That is exactly as he and his team planned it.
Why is the Cassini mission coming to an end?
With Cassini’s fuel running low, NASA is cleaning up after itself, leaving the Saturn system as pristine as it found it. Any spacecraft, even one launched in 1997, has unwanted microbial hitchhikers aboard. In particular, planetary scientists want to ensure that there is zero chance of the spacecraft crashing and contaminating Titan or Enceladus, two moons that could be hospitable for life, with hidden passengers from Earth.
NASA did the same thing with its Galileo orbiter in 2003, sending it plunging into the clouds of Jupiter to protect Europa, another moon where scientists think life could exist.
How will the Cassini mission conclude?
The beginning of the end was Monday, when Cassini flew close to Titan, the biggest of Saturn’s moons, for the 127th time. The flybys have provided a close-up examination of an intriguing haze-shrouded world; Cassini’s navigators on Earth have also enlisted the flybys as gravitational kicks to send it to the next target.
This last flyby was “just close enough, just the right orientation to seal Cassini’s fate,” Dr. Maize said.
The mission’s end has drawn team members, past and present, back here for a reunion, a celebration and a wake.
Some, like Robert T. Mitchell, who was the mission’s project manager from 1998 until his retirement in 2013, will be at the Jet Propulsion Laboratory, close to mission control. Others will bring friends and family to a gathering at the California Institute of Technology nearby.
Mr. Mitchell said he would probably get up at about 2:30 a.m. local time and drive from his home in Northridge to Pasadena, a half-hour trip without traffic. “And there shouldn’t be any at that time of the morning,” he said.
On the final plunge, the intake collector for an instrument to identify the constituents of the atmosphere will be pointed forward, giving scientists their deepest look so far at the gases that make up Saturn. “Essentially it’s just getting full blast of atmosphere,” Dr. Maize said.
But the data collection will be short-lived. As the drag of gas molecules starts twisting the spacecraft, eight small thrusters will fire to keep it upright. But each thruster is tiny, exerting about an eighth of a pound of force, and Cassini is about the size and mass of a 30-passenger school bus.
For the last five orbits, the spacecraft has dipped into the upper wisps of Saturn’s atmosphere, its thrusters keeping the spacecraft oriented in the right direction.
This time, Cassini will not emerge on the other side.
“What will happen is the thrusters will eventually be overpowered by the atmosphere,” Dr. Maize said.
Soon afterward, Cassini will be ripped apart.
Much of the spacecraft, made of aluminum will melt very quickly. The most resilient bits will likely be the casings around its plutonium power source — the 72 marshmallow-sized pellets are encased in iridium and graphite containers designed to withstand re-entry into Earth’s atmosphere or an explosion at launch. “Those will be the last pieces,” Dr. Maize said.
Cassini’s radio transmissions will disappear at 7:55 a.m. Eastern time, according to calculations by NASA engineers. The time of death at Saturn will actually have been one hour, 23 minutes earlier, but that is the time it takes the signals, moving at the speed of light, to travel the 1 billion miles that currently separate Saturn and Earth, picked up by radio telescopes in Australia and then sent to NASA’s Jet Propulsion Laboratory here.
Then, for the foreseeable future, there will be no new data coming from Saturn.
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