Difference between revisions of "Cheat sheet"
From Kerbal Space Program Wiki
(* formulas to <math>. ! other stuff.) |
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*Equation: | *Equation: | ||
| − | :<math>\Delta{v} = ln(\frac{M_{start}}{M_{end}}) \cdot I_{sp} \cdot | + | :<math>\Delta{v} = ln\left(\frac{M_{start}}{M_{end}}\right) \cdot I_{sp} \cdot g_0</math> |
*Explained: | *Explained: | ||
| − | :<math>\Delta{v} = ln(\frac{Starting Mass}{Ending Mass}) \cdot Specific Impulse \cdot 9.81 \frac{m}{s^2}</math> | + | :<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> |
*Example: | *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. | :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. | ||
| − | :<math>\Delta{v} = ln(\frac{23t}{15t}) \cdot 120 s \cdot 9.81 \frac{m}{s^2} = 1803.2 \frac{m}{s^2}</math> | + | :<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> |
==== Transitional Δv (true Δv when launching from Kerbin) ==== | ==== Transitional Δv (true Δv when launching from Kerbin) ==== | ||
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*Explained: | *Explained: | ||
| − | :<math>TWR = \frac{Thrust Force}{Total Mass \cdot | + | :<math>TWR = \frac{\text{Thrust Force}}{\text{Total Mass} \cdot \text{Local gravitational acceleration}}</math> |
*Example: | *Example: | ||
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*Equation: | *Equation: | ||
| − | :<math>I_{sp} = \frac{(F_1 + F_2 + | + | :<math>I_{sp} = \frac{(F_1 + F_2 + \dots)}{\frac{F_1}{I_{sp1}} + \frac{F_2}{I_{sp2}} + \dots}</math> |
*Explained: | *Explained: | ||
| − | :<math>I_{sp} = \frac{Thrust Of Engine 1 + Thrust of Engine 2 + ...}{\frac{Thrust Of Engine 1}{I_{sp} Of Engine 1} + \frac{Thrust Of Engine 2}{I_{sp} Of Engine 2} + | + | :<math>I_{sp} = \frac{Thrust Of Engine 1 + Thrust of Engine 2 + ...}{\frac{Thrust Of Engine 1}{I_{sp} Of Engine 1} + \frac{Thrust Of Engine 2}{I_{sp} Of Engine 2} + \dots}</math> |
*Example: | *Example: | ||
Revision as of 18:45, 25 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.
Contents
Mathematics
Delta-v (Δv)
Basic calculation
- For atmospheric ΔV value, use atmospheric thrust values.
- For vacuum Δv value, use vacuum thrust values.
- 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)
- How to calculate the Δv of a rocket stage that transitions from Kerbin atmosphere to vacuum.
- 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.
- 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
- http://wiki.kerbalspaceprogram.com/w/images/7/73/KerbinDeltaVMap.png
- http://www.skyrender.net/lp/ksp/system_map.png
- Δv Change Values
- Δv KSP Nomogram
Thrust to weight ratio (TWR)
- This is Newton's Second Law.
- If ratio is less than 1, the craft will not lift off the ground.
- Equation:
- Explained:
- Example:
- 200 kN rocket engine under a 15 t rocket launching from Kerbin.
- The TWR is higher than 1, so the craft will lift off!
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. So six engines with 200 s of Isp still yield only an Isp of 200 s.
- If the Isp is different for engines in a single stage, then use the following equation:
- Equation:
- Explained:
- Example:
- Two engines, the first one with 200 N of thrust and 120 s of Isp; the second one with 50 N of thrust and 200 s of Isp.
See also
Links to collections of reference materials.
