. *Hot Gas Thrusters* (TL5): are cold gas thrusters with a heat exchanger in the fuel line. The usual design uses a thermal storage energy bank as the power accumulator to make a necessarily high thrust orbit insertion burn aboard a space probe with a low thrust main engine. *Steam Rockets* (TL5): are hot gas thrusters using liquid water rather than a gas as the reaction mass. Power may be supplied by either a thermal storage energy bank or a steam engine, much of it is wasted boiling the water rather than producing thrust. *Liquid Fuel Rockets* (TL6): generate thrust by expelling hot gases produced by a chemical reaction in a liquid fuel. There are several subtypes: *Monopropellant Rockets* (TL6) consume a single unstable liquid fuel, which releases energy as it decomposes. *Storable Liquid Rockets* (TL6) burn a fuel and oxidizer which are both liquids under ordinary conditions. *Cryogenic Liquid Rockets* (TL6) also burn a mixture of liquids, at least one of which must be stored at low temperatures. *Metal Oxide Rockets* (TL7) burn a powdered metal in a liquid oxidizer. They must be considerably tougher to resist abrasion from particles, which are normally carried to the engine as slurry in the oxidizer. *Excited State Rockets* (TL9+) consume a fuel somehow stored in a high energy state, which releases energy on returning to the ground state in the engine. They require specialized (and heavy) fuel handling equipment to prevent the fuel from spontaneously exploding. *Ion Drive* (TL7): The TL7 ion drive on p36 is possible, but draws too much power to be really useful. The ion engines actually flying at late TL7 perform more like the engine given here. *Electric Rockets* (late TL7): produce thrust by heating reaction mass electrically. There are various kinds - arcjets, resistojets, microwave electrothermal, magnetoplasmadynamic and so on. They are fuel efficient but energy intensive, and are usually small engines used where fuel economy counts more than high thrust. *Fission Rockets* (TL7): use a built in fission reactor to heat reaction mass. There are three basic designs: *Solid Core Fission Rockets* (TL7) use a fairly conventional reactor design. The exhaust is only slightly radioactive and the reactor can operate for 2 years without refueling. Solid core fission rockets were actually tested in the late 1960s and early 1970s (the NERVA project) *Gas Core Fission Rockets* (TL8) operate at much higher temperatures. This improves performance, but the reactor core is no longer solid, and inevitably the fission fuel mixes with the exhaust. This means the exhaust is lethally radioactive and the reactor must be refueled after only 2 hours of operation. Fuel is 5% of the engine weight, but replacing it costs as much as a new engine (because of the complications of working in the now highly radioactive interior of the engine). *Nuclear Light-bulb Fission Rockets* (TL9) are gas core reactors contained in a transparent vessel. The reaction mass is heated by thermal radiation rather than contact with the core. This raises weight and lowers performance, but the exhaust is completely non-radioactive and the core operates for 2 years without needing fresh fission fuel. *Solar Thermal Rockets* (TL7): use focused sunlight to heat reaction mass. Power consumption must be met by the light power of a mirror array (p.86a), not a power plant. If the mirror array cannot supply the full power needed (usually because the vehicle is operating further from the sun than planned) reduce both thrust and the fuel consumption proportionally. Higher available power has no effect. *Laser Thermal Rockets* (TL7): heat a reaction mass with an external laser pulse. The power requirement is met by a remote beamed power transmitter (p87), no receiver is needed. Because beamed power has a limited range, they are primarily used as launch systems or for local traffic around worlds with a network of ground or orbital power transmitters. Beamed microwave systems have the same statistics, though the heat transfer to the propellant is engineered differently. *Mass Driver Engines* (TL7): use a coil gun propelled bucket chain to launch reaction mass. Fuel consumption is in pounds per hour per pound of thrust; anything will work, though safety regulations may require liquids or dust to avoid creating hazardous artificial meteor