EROS Radome: 20 Things You Didn't Know
Landsat satellites move in a polar orbit from north to south at over 27,000 kilometers per hour. For the ten meter antenna at EROS, a typical flyover, also known as a pass, lasts 14 minutes from horizon to horizon.
The primary radome is a 60 foot sphere resting on a 12 foot ring wall. An air traffic light and a lightning rod are mounted on top. The antenna within has a ten meter dish.
The ten meter EROS antenna has counterweights to offset its four ton reflector. The entire system is so well balanced it can be moved by hand. The radome’s 267 fiberglass panels are held together by 13,866 bolts, which must be checked for tightness every five years.
The EROS antenna requires an extremely stable base. Its concrete footings reach 29.5 feet down to the bedrock. 16 anchor bolts reach the entire depth and connect to the pedestal.
The ten meter antenna at EROS has two primary axis motors: azimuth and elevation. They allow a full range of motion in theory, but for a full overhead pass, the motors would need to move impossibly fast near the zenith point to keep up with satellites. With a two axis system, zenith data is often lost. To account for this the EROS antenna includes a third motor installed with a seven degree offset. The three rotation points work together to execute full passes without overworking any single motor.
Signals coming in from orbit are thousands of times weaker than a cell phone, which is why a dish is necessary to receive them. The antenna’s transmitter sends commands at 100 watts and must be aimed extremely accurately to hit satellites over 400 miles away.
Between passes the EROS antenna moves to stow position, the point of balance where the least amount of pressure is on all moving parts. This stow position is sometimes referred to as birdbath mode.
The waxy and warm surface of the radome typically sheds snow, but sometimes a crust can form. Two snow ropes are attached to the top of the dome for removal. It's not high tech, but it works.
The radome is washed and waxed every five years. The bolts are tested at the same time and tightened if needed. In 2023 nine gallons of wax were needed to cover the dome.
The EROS campus is also home to a 5.4 meter antenna with its own dome. It's primarily used for the Landsat 7 mission today.
The first ten meter antenna was installed in 1996, and just prior to commissioning it was destroyed by softball sized hail. It was rebuilt in 1997 and covered by a dome structure to avoid a similar fate.
Most of the time there are no staff in the radome. Data moves between the antenna and control room within the building via solid underground cables. Control room staff monitor passes and data flow 24 seven every day of the year.
Visitors to EROS often comment that the radome resembles a giant golf ball. To be exact, it’s 429 times larger than a standard golf ball. To play 18 holes with it, you'd need a super sized course over 62,000 acres. That's approximately the size of Milwaukee, Wisconsin.
The EROS water tower was originally installed to support the film lab. Today, it provides pressure to the building and local area. The antennas must avoid a small notch around the tower to avoid problems when transmitting and receiving.
The radome’s 267 fiberglass panels have little effect on the reception or transmission of signals. Dirt buildup, rain and snow accumulation affect signals more than the panels themselves. Occasionally, data transmissions are missed due to heavy snow, ice or rain, but recovered on subsequent passes.
EROS isn't the only ground station used to collect Landsat data. In fact, over 40 international stations have worked together over the past 50 years, and there are currently 15 stations actively receiving data from Landsats 8 and 9.