Canonical List of Space Transport and Engineering Methods Version 0.75 28 Jun 1994 Dani Eder Route 1, Box 188-2 Athens, AL 35611 eder@hsvaic.hv.boeing.com Introduction This document is a list of all known space transport methods and some space engineering methods. It includes only those methods whose underlying physical principles are understood (i.e. no warp drives as in Star Trek). It is the product of a number of years of collecting - and occasionally inventing - them. I am motivated by a desire to see civilization expand into space and my frustration by the slow pace of progress at the current time. Most current space vehicles and projects use techniques that existed in the 1950's and 1960's. Some new ideas were developed as early as 1960, but have not been put into used even today. From the 1970's to today many additional ideas have been generated. Most of these have received scant attention. By disseminating information on these ideas, I hope others will realize the vast untapped potential contained in these ideas. This draft (version 0.75) lists all the concepts I am aware of, with at least a basic description of each. As you can tell by the version number, which is less than one, this is still very much a work in progress. Later versions of this document are intended to flesh out each method with improved descriptions and current references. If you know of a method which is not on this list, I would appreciate being informed of it. If you have references or text descriptions on a concept, they would be appreciated also. Some related information on the basics of space transport, the forces and energies used, and space project engineering are included. Editorial comments and material that needs lots of editing appear in square brackets. The document contains the following sections: Section A: Basics of Space Transport Section B: Propulsive Forces List Section C: Energy Sources List Section D: Propulsion Concepts List Section E: Space Engineering Methods Section F: General References Revision History: version date comments 0.1-0.7 <5/94 Various in house drafts 0.71 3 Jun 94 Translated from Word to ASCII and posted to sci.space.tech 0.72 8 Jun 94 Cleaned up text, added ideas from Landis. ------------------------------------ Section A: Basics of Space Transport ------------------------------------ The traditional job of the rocket designer has been to find the best compromise between high cost and small payload. Larger payloads can be achieved by making a rocket last a single flight (thus using lighter structures than ones built to last many flights), and by dropping parts of the propulsion system (as fuel is used up less thrust is required to maintain acceleration, so you can drop engines). These measures are expensive (you have to replace or re-assemble the rocket), but were necessary in the past because of the weight of structures and the low performance of chemical rockets. A.1 The rocket equation Some numbers will illustrate the problem. A good chemical rocket has an exhaust velocity (the speed of the gases coming out the nozzle) of 4500 m/s. The velocity to reach orbit is about 9000 m/s. The basic equation of rocketry, the "rocket equation" tells you that the ratio of rocket mass when full of fuel to rocket mass after burning the fuel is: m(i) / m(f) = exp ( dV / v(e) ) Where: m(i) = intial mass m(f) = final mass dV = velocity change (9000 m/s in this case) v(e) = exhaust velocity (4500 m/s in this case) So in our example, dV/v(e) = 2, so m(i)/m(f) = exp(2) = 7.39. Therefore 1/7.39, or 13.5% of the initial weight is left on reaching orbit. In the past (before 1980s), the structure would be about 15% of the takeoff mass, so there was a negative payload (i.e. you couldn't get to orbit), even with a throw-away structure. The rocket equation is generally valid for any type of reaction engine with any velocity change. A.2 Staging In an attempt to increase the payload fraction, staging (dropping part of the rocket during the ascent) has been used. The vehicle is much lighter as it burns off fuel. Less thrust, and hence fewer or smaller engines are required in the later part of the launch. As propellant tanks are emptied, they can be dropped off. A set of engines and tanks dropped as a unit is called a 'stage', and they are numbered in the order they are used and dropped (hence first stage, second stage, etc.). The drawback to staging is that your vehicle must be re-assembled before the next flight. This makes operating the vehicle more expensive. To continue the example above, let us split the vehicle into two stages, each of which provides half of the velocity to orbit. Using the rocket equation, each stage has a ratio of initial to final mass, or mass ratio, of exp (1) = 2.72:1. Thus after the first stage burns it's fuel, 1/2.72 = 36.8% of the initial vehicle remains. The fuel for the first stage represents 85% of the total first stage mass. The other 15%, the structure and engines, is 11.1% of the total vehicle mass. So the first stage in total is 74.4% of the total vehicle. The second stage and payload is then 25.6% of the takeoff mass. Similarly, the second stage has the same mass ratio, and so 36.8% of it's mass is left after it burns it's fuel. Taking 15% for the structure, we have 21.8% of the second stage+payload for the payload alone. Thus the payload = 21.8% of 25.6% = 5.6% of the total vehicle mass. This is a positive figure, unlike the single stage case, which is why all rockets so far have used more than one stage. A.3 Structures The non-fuel mass of a stage can be grouped into engines, tanks, and 'other'. Engines produce 40-100 times their weight in thrust. For liftoff from the ground, you want about 1.3 times the vehicle weight in thrust, so the engines are about 1.3-3% of the total weight. A large tank, such as the Shuttle External Tank, can weigh 4% of the fuel weight, but other tanks can range up to 10% of the fuel weight. 'Other' inlcudes plumbing, parachutes (if you want to use it again) guidance systems, and such non-propulsion parts. It can range from 1% up to 10% of the total weight. Older materials required 15% of the total weight for one-use structures. Modern materials require about 10% of the total weight for re-useable structures. Structures tend to get heavier at the rate of 10% for each factor of 10 in life. So a 100-use structure will be about 20% heavier than a one-use structure. A.4 Orbit equations The circular orbit velocity, v(circ), for any body can be found from: v(circ) = sqrt ( GM/r ) Where: G = Gravitational constant M = Mass of body orbited r = radius to center of body orbited G is a univeral constant, and the mass of the Earth is essentially constant (neglecting falling meteors and things we launch away from Earth), so often the product G*M = K = 3.986 x 10^14 m^3/s^2 is used. Escape velocity = sqrt ( 2GM/r ), or sqrt(2) = 1.414 times circular orbit velocity. A.5 Ascent Trajectories Circular orbit velocity at the earth's surface is 7910 meter/sec. At the equator, the Earth rotates eastward at 465 meters/sec, so in theory a transportation system has to provide the difference, or 7445 meters/sec. The Earth's atmosphere causes losses that add to the theoretical velocity increment for many space transportation methods. In the case of chemical rockets, they normally fly straight up intially, so as to spend the least amount of time incurring aerodynamic drag. The vertical velocity thus achieved does not contribute to the circular orbit veloicty (since they are perpendicular), so an optimized ascent trajectory rather quickly pitches down from vertical towards the horizontal. Just enough climb is used to clear the atmosphere and minimize aerodynamic drag. The rocket consumes fuel to climb vertically and to overcome drag, so it would achieve a higher final velocity in a drag and gravity free environment. The velocity it would achieve under these conditions is called the 'ideal velocity'. It is this value that the propulsion system is designed to meet. The 'real velocity' is what the rocket actually has left after the drag and gravity effects. These are called drag losses and gee losses respectively. A real rocket has to provide about 9000 meters/sec to reach orbit, so the losses are about 1500 meters/sec, or a 20% penalty. A.6 Combining Methods There is no law that says you have to use the same method of propulsion all the way from the ground to orbit. In fact, it makes sense to use different methods if one does better in the atmosphere and another does better in the later, vacuum part of the ascent. In past rockets, this has been done by using different type of fuel for different stages in a rocket. In the early part of the flight, air drag is important, so a dense fuel is preferred. A dense fuel means smaller fuel tanks, and hence less area to create drag. Thus the Saturn V used liquid oxygen/kerosine and the Shuttle uses solid rockets for the first stage, both being dense fuels. Both use liquid oxygen/ liquid hydrogen for the second stage. This has the highest performance in use for a chemical rocket fuel. The Pegasus rocket uses an aircraft to get above the bulk of the atmosphere. A sub-sonic jet engine has about ten times the performance of a chemical rocket, mostly because it does not have to carry oxygen to burn. Many, many propulsion combinations are possible in getting to Earth orbit and beyond. A large part of space propulsion design is choosing which methods to use and when to switch from one to another. --------------------------------- Section B: Propulsive Forces List --------------------------------- This section lists the forces that can be used for propulsion. The forces can be broken into two classes. The first class is reaction force from an expelled material. The second class are forces created by interaction with an entity outside the vehicle. B.1 Reaction Against Exhaust The list of expelled materials is generally in order of velocity. The reaction law is Force = Mass x Acceleration (F = ma). Acceleration is change in velocity per time (dv/dt), so we can move the dt term to the mass and re-write the reaction law as F = (dm/dt)v (Force equals mass change per time times velocity). In this form we can see the factors that affect propulsion performance. If we want more force (thrust), we can either increase the mass flow rate, or increase the velocity, or some combination. Since a rocket by definition carries its own fuel, which is a finite quantity, to get more performance we generally