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Cassini-Huygens Reaches Orbit Around Saturn
Mick Ohrberg writes "The probe Cassini-Huygens is now officially in orbit around Saturn. Last nights' retro-burn was completed according to plan, down to the second, which in and of itself is an amazing feat, considering all data received is 1h24m old, as well as 900 million miles away. I must say, it was fairly exciting to watch the webcast, and see the signal fade behind the A-ring, and all but disappear behind the B-ring - all in (somewhat delayed) real-time. The SOI (Saturn Orbit Insertion) also saw Cassini-Huygens whisk by Saturn at around 68,000 mph at an altitude of about 12,000 miles from the cloud tops - the closest to the gas giant the probe will ever be during its planned 4-year mission, for instance the much awaited Huygens mission to Titan."
Not sure when the article was written but there are already raw and press images released as well as some others. The quality isn't as good as some may think and it really doens't show much detail into the rings at all.
Hmmm.
wikipedia has a great bit of information on the history of this project including a section called "Plutonium power source and controversy".
steal this sig
nice image showing gravitonal waves in the ringshttp://spaceflightnow.com/cassini/images/0407 01rings1.jpg
SHE does throw dice.
There wasn't much danger of a serious collision. They passed through a gap in the rings and the probe was checking the region out several weeks ago for possible threats. Besides, Cassini will be using the high-gain antenna dish as a shield when passing through the rings, so the spacecraft itself isn't in a lot of danger.
I was at the small (public) meeting held at Goddard Space Flight Center just last night, regarding Cassini's SOI.
Basically they did a few basic things to mitigate risk when attempting this.
- Massive retro burn to decrease velocity: Saturn's gravity was speeding the probe up.
- Aimed at the space between rings so it go through *mostly* empty space... twice, since it had to come back through the rings on its way back out.
- Flipped the craft around 180-degress so the high-gain antenna dish would act as a shield for the rest of the probe. (pretty clever if you ask me).
I'm just happy to see that it worked. Although I wonder what condition the dish is in now.
"The photo sequence began around 12:30 a.m., 18 minutes or so after Cassini finished a 96-minute rocket firing to brake into orbit around Saturn. Streaking just above the rings at speeds greater than 50,000 mph, Cassini's narrow-angle camera took a series of snapshots, opening its shutter for just five milliseconds per picture to avoid blurring. Each picture was separated from those on either side by about 600 miles because of Cassini's extreme velocity."
"It takes us about a minute to take a picture and so in the time we shutter the exposure, read out the camera and get ready to take a picture again, we have crossed a thousand kilometers."
They never had a chance to get a close up of the debris in the rings. In fact, it would take a significant effort, timing it just right, to do so; and, they would risking damage by exposing the camera lens to any dust in the path. If you remember, they were turning Cassini so the big dish pointed in the direction of travel to act as a shield against any small objects in their path, as they crossed the rings.
I find myself curious what compression algorithms they are using... is it lossless?
:-)
I was reading an interesting page on how the cameras process the data and on some of the technical aspects regarding the images - the FAQ on the raw images available for downloading.
Apparently, there are both lossless and lossy compression schemes, and it sounds like the compression is done within the cameras themselves - it's not like, say, the Mars Rovers which have a fairly big processor in the middle doing all the work. I don't think it mentions the specific compression algorithms themselves; I wouldn't be surprised if the lossy one is a form of JPEG. I know that was used on Mars Pathfinder, also launched in 1997...
The raw images I have seen are pretty messy, and for trulyspectacular views of Saturn, its rings and its moons it's probably best to wait for them to be processed properly. The FAQ details some of the ways in which they're processed on the ground, too - anyone want a go themselves?
Tedious Bloggy Stuff - hooray?
It's not several billion - it's only 900 million miles away, plus or minus 2 AUs or so. ;)
Cassini TRAVELED several billion miles to get there - its path looks like an archimedes spiral because of the multiple slingshot maneuvers it used to gain speed. This is also why it took so long to get there.
They did not use the sun's gravitational pull; they used the gravity fields of Venus (twice), Earth, and Jupiter to overcome the sun's gravitational pull.
The "risk" of a Columbia/Challenger type accident - breaking apart from a launch vehicle failure or atmospheric stresses - had nothing to do with the slingshot trajectory, and the RTG was packaged against that contingency. The risk of the slingshot maneuver around earth leading to an accident was infinitesimal.
As the linked article discusses at greater length, the wisdom of the plan was disputed by some, but calling it "very dangerous" is getting close to tin foil hat territory.
Yep, it is, according to dictionary.com:
Saturnian ( P ) Pronunciation Key (s-tûrn-n, s-)
adj.
Of or relating to the planet Saturn or to its supposed astrological influence.
Archaic. Of or relating to the god Saturn or his reign.
>insert witty sig file here