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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."
...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
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.
And yet your comment is the usual back-biting. Ah well.
delta-V is *always* measured in m/s. It's a change in velocity.
General Relativity: Space-time tells matter where to go; Matter tells space-time what shape to be.
It's very simple:
You have no fucking clue how this kind of science works, and you don't seem to remember the 'failures'
But hey, you let your experience with fictional TV show dictate how you think of the world, because I don't think you could really do any better then that.
The Kruger Dunning explains most post on
The graphic said "In the series of 17 Titan flybys shown below..."
"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.
Because everything costs so much to launch that they design something to absolutely be capable of fulfilling its mission parameters. If they screw it up, it crashes and dies with billions lost. If they get it right, they might have some triplicate backup resources used to ensure function for 90 days that are left over. And because it would cost billions to get those resources up with a new mission, they might as well take advantage of what is left.
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.
No, they got their project picked out of the hundreds submitted for funding because they had a particular plan that met particular objectives.
They engineered the spacecraft with normal margins over and above the basic requirements to allow for the sort of uncertainties that enter into designing every part of a device this complicated and limited in mass and power. One of the simplest of these is to put in twice as much fuel as your nominal model tells you to, giving yourself 100% margin to deal with exigent circumstances.
This sort of margin is not just good for business, it's generally required by the funding authority (NASA and the government), because they got tired of being bitten on the ass by penurious aerospace craft design in the '00s. That's the 19'00s, not the 20'00s.
Then, as the mission goes along, their managers and technical staff made careful decisions that didn't waste their fuel margins. The result is that they have a free spacecraft on-orbit with which to do new science. Which again they have to propose to the funding authority, since ground systems and personnel still cost money. The funding authority sees the variable costs as incredibly cheap compared with developing and emplacing a whole new device, so they give it a green light.
A few months later, we get to see a pretty picture that blows the minds of the smaller-minded among us, and makes the bigger-brained among us yawn at the idea that anyone is impressed with 64 loops around a couple of rocks that aren't going anywhere fast...
My thought as well. How long after it enters the atmosphere, but before it breaks up will there be. Is it possible that it could end up "floating" on the atmosphere and not actually break up, that would be some great pictures. Though I am sure that is very unlikely. The most likely occurrence I see is that as the craft enters enough of the atmosphere to be called an atmosphere all the sensors would be ripped off from the deceleration and we would cease to receive signal from it.
APK likes to ask for responses to the same things over and over. Maybe he just likes the responses?
I think you may be the one who needs a therapist...
Is 1563649 a prime number?
and makes the bigger-brained among us yawn at the idea that anyone is impressed with 64 loops around a couple of rocks that aren't going anywhere fast...
That's a bit of an arrogant statement. While you hit the nail right on the head with the margins in spacecraft design, I have to say that seeing the orbital plots of a mission as complex as Cassini, is, in no way, a yawning experience. While you may think that it's nothing more than a few geometric loops around some rocks that aren't going anywhere, those of us who have worked on orbital mechanics problems understand, in no small part, just how complex the math must have been to work out those solutions. Furthermore, we have a fascination with the idea of getting to fiddle with problems like that ourselves one day. In fact, this particular plot has inspired me to pull out my 3-body problem source code when I get home and revisit some of the algorithms used to optimize fuel consumption for 3 body orbital problems.
What I am getting at is that those 64 loops around a couple of rocks, which you so trivialize, represent, to those of us involved in this field, a visual depiction of a very high level of hard, computer intensive work that we are familiar with. It's kind of like hearing a symphony play a composer's final musical construct. Those who are composers can appreciate the symphony as it depicts, audibly, just how intensive, deep, and subtle the composer must have been in his work. Likewise, those of us that are familiar with these types of problems can look at the visualization and appreciate the incredible mathematical nuance and finagling that must have gone into doing these calculations.
Then again, very few people tend to have any appreciation for the engineering intensive processes that go into even common, everyday appliances like computers and cars, so I suppose I shouldn't be surprised when a self-proclaimed 'bigger-brained' person cannot appreciate the depth and culmination of work that a plot like the one linked to in the summary represents.
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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.
Ding. We have a winner. Orbital calculations, and optimizing on burn, delta-v and minimizing fuel consumption is really hard. I took a celestial mechanics course as part of my graduate work in Physics, and while I was really good at analytical solutions where they could be achieved, the aerospace engineers who couldn't solve a closed form integral equation to save their lives, could give outstanding solutions for Hohmann transfer orbits, LEO mechanics solutions, and many harebrained options. I was amazed at their creativity, while I was grinding really hard for closed form analytical solutions.
This is brilliant stuff, and their creativity of minimizing the burns yet extending the mission is way cool.
Suppose you were an idiot and suppose you were a member of Congress
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.
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