¶ Ballistic Transfer Graph (AKA “Porkchop Plot”)
A Ballistic Transfer Graph is a tool used in astrodynamics and spacecraft navigation to visualize and analyze ballistic transfer trajectories between celestial bodies. These graphs help engineers and mission planners determine the most efficient paths for spacecraft to follow when moving from one orbit to another without the use of propulsion (hence “ballistic”).
¶ Key aspects of a Ballistic Transfer Graph:
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Trajectories: The graph shows different possible paths a spacecraft can take between the selected asteroids. These trajectories are influenced by gravitational forces and the initial velocity of the selected ship.
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Propellant Usage: The graph showcases the hydrogen propellant required for each trajectory, helping to identify which paths require less energy or time, which is crucial for travel planning.
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Launch Windows: The graph can indicate optimal launch windows when the alignment of the asteroids makes certain transfers more efficient.
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Transfer Times: It can also show the time it takes for a spacecraft to travel along different trajectories, allowing planners to balance energy use with flight duration.
¶ Reading Porkchop Plots
- X axis is how long your ship delays in orbit before it leaves on its journey
- Y axis is how long your ship will travel on its transfer orbit after leaving
- So X + Y = the total time until arrival. Total time increases diagonally from the bottom left corner to the top right corner.
- The “greyed out” section in the upper right corner is unreachable because your Crew would run out of food.
- The colors display the needed delta-V for the trip represented by each point, relative to how much of your ship’s propellant would be needed:
- Black = more propellant than your ship has (can’t travel)
- Dark blue = ~100%
- Pink = ~50%
- White = ~0%
- If you want the fastest possible trip, pick the point on the chart that is diagonally closest to the lower left corner, which is not black.
- If you want the trip that uses the least propellant, pick the point on the chart with the brightest color on the blue->pink->white scale.
- Make sure to leave some propellant for the return trip! But keep in mind that the last 50% of your propellant is a lot more than 50% of your total delta-V, so you’ll need less propellant for the return trip, all other things being equal.
¶ Time adjustment
(found at the bottom right of the screen. Click the time to expand to see controls)
Adjusting the time will allow you to see flight plans for times in the future and past. This is mostly relevant to see when the best time to leave would be.