want as high an expelled velocity as possible. In the list that follows, the range of reasonably achieved velocities is listed. Note that what we mainly use today (combustion gas) is among the lowest in performance. B.1a Bulk Solid 5 km/s B.1b Heated Gas 10 km/s B.1c Combustion Gas 5 km/s B.1d Plasma 20 km/s B.1e Ion 100 km/s B.1f Atomic Particle 10,000 km/s B.1g Photon 300,000 km/s B.2 External Interaction B.2a Mechanical Traction B.2b Cable Tension B.2c Friction B.2d Gas Pressure B.2e Aerodynamic Forces B.2f Photon Reflection B.2g Solar Wind Deflection B.2h Magnetic Field B.2i Gravity Field ------------------------------ Section C: Energy Sources List ------------------------------ This section lists the sources of energy that can be used for space transport. C.1 Mechanical Sources C.1a Compressed Gas C.1b Potential Energy C.1c Kinetic Energy C.2 Chemical Sources C.2a Fuel-Atmosphere Combustion C.2b Fuel-Oxidizer Combustion C.3 Thermal Sources C.3a Heated Storage Bed C.3b Concentrated Sunlight C.4 Electrical Sources C.4a Power Line C.4b Battery Storage C.4c Magnetic Storage C.4d Photovoltaic Array [C1] Anonymous "Conference Record of the Nineteenth IEEE Photovoltaic Specialists Conference- 1987", New Orleans, Louisiana, 4-8 May 1987. [C2] Anonymous "NASA Conference Publication 2475: Space Photovoltaic Research and Technology 1986: High Efficiency, Space Environment, and Array Technology", Cleveland, Ohio, 7-9 October 1986. [C3] Chubb, Donald L. "Combination Solar Photovoltaic Heat Engine Energy Converter", Journal of Propulsion and Power, v 3 no 4 pp 365-74, July-August 1987. C.4e Solar-Driven Turbine/Generator [C4] Spielberg, J. I. "A Solar Powered Outer Space Helium Heat Engine", Appl. Phys. Commun. vol 4 no 4 pp 279-84, 1984-1985. C.4f Microwave Antenna Array C.5 Beam Sources C.5a Laser C.5b Microwave C.5c Neutral Particle C.6 Nuclear Sources C.6a Radioactive decay [C5] Lockwood, A.; Ewell, R.; Wood, C. "Advanced High Temperature Thermo-electrics for Space Power", Proceedings of the 16th Intersociety Energy Conversion Engineering Conference, v 2 pp 1985- 1990, 1981. C.6b Nuclear Fission [C6] El Genk, M.S.; Hoover, M. D. "Space Nuclear Power Systems 1986: Proceedings of the Third Symposium", 1987. [C7] Sovie, Ronald J. "SP-100 Advanced Technology Program", NASA Technical Memorandum 89888, 1987. [C8] Bloomfield, Harvey S. "Small Space Reactor Power Systems for Unmanned Solar System Exploration Missions", NASA Technical Memorandum 100228, December 1987. [C9] Buden, D.; Trapp, T. J. "Space Nuclear Power Plant Technology Development Philosophy for a Ground Engineering Phase", Proceedings of the 20th Intersociety Energy Conversion Engineering Conference vol 1 pp 358-66, 1985. C.6c Nuclear Fusion [C10] Miley, G. H. et al "Advanced Fusion Power: A preliminary Assessment, final report 1986-1987". National Academy of Sciences report #AD-A185903, 1987. [C11] Eklund, P. M. "Quark-Catalyzed Fusion-Heated Rockets", AIAA paper number 82-1218 presented at AIAA/SAE/ASME 18th Joint Propulsion Conference, Cleveland, Ohio, 21-23 June 1982. C.6d Nuclear Explosions C.7 Matter Conversion Sources C.7a Antimatter [C12] Hora, H.; Loeb, H. W. "Efficient Production of Antihydrogen by Laser for Space Propulsion", Z. Flugwiss. Weltraumforsch., v. 10 no. 6 pp 393-400, November-December 1986. [C13] Forward, R. L., ed. "Mirror Matter Newsletter", self published, all volumes, contains extensive bibliography. C.7b Quantum Black Hole ----------------------------------- Section D: Propulsion Concepts List ----------------------------------- This section lists propulsion concepts grouped into categories by type. D.1 Structural Methods D.1a Static Structures Static structures have parts which are mostly fixed in relation to each other, although the structure as a whole may move with respect to the ground. Large structures are primarily governed in their design by the ratio of strength to density, or specific strength. Other important properties in certain cases include stiffness, temperature dependance of properties, and resistance to decay from the surrounding environment. Methods of movement on the structure include: (i) Standard elevator: (refer to standard engineering references for design details) (ii) Inchworm type winch: A small motor driven trolley pulls a length of cable behind it as it climbs up the structure. It then hooks the cable to a fixed point on the structure. The cargo elevator remains attached to the next lower point on the structure during this time. The elevator then uses an on-board winch to reel itself up from one attachment point to the next. This type of winch is useful where continuous attachment track or full length elevator cable would be too heavy. Requires independant power for winch. (iii) Fluid transfer in pipes: For example, Dr. Dana Andrews has suggested pumping gas generated on the Lunar surface up to the Lunar L2 point. A column of Oxygen at .1 atmosphere at L2, and a temperature of 1000 K (a solar heated pipe can be used to keep the gas hot) would have a pressure of 2310 atm (234 MPa) at the bottom. Another approach is to have pumping stations spaced along the tower. 1 Large Towers Alternate Names: Type: C.1b/B.2a (Potential Energy via Mechanical Traction) Description: Use of advanced aerospace materials makes possible the construction of towers that are many kilometers tall. Such towers can be used as a high altitude platform, as a launch platform for a propulsive vehicle, or a support structure for an accelerator system. Structural design is a major issue. If a tall structure is being considered, the weight of the tower structure becomes the driving issue, because it can end up being many times the weight of the 'payload' the tower is supporting. If the 'payload' is at the top of the tower, the structure just underneath only has to support the payload's weight. The next piece of structure below that must support the payload plus the top bit of structure, so it has to be a little bit beefier (have a larger cross sectional area). Going down the structure, it has to get stronger and stronger to support the greater weight above. To put some numbers to the problem, let us take a plain carbon steel structure (the type of steel used for ordinary building construction). It has an allowable load of 125 MPa. To make the problem simple, assume we are holding up a 1275 kg payload on top of the tower, which under one gravity has a weight of 12,500 N. Therefore we need one square centimeter of cross sectional area of steel to hold up the weight. Steel has a density of 7800 kg per cubic meter. The top meter of the tower has a volume of 0.01x0.01x1.0= 0.0001 cubic meter. This has a mass of 0.78kg. So the structure 1 meter down from the top has to support a mass of 1275.78 kg, i.e. the payload plus the top meter of steel. The load has increased by 0.06%, so the cross sectional area also increases by 0.06%. The area increases in a compound interest fashion at the rate of 0.06% per meter as you go down the tower. Over the course of 1 km in height, the increase is by a factor of 1.8433. We define the scale height of a structure as the length over which the cross sectional area increases by a factor of e (2.71828...). In the case we have been using it is 1635 meters. The scale height can be found by dividing the allowable load of the material by the density times the local acceleration (one gravity in the case of the Earth): h(scale) = load / (density x acceleration) = 125 MPa / (7800 kg/m^3 x 9.80665 m/s^2) = 1635 meters So a tower 4.9 km tall would have an area at the bottom e cubed (20.08) times the area at the top, and the weight of steel would be e^3 - 1, or 19.08 times the payload weight. Now, plain carbon steel is not a very good material to use if you want a really big tower. Let us look at advanced carbon composites, such as is used in modern aircraft and spacecraft. One specific formulation (Amoco T300/ERL1906 if you must know) has a compressive strength of 1930 MPa (280,000 psi). We derate this by half to get the allowable load. This is the same as is done for the steel, where you only use 50% of the strength to give you a safety margin. So we have 965 MPa (140,000 psi) as an allowable load. The density is 1827 kg/m3 (0.066 lb/cu in.) Dividing we have a scale height of 53,878 meters (176,800 feet, or 33.5 miles) If you build several scale heights tall, you can see in theory you could build structures hundreds of kilometers tall. In a real structure the payload probably won't all be at the top. For the bottom 20 kilometers or so wind loads, ice build-up, and other environmental effects have to be accounted for. Above this height, atomic oxygen can attack your carbon/epoxy structural material, so a protective layer is needed. This adds weight so there will be some reduction in how high you can build. But you still can build many times taller than anything built so far. These types of towers can be built 'from the top down' in order to avoid construction work in a vacuum. In this process, the top section of the tower is assembled at ground level. Jacks raise the section up by one section length. The next section down is then installed underneath. The process is repeated for the whole tower height, so all the construction work takes place near ground level. Special anchoring provisions are required to stabilize the tower while being built in this fashion. Status: The tallest existing structure is a TV antenna which is 655m (2150 ft ) tall. Some engineering/ architectural studies on very large towers have been done. No attempts to build anything over 1000 meters tall are known. This concept should be within current technology for structural materials, although it may require an advance in construction techniques. 1a Unguyed Mast In this approach the base of the tower needs to be 1/10 to 1/20 of the tower height to provide stability. In the lower part of the tower, wind loads will require the base to spread at a greater slope than the upper part, which only depends on buckling for its necessary base width. This approach assumes that most of the loads on the tower act vertically, as in an elevator riding up and down the tower height. 1b Guyed Mast If the loads are substantially sideways the tower mast may be stabilized by a set of guy wires that spread out at a 30-45 degree angle. 