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Wikipedia, Deltav budget (or velocity change budget) is an astrogation term used in astrodynamics and aerospace industry for velocity change (or deltav) requirements for the various propulsive tasks and orbital maneuvers over phases of a space mission. Sample deltav budget will enumerate various classes of maneuvers, deltav per maneuver, number of maneuvers required over the time of the mission. In the absence of an atmosphere, the deltav is typically the same for changes in orbit in either direction; in particular, gaining and losing speed cost an equal effort. General principlesThe deltav requirements for suborbital spaceflight can be surprising. For the Ansari X Prize altitude of 100 km, Space Ship One required a deltav of roughly 1.4 km/s. To reach low earth orbit of the space station of 300 km, the deltav is over six times higher about 9.4 km/s. Course corrections usually also require some propellant budget. Propulsion systems never provide precisely the right propulsion in precisely the right direction at all times and navigation also introduces some uncertainty. Some propellant needs to be reserved to correct variations from the optimum trajectory. 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 deltav necessary to change the plane of the orbit, the velocity of the vehicle needs a substantial change and the deltav 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. From the rocket equation, the deltav of a rocket is logarithmically related to the mass ratio of the vehicle, minimising the deltav budget as far as possible is usually very important to avoid the necessity for infeasibly big and expensive rockets. 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 (or lose) much of that body's orbital speed relative to the Sun or a planet. Another effect is the Oberth effect this can be used to greatly decrease the deltav needed, as using propellant at low potential energy/high speed multiplies up the effect of a burn. Thus for example the deltav for a Hohmann transfer from Earth's orbital radius to Mars' 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 than if the burn to reach a Mars transfer orbit is performed outside the Earth's gravity. Launch/landing budget
Stationkeeping budgetEarthMoon space budgetDeltav 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 Deltav figure applies.
Interplanetary budget
According to Marsden and Ross, "The energy levels of the SunEarth L1 and L2 points differ from those of the EarthMoon system by only 50 m/s (as measured by maneuver velocity)." Deltavs between Earth and MarsDeltav's in km/s for various orbital maneuvers using conventional rockets. Red arrows show where optional aerobraking can be performed in that particular direction, black numbers give deltav in km/s that apply in either direction. Lower deltav 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 alsoExternal links
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Published  July 2009
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