“I drive past this thing all the time, and I am dying to know what it is. None of my friends can identify this thing, either. There’s even a foreboding sign near the road telling passersby not to enter.”

So wrote a Seven Days reader who regularly commutes past rolling fields on Dorset Street in Shelburne. What puzzles him is the “Jetsons”-esque building standing on a hill on the road’s west side. Crowned by a white capsule and a ring of inward-facing white cubes, the structure is almost disorienting at first glance, like a blip in the space-time continuum. The entire thing is necklaced by a quaint wooden fence, as if someone tried, in vain, to make it look like it belonged in this farming landscape.

At the foot of the hill, a menacing sign commands in red block letters, “STOP! This road is PRIVATE. Land on both sides of road is POSTED. No Hunting • No Shooting • No Trespassing. Violators will be prosecuted.”

One recent, gloomy March afternoon, I rolled my car past a string of these warnings. No sentries or black vehicles were in sight, just the lonely and seemingly orphaned station. The only sign of life was a low-swooping hawk. Yet the hill was so exposed that I felt like I was being watched — by a camera, maybe, or someone at the windows of a nearby home. The approach reminded me of driving up to Stonehenge for the first time, its silent bulk reaching toward the sky.

Closer still, more signs warned that meddling with the building’s operation could result in loss of human life, and that I was now liable to be prosecuted under federal law. One sign also yielded a clue: If I parked within 500 feet, “disruption of aircraft navigation signals may occur.”

I snapped a few hasty photos and retreated. Googling “air navigation” and “Shelburne” in various combinations produced nothing useful. When I went to the Shelburne town office, though, town clerk Colleen Haag waved her hand nonchalantly and said, “Oh, the VORTAC tower. Follow me.”

Never heard of VORTAC? Neither had I. It’s an acronym for Very High Frequency Omnidirectional Range Tactical Air Navigation. The first half of that complicated moniker refers to civilian air traffic, the second half to TACAN, the tactical air navigation system used by military aircraft. VORTAC towers, I learned, make up the spine of the United States’ air navigation system, built in the 1950s and ’60s to guide aircraft safely to their destinations. The antiquated architecture hasn’t changed much since.

Those little white cubes that look like lights? They’re actually 16 tiny antennae, especially valuable in times of bad weather or instrument malfunction. The tower’s nearest cousins are in Montpelier and Plattsburgh.

So, what resembles a vintage government outpost is actually a buzzing organism that transmits bearing and distance information to pilots as they approach Burlington International Airport. “It is essential for navigation in this area” if a pilot is relying on instruments, explained Shelburne Flight School owner Paul Potter in a phone conversation.

The frequency pilots tune into to hear the beacon, he said, is 117.50. When they find it, they capture a series of signals that guide them through a safe Burlington approach. Without it, pilots would use visual reckoning or have to rely on the busy Burlington Airport Control Tower. The unmanned VORTAC station can guide dozens of aircraft at a time, up to a distance of 100 miles away.

Shelburne’s VORTAC tower — which shares its bizarre design with hundreds of brethren nationwide — was built in 1958 on land belonging to Philiza and Blanche Lamothe. The Lamothes had owned the lonesome tract since 1919, and in 1975 they sold an easement to the federal government for $52,910.

One of the adjoining tracts now belongs to Bill Bissonette, a co-owner of Al’s French Frys in South Burlington. Though he said it “looks like a bomb site” and that maintenance folks come and go regularly, Bissonette added that the structure emits no sound and has no negative impact on its surroundings. However, he was dismayed that tree surgeons appeared a few weeks ago to clear-cut the brush boundary that obscured his view of the tower. “No question it was overkill,” said Bissonette, “but at the end of the day, you can’t argue with the U.S. government.”

As air control migrates toward GPS-based systems, Bissonette wondered if the antiquated VORTAC towers may be phased out.

“There’s been talk of replacing these for the last 30 or 40 years,” said Eddie Cyr, service manager for the Burlington control tower. But, it appears, engineers nailed the design the first time around. “Pilots still use these all of the time,” Cyr said.