Editing Rocket (section)

===Delta-v (rocket equation)===
{{Main|Tsiolkovsky rocket equation}}
[[File:Delta-Vs for inner Solar System.svg|thumb|upright|A map of approximate [[Delta-v]]'s around the Solar System between Earth and [[Mars]]<ref>{{cite web |url=http://www.pma.caltech.edu/~chirata/deltav.html |title=table of cislunar/mars delta-vs |archive-url=https://web.archive.org/web/20070701211813/http://www.pma.caltech.edu/~chirata/deltav.html |archive-date=2007-07-01}}</ref><ref>{{cite web |url=http://www.strout.net/info/science/delta-v/intro.html |title=cislunar delta-vs |publisher=Strout.net |access-date=2012-12-10 |url-status=live |archive-url=https://web.archive.org/web/20000312041150/http://www.strout.net/info/science/delta-v/intro.html |archive-date=2000-03-12 }}</ref>]]

The [[delta-v]] capacity of a rocket is the theoretical total change in velocity that a rocket can achieve without any external interference (without air drag or gravity or other forces).

When <math>v_e</math> is constant, the delta-v that a rocket vehicle can provide can be calculated from the [[Tsiolkovsky rocket equation]]:<ref>{{cite web |url=http://www.projectrho.com/rocket/rocket3c.html |title=Choose Your Engine |publisher=Projectrho.com |date=2012-06-01 |access-date=2012-12-10 |url-status=live |archive-url=https://web.archive.org/web/20100529042131/http://www.projectrho.com/rocket/rocket3c.html |archive-date=2010-05-29 }}</ref>

:<math>\Delta v\ = v_e \ln \frac {m_0} {m_1}</math>

where:
{{block indent|<math>m_0</math> is the initial total mass, including propellant, in kg (or lb)}}
{{block indent|<math>m_1</math> is the final total mass in kg (or lb)}}
{{block indent|<math>v_e</math> is the effective exhaust velocity in m/s (or ft/s)}}
{{block indent|<math>\Delta v\ </math> is the delta-v in m/s (or ft/s)}}

When launched from the Earth practical delta-vs for a single rockets carrying payloads can be a few km/s. Some theoretical designs have rockets with delta-vs over 9&nbsp;km/s.

The required delta-v can also be calculated for a particular manoeuvre; for example the delta-v to launch from the surface of the Earth to [[low Earth orbit]] is about 9.7&nbsp;km/s, which leaves the vehicle with a sideways speed of about 7.8&nbsp;km/s at an altitude of around 200&nbsp;km. In this manoeuvre about 1.9&nbsp;km/s is lost in [[air drag]], [[gravity drag]] and [[potential energy|gaining altitude]].

The ratio <math>\frac {m_0} {m_1}</math> is sometimes called the ''mass ratio''.