streams. *Microfusion Pulse Engines* (late TL8): are a cross between an Orion drive and an inertial confinement fusion reactor. Small pellets of fusion fuels clad in a fissionable igniter are launched through a ring of powerful lasers or ion beams, compressed until they detonate in a small nuclear explosion (about a ton of TNT) and the plasma expelled to produce thrust. Fuel usage is in pounds of pellets per hour. Pellets are 0.02 cf per lb, weigh about an ounce each, are only slightly radioactive and can not be made to explode outside the engine. A variant catalyzes fission in far subcritical pellets of fissionables using beams of antiprotons, use the same statistics. *Fusion Rockets* (TL9): The optimized fusion rocket (p36) is simply a fusion reactor with a leak in the bottle, and is reasonably realistic, but the standard high thrust fusion rocket is quite implausible. These systems are somewhat more realistic. The Controlled Thermonuclear Reaction system has statistics comparable to the fusion power-plant (p85), the Quantum Electrodynamic rocket is one of the more optimistic high thrust designs in the actual rocketry literature. *High Impulse Antimatter Thermal Rockets*: Standard antimatter thermal rockets are designed for high thrust applications, but it is possible to design drives which use antimatter to heat reaction mass to plasma for better fuel economy. Liquid Chemical Rocket Table TL Rocket Engine Weight Fuel Power Isp 6 Monopropellant 0.012 x thrust 2.4R 0 150 7+ Monopropellant 0.010 x thrust 2.0R 0 180 6 Storable Liquid 0.015 x thrust 1.5R 0 240 7 Storable Liquid 0.012 x thrust 1.25R 0 290 8+ Storable Liquid 0.010 x thrust 1.1R 0 330 6 Cryogenic Liquid 0.020 x thrust 4.4HO 0 390 7 Cryogenic Liquid 0.015 x thrust 3.7HO 0 460 8+ Cryogenic Liquid 0.012 x thrust 3.3HO 0 520 7 Metal Oxide 0.030 x thrust 1.3MOX 0 230 8+ Metal Oxide 0.025 x thrust 1.08MOX 0 280 9+ Excited State 0.060 x thrust 8.2SAH 0 930 Rocket Engine Table TL Rocket Engine Weight Fuel Power Isp 5+ Cold Gas Thruster 0.02 x thrust 7.7N2 0 70 5+ Hot Gas Thruster 0.02 x thrust 4.0N2 3 135 5+ Steam Rocket 0.02 x thrust 3.2W 12 135 7 Realistic Ion Drive (1000 x thrust) + 5 0.085Ar 80 3650 7 Electric Rocket (60 x thrust) + 20 4.0H 80 1550 8+ Electric Rocket (10 x thrust) + 20 2.0H 80 3100 7 NERVA Test Fission (0.420 x thrust) + 4000 8.3H 0 750 7 Solid Core Fission (0.325 x thrust) + 4000 6.0H 0 1030 8+ Solid Core Fission (0.150 x thrust) + 1000 6.0H 0 1030 8+ Gas Core Fission (0.050 x thrust) + 1000 0.8H 0 7760 9+ Nuclear Light-bulb (0.450 x thrust) + 1000 2.6H 0 2390 7 Solar Thermal 0.020 x thrust 6.0H 25 1030 8+ Solar Thermal 0.020 x thrust 4.0H 40 1550 7 Laser Thermal 0.020 x thrust 6.0H 30 1030 8+ Laser Thermal 0.016 x thrust 4.0H 40 1550 7 Mass Driver Engine (100 x thrust) + 100 10 lb 20 360 8+ Mass Driver Engine (30 x thrust) + 30 5 lb 20 720 9+ Microfusion Pulse (0.03 x thrust) + 6000 0.35lb 0 10300 9+ QED Fusion (0.30 x thrust) + 1000 0.2W 0 2160 9 CTR Fusion (50.0 x thrust) + 20000 0.5H 0 12400 10+ CTR Fusion (10.0 x thrust) + 2000 0.5H 0 12400 10 Hi Imp. Antimatter (10 x thrust) + 1000 0.02W 0 21600 Cost: add 'by $15 if gas thruster or monopropellant chemical rocket' Fuel Consumption: see the tables on p89a for abbreviation meanings. High Impulse Antimatter Thermal engines also consume antimatter at a rate of 10 micrograms per hour per pound of thrust. ________________________________________ Propulsion and Lift p37a Alternative Reaction Engine Fuels ________________________________________ *Alternative Rocket Fuels:* Chemical rockets can use many other fuels. To determine the statistics of a rocket using an alternate fuel design the engine normally, select a fuel from the Rocket Fuels Table (p89a) and multiply the design thrust by its thrust factor. All other statistics, including the volume of fuel used, remain the same. *Alternative Reaction Mass:* Engines that produce thrust by heating a reaction mass (including electric, fission, non-optimized fusion, solar, laser, and antimatter thermal rockets) can use alternate reaction masses. So can gas thrusters, as long as the alternate reaction mass is a gas. Design the engine normally, look up the standard and alternate fuels on the Reaction Mass Table (p89a), multiply the thrust by ratio of their thrust factors. Since thrust factors assume constant operating temperature, engines