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Cassini's Elaborate Orbital Mechanics
jamie found an article at the NY Times about the extreme orbital mechanics gyrations required to extend the Cassini mission at Saturn by seven more years. Here's a graphic of the mission extension, which NASA took two years to arrive at. "The plans are for Cassini to keep working for seven more years, but it currently has only 22 percent of the maneuvering propellant it had when it started. Figuring out how to more than double the duration of the mission with less than a quarter of the fuel is hard. Cassini's orbital mechanics present an astonishingly complex exercise in Keplerian physics and geometry. The enormous array of science objectives and targets — moons, rings, Saturn itself — makes it one of the most complex missions ever flown. ... 'Without Titan,' Mr. Seal [Cassini's mission planning supervisor] said, 'we would go into one orbit around Saturn and be stuck there.' Thus Titan, in the argot of orbital mechanics, is Cassini's 'tour engine.' [T]he final 'reference trajectory' ... now includes 56 passes over Titan, 155 orbits of Saturn in different inclinations, 12 flybys of Enceladus, 5 flybys of other large moons — and final destruction."
Enceladus
What are the chances we can get some images from it entering Saturn's atmosphere?
...to see the software and user interface that NASA uses to plan the orbits? I wonder how much of it is automated and how much is interactive. We could envision a totally automated system in which they input a desired list of waypoints, some of which might have required time-windows, and the software cranks out the flight plan.
Does anybody here have experience with this?
Cassini spent a lot of time in the vicinity of Enceladus and its water geysers; another place where there could be life, with some traces of it hatched for the ride on our spaceship.
Alas, there's way too litle fuel even for routes with lowest energy requirements :(
One that hath name thou can not otter
No passes over Titan. No Enceladus flybys. Saturn orbits only. Final destination.
they used genetic algorithms to solves this? Or something alike
kdawson actually posted a story worthy of the front page of Slashdot. I acutally did a doubletake.
See my journal for slashdot ID's by year. Mine created in 2005. http://slashdot.org/journal/289875/slashdot-ids-by-year
Why don't they just schedule another shuttle mission to refuel this, like they do with the Hubble telescope?
Who would win this election: Andrew Weiner vs Andrew Weiner's weiner.
The article refers to a delta-V budget, which I hadn't heard of before, and my first thought was that they'd gotten their units wrong, but apparently "delta-V" in this context is actually measured in m/s, not m/s^2.
Why does it seem to me like people dealing with probes in space always pull Scotty's?
'Oh capt'n, she can not take it, I'll need at least 2 days to repair it'
Six hours later
'Its ready capt'n'
EVERY ONE of these missions either fails right off the start (understandable, this is rocket science after all) or ... gets extended. Why are we not planning better to start with rather than getting there and saying ...
'oh gee, our probe can live longer, but we'll have to 'figure out how' since we didn't plan on actually doing anything for any length of time once we got here.'
It just doesn't make sense. They're padding the numbers to make themselves look good, I'm sure of it.
Persistent Volume manager for Kubernetes - https://github.com/dwimsey/openshift-pvmanager
science!
The Kruger Dunning explains most post on
Did they use some fantastical optimisation algorithm to find the optimal path? I would be curious to know how they did this.
"If all goes as planned, on Sept. 15, 2017, Cassini will die a warrior’s death, diving inside the rings for 22 spectacular orbits on the fringes of Saturn’s atmosphere before plunging into the planet." ...they hope to orbit inside the rings! that's just as cool as it gets outside of riding a comet out of the solar system.
Optimal control theory gives you a function (trajectory over time, or acceleration vector over time) which minimizes a given functional (a function of functions) in this case I imagine that the total amount of fuelt spent (with the constraint that it reaches the lifetime desired). Summary: find the trajectory x(t) such that Fuel(x(t)) is minimized. This algorithm is well developed, you can even use it in quantum mechanics (give the desired hamiltonian(t) such that the evolution of the state is such and such at the end of the evolution, with the minimum of $whatever achieved along time).
I had the good fortune to be working on the Galileo mission during its Mission Design phase. Many of the techniques used by the Cassini mission designers were developed for Galileo. Disclamer: I was not on the mission design team.
First of all, the Voyager encounters with Jupiter and Saturn were always when the spacecraft were moving away from the sun. However, during the Galileo satellite tour the mission designers realized that the Galileo spacecraft could encounter Callisto, Ganymede, and Europa when moving away and moving toward Jupiter. Furthermore, the closest approach ("encounter") could be targeted to be either in front of the moon (with respect its orbit around Jupiter) or behind it. These choices allowed the designers a great deal of freedom to use the moons' gravity to shape the spacecraft's orbit. As I understand it, they did not just plan the current encounter to obtain the next encounter, but also the encounter after that.
The ability to use a moon to shape a spacecraft orbit depends on the ratio of the mass of the planet to the mass of the moon (for all practical purposes the spacecraft is massless.) Only Io, Callisto, Ganymede, and Europa are able to provide gravity assists at Jupiter, and only Titan at Saturn.
I spoke to Bob Mitchell, Cassini Project Manager, a few years ago and asked him about this specifically. He told me that while it was true that having to go back to Titan every time to change the orbit was a constraint, it also provided the freedom to send the spacecraft out of the "plane" where the moons orbited. At Jupiter it was necessary to stay in the plane to make multiple visits to all the moons, but since at Saturn you must visit the same moon to change the spacecraft's orbit every time (Titan) there is fewer reasons to stay in the plane. And, as you can see from the orbit diagrams, Cassini has traveled outside of the plane many times.
