Optimal engine selector for v.1.0.2

[Mesklin]

This thread was inspired by Meithan’s thread “Optimal engine charts for 1.0.2â€Â, he did a great job and I suddenly found that KSP world was changed. Now rocket engines are very diverse and I need to have instrument for fast and pinpoint selection of optimal engine, especially when rocket will be firing in atmosphere.

After several days thinking, remembering mathematic and fighting with google docs system, special spreadsheet was born and I decided to share my tools for all KSP community. This spreadsheet can answer for next question: If I have payload of certain mass and my ship should have certain ÃŽâ€v, what is engine (engines) and how many I need to use for make this ship with minimal mass. And what is the next engine in this competition for certain task? This decision is not as so simply as it was before, especially if you want to return something from Eve surface back to orbit.

And stop talking, here is this spreadsheet:

Optimal engine selector 1.0.2 v1

Table has 3 sheets (and several hidden sheets in Russian language):

1. “Optimal engine†– calculation for selection of optimal engine (engines)

2. “Craft dV†– calculation of craft dV based on liquid fuel and oxidizer quantities on board and total ship mass (all these data you can easily extract from stock game without any mods). Also you can see how many LF or oxidizer you need to flush for reach optimal ratio (useful for spaceplanes). And finally here is special calculation of dV for atomic engine LV-N “Nervâ€Â.

3. “Planets data†– this sheet contains all needed reference data about KSP planets and moons.

Sheet “Optimal engine†has two section: calculations for vacuum and for atmosphere.

1. Refernce body selection – You need to select body where you want to fly (A3 cell), minimal TWR will be calculated based on surface gravity of selected body.

2. Vacuum section – set payload mass, required dV, minimal TWR and wet-to-dry mass ratio (cells B7-B10). All fields for your inputs are marked by magenta color. Then you can see list of engines with solution: numbers of engine what you should place on your ship, resulted TWR and total ship mass. Results are not sorted, but masses marked with color scale from green to red thought white color (from min to max resulted mass). If your task does not have solution for one or several engines you will see “UNUSABLE†in column D in corresponding row.

In column L you can see maximum dV what you can reach for engine with certain TWR (with infinity number of engines).

3. Atmospheric section – you need to set same data as in previous section with addition of altitude above surface (altitude need for calculating atmospheric pressure for calculating right Isp and thrust of engines) . All data for atmospheric pressure calculation I took from KSP wiki and when I compare my results with KER I found some mismatches (looks like KER and I are using different scale height values). I will be very pleased for more exact information about KSP planet’s atmosphere.

I included in the list of engines RAPIER in close cycle mode and LFB KR-1x2 "Twin-Boar" engine. I calculated mass of this engine alone as difference between wet mass and fuel mass, also I subtracted dry tank mass based on total fuel quantity and wet-to-dry mass ratio.

[HANNIBALLA]

Thank you for the spreadsheet. This has helped a lot with building landers.

[Mesklin]

Thank you for the spreadsheet. This has helped a lot with building landers.

Thank you, but be careful, when are using this table for atmospheric calculation, results are not very exactly (error can be 5-10%, especially on Eve)

[Dispatcher]

Thanks for your charts and the work that went into them.

[Whizzkid]

What do the columns Z, C and C1 mean in the table, as i was trying to add a mod engine to the table.

[Mesklin]

Z - fuel-to-dry mass ration for tanks (almost all cells are linked to B10 or B34, with exception for LV-N and O-10 engine, see notes for cells)

C and C1 - middle calculations for simplifying formulas (simple copy it)

For new engine addition simple copy whole line of table and replace values in columns G, H, I, J and maybe column K, if your new engine is using only liquid fuel, like LV-N. For atmospheric part of calculations you also need to change value in column P, Q

[Whizzkid]

Z - fuel-to-dry mass ration for tanks (almost all cells are linked to B10 or B34, with exception for LV-N and O-10 engine, see notes for cells)

C and C1 - middle calculations for simplifying formulas (simple copy it)

For new engine addition simple copy whole line of table and replace values in columns G, H, I, J and maybe column K, if your new engine is using only liquid fuel, like LV-N. For atmospheric part of calculations you also need to change value in column P, Q

Ok thanks, i'll try that.