Editing Hohmann transfer orbit (section)

== Example ==
The diagram shows a Hohmann transfer orbit to bring a spacecraft from a lower circular orbit into a higher one. It is an [[elliptic orbit]] that is tangential both to the lower circular orbit the spacecraft is to leave (cyan, labeled ''1'' on diagram) and the higher circular orbit that it is to reach (red, labeled ''3'' on diagram). The transfer orbit (yellow, labeled ''2'' on diagram) is initiated by firing the spacecraft's engine to add energy and raise the [[apsis|apoapsis]]. When the spacecraft reaches the apoapsis, a second engine firing adds energy to raise the periapsis, putting the spacecraft in the larger circular orbit.

[[File:Hohmann transfer orbit2.svg|thumb]]
Due to the [[reversibility of orbits]], a similar Hohmann transfer orbit can be used to bring a spacecraft from a higher orbit into a lower one; in this case, the spacecraft's engine is fired in the opposite direction to its current path, slowing the spacecraft and lowering the periapsis of the elliptical transfer orbit to the altitude of the lower target orbit. The engine is then fired again at the lower distance to slow the spacecraft into the lower circular orbit. 
The Hohmann transfer orbit is based on two [[Impulse function|instantaneous velocity changes]]. Extra fuel is required to compensate for the fact that the bursts take time; this is minimized by using high-thrust engines to minimize the duration of the bursts.  For transfers in Earth orbit, the two burns are labelled the ''perigee burn'' and the ''apogee burn'' (or [[Apogee kick motor|''apogee kick'']]<ref>Jonathan McDowell, "[https://arc.aiaa.org/doi/pdf/10.2514/6.1997-3133 Kick In the Apogee: 40 years of upper stage applications for solid rocket motors, 1957-1997]", 33rd AIAA Joint Propulsion Conference, July 4, 1997. [https://arc.aiaa.org/doi/abs/10.2514/6.1997-3133 abstract]. Retrieved 18 July 2017.</ref>); more generally, for bodies that are not the Earth, they are labelled ''periapsis'' and ''apoapsis'' burns.  Alternatively, the second burn to circularize the orbit may be referred to as a ''circularization burn''.

===Type I and Type II===

An ideal Hohmann transfer orbit transfers between two circular orbits in the same plane and traverses exactly 180° around the primary.  In the real world, the destination orbit may not be circular, and may not be coplanar with the initial orbit.  Real world transfer orbits may traverse slightly more, or slightly less, than 180° around the primary.  An orbit which traverses less than 180° around the primary is called a "Type I" Hohmann transfer, while an orbit which traverses more than 180° is called a "Type II" Hohmann transfer.<ref name= "NASA-trajectories">NASA, ''Basics of Space Flight'', Section 1, Chapter 4, "[https://solarsystem.nasa.gov/basics/chapter4-1 Trajectories]". Retrieved 26 July 2017. Also available [https://spaceodyssey.dmns.org/media/57432/hohmann_transfer_orbits.pdf spaceodyssey.dmns.org] {{Webarchive|url=https://web.archive.org/web/20170728080707/https://spaceodyssey.dmns.org/media/57432/hohmann_transfer_orbits.pdf |date=2017-07-28 }}.</ref><ref>Tyson Sparks, [http://ccar.colorado.edu/asen5050/projects/projects_2015/Students/Alpert_Brian/interplanetary_transfer.html Trajectories to Mars] {{Webarchive|url=https://web.archive.org/web/20171028085842/http://ccar.colorado.edu/asen5050/projects/projects_2015/Students/Alpert_Brian/interplanetary_transfer.html |date=2017-10-28 }}, Colorado Center for Astrodynamics Research, 12/14/2012. Retrieved 25 July 2017.</ref>

Transfer orbits can go more than 360° around the primary. These multiple-revolution transfers are sometimes referred to as Type III and Type IV, where a Type III is a Type I plus 360°, and a Type IV is a Type II plus 360°.<ref>Langevin, Y. (2005). "Design issues for Space Science Missions," ''Payload and Mission Definition in Space Sciences'', V. Mártínez Pillet, A. Aparicio, and F. Sánchez, eds., Cambridge University Press, p. 30. {{ISBN|052185802X}}, 9780521858021</ref>

=== Uses ===
A Hohmann transfer orbit can be used to transfer an object's orbit toward another object, as long as they co-orbit a more massive body. In the context of Earth and the [[Solar System]], this includes any object which orbits the [[Sun]]. An example of where a Hohmann transfer orbit could be used is to bring an asteroid, orbiting the Sun, into contact with the Earth.<ref>{{Cite arXiv|eprint=1808.05099|last1=Calla|first1=Pablo| last2=Fries|first2=Dan|last3=Welch|first3=Chris|title=Asteroid mining with small spacecraft and its economic feasibility| year=2018|class=astro-ph.IM }}</ref>