that consume power also change power consumption; multiply by the ratio of the power factors of the fuels. *Example:* Electric Rockets normally consume hydrogen (thrust and power factors both 1.0). To build one that uses hydrazine (thrust factor 3.62, power factor 0.91) design a hydrogen rocket, then multiply the thrust by (3.62/1) and the power used by (0.91/1). You pay for the increased thrust and lower power consumption by using a fuel that is 15 times as heavy. *Converting Other Fuels:* Chemical rocket thrust factors are proportional to the density of the fuel mixture times the vacuum specific impulse of mix. Reaction mass thrust factors are proportional to the density divided by the square root of the molecular weight, and power factors are proportional to the density divided by the molecular weight, in all case normalized to the standard engine fuels (usually hydrogen, 'rocket fuel' or HO). ________________________________________ Propulsion and Lift p37a Fission Fragment Thruster ________________________________________ This engine produces thrust by magnetically directing the charged particles emitted by the spontaneous fission of a radioactive source. A built in RTG powers the magnetic field; the thruster requires no external power or fuel. Choose a thrust (in lbs) and the isotope half-life (in days). The thruster is late TL7 technology if there is any demand. It weighs 200 + 4 x (thrust x half-life) lbs, occupies weight/50 cf and costs $100 x weight. Each half-life thrust is reduced by 50%, whether it has been used during that time or not. ________________________________________ Propulsion and Lift p38a Electrodynamic Tether ________________________________________ A long wire orbiting a planet with a magnetic field will develop a voltage across the wire. If a closed circuit is possible (and the ionosphere plasmas above a planetary atmosphere allow this) the voltage can be used to generate power at the expense of kinetic energy relative to the field. Conversely if a current is forced to flow against the voltage, it is converted into kinetic energy. Since the magnetic field co-rotates with the planet, power generation below synchronous orbit causes the tether to slow down and fall toward the planet. Outside synchronous orbit but within the magnetosphere power generation drives a tether orbiting in the same direction as the rotation of the planet into a higher orbit. For simplicity a TL7 electrodynamic tether weighs 50 lb x kW and generates 0.025 x kW pounds of thrust. Adding an engine able to counter the thrust can be an efficient way of converting the engine fuel into electric power. ________________________________________ Propulsion and Lift p38a Gravitic Propulsion ________________________________________ Several useful propulsion technologies can be extrapolated from the statistics of grav guns, tractor beams and contragravity. Grav propulsion is potential energy based, the same weight flow generates the same thrust, so the usual rules for alternate reaction masses involving molecular weights do not apply. Gravfans (TL11): pull in the surrounding air, drop it down a tractor scale gravity gradient to accelerate it to modest speeds, and expel it to produce thrust. At low fluid densities performance is volume flow limited, at high densities it becomes mass flow limited; multiply thrust by the density of the air up to 40 lbf per kW. Performance is: 11 Gravfan 8 4xkW (0.5xkW) + 17.5 (as an 'airscrew' in Earth's atmosphere) 11 Gravfan 4xkW (0.5xkW) + 17.5 40 (as an aquatic propulsion system) Volume is Wt/50. Cost is $2 x Wt Gravjets (TL11): are the equivalent system using a grav gun scale gravity gradient. Performance is always mass limited, so fluid density has no effect. As a reaction drive: 11 Gravjet (0.01 x thrust) 0.8W 1kW Volume is Wt/50. Cost is $75 x Wt Repulsorlift (TL12): a hovercraft system using repulsor beam technology. Standard repulsorlifts float 1 yard off the ground, for other ceilings multiply weight and power consumption by the maximum height in yards. Repulsorlift exerts a ground pressure of [lift/(vehicle surface area/10)]. This has no effect on performance but will displace water traveled over to a depth of one inch per 5 lb/sf, leaving a wake, and can damage things the repulsorlift runs over. Statistics are: 12 Repulsorlift (0.0005 x lift) + 20 lb (0.025 x