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Thread: Huygens encounter with Titan

  1. #1
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    Huygens encounter with Titan

    I'm going to start a new topic for this (mostly because the erroneous apostrophe in the title of the topic I've been using annoys me!).

    Splash, Thud, or Whimper? Cassini's Huygens Probe Rendezvous with Titan



    On December 24th, 2004, at 7:08 PM Pacific Standard Time, the Cassini spacecraft will release a probe that has hitched a ride all the way from Earth out to Saturn. The Huygens Probe, named after the Dutch scientist Christiaan Huygens, who discovered Titan and Saturn’s rings in the 17th century and built by the European Space Agency, will spend 22 days traveling to its rendezvous with Saturn’s mysterious moon Titan on January 14th. Titan is one of the remaining puzzles of the solar system – while Cassini’s imaging cameras and radar instrument have begun to reveal the details of its surface, the Huygens probe will be the first spacecraft to venture beneath Titan’s thick clouds
    Everything I need to know I learned through Googling.

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    Why will it be so long between separation and entry?

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    Quote Originally Posted by Disinfo Agent
    Why will it be so long between separation and entry?
    Since Huygens has no propulsion system, Cassini must be on the same track as Huygens at the time of release, i.e., a collision course with Titan. The long lead time gives Cassini enough room to change its course so as not to collide with Titan.
    Everything I need to know I learned through Googling.

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    Is a 2.5 hour battery the best that could be done? Was this an engineering contraint, budgetary or was that the best battery when the thing was originally designed/built?

    CJSF
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    lonelybirder.org

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    Don't know if this was posted here before, but here is a webpage with some test images taken by the camera. Just to give an idea what to expect.


    Harald

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    Quote Originally Posted by Christopher Ferro
    Is a 2.5 hour battery the best that could be done? Was this an engineering contraint, budgetary or was that the best battery when the thing was originally designed/built?

    CJSF
    Cassini will go below the horizon after this time, so it wouldn't pay to have a battery that lasts longer.

    Harald

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    Quote Originally Posted by kucharek
    Quote Originally Posted by Christopher Ferro
    Is a 2.5 hour battery the best that could be done? Was this an engineering contraint, budgetary or was that the best battery when the thing was originally designed/built?
    CJSF
    Cassini will go below the horizon after this time, so it wouldn't pay to have a battery that lasts longer.
    Harald
    This one I do not understand. I can run my trawlin motor for a days on one battery, and Cassina completes another orbit in a month, why not shut Huygens down for a month and and fire it up again?????
    “It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.” ― Arthur Conan Doyle, Sherlock Holmes

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    Quote Originally Posted by Jerry
    This one I do not understand. I can run my trawlin motor for a days on one battery, and Cassina completes another orbit in a month, why not shut Huygens down for a month and and fire it up again?????
    How would you do that? If Huygens is shut down all the way, then there's no way of waking it up again. If you want to allow for waking it up again, then it has to either have some sort of timer running or have some portion of the communications system remain on and listening. Even then you've got to assume it's going to survive the landing and then be able to hold out for a month. It doesn't seem like a possibility worth planning for.
    Everything I need to know I learned through Googling.

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    Quote Originally Posted by Jerry
    Quote Originally Posted by kucharek
    Quote Originally Posted by Christopher Ferro
    Is a 2.5 hour battery the best that could be done? Was this an engineering contraint, budgetary or was that the best battery when the thing was originally designed/built?
    CJSF
    Cassini will go below the horizon after this time, so it wouldn't pay to have a battery that lasts longer.
    Harald
    This one I do not understand. I can run my trawlin motor for a days on one battery, and Cassina completes another orbit in a month, why not shut Huygens down for a month and and fire it up again?????
    My guess would be, apart from size and weight issues, that without heating the battery, once it drops below a critical temperature it wouldn't be able to emerge from hibernation

    Solar Views: Titan

    Titan's surface temperature appears to be about -178°C (-289°F).
    That's a real low temperature to kep a battery at for a month. To keep the battery warm would take power which would drain the battery so it would be self defeating.

