Delta-v budget (or velocity change budget) is a term used in astrodynamics and aerospace industry for velocity change (or delta-v) requirements for the various propulsive tasks and orbital maneuvers over phases of the space mission.

Sample delta-v budget will enumerate various classes of manoeuvres, delta-v per manoeuvre, number of manoeuvres required over the time of the mission.

In the absence of an atmosphere, the delta-v is the same for changes in orbit in either direction; in particular, gaining and losing speed cost an equal effort.

General principles

The simplest budget can be calculated with Hohmann transfer, which moves from one circular orbit to another coplanar circular orbit via an elliptical transfer orbit.

A more complex transfer occurs when the orbits are not coplanar, in that case there is an additional delta-v necessary to change the plane of the orbit, the velocity of the vehicle needs a substantial change and the delta-v is usually high. These plane changes can be almost free in some cases if the gravity and mass of a planetary body is used to perform the deflection.

The slingshot effect can be used in some cases to give a boost of speed/energy; if a vehicle goes past a planetary or lunar body, it is possible to pick up much of the planet's orbital speed relative to the Sun or other central body.

Another effect is the Oberth effect- this can be used to greatly decrease the delta-v needed, as using propellant at low potential energy/high speed multiplies up the strength of the burn. Thus for example the delta-v for a Hohmann transfer from Earth's orbital radius to Mar's orbital radius is many kilometres per second, but the incremental burn from LEO over and above that to reach Earth escape velocity is far less if the burn is performed close to the Earth.

Launch/landing budget

• Launch to LEO — this not only requires an increase of velocity from 0 to 7.8 km/s, but also typically 1.5–2 km/s for atmospheric drag and gravity drag
• Re-entry from LEO — the delta-v required is the orbital manoeuvring burn to lower perigee into the atmosphere, atmospheric drag takes care of the rest.

Stationkeeping budget

Earth-Moon space budget

Delta-v needed to move inside Earth Moon system (speeds lower than escape velocity) in km/s

The return to LEO figures assume that a heat shield and aerobraking/aerocapture is used to reduce the speed by up to 3.2 km/s. The heat shield increases the mass, possibly by 15%. Where a heat shield is not used the higher from LEO Delta-v figure applies.

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Interplanetary budget

According to Marsden and Ross, "The energy levels of the Sun-Earth L1 and L2 points differ from those of the Earth-Moon system by only 50 m/s (as measured by maneuver velocity)."^[7]

Delta-vs between Earth and Mars

Delta-v's in km/s for various orbital maneuvers^[5][8] using conventional rockets. Red arrows show where optional aerobraking can be performed in that particular direction, black numbers give delta-v in km/s that apply in either direction. Lower delta-v transfers than shown can often be achieved, but involve rare transfer windows or take significantly longer, see: fuzzy orbital transfers. Not all possible links are shown.

Abbreviations used

See also

• Bi-elliptic transfer
• Gravity assist
• Hohmann transfer
• The Oberth effect
• Tsiolkovsky rocket equation

References

External links

• Javascript Delta V calculator

fi:Nopeuslisä

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