A spiral transfer is an orbital maneuver, much like a

Hohmann transfer. It is used to move a

spacecraft from one

orbit to another.

A spiral transfer has the shape of a spiral that starts at the spacecraft's original orbit and extends outward from the body of gravity (i.e. Earth). The spiral transfer requires constant acceleration and because of this, the spiral transfer is only useful for spacecraft with electrical propulsion.

The delta-v is given by the equation below.

del_v = sqrt( Vc1^{2} - 2Vc1Vc2 + Vc2^{2} )

Where

Vc1 is the velocity required for the first orbit

Vc2 is the velocity required for the second orbit