Orbital maneuver

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http://en.wikipedia.org/wiki/Orbital_maneuver

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 deep-space maneuver (DSM).

## Impulsive maneuvers

An "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 delta-v (Δ V), the total delta-v for all maneuvers required in the mission is called a delta-v budget. With a good approximation of the delta-v 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 thrust-to-weight propulsion systems, e.g. chemical rockets. However, even for long burns, impulsive maneuver approximations remain very accurate outside the Earth's atmosphere.

## Non-impulsive maneuvers

Applying a low thrust over longer periods of time is referred to as non-impulsive 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 thrust-to-weight propulsion systems are used (e.g. ion engines). They are not possible for a launch.

## Finite burn trajectories

For 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.

Published in July 2009.