


By
Wikipedia, In spaceflight, an orbital maneuver is the use of propulsion systems to change the orbit of a spacecraft. For spacecraft far from Earth  for example those in orbits around the Sun  an orbital maneuver is called a deepspace maneuver (DSM). Impulsive maneuversAn "impulsive maneuver" is one which involves a single, nearly instantaneous change in the spacecraft's velocity. Because even small spacecraft have mass, no truly instantaneous change in velocity is possible. But during the planning phase of most space missions, designers will first approximate their intended orbital changes using impulsive maneuvers. This greatly reduces the complexity of finding the correct orbital transitions. The instantaneous changes in velocity are referred to as deltav (), the total deltav for all maneuvers required in the mission is called a deltav budget. With a good approximation of the deltav budget designers can estimate the fuel to payload requirements of the spacecraft. Using these approximations is most useful when finite thrusts are to be executed in short bursts. Finite maneuvers like these are possible with high thrusttoweight propulsion systems, e.g. chemical rockets. However, even for long burns, impulsive maneuver approximations remain very accurate outside the Earth's atmosphere. Nonimpulsive maneuversApplying a low thrust over longer periods of time is referred to as nonimpulsive maneuvers (even though any thrust can be said to produce an amount of impulse). They are less efficient as very high amounts of energy can be lost due to the Oberth effect and other inefficiences. However those maneuvers can be the only option when low launch weights are desirable and hence high specific impulse but low thrusttoweight propulsion systems are used (e.g. ion engines). They are not possible for a launch. Finite burn trajectoriesFor a few space missions, such as those including a space rendezvous, high fidelity models of the trajectories are required to meet the mission goals. Calculating a finite burn requires a detailed model of the spacecraft and its thrusters. The most important of details include: mass, center of mass, moment of inertia, thruster positions, thrust vectors, thrust curves, specific impulse, thrust centroid offsets, and fuel consumption. See also
Text from Wikipedia is available under the Creative Commons Attribution/ShareAlike License; additional terms may apply.
Published  July 2009