lift) kW Volume is Wt/50, cost is $2 x Wt ________________________________________ Propulsion and Lift p38a Reactionless Thrusters and Other Incredible Drives ________________________________________ Boost Drives (TL10): A class of space drives that (almost) instantly boost a ship to a substantial velocity without acceleration effects. Boosts are measured in the initial frame of the ship, and are often a large fraction of the speed of light. If not the drive can often be cycled to build up such a speed eventually. Most boost drives produce a fixed delta-v, double weight volume and cost for a drive able to make variable velocity boosts. Weight is 0.01 x maximum load, volume is Wt/50, and cost is $500 x Wt. Realistic energy consumption is [0.000046 kWs/lb] * delta-v(mph)^2 (if v > 0.1 c use the relativistic version [4.1x10^13 kWs/lb] * ((1/gamma)-1), where gamma is the square root of (1-(v/c)^2). Fictional versions often draw power from the vacuum, the flow of the ether or the angular momentum of the galaxy and use less energy - I suggest 180kWs/lb x (v/c) Contragravity Thrust (TL?): In some settings pseudo-reactionless thrust is described as pushing against a planet (true antigravity) or selectively cutting off gravity from certain directions (the cavorite with windows or gravity planar effect). These are best modeled as reactionless thrusters. Some have an operating limit from the planets or stars pushed against (in Traveller it is 100 AU), though if they worked at all the galactic gravitational field should be sufficient. Conversion Thrusters (TL?): convert fuel directly into propulsive energy at the maximum possible efficiency. Use the statistics for reactionless drives, but drop the power requirement and substitute a fuel consumption of 0.0002H or 0.000015W (gph/lbf) instead. Depending on the technobabble, conversion thrusters may exhaust nothing detectable, harmless colored light, or ravening beams of heat, laser light, gamma-rays or gravity waves with intensities up to 1,335,000 kW/lbf. Unlike reactionless thrusters, conversion thrusters don't actually violate conservation of energy, so they can work in hard science settings that require the rather cinematic performance levels of reactionless thrusters. Many fictional photon drives or drive lasers are best modeled as conversion thrusters. Grav Drives (TL12): generate a bubble of space-time with its own arbitrary gravity, similar in principle to contragravity generators. Since the bubble occupants don't feel the acceleration, grav drive ships can safely pull hundreds of Gs. Grav drives are logical precursors to or spin-offs from warp drive - indeed some of the recently popular 'real' warp drives have STL cousins that do not involve negative energy densities and hence may even be really possible, though the energy consumption would be on the order of a photon drive. Some purely fictional versions ignore relativity, allowing the bubble to accelerate up to (and sometimes past) the speed of light using the Newtonian relationships. Hyperdrives (TL10): In some settings hyperdrives work within a solar system, allowing interplanetary travel by making microjumps. Unlike low speed warp, this won't entirely replace STL engines, but it will usually replace them for interplanetary (as opposed to cislunar) applications. Inertial Brakes (TL 14): These are inertia sinks able to dump some of the vehicle's momentum into the motion of a nearby planet, another dimension, the galactic gravitational field etc, providing an undetectable deceleration. Reduce the effective G-force of any maneuver by (dumping thrust/Lwt) Gs, and add 21.9 mph/s x (dumping thrust/Lwt) to all Decel ratings. Incidentally there is no reason standard reactionless drives can't be redefined as inertialess - causing no perceptible G-forces on the vehicle occupants. Magnetic Planetary Drive (TL 12): A Warehouse 23 UFO technology for maneuvering near a planet. An MPD produces apparently reactionless thrust by surfing on the planetary magnetic (or in some variations gravitational) field. For the realistic version see Magnetic Sails (p31a). MPD Side-Effects: An operating MPD causes odd electrical or magnetic effects. Headlights blink out, instruments (particularly compasses) react wildly, and so on. Many factors can affect this; in game terms, it happens whenever the GM wants it to. Warp Drive (TL10): Warp engines do not have a minimum speed; if they work in a star system, all other space propulsion systems are obsolete. The thrust factor needed for STL travel is WTF = 0.00084 x Lwt (in tons) x speed(in fractions of c). A very modest 0.084kW/ton allows travel at the speed of light. Notice the inertialess quality of warp, turn off the engine and the vehicle stops dead. This is also common in sublight engines in bad SF. Reactionless Thruster Table 12 Grav Drive (0.0010 x thrust) +20 0.001 $50 13+ Grav Drive (0.0005 x thrust) +10 0.001 $20 14 Inertial Brakes (0.001 x thrust) 0.2 $1000 Volume is weight/100. 