1c Series of Towers A very long, tall structure, such as a 300 km long electromagnetic accelerator, may use a series of towers as supports. References: 2 Tethers Alternate Names: Beanstalks, Jacob's Ladder, Space Bridge, Geosynchronous Towers Type: Description: Tensile members in orbit store and transfer momentum to vehicles. The tethers may be gravity-gradient stabilized or rotating endwise. A ground-to- geosynchronous cable is not feasible with today's structural materials. Tethers, of which a geosynchronous cable is a special case, obey an exponential mass-ratio-to-payload-weight relation similar to that for chemical rockets. It is possible, with existing materials, to build tethers which will provide several km/s of delta v. In a launch system application, an orbiting tether can be set rotating so that the lower end travels slower than orbital velocity. A launch vehicle could rendezvous with the tether, drop a payload, then release. Since only the payload remains in orbit, the propulsion system on the tether only has to provide momentum to add to the payload; the launch vehicle never has to take itself to orbital velocity. In this case the tether acts as a 'momentum bank', lending velocity to the launch vehicle temporarily while the payload is unloaded. Tethers are the generalization of the 'beanstalk' or geosynchronous tower concept. In the original concept, a cable is placed so that it hangs vertically over the equator, and is in a 24 hour orbit. It thus appears to hang vertically over one spot on the Earth. The task of reaching Earth orbit then reduces to a very long (35,000 km) elevator ride. Unfortunately for the original idea, tensile strengths approaching 2 million pounds per square inch (12.5 GPa) are required for reasonable designs. Tethers generalize on the original concept by (1) allowing any length, (2) allowing any orbital period, (3) allowing any swinging or rotating states, and, (4) allowing multiple tethers to be connected in various geometries. One simple case would be a tether vertically oriented in earth orbit, spanning the altitudes from 300km to 2000km. A cargo could be carried on an elevator over this altitude range. While it is not as elegant as the geosynchronous case, it is constructable with existing materials. Material strength to density ratio is the critical criterion for designing tethers. To build a minimum mass tether, one wishes to taper it's cross section by a factor of e per scale length. The scale length is the length at which under one gravity, the weight of a constant section cable equals the tensile strength (i.e. just breaks). While the gravitational field around a planet is non-uniform, the 'depth' of the gravity well is equal to the surface gravity times the radius of the planet. The following table shows the taper factors derived for each gravity well given materials available at different times: ======================================================================== Taper Factors Required For Various Gravity Wells and Technology Levels | ------------------------------------------------------------------------ Gravity Depth ---------------- Time Period -------------- Well (g-km) 1960s 1970s 1980s 1990s 2000s ---------- ------ ----- ----- ----- ----- ----- Moon's 287 21 3.1 2.5 2.1 1.9 Mars' 1289 7.8E5 160 58 28 17 1/2 Earth's 3190 3.8E14 2.7E5 2.3E4 4000 1060 Earth's 6375 1.4E29 7.2E10 5.1E8 1.5E7 1.1E6 ------------------------------------------------------------------------ Material Fiber- Kevlar Carbon Carbon Adv. glass Carbon Tensile Str. (MPa) 2410 3625 5650 6895 8273 Density (kg/m^3) 2580 1450 1810 1827 1840 Scale length (km@1g) 95 255 318 385 458 ======================================================================== Status: Variations: 2a Orbital Hanging Tether 2b Orbital Rotating Tether 2c Terrestrial Tether One vehicle pulls another without direct mechanical attachment. Allows modification of one vehicle without reconfiguration of joined pair. Allows one type of vehicle to pull another. Reduces loads on lead vehicle by lift-to- drag ratio. References: [D1] Ebisch, K. E. "Skyhook: Another Space Construction Project", American Journal of Physics, v 50 no 5 pp 467-69, 1982. [D2] Carroll, J. A. "Tether Space Propulsion", AIAA paper 86-1389, 1986. [D3] Penzo, P.A. and Mayer., H.L. "Tethers and Asteroids for Artificial Gravity Assist in the Solar System" Journal of Spacecraft and Rockets, Jan- Feb 1986. (Details how a spacecraft with a kevlar tether of the same mass can change its velocity by up to slightly less than 1 km/sec. if it is travelling under that velocity wrt a suitable asteroid.) [D4] Baracat, William A., Applications of Tethers in Space: Workshop Proceedings Vols 1 and 2. (Proceedings of a workshop held in Venice, Italy, Octover 15-17, 1985) NASA Conference Publication 2422, 1986. [D5] Anderson, J. L. "Tether Technology - Conference Summary", American Institute of Astronautics and Aeronautics paper 88-0533, 1988. [D6] Penzo, Paul A. and Ammann, Paul W. Tethers in Space Handbook, 2nd Edition, NASA Office of Advanced Program Development, 1989. (NTIS N92-19248/3) 3 Aerostat Alternate Names: High altitude balloon Type: Description: One approach to minimizing drag and gravity losses is to carry a vehicle aloft with a high altitude balloon. Research balloons have carried ton-class payloads in the range of 15-30 km high, which is above the bulk of the atmosphere. Status: Variations: References: 4 Low-Density Tunnel 4a Light Gas Tunnel Alternate Names: Type: Description: One or more light gas balloons are strung along the path of a vehicle or projectile. The gas has a lower density than air. The formula for drag is 0.5*C(d)*Rho*A*v^2, where Rho is the density. Thus the lower density will lower drag. Status: Variations: References: 4b Evacuated Tunnel Alternate Names: Type: Description: An evacuated tunnel is supported up through the atmosphere (as by one or more towers). A launch system such as an electromagnetic accelerator fires a projectile up through the tunnel. Drag losses are minimized within the tunnel, and are low in the remaining part of the atmosphere which must be traversed. If the top end requires some means of keeping air from flowing in and filling the tunnel - such as a hatch that remains closed until the accelerator is about to fire. Status: Variations: References: D.1b Dynamic Structures Static structures rely on the strength of materials to hold themselves up. Dynamic structures rely on the forces generated by rapidly moving parts to hold up the structure. The advantage of this approach is it can support structures beyond the limits of material strengths. The disadvantage is that if the machinery that controls the moving parts fails, the structure falls apart. 5 Fountain/Mass Driver Alternate Names: Type: Description: An electromagnetic accelerator provides a stream of masses moving up vertically. A series of coils decelerates the masses as they go up, then accelerates them back down again, at a few gravities. When they reach bottom, the accelerator slows them down and throws them back up again, at hundreds of gravities. Thus the accelerator is many times shorther than the fountain height. The reaction of the coils to the acceleration of the fountain of masses provides a lifting force that can support a structure. The lifting force is distributed along where the coils are located. This can be along the length of a tower, or concentrated at the top, with the stream of masses in free-flight most of the way. Status: Variations: References: 6 Launch Loop Alternate Names: Type: Description: A strip or sections of a strip are maintained at super-orbital velocities. They are constrained by magnetic forces to support a structure, while being prevented from leaving orbit. A vehicle rides the strip, using magnetic braking against the strip's motion to accelerate. Several concepts using super-orbital velocity structures have been proposed. One is known as the 'launch loop'. In this concept a segmented metal ribbon is accelerated to more than orbital velocity at low Earth orbit. The ribbon is restrained from rising to higher apogees by a series of cables suspended from magnetically levitated hardware supported by the ribbons. The ribbon is guided to ground level in an evacuated tube, and turned 180 degrees using magnets on the ground. A vehicle going to orbit rides an elevator to a station where the cable moves horizontally at altitude. The vehicle accelerates using magnetic drag against the ribbon, then releases when it achieves orbital velocity. Status: Variations: References: 7 Multi-Stage Tethers Alternate Names: Type: Description: A multi-stage tether has more than one tether, with the tethers in relative motion. For example, a vertically hanging tether in Earth orbit can have a rotating tether at it's lower end. The advantage of such an arrangement is to lower the mass ratio of tether to payload compared to a single tether. The mass ratio of a rotating tether is approximately proportional to exp(tip velocity squared). If two tethers each supply half the tip velocity, then the ratio becomes exp(2(tip velocity/2)squared), which is a smaller total mass ratio. Another feature of a multi-stage tether is that the tip velocity vector of the two stages add. Since one rotates with respect to the other, the sum of the vectors changes over time. Given suitable choices of tip velocities and angular rates, one can receive and send payloads with arbitrary speed and direction up to the sum of the two vectors. Status: Variations: References: D.2 Guns and Accelerators D.2a Mechanical Accelerators 8 Leveraged Catapult Alternate Names: Type: Description: A leveraged catapult uses a relatively large or heavy driver to accelerate a smaller payload at several gravities by mechanical means. Devices such a multiple sheave pulley or a gear train convert a large force moving slowly to a small force moving fast, and transmit the force along a cable. The mechanical advantage produces more than one gravity of acceleration. This concept may be the simplest to implement on a small scale. It consists of a large weight connected via cableJ and pulley arrangement to a much lighter projectile. The weight is allowed to fall under gravity, and the projectile accelerates at much more than one gravity due to the mechanical leverage of the pulley.J Despite the seeming simplicity of the concept, velocities of severalJ km/s are possible, which would greatly reduce the size of a rocket needed to provide the balance of the velocity. The performance of this concept reaches a limit due to the weight, drag, and heating of the cable attached to the payload and the magnitude of the