The Final Countdown: Dr. Jared Espley on Juno’s Epic Journey to Jupiter
published during a waning crescent moon.

Dr. Jared Espley

This illustration depicts NASA’s Juno spacecraft approaching Jupiter. Credits: NASA/JPL-Caltech

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–a mission that 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, must be a long time coming. The launch was in 2011, but I imagine you were working on this project well before then.

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.

NASA is sending the Juno spacecraft to Jupiter, to peer beneath its cloudy surface and explore the giant planet’s structure and magnetic field. Juno’s twin magnetometers, built at Goddard Space Flight Center, will give scientists their first look within Jupiter at the powerful dynamo that drives its magnetic field. Credit: NASA

HD: What was Juno’s journey like since it launched?

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.


When NASA’s Juno spacecraft flew past Earth on Oct. 9, 2013, it received a boost in speed of more than 7.3 kilometer per second, which set it on course for a July 4, 2016, rendezvous with Jupiter. Credit: NASA/JPL

HD: What will Juno do when it approaches Jupiter?

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: Everyone I talk to wants to know: was the July 4th date for the Jupiter orbit insertion really planned? It seems impossible!

JE: I ask that question as well! We’ve all asked that. And it does seem impossible, I agree. But the mission navigators genuinely claim that it 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.

Dr. Jared Espley

Credit: NASA’s Goddard Space Flight Center

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 end.

Juno Vault – Radiation Ricochet Credit: NASA/JPL

 Dr. Jared Espley

Setting up Juno’s Radiation Vault. Credit: NASA/JPL

HD: That said, JPL has a reputation for building spacecraft that outlive their intended lifetimes. Do you think Juno will last longer than a year?

JE: That’s true. The engineers work really hard to meet their requirements, and if they can they build in a little extra margin on the time. So it’s almost inevitable that if everything goes well, things could last longer. We would definitely be interested in extending the mission if it’s a possibility.

HD: When it comes to spacecraft, a fan favorite seems to be Cassini because of the amazing imagery it took of Saturn. Can we expect that kind of imagery of Jupiter?

JE: Yes, we can expect some really spectacular photos. The camera isn’t technically a science instrument, but it has a cool feature built in—we’re going to open its photos up to the public. So the public will be able to decide which images it should take of Jupiter. Obviously, one of the features it’ll photograph is the Great Red Spot, the poles, but maybe there will be other interesting things we’ll see in the clouds that the public will want to look at.

Dr. Jared Espley

This trio of Junocam views of Earth was taken during Juno’s close flyby on October 9, 2013. Credit: NASA/JPL-Caltech/MSSS

HD: What has the mission accomplished so far?

JE: Juno has already taken some photographs of Jupiter and its moons. The imagery that we’re getting is just slightly above that ecliptic plane, which is the plane in which the planet orbits the sun, giving us a top-down view of Jupiter.

Dr. Jared Espley

As Juno makes its initial approach, the giant planet’s four largest moons — Io, Europa, Ganymede and Callisto — are visible, and the alternating light and dark bands of the planet’s clouds are just beginning to come into view. Credit: JPL

The other thing I’m personally really excited about is that we’re just starting to get the first hint of our entrance into the domain of Jupiter, its magnetosphere. Some of the data is straightforward, looking like we’ve definitely crossed the domain, but some of the data is confusing, which is confusing but also really cool because as a scientist you want stuff to be confusing!

This chart presents data that the Waves investigation on NASA’s Juno spacecraft recorded as the spacecraft entered Jupiter’s magnetosphere on June 25, 2016, while approaching Jupiter. Audio accompanies the animation, with volume and pitch correlated to the amplitude and frequency of the recorded waves. Credit: JPL

More information on the Juno mission is available at:

Follow the mission on Facebook and Twitter at:

Watch the live stream on NASA TV, or on Ustream, which will have a live moderated chat. The live stream is embedded below. The broadcast will begin on Monday at 10:30pm EDT/7:30pm PDT.