Orbital maneuver

In spaceflight, an orbital manoeuvre 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 manoeuvre is called a deep-space manoeuvre (DSM).

delta-v

Main article: delta-v

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

Delta-v budget

Main article: delta-v budget

The total delta-v for all and each manoeuvre 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 manoeuvres

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

An "impulsive manoeuvre" is the mathematical model of a manoeuvre 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 manoeuvre 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 manoeuvre is only caused by the difference in gravitational force along the two paths (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 manoeuvres what greatly reduces the complexity of finding the correct orbital transitions.

Non-impulsive manoeuvres

Applying a low thrust over longer periods of time is referred to as non-impulsive manoeuvres (where 'non-impulsive' refers to the manoeuvre not being of a short time period rather than not involving impulse- change in momentum, which clearly must take place).^{[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, centre of mass, moment of inertia, thruster positions, thrust vectors, thrust curves, specific impulse, thrust centroid offsets, and fuel consumption.

See also

• Bi-elliptic transfer
• Delta-v
• Delta-v budget
• Docking manoeuvre
• Gravitational slingshot
• Hohmann transfer
• Low energy transfers
• Orbital inclination change
• Orbit phasing
• The Oberth effect
• Collision avoidance (spacecraft)

External links

• Handbook Automated Rendezvous and Docking of Spacecraft by Wigbert Fehse