driving force, which is divided by the leverage ratio to yield the force on the payload. Status: Variations: 8a Drop Weight A falling mass is connected to a vehicle by a multiple-sheave pulley and high strength cable. Two types of location are possibilities - river gorges and mountain peaks. Locations such as the Grand Canyon and the Columbia River gorge have lots of vertical relief for the drop weight. At these locations the weight can consist of a large fabric bag filled with water from the river at the bottom. The bag can be emptied before hitting bottom. This reduces the weight that has to be stopped by a braking system. For mountain peak locations, the drop weight runs down a set of rails and is stopped by running into a body of water or running up an opposing hillside plus possibly wheel braking. The mountain location may be preferred because of the greater launch altitude.J 8b Locomotive Driver A set of railroad locomotives provides the motive force, which is multiplied by a gear mechanism to a higher speed. Example: launching a 20,000 lb vehicle at 3 g's to 1100 m/s: * Need 20 km straight run of rail. * Rail cars needed: - 1 tank car - 1 car special purpose to carry glider - 2-3 cars with tow rope guides - 1 car pulley system - 30 locomotives in tandem We assume the locomotive top speed is about 27 m/s, therefore a 40:1 gear ratio will provide the desired speed at the vehicle. Locomotive traction averages 80,000 lb/engine, or 2000 lb per engine when reduced through the gear ratio. The gear-down mechanism and launch cable drum are mounted on a flatbed rail car. This car can be anchored to a foundation on either side of the railroad track to hold it in place when the combined pull of the locomotives is exerted. The starting traction of 30 locomotives is 1800 tons. Since the couplings between engines are probably not designed for this load, a set of steel cables on both sides of the locomotives are used to transmit the traction force from each engine to the gear mechanism. The vehicle is attached to the anchored rail car by a high-strength cable which is 20 km long. At 3 g's it takes this distance to accelerate to the desired speed. Two or three rail cars are spaced out along the 20 km with erectable towers with a pulley wheel on top, to guide the cable and keep it off the ground during the initial acceleration. The vehicle has glider type wings attached that will generate lift as it gains speed, so the vehicle will climb once it reaches 100 m/s or so. When the vehicle reaches the desired speed, the cable is released and the vehicle continues to climb under the glider's lift. Eventually the glider drops the vehicle, which proceeds under rocket power. A small prototype: Single Locomotive driver. 1250 lb rocket @ 4 g peak. Final velocity = 700 m/s. Accel time = 17.5 sec distance = 0.5at2 = 6.1 km. Engine traction = 80,000 lb average @ 25:1 gear ratio. 8c Jet Driver This is similar to the locomotive case, but the gear ratio is lower since the jet can reach a higher speed on a take-off run. Example: an F-15 can tow 40,000 lb rope tension if near empty. @10:1 gear ratio can accelerate 1000 lb object @ 4 g's. Aircraft top speed on deck = 300 m/s. Object top speed in theory would be 3000 m/s. In practice would be limited by aerodynamics and cable heating (perhaps to 1500 m/s? limit is not well understood) References: 9 Rotary Sling Alternate Names: Centrifuge Catapult Type: Description: In principle, this is a sling or bolo scaled up and using aerospace materials. A drive arm is driven in rotation by some means. A cable with the payload attached to the end is played out gradually as the system comes up to speed. The drive arm leads the cable slightly so the cable and payload see a torque that continues to accelerate them. When the desired payload velocity is reached, the payload releases and flies off. The cable is then retracted and the drive arm slows down. When it stops, another payload is attached. In a vacuum, such as on the Lunar surface, this is theoretically a very efficient system, as the sling can be driven by an electric motor and the mechanical losses can be held to a low value. Some method of recovering the energy of the arm and cable (such as by transferring it to a second system by using the motor as a generator), can lead to efficiencies over 60% in theory. On Earth such a system is hindered by air drag. One method of reducing drag is to attach a shaped fairing to the cable material, so as to lower drag compared to a circular cable. Another is to mount the drive arm on the top of a large tower, so the cable is not moving in dense air. A third is to generate lift along the cable or at the payload, so the rapidly moving part of the cable, near the payload, is at a high altitude, where there is less drag. Example #1: Single cable * Assume v(tip) = 3000 m/s and a(tip) = 1000 m/s2 * Then r = 9000 meters. * For 1000 kg projectile at end, cable tension is 1 MN. If carbon fiber at 3400 MPa design stress, then cable area is 1/3400 m2, or about 3 cm2. * Cable weight is 0.6 kg/meter, adds 600 N/meter at tip, or 0.06%/meter. Over 9 km, area increases by factor of 6. * Accelerating force to spin up in 1 hour is 1 m/s/s or 1000 N. * Drag force/meter @ sea level = ~0.5 x drag force/meter at tip = 0.5Cd rho A v2. Cd = 0.04 for shaped airfoil. rho =1.225 kg/m3 . A = 0.01 m2. v= 3000 m/s. Drag = 2205 N/m x 0.5 factor = 1102 N/m. * Want drag<= spin up force, thus want drag < 0.11 N/m. * Therefore want air density at 10-4 x sea level = 240,000 ft = 73 km high. * Thus put 9000 meter cable at top of 73 km tall tower with drive motor to spin up cable. Example #2: Two Stage Centrifuge Catapult % High g's small payload catapult. % Assume 3 km/s/stage % 33 g's in 1st stage and 67 g's in second stage. (this example is incomplete) Status: Variations: References: D.2b Artillery 10 Solid Propellant Charge Alternate Names: Type: Description:Explosive vaporizes behind projectile in barrel. Gas pressure accelerates projectile to high velocity. Conventional artillery reaches speeds of around 1000 m/s. Status: Artillery has a long history and extensive use. The High Altitude Research Probe project attached two naval gun barrels in series and used relatively light shells to reach higher muzzle velocities than conventional artillery. Variations: References: Verne, Jules, "From the Earth to the Moon". 11 Liquid Propellant Charge Alternate Names: Type: Description: Similar to conventional solid propellant artillery except liquid propellants are metered into the chamber, then ignited. Liquid propellants have been studied because they produce lighter molecular weight combustion products, which leads to higher muzzle velocities, and because bulk liquids can be stored more compactly than shells, and require less handling equipment to load. Status: Variations: References: 12 Gaseous Charge 12a Fuel-Oxidizer Charge Alternate Names: Type: Description: Similar to conventional artillery except gaseous propellants are metered into the chamber. This is essentially what happens in the cylinder of a car engine, as a point of reference. Status: Used as the driver for the Livermore gas gun (fuel-air mix drives 1 ton piston, which in turn compresses hydrogen working gas). Variations: References: 12b Scramjet Gun Alternate Names: Ram Accelerators Type: Description: Fuel/oxidizer mixture present in barrel is burned as projectile travels up barrel. If projectile shape resembles two cones base to base, as in an inside- out scramjet, the gas is compressed between the projectile body and barrel wall. The combustion occurs behind the point of peak compression, and produces more pressure on the aft body than the compression on the fore- body. This pressure difference provides a net force accelerating the projectile. One attraction of this concept is that a high acceleration launch can occur without the need for the projectile to use onboard propellants. If the projectile has a inlet/nozzle shape (hollow in the middle) it might continue accelerating in the atmosphere by injecting fuel into the air-only incoming flow, extending the performance beyond what a gun alone can do. Another attraction of this concept is the simplicity of the launcher, which is a simple tube capable of withstanding the internal pressure generated during combustion. Status: Research being performed at the University of Washington under Prof. Adam Bruckner. Research gun in basement of building. Variations: References: [ D7] A. Hertzberg, A.P. Bruckner, and D.W. Bogdanoff, "The Ram Accelerator: A New Chemical Method of Accelerating Projectiles to Ultrahigh Velocities" , AIAA Journal, Vol. 26, No. 2, February, 1988. (The seminal reference.) [ D8] P. Kaloupis and A.P. Bruckner, "The Ram Accelerator: A Chemically Driven Mass Launcher" , AIAA Paper 88-2968, AIAA/ASME/SAE/ASEE 24th Joint Propulsion Conference, July 11-13, 1988, Boston, MA. (Applications to surface-to-orbit launching.) [ D9] Breck W. Henderson, "Ram Accelerator Demonstrates Potential for Hypervelocity Research, Light Launch," , Aviation Week & Space Technology, September 30, 1991, pp. 50-51. [ D10] J.W. Humphreys and T.H. Sobota, "Beyond Rockets: the Scramaccelerator" , Aerospace America , Vol. 29, June, 1991, pp. 18-21. 13 Rocket Fed Gun Alternate Names: Type: Description: Rocket engine at chamber end of gun produces hot gas to accelerate projectile. In a conventional gun, all the gas is formed at once as the charge goes off. In this concept the gas is produced by a rocket type engine and fills the barrel with gas as the projectile runs down it. Compared to a conventional gun, the peak pressure is lower, so the barrel is lighter. Status: Variations: References: D.2c Light Gas Gun Light gas guns are designed to reach higher muzzle velocities than combustion guns. They do this by using hot hydrogen (or sometimes helium) as the working gas. These have a lower molecular weight, and therefore a higher speed of sound. Guns are strongly limited by the speed of sound of the gas they use. The drawback to light gas guns is that the gas does not generate high pressures and temperatures by itself (as do combustion byproducts). Therefore some external means are required to produce the gas conditions desired. 14 Pressure Tank Storage Alternate Names: Type: Description: The gas is stored in a chamber, then adiabatically expanded in a barrel, doing work against a projectile. Status: Variations: References: [D11] Taylor, R. A. "A Space Debris Simulation Facility for Spacecraft Materials Evaluation", SAMPE Quarterly , v 18 no 2 pp 28-34, 1987. 