Difference between revisions of "Cheat sheet"

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(Undo revision 20837 by Dgelessus (talk): AAAAND I hit enter too soon. oops!)
(* major change, made it shorter and more cheat-sheet-like. - examples. + various stuff.)
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=== Delta-v (Δv) ===
 
=== Delta-v (Δv) ===
 
==== Basic calculation ====
 
==== Basic calculation ====
#For atmospheric ΔV value, use atmospheric thrust values.
+
Basic calculation of a rocket's Δv. Use the atmospheric and vacuum thrust values for atmospheric and vacuum Δv, respectively.
#For vacuum Δv value, use vacuum thrust values.
 
#Use this equation to figure out the Δv per stage:
 
  
*Equation:
+
<math>\Delta{v} = ln\left(\frac{M_{start}}{M_{end}}\right) \cdot I_{sp} \cdot 9.81 \frac{m}{s^2}</math>
:<math>\Delta{v} = ln\left(\frac{M_{start}}{M_{end}}\right) \cdot I_{sp} \cdot g_0</math>
 
  
*Explained:
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==== Transitional (true) &Delta;v ====
:<math>\Delta{v} = ln\left(\frac{\text{Starting mass}}{\text{Ending mass}}\right) \cdot \text{Specific impulse} \cdot 9.81 \frac{m}{s^2}</math>
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{| class="wikitable" align="left"
 +
! Body !! &Delta;v<sub>out</sub>
 +
|-
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| [[Kerbin]] || 1000 m/s<sup>2</sup>
 +
|-
 +
| other bodies' || data missing
 +
|}
 +
Calculation of a rocket's &Delta;v, taking an atmosphere into account. &Delta;v<sub>out</sub> is the amount of &Delta;v required to leave a body's atmosphere.
  
*Example:
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<math>\Delta{v}_T = \frac{\Delta{v}_{atm} - \Delta{v}_{out} \frac{m}{s^2}}{\Delta{v}_{atm}} \cdot \Delta{v}_{vac} + \Delta{v}_{out} \frac{m}{s^2}</math>
:Single stage rocket that weighs 23&nbsp;t when full, 15&nbsp;t when fuel is emptied, and has an engine with a specific impulse of 120&nbsp;s.
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{{clear|left}}
:<math>\Delta{v} = ln\left(\frac{23t}{15t}\right) \cdot 120 s \cdot 9.81 \frac{m}{s^2} =  1803.2 \frac{m}{s^2}</math>
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==== Maps ====
 +
Various fan-made maps showing the &Delta;v required to travel to a certain body.
  
==== Transitional &Delta;v (true &Delta;v when launching from Kerbin) ====
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'''Total &Delta;v values'''
#How to calculate the &Delta;v of a rocket stage that transitions from Kerbin atmosphere to vacuum.
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* http://wiki.kerbalspaceprogram.com/w/images/7/73/KerbinDeltaVMap.png
#Assumption: It takes approximately 1000&nbsp;m/s<sup>2</sup> of &Delta;v to escape Kerbin's atmosphere before vacuum &Delta;v values take over for the stage powering the transition.
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* http://www.skyrender.net/lp/ksp/system_map.png
#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.
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'''&Delta;v change values'''
 
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* http://i.imgur.com/duY2S.png
*Equation:
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'''&Delta;v nomogram'''
:<math>\Delta{v}_T = \frac{\Delta{v}_{atm} - 1000 \frac{m}{s^2}}{\Delta{v}_{atm}} \cdot \Delta{v}_{vac} + 1000 \frac{m}{s^2}</math>
+
* http://ubuntuone.com/1kD39BCoV38WP1QeG6MtO6
 
 
*Explained:
 
:<math>\text{Transitional Delta-v} = \frac{\text{Atmospheric Delta-v} - 1000 \frac{m}{s^2}}{\text{Atmospheric Delta-v}} \cdot \text{Vacuum Delta-v} + 1000 \frac{m}{s^2}</math>
 
 
 
*Example:
 
:Single stage with total atmospheric &Delta;v of 5000&nbsp;m/s<sup>2</sup> and with a &Delta;v of 6000&nbsp;m/s<sup>2</sup> in vacuum.
 
:<math>\Delta{v}_T = \frac{5000 \frac{m}{s^2} - 1000 \frac{m}{s^2}}{5000 \frac{m}{s^2}} \cdot 6000 \frac{m}{s^2} + 1000 \frac{m}{s^2} = 5800 \frac{m}{s^2}</math>
 
 
 
==== &Delta;v maps ====
 
Various maps developed by KSP fans.
 
