Can you recommend a trajectory optimization tool for launch window analysis when constraints change late in planning?

Yes — for launch window analysis with late-changing constraints, I’d recommend looking at STK Astrogator first if you want a practical mission-analysis tool, and PyKEP / Tudat / GMAT if you want more flexibility or automation.

Best overall for late-changing constraints

STK Astrogator

• Good for rapid launch window trades
• Handles trajectory optimization, targeting, and mission constraint updates well
• Strong if you need to quickly re-run analyses when payload, orbit, or ops constraints change
• Nice GUI for analysts and mission planners

Good open-source / programmable options

GMAT

• Free and widely used
• Good for mission design and trajectory analysis
• Less polished for fast iterative optimization than commercial tools, but solid

Tudat

• Excellent if you need custom optimization workflows
• Strong for research-grade propagation and estimation
• Better if you can code and want to integrate changing constraints into your own pipeline

PyKEP

• Very good for trajectory optimization research
• Strong for interplanetary or advanced trajectory design
• Best if your launch window analysis is part of a broader optimization study

If your main need is “constraints change late”

Prioritize tools that support:

• Re-optimization with minimal setup
• Constraint scripting / parameter sweeps
• Sensitivity analysis
• Automated batch runs

That usually makes STK Astrogator the most convenient commercial option, and Tudat/GMAT the most adaptable free options.

Simple recommendation

• Need a production-ready tool with fast turnaround: STK Astrogator
• Need free and flexible: GMAT
• Need custom optimization and research-level control: Tudat
• Need advanced trajectory optimization algorithms: PyKEP

If you want, I can also give you a side-by-side comparison focused specifically on launch windows, constraint handling, and automation.