WASHINGTON — Technicians at Lockheed Martin Space Systems of Denver began assembly April 1 of NASA’s Juno probe, a uniquely designed spacecraft that will be the first solar-powered mission to orbit Jupiter.

Scheduled to launch in August 2011 and reach Jupiter in 2016, Juno will operate in an elliptical polar orbit gathering data on the formation and composition of the largest planet in the solar system. Engineers will spend the next several months building the spacecraft platform and integrating and testing its instrument payload.

NASA plans to spend slightly more than $1 billion on the Jupiter orbiter, including the cost of the spacecraft, nine scientific instruments, launch aboard a United Launch Alliance Atlas 5 rocket and all aspects of the program from design to post-mission data analysis. The mission is being managed by NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif.

Juno principal investigator Scott Bolton said the project has remained on cost and schedule since 2006, when NASA settled on a budget and launch date. Although previous missions to the solar system’s outer planets typically have relied on nuclear generators for power, Juno’s solar powered spacecraft avoids the cost and potential delays associated with an uncertain supply of radioactive material.

“We studied the nuclear option and while it had some advantages, it was a risk because it required development,” said Bolton, who holds an appointment at the San Antonio-based Southwest Research Institute. “The risk is the reason we looked into solar power, which turned out to be feasible, but also needed some development. In the end, we decided the solar power was less risky. It might be a bit less expensive as well.”

Orbiting the gas giant more than 644 million kilometers away from the sun, Juno will be exposed to less sunlight and more radiation than any of NASA’s other solar-powered spacecraft. Radiation saps the ability of solar arrays to generate power.

To compensate, Juno is designed to carry extremely efficient solar arrays and to travel in a path that helps it avoid Jupiter’s radiation belts. In addition, Lockheed Martin has designed a titanium vault that will shield avionics for the mission’s scientific instruments in a central location inside the spacecraft.

“It’s somewhat unique to have the electronics for the instruments in one place and the sensors somewhere else,” Bolton said. “Normally they are all packaged together. So most of the [instrument avionics] are in this vault and their sensors are out on the edges looking out.”

Bolton said the sheer size of the spacecraft’s solar arrays — which have a combined area of 60 square meters and each extend 8.86 meters in length from the spacecraft — makes test and integration of Juno’s subsystems and instruments more complicated.

“It’s huge,” Bolton said of the spacecraft, the second of NASA’s medium-class New Frontiers missions. “We look very much like a flagship-class mission being disguised as a [principal investigator-led] mission, and that’s what makes it even more amazing that we’ve been able to stay on schedule and within the budget.”

Tim Gasparrini, Juno program manager at Lockheed Martin Space Systems, said the solar cells generate 12 kilowatts of power on Earth, but by the time the spacecraft reaches Jupiter, its three giant arrays will generate only 400 watts.

“It’s about a quarter of the amount you need to run the typical hairdryer,” Gasparrini said. “It’s the first solar-powered spacecraft to Jupiter, and the furthest distance from the Earth using a solar powered spacecraft.”

Bolton said over the course of Juno’s one-year mission, the energy output of the solar arrays will erode.

“Radiation that hits the solar arrays degrades them, so at the end of the mission they are pumping out a lot less than they are at the beginning,” he said.

And despite the thick titanium vault shielding Juno’s instrument avionics, those capabilities will gradually weaken as well.

“We’ll only get 31 orbits out of the spacecraft before we get to the point where we have exceeded the radiation capability of our avionics,” Gasparrini said.

Bolton said Juno’s instrument payload, which includes a color camera provided by Malin Space Science Systems of San Diego, will offer planetary scientists a “smorgasbord” of sensing and data-gathering capabilities.

To study Jupiter’s atmosphere, Juno will use a Microwave Radiometer built by JPL and the Jovian Infrared Auroral Mapper designed by the Italian Space Agency.

The Italian Space Agency also will build a high-frequency Ka-band transponder for the spacecraft.

Jupiter’s magnetic field will be studied with three instruments: a Fluxgate Magnetometer built by NASA’s Goddard Space Flight Center, Greenbelt, Md.; a Scalar Helium Magnetometer made by the Southwest Research Institute; and an Advanced Stellar Compass manufactured by the Danish Technical University in Lyngby, Denmark.

Scientists will study Jupiter’s poles with a Jovian Auroral Distribution experiment and an Ultraviolet Spectrograph designed by the Southwest Research Institute, a Jovian Energetic Particle Detector built by Johns Hopkins University in Baltimore, and a Radio and Plasma Wave Sensor made by the University of Iowa in Iowa City.

Gasparrini said Lockheed Martin engineers will spend the next few months building the spacecraft and integrating key subsystems, including telecommunications and guidance and navigation capabilities. Juno’s next major milestone is July 1, when instrument integration and test are slated to begin. Environmental testing will follow in the fall, with delivery of the spacecraft to Cape Canaveral Air Force Station, Fla., slated for April 2011.

Once on orbit, the mission will conduct a deep-space maneuver in September 2012, “and then we fly by the Earth in October of 2013, arrive at Jupiter in July of 2016, and end the mission with a de-orbit burn in October 2017,” Gasparrini said.