 
 
*&Delta;v Total Values
 
#http://wiki.kerbalspaceprogram.com/w/images/7/73/KerbinDeltaVMap.png
 
#http://www.skyrender.net/lp/ksp/system_map.png
 
*&Delta;v Change Values
 
#http://i.imgur.com/duY2S.png
 
*&Delta;v KSP Nomogram
 
#http://ubuntuone.com/1kD39BCoV38WP1QeG6MtO6
 
  
 
=== Thrust to weight ratio (TWR) ===
 
=== Thrust to weight ratio (TWR) ===
#This is Newton's Second Law.
+
This is Newton's Second Law. If the ratio is less than 1 the craft will not lift off the ground.
#If ratio is less than 1, the craft will not lift off the ground.
 
  
*Equation:
+
<math>\text{TWR} = \frac{F}{m \cdot g}</math>
:<math>\text{TWR} = \frac{F}{m \cdot g}</math>
 
 
 
*Explained:
 
:<math>\text{TWR} = \frac{\text{Thrust force}}{\text{Total mass} \cdot \text{Local gravitational acceleration}}</math>
 
 
 
*Example:
 
:200&nbsp;kN rocket engine under a 15&nbsp;t rocket launching from Kerbin.
 
:<math>\text{TWR} = \frac{200 kN}{15 t \cdot 9.81 \frac{m}{s^2}} = 1.36</math>
 
:The TWR is higher than 1, so the craft will lift off!
 
  
 
=== Combined specific impulse (I<sub>sp</sub>) ===
 
=== Combined specific impulse (I<sub>sp</sub>) ===
#If the I<sub>sp</sub> is the same for all engines in a stage, then the I<sub>sp</sub> is equal to a single engine. So six engines with 200&nbsp;s of I<sub>sp</sub> still yield only an I<sub>sp</sub> of 200&nbsp;s.
+
If the I<sub>sp</sub> is the same for all engines in a stage, then the I<sub>sp</sub> is equal to a single engine. If the I<sub>sp</sub> is different for engines in a single stage, then use the following equation:
#If the I<sub>sp</sub> is different for engines in a single stage, then use the following equation:
 
 
 
*Equation:
 
:<math>I_{sp} = \frac{(F_1 + F_2 + \dots)}{\frac{F_1}{I_{sp1}} + \frac{F_2}{I_{sp2}} + \dots}</math>
 
 
 
*Explained:
 
:<math>I_{sp} = \frac{\text{Thrust of engine 1} + \text{Thrust of engine 2} + \dots}{\frac{\text{Thrust of engine 1}}{\text{Specific impulse of engine 1}} + \frac{\text{Thrust of engine 2}}{\text{Specific impulse of engine 2}} + \dots}</math>
 
  
*Example:
+
<math>I_{sp} = \frac{(F_1 + F_2 + \dots)}{\frac{F_1}{I_{sp1}} + \frac{F_2}{I_{sp2}} + \dots}</math>
:Two engines, the first one with 200&nbsp;N of thrust and 120&nbsp;s of I<sub>sp</sub>; the second one with 50&nbsp;N of thrust and 200&nbsp;s of I<sub>sp</sub>.
 
:<math>I_{sp} = \frac{200 N + 50 N}{\frac{200 N}{120 s} + \frac{50 N}{200 s}} = 130.89 s</math>
 
  
 
== See also ==
 
== See also ==
Links to collections of reference materials.
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Links to collections of reference material.
*[[Tutorials]]
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* [[Tutorials]]
*[[thread:28352|The Drawing Board: A library of tutorials and other useful information]]
+
* [[Terminology]]
 +
* [[thread:28352|The Drawing Board: A library of tutorials and other useful information]]

Revision as of 15:07, 28 June 2013

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.

Mathematics

Delta-v (Δv)

Basic calculation

Basic calculation of a rocket's Δv. Use the atmospheric and vacuum thrust values for atmospheric and vacuum Δv, respectively.

Transitional (true) Δv

Body Δvout
Kerbin 1000 m/s2
other bodies' data missing

Calculation of a rocket's Δv, taking an atmosphere into account. Δvout is the amount of Δv required to leave a body's atmosphere.

Maps

Various fan-made maps showing the Δv required to travel to a certain body.

Total Δv values

Δv change values

Δv nomogram

Thrust to weight ratio (TWR)

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

Combined specific impulse (Isp)

If the Isp is the same for all engines in a stage, then the Isp is equal to a single engine. If the Isp is different for engines in a single stage, then use the following equation:

See also

Links to collections of reference material.