That's no moon
For justice, we must go to Don Corleone
[T]he final 'reference trajectory' ... now includes 56 passes over Titan, 155 orbits of Saturn in different inclinations, 12 flybys of Enceladus, 5 flybys of other large moons — and final destruction."
So the CD with 616,420 signatures on it is not going to out last us all after all.
When the signature drive began in 1996 an implied promise was made that Cassini, and the disk would remain in orbit around Saturn forever. See, for example this remark: "Indeed, some of us may even experience a small taste of immortality as we envision our signatures outliving our bodies." http://web.archive.org/web/19990428132214/www.jpl.nasa.gov/cassini/MoreInfo/dvd.html.
Objectively, gaining additional science by crashing it into Saturn is a more worthwhile endeavor than using it as an eternal postcard to the planets, but to those of us with our signatures on it (and who remember people who signed but have passed on, and cannot now add their signature to a outer solar system probe) it is a disappointment. Maybe they could launch a copy on a new deep space probe.
Starships were meant to fly, Hands up and touch the sky - Nicky Minaj
Am I the only one who remembers the protesters around Cape Canaveral when Cassini launched? That's because its initial trajectory was unbelievably convoluted: the ship actually traveled to Venus first, got a gravity boost then traveled back out and used the Earth for its next boost.
The protesters feared that a miscalculation could cause Cassini to re-enter Earth's atmosphere on this near-miss flyby and disgorge its thermopile of plutonium into the stratosphere.
So it was a crazy flight from the very first day.
Don't worry, I thought it was a good one.
DAMN FUCKING STRAIGHT! Seriously, how the hell does that bit NOT make the summary?!
Pardon me, I've gotta go look up the science package on Cassini and figure out what resolution of images might be expected... that's gonna be some awesome wallpaper. (2017... already the waiting breaks my heart).
The "damn computers too slow" comment tells me that he really means the problem can't be solved numerically. A simple computer program can certainly tell you what will happen if you perform a certain burn. But it can't tell you what burn will achieve a certain outcome with minimal fuel expenditure. It can try to grind through all the possible variations, but if the variations are too numerous and the computations are too strenuous then it's not practical. Hence, the damn computers are too slow.
that's just as cool as it gets outside of riding a comet out of the solar system.
Know what would make that even cooler? If Cassini were wearing a cowboy hat and yelling "Yee-haw!" as it dove into the planet. Best. Re-entry. Ever.
God invented whiskey so the Irish would not rule the world.
Regardless of the size of your brain, I think you may have a small mind ;)
Like solving problems currently applicable to stuff on Earth. Dunno' maybe outmaneuvering volcano ash?
Like solving problems currently applicable to stuff on Earth. Dunno' maybe outmaneuvering volcano ash?
I was thinking the same thing... though more on the lines of figuring out ways for cars to take advantage of gravity assists of a semi-truck passing on the highway or creating water slides where you get a few seconds of weightlessness.
Wait, maybe they only know how to do that in space. I don't know where my mind wanders sometimes.
I haven't read TFA, but I just hope the usual hack journalists haven't used the tired phrase "and like a giant slingshot, Titan (or Eros or Uranus - whatever) hurled Cassini into a new orbit!..."
Someday, I'd like grab one of these unimaginative, unscientific ink-stained wretches and hurl them with my giant digital slingshot to an orbit around the planen Zqarqon. It's where they belong.
.
- aqk
F U
Yes, it is cool. And you don't have to wait 7 years. Cassini already completed a trans-ring intersection on it's breaking maneuver when it arrived at Saturn. You can probably find videos on the Net. There are some awesome high-res shots available. Go and find them.
The fear then was that a mis-calculation might be the cause of the worst man-made environmental impact in the solar system -- crashing into the rings and disrupting their delicate balance, causing them to collapse into the planet. Of course with it's tiny mass the most likely outcome would have been just losing the probe as some chunk of ice smashed into it, even with the high velocity it had on it's way from Jupiter. Now presumably the probe's velocity is even lower, so it should be okay.
“Our opponent is an alien starship packed with nuclear bombs. We have a protractor.” — Neal Stepnenso
It was, but it wasn't first. ):
"There is a way that seems right to a man, but its end is the way of death." Proverbs 16:25 (NKJV)
The story has a hero, Boris Smeds, a Swedish radio engineer for the ESA, who pushed and pushed because he found out something was very wrong with the Huygens payload to be launched from Cassini probe.
Slashdot covered this well and humorously. See substitute links provided for 6 years of bit rot on URL's
Saving Huygens
"Titan Calling: How a Swedish engineer saved a once-in-a-lifetime mission to Saturn's mysterious moon"
and The story behind "Titan Calling"
For completeness sake, here is a NASA/JPL paper on "What we can do to fix the problem"
Resolving the Cassini/Huygens Relay Radio Anomaly
The paper's "lessons learned" are particularly important:
"It is important to keep proper documentation of all tests so this information is available when something goes wrong."
Spacecraft systems need to have an appropriate level of reconfigurability in flight. "This anomaly would have been easy to solve if there has been even a modest amount of reconfigurability in the PSA."
Doppler Shift? What is this Doppler Shift thing you speak of? :-)