  10. #10
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    Quote Originally Posted by ToSeek
    Quote Originally Posted by Disinfo Agent
    Why will it be so long between separation and entry?
    Since Huygens has no propulsion system, Cassini must be on the same track as Huygens at the time of release, i.e., a collision course with Titan. The long lead time gives Cassini enough room to change its course so as not to collide with Titan.
    The signal timing problem was another issue. I found this article absolutely fascinating:

    http://www.spectrum.ieee.org/WEBONLY...1004titan.html

    The Cassini receiver for the Huygens probe couldn't fully account for doppler shift. The article covers how the problem was found and a workaround devised. From the article:

    FROM A VARIETY OF PROPOSED FIXES, the Cassini team crafted a response plan that centered on reducing the Doppler shift sufficiently to keep the data signal within the recognition range of the receiver. They accomplished this trick by altering the planned trajectory of Cassini. Now, Cassini will be much farther from Titan when Huygens enters its atmosphere.
    and ...
    So the navigators designed a trajectory in which Cassini initially enters a lower and faster orbit around Saturn, drops off Huygens, and then hits a specific point in space that coincides with a point on the previously planned path. There Cassini fires its rocket engine again to get back on the original course.
    The effect is that the flight takes longer and the landing is later than originally planed. If they hadn't done the testing and had gone with the original plan, though, we likely woudn't have gotten any useful data from the probe. Still, I hope there aren't any other real issues yet to be found ...

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    This one I do not understand. I can run my trawlin motor for a days on one battery, and Cassina completes another orbit in a month, why not shut Huygens down for a month and and fire it up again?????
    And just how long will your motor last at -300F?

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    From looking through the PDF on the Huygens misison from the NASA/ESA site, here's a head's-up. To verify the exact departure trajectory, the orbiter will take a 5x5 imaging mosaic to show the probe at about 1400 UT on Christmas Day. After 11 hours or so it may look like just another faint star, but it should be encouraging enough to just see the thing. The timeline shows a 2.5-day window allotted for probe imaging, in fact.

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    Disappointing mission coverage on Cassini homepage

    On a slightly whining note:

    Does anyone else find the Cassini mission homepage incredibly disappointing, especially as compared to the MER effort?

    I mean, one of the top items STILL remains the story of the high school ballet dancer who participated in the planning. That stuff is fine for the cruise segment of the mission. But Cassini is in orbit and Huygens is being released. Can't we see more than the occasional wallpaper and human-interest story?

    Who do I complain to about this?

    (Done venting now.)

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    Re: Disappointing mission coverage on Cassini homepage

    Quote Originally Posted by Tom Ames
    Who do I complain to about this?
    It might help: http://saturn.jpl.nasa.gov/news/contact-us.cfm

    On the MER mission page, I used a similar outreach address to ask a technical question that got answered.

    The bottom of http://saturn.jpl.nasa.gov/home/index.cfm lists editor and writer credits if you want to go into JPL and do some persuading.
    0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 ...
    Skepticism enables us to distinguish fancy from fact, to test our speculations. --Carl Sagan

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    On its way:
    Ground controllers received a signal at about 7:24 p.m. Pacific time (10:24 p.m. EST) indicating that Huygens had separated from NASA's Saturn probe Cassini, as small explosives sheared away locking bolts and a set of springs gently pushed the probe off on a collision course with Titan.

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    Re: Disappointing mission coverage on Cassini homepage

    Quote Originally Posted by 01101001
    Quote Originally Posted by Tom Ames
    Who do I complain to about this?
    It might help: http://saturn.jpl.nasa.gov/news/contact-us.cfm

    On the MER mission page, I used a similar outreach address to ask a technical question that got answered.

    The bottom of http://saturn.jpl.nasa.gov/home/index.cfm lists editor and writer credits if you want to go into JPL and do some persuading.
    Thanks, 69,

    I was being kinda' facetious -- I don't really intend to complain. It just seems like the web coverage on Cassini has been a big letdown in comparison to what has been done with MER.

    Thankfully S & O have been keeping me entertained longer than I had counted on.