15 Underwater Storage Alternate Names: Type: Description: In a gas gun on land the amount of structural meterial in the gun is governed by the tensile strength of the barrel and chamber. In an underwater gun, an evacuated barrel is under compression by water pressure. The gas pressure in the gun can now be the external water pressure plus the pressure the barrel wall can withstand in tension, which is up to twice as high as the land version. Other features of an underwater gun are the ability to store gas with very little pressure containment (the storage tank can be in equilibrium with the surrounding water), and the ability to point the gun in different directions and elevations. The underwater gas gun consists of a gas storage chamber at some depth in a fluid, in this case the ocean, a long barrel connected to a chamber at one end and held at the surface by a floating platform at the other end, plus some supporting equipment. The chamber is a made of structural material such as steel. An inlet pipe allows filling of the chamber with a compressed gas. A valve is mounted on the inlet pipe. An outlet pipe of larger diameter than the inlet pipe connects to the gun barrel. An outlet valve is mounted on the outlet pipe. This valve may be divided into two parts: a fast opening and closing part, and a tight sealing part. The interior of the chamber is lined with insulation. The inner surface of the insulation is covered by a refractory liner, such as tungsten. An electrical lead is connected to a heating element inside the chamber.J An inert gas such as argon perfuses the insulation. The inert gas protects the chamber structure from exposure to hot hydrogen, and has a lower thermal conductivity. An inert gas fill/drain line is connected to the volume between the chamber wall and the liner. A pressure actuated relief valve connects the chamber with a volume of cold gas. This cold gas is surrounded by a flexible membrane such as rubber coated fiberglass cloth. In operation, the gas inside the chamber, the inert gas, and the water outside the chamber are all at substantially the same pressure. Thus the outer structural wall does not have to withstand large pressure differences from inside to outside. One part of the chamber wall is movable, as in a sliding piston, to allow variation in the chamber volume. The gas in the chamber is preferably hot, so as to provide the highest muzzle velocity for the gun. When the gun is operated, this gas is released into the gun barrel. In order to preserve the small pressure difference across the wall of the chamber, either the chamber volume must decrease or gas from an adjacent cold gas bladder must replace the hot gas as it is expelled. This arrangement prevents ocean water from contacting the chamber walls or hot gas. In the case of the sliding piston, the membrane collapses, with the gas formerly within it moving in behind the piston. In the alternate case, the membrane also collapses, with the gas formerly within it moving through a valve into the chamber. The chamber has an exit valve which leads to the gun barrel. It also has gas supply lines feeding the interior of the chamber and the volume between the chamber walls. These lines are connected to regulators which maintain nearly equal gas pressures, which in turn are nearly equal to the ocean pressure. This allows the chamber to be moved to the surface for maintenance, and to be placed at different depths for providing different firing pressures or different gun elevations. The muzzle of the gun is at the ocean surface, so elevation of the gun can be achieved by changing the depth of the chamber end. Since the gun as a whole is floating in the ocean, it can be pointed in any direction. Some means for heating the gas stored in the chamber is needed, such as an electric resistance heater. At the muzzle end of the gun, a tube surrounds the barrel, with a substantial volume in beween the two. There are passages through the wall of the barrel that allow the gas to diffuse into the tube rather than out the end of the gun, thus conserving the gas. At the muzzle of the gun is a valve which can rapidly open, and an ejector pump which prevents air from entering the barrel. In operation, the ejector pump starts before the gun is fired, with the valve shut. The valve is opened, then the gun is fired. In this way, the projectile encounters only near vacuum within the barrel, followed by air. Status: Variations: References: 16 Thermal Bed Heated Alternate Names: Type: Description: Hot gas is generated by flowing hydrogen through a chamber which contains refractory oxide particles. The particles are heated slowly (roughly 1 hour time period) by some type of heater near the center of the chamber. This sets up a temperature gradient, so the exterior of the chamber is relatively cool, and can thus be made of ordinary steels. When the hydrogen flows through the chamber, the large surface area of the particles allows very high heat transfer rates - so the heat in the chamber can be extracted in a fraction of a second. Example: % To match Livermore hypersonic gun, want 40 MJ projectile energy. % Assume losses and initial gas pressure are equal contributors. % Want aluminum oxide to drop 500K in operation. At 1 J/K/gm, need 80 kg of aluminum oxide. In the form of grinding wheels, we are looking at about $600 of materials. 25 wheels, 30 cm diam x 2.5 cm thick. % If pressure is 3000 psi (20.7 MPa), then 10 cm diam, 5 kg projectile will see 162,600 N force, or 32,470 m/s2. To reach 4 km/s requires 0.123 sec, distance = 250 m. Allow 500 m for losses. Alignment = 1/6 mm along length. % Final gas temp average 2000 K. Barrel volume = 4 m3. Storage tank = 0.65 m3. % Storage tank diam = 50 cm. Length = 3.3 m. % Chamber = 32 cm diam ID x 65 cm long. Status: A small research gun of this type has been built at Brookhaven Natl. Lab. Variations: References: 17 Particle Bed Reactor Heated Alternate Names: Type: Description: Hot gas is generated by flowing through particle bed type reactor. Gas expands against projectile, accelerating it. Light gas guns have been operated to above orbital velocity, and 1 kg projectiles have been accelerated to over half orbital velocity. This type of gun rapidly becomes less efficient above the speed of sound of the gas. As a consequence the working fluid is usually hot hydrogen. Conventional gas guns have used powder charge driven pistons to compress and heat the gas. This is not expected to be practical on the scale needed to launch useful payloads to orbit. One way to heat the gas is to pass it through a small particle bed nuclear reactor. This type of reactor produces a great deal of heat in a small volume, since the small particles of nuclear fuel have a large surface/volume ratio and can efficiently transfer the heat to working fluid. This uses the benefits of nuclear power for space launch, without the drawbacks of a flying reactor. Status: Variations: References: 18 Electric Discharge Heated Alternate Names: Type: Description: Gas is heated by electric discharge, then pushes against projectile in barrel. The limiting factor for a light gas gun is the speed of sound in the gas. One way to heat the gas to much higher temperatures is an electric discharge within the gas. Status: Variations: References: 19 Nuclear Charge Heated Alternate Names: Type: Description: Similar to artillery, except explosive in chamber is atomic bomb. This concept makes sense in a situation where very large payloads need to be launched. A large underground chamber is excavated, and filled with hydrogen gas as the working fluid. A large barrel leads off the chamber upward at an angle. A crossbar is set into the barrel near the chamber, and the projectile is attached to the crossbar with a bolt that is designed to fail at a pre-determined stress. This restrains the projectile until the operating pressure is reached. A small atomic bomb is suspended in the chamber and detonated to create lots of hot hydrogen in a very short time. Status: Variations: References: 20 Combustion Driven Piston Alternate Names: Type: Description: This is a type of two-stage gas gun. A cylindrical chamber contains a piston. On the back side of the piston high pressure gas is generated by combustion. This can be gunpowder or a fuel-air mixture. On the front side of the piston is the working gas, which is usually hydrogen. The hydrogen is compressed and heated until a valve or seal is opened. Then the working gas accelerates the projectile. Status: This type of gas gun is the most common that has been built. They were first constructed in the 1960's or earlier. The largest gun of this type is a Lawrence Livermore Laboratory, where it is being used to test scramjet components at 2.4 km/s (Mach 8) (Dec. 1993). It has a 4 inchx150ft barrel and a larger diameter, 300 ft long chamber. Variations: References: [D12 ] Aviation Week & Space Technology, July 23, 1990. [D13 ] "World's Largest Light Gas Gun Nears Completion at Livermore." Aviation Week & Space Technology, August 10,1992. 21 Gravity Driven Piston Alternate Names: Type: Description: A sliding or falling mass is used to compress gas in a chamber. The gas is then expanded in a barrel. An alternate method of compressing and heating the working fluid in a light gas gun is a rapidly moving, massive piston. If the gun is built on the side of a mountain, the energy for launch is stored as potential energy in the piston. The piston floats on an air or lubricated bearing and slides down the mountain to a cylinder. The cylinder leads to a barrel containing the projectile, which accelerates upward. Status: Variations: References: D.2d Electric Accelerators Electric accelerators typically require high peak power for a short period of time. Hence inexpensive energy storage is very important for these concepts. Two places to look for inexpensive energy storage are (1) Magnetic fusion experiments, and (2) Inductive energy stores. The latter falls into subcategories: cooled normal conductors, and superconductors. 