It's a rocket launch facility. 

https://files.hawaii.gov/dlnr/meeting/submittals/150925/D-1.pdf bottom of page 1 "ORS-4 Super Srypi launch vehicle will be launched from Pad 41 located at Kokole Point on the southern end of PMRF. "

Here's a video of the launch https://www.youtube.com/watch?v=987s75I8MKI