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Arrowstar / ksptot

KSP Trajectory Optimization Tool
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Compute Departure Burn yields inefficient transfers #31

Open walkthechunk opened 1 year ago

walkthechunk commented 1 year ago

First of all, thank you for all your work on this tool. I tried to get into it but I ran into a number of issues. I tried to follow the Mission Architect tutorial for a simple transfer to Eve but I ran into problems:

  1. Computing the porkchop plot works as expected: grafik
  2. Now I click on "Compute Depature Burn". Here I run into the first issue: "Select Departure / Arrival Date" does not work - If I then click on the plot, I hear an error sound and nothing happens. However, I can enter the values of the clicked data point manually: grafik
  3. Clicking "Compute Departure Burn" and waiting 20 seconds yields the following: grafik

There is a clear discrepancy between the expected 1.100 m/s and the actual 1.900 m/s maneuvre. Also, the huge radial component could be avoided by simply executing the maneuvre a few minutes earlier on the orbit. Am I doing something wrong here?

I am using KSPTOT binaries v.1.6.9 and MATLAB runtime R2022a (9.12).

Arrowstar commented 1 year ago

First, thank you for the report about the Select Departure/Arrival Date button being broken. I've resolved the issue and it'll be in the next release.

Second, I'm not sure what you meant by "There is a clear discrepancy between the expected 1.100 m/s and the actual 1.900 m/s maneuvre." Can you clarify?

Third, the Compute Departure stuff from the porkchop plot tries to find an orbit with the correct output hyperbolic velocity vector that intersects the initial orbit. That's why you're seeing the large radial component there. If you actually want to perform the maneuver correctly, departing from the correct orbit plane will help significantly as well. I'd recommend taking the hyperbolic excess velocity vector elements shown in the final dialog box and model the mission in Launch Vehicle Designer (which despite its name is now an all purpose spacecraft trajectory design tool). I did all this and was able to achieve a marked improvement over what the lower fidelity Compute Departure tool was able to provide me.

image

I can provide an example of what I did in LVD if you're interested. Let me know!

walkthechunk commented 1 year ago

Thank you for the response!

Second, I'm not sure what you meant by "There is a clear discrepancy between the expected 1.100 m/s and the actual 1.900 m/s maneuvre." Can you clarify?

What I meant is that the tooltip in the porkchop plot says "Estimated departure Delta-V 1.108 m/s" but the computed departure burn had a delta-v of 1.900 m/s, which is much greater than the estimate.

I will also definitely check out the Launch Vehicle Designer!