Cheat sheet

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Kerbal Space Program rocket scientist's cheat sheet: Delta-v maps, equations and more for your reference so you can get from here to there and back again.

Delta-v (Δv)

Basic calculation

  1. For atmospheric ΔV value, use atmospheric thrust values.
  2. For vacuum 6Delta;v value, use vacuum thrust values.
  3. Use this equation to figure out the Δv per stage:
  • Equation:
  • Explained:
  • Example:
Single stage rocket that weighs 23 t when full, 15 t when fuel is emptied, and has an engine with a specific impulse of 120 s.

Transitional Δv (true Δv when launching from Kerbin)

  1. How to calculate the Δv of a rocket stage that transitions from Kerbin atmosphere to vacuum.
  2. Assumption: It takes approximately 1000 m/s2 of Δv to escape Kerbin's atmosphere before vacuum Δv values take over for the stage powering the transition.
  3. Note: This equation is an approximation and not completely accurate, so the results will vary a bit depending on the TWR and such. The result is accurate enough for normal purposes though.
  • Equation:
  • Explained:
  • Example:
Single stage with total atmospheric Δv of 5000 m/s2 and with a Δv of 6000 m/s2 in vacuum.

Δv maps

Various maps developed by KSP fans.

  • Δv Total Values
  1. http://wiki.kerbalspaceprogram.com/w/images/7/73/KerbinDeltaVMap.png
  2. http://www.skyrender.net/lp/ksp/system_map.png
  • Δv Change Values
  1. http://i.imgur.com/duY2S.png
  • Δv KSP Nomogram
  1. http://ubuntuone.com/1kD39BCoV38WP1QeG6MtO6

Thrust to weight ratio (TWR)

  1. This is Newton's Second Law.
  2. If ratio is less than 1, you will not lift off the ground.


  • Equation:
TWR = F / (m * g) > 1
  • Explained:
TWR = Force of Thrust / ( Total Mass X 9.81 ) > 1
  • Example:
200 kiloNewton rocket engine on a 15 ton rocket launching from Kerbin Space Center.
TWR = 200 kN / ( 15 Tons total Mass X 9.81 m/s2 ) = 1.36 which is > 1 which means liftoff!


Combined specific impulse (Isp)

  1. When Isp is the same for all engines in a stage, then the Isp is equal to a single engine. So six 200 Isp engines still yields only 200 Isp.
  2. When Isp is different for engines in a single stage, then use the following equation:
  • Equation:
Isp = ( F1 + F2 + ... ) / ( ( F1 / Isp1 ) + ( F2 / Isp2 ) + ... )
  • Explained:
Isp = ( Force of Thrust of 1st Engine + Force of Thrust of 2nd Engine...and so on... ) / ( ( Force of Thrust of 1st Engine / Isp of 1st Engine ) + ( Force of Thrust of 2nd Engine / Isp of 2nd Engine ) + ...and so on... )
  • Example:
Two engines, one rated 200 Newtons and 120 Specific Impulse; another engine rated 50 Newtons and 200 Specific Impulse.
Isp = (200 Netwons + 50 Newtons) / ( ( 200 Newtons / 120 ) + ( 50 Newtons / 200 ) = 130.89 Specific Impulse

See also

Links to collections of reference materials.