Overview
Sometimes it can be tricky to decide from the start how many thrusters you need to put on a ship to get the desired performance, especially when designing ships for multiple environments. I would like to share with you a spreadsheet I made to help me with estimating how many thrusters I need when starting a ship.
Introduction
The idea of this calculator is to use as few variables as possible and give you a picture of how a ship will fly in different environments with the emphasis on launching and landing on planets. It supports both small and large ships, multiple customizable environments and optionally can provide you information about hydrogen, power and jump range.
So, without further ado, here is the link:
Thrusters Calulator[docs.google.com]
Making a copy
To copy it to your google drive, open the File menu and select “Make a Copy” option. If you want to download it, there is a “Download As” item in the same menu. Here the only viable options are Microsoft Excel and Open Document formats. There rest, I am pretty sure, will break not have any formulas or interactive elements that the spreadsheet has.
Overview
There are three tabs in the document, but only one of them is used for calculations: PayloadCalc. It also has data for a ship I built as an example. The others two tabs contain constants for different kinds of modules factored in the calculations and some statistics you might find curious, but nothing interactive.
The main page is organized in blocks to be easily manageable. Before I go over them, there is a simple rule for interacting with the spreadsheet:
Orange blocks are for input, grey blocks are for calculated values.
Now, you only need to look at three of the blocks to make any use of the spreadsheet. The rest is optional.
Main blocks
First, in the General Ship Info you set up grid size and its dry mass in tons. The game displays mass in kilograms, so if you already have your ship, look at its mass on the panel in the lower right and divide it by 1000 (basically, discard the last three digits) and put that into the spreadsheet. If you are only planning to build your ship, put an estimation here and you will get the general idea for what kind of propulsion you are going to need.
This block also gives you some statistics as well. In the first column, it shows how much power your ships will have available (based on the information you enter in the optional blocks discussed below), how long will your hydrogen last and, more importantly, how much power your thrusters will require. The latter is given both as a flat number and as a ratio. If thrusters require more power than your systems can provide, the number will turn red. It also displays what percentage of your dry mass various systems take and how much of it you will be able to devote to structure and mission equipment.
What is peak power draw? This is not the sum of how much power all thrusters on your ship will require. The calculator finds two directions that require most power and assumes thrusters there are firing at full power. From my experience, this is the most likely scenario that might put strain on your ship’s power plant.
Then look at the Ship Thrusters block. It is pretty straight forward: you fill the number of each type of thrusters that push your ship in each of the major directions.
The final of the three main blocks is the Environments block. This is really the purpose of this spreadsheet. It has four environments, three of which are configured for the most common scenarios in Space Engineers. The forth is for custom planets or deeps space. OF course, with no gravity there is no limit on how low your thrust can get. The payload values are entirely based on the “Required excess acceleration” option discussed below.
For each environment, you have two columns of statistics for forward and vertical thrust. This is because most of the ships in Space Engineers are belly landers, and the game leans towards that design with many options for ramps and ladders, but no elevators. In this configuration ships first need enough of upwards thrust to lift them off the ground before sometimes turning vertical and using their main thrusters to reach space. This is why both directions are important. Tail landers don’t have that problem, but there are very few of them.
Each column lists thrust in that direction, acceleration and thrust to weight ratio (TWR). The latter is how much thrust you have compared to the mass (dry mass, specifically) of your ship. If it is above 1 you’re good. Below 1 your ship will plunge to the ground most likely.
The last row for each environment and direction is payload. That is how much mass you can take onboard before you get below the safety margin in that environment and for that direction of thrust. For a belly lander you probably want to ensure that your payload in each environment is roughly equal for both vertical and forward thrust if you plan to thrust vertically on your way to space.
That margin of error I mentioned is defined by “Required excess acceleration field”. This is the amount acceleration above acceleration due to gravity that the ship must reach carrying maximum payload. It is not a good idea to have exactly as much acceleration as required to overcome gravity on your ship because in this case you won’t be able to ascend, and the larger this margin the better. For example with the default value of 2 m/s/s of excess acceleration it will take 50 seconds and 2500 meters of altitude drop to go from 100 m/s to a complete stop.
Optional blocks
Hydrogen tanks. Here you simple fill in the number of hydrogen tanks on your ship to get their mass, total amount of hydrogen and how long will hydrogen last in worst-case scenario. Like with peak power, it is calculated based on the amount of thrusters in two directions that consume most hydrogen when fired. Usually it will last a lot longer, but you don’t want to drop below 200 seconds if you plan to go to space from an Earth-like planet and I usually like having above 300 seconds of fuel on my ships.
Power systems. Here you set the amount of batteries reactors and solar cells to see how much power your ship can generate. It assumes all batteries are charged. “Don’t count solar cells” option is there because solar cells are weak and require you to stay oriented the certain way, so you typically don’t want to count on the for propulsion.
If it is a large grid adding small batteries won’t do anything because they are only available for small ships.
“Hydrogen in engines” field shows how much hydrogen can be stored in Hydrogen Engines’ internal fuel tank. “H2 Consumption” shows how much hydrogen the engines will consume each second. “H2 engines use external tanks” determines whether hydrogen engine consumption is factored in fuel duration. If set to yes, it is assumed hydrogen engines only draw hydrogen from external tanks and are working at full capacity. If set to off it is assumed hydrogen engines only use internal hydrogen storage.
Jump drive. You specify the amount of jump drives your ship has and the spreadsheets calculates their mass, power draw when recharging and estimated jump range based on the dry mass of your ship. Jump range estimation is an approximation but it should usually stay within a few kilometers of what you will see in the game.
The other parameters are about additional fuel endurance afforded by the generators. First is a ratio between hydrogen production by generators and peak consumption by thrusters. If this ratio is above one, you can sustain maximum thrust as long as you have ice just from generation. Added fuel duration is the amount of time by which hydrogen generation extend fuel duration. Ice per second is ice consumption in kg by generators. If the generation ratio is above 1, this field says “Sustained”.
Below all this is a toggle called “Add gen. duration to total”. If set to yes, it will add addtional fuel duration calculated above and power consumption of the generators to total fuel duration and peak thrust power draw at the top of the page. It is a toggle because you might not want to bring ice with you on your trip. Below it, there are two fields that calculate the total amount of ice (in kg and liters) needed to sustain generators for the total fuel duration. They are not affected by the toggle, but will show “N/A” if generation can sustain maximum thrust.
Detailed thruster statistic blocks. Below and to the right of Environments block are blocks with detailed statistics for your thrusters, by thruster type and by direction. There are blocks for fuel and power consumption, mass and, more importantly, for thrust and acceleration in each of the four environments. Here you can get acceleration values for all directions, instead of just forward and vertical that environment block gives you.
Generation-powered thrust Below the detailed thruster statistics is the block which calculates thrust and TWR for different environments if the only source of hydrogen are oxygen generators (i.e. hydrogen tanks are initially empty). The first four rows calculate thrust for four environments detailed above per facing. The bottom four rows do the same for thrust to weight ratio (TWR). These values do not take into account required excess acceleration, but they do change with environment parameters.
Final notes
I hope you will find this calculator useful, and I did try to make it as easy to use as possible. Of course, I will be glad to hear your feedback.