If you get some civilians and/or cops, you could do some sort of hostage scenario. Also, the hazmat suited guys could be used in a similar fashion to the scientists, having them go into an alien spaceship to gather data of some sort. If you give the humans a couple of them, the challenge being to get in, complete the mission and get at least one of them out alive. Pretty basic I guess, but it’s a classic for a reason
Very X-com in some ways… why I forgot about X-com is beyond me, as I have the games and love playing them.