the accident happened at approximately 2:45 a.m. EDT (0645 GMT)
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Middle of the night. Wonder if there are cameras to monitor the facility 24X7?
Radio astronomy goes on night and day. It's odd that it was idle. Arecibo was originally funded in part by the Navy to perform ionospheric studies, but they pulled out decades ago. It's been something of an orphan, really. The Chinese build a larger passive array (and had to relocate an entire village to do so) but Arecibo was still the largest active radio telescope (radar).
Security is obviously an issue, considering the location.