The final countdown: Dr. Jared Espley on Juno’s epic journey to Jupiter

July 1, 2016

On August 5th, 2011, the Juno spacecraft launched aboard a United Launch Alliance Atlas V-551 rocket and began its incredible five-year-long journey to Jupiter. Now, the spacecraft is just a few days shy of entering orbit around the gas giant, where it will commence its year-long mission. This mission will achieve a staggering series of firsts, such as becoming the first solar-powered spacecraft at Jupiter, the first space mission to orbit an outer planet from pole to pole, and the first space mission to skim within 5,000 kilometers of Jupiter’s stormy cloud tops every 14 days. This groundbreaking mission will yield new insights into the origin and evolution of our solar systems’ largest planet.

NOW.SPACE editor Heather D’Angelo recently caught up with Dr. Jared Espley, Juno program scientist for NASA, to get the details about the mission and his take on this historic day for space exploration.

Heather D’Angelo: This is a really big day—one that, for you, has been a long time coming.

Jared Espley: It’s true! Before I was a program scientist, I worked on one of the instrument teams on the magnetometer—the instrument that measures the magnetic field. We were working on calibrating that instrument as early as 2007, and obviously, the mission has been in development since 2004—so it’s been a decade of my life. And that is one of the spectacular things, but also terrifying things, about working in planetary science versus any other aspect of space science. These missions just take so long to develop. So much of your professional life is invested in a mission; you really want it to succeed.

HD: What has Juno’s journey been like since it launched in 2011?

JE: After the launch, Juno flew into interplanetary space towards Jupiter. We went past Mars but then went back again in 2013, flew by Earth to pick up a gravity assist to give us extra speed to get to Jupiter, and we’ve been traveling in interplanetary space between Earth and Jupiter ever since. So that’s approximately five years of cruise since the launch.

HD: What will Juno do when it approaches Jupiter?

JE: Juno’s main engine burn will be at 8:18 PT on July 4th. When that happens, the spacecraft will go into a highly elliptical orbit, 53.5 days in length—a tremendous amount of time for Juno to come back around. That big orbit was purposefully designed to give us the chance to make sure everything is working in Jupiter’s extreme environment before going back around again for another 53.5-day orbit. If everything looks good, the engines will be fired again, and then in October—about 107 days from July 4th—we’ll settle into the science orbits, which are 14 days in length. That’s still a pretty big orbit, but it’ll be considerably closer.

HD: Was the July 4th date for the Jupiter orbit insertion planned?

JE: The mission navigators genuinely claim that the July 4th date was on purpose. They had originally targeted a slightly different day back in the early design phases, but then between the timing of the launch and the availability of the Deep Space Network to provide 100% coverage of the mission, it was unavoidable that it had to be July 4th. At least, that’s what they say.

HD: What are some of the biggest challenges ahead?

JE: Between now and the 4th, there aren’t really any specific things for the team to do. Before July 4th, we’ll be uploading the final sequence to make the spacecraft a robot—it’ll be completely autonomous. All the humans here on Earth can do is hope for the robot to do its thing correctly, which is to go into orbit.

After it gets into orbit, the main thing we’re worried about is the radiation environment. It’s extremely harsh. The reason it’s so harsh is because Jupiter has an intense planetary magnetic field. This field traps particles, causing the particles to bounce back and forth, picking up more speed until they travel close to the speed of light—forming a dangerous band around the planet. The radiation is confined mainly to the equatorial region. Juno will fly in an elliptical orbit that comes in over the poles and dives straight down through the equator region as fast as we can to limit the amount of time the spacecraft is exposed to radiation.

Juno is equipped with a titanium vault that contains all the really sensitive electronic instruments—the “brains and organs” of the spacecraft—to provide extra protection from the radiation. Juno will still receive a dose of radiation that will eventually fry all the instruments. The design lifetime for Juno is approximately just over one Earth year, so sometime in February 2018, we expect the mission to come to an end.