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Cassini's Primary Mission Ends, Two-Year Extension Begins
wooferhound points out recent news that the Cassini probe has completed its original four-year mission and is beginning a two-year extended mission, which was authorized earlier this year. Cassini's first mission brought us a treasure trove of information about Saturn and its various moons. The new mission will target two of those moons in particular for further study: Titan and Enceladus. Quoting:
"The spacecraft is extremely healthy and carries 12 instruments powered by three radioisotope thermoelectric generators. Data from Cassini's nominal and extended missions could lay the groundwork for possible future missions to Saturn, Titan or Enceladus. [The two moons] are primary targets in the two-year extended mission, dubbed the Cassini Equinox Mission. This time period also will allow for monitoring seasonal effects on Titan and Saturn, exploring new places within Saturn's magnetosphere, and observing the unique ring geometry of the Saturn equinox in August of 2009 when sunlight will pass directly through the plane of the rings."
Authorized? What exactly would NASA/whomever have talked about when they were deciding this?
Is it still working? Yes.
How well is it working? Everything seems to be responding within operational parameters.
How much does it cost to keep listening for another couple of years, while it continues exploring? We estimate it to be maybe 0.01% of the cost of sending a new probe to do the same thing.
Sir, since we are at the end of it's planned lifespan, do we have authorization to keep listening to it or shall we send it the destruct signal? I'm leaning towards self-destruct, but maybe we can get some good PR showing how reliable some of our stuff is w.r.t. those shuttle disasters, so I guess we'll keep listening.
Sleep your way to a whiter smile...date a dentist!
Its five^Wfour-year mission: to explore strange new worlds, to seek out new life and new civilizations, to boldly go where no man has gone before.
Not bad. It completed 2 of the 3 objectives.
I simply think that the fact that many of these machines we are sending into space are lasting so much longer than their intended missions is simply an incredible feat of engineering. My hats off to those engineers.
The doors opened with a hiss and I approached the towering desk. The obese
figure of Cornellius Wrak, Controller of Primus, didn't acknowledge mypresence - instead, he tapped a few words on the keyboard to his side and
gazed at the monitor. Checking my records, obviously. I was glad I'd paid that
hacker to clear my police file, or they would've made me a permanent resident
of Titan on the spot.
"What can I do for you, Mr. Jetland?" asked Wrak.
"My ship broke down," I said, "And I had to scrap her. Until I come up with
some money, I'm stuck in this pit you call a city. I heard you Controllers are
offering a shipload of credits to anyone who finds out why we've lost contact
with Proscenium. As I see it, I need the money - you need a favor."
Wrak nodded slowly, eyeing me. "We do need a few skilled agents," he said,
"but we're opening the investigation to all interested parties."
"Too bad," I said, "I hate sharing a reward."
Wraks lips curled back into something like a smile. "Whether you share a
reward or not depends upon how fast you can muster a few warm bodies and get
to Proscenium. But let me warn you, Mr. Jetland, not to take this assignment
too lightly. We don't know what dark fate has befallen Proscenium. You should
worry more about coming back alive..."
-Tom Jetland
Veramocor
Not bad. It completed 2 of the 3 objectives.
Explored strange new worlds? Check
Boldly gone where no man has gone before? Check
See out new life and civilizations? Check (If the mission was to find new life, it failed miserably. But it doesn't have to find any to complete the mission as stated.
You told me to go back to the beginning, so I have.
Weaselmancer
rediculous.
I've looked all over the Cassini web site and I can't seem to find out anything that says how much fuel is left. Not the plutonium in the RTGs (that should last another decade or so) but rather the (bi-propellant?) in the main fuel tanks or the (mono-propellant? hydrazine?) used in the thrusters.
Not only is the lack of thruster propellant typically what ends the life of otherwise useful satellites (Cassini is not spin stabilized so attitude correction is ultimately performed by the thrusters) but in addition to keeping Cassini pointed in the right direction, it REQUIRES a significant (compared to most space probes), delta-v capability. This is because it must be able to change its trajectory to take advantage of gravity assist from Titan, if it cannot precisely hit the "window" it is aiming for, it will be sent into a totally different (and unrecoverable) orbit. (Of course if it were not for the "space billiards" gravity assist maneuvers there is no way Cassini would have been able to achieve more than a tiny fraction of its current mission. This, to me is the most impressive and gratifying part of the entire mission).
These relatively large changes in delta-v are what Cassini needs its two main engines for (one's a backup). Unfortunately due to a mistake in design, Cassini had to unexpectedly use up about a third(?) of its propellant because it had to carry the Huygens probe into Saturn orbit with it (rather than releasing it on its inbound trajectory). This was because the engineers neglected to design the radio to handle the large doppler shift that would have occurred had Cassini whizzed by on its hyperbolic trajectory before the orbital insertion burn while Huygens slowly parachuted to Titan's surface. By decelerating Cassini into Saturn orbit, THEN releasing the probe they were able to receive MOST of the data transmitted (another goof lost one channel) so it saved that part of the mission but at the expense of fuel.
Now if the orbital planners have been very careful (are you reading this Sherman? ;) they may have been able to use less fuel than planned by being very accurate with their burns. So the question is: What will run out first? The main propellant used for orbital changes or the hydrazine used for attitude adjustments? (Also remember that Cassini doesn't have a separate instrument platform so every instrument pointing activity requires turning the entire spacecraft, most of this is done with reaction wheels but there is friction and sometimes the wheels must be desaturated).
Or is something else going to run out first? (Kodak film, videotape, mailing envelopes, postage stamps ;) Or am I completely wrong about this? (Perhaps they've figured out how to use Saturn's magnetic field to help stabilize the spacecraft).
I hope that after this mission extension (and the next) they'll do something really crazy like use up a ton of fuel for a really really risky low slow flyby THROUGH the rings. Imagine seeing thousands and thousands of boulder-to-mountain sized rocks in a vast plain far as the eye can see with Saturn looming in the background! Just like the paintings by Chesley Bonestell (and lots of science fiction shows like Voyager). Good science too.
I guess this beats crashing it into something to check out the big plume of debris! :-D
Build it, Drive it, Improve it! Hybridz.org
My wife dian, who was in charge of the propellants on Cassini-Huygens (and won one of NASA's highest achievement awards for that work), tells me that yes, it's hydrazine, and though she has no access to those records these days (a *very* unamicable parting of the ways), estimates that there might be a year's left, if they don't need to do too much maneuvering.
She notes that there was a *fuck* of a lot of propellant, which is why it needed a Titan IV-b, a *big* rocket.
mark
Isn't trying to study Saturn's seasonal effects over a two year period like trying to study Earth's seasonal effects during a three week visit in February?
US2B
Notice that nothing in any of the articles suggests there was debate about whether or not to approve the mission extension. The discussion probably consisted of:
"Is there any serious probability of the spacecraft dying early on in the extension? (ie - should we shorten the extension term and re-evaluate later?)"
"What will we do during the extension? (Answer: a lot)"
"Will the returns be of greater value above and beyond what Cassini has already produced than spending the money elsewhere? (Answer: absolutely with a cherry on top)"
"Alright then. Let's do it."