By Mary O’KEEFE

“The fact that the mission is ending is bittersweet,” said Joan Stupik, a guidance and control engineer. 

Stupik has been at Jet Propulsion Laboratory for four years and started on Cassini on day one. 

“I was welcomed into the fold of the Cassini family,” she added.

Cassini is minutes away from the Grand Finale, when it ends its 20 years in space with a dive into Saturn’s atmosphere.  For 13 of those years Cassini has toured Saturn, its rings and moons. 

“…In particular Enceladus, with its subsurface ocean and signs of hydrothermal activity – remain pristine for future exploration. The spacecraft’s fateful dive is the final beat in the mission’s Grand Finale, 22 weekly dives, which began in late April, through the gap between Saturn and its rings. No spacecraft has ever ventured so close to the planet before,” according to a JPL/NASA statement. 

The end will be as dramatic as its exploration. At 4:55 a.m.(PDT) Cassini will lose contact with Earth — with those scientists and engineers that have been communicating with the spacecraft as part of their daily routine. 

“For four years [I have been] checking the health of Cassini every day,” Stupik said. 

Cassini, which began as Cassini-Huygens, launched on Oct. 15, 1997 from Cape Canaveral Air Force Station in Florida. It flew by Venus on April 26, 1998 and Earth flybys on Aug. 18, 1999 then again on Dec. 30, 2000. 

On Jan. 14, 2005 the Huygens probe descended into Saturn’s moon Titan. 

Cassini’s primary mission was four years, but like most NASA/JPL missions it has gone far beyond that primary date. 

“Beginning in 2010, Cassini began a seven-year mission extension in which it completed many moon flybys while observing seasonal changes on Saturn and Titan. The plan for this phase of the mission was to expend all of the spacecraft’s propellant while exploring Saturn, ending with a plunge into the planet’s atmosphere. In April 2017, Cassini was placed on an impact course that unfolded over five months of daring dives—a series of 22 orbits that each pass between the planet and its rings. Called the Grand Finale, this final phase of the mission has brought unparalleled observations of the planet and its rings from closer than ever before. A final close flyby of the moon Titan on April 22 used the moon’s gravity to reshape Cassini’s trajectory so that the spacecraft leapt over the planet’s icy rings to pass between the rings and Saturn,” stated NASA/JPL. 

Stupik said it was exciting and the best way to end the mission. There is an international treaty in place to protect locations in the solar system which could be habitable for life. To ensure the protection of Saturn’s moons, the decision was made to plunge Cassini into the atmosphere of Saturn to burn up.

Stupik said from an engineering standpoint, Cassini was a good spacecraft.

“It was one of the most well behaved spacecraft,” she said.

Normally when a spacecraft has issues, it is designed to shut down and then, in a way, reboot and continue on. This only happened to Cassini six times in the 20 years in space, she said. 

This is going to be a dramatic end to an amazing mission.

“During 22 such passes over about five months, the spacecraft’s altitude above Saturn’s clouds varied from about 1,000 to 2,500 miles (1,600 to 4,000 kilometers), thanks to occasional distant passes by Titan that shifted the closest approach distance. At times, Cassini skirts the very inner edge of the rings; at other times, it skimmed the outer edges of the atmosphere. During its final five orbits, its orbit passes through Saturn’s uppermost atmosphere, before finally plunging directly into the planet today,” NASA/JPL stated. “Soon after, Cassini will burn up and disintegrate like a meteor.”

“I will say the past several months of Grand Finale [has brought everything] to a new level of excitement,” Stupik said.