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I'm trying to learn trajectory design and optimization, and I'm struggling to understand how one determines the launch window using trajectory design programs.

I know that my satellite's initial orbital parameters depend on:

  • latitude of launch and azimuth (determines inclination)
  • longitude of launch and days since vernal equinox (determines longitude of ascending node)
  • flight path angle, radius, and velocity at insertion

So far, I've been following this procedure:

  1. Setup orbital parameters using geographic coordinates (28.5 deg latitude, -80 deg longitude for Cape Canaveral, some epoch, FPA of 0, and an initial orbital angular momentum which gives a GTO).
  2. Minimize DVs for departure and arrival at the destination, allowing the initial time to change.
  3. Move initial date according to how much the initial time changed during the optimization.
  4. Repeat, but perhaps this time freezing the initial time in step 2.

I can get a low delta-V this way, but the initial parameters clearly don't reflect a Cape Canaveral launch any longer (because the epoch and initial time are no longer the same, earth rotates, etc.).

I can freeze the initial time to be equal to the epoch time, but this clearly doesn't guarantee an optimal launch window.

If one knows the launch site, how does one usually find optimal launch windows for a mission?

I found a link explaining the launch windows for Apollo, but it's descriptive and doesn't really advise on how to set up an optimization routine.

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