Cassini ready for fa­tal ren­dezvous with Saturn

Waikato Times - - WORLD -

UNITED STATES: The course has been set. The end is in sight. There’s no turn­ing back now. Af­ter 13 years of mak­ing daz­zling dis­cov­er­ies in the Saturn sys­tem, Cassini’s time is just about up.

To­mor­row, the Nasa space probe will dive into Saturn at 112,000kmh. Within min­utes, it will va­por­ise in the cloud tops of the ringed planet af­ter valiantly fight­ing a bat­tle it has no hope of win­ning.

Cassini’s small thrusters, de­signed to ma­noeu­vre the twotonne space­craft around the vac­uum of space, will be no match for Saturn’s thicker-than-ex­pected at­mos­phere. Within min­utes of div­ing into the planet’s up­per lay­ers, the in­stru­ments that re­vealed the great hy­dro­car­bon seas on Ti­tan and the plumes of wa­ter ice shoot­ing off Ence­ladus will be torn apart and melted.

Af­ter a small flash of light in the Satur­nian sky, the space­craft will be gone.

‘‘There’s no doubt about it, we’ll be sad at the loss of such an in­cred­i­ble ma­chine,’’ said Earl Maize, pro­gramme man­ager for the Cassini mis­sion at the Jet Propul­sion Lab­o­ra­tory in La Canada Flin­tridge, Cal­i­for­nia. ‘‘But we have a great sense of pride in what the mis­sion ac­com­plished.

‘‘We left the world in­formed, but still won­der­ing. I couldn’t ask for more.’’

Cassini’s fate was sealed on Tues­day, when it made its fi­nal flyby past Ti­tan, Saturn’s largest moon.

‘‘That slowed it down just enough so that what is go­ing to hap­pen on Fri­day is ab­so­lutely in­evitable,’’ Maize said. ‘‘It got the ve­loc­ity change it needed, and now it’s on its way into Saturn.’’

The space­craft’s fi­nal mo­ments have been sched­uled down to the minute. It will be­gin a five-minute roll that will point its Ion Neu­tral Mass Spec­trom­e­ter to­wards the di­rec­tion of flight, al­low­ing the in­stru­ment to gather as much data as pos­si­ble about the chem­i­cal makeup of Saturn’s at­mos­phere in its fi­nal sec­onds.

At the same time, the space­craft will re­con­fig­ure its sys­tems to al­low real-time data trans­mis­sion back to Earth. One minute later, its high-gain an­tenna will point away Earth, and the sig­nal from the space­craft will be gone for good. It will take an ad­di­tional 84 min­utes for the ra­dio si­lence to reach Earth.

‘‘We won’t watch it burn up,’’ Maize said. ‘‘We’ll watch it turn away from us.’’

Even in this fi­nal jour­ney, Cassini has crit­i­cal sci­ence du­ties to per­form. The sui­cide dive has the ad­van­tage of tak­ing the space­craft’s in­stru­ments deeper into Saturn’s sky than they have ever been be­fore. Hunter Waite, di­rec­tor of mass spec­trom­e­try at the South­west Re­search In­sti­tute in San An­to­nio, Texas, and his team will also in­ves­ti­gate the phe­nom­e­non of ‘‘ring rain’’, when wa­ter vapour and ice grains from the rings de­scend into the gas gi­ant’s at­mos­phere.

Al­though most of Cassini’s in­stru­ments are still func­tion­ing flaw­lessly, its fuel tank is empty.

Mis­sion plan­ners de­cided that va­por­is­ing the space­craft in Saturn’s at­mos­phere was the best way to keep it from ac­ci­den­tally con­tam­i­nat­ing the moons Ence­ladus and Ti­tan, two of the so­lar sys­tem’s most promis­ing can­di­dates for host­ing ex­trater­res­trial life.

‘‘Be­cause of the im­por­tance of Ence­ladus that Cassini has shown us, and of Ti­tan, we had to make de­ci­sions on how to dis­pose of the space­craft,’’ said Jim Green, Nasa’s di­rec­tor of plan­e­tary sci­ence. ‘‘We must pro­tect those bod­ies for fu­ture ex­plo­ration.’’

- LA Times


An artist’s ren­di­tion of what Cassini’s last mo­ments above Saturn will look like. The space probe will go out in a blaze of glory af­ter 13 years ex­plor­ing the ringed planet and its moons.

Cassini has made a se­ries of dives be­tween Saturn and its rings since April to gather more data be­fore its fi­nal plunge into the planet’s at­mos­phere.

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