Click here if you are having trouble logging into the forums
Privacy Policy |
Please read our Terms
of Service | Signup and
Troubleshooting FAQ | Problems? PM a Red or a Green Gu.... uh, User
Achernar
Post Laureate
Reged: 02/25/06
Posts: 3721
Loc: Alabama, USA
|
|
I wouldn't be surprised after the two year extension is up, Cassini would still be functioning well and have enough electrical power and fuel aboard for two more years of operations. Cassini will be the last spacecraft to go to Saturn for a long time before the next mission is ready for launch, so it would make sense to do as much with the spacecraft until it expires. It would cost very little money to listen to what Cassini has to say about Saturn and it's amazing family of moons compared to developing and launching another mission, and I'm sure scientists would rather send an orbiter to Uranus or Neptune instead of another similar spacecraft to Saturn. When a follow up mission does go to Saturn, Cassini's findings will no doubt have a major hand in it's development.
Taras
--------------------
10-inch F/4.5 Discovery Dob
6-inch F/8 Homebuilt Dob
4 1/4-inch F/4 Homebuilt reflector
|
llanitedave
Humble Megalomaniac
Reged: 09/26/05
Posts: 10477
Loc: Amargosa Valley, NV, USA
|
|
Quote:
Vote Dave for Unquestioned Totalitarian Dictator!!! 
You don't vote for dictator!
llanite(Still negotiating with the Lady of the Lake)dave.
--------------------
"S.O.E." (Sauron's Other Eye) 16" Royce conical mirror: A permanent work in progress.
10" Homebuilt dob, old Coulter mirror
Next Project: The "Eye of Sauron" Observatory!
|
jupiterzkool
Pooh-Bah
Reged: 05/08/06
Posts: 1341
Loc: Pasadena, CA
|
|
Quote:
Quote:
Vote Dave for Unquestioned Totalitarian Dictator!!!
You don't vote for dictator!
llanite(Still negotiating with the Lady of the Lake)dave.
Doh!!!
--------------------
Scott G. Edgington, Planetary Scientist
Cassini-Huygens: Mission to Saturn & Titan
Yes, Asia, John Wetton Fan
|
Rick Woods
Post Laureate
Reged: 01/27/05
Posts: 4301
Loc: Inner Solar System
|
|
Quote:
Quote:
Vote Dave for Unquestioned Totalitarian Dictator!!!
You don't vote for dictator!
llanite(Still negotiating with the Lady of the Lake)dave.
Some moist bink lobbing a scimitar at you is no basis for supreme executive power! (Ni!)
--------------------
- Rick
14" LX200GPS
8" Meade 826C
|
LadyAstronomer
Bookworm
Reged: 11/15/07
Posts: 2951
Loc: Library of Congress
|
|
Quote:
Quote:
Quote:
.. There is no orbit in which we can "park" it until we are ready to use it again. -S
So if we just decided to stop making course corrections right now, the craft would end up smashing on Titan or be ejected from the system?
To "park" it, we would need to use a significant amount of the remaining fuel to ensure that it is in an orbit where nothing in the system is hit.
If we just stopped controlling it now and we were not on a Titan impacting trajectory, eventually (anywhere from years to decades to centuries), it would smash into some object in the system. Otherwise, Titan will be hit the next time around.
It would take much of the remaining fuel to eject it from the system.
-S
Even if it could be "parked" in some stable orbit for many years, space weathering, the lack of monitoring and upkeep, and a host of other innumerable factors severely diminish the odds of success.
However, let's say it could be "restarted." If so, we may not be able to glean any science. I'm no expert on Cassini's instrumentation, but I'm guessing at least some require consumables. Then there are the effects of space weathering on electronics. Even with radiation-hardened electronics, processors, etc. as well as redundancies built into these systems; the instrumentation, if it restarts, may yield nothing but noise.
The number of variables running through my head right now is overwhelming. Our resounding successes seem to give the appearance of ease in accomplishing such feats. That, and science fiction, make it seem as easy as flicking a switch and turning the systems back on. If only that were true!
--------------------
"I do not know what I may appear to the world, but to myself I seem to have been only a boy playing on the sea-shore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me." -- Sir Isaac Newton
|
matt
Vendor (Scopemania)
Reged: 07/28/03
Posts: 10022
Loc: Chaville, France
|
|
Of course. I don't mean "parking" the satellite is a goal per se. I mean once all your primary and secondary mission goals have been achieved, that there is too little to obtain from a third mission to justify funding it, instead of pulling the plug, put it in an orbit where you know it's not going to hit anything for a few years and into safe mode, and you have a craft which in case of need may be revived with hopefully a few instruments still operational; which would be better than simply turning it off.