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    Quote Originally Posted by Squink
    Live pictures! Just kidding. Artwork:













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    Skepticism enables us to distinguish fancy from fact, to test our speculations. --Carl Sagan

  18. #18
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    Just for scale, a picture of Huygens with people.



    It's 2.7 meters, about the same diameter as a MER spacecraft.
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    Skepticism enables us to distinguish fancy from fact, to test our speculations. --Carl Sagan

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    Re: Disappointing mission coverage on Cassini homepage

    Quote Originally Posted by Tom Ames
    On a slightly whining note:

    Does anyone else find the Cassini mission homepage incredibly disappointing, especially as compared to the MER effort?

    I mean, one of the top items STILL remains the story of the high school ballet dancer who participated in the planning. ...
    Who do I complain to about this?

    (Done venting now.)
    I have been harping about the lack of detail in the orbital science work, doppler measurements, the list goes on and on. The ESA site is slightly better, but they are holding the science data close to the vest
    “It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.” ― Arthur Conan Doyle, Sherlock Holmes

  20. #20
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    Part of the reason the Huygens probe has such a short battery life is because of what it's mission goals are: To study the atmosphere. The 2.5 hour life should be enough time to do that. Furthermore, when it does land, it doesn't need a long battery life since it's going to be sitting still. It should have enough time to sample whatever's there and be done with it.

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    Quote Originally Posted by ngc3314
    From looking through the PDF on the Huygens misison from the NASA/ESA site, here's a head's-up. To verify the exact departure trajectory, the orbiter will take a 5x5 imaging mosaic to show the probe at about 1400 UT on Christmas Day. After 11 hours or so it may look like just another faint star, but it should be encouraging enough to just see the thing. The timeline shows a 2.5-day window allotted for probe imaging, in fact.
    See some Huygens post-release imagery:

    Huygens Probe Zoom
    December 25, 2004

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    Huygens Probe Shines for Cassini's Cameras

    Huygens is the bright "star" in lower right corner:



    Processed close-up view of the Huygens probe:


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    100 kilometers milestone

    The probe was 100 kilometers from Cassini orbiter at 01:17 UTC on 2004-Dec-28.

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    Check out the program Celestia. It can let you view the motions and give a real feel for what's going on.

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    1000 kilometers milestone

    The probe was 1000 kilometers from Cassini orbiter at 12:20 UTC on 2004-Dec-28.

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    Parachuting to Titan

    Get ready for two of the strangest hours in the history of space exploration.

    Two hours. That's how long it will take the European Space Agency's Huygens probe to parachute to the surface of Titan on January 14th. Descending through thick orange clouds, Huygens will taste Titan’s atmosphere, measure its wind and rain, listen for alien sounds and, when the clouds part, start taking pictures.

    No one knows what the photos will reveal. Icy mountains? Liquid methane seas? Hot lightning? "It's anyone's guess," says Jonathan Lunine, a professor of planetary science at the University of Arizona and a member of the Huygens science team. "We might not even understand what we see, not immediately."
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    ESA taking the wrong tack on Huygens imagery?:

    Live from another world

    Nothing remotely like the Voyager, Pathfinder, or MER experience is about to repeat when Huygens lands on Titan, according at least to the current plans by the European Space Agency. The incoming raw images for the DISR cameras will only be seen by the scientists directly involved in the project: They will work on them and release them only hours later, after much processing of contrast and resolution. A few glimpses of the DISR images may be shown some hours after they arrived, but the majority of them, plus all the other data collected during the descent, are only to be released during a news briefing the next day. Now it is understandable that the European Space Agency wants to release only the best material, but to deprive the public of the chance to experience the mission as it happens (or happened) is a major blunder.
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    Quote Originally Posted by ToSeek
    ESA taking the wrong tack on Huygens imagery?:

    Live from another world
    Wow. Will ESA ever get this right?

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    Quote Originally Posted by um3k
    Quote Originally Posted by ToSeek
    ESA taking the wrong tack on Huygens imagery?:

    Live from another world
    Wow. Will ESA ever get this right?
    I didn't know that and I'm very disappointed. I agree, bad PR move.
    At night the stars put on a show for free (Carole King)

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