I can appreciate the comments here. Judging the project for FLL is hard. Especially when you consider that all of the judges are volunteers and may not have any experience in the area that is being presented. Even if they had an actual astronaut as one of the judges, that wouldn't necessarily help at all if the team's project was about a piece of equipment to use on Mars to help with mining oxygen or minerals. Astronauts don't necessarily get training in mining. But that's not the point. You shouldn't need an expert to evaluate the presentation. Nor should you expect one. Look at the rubric. No where does it say, "How perfect is the idea? Is the idea ready for deployment?". It would definitely take an expert to make that assessment. Instead, the judges are looking to see if they did an appropriate amount of research. Is the solution clearly explained? Is there demonstrated added value with your idea? Was there a systematic approach taken by the team over the course of the research and presentation development? Again, look at the rubric and be sure that your presentation covers everything on it.
So, what do you do as a coach?
Explain to the team that the judges are volunteers, and you may not get a judge that knows anything about what you are presenting. So, you need to present to a level that any fifth grader could understand. If you are using special terms or concepts, explain them clearly in your presentation. Test your presentation on multiple audiences, especially with people that you can trust to give you honest, critical feedback. Keep finding new audiences to share with in order to assess if changes actually result in an improvement in clarity. It should be completely and perfectly clear to everyone what problem you are trying to solve, and what your proposed solution is. If your test audiences don't fully understand what you are trying to accomplish, then maybe you are attempting too much? You may need to address a smaller part of your problem.
Finally, be on the lookout for your own experts. Ask them the questions I wrote above. "How perfect is our idea? Is our idea ready for deployment?". Put the feedback from that in your presentation and tell the judges what the experts think. You may have done that in your presentation, but I am including it here for completeness.