PIA18347
Why NASA Will Destroy One of Their Most Beloved Spacecraft
published during a waning gibbous moon.
03/01/2016
Spacecraft

Enceladus dramatically displays the contrast between its older and newer terrain. Credit: NASA/JPL

Ending a spacecraft’s life is a delicate area of exploration, and one not often discussed. Humans have sent many spacecraft to orbit the Moon, Mercury, Jupiter and of course, Saturn but all missions have end dates—LADEE collided with the Moon on April 18, 2014, Galileo flew into the gaseous heart of Jupiter on September 21, 2003, and just last year Messenger crashed onto Mercury’s surface on April 30, 2015. And now, after almost 20 years in space, NASA’s Cassini mission to Saturn is about to come to an end. Sadly, once a mission like Cassini is over, the spacecraft can’t be left to orbit its host forever. So in 2017, Cassini will go racing directly into Saturn until it breaks apart at speeds upward of 22 miles a second.

Spacecraft

With giant Saturn hanging in the blackness and sheltering Cassini from the sun’s blinding glare, the spacecraft viewed the rings as never before, revealing previously unknown faint rings and even glimpsing its home world. Credit: NASA/JPL/Space Science Institute

One of the main reasons for disposing of a spacecraft this way is mandated by the Department of Planetary Protection. Everything we launch from Earth is dirty and covered in our microbes. Clean rooms can only stay so clean given that particularly hardy organisms show up regardless of bunny suits and chemical cleaning. Because of this, there is no way to be sure that bacteria from Earth are not still present on the spacecraft even after it’s been zapped by cosmic rays. In this case, scientists are looking out for the integrity of Saturn’s moons Enceladus and Titan. These two moons have garnered attention in the scientific community as potential harbingers of life, thus raising the red flag of planetary protection. NASA didn’t want to risk the event that Cassini would ever collide with these moons and contaminate our own search for life on those bodies; leading them to the plan of disposing it directly into Saturn. There is however, one big plus to crashing a massive scientific instrument into a planet: science.

NASA is calling the final orbiting sequence for Cassini, “The Grand Finale.” The new maneuvers will begin in April of 2017 and will send Cassini on 22 orbits through a 1,240-mile wide gap between the atmosphere of Saturn and the inner most rings.

During these final orbits, Cassini will have a once in a spacecraft-lifetime chance to gather new data that the team would otherwise never be able to safely collect.

“It’s a unique opportunity for science that we can never do if we stayed outside of the rings,” says Cassini Deputy Project Scientist, Scott Edgington.

As Cassini flies in between the rings and the atmosphere, the instruments onboard will survey the planet’s magnetic field in more detail than ever.

Edgington tells NOW.SPACE, “Orbiting that close will allow us to understand how Saturn’s magnetic field is distributed. Some think that there are currents that flow throughout the Saturn system, and the rings are a part of that current loop—so when you’re outside of the rings, you’re basically getting the magnetic field plus the effect of this current loop. So you want to be as close as possible.”

Another science objective for the Grand Finale is to understand the total mass of the main rings, which will help scientists to estimate the age of Saturn’s ring system and how long it might exist in the future. During the final orbits and last few minutes of entry, the team will use the Ion and Neutral Mass Spectrometer to gather data on the composition of Saturn’s atmosphere, and use the spacecraft’s cameras to capture some spectacular last minute close ups.

Eventually, towards the end of the 22 orbits, Cassini will get a tiny gravity kick from Titan. Three days later, on September 15, 2017 at 4am Pacific time, they expect a LOS or loss of signal from mission control at NASA’s Deep Space Network.

“I will be at the Jet Propulsion Laboratory watching that last little bit of data trickle in and hoping it lasts as long as possible because every minute that we are still transmitting to Earth is another piece of information about the atmosphere that we will never get again,” says Edgington.

Spacecraft

Enceladus plume. Credit: NASA/JPL/ Shannon Stirone

The Cassini mission has understandably ranked among the top scientific endeavors of NASA’s history. It’s given us over 11 years of incredible science, as well as some of the most iconic images of space. Edgington is pleased with what they have accomplished as a team, but has mixed feelings about the end of Cassini’s life. “It’s going to be very bittersweet, but every time I think about we’ve contributed. It’s a great legacy. I hope that what we’ve learned from Titan and Enceladus will help us to plan that next mission and go and explore those worlds.”