Orbital maneuver

Encyclopedia

In spaceflight

, an

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

().

. With a good approximation of the delta-v budget designers can estimate the fuel to payload requirements of the spacecraft using the rocket equation

.

(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.

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.

, 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.

Spaceflight

Spaceflight is the act of travelling into or through outer space. Spaceflight can occur with spacecraft which may, or may not, have humans on board. Examples of human spaceflight include the Russian Soyuz program, the U.S. Space shuttle program, as well as the ongoing International Space Station...

, an

**orbital maneuver**is the use of propulsionSpacecraft propulsion

Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. There are many different methods. Each method has drawbacks and advantages, and spacecraft propulsion is an active area of research. However, most spacecraft today are propelled by forcing a gas from the...

systems to change the orbit

Orbit

In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...

of a spacecraft

Spacecraft

A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....

.

For spacecraft far from Earth—for example those in orbits around the Sun—an orbital maneuver is called a

*deep-space maneuver (DSM)*.## delta-v

The applied change in speed of each maneuver is referred to as delta-vDelta-v

In astrodynamics a Δv or delta-v is a scalar which takes units of speed. It is a measure of the amount of "effort" that is needed to change from one trajectory to another by making an orbital maneuver....

().

## Delta-v budget

The total delta-v for all and each maneuver is estimated for a mission is called a delta-v budgetDelta-v budget

In the astrodynamics and aerospace industry, a delta-v budget is the estimated delta-v requirements for the various propulsive tasks and orbital maneuvers over one or more phases of a space mission.Sample delta-v budget will enumerate various classes of maneuvers, delta-v per maneuver, number of...

. With a good approximation of the delta-v budget designers can estimate the fuel to payload requirements of the spacecraft using the rocket equation

Tsiolkovsky rocket equation

The Tsiolkovsky rocket equation, or ideal rocket equation is an equation that is useful for considering vehicles that follow the basic principle of a rocket: where a device that can apply acceleration to itself by expelling part of its mass with high speed and moving due to the conservation of...

.

## Impulsive maneuvers

An "impulsive maneuver" is the mathematical model of a maneuver as an instantaneous change in the spacecraft's velocityVelocity

In physics, velocity is speed in a given direction. Speed describes only how fast an object is moving, whereas velocity gives both the speed and direction of the object's motion. To have a constant velocity, an object must have a constant speed and motion in a constant direction. Constant ...

(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 effectOberth effect

In astronautics, the Oberth effect is where the use of a rocket engine when travelling at high speed generates much more useful energy than one at low speed...

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

Specific impulse

Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...

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 rendezvousSpace rendezvous

A space rendezvous is an orbital maneuver during which two spacecraft, one of which is often a space station, arrive at the same orbit and approach to a very close distance . Rendezvous requires a precise match of the orbital velocities of the two spacecraft, allowing them to remain at a constant...

, high fidelity models of the trajectories are required to meet the mission goals. Calculating a finite burn requires a detailed model of the spacecraft

Spacecraft

A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....

and its thrusters. The most important of details include: mass

Mass

Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

, center of mass

Center of mass

In physics, the center of mass or barycenter of a system is the average location of all of its mass. In the case of a rigid body, the position of the center of mass is fixed in relation to the body...

, moment of inertia

Moment of inertia

In classical mechanics, moment of inertia, also called mass moment of inertia, rotational inertia, polar moment of inertia of mass, or the angular mass, is a measure of an object's resistance to changes to its rotation. It is the inertia of a rotating body with respect to its rotation...

, thruster positions, thrust vectors, thrust curves, specific impulse

Specific impulse

Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...

, thrust centroid

Centroid

In geometry, the centroid, geometric center, or barycenter of a plane figure or two-dimensional shape X is the intersection of all straight lines that divide X into two parts of equal moment about the line. Informally, it is the "average" of all points of X...

offsets, and fuel consumption.

## See also

- Bi-elliptic transferBi-elliptic transferIn astronautics and aerospace engineering, the bi-elliptic transfer is an orbital maneuver that moves a spacecraft from one orbit to another and may, in certain situations, require less delta-v than a Hohmann transfer....
- Delta-vDelta-vIn astrodynamics a Δv or delta-v is a scalar which takes units of speed. It is a measure of the amount of "effort" that is needed to change from one trajectory to another by making an orbital maneuver....
- Delta-v budgetDelta-v budgetIn the astrodynamics and aerospace industry, a delta-v budget is the estimated delta-v requirements for the various propulsive tasks and orbital maneuvers over one or more phases of a space mission.Sample delta-v budget will enumerate various classes of maneuvers, delta-v per maneuver, number of...
- Docking maneuver
- Gravitational slingshotGravitational slingshotIn orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement and gravity of a planet or other celestial body to alter the path and speed of a spacecraft, typically in order to save propellant, time, and expense...
- Hohmann transfer
- Low energy transfersLow energy transfersA low energy transfer, or low energy trajectory, is a route in space which allows spacecraft to change orbits using very little fuel. These routes work in the Earth-Moon system and also in other systems, such as traveling between the satellites of Jupiter...
- Orbital inclination changeOrbital inclination changeOrbital inclination change is an orbital maneuver aimed at changing the inclination of an orbiting body's orbit. This maneuver is also known as an orbital plane change as the plane of the orbit is tipped. This maneuver requires a change in the orbital velocity vector at the orbital nodes Orbital...
- Orbit phasingOrbit phasingIn astrodynamics orbit phasing is the adjustment of the time-position of spacecraft along its orbit, usually described as adjusting the orbiting spacecraft's true anomaly....
- The Oberth effect
- Collision avoidance (spacecraft)Collision avoidance (spacecraft)In spaceflight, collision avoidance is the process of preventing a spacecraft from colliding with any other vehicle or object.-Launch Windows:Collision avoidance, or COLA is a concern during spaceflight launch windows...

## External links

- Handbook Automated Rendezvous and Docking of Spacecraft by Wigbert FehseWigbert FehseWigbert Fehse is a German engineer and researcher in the area of automatic space navigation, guidance, control and docking/berthing.- Biography :...