Robot Manufacturer, Astronomers Battle Over Lawnmower

Could our view of distant galaxies be obstructed by a lawnmower?

That unlikely question is at the heart of a growing debate between the National Radio Astronomy Observatory (NRAO) and a robot manufacturer that seeks to build self-guided lawnmowers. NRAO, which uses radio telescopes to study distant stars and interstellar chemistry, says the lawnmower's use of radio waves for guidance would interfere with its view of the heavens.

"Their frequency band crosses a protected radio astronomy band," Harvey Liszt, astronomer and spectrum manager for NRAO in West Virginia, told Design News. "They can still operate over the vast majority of the United States without worrying about interference. But, by the book, 55 miles is the minimal distance they can get to a radio telescope."

The frequency band in question, 6650-6675.2 MHz, is considered important for astronomical observations of methanol spectral lines. Astronomers study the 6.66852-GHz methanol line as part of an effort to understand the formation of our solar system, according to the Committee of Radio Astronomy Frequencies.

Bluetooth and WiFi devices, which generally operate in frequency bands at or below 2.5 GHz, don't present an interference issue for radio telescopes, Liszt said. The proposed lawnmower does present a problem, however, because its band of operation lands smack in the middle of the radio telescope band.

iRobot, the well-known manufacturer of Roomba vacuum cleaner robots, originally proposed the idea of using a frequency in the ultra-wide band to the Federal Communications Commission (FCC) while working on an autonomous lawn-mowing robot. Details about the proposed lawnmower are still scarce, but it is known that iRobot engineers want to use that particular frequency to guide the lawnmowers from portable beacons in the ground. The radio-controlled design is considered a departure for autonomous lawnmowers, which typically rely on wires to create boundaries.

iRobot engineers who have studied the situation say that the 55-mile exclusion zone is vastly overstated. The company says the zone should be no bigger than 610 meters. "Calculations based on the correct interference levels, terrain blockage, ground attenuation, and foliage demonstrate that no iRobot RLM will be operated within the harmful interference threshold," the company wrote in a reply to the FCC, which it recently emailed to Design News.

"We feel the chances of interference are infinitesimal," Matt Lloyd, spokesman for iRobot, told us.

As part of its reply to the FCC, iRobot also argued that its proposed lawnmower would have societal benefits, including reduced death and injuries due to lawn mowing, reduced emissions, and reduced noise pollution. Because the product is still being developed, however, iRobot has not yet explained why it needs that particular frequency band.

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NRAO astronomers proposed that iRobot solve the problem by endowing the lawnmower with the intelligence to "know" where it is at all times. That way, they said, it couldn't be operated near a radio telescope. "We suggested they put in a GPS chip," Liszt said. "It wouldn't be unusual. Many things in the radio industry today have to know where they are before they can broadcast."

Senior technical editor Chuck Murray has been writing about technology for 31 years. He joined Design News in 1987, and has covered electronics, automation, fluid power, and autos.

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