Cassini/Huygens Mission Update Thread

[Leovinus]

<i>A gorgeous Dione poses for Cassini, with shadowed craters and bright, wispy streaks first observed by the Voyager spacecraft 24 years ago. The wispy areas will be imaged at higher resolution in mid-December 2004. Subtle variations in brightness across the surface of this moon are visible here as well. Dione's diameter is 1,118 kilometers, (695 miles).<br /><br />The image shows primarily the trailing hemisphere of Dione, which is the side opposite the moon's direction of motion in its orbit. The image has been rotated so that north is up.<br /><br />The image was taken in visible light with the Cassini spacecraft narrow angle camera on Oct. 27, 2004, at a distance of about 1.2 million kilometers (746,000 miles) from Dione and at a Sun-Dione-spacecraft, or phase, angle of 28 degrees. The image scale is 3.5 kilometers (2.2 miles) per pixel. </i> <div class="Discussion_UserSignature"> </div>

 

[teije]

Question:<br />How is Huygens' separation speed off Cassini controlled. As far as I know it has no propulsion system of its own, so I suppose Cassini has to nudge it in the right direction somehow...<br />That sounds like a big risk, if somehow the speed isn't exactly right, Huygens might miss Titan or enter at a too steep angle.<br />Am I wrong?<br /><br />

 

[Leovinus]

Here is the Huygens home page. Perhaps your answer lies there. <div class="Discussion_UserSignature"> </div>

 

[Leovinus]

<i>The Huygens probe is due to separate on the morning of 25 December at about 05:08 CET. Since the Cassini orbiter will have to achieve precise pointing for the release, there will be no real-time telemetry available until it turns back its main antenna toward Earth and beams the recorded data of the release. It will take over an hour (67 min) for the signals to reach us on Earth. The final data confirming the separation will be available later on Christmas Day.<br /><br />After release, Huygens will move away from Cassini at a speed of about 35 cm per second and, to keep on track, will spin on its axis, making about 7 revolutions a minute. Huygens will not communicate with Cassini for the whole period until after deployment of the main parachute following entry into Titan’s atmosphere. On 28 December Cassini will then manoeuvre off collision course to resume its mission and prepare itself to receive Huygens data, which it will record for later playback to Earth.<br /><br />Huygens will remain dormant until a few hours before its arrival at Titan on 14 January. The entry into the atmosphere is set for 11:15 CET. Huygens is planned to complete its descent in about two hours and 15 minutes, beaming back its science data to the Cassini orbiter for replay to Earth later in the afternoon. If Huygens, which is designed as an atmospheric probe rather than a lander, survives touchdown on the surface, it could deliver up to 2 hours of bonus data before the link with Cassini is lost.</i> <div class="Discussion_UserSignature"> </div>

 

[centsworth_II]

<font color="yellow">"How is Huygens' separation speed off Cassini controlled."</font><br /><br />It looks like Cassini, with Huygens still attached, will put <b>itself</b> on the proper trajectory (direction and speed) for Huygens' entry into Titan's atmosphere. Then Huygens will detatch and follow the same trajectory while Cassini changes its trajectory to avoid accompanying Huygens into Titan.<br /><br />From THIS article:<br /><i>"On 17 December the orbiter [Cassini] will be placed on a controlled collision course with Titan in order to release Huygens on the proper trajectory..."</i> <div class="Discussion_UserSignature"> </div>

 

[chew_on_this]

"...while Cassini changes its trajectory to avoid accompanying Huygens into Titan."<br /><br />Hopefully... <br />

 

[teije]

Thanks for the answers provided, but it's still not quite clear to me. E.g. in the article mentioned by centsworth_II it says: <br />... After release, Huygens will move away from Cassini at a speed of about 35 cm per second .... <br />from release to Titan entry that's about 635 km. (Just counting days, no hours or minutes.) So, if the speed difference between Cassini and Huygens is something else then 35 cm per second this may have a big impact on the atmospheric entry point.<br /><br />It may be, as centsworth_II mentions that in fact Cassini is breaking away from Huygens' but still, it has to detach before cassini can break away. Anyone know how this is done? Pyrotechnics of some sort I suppose?<br /><br />thx adv.<br />Teije<br />

 

[centsworth_II]

