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GPS Correction Technology Lets Tractors Drive Themselves

NASA satellite navigation software enables autonomous farm equipment.

Spinoff is NASA’s annual publication featuring successfully commercialized NASA technology. This commercialization has contributed to the development of products and services in the fields of health and medicine, consumer goods, transportation, public safety, computer technology, and environmental resources.

For more than a decade, John Deere’s StarFire GPS receivers used NASA’s global network of ground stations and the JPL software, which the company licensed, to enable self-guided tractors.

Farmers have enjoyed self-driving tractors for more than a decade, in part due to a partnership between John Deere and NASA’s Jet Propulsion Laboratory (JPL). Working primarily with NavCom, which the company later purchased, John Deere engineers began developing GPS receivers that enabled capabilities such as yield mapping, which incorporates mass flow and moisture data from sensors on a harvesting combine with GPS location data to determine how much of the harvest is coming from each part of the field. Such information can help farmers allocate future resources and determine which hybrids and management practices are the most productive.

The challenge was that uncorrected GPS can be off by up to 30 feet due to data errors, drift in the GPS satellites’ internal clocks, and inaccurate orbital parameters. What the company ultimately wanted was a system that could correct the signals with a high enough accuracy that GPS could be used to actually guide the tractor.

Meanwhile, scientists at JPL, where the first global tracking system for GPS satellites had already been developed, were working to stream satellite tracking data in real time via the Internet, rather than collecting it intermittently by phone lines. A major infusion of R&D funding from the Federal Aviation Administration, which wanted to provide pilots with reliable GPS data, enabled them to develop the necessary software.

The result was the Real-Time GIPSY (RTG) software. GIPSY refers to the GNSS-Inferred Positioning System, wherein GNSS stands for Global Navigation Satellite System. RTG ended up being one of NASA’s most important contributions to modern society, enabling highly accurate GPS navigation anywhere on the planet. Once NASA demonstrated real-time tracking on a global scale with realtime data processing, it represented a breakthrough capability. By 2000, John Deere had just introduced its StarFire GPS receiver, which was capable of accuracy down to about six inches.

A long partnership with JPL helped John Deere spread self-driving tractor capabilities all over the world, lowering costs and improving yields for farmers while popularizing the idea of precision agriculture.

In 2001, NavCom licensed the RTG software, and contracted with JPL to receive data from the center’s global network of reference stations. While it was testing the system in the field, the company continued to work on its own technology for correcting GPS signals, and released its first GPS-based guidance system for tractors in 2002. The system, known as AutoTrac, was initially available only in North America and Australia, with Europe following shortly thereafter. By the following year, John Deere had begun developing a highly accurate self-guidance system based on a technique known as real-time kinematics (RTK).

While it was accurate down to about an inch, the RTK-based navigation system wasn’t entirely reliable, as its radio signal could go down or be lost behind a hill. It also was expensive and required the purchase of one or more signal towers. By 2004, the company released the first StarFire receivers to tap into NASA’s global network of ground stations and incorporate JPL’s software, which it licensed. The system was accurate down to four inches, which was a significant improvement to AutoTrac. More importantly, with this solution, John Deere could finally offer self-driving agricultural equipment to its customers worldwide.

Typically, when a farmer crisscrosses a field pulling a seeder, plow, or other equipment behind the tractor, the rows that are created overlap by about 10 percent. This means a significant portion of the field receives double the necessary seed, fertilizer, and pesticide, and the job also takes longer than necessary. Eliminating overlap cuts down on fuel costs, wear and tear on the machinery, and the time for which a farm had to pay a tractor operator.

The second-generation StarFire GPS receiver enabled the iTEC-Pro capability, which allowed a tractor to finish a row, lift the equipment it was pulling, turn around, and pick up exactly where it left off, all with no input from the driver.

By 2015, 60–70 percent of the crop acreage in North America was being farmed using self-guidance systems, as was 30–50 percent of the farmland in Europe and South America, and more than 90 percent of Australian farmland.

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