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Delta-v budget

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.

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

Maneuver	Average delta-v per year [m/s]	Maximum per year [m/s]
Drag compensation in 400–500 km LEO	<25	<100
Drag compensation in 500–600 km LEO	< 5	< 25
Drag compensation in > 600 km LEO		< 7.5
Station-keeping in geostationary orbit	50 – 55
Station-keeping in L1/L2	30 – 100
Station-keeping in Moon orbit	0 – 400
Attitude control (3-axis)	2 – 6
Spin-up or despin	5 – 10
Stage booster separation	5 – 10
Momentum wheel unloading	2 – 6

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.

FromTo	LEO-Ken	LEO-Eq	GEO	EML-1	EML-2	EML-4/5	LLO	Moon	C3
Earth	9.3 - 10
Low Earth Orbit (LEO-Ken)		4.24	4.33	3.77	3.43	3.97	4.04	5.93	3.22
Low Earth Orbit (LEO-Eq)	4.24		3.90	3.77	3.43	3.99	4.04	5.93	3.22
Geostationary Orbit (GEO)	2.06	1.63		1.38	1.47	1.71	2.05	3.92	1.30
Lagrangian point 1 (EML-1)	0.77	0.77	1.38		0.14	0.33	0.64	2.52	0.14
Lagrangian point 2 (EML-2)	0.33	0.33	1.47	0.14		0.34	0.64	2.52	0.14
Lagrangian point 4/5 (EML-4/5)	0.84	0.98	1.71	0.33	0.34		0.98	2.58	0.43
Low Lunar orbit (LLO)	1.31	1.31	2.05	0.64	0.65	0.98		1.87	1.40
Moon (Moon)	2.74	2.74	3.92	2.52	2.53	2.58	1.87		2.80
Earth Escape velocity (C3)	0.00	0.00	1.30	0.14	0.14	0.43	1.40	2.80

Interplanetary budget

From	To	delta-v in km/s
Earth Escape velocity (C3)	Mars Transfer Orbit	0.6
Mars Transfer Orbit	Mars Capture Orbit	0.9
Mars Capture Orbit	Deimos Transfer Orbit	0.2
Deimos Transfer Orbit	Deimos surface	0.7
Deimos Transfer Orbit	Phobos Transfer Orbit	0.3
Phobos Transfer Orbit	Phobos surface	0.5
Mars Capture Orbit	Low Mars Orbit	1.4
Low Mars Orbit	Mars surface	4.1
Earth Escape velocity (C3)	Closest NEO Asteroids	0.8 - 2.0

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).

Delta-vs between Earth and Mars

Abbreviations used

C3	Escape orbit
GEO	Geosynchronous orbit
GTO	Geostationary transfer orbit
L5	Earth-Moon fifth Lagrangian point
LEO-Eq	Low Earth orbit - equatorial
LEO-Ken	Low Earth orbit - "Kennedy inclination orbit"