From THIS interesting technical brief on Huygens:<br /><i>"Huygens consists of two pieces of apparatus: the probe and the probe support equipment (PSE).... The PSE, although a part of the Huygens system, remains attached to the Cassini orbiter. Its purpose is to support the probe and provide power to the probe prior to separation and to provide communications between the probe and orbiter both prior to and after separation. It also provides the spin given to the probe during the separation process."</i><br /><br />So Technically, Huygens is not actually separating from Cassini. It is separating from a portion of itself that remains attached to Cassini. As far as the separation devices: pyrotecnics, latches, springs, or combination, I don't know.<br /><br />Also from the same brief:<br /><i>"The two spacecraft will separate with a relative velocity of 0.3-0.4 m/s but remain in the same orbit for about three weeks. At that time, Cassini will execute a deflection maneuver to enable it to fly by Titan at an altitude of 60,000 km and positioning it to receive transmissions from Huygens as it enters Titan's atmosphere, some 2.1 hours prior to Cassini's closest approach."</i><br /><br />My guess is that the separation pushes Huygens away from Cassini along the line of their trajectory toward Titan, rather than at an angle to it. This would keep the paths of the two craft the same, with a small speed difference. I don't know whether Hygens is pushed ahead of Cassini or behind.<br /><br /> <div class="Discussion_UserSignature"> </div>

 

[centsworth_II]

Some more info on the separation device from THIS article:<br /><br />"The Cassini/Huygens separation subsystem (SEPS) is more elaborate. The main engines must fire before release to slow the probe down before it approaches the comparatively rarefied atmosphere of Titan. Therefore, Huygens is mounted on the side of the orbiter, clear of the engines. The SEPS provides the orbiter/probe structural load path and electrical attachment, and supports the separation device. <br /><br />This device incorporates three stainless-steel springs that provide separation force; three guiding devices, each with two axial rollers that follow a T-shaped helical track for orienting the probe on release; a carbon fiber ring to compensate for dissymmetry in orbiter truss loads and to provide necessary stiffness; and three pyronuts to secure everything in place prior to separation." <br /><br /><br />Being reminded that Huygens is on the side of Cassini makes me rethink my guess about its being released along the line of Cassini's flight. Good thing the mission doen't rely on MY understanding! Anyway I'm sure THEY know what THEY'RE doing. <div class="Discussion_UserSignature"> </div>

 

[Leovinus]

I see that Cassini has successfully flown by Titan a second time. But there are no new pictures yet. <div class="Discussion_UserSignature"> </div>

 

[Leovinus]

From the JPL recent raw image page:<br /><br /><i> N00025365.jpg was taken on December 12, 2004 and received on Earth December 12, 2004. The camera was pointing toward IAPETUS at approximately 4,698,454 kilometers away, and the image was taken using the CL1 and CL2 filters. This image has not been validated or calibrated. A validated/calibrated image will be archived with the NASA Planetary Data System in 2005. </i> <div class="Discussion_UserSignature"> </div>

 

[tekdeth]

If you check the mission timeline for the flyby, it says data will start coming in at 4pm. Should be cool.

 

[teije]

Thank you centsworth_II. <br /><br />It's more clear to me now. I'm still a bit in the dark how exactly they control those springs 'n stuff, but then again, I guess that's why it's not me that designed the thing. <img src="/images/icons/smile.gif" /><br /><br />One thing still worries me though. I seem to remember that the beagle lander on mars express had a similar separation device. Let's hope this one works a bit better...<br /><br />Teije

 

[alexblackwell]

<i>f you check the mission timeline for the flyby, it says data will start coming in at 4pm.</i><br /><br />Data have been hitting the ground for the past 1-2 hours.

 

[centsworth_II]

<font color="yellow">"...still a bit in the dark how exactly they control those springs..."</font><br /><br />I guess the only control is the degree to which the springs are compressed during assembly. Then when the pyrotechnic devices holding the Huygens lander fast (and the springs compressed) are fired, the springs extend and send the lander off at a pre-determined velocity. I don't know, but I doubt that it would be necessary to devise a system to alter the degree of spring compression -- and thus force of separation -- after launch. And thanks for the question -- made me think about some things I ordinarily wouldn't have. <div class="Discussion_UserSignature"> </div>

 

[titanian]

We have to remind that Europeans ( except Great Britain!) have no experience in the landing processes of space probes contrary to Russia and the US.But they put the price and the time to conceive huygens ( around 3.5 billion euro instead of 2).Perhaps,ESA, Alcatel Space ( ex Aérospatiale, site of Cannes), and the Italian Space Agency should have started a first mission on the martian soil before experimenting this unprecendented venture?But it's a good opportunity to evaluate their space technology ( nuclear power, landing systems etc).Let's pray now!

