Juno broke the interplanetary distance record for solar-powered spacecraft on Wednesday morning. The Jupiter explorer is close to half a billion miles from the Sun, setting a new standard for using solar power for deep space exploration.
The spacecraft crossed the record-breaking 493 million miles from the Sun at 2pm ET on Wednesday. This is the farthest any solar-powered explorer has ventured into deep space, which is usually occupied solely by robots running on radioisotope thermoelectric generators (RTGs). The previous record-holder is the European Space Agency’s still-functioning Rosetta spacecraft when it first intercepted comet 67P/Churyumov-Gerasimenko in October 2012. Before that, no solar powered craft had even made it past the asteroid belts.
Now Juno is going to keep pushing the record further, out to Jupiter. Once it reaches the gas giant, the explorer will be serving as a proof of concept for a new, more efficient solar power system. At up to 517 million miles from the Sun, the spacecraft is basking in only 1/25th of the sunlight we receive on Earth. But what the panels get, they use well—Juno has a 28 percent conversion rate turning sunlight into power.
Juno’s solar power arrays are so big, they were nearly too heavy to launch in 2011. The spacecraft has three 30-foot-long solar arrays with 18,698 individual solar cells. While they’ll only generate 500 watts of power out by Jupiter, they’re big enough that they’d generate 14 kilowatts here on Earth.
Yet they’re just barely enough to keep the spacecraft fully operational at distant Jupiter. If we want to use solar power to explore planets even further away, we’re going to need better technology to make more efficient, lighter panels that can be even larger, paired with more powerful rockets.
Why pack a proof-of-concept solar power system onto an active solar system explorer? Juno’s principal investigator, Scott Bolton of the Southwest Research Institute, thinks it fits the theme:
Juno is all about pushing the edge of technology to help us learn about our origins. We use every known technique to see through Jupiter’s clouds and reveal the secrets Jupiter holds of our solar system’s early history. It just seems right that the sun is helping us learn about the origin of Jupiter and the other planets that orbit it.
Juno made a close flyby of Earth last year, and will be arriving at Jupiter on July 4 2016. During its 16 months of primary science operations, it will be skimming to within 3,100 miles of the Jovian clouds every two weeks. The objective is to learn more about how the gas giant formed, its structure, atmosphere, and magnetosphere.