A Propulsive Fluid Accumulator is an artificial Earth satellite which collects and stores oxygen and other atmospheric gases for in-situ refuelling of high-thrust rockets. This eliminates the need to lift oxidizer to orbit and therefore brings significant cost benefits. A major portion of the total world payload sent into low Earth orbit each year is either liquid oxygen or water.
In the period 1956 to 1963, S.T. Demetriades proposed methods of atmospheric gas accumulation by means of a satellite moving in low Earth orbit, at an altitude of around 120 km, or propellant accumulation by stations on the surface of a planet or by gathering and exploiting interstellar matter. [1] In its simplest form, Demetriades' proposed satellite extracts air from the fringes of the atmosphere, compresses and cools it, and extracts liquid oxygen. The remaining nitrogen is, in part, used as propellant for a nuclear-powered magnetohydrodynamic electromagnetic plasma thruster, which maintains the orbit at about 120 km, or a solar powered thruster (and collection system) for altitudes above 150 km (as stated in the original 1959 JBIS article, p119) compensating for atmospheric drag. [2] This system was called “PROFAC” (PROpulsive Fluid ACcumulator). [3] Several systems were studied, e. g. PROFAC-S for Surface, PROFAC-C for Orbital, PROFAC-A for combination with aerospaceplane making one reusable stage to orbit possible, etc. Several inlets (e. g. conical as in AIEE 10 Aug 1960 San Diego meeting, or funnel) and cryopumps were studied for orbital air collection. The work slowed down in late 1961 although much progress was made in later years on such items as a solar-powered PROFAC.
There are, however, safety concerns with placing a nuclear reactor in low Earth orbit.
Demetriades' proposal was further refined by Christopher Jones and others in 2010. In this proposal, multiple collection vehicles accumulate propellant gases at around 120 km altitude, later transferring them to a higher orbit. However, Jones' proposal does require a network of orbital power-beaming satellites, to avoid placing nuclear reactors in orbit. [4]
Klinkman and Wilkes proposed, at the AIAA Space 2007 and Space 2009 conferences, that gases could be harvested at the very edge of the Earth's atmosphere by a high vacuum pump. An ion propulsion engine would consume a portion of the harvested gases and would restore the spacecraft's orbital momentum. Klinkman's proposal has a fairly low energy threshold for a small-scale harvesting operation, and air friction is far more forgiving at 200 km than at 100 km. [5]
Note that S. T. Demetriades pioneered in space propulsion, from the atomic oxygen ramjet (he proved it not feasible in the 1950s) to nuclear, ion, and plasma thrusters. He received the 2010 AIAA Award for Plasmadynamics and Lasers.
Boeing has suggested a non-extractive propellant depot, or "space gas station," which accumulates material launched from the planet at low cost, allowing future lunar missions without the need for large launch vehicles like the Saturn V. [6] MIT has recently proposed a similar plan which would store emergency fuel reserves left over from lunar missions. [7]
Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. In-space propulsion exclusively deals with propulsion systems used in the vacuum of space and should not be confused with space launch or atmospheric entry.
A monopropellant rocket is a rocket that uses a single chemical as its propellant.
A resistojet is a method of spacecraft propulsion that provides thrust by heating a typically non-reactive fluid. Heating is usually achieved by sending electricity through a resistor consisting of a hot incandescent filament, with the expanded gas expelled through a conventional nozzle.
An ion thruster, ion drive, or ion engine is a form of electric propulsion used for spacecraft propulsion. It creates thrust by accelerating ions using electricity.
A mass driver or electromagnetic catapult is a proposed method of non-rocket spacelaunch which would use a linear motor to accelerate and catapult payloads up to high speeds. Existing and contemplated mass drivers use coils of wire energized by electricity to make electromagnets, though a rotary mass driver has also been proposed. Sequential firing of a row of electromagnets accelerates the payload along a path. After leaving the path, the payload continues to move due to momentum.
Beam-powered propulsion, also known as directed energy propulsion, is a class of aircraft or spacecraft propulsion that uses energy beamed to the spacecraft from a remote power plant to provide energy. The beam is typically either a microwave or a laser beam and it is either pulsed or continuous. A continuous beam lends itself to thermal rockets, photonic thrusters and light sails, whereas a pulsed beam lends itself to ablative thrusters and pulse detonation engines.
A propellant is a mass that is expelled or expanded in such a way as to create a thrust or another motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicles, the engine that expels the propellant is called a reaction engine. Although technically a propellant is the reaction mass used to create thrust, the term "propellant" is often used to describe a substance which contains both the reaction mass and the fuel that holds the energy used to accelerate the reaction mass. For example, the term "propellant" is often used in chemical rocket design to describe a combined fuel/propellant, although the propellants should not be confused with the fuel that is used by an engine to produce the energy that expels the propellant. Even though the byproducts of substances used as fuel are also often used as a reaction mass to create the thrust, such as with a chemical rocket engine, propellant and fuel are two distinct concepts.
