Gravity assist The trajectories that enabled NASA's twin Voyager spacecraft to tour the four gas giant planets and achieve velocity to escape our solar system The "assist" is provided by the motion of the gravitating body as it pulls on the spacecraft.[1] The technique was first proposed as a mid-course manoeuvre in 1961, and used by interplanetary probes from Mariner 10 onwards, including the two Voyager probes' notable fly-bys of Jupiter and Saturn. Explanation[edit] A gravity assist around a planet changes a spacecraft's velocity (relative to the Sun) by entering and leaving the gravitational field of a planet. A close terrestrial analogy is provided by a tennis ball bouncing off a moving train. Simplified example of gravitational slingshot: the spacecraft's speed changes by up to twice the planet's speed Translating this analogy into space, then, a "stationary" observer sees a planet moving left at speed U and a spaceship moving right at speed v. Two-dimensional schematic of gravitational slingshot.
Ram accelerator A ram accelerator is a device for accelerating projectiles to extremely high speeds using jet-engine-like propulsion cycles based on ramjet and/or scramjet combustion processes. It is thought to be possible to achieve non-rocket spacelaunch with this technology. They consist of a long tube (barrel) filled with a mixture of combustible gases with a frangible diaphragm at either end to contain the gases. The projectile, which is shaped like a ramjet core, is fired by another means (e.g., a light gas gun) supersonically through the first diaphragm into the tube. It then burns the gases as fuel, accelerating down the tube under jet propulsion. Other physics come into play at higher velocities. Description[edit] In a normal ramjet, air is compressed between a spike-shaped centerbody and an outer cowling, fuel is added and burned, and high speed exhaust gases are expanded supersonically out the nozzle to generate thrust. Advantages[edit] Uses[edit] See also[edit] External links[edit]
Light gas gun The light-gas gun is an apparatus for physics experiments, a highly specialized gun designed to generate very high velocities. It is usually used to study high speed impact phenomena (hypervelocity research), such as the formation of impact craters by meteorites or the erosion of materials by micrometeoroids. Some basic materials research relies on projectile impact to create high pressure: such systems are capable of forcing liquid hydrogen into a metallic state. Operation[edit] A light-gas gun works on the same principle as a spring piston airgun. In a light-gas gun, the piston is powered by a chemical reaction (usually gunpowder), and the working fluid is a lighter gas, such as helium or hydrogen (though helium is much safer to work with, hydrogen offers the best performance [as explained below], and causes less launch-tube erosion). One particular light-gas gun used by NASA uses a modified 40 mm cannon for power. Design physics[edit] Hybrid electrothermal light-gas gun[edit]
Railgun Naval Surface Warfare Center test firing in January 2008[1] A railgun is an electrically powered electromagnetic projectile launcher based on similar principles to the homopolar motor. A railgun comprises a pair of parallel conducting rails, along which a sliding armature is accelerated by the electromagnetic effects of a current that flows down one rail, into the armature and then back along the other rail.[2] Railguns have long existed as experimental technology but the mass, size and cost of the required power supplies have prevented railguns from becoming practical military weapons. However, in recent years, significant efforts have been made towards their development as feasible military technology. Basics[edit] Schematic diagram of a railgun In its simplest (and most commonly used) form, the railgun differs from a traditional homopolar motor in that no use is made of additional field coils (or permanent magnets). A railgun requires a pulsed, direct current power supply. History[edit]
Space gun A space gun, sometimes called a Verne gun because of its appearance in From the Earth to the Moon by Jules Verne, is a method of launching an object into space using a large gun, or cannon. It provides a method of non-rocket spacelaunch. In the Project HARP a U.S. Navy 16 in (410 mm) 100 caliber gun was used to fire a 180 kg (400 lb) slug at 3600 m/s or 12,960 km/h (8,050 mph), reaching an apogee of 180 km (110 mi), hence performing a suborbital spaceflight. Technical issues[edit] The large g-force, likely to be experienced by a ballistic projectile, would likely mean that a space gun would be incapable of safely launching humans or delicate instruments, rather being restricted to freight, fuel or ruggedized satellites. Atmospheric drag also makes it more difficult to control the trajectory of any projectile launched, subjects the projectile to extremely high forces, and causes severe energy losses that may not be easily overcome. Getting to orbit[edit] Acceleration[edit] ), and a velocity (
