Ultimate Fate of Cassini Spacecraft

RJ Emery · Post by **RJ Emery** » Tue Sep 12, 2006 9:37 am

When the Cassini mission finally ends, what is the fate of the spacecraft?

craterchains · Post by **craterchains** » Tue Sep 12, 2006 11:02 am

Probably crash it into Saturn.

But, seventy pounds of plutonium should last quite awhile.

Norval

iamlucky13 · Post by **iamlucky13** » Tue Sep 12, 2006 9:27 pm

Craterchains may be right. The mission is planned to last 4 years, and I believe an additional six years of less active observations may be tacked on to the end.

If you remember, the Galileo probe to Jupiter back in the 90's was crashed into Jupiter. It discovered that the moon Europa had an icy surface and possibly liquid water below that could harbor life. NASA did not want to risk Galileo eventually crashing into Europa and contaminating it with bacteria from earth. If there is life there and bacteria survived in a dormant state on Galileo, that could seriously effect what is there. If there isn't, bacteria from earth could spread and be "discovered" by future missions and mistaken for native life.

Several of Saturns moons are icy. Encladeus (sp?) has been found to spew water out like geysers (actually more like volcanoes since it seems to be ice pressure acting analogously to tectonics), possibly from liquid water pockets. Titan is known to have a methane atmosphere that might support life.

However, I believe there is less concern with Cassini because it was more thoroughly sterilized before launch due to the Hguyens it carried to land on Titan. Also, Titan has a significant atmosphere that would further sterilize any fragments left over if Cassini entered it and burned up.

Cassini's radiothermal generators (RTG's) will supply useable amounts of power for something like 50-100 years. The real key is fuel. Any action Cassini takes requires at least small amounts of fuel: Turning to point its instruments, turning to radio data back to earth, changing its orbit, etc.

FYI, I found a very thorough calendar of events for the 4 year mission on the JPL website. I noticed there was an orbital correction engine burn on Sunday and there will be another one tomorrow.

BMAONE23 · Post by **BMAONE23** » Wed Sep 13, 2006 1:58 pm

I wonder if they could redirect it into a stable Titan orbit for the remainder?

craterchains · Post by **craterchains** » Wed Sep 13, 2006 2:38 pm

I would rather they parked it around Iapetus (sp) and do some really great mapping.

Good post there Lucky. and a good question from Emery.

Norval

RJ Emery · Post by **RJ Emery** » Wed Sep 13, 2006 4:18 pm

craterchains wrote:I would rather they parked it around Iapetus (sp) and do some really great mapping.

Good post there Lucky. and a good question from Emery.

Norval

I suspect mission investigators will weigh all the evidence gathered and determine where would be the best place to park the craft for any continuing studies after 2010. It is probably too early to make all but the most preliminary of plans.

Plunging Cassini into Saturn seems the least productive manuever in yielding any observation of scientific value. I would also argue life in some form could exist in the depths of the gaseous planets. I base that on the chemical reactions that, depsite the cold temperatures, could take place under high pressure or at a gas-liquid boundary, including the areas above and below.

orin stepanek · Post by **orin stepanek** » Wed Sep 13, 2006 5:07 pm

We worry about contamination while exploring space; and yes, we should be careful. Space itself may already be contaminated from debris ejected into space from volcanoes when they erupt. Earth itself may have been given life from spores drifting through space;or from comets when they come visiting.
Orin

iamlucky13 · Post by **iamlucky13** » Wed Sep 13, 2006 5:16 pm

That's a very good point Emery. I wondered as much about Galileo being crashed into Jupiter, but I'm sure they considered the idea, as well. We naturally tend to expect life to form in the conditions where we've seen it before. Of course, another argument that can be made is that conditions in Jupiter's and Saturn's atmospheres are so unlike earth that any biological contamination from earth would stand almost no chance of surviving. Additionally, there's the point I made previously about the spacecraft burning up during entry. Unlike some of the other candidates for life, I don't believe Europa has a dense enough atmosphere to accomplish that.

I would be willing to bet there's not enough fuel, even now, to park Cassini in a long term orbit around one of the moons. It is currently in a very large, rather elliptical orbit around Saturn that was planned out to give as many close passes by Titan and the other moons as possible over it's 4 year main mission and 74 orbits. To change it enough to be captured by one of the moons in a stable orbit would require quite a bit of energy.

Ultimately, when Cassini runs out of fuel, it becomes basically comatose. It can no longer point its instruments or its antenna. The best bet for getting further science would probably be to leave it pointed at earth so it can communicate, and wait for opportunities where items of interest to pass in front of it.

At this point, you get diminishing returns back. You may occasionally get an angle or capture an useful event like a solar transit by a moon you haven't seen yet, but discoveries could be expected to be few and far between. At the same time, NASA would still be paying a skeleton crew of mission controllers and scientists for the mission who may or may not be more productive on other missions, as well as dedicating valuable time on the busy deep space network for downloading data.

On the other hand, if you just abandon your $2 billion probe, you may genuinely miss something important. NASA considered ending the Voyager missions due to the cost and deep space network time just last year, at a time when they became the first craft to every enter the interface between the solar system and interstellar space. Fortunately, they thought better of the opportunity, recognizing that we won't have any other craft with similar capabilities that far for at least another 20 years.

Tough decision.