 

[teije]

"...I guess the only control is the degree to which the springs are compressed during assembly..."<br /><br />That's what I was thinking, easy enough to calculate the force of the springs during assembly. I was just wondering what 7,5 years of being subjected to the coldness of space while being completely strained would do to that force...<br />Maybe they are electrically warmed up to a certain temperature before release or something...<br />Anyone who knows?<br /><br />Teije<br />

 

[Leovinus]

<i>This map of Saturn's moon Dione, generated from Cassini images taken during the spacecraft's first two orbits of Saturn, illustrates the imaging coverage planned during Cassini's first Dione flyby on Dec. 14, 2004.<br /><br />Colored lines enclose regions that will be covered at different imaging scales as Cassini approaches Dione.<br /><br />Cassini will zoom past Dione at a distance of approximately 81,400 kilometers (50,600 miles) during this flyby. An even closer encounter with Dione is in store for Cassini in October 2005, when the spacecraft is slated to fly past the icy moon at a mere 500 kilometers (311 miles).<br /><br />Images from this week's flyby will be superior in resolution to those obtained by NASA's Voyager 1 in November 1980. Voyager 1 passed Dione at a distance of 161,520 kilometers (100,364 miles) at closest approach, yielding a best resolution of approximately 1 kilometer per pixel. The area to be imaged at highest resolution by Cassini during this upcoming flyby will be centered on the bright, wispy terrain on Dione's trailing hemisphere, marked by the red outline on this map. The resolution of Cassini images in this region will be 500 meters per pixel and better.<br /><br />The map was created by images acquired in visible light using the Cassini narrow angle camera. The highest southern latitudes on Dione have not yet been seen by Cassini, resulting in the map's lower limit of approximately 80 degrees south latitude. </i><br /><br />Wow -- two flybys in as many days. <div class="Discussion_UserSignature"> </div>

 

[Leovinus]

<i>This view from Cassini's second close flyby of Titan on Dec. 13, 2004 shows bright material within the large dark region west of Xanadu. The area in this image is a region that has not previously been seen by Cassini at this high resolution.<br /><br />The image was taken with the Cassini spacecraft narrow angle camera at a distance of approximately 125,900 kilometers (78,200 miles) from Titan, using a filter centered at 938 nanometers that emphasizes the moon's surface and clouds. The image scale is 735 meters (2,400 feet) per pixel. </i> <div class="Discussion_UserSignature"> </div>

 

[Leovinus]

<i>This image was taken during Cassini's very close approach to Titan on Dec. 13, 2004.<br /><br />Bright streaks of cloud in Titan's southern hemisphere are visible. Linear clouds such as these have appeared intermittently in this region of Titan.<br /><br />The image was obtained with the Cassini spacecraft wide angle camera at a distance of approximately 178,600 kilometers (111,000 miles) from Titan, through a filter sensitive to wavelengths of infrared light centered at 918 nanometers. The Sun-Titan-spacecraft, or phase, angle is 15 degrees. The image scale is about 10.5 kilometers (6.5 miles) per pixel. </i> <div class="Discussion_UserSignature"> </div>

 

[Leovinus]

<i>This image was taken during Cassini's very close approach to Titan on Dec. 13, 2004.<br /><br />The view shows pronounced banding in the Titan atmosphere. The image has been processed to enhance the banding, but a few artifacts of the imaging process, such as the small "doughnut" shape at right, remain.<br /><br />The image was obtained with the Cassini spacecraft wide angle camera at a distance of approximately 124,800 kilometers (77,500 miles) from Titan, through a filter sensitive to wavelengths of infrared light centered at 890 nanometers. The Sun-Titan-spacecraft, or phase, angle is 15 degrees. The image scale is about 7.5 kilometers (4.6 miles) per pixel. </i> <div class="Discussion_UserSignature"> </div>

 

[krrr]

What on Dione is that?<br /><br />A straight line which must be dozens of miles long. Doesn't look like an image artifact.

 

[Leovinus]

There are three things I can think of that could create absolutely straight lines like that.<br /><br />First, something came in horizontally and had a ton of momentum and plowed a straight line as it went.<br /><br />Second, the thing is a big crystal and that line is on one of the edges of the lattice.<br /><br />Third, someone carved it that way. <div class="Discussion_UserSignature"> </div>

 

[spacechump]

A comet or asteroid tidally pulled apart can do something like that. It's refered to as a crater chain.

 

[mooware]

Have we seen a natural phenomenon this straight before anywhere else?<br /><br />Boy wouldn't that send shockwaves if it was carved. Alhtough, i HIGHLY doubt it was.<br /><br />