Orbital maneuver

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).[not verified in body]

Contents

delta-v

The applied change in speed of each maneuver is referred to as delta-v (\Delta\mathbf{v}\,).

Delta-v budget

The total delta-v for all and each maneuver is estimated for a 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 the rocket equation.

Impulsive maneuvers

Figure 1: Approximation of a finite thrust maneuver with an impulsive change in velocity

An "impulsive maneuver" is the mathematical model of a maneuver as an instantaneous change in the spacecraft's velocity (magnitude and/or direction) as illustrated in figure 1. In the physical world no truly instantaneous change in velocity is possible as this would require an "infinite force" applied during an "infinitely short time" but as a mathematical model it in most cases describes the effect of a maneuver on the orbit very well. The off-set of the velocity vector after the end of real burn from the velocity vector at the same time resulting from the theoretical impulsive maneuver is only caused by the diffence in gravitational force along the two pathes (red and black in figure 1) which in general is small.

In the planning phase of space missions designers will first approximate their intended orbital changes using impulsive maneuvers what greatly reduces the complexity of finding the correct orbital transitions.

Non-impulsive maneuvers

Applying a low thrust over longer periods of time is referred to as non-impulsive maneuvers (where 'non-impulsive' refers to the maneuver not being of a short time period rather than not involving impulse- change in momentum, which clearly must take place). 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 a large total delta-v has to be produced with a small amount of reaction mass 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.[citation needed]

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.

See also

External links


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