Again, engaging the enemy is not only not required, but could be detrimental to the mission.  Rocket-pack over the silos and drop your mines directly down the openings. Move quickly on the first mesa and destroy the gun emplacements on the second mesa before the dropship lands. If you take too long to complete your mission, inbound flyer units will attack your team as well as the science dropship.  

Also, watch out for enemies buried under the sand. They will emerge to ambush your team and the science dropship.