Space tether Artist's conception of satellite with a tether Space tethers are long cables which can be used for propulsion, momentum exchange, stabilization and attitude control, or maintaining the relative positions of the components of a large dispersed satellite/spacecraft sensor system.[1] Depending on the mission objectives and altitude, spaceflight using this form of spacecraft propulsion may be significantly less expensive than spaceflight using rocket engines. Four main techniques for employing space tethers are in development:[2][3] Electrodynamic tethers Electrodynamic tethers are primarily used for propulsion. These are conducting tethers that carry a current that can generate either thrust or drag from a planetary magnetic field, in much the same way as an electric motor does. Momentum exchange tethers Tethered formation flying Electric sail A form of solar wind sail with electrically charged tethers that will be pushed by the momentum of solar wind ions. History[edit] In 1990, E. Missions[edit]
Electrodynamic tether Electrodynamic tethers (EDTs) are long conducting wires, such as one deployed from a tether satellite, which can operate on electromagnetic principles as generators, by converting their kinetic energy to electrical energy, or as motors, converting electrical energy to kinetic energy.[1] Electric potential is generated across a conductive tether by its motion through the Earth's magnetic field. Tether propulsion[edit] As part of a tether propulsion system, crafts can use long, strong conductors (though not all tethers are conductive) to change the orbits of spacecraft. It has the potential to make space travel significantly cheaper. In 2012, the company Star Technology and Research was awarded a $1.9 million contract to qualify a tether propulsion system for orbital debris removal.[2] Uses for ED tethers[edit] Over the years, numerous applications for electrodynamic tethers have been identified for potential use in industry, government, and scientific exploration. and along the tether. , and
Variable Specific Impulse Magnetoplasma Rocket Artist's impression of multi-megawatt VASIMR spacecraft VASIMR are manufactured by the Ad Astra Rocket Company, headquartered in the city of Houston, Texas, United States.[2] Design and operation[edit] VASIMR schematic The Variable Specific Impulse Magnetoplasma Rocket, sometimes referred to as the Electro-thermal Plasma Thruster or Electro-thermal Magnetoplasma Rocket, uses radio waves[3] to ionize and heat propellant, which generates plasma that is accelerated using magnetic fields to generate thrust. VASIMR can be most basically thought of as a convergent-divergent nozzle for ions and electrons. A second coupler, known as the Ion Cyclotron Heating (ICH) section, emits electromagnetic waves in resonance with the orbits of ions and electrons as they travel through the engine. Benefits and drawbacks of design[edit] Research and development[edit] The testing vacuum chamber, containing the 50 kW VASIMR, operated in ASPL in 2005–2006 Development of the 200 kW engine[edit] VF-200[edit]
Magnetoplasmadynamic thruster An MPD thruster during test firing A magnetoplasmadynamic (MPD) thruster (MPDT) is a form of electrically powered spacecraft propulsion which uses the Lorentz force (the force on a charged particle by an electromagnetic field) to generate thrust. It is sometimes referred to as Lorentz Force Accelerator (LFA) or (mostly in Japan) MPD arcjet. Generally, a gaseous fuel is ionized and fed into an acceleration chamber, where the magnetic and electrical fields are created using a power source. There are two main types of MPD thrusters, applied-field and self-field. Expected the applications of magnetoplasmadynamic thrusters include main propulsion engine for heavy cargo and piloted space vehicles (example engine for Manned mission to Mars).[3][2] Advantages[edit] Problems with MPDT[edit] CGI rendering of Princeton University's lithium-fed self-field MPD thruster (from Popular Mechanics magazine) Another plan, proposed by Bradley C. Research[edit] See also[edit] References[edit] External links[edit]