22 Railgun Alternate Names: Electromagentic Gun Type: Description: High current electricity supplied by rails is shorted through plasma arc. Plasma is accelerated by reaction against magnetic field produced by current. Plasma pushes projectile. A railgun uses magnetic forces to accelerate payloads. Typically two parallel conducting rails are bridged by a plasma arc. The plasma is accelerated downJthe gun by the arrangement of currents and fields. Given suitable power supplies, it can be considered for earth launch systems at lower accelerations than those proposed for weapon systems. Status: This device was under intensive development for the Strategic Defense Initiative. A large gun was built at Eglin AFB in Florida and used a bank of thousands of car batteries wired in parallel as a power supply. Prototype railguns achieved high velocities, but the high currents produced rail erosion. Variations: References: [D14] Robinson, C. A. "Defense Department Developing Orbital Guns", Aviation Week and Space Technology, v 121 no 12 pp 69-70, 1984. [D15] Bauer, D. P. et al "Application of Electromagnetic Accelerators to Space Propulsion" IEEE Trans. Magnetics vol MAG-18 no 1 pp 170-5, Jan. 1982. 23 Coilgun Alternate Names: Mass Driver Launcher Type: Description: Series of coils forming gun react with coil(s) on projectile magnetically, producing thrust. Popularly known as a 'mass driver', this concept uses magnetic attraction between two current carrying coils to accelerate a projectile. The concept has been developed in connection with launching lunar materials for space manufacturing.J Accelerator designs with high efficiency (>90%) and high muzzle velocitiesJ (>8 km/s) have been proposed. This potentially leads to a transportationJ system whose operating costs consist mostly of electricity, or $0.28/lb. Laboratory versions of electromagnetic accelerators have reached 1800 gravities acceleration. Accelerations in the range of ~100 gravities are sufficient for cargo launch from the surface of the earth. Status: Variations: References: [D16] Nagatomo, Makoto; Kyotani, Yoshihiro "Feasibility Study on Linear-Motor-Assisted Take-Off (LMATO) Of Winged Launch Vehicle", Acta Astronautica, v 15 no 11 pp 851-857, 1987. [D17] Kolm, H.; Mongeau, P. "Alternative Launching Medium", IEEE Spectrum, v 19 no 4 pp 30-36, 1982. [D18] Kolm, H. "An Electromagnetic 'Slingshot' for Space Propulsion", Spaceworld pp 9-14, Feb. 1978. D.3 Combustion Engines D.3a Air-Breathing Engines Concepts 24 through 27 all involve using a planet's (usually the Earth's) atmosphere as a supply of oxygen to support combustion with a fuel carried on the vehicle. It should be noted that some vehicle concepts (such as the National Aerospaceplane (NASP) would integrate more than one engine concept in a single engine. For example, most NASP configurations would have ramjet and scramjet propulsion combined in the same engine. 24 Fanjet Alternate Names: Type: Description: The fanjet is the standard type of jet engine found on passenger aircraft and military aircraft. The original form of the engine, the turbojet, has a series of turbine compressor stages to compress the incoming air flow. This is followed by a combustor where fuel is added and burned, creating a hot gas. The gas is then expanded through a turbine which is connected by a shaft to the compressor. The expanded gas emerges at high velocity from the back of the engine. The modern fanjet adds a fan which is also driven by the turbine. All of the airflow goes through the fan, but only a part goes into the compressor. The air which does not go into the compressor is said to have 'bypassed' the compressor. The 'bypass ratio' is the ratio of bypass air to combustor air. Generally higher bypass ratio engines are more fuel efficient (in units of thrust divided by fuel consumption rate). Also in general, engines that operate at higher speeds are designed with lower bypass ratios. Typical modern performance values are engine thrust-to weight ratios (T/W) of 6:1 for large subsonic engines, trending towards about 10:1 for high performance military jets. Fuel efficiency is measured in units of thrust divided by mass flow rate. In English units this is pounds divided by pounds per second, or just seconds, and is termed 'specific impulse'. In SI units this is Newtons per kilogram per second, which has the units of meters per second. In some propulsion systems, such as chemical rockets, the SI unit corresponds to the actual exhaust jet velocity. In the case of air- breathing propulsion it is not, the velocity result is just an indicator of engine efficiency. In English units the performance of subsonic engines is about 10,000 seconds, trending to about 7000 seconds for supersonic military engines. Fanjets and turbojets operate up to about 3.5 times the speed of sound (M=3.5). Status: In common use on aircraft for aircraft propulsion. The B-52 bomber has been used to carry the Pegasus three stage solid rocket to 35,000 ft altitude. The B-52 uses 8 fanjet type engines for propulsion. Numerous paper studies have been made of using aircraft as carriers for rocket stages. Variations: References: 25 Turbo-Ramjet Alternate Names: Type: Description: A fan compresses incoming air stream, which is then mixed with fuel, burned and exhausted. Compressor is driven by gas generator/turbine. In a fanjet, the incoming air is compressed and heated by the compressor stages, then mixed with fuel and run through the turbine stages. At higher velocities the air gets hotter in compression since it has a higher incoming kinetic energy. This leads to a higher turbine temperature. Eventually a turbine temperature limit is reached based on the material used, which sets a limit to the speed of the engine. In the turbo-ramjet the compressor is driven by a gas generator/turbine set which use on-board propellant for their operation. Since the gas generator is independant of the flight speed, it can operate over a wider range of Mach numbers than the fanjet ( to Mach 6 vs. to Mach 3) Status: Variations: References: 26 Ramjet Alternate Names: Type: Description: Incoming air stream is accelerated to subsonic relative to engine, mixed with fuel, then exhausted. The incoming air is moving at the vehicle velocity entering the engine. After burning the fuel, the air is hotter and can expand to a higher velocity out the nozzle. This sets up a pressure difference that leaves a net thrust. Ramjets cannot operate at zero speed, but they can reach somewhat higher limits than an engine with rotating machinery (range Mach 0.5 to about Mach 8). Status: Variations: References: 27 Scramjet Alternate Names: Type: Description: Incoming air stream is compressed by shock waves, mixed with fuel, and expanded against engine or vehicle. Tha airstream remains supersonic relative to the vehicle. The forward thrust is produced by expanding the exhaust against a nozzle shape. Even though the gas is moving supersonically relative to the vehicle, the sidewise expansion can act on the vehicle if the slope of the nozzle is low enough. Thus the vehicle can fly faster than the exahust gas moves. Scramjets may provide useful thrust up to about Mach 15, or 60% of orbital speed. Status: Variations: References: 28 Inverted Scramjet Alternate Names: Buoyant Scramjet Type: Description: Series of balloons floated in atmosphere through which projectile flies. Projectile carries oxygen and flies through hydrogen (oxygen is much denser, so cross section is reduced. Status: Variations: References: 29 Laser-Thermal Jet Alternate Names: Type: Description: Laser is focussed and absorbed in heat exchanger, or laser- sustainedJ plasma.J Status: Variations: References: [D19] Myrabo, L. N. "Concept for Light-Powered Flight", AIAA paper number 82-1214 presented at AIAA/SAE/ASME 18th Joint Propulsion Conference, Cleveland, Ohio, 21-23 June 1982. D.3b Internally Fuelled Engines 30 Solid Rocket Alternate Names: Type: Description: A solid rocket consists of a high-strength casing, a nozzle, and a solid propellant grain which burns at a pre-designed rate. The grain is a mixture of materials containing both fuel and oxidizer, so combustion can proceed without any external action once it is ignited. Modern solid propellants have a formulation close to the following: About 15% by weight organic fuel, usually a type of rubber, about 20% by weight aluminum powder (which acts as a metallic fuel), and about 65% ammonium perchlorate (NH3ClO4), which is the oxidizer. About 1-2% epoxy is added to the powders to hold them together. The epoxy, being an organic material, is also part of the fuel. Status: Variations: References: 31 Hybrid Rocket Alternate Names: Type: Description: The hybrid rocket consists of a solid fuel grain and a liquid oxidizer. One combination is rubber for the fuel and liquid oxygen for the oxidizer. The fuel is in the form of a hollow cylinder or perforated block. The oxidizer is sprayed onto the fuel and the material is ignited. By not being self-supporting in combustion, the fuel part can be treated as non- hazardous when being made and shipped. Only when on the launch pad and the oxidizer tank is filled is there a hazardous combination. With only a single liquid to handle, the harware is relatively simple in design. Status: Variations: References: 32 Liquid Rocket Alternate Names: Type: Description: Mixture of fuel and oxidizer are burned in combustion chamber which leads to a converging-diverging nozzle. The flow becomes sonic at the narrow part of the nozzle, then continues to accelerate in the diverging part of the nozzle. A variety of propellant combinations have been used, including mono- bi-, and even tri-propellant combinations. Status: This is the most common form of launch propulsion used to date to put things into Earth orbit. Variations: Number propellant variants by oxidizer/fuel letters (incomplete list of propellants) ------------------------------ LIQUID ROCKET PROPELLANT TABLE ------------------------------ Chemical Name Formula Mol. M.P. B.P. Density Weight (K) (K) (kg/m^3) ------------------------------------------------------------------------ Oxidizers: a Oxygen O2 32 b Hydrogen Peroxide O2H2 34 c Fluorine F2 38 d Nitrogen Tetroxide N2O4 92 e Chlorine Pentafluoride ClF5 125.5 Fuels: a Hydrogen H2 2 b Methane CH4 16 c Propane C3H8 44 d Monomethyl Hydrazine CH3N2H3 46 e Kerosine (RP-1) ~CnH2n ~14n Pump-fed Variant Pressure-fed Variant References: [D20] Cooper, Larry P. "Status of Advanced Orbital Transfer Propulsion", Space Technology (Oxford), v 7 no 3 pp 205-16, 1987. [D21] Godai, Tomifumi "H-II Rocket: New Japanese Launch VehicleJ in the 1990s", Endeavour , v 11 no 3 pp 116-21, 1987. [D22] Wilhite, A. W. "Advanced Rocket Propulsion Technology Assessment for Future Space Transportation", Journal of Spacecraft and Rockets, v 19 no 4 pp 314-19, 1982. 