12 MPD Core (0.04 x thrust) 0.1 $250 ________________________________________ Propulsion and Lift p39a Stardrives ________________________________________ *Jump Reaction Mass*: For some reason Traveller jump drives consume huge volumes of hydrogen, with significant effects on starship tactics. The easiest way to preserve this feel is to design the drives as ordinary jump drives and add a fuel consumption of 60H per ton of jump capacity per parsec jumped. *Hyperspace Maneuvering*: Some forms of jump/hyperspace allow ships to maneuver and even engage in combat while in FTL space. This could use the normal space drives, or it might use warp drives with the 'hyperspace' being simply a special effect. ________________________________________ Propulsion and Lift p40a Hot Air Balloons ________________________________________ Some fairly simple rules can be much more realistic than negligible weight and flat fuel costs. Find the heat flow to maintain the balloon temperature - about 0.00025 kW x surface area(sf) x temperature difference (K) - less in near vacuum or through thick walls, but those are bad conditions for balloons. For the standard hot air temperature, this is 0.02 kW x surface area(sf). Install a heat source to supply that. A burner weighs 0.025 lb/kW, uses 0.3G/hr/kW and costs $25/lb. An electric heater weighs 0.5 lb/kW, costs $50/lb and consumes 1kWe/kW of heat. Other sources are possible - nuclear reactors for example produce about 3 times as much waste heat as electric power. High Temperature Balloons. For 3 times the weight and 50 times the cost gasbag fabrics can withstand up to 3000K, and for rigid airships fireproof ablative armor hulls can do the same. Usually there is no reason to do this, but hydrogen superheated by a fission reactor is a serious proposal for supporting a Jupiter atmosphere probe. At 1500 K, about the limit of burner performance, hot air lift is 15.4 cf/lb and consumes 0.3 kW x area. ________________________________________ Propulsion and Lift p40a Lifting Gas ________________________________________ In general, the lift produced by any lifting gas depends on the difference between its density and the density of the atmosphere outside the gasbag. The density of a gas is 0.751 x (P x mw/T) lb/cf, where P is the pressure in bars, mw is the molecular weight and T is the temperature in Kelvins. For a nonrigid gasbag the pressure of the gas is the same as the pressure of the outside air, so the options for obtaining lift are to use a lower molecular weight (the average molecular weight of terrestrial air is 28.9) or a higher temperature. Some other lifting gasses Coal Gas (TL5): also called illuminating gas, town gas, or synthesis gas, is a mixture of hydrogen and carbon monoxide, with an average molecular weight of 15.01. Town gas is manufactured by reacting water with hot carbon, and is generated in huge volumes for TL5 gaslights. CO is very toxic; in gaslights it burns to non-toxic CO2, but a balloon this is a serious hazard. Coal gas is also quite explosive, treat it as hydrogen for fire and explosion risks. Methane (TL5): CH4 (mol. wt. 16.04) methane is the major component of natural gas, found in association with oil, and a common product of biomass to fuel conversion schemes. Treat as hydrogen for fire and explosion risks. Balloons are sometimes proposed as a method of transporting natural gas to market. Steam (TL5): water (mol. wt. 18.02) is a marginal lifting gas under terrestrial conditions, because it cools and condenses on the surface of the gas cells. It could probably work with a rigid hull (condensed water would soak into a fabric gasbag) with a 0.25 kW x gas bag surface area power source to keep evaporating the water. Lift assumes steam at the boiling point (373K). Construction Foam (TL9): Construction foam isn't a gas, but when expanded in an atmosphere with helium replacing nitrogen it should harden normally into a lighter than air structure. Hardened construction foam is a rigid, fireproof DR4 HT30 material. 