NASA’s Juno spacecraft arrives at Jupiter!

From Sky to Space


Flashback to July 14, 2015, when NASA’s New Horizons spacecraft performs historic Pluto flyby after a nine-year voyage in the dark and cold territory of outer space. Then fast forward to July 4, 2016 when NASA’s Juno spacecraft enters gas giant Jupiter’s orbit after a five-year trip in the solar system’s neighbourhood. These sort of galactic milestones are years in the making.

But unlike its colleague New Horizons, Juno wasn’t the first space probe to successfully reach and explore mighty Jupiter.

Both Pioneer spacecrafts flew past the gas giant in 1973 and 1974 as well as Voyager 1 and Voyager 2 in 1979, as did New Horizons when it used a gravity assist from the planet in 2007, en route to Pluto. By borrowing Jupiter’s gravity, New Horizons increased its speed by 23 km/s (83,000 km/h), which in turn shaved three years of travel time off the spacecrafts’ trip to Pluto.

But don’t think that Jupiter’s quasi routine to welcome visitors undermines the importance or scientific value of Juno’s mission. Being the second spacecraft ever to enter Jupiter’s orbit, – the first one being Galileo, which navigated around Jupiter’s surroundings from 1995 to 2003 – there will be plenty of untapped data for it gather and a significant study to maintain.

Launched on August 5, 2011, from an Atlas V rocket at the Cape, Juno inherited a seemingly particular flight trajectory to get to the fifth planet from the Sun. 


In October 2013, two years after takeoff, Juno travelled back to mother Earth for agravity assist, increasing speed by 3.9 km/s (more than 14,000 km/h). The Earth-flyby was also a good opportunity for the maintenance teams on the ground to test some of Juno’s systems before the do-or-die manoeuvres of Jovian orbital insertion.

And then came the American Independence Day of 2016. As I tweeted that day, were I American, I would have had trouble prioritizing between celebrating my country’s birthday and Juno’s entrance into Jupiter’s orbit (which happened that day at 11:53 p.m. ET). But again, as my tweet said, Independence Day happens every year.  

To get into orbit, Juno needed to slow down – a lot. That’s why it fired its thrusters for more than 35 minutes. Thirty-five minutes is a very long time for a spacecraft to  burn; the ground teams where getting increasingly excited as they waited to know whether the burn worked or not – and they needed to wait a relatively long time, because a signal from Juno to Earth, traveling at the speed of light, takes 48 minutes to complete. A 20-minute burn would have been enough to get the spacecraft into orbit, but not into the correct one, hence the additional 15-minute burn. In total, the slow-down burn lasted 2,102 seconds and was only one second off the predicted value, which is too small to have a disturbing effect on anything.

And that’s how you get a spacecraft into Jupiter’s orbit!

There’s something a bit special about Juno’s systems. As an interplanetary probe, it needs a stable source of power to be able to function in the arid and unfriendly conditions of space. Normally, a spacecraft of that kind uses nuclear power to maintain its instruments and to keep warm.

But Juno is not like that. It uses the old school, but still effective method of solar power, which is normally never used for interplanetary missions but just for Earth-orbiting satellites or similar spacecrafts.

Using its three 10-meter long solar panels, for a huge total of 18,000 solar cells, it can produce the 405 watts needed for keeping the instruments and avionics working. Mind you, 405 watts is not a lot of power; not even enough to run your hair dryer.

This is why, once in stable Jovian orbit, Juno’s number one task was to turn and face the sun to recharge its 750-pound solar arrays. Then Juno had to turn its antenna towards Earth before it was able to send new data home.

Juno is equipped with fantastic systems, notably the JunoCam. However, the JunoCam is not considered a scientific instrument; it’s more for the public. As a high-resolution, visible-light and colour camera, it is considered to be Juno’s eyes. It provides the public with the opportunity to see the work that Juno is doing.


The first image of Jupiter from Juno in orbit took by the JunoCam and sent to Earth on July 12.

But Juno’s mission, which will start for real on October 19, isn’t just space photography. On October 19, Juno will use an engine burn to pass from the 54-day orbit it is currently in, to a shorter 14-day orbit. That’s when the real science will begin.

By recording data from Jupiter’s internal composition, Juno will help scientists answer critical and lasting questions about the gas giant, such as: “Does it have a rocky core?”, or “how does it have so much water?”, and even, “how was Jupiter formed?”.

Because Jupiter plays a major role in the gravitational features of our solar system, this data could literally be a critical key to answering the broader existential question (at least, for me): “How was the solar system formed?”

This is awe-inspiring! We humans often look at the sky and wonder how it all happened. But wondering isn’t enough to get real and rigorous answers. So what do we do? We build probes, launch them on a rocket, and send them into space to do the science for us. And not only that, but we also build it to takes pictures of what we used to see as only a little point of light in the night sky. Maybe all this could make a person feel smaller. But for me it has the opposite affect – it makes me feel bigger. We are actually able to build something, and to make it take pictures – which I remind you was completely impossible to even do on Earth a couple decades ago – of something nearly 900 million km from home! How can someone not be inspired, or at least impressed by that?

It’s also worth remembering that our big brother planet, the mighty Jupiter, is constantly protecting us from asteroids that would otherwise wipe Earth out. Personally, I think understanding more about Jupiter is a good way to show thanks for that.