Delta v
Delta v () is the change (delta or Δ ) of the velocity ( vector) and, in time per distance (m / s). It results from the subtraction of two speeds,
Wherein the speed is above the speed of an event and after the event. There is calculated the difference of the velocity vectors, or changes in the direction to be taken into account in which the amount of the speed remains constant.
Space dynamics
In space is delta v, often advertised instead of symbols to perform a measure of the ability of a spacecraft maneuver. In the simplest case, without the action of gravity, delta V is the integral of the amounts of changes in speed along the desired trajectory. This integral is the mass of the spacecraft maneuvers exporting over invariant, as well as to the technological details of which drive. The invariance of the size has obvious advantages, allowing for space vehicles instead of mass, thrust and propellant supply the entire Delta v ( ) is specified to which the spacecraft with the existing fuel resources is capable of. Is the value of the remaining, all of the fuel consumed, and no change of course is possible.
In the gravitational field, eg at startup or when a swing-by, corresponds to the applied by the spacecraft delta v no change in velocity directly, but can be calculated as the size yet. It depends on the atmosphere and in a non- free-fall situation, however, addition of the aerodynamic properties of the vehicle and the time required for the spacecraft to move a free-fall situation of a stable orbit, i.e., from. A start to a low earth orbit is approximately required in order to increase the speed of the rotation speed at the surface of the orbital velocity. This proportion is the design of the spacecraft towards invariant. These typically come due to the air resistance and the overcoming of gravity. The balance is reduced by the Earth's rotation to a maximum of 465 m / s, when the start is at the equator with an inclination of 0 ° in an easterly direction.
It should be noted here that, in this specification, the weight of the payload ( weight of persons on board / spacecraft ) has an impact on the available DeltaV a spaceship, because with the increase of mass and thus increased inertia disposable Delta v is smaller. In other words: Had the astronauts packed too many moon stones in the Apollo missions, although this would require Delta v of the ascent stage to reach the mother ship, remain the same, the delta v, which would be available, but would decrease and the value of the required Delta v below, making the ascent stage would be too heavy and the mother ship would not have been achievable.
The fully fueled the Apollo spacecraft was, for example, at maximum payload 2,804 m / s, the descent module of 4.690 m / s