33 Gaseous Thruster Alternate Names: Type: Description: The propellant is introduced in gas form to the chamber. It may be a mono-propellant (a single gas) or a bi-propellant combination. Status: Variations: References: 34 Mechanically Augmented Thruster Alternate Names: Type: Description: Velocity of exaust gases is increased by placing thrusters on end of rotating arm. Adds 200-300 sec to specific impulse based on structual material capabilities. Status: Variations: References: D.4 Thermal Engines 35 Electric-Rail Rocket Alternate Names: Type: Description: High voltage electricity supplied by rails is shorted through tungsten heat exchanger, which heats hydrogen carried by vehicle flying between rails. Status: Variations: References: [D23] Wilbur, P. J.; Mitchell, C. E.; Shaw, B. D. "Electrothermal Ramjet", AIAA paper number 82-1216 presented at AIAA/SAE/ASME 18th Joint Propulsion Conference, Cleveland, OH, 21-23 June 1982. 36 Resistojet Alternate Names: Type: Description: Sunlight generates electricity, which is used to heat gas passed over or through a heating element. Status: Variations: References: [D24] Louviere, Allen J. et al "Water-Propellant Resistojets for Man- Tended Platforms", NASA Technical Memorandum 100110, 1987. 37 Solar-Thermal Alternate Names: Type: Description: Sunlight is concentrated by a reflector or lens, then heats an absorber. The absorber transfers heat to a working fluid, usually hydrogen. The hydrogen is then expanded through a nozzle. Status: Variations: References: [D25] Gartrell, C. F. "Future Solar Orbital Transfer Vehicle Concept", IEEE Transactions on Aerospace Electronic Systems, vol AES-19 no 5 pp 704-10, 1983. 38 Laser-Thermal Alternate Names: Type: Description: Beam is passed through window in rocket engine. It is then absorbed by a heat exchanger or is focussed to create laser-sustained plasma. Hot gas is then expelled through nozzle. By using an energy source external to the propellant, specific impulse increases of 100% can be achieved by using hydrogen rather than oxygen/hydrogen.J One method of doing this is with a large, ground-based laser to heat the hydrogen. This concept is applicable from the ground to orbital velocity, and may be used in conjunction with another concept. Use of laser propulsion only in an upper stage would allow smaller lasersJthan are required for a first stage laser rocket, hence a laser upper stage has nearer term technical viability than a first stage. Status: Variations: References: [D26] Abe, T.; Shimada, T. "Laser Assisted Propulsion System Experiment on Space Flyer Unit", 38th International Astronautical Federation Conference paper number IAF-87-298, 1987.J [D27] Abe, T.; Kuriki, K. "Laser Propulsion Test Onboard Space Station", Space Solar Power Review vol 5 no 2 pp 121-5, 1985. [D28] Jones, L. W.; Keefer, D. R. "NASA's Laser Propulsion Project", Astronautics and Aeronautics, v 20 no 9 pp 66-73, 1982. 39 Laser Detonation-Wave Engine Alternate Names: Type: Description: Propellant is a solid block with a flat bottom. First laser pulse evaporates a layer of propellant. Second, larger, pulse creates plasma detonation wave, which shocks and heats the propellant layer. Layer expands against base of solid block. Status: Variations: References: [D29] Kare, J.T. "SDIO/DARPA Workshop on Laser Propulsion, Volume 1: Executive Summary" Lawrence Livermore National Laboratory report number DE87-003254, 1987. 40 Microwave Thermal Alternate Names: Type: Description: Microwaves are absorbed by engine, which becomes hot. Hydrogen is flowed through engine, gets hot, and is then exhausted. A large phased microwave array on the ground can focus onto a rocket-sized area over a range of hundreds of kilometers. Given a way to couple the microwave energy to a working fluid such as hydrogen, this type of propulsion could provide significant launch vehicle velocities. High power microwave amplifiers exist in a variety of forms with efficiencies up to 75% and power levels up to one megawatt. This concept uses direct heating of the engine structure, which acts as a heat exchanger to heat the working fluid. Example: 10 meter diameter receiver, 5 cm wavelength, 1 km phased array, range = 200 km. Status: Variations: References: 41 Solid Core Nuclear Alternate Names: Type: Description: Hydrogen is heated by flowing through nuclear reactor, then exhausted in rocket nozzle. Although the nuclear rocket program was stopped a number of years ago, more recent work at Brookhaven National Laboratories on fluidized particle bed reactors warrants their consideration for launch vehicles. The small particle size (.3 mm) allows high heat transfer rates to the working fluid, hydrogen, and hence potentially high thrust to weight ratios. Status: Variations: References: [D30] Thomas, Ulrich "Nuclear Ferry - Cislunar Space Transportation Option of the Future", Space Technology (Oxford) v 7 no 3 pp 227-234, 1987. [D31] Holman, R.R.; Pierce, B. L. "Development of NERVA reactor for Space Nuclear Propulsion", presented at AIAA/ASME/SAE/ASEE 22nd Joint Propulsion Conference, Huntsville, Alabama, 16-18 Jun 1986, AIAA paper number 86-1582, 1986. [D32] Thom, K. et al "Physics and Potentials of Fissioning Plasmas for Space Power and Propulsion", Acta Astronautica vol 3 no 7-8 pp 505-16, Jul. -Aug. 1976. [D33] DiStefano, E. "Space Nuclear Propulsion - Future Applications and Technology", 2nd Symposium on Space Nuclear Power Systems, Albequerque, New Mexico, 14 January 1985, pp 331-342, 1987. 42 Liquid Core Nuclear Alternate Names: Type: Description: In order to attain higher performance than a solid core rocket, the reactor core is raised to a high enough temperature to become liquid. Hydrogen is bubbled through the liquid, then exhausted out a nozzle. Status: Variations: References: 43 Gas Core Nuclear Alternate Names: Type: Description: The reactor core is hot enough that the core is gasseous in form. The hydrogen flow is seeded with an absorbent material to directly absorb the thermal radiation from the core. The core is kept from leaking out the nozzle by a transparent container (nucear light bulb), a flow vortex, which uses the density difference between uranium and hydrogen, or magnetic separation, which uses the ionization difference between the uranium and the hydrogen. Status: Variations: References: 44 Muon-Catalyzed Fusion Alternate Names: Type: Description: A beam of muons is directed at a deuterium/tritium mixture, where the muons catalyze mutiple fusion reactions. The heated gas powers an electric generator to power an ion or neutral particle beam thruster. Status: Variations: References: D.5 Bulk Matter Engines 45 Rotary Flinger Alternate Names: Type: Description: A one or two stage rotary mechanism mechanically accelerates a small amount of reaction mass, then releases it. In the two stage version, top speeds of 6 km/s are possible. Status: Variations: References: 46 Coilgun Engine Alternate Names: Mass Driver Reaction Engine Type: Description: A carrier, or bucket, is accelerated by interaction of magnetic fields from 'driver' coils. The carrier holds a reaction mass, which is released. The bucket is slowed down and reused. Status: Variations: References: 47 Railgun Engine Alternate Names: Type: Description:The interaction of the fields in current carrying rails and a plasma short circuit of the rails accelerates the plasma, and anything in front of it. Status: Variations: References: D.6 Ion and Plasma Engines 48 Arc Jet Alternate Names: Type: Description: Sunlight is converted to electricity by a photovoltaic array. The electricity is arced through a propellant stream, heating it. The propellant is then expanded through a nozzle. Status: Variations: References: [D34] Hardy, Terry L.; Curran, Francis M. "Low Power DC Arcjet Operation with Hydrogen/Nitrogen/Ammoinia Mixtures", NASA Technical Memorandum 89876, 1987. [D35] Stone, James R.; Huston, Edward S. "NASA/USAF Arcjet Research and Technology Program", NASA Technical Memorandum 100112, 1987. [D36] Kagaya, Y. et al "Quasi-steady MPD Arc-jet for Space Propulsion", Symposium for Space Technology and Science, Tokyo, Japan, 19 May 1986, pp 145-154, 1986. [D37] Manago, Masata et al "Fast Acting Valve for MPD Arcjet", IHI Engineering Review, v 19 no 2 pp 99-100, April 1986.J J [D38] Pivirotto, T. J.; King, D. Q. "Thermal Arcjet Technology for Space Propulsion", Chemical Propulsion Information Agency, Laurel, Maryland, 1985. 49 Electrostatic Ion Alternate Names: Type: Description: Status: Variations: References: [D39] Rawlin, Vincent K; Patterson, Michael J. "High Power Ion Thruster Performance", NASA Technical Memorandum 100127, 1987. 49a Solar-Electric Ion Sunlight is converted to electricity by a photovoltaic array. The electricity is used to ionize and electrostatically accelerate the propellant. [D40] Mitterauer, J. "Liquid Metal Ion Sources as Thrusters for Electric Space Propulsion", J. Phys. Colloq. (France) vol 48, no C-6, pp 171-6, Nov. 1987. [D41] Mitterauer, J. "Field Emission Electric Propulsion - Emission Site Distribution of Slit Emitters", IEEE Trans. on Plasma Sci. vol PS-15, pp 593-8, Oct. 1987. [D42] Stuhlinger, E. et al "Solar-Electric Propulsion for a Comet Nucleus Sample Return Mission" presented at 38th Congress of the International Astronautical Federation, Brighton, England, 10 Ocotober 1987. [D43] Nakamura, Y.; Kuricki, K. "Electric Propulsion Test Onboard the Space Station", Space Solar Power Review vol 5 no 2 pp 213-9, 1985. [D44] Voulelikas, G. D. "Electric Propulsion: A Review of Future Space Propulsion Technology" Communications Research Centre, Ottawa, Ontario, report number CRC-396, October 1985. [Dnn] Bartoli, C. et al "A Liquid Caesium Field Ion Source for Space Propulsion", J. Phys. D vol 17 no 12 pp 2473-83, 14 Dec. 1984. [D45] Imai, R.; Kitamura, S. "Space Operation of Engineering Test Satellite -III Ion Engine", Proceedings of JSASS/AIAA/DGLR 17th Intl. Electric Propulsion Conf. pp 103-8, 1984. [D46] Jones, R. M.; Poeschel, R. L. "Primary Space Propulsion for 1995- 2000 - Electrostatic Technology Applications" AIAA/SAE/ASME 20th Joint Propulsion Conference, AIAA paper number 84-1450, 1984. [D47] Bartoli, C. et al "Recent Developments in High Current Liquid Metal Ion Sources for Space Propulsion", Vacuum vol 34 no 1-2 pp 43-6, Jan. -Feb. 1984. [D48] Brophy, J. R.; Wilbur, P. J. "Recent Developments in Ion Sources for Space Propulsion", Proceedings of the Intl. Ion Engineering Congress vol 1 pp 411-22, 1983. [Dnn] Anon. "Ion Propulsion Engine Tests Scheduled", Aviation Week and Space Technology, v 116 no 26 pp 144-5, 1982. [D49] James, E.; Ramsey, W., Sr.; Steiner, G. "Developing a Scaleable Inert Gas Ion Thruster", AIAA paper number 82-1275 presented at AIAA/SAE/ASME 18th Joint Propulsion Conference, Cleveland, OH, 21- 23 June 1982. [D50] Zafran, S. et al "Aerospace Highlights 1982: Electric Propulsion", Astronautics and Aeronautics, v 20 no 12 pp 71-72, 1982. [D51] Clark, K. E.; Kaufman, H. B. "Aerospace Highlights 1981: Electric Propulsion", Astronautics and Aeronautics, v 19 no 12 pp 58-59, 1981. [D52] Kaufman, H. R. "Performance of Large Inert-Gas Thrusters", AIAA paper number 81-0720 presented at 15th International Electric Propulsion Conference, Las Vegas, Nevada, 21-23 April 1981. [D53] Byers, D. C.; Rawlin, V. K. "Critical Elements of Electron- Bombardment Propulsion for Large Space Systems", J. Spacecraft and RocketsJ vol 14 no 11 pp 648-54, Nov. 1977. [D55] Mutin, J.; Tatry, B. "Electric Propulsion in the Field of Space", Acta Electron. (France) vol 17 no 4 pp 357-70, Oct. 1974 (in French). 