One of NASA’s most successful spacecraft to date, Cassini, is slated to make its fateful plunge into Saturn’s atmosphere today, ending its 13 year tour of the Saturn system and countless historic scientific discoveries.
Cassini began making weekly dives toward Saturn’s atmosphere in April, collecting never before seen data on Saturn’s ring system and atmosphere as it traveled between the planet and its rings on 22 approaches – something no man-made craft has ever done before. This week, however, Cassini will execute its final plunge toward Saturn, this time, with no intention of surfacing again.
According to NASA’s calculations, contact will be permanently severed with the spacecraft at approximately 7:55 a.m. EST, approximately one minute after it enters Saturn’s atmosphere, which begins at an altitude of 1,190 miles about the planet’s estimated cloud tops. Saturn, as a gas giant, does not have a surface to speak of. As Cassini plunges into Saturn’s cloudy exterior, it will reach speeds approaching 70,000 miles per hour, and ultimately be destroyed by the combination of heat and pressure applied to it by the giant planet as it plummets.
The spacecraft will use its thrusters as it falls, to try to angle itself to keep its radio antennae dialed in on Earth-based receivers, so scientists and researchers can glean as much as possible from the craft’s final moments before its systems suffer too much damage to continue transmitting. If the antennae shifts any more than a few degrees away from Earth as it falls, communications will cease immediately, so NASA’s team intends to ramp the craft’s thrusters from 10% to 100% capacity within less than a minute, in order to try to maintain pitch control as it truly heads where no man, or man-made object, has gone before.
“The spacecraft’s final signal will be like an echo. It will radiate across the solar system for nearly an hour and a half after Cassini itself has gone,” said Earl Maize, Cassini project manager at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “Even though we’ll know that, at Saturn, Cassini has already met its fate, its mission isn’t truly over for us on Earth as long as we’re still receiving its signal.”
Cassini first took to the skies on October 15th, 1997, when it began its nearly seven-year voyage to our solar system’s ringed giant, Saturn. The spacecraft covered some 2.2 billion miles along the way, collecting data on Venus, the sun, and Jupiter along the way. It first arrived at its final destination on July 1st, 2001, where it began studying the planet itself, but possibly even more importantly, its system of moons.
“I remember very clearly we were in the mission operation room, and we were coming close, you know, to fire the engine, and here we have an engine which we have fired only once over seven years, and it had to work,” Charles Elachi, the former JPL director recalled. “You can imagine the tension that was in the room, in the mission operation room when we were waiting to get the signal that the engine had fired.”
Throughout the following years, Cassini would achieve unprecedented successes, including the launch of mankind’s furthest reaching lander ever, when it deployed a small lander built by the European Space Agency called Huygens which successfully touched down on Saturn’s moon Titan. Soon thereafter, another of Saturn’s moons, Enceladus, became Cassini’s focus, as it snapped photographs of massive geysers of water vapor, ice, and other particles erupting from its surface and shooting thousands of miles into space.
“You have water shooting out of that planet [Enceladus] up to literally tens of thousands of feet,” said Elachi. “So just imagine you are standing at Yellowstone and you see a geyser which goes all the way up to where a jet airline is flying.”
Those geysers led to the discovery of hydrothermal vents beneath the icy surface of Enceladus in April of this year, indicating that the ingredients for life may well exist in the massive water ocean beneath the moon’s frozen exterior. Ironically, it was discoveries like this that ultimately led NASA to choose to doom Cassini to plummet into Saturn’s atmosphere, rather than continue to operate it until it ran out of power. If they had chosen to run Cassini until it died and went adrift, it could potentially crash into a moon like Enceladus, potentially exposing it to Earth-borne material that could affect future scientific discoveries.
NASA will be broadcasting live mission commentary and video from the Jet Propulsion Lab’s Mission Control as Cassini makes its final plunge into Saturn on Friday morning. The stream will be on NASA TV, as well as the agency’s website starting at 7:00 a.m. EST.
“Yeah, it’s going to come to an end,” said Elachi. “But cheer up, this has accomplished amazing things, this mission, and it will probably be in the history books for centuries.”
Images courtesy of NASA