--------------------
Matt
CI700 mount with various scopes on top.
|
llanitedave
Humble Megalomaniac
Reged: 09/26/05
Posts: 10477
Loc: Amargosa Valley, NV, USA
|
|
Quote:
Some moist bink lobbing a scimitar at you is no basis for supreme executive power! (Ni!)
Bloody Peasant! 
That said, I tend to agree with Matt. I've always questioned the logic (from within my state of naive ignorance, of course -- otherwise known as Nevada) of simply shutting down and walkling away forever from an operation that still had the potential for productive returns.
Accepting the risks that Lady Astronomer outlines, it still seems that simply leaving it in an orbit that's not immediately dangerous, and leaving the phone plugged in, would be a better long-term decision. Maybe it would die quietly. Maybe it would no longer be available if we tried to reach again.
But maybe it would. And maybe there are things we could do with it that we haven't yet thought of.
And maybe that's what's already being done anyway with old missions in general, and I'm just babbling.
--------------------
"S.O.E." (Sauron's Other Eye) 16" Royce conical mirror: A permanent work in progress.
10" Homebuilt dob, old Coulter mirror
Next Project: The "Eye of Sauron" Observatory!
|
Achernar
Post Laureate
Reged: 02/25/06
Posts: 3721
Loc: Alabama, USA
|
|
That will not work because Cassini's powered by radioisotope thermoelectric generators. They will run down no matter if the spacecraft is shut down or not. With a half life of 87 years, the Plutonium 238 powered RTG's and the radiosotope heater units will eventually be unable to power the spacecraft as well as keep the fuel tanks and electronics from freezing up. Once that happens, Cassini will die for good. It would be better to lower the perigree of Cassini's orbit by a series of short bursts at apogee so the spacecraft will strike the atmosphere and burn up. To eject the probe from the Saturnian system would require many passes at Titan to gain the velocity needed. I doubt the on-board rocket engines even if both were fired at the same time could accelerate Cassini to escape velocity.
Taras
--------------------
10-inch F/4.5 Discovery Dob
6-inch F/8 Homebuilt Dob
4 1/4-inch F/4 Homebuilt reflector
|
matt
Vendor (Scopemania)
Reged: 07/28/03
Posts: 10022
Loc: Chaville, France
|
|
Most of the fuel was used to brake the craft into Saturn orbit so escape is not an option, and probably not a goal either.
I know RTGs have a finite lifetime, but am I right to believe that a 87 half-life means that after 87 years we should have 50% of the original power output? Taking into account of course how the mechanism might degrade over time, it might be reasonable to say we should still have enough power to operate many instruments 10 years from now, no?
--------------------
Matt
CI700 mount with various scopes on top.
|
jupiterzkool
Pooh-Bah
Reged: 05/08/06
Posts: 1341
Loc: Pasadena, CA
|
|
Oh, believe me, we can escape the Saturn system with the fuel we will have on board after the first extended mission. However, very few Cassini scientists wish to do this.
We also know that we can put Cassini in an orbit where it will not impact anything within the system for 500+ years. However, we would only do this after all available fuel is spent.
While the jury is still out on what 2010 and beyond brings, we are working get the most scientific bang for the buck, fuel, and power.
-S
--------------------
Scott G. Edgington, Planetary Scientist
Cassini-Huygens: Mission to Saturn & Titan
Yes, Asia, John Wetton Fan
|
matt
Vendor (Scopemania)
Reged: 07/28/03
Posts: 10022
Loc: Chaville, France
|
|
thanks for the update Scott.
yes, I believe there is no point in trying to escape the Saturn orbit, unless there is some weird Centaur-type asteroid to see in the neighborhood.
--------------------
Matt
CI700 mount with various scopes on top.
|
|
0 registered and 2 anonymous users are browsing this forum.
Moderator: llanitedave
Print Thread
|
Forum Permissions
You cannot start new topics
You cannot reply to topics
HTML is disabled
UBBCode is enabled
|
Thread views: 525
|
|
|
|
|
|
|
Previous
Index
Next
Threaded
[Re: 
Edit
Reply
Quote