49b Thermoelectric Ion Radioactive isotope decay produces heat. Heat is converted to electricity by semiconductors. Electricity ionizes and accelerates atoms in engine.J 49c Laser-Electric Ion Laser tuned to optimum absorption wavelength of photovoltaic cells. Cells convert laser light to electricity, which is used to power ion engine. Ion engine accelerates ionized propellants electrostatically. [D56] Maeno, K. "Advanced Scheme of CO2 Laser for Space Propulsion", Space Solar Power Review vol 5 no 2 pp 207-11, 1985. 49d Microwave-Electric Ion A microwave receiving antenna (rectenna) on spacecraft converts microwaves to electricity. Electricity is used to ionize and accelerate atoms. [D57] Nordley, G. D.; Brown, W. C. "Space Based Nuclear-Microwave Electric Propulsion", 3rd Symposium on Space Nuclear Power Systems, Albuquerque, New Mexico, 13 January 1986, pp 383-95, 1987. 49e Nuclear-Electric Ion Nuclear reactor generates heat, which is converted to electricity in thermoelectric or turbine/generator cycles. Electricity is used to ionize propellant and accelerate it by electrostatic voltage. [D58] Cutler, A. H. "Power Demands for Space Resource Utilization", Space Nuclear Power Systems 1986 pp 25-42. [D59] Buden, D.; Garrison, P. W. "Space Nuclear Power Systems and the Design of the Nuclear Electric Propulsion OTV", presented at AIAA/SAE/ASME 20th Joint Propulsion Conference, AIAA paper number 84-1447, 1984. [D60] Powell, J. R.; Boots, T. E. "Integrated Nuclear Propulsion/Prime Power Systems", AIAA paper number 82-1215 presented at AIAA/SAE/ASME 18th Joint Propulsion Conference, Cleveland, Ohio, 21-23 June 1982. [D61] Powell, J. R.; Botts, T. E.; Myrabo, L. N. "Annular Bed Nuclear Power Source for Electric Thrusters", AIAA paper number 82-1278 presented at AIAA/SAE/ ASME 18th Joint Propulsion Conference, Cleveland, Ohio, 21-23 June 1982. [D62] Ray, P. K. "Solar Electric versus Nuclear Electric Propulsion in Geocentric Space", Trans. Am. Nucl. Soc. vol 39 pp 358-9, Nov.-Dec. 1981. [D63] Hsieh, T. M.; Phillips, W. M. "An Improved Thermionic Power Conversion System for Space Propulsion", Proceedings of the 13th Intersociety Energy Conversion Engineering Conference pp 1917-1923, 1978. [D64] Reichel, R. H. "The Air-Scooping Nuclear-Electric Propulsion Concept for Advanced Orbital Space Transportation Missions", J. British Interplanetary Soc. vol 31 no 2 pp 62-6, Feb. 1978. 50 Electron Beam Heated Plasma Alternate Names: Type: Description: A high voltage (hundreds of keV) electron beam is injected axially into a propellant flow. The electron beam heats the flow to plasma temperatures, which produces high specific impulse. Cool gas is injected along the chamber walls to provide film cooling and protect the chamber from the very high temperature plasma. Status: Variations: References: 51 Microwave Heated Plasma Alternate Names: Electron-Cyclotron Absorption Rocket Type: Description:J Partially ionized gas directly absorbs microwaves, becomingJhot, then expands through rocket nozzle. Status: Variations: References: 52 Fusion Heated Plasma Alternate Names: Type: Description: Exhaust of pure fusion rocket is a thin, extremely hot plasma. If higher thrust is needed, hydrogen can be mixed with plasma. This increases thrust at the expense of performance. Status: Variations: References: 52a Reactor leakage mixed 52b Plasma Kernal Mixed 53 Antimatter-Heated Plasma Alternate Names: Type: Description: Exhaust of pure antimatter rocket is a charged particles. If higher thrust is needed, hydrogen can be mixed with plasma. This increases thrust at the expense of performance. Status: Variations: References: D.7 High Energy Particles D.7a Particle Rockets 54 Pulsed Fission Nuclear Alternate Names: Orion Type: Description: A series of small atomic bombs yield debris/particles which pushes against plate/shock absorber arrangement. The shock absorber evens out the explosion pulses to an even acceleration for the vehicle. Status: Variations: References: 55 Microfusion Alternate Names: Type: Description: A conventional atomic bomb requires a certain minimum size to operate with reasonable efficiency (a few kilotons). In the microfusion approach, a fuel pellet consists of a fusion core material (deuterium/tritium) surrounded by a fission shell (uranium 235). This is similar to the arrangement of a fusion atomic bomb. Instead of chemical explosives, which are what trigger a fusion bomb, a set of lasers or a heavy ion beam are used to compress and set off the fission shell, which in turn sets off the fusion core. A laser or ion compression can get higher compressions than a chemical explosion, thus can set off smaller pellets. It is easier to set off a fission shell than directly causing the fusion core to ignite (as in the inertial fusion program). If explosions in the ton range rather than kiloton range can be achieved, it will produce a more useful vehicle than the pulsed fission concept in the previous item. Status: Variations: References: 56 Alpha Particle Alternate Names: Type: Description: Radioactive element coats one side of thin sheet which is capable of absorbing alpha particles. Particles emitted into sheet are absorbed, particles emitted in opposite direction escape, providing net thrust. Status: Variations: References: 57 Fission Fragment Alternate Names: Type: Description: Thin wires containing fissionable material are at the heart of this concept. Thin wires are used to allow the nuclear fragments from the fission to escape. They are aimed by electrostatic or electromagnetic fields to mostly go out the back end of the thruster. The performance is very high because of the high speed of the fragments. Status: Variations: References: 58 Fusion Particle Alternate Names: Type: Description: Various thermonuclear fusion reactors have been proposed. The results of a fusion reaction are high energy particles which can, in priniple, be harnessed for propulsion. Status: Variations: 58a Magnetic Confinement Plasma in chamber similar to fusion power reactor is intentionally leaked to magnetic nozzle. References: [D65] Freeman, M. "Two Days to Mars with Fusion Propulsion", 21st Century Science and Technology, vol 1, pp 26-31, Mar.-Apr. 1988. [D66] Kammash, T.; Galbraith, D. L. "A Fusion-Driven Rocket Propulsion Scheme for Space Exploration", Trans. Am. Nucl. Soc. vol 54 pp 118-9, 1987. [D67] Mitchell, H. M.; Cooper, R. F.; Verga, R. L. "Controlled Fusion for Space Propulsion. Report for April 1961-June 1962", US Air Force report number AD-408118/8/XAB, April, 1963. 58b Inertial Confinement Fuel pellet is heated and compressed by lasers, electron beam, or ion beam. After fusing, the resulting plasma is directed by a magnetic nozzle. References: [D68] Kammash, T.; Galbraith, D. L. "A Fusion Reactor for Space Applications", Fusion Technology, v. 12 no. 1 pp 11-21, July 1987. [D69] Orth, C. D. et al "Interplanetary Propulsion using Inertial Fusion", report number UCRL--95275-Rev. 1: 4th Symposium on Space Nuclear Power Systems, Albequerque, New Mexico, 12 January 1987. [D70] Hyde, Roderick, "A Laser Fusion Rocket for Interplanetary Propulsion" , LLNL report UCRL-88857. (Fusion Pellet design: Fuel selection. Energy loss mechanisms. Pellet compression metrics. Thrust Chamber: Magnetic nozzle. Shielding. Tritium breeding. Thermal modeling. Fusion Driver (lasers, particle beams, etc): Heat rejection. Vehicle Summary: Mass estimates. Vehicle Performance: Interstellar travel required exhaust velocities at the limit of fusion's capability. Interplanetary missions are limited by power/weight ratio. Trajectory modeling. Typical mission profiles. References, including the 1978 report in JBIS, "Project Daedalus", and several on ICF and driver technology.) [D71] Bussard, Robert W., "Fusion as Electric Propulsion", Journal of Propulsion and Power, Vol. 6, No. 5, Sept.-Oct. 1990. (Fusion rocket engines are analyzed as electric propulsion systems, with propulsion thrust- power-input-power ratio (the thrust-power "gain" G(t)) much greater than unity. Gain values of conventional (solar, fission) electric propulsion systems are always quite small (e.g., G(t)<0.8). With these, "high-thrust" interplanetary flight is not possible, because system acceleration (a(t)) capabilities are always less than the local gravitational acceleration. In contrast, gain values 50-100 times higher are found for some fusion concepts, which offer "high-thrust" flight capability. One performance example shows a 53.3 day (34.4 powered; 18.9 coast), one-way transit time with 19% payload for a single-stage Earth/Mars vehicle. Another shows the potential for high acceleration (a(t)=0.55g(o)) flight in Earth/moon space.) 58c Electrostatic Confinement The fusion fuel is confined by a spherical potential well of order 100 kV. When the fuel reacts, the particles are ejected with energy of order 2 MeV, so escape the potential well. The potential well is at the focus of a paraboloidal shell, which reflects the fusion particles to the rear in a narrow beam (20-30 degree width). References: [D72] Bussard, Robert W., "The QED Engine System: Direct Electric Fusion-Powered Systems for Aerospace Flight Propulsion" by Robert W. Bussard, EMC2-1190-03, available from Energy/Matter Conversion Corp., 9100 A. Center Street, Manassas, VA 22110. (This is an introduction to the application of Bussard's version of the Farnsworth/Hirsch electrostatic confinement fusion technology to propulsion. 1500