5 Coal Gas 28 $0.02 5 Methane 30 $0.05 5 Steam 24 $0 9 Construction Foam 52 $0.50 ________________________________________ Propulsion and Lift p40a Pulp Lifting Agents ________________________________________ The puny lift of hydrogen will never do for the flyers of Barsoom or the aerial fortress of the fiendish Dr. Abdul Khan. In science fantasy and nineteenth century adventure novels a variety of other 'lighter than air' lifting agents can be found. Liftwood (TL0): is the Martian antigravity wood in Space 1889. To use it, build the vehicle with a wooden structure (p19) or armor (p21). Lift in the standard atmosphere is 5 lb per lb of liftwood used. Cost is $25/lb. In other settings it may grow on clouds or floating islands, or other materials such as the rock of those floating islands, or the bones of dragons may have similar performances. Vacuum Balloons (TL5): a balloon filled with vacuum would lift slightly better than hydrogen (13.6 cf/lb lift). The catch is a container full of vacuum has to be fairly strong or it will be crushed by the air pressure. Under 1 bar pressure this requires DR12 (x4 if extra light frame, x2 if light, x0.5 if heavy, x0.25 if extra heavy), though after TL11 a pressure screen (p72a) could be used instead. Imaginary Elements (late TL5): between the invention of spectroscopy and the discovery of atomic number, many new low atomic weight elements were reported, mostly in astronomical spectra. Helium turned out to be real, and in an early pulp or steampunk setting others might also. Some 'elements' reported in the period scientific literature include arconium (atomic weight 2.9), coronium (2.1, also detected in volcanic gasses), aurorium (1.31, also called nebulium), protohydrogen (0.082), and etherion (0.001, an emission from heated finely powdered glass). They might also form gaseous compounds, hydrogen coronide (H2Cn molecular weight 4.1) could be a nonflammable gas more common than helium.... Antigravity Gasses (TL5): provide lift beyond that possible for buoyancy alone. The least farfetched provide the same lift as vacuum, but most are better than that; ten times the lift of hydrogen (1.48 cf/lb) is a popular figure. Even though they work by antigravity rather than buoyancy, most work only in an atmosphere, and many even change lift with changing air pressure. Origin and cost are up to the GM, but most are either cheap (so our heroes can afford them) or easily made (so they can be whipped up from the materials available in Darkest Africa). Destructive distillation of liftwood or its biological relatives is a logical source, but exposure to radioactivity and the action of acid on unobtainum metal are also popular. Of course if the fiendish doctor's flying fortress is lifted by gases exhaled by small children who have had a lethal dose of radium blown into their lungs, the heroes are unlikely to duplicate at least that particular bit of world altering technology. ________________________________________ Propulsion and Lift p41a Hoverfans ________________________________________ Hovercraft need not be lifted with ducted fans. Any reaction engine close to the ground doubles lift from reflection, and could increase the effect with a properly designed GEV or SEV system. Horizontal thrust is not increased, so a vectored thrust system must apportion the thrust *first*, then multiply the lift component, not multiply total thrust. _________________________________________ Propulsion and Lift p41a Progravity Generators (TL12) _________________________________________ Progravity artificially enhances the pull of gravity, increasing the apparent weight of the vehicle. Use the statistics for Contragravity Generators, effective gravity increases by ('lift'/Lwt) Gs. Mass does not change, so mass based statistics (accel, MR) are usually unaffected. Though less useful than Contragravity, there are some applications: increasing aircraft dive speed, increasing orbital velocity without changing orbits, exceeding the gMR limit on low gravity worlds, or building submersibles that only sink when the power is on.