The penultimate satellite in the current generation of Global Positioning System spacecraft was airborne this morning, jetting from its Lockheed Martin factory in Pennsylvania to the Florida launch site.

Boxed in a protective shipping container, the GPS 2R-20 satellite was flown to Cape Canaveral on an Air Force C-17 transport aircraft to begin preparations for this summer's trip into space.

File image of a GPS satellite arriving at the Cape. Credit: Air Force

Although 2R-20 will be the next-to-last spacecraft in the GPS Block 2R satellite series to launch, it was the final one to leave the manufacturing plant. That's because workers spent the past year installing a special demonstration payload for transmitting an additional civilian navigation signal.

Lockheed Martin hosted a ceremony at the factory on Tuesday with the Air Force and other organizations as the craft was readied for shipment, concluding nearly 15 years of satellite construction work on the program.

"It was a bittersweet situation," Dave Podlesney, the GPS programs director at Lockheed Martin, said in an interview. "Yeah, there's sadness, but there's also a sense of pride in being able to accomplish something of this nature."

Development of the Block 2R series began nearly two decades ago, aimed at replenishing the orbiting GPS satellite constellation as the older Block 2 and 2A spacecraft surpassed their useful life-spans.

Production of the new satellites began in earnest by 1994, Podlesney recalls, and the first craft, known as GPS 2R-1, was headed skyward in January 1997. But the satellite was lost soon after liftoff when its rocket exploded during launch.

The 2R-2 launch a few months later went smoothly, beginning a string of successful deployments that has continued through 2R-19 that ascended to orbit just last month. All 18 in space today remain operational, broadcasting navigation signals that allow users to find their position in latitude, longitude and altitude and determine time.

"The vehicles on-orbit are not only producing the navigational signals and performing well, but the number of problems are at a minimum," Podlesney said.

The newest satellite began operations a record-setting 9 days after launch.

"I hate to say it, sometimes we don't appreciate each time we place these vehicles into the constellation it almost goes like clockwork," Podlesney said.

With today's delivery to the Cape, the 2R-20 satellite joins the 2R-21 craft already stored at the Florida spaceport. Current schedules call for 2R-20 to launch on June 30, followed by 2R-21 on Sept. 11.

A three-month launch campaign is planned for the 2R-20 mission. Once unpacked in the cleanroom facility, the satellite will undergo system checks, its batteries and orbit-circularizing kick motor installed, hydrazine maneuvering propellant loaded aboard and spin testing performed to ensure the craft will be balanced while rotating at 55-rpm during the late stages of the launch sequence.

Meanwhile, assembly of Delta 2 rocket will be underway at the Complex 17 pad. United Launch Alliance workers will erect the first stage, connect nine solid rocket boosters and attach the second stage.

The solid-propellant booster that serves as the Delta 2 rocket's third stage will be brought to the satellite processing site for attachment. The combined booster and satellite then travel to the launch pad for hoisting atop the rest of the Delta in mid-June.

The final two Block 2R satellite launches also mark the last Air Force missions using Delta 2 rockets.