The Juno spacecraft, which was launched by NASA in 2011 to explore the gas giant planet Jupiter, has encountered some technical problems on its' swing by Earth in order to gain momentum for the long trip to the outer planet, but scientists are hopeful that the problem can be fixed and the spacecraft continue on its' mission.
Despite the snag, the team of engineers said Wednesday that Juno was on track to arrive at the giant gas planet in 2016.
"We did not plan for this," said project manager Rick Nybakken of the NASA Jet Propulsion Laboratory, which manages the $1.1 billion mission. He also added, however, that he was hopeful that the problem could be fixed.
After the Earth rendezvous, engineers noticed that Juno returned little data, a sign that something was wrong. NASA later learned that Juno had entered safe mode, a state that spacecraft are programmed to go into when they sense there's a problem.
Up until Wednesday when Juno whipped around Earth in a momentum-gathering flyby, the spacecraft had been in excellent health. While in safe mode, it can communicate with ground controllers, but its activities are limited.
Previous missions to the outer solar system have used Earth as a gravity slingshot since there's no rocket powerful enough to make a direct flight. The Galileo spacecraft buzzed by Earth twice in the 1990s en route to Jupiter, the solar system's largest planet located 484 million miles from the sun.
Launched in 2011, Juno flew beyond the orbit of Mars, Earth's closest planetary neighbor, before looping back toward our home planet for a quick visit. Wednesday's rendezvous increased Juno's speed from 78,000 mph relative to the sun to 87,000 mph — enough momentum to cruise past the asteroid belt to Jupiter, where it should arrive in 2016.
During the swing past Earth, Juno snapped pictures of our home planet and the moon. The solar-powered, windmill-shaped spacecraft slipped into Earth's shadow as planned, but engineers were puzzled when it emerged. At closest approach, it hurtled 350 miles above the ocean off the coast of South Africa.
One of the interesting differences between Juno and other spacecraft that have explored the outer reaches of the solar system, such as Galileo and the New Horizons spacecraft slated to arrive at the dwarf planet Pluto, also in 2016, is that it is powered by solar energy, rather than nuclear power as the other spacecraft were. This means that Juno depends on panels of solar cells for it's power, rather than a nuclear reactor. These panels each have to be the size of a small bus, because the sun's light is far weaker near Jupiter than it is near Earth. Some people had expressed concerns about the other spacecraft that had performed flybys, such as Galileo, that in the event of an accident , there could have been a release of harmful radiation, but since Juno is powered by solar energy, even if it had hit Earth, there would have been no cause for concern.
Juno promises to inch closer to Jupiter than any previous spacecraft, orbiting the planet for at least a year and studying its cloud-covered atmosphere and mysterious interior to better understand how the giant planet formed.