A solar thermal rocket is a theoretical spacecraft propulsion system that would make use of solar power to directly heat reaction mass, and therefore would not require an electrical generator, like most other forms of solar-powered propulsion do. The rocket would only have to carry the means of capturing solar energy, such as concentrators and mirrors. The heated propellant would be fed through a conventional rocket nozzle to produce thrust. Its engine thrust would be directly related to the surface area of the solar collector and to the local intensity of the solar radiation.
Laser propulsion is a form of beam-powered propulsion where the energy source is a remote laser system and separate from the reaction mass. This form of propulsion differs from a conventional chemical rocket where both energy and reaction mass come from the solid or liquid propellants carried on board the vehicle.
An orbital spaceflight is a spaceflight in which a spacecraft is placed on a trajectory where it could remain in space for at least one orbit. To do this around the Earth, it must be on a free trajectory which has an altitude at perigee around 80 kilometers (50 mi); this is the boundary of space as defined by NASA, the US Air Force and the FAA. To remain in orbit at this altitude requires an orbital speed of ~7.8 km/s. Orbital speed is slower for higher orbits, but attaining them requires greater delta-v. The Fédération Aéronautique Internationale has established the Kármán line at an altitude of 100 km (62 mi) as a working definition for the boundary between aeronautics and astronautics. This is used because at an altitude of about 100 km (62 mi), as Theodore von Kármán calculated, a vehicle would have to travel faster than orbital velocity to derive sufficient aerodynamic lift from the atmosphere to support itself.
In astrodynamics, orbital station-keeping is keeping a spacecraft at a fixed distance from another spacecraft or celestial body. It requires a series of orbital maneuvers made with thruster burns to keep the active craft in the same orbit as its target. For many low Earth orbit satellites, the effects of non-Keplerian forces, i.e. the deviations of the gravitational force of the Earth from that of a homogeneous sphere, gravitational forces from Sun/Moon, solar radiation pressure and air drag, must be counteracted.
In space exploration, in situ resource utilization (ISRU) is the practice of collection, processing, storing and use of materials found or manufactured on other astronomical objects that replace materials that would otherwise be brought from Earth.
Spacecraft electric propulsion is a type of spacecraft propulsion technique that uses electrostatic or electromagnetic fields to accelerate mass to high speed and thus generate thrust to modify the velocity of a spacecraft in orbit. The propulsion system is controlled by power electronics.
Non-rocket spacelaunch refers to theoretical concepts for launch into space where much of the speed and altitude needed to achieve orbit is provided by a propulsion technique that is not subject to the limits of the rocket equation. Although all space launches to date have been rockets, a number of alternatives to rockets have been proposed. In some systems, such as a combination launch system, skyhook, rocket sled launch, rockoon, or air launch, a portion of the total delta-v may be provided, either directly or indirectly, by using rocket propulsion.
An orbital propellant depot is a cache of propellant that is placed in orbit around Earth or another body to allow spacecraft or the transfer stage of the spacecraft to be fueled in space. It is one of the types of space resource depots that have been proposed for enabling infrastructure-based space exploration. Many different depot concepts exist depending on the type of fuel to be supplied, location, or type of depot which may also include a propellant tanker that delivers a single load to a spacecraft at a specified orbital location and then departs. In-space fuel depots are not necessarily located near or at a space station.
Rocket propellant is the reaction mass of a rocket. This reaction mass is ejected at the highest achievable velocity from a rocket engine to produce thrust. The energy required can either come from the propellants themselves, as with a chemical rocket, or from an external source, as with ion engines.
Atmospheric mining is the process of extracting valuable materials or other non-renewable resources from the atmosphere. Due to the abundance of molecular hydrogen and helium in the outer planets of the Solar System, advances in technology may eventually make mining their atmospheres a favorable alternative to mining terrestrial surfaces.
Atmosphere-breathing electric propulsion, or air-breathing electric propulsion, shortly ABEP, is a propulsion technology for spacecraft, which could allow thrust generation in low orbits without the need of on-board propellant, by using residual gases in the atmosphere as propellant. Atmosphere-breathing electric propulsion could make a new class of long-lived, low-orbiting missions feasible.
This glossary of aerospace engineering terms pertains specifically to aerospace engineering, its sub-disciplines, and related fields including aviation and aeronautics. For a broad overview of engineering, see glossary of engineering.
NASA's Pathfinder Technology Demonstrator (PTD) Project will test the operation of a variety of novel technologies on a type of nanosatellites known as CubeSats, providing significant enhancements to the performance of these versatile spacecraft. Each of the five planned PTD missions consist of a 6-unit (6U) CubeSat with expandable solar arrays.