Juno Jumps the Shadow to Avoid Mission Failure

Juno Jumps the Shadow to Avoid Mission Failure
Juno Jumps the Shadow to Avoid Mission Failure
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NASA’s Juno mission to study Jupiter up close has been underway since 2011. The spacecraft reached Jupiter in 2016, at which point it took up an orbit around the planet and commenced data-gathering.

Jupiter is framed by radiation belts. This requires Juno to dip below the radiation on each orbit. But after prolonged exposure, and even with the titanium “vaults” protecting them, Juno’s instruments will eventually go dark because of this radiation and its mission will end.

That’s not the only hazard Juno faces. The craft is solar-powered, which means its batteries only have around a 12-hour lifespan before the craft depletes its energy reserves and loses control.

Juno’s creators hadn’t planned on the darkness of a Jupiter eclipse potentially ending the Juno mission early. So how’d they get around the problem?

A Mission in Peril
More specifically, NASA’s problem was this:

  • Due to a problem with Juno’s main propulsion system, what started as a planned 14-day orbital period had become a 53-day orbital period instead.
  • On November 3, the longer orbit would have caused Juno to pass through the intense darkness of Jupiter’s shadow.
  • Juno would have spent more than 12 hours in darkness, which would have depleted the craft’s batteries and heating equipment, leaving it derelict in the cold of space.
  • NASA needed a creative solution to ensure Juno didn’t spend those 12 mission-ending hours in darkness.

Juno had essentially been stranded in its 53-day orbital period. This wasn’t accounted for in the mission planning, and it greatly extended the time required for Juno to complete its dozens of planned flybys.

Now, without enough time for the mission to come to its intended conclusion, NASA scientists had an unexpected emergency on their hands that took some out-of-the-box (and record-breaking) maneuvering to solve.

A Way to ‘Jump’ Jupiter’s Shadow
To save Juno, scientists at NASA’s Jet Propulsion Laboratory set out to conduct what they called an “unprecedented” engine burn. The idea was radical but also quite simple: Juno needed an unplanned push to keep its solar panels within view of the sun.

Starting on September 30 and ending on October 1, Juno performed a 10.5-hour burn of its maneuvering thrusters to “jump” Jupiter’s shadow — or, rather, to adjust its speed and direction just enough that the sun stayed in view. It worked.

Scott Bolton, the principal investigator attached to the Juno project, said this: “Jumping over the shadow was an amazingly creative solution to what seemed like a fatal geometry. Now, instead of worrying about freezing to death, I am looking forward to the next science discovery that Jupiter has in store for Juno.”

A Reprieve and Unfinished Business
Using reaction-control thrusters for this length of time is unusual. In fact, NASA indicated that this maneuver was five times as long as the previous longest-lasting use of the reaction-control system. The maneuver depleted some 160 pounds of fuel, but Juno is on-track to circumvent Jupiter’s shadow as planned on November 3.

Until this near-death experience, Juno had spent just 10 minutes in darkness in the entire course of its journey – within earth’s own shadow as the craft performed an early flyby.

Darkness of the kind that Juno would have encountered in Jupiter’s shadow isn’t usually enough to finish off a craft like this, either. Previous missions have used radioisotope thermoelectric generators, whereas Juno is the farthest-venturing mission from our sun so far that has relied on solar power the entire way.

Juno isn’t the first craft to orbit Jupiter — that honor belongs to the Galileo mission which ran from 1995 to 2003 — and there is definitely unfinished business there. NASA maintains an online gallery of raw photographs from the mission called “JunoCam.”

Some of the highlights of Juno’s trip so far include imaging the moon Io, which we now know is one of the most volcanically active places we’ve discovered in the solar system, as well as several passes over Jupiter’s iconic Great Red Spot. Juno confirmed that the Spot is 1.5 times wider across than earth’s diameter and that it extends 200 miles into the planet’s atmosphere.

We’ve always known that Juno has a finite lifespan. As mentioned, the radiation surrounding Jupiter means all of the sensitive equipment aboard the craft will eventually fail. The conditions in outer space present challenges we don’t always expect.

Juno is expected to last until the anticipated July 2021 conclusion of its journey. At that point, the craft will have relayed its last data packets and photographs and will descend into Jupiter’s atmosphere at last for a quiet but dignified disintegration.

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