Why Did Cassini release Huygens probe so early?

brellis · Aug 21, 2005

Wouldn't it have been prudent to have Cassini make several flybys of Titan and 'scout' for the ideal location for the Huygens probe before realeasing it? Each flyby has transformed our understanding of Titan. <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

vogon13 · Aug 21, 2005

Have you heard any scientist involved in the project voice your concern? Is it barely possible that several alternative plans for deployment of the probe were debated during the mission design phase and the consensus was to do exactly what was done? BTW, welcome to SDC. <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

Leovinus · Aug 22, 2005

I believe they did make a flyby of Titan before release. However, you never know how long the mothership is going to last. If it died early, you'd miss your chance to land on Titan. Are you disappointed with the landing and its results? <div class="Discussion_UserSignature"> </div>

CalliArcale · Aug 22, 2005

Yep; you take care of the most critical events early in the mission to reduce your losses in the event of a catastrophic failure down the road. Of course, Huygens couldn't really be targeted all that accurately anyway, and its entry was timed more to make sure it got plenty of light during the descent than to make sure it hit a particular spot; it was really a one-shot deal, after all. Furthermore, Huygens began its design process over 20 years ago, when we knew even less about Titan; the probe was therefore designed primarily to study the atmosphere, with surface studies being basically a bonus since they really didn't know enough about Titan to make the instrumentation very specific for it. Vastly more is known now, largely as a result of Huygens; the second lander on a planet/moon/whatever always has an easier design phase. <img src="/images/icons/wink.gif" /> Another problem with targeting is that Huygens had to be aimed *by* Cassini. That means Cassini had to be on a Titan-impacting trajectory prior to release. To give Cassini enough time to fire its engines and miss Titan, Huygens was jettisoned 21 days prior to the Titan flyby. The longer that period of time, the more uncertainty in the targeting. So I'm not sure they would've gained much by waiting a few flybys anyway. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

gregoire · Aug 22, 2005

If I remember correctly they also had to revise due to a dopler shift problem with the receivers between both craft. The distance between the craft had to be increased, so not just any pass of Titan would do.

brellis · Aug 30, 2005

thanks vog, glad to be here <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

brellis · May 20, 2006

i went to the JPL open house today, and i was ready with all my "Ask the Rocket Engineer" questions, hehee. the answer guy said they were really worried about dust particles hitting the probe as it passed thru the ring plane. he said they weren't concerned about any as-yet undiscovered moons in that area ["worry about the small stuff, and it's ALL small stuff", or something like that] JPL is open tomorrow as well. i highly recommend it for kids of all ages! <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

willpittenger · May 20, 2006

Yeah, well, it help to live in the Pasadena area. Illinois is a little far away for a convenient afternoon trip. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

sponge · May 22, 2006

Haha yeah the mining town of Kalgoorlie Western Australia is a little far off aswell. <div class="Discussion_UserSignature"> SPONGE </div>

brellis · May 22, 2006

[one of the tidbits i learned at jpl...] if you were travelling as fast as the voyagers, you would get there from australia in around 15 minutes! <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

brellis · Jul 28, 2007

Hicup's nOObish thread in FS got me thinking about my "virgin" thread here at SDC. CalliArcale's response is spot-on: Yep; you take care of the most critical events early in the mission to reduce your losses in the event of a catastrophic failure down the road. Of course, Huygens couldn't really be targeted all that accurately anyway, and its entry was timed more to make sure it got plenty of light during the descent than to make sure it hit a particular spot; it was really a one-shot deal, after all. Furthermore, Huygens began its design process over 20 years ago, when we knew even less about Titan; the probe was therefore designed primarily to study the atmosphere, with surface studies being basically a bonus since they really didn't know enough about Titan to make the instrumentation very specific for it. Vastly more is known now, largely as a result of Huygens; the second lander on a planet/moon/whatever always has an easier design phase. Another problem with targeting is that Huygens had to be aimed *by* Cassini. That means Cassini had to be on a Titan-impacting trajectory prior to release. To give Cassini enough time to fire its engines and miss Titan, Huygens was jettisoned 21 days prior to the Titan flyby. The longer that period of time, the more uncertainty in the targeting. So I'm not sure they would've gained much by waiting a few flybys anyway. After much rumination, reconsideration and re-something-or-otherification, I still think they should have waited for more Titan encounters before releasing the Huygens probe. Granted, they wouldn't have known if it would land in a methane lake, mud, or dry-ish land, but they built the probe to survive any of those scenarios. The key to me is the de <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

MeteorWayne · Jul 28, 2007

IIRC, one reason they released it early was to control the velocity difference between the probes. After launch, they found that then "redshift" of the radio waves fropm Huygens would shift the frequency beyond what Cassini would be able to lock on to. So by releasing early (at a greater distance), the frequency shift was small enough that Cassini could receive the signal. That was avery high priority!! <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

brellis · Jul 28, 2007

By "early" I mean why not learn more from a few Cassini flyby's, at least until after the first really close one two months later, before letting Huygens go. Huygens lasted much longer than the limited time during which Cassini did manage to receive its signal; perhaps they could have jiggered Cassini's path even better than they did. This is all just fun speculation on my part. The entire Cassini mission has been an astounding success, and the Huygens probe gave us very valuable data and images. From its launch in '97, I followed the status reports on the NASA site. The old status reports were so great to read. (I was just looking for them, they've disappeared from the Cassini page -- too bad!) They had a standard opening sentence like "the spacecraft is in excellent condition and all monitored systems are functioning normally." That was good to hear, since IIRC it has 7,000 - 'systems' wasn't the word they used - er, thingamajigs they were monitoring. When Cassini flew by earth in '99, a bunch of no-nuke protesters brayed loudly about the danger we faced if their telemetry was off and Cassini crashed back to earth. Those warnings resonated that year when both MCO and MPL were lost. Glad they didn't have any such confusion on this mission. Anyhoo, I'm a total Cassini-Huygens fan! <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

dragon04 · Jul 28, 2007

I don't know much about Rocket Science, but I assume that Cassini needs to fire its thrusters now and then to keep it on track for its fly-by's. If you add the mass of Huygens into the mix, I'd think more propellant would have been required for course adjustments, thereby shortening the length of the overall mission. Or am I wrong? <div class="Discussion_UserSignature"> "2012.. Year of the Dragon!! Get on the Dragon Wagon!". </div>

brellis · Jul 28, 2007

hi Dragon, Good point there 'bout carrying Huygens around. I recall reading somewhere that Cassini still has a bunch of fuel left. Trying to find it. Emily Lackdawalla's 27 June 2007 Planetary blog covers the topic of maneuvers. According to Cassini lead propulsion engineer Todd Barber, they recently accomplished their 100th successful trajectory change since launch -- congrats!! Here's a space.com article posing various scenarios for Cassini's final act. SDC has a thread asking how the mission might end - I'm going to add that thread to my fave's <img src="/images/icons/cool.gif" /> <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

3488 · Jul 28, 2007

Dragon04 is perfectly correct. The mass of Huygens attached to Cassini would have used more thruster fuel on board Cassini. The point of Huygens release was such, thast assuming a successful jettison, Newtonian laws would ensure Huygens arrival at Titan. The angle of approach was known by Cassini's position & heading, & the tiny gravitational influence of Iapetus, was taken into account (as Iapetus was not that far from Huygens flight path just post jettison). So really carrying Huygens around for longer than necessary was not a prudent thing to do. Also not only that, any fuel surplusses can be used for a scientifically rewarding extended mission. Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

MeteorWayne · Jul 28, 2007

Here's what I was talking about. "02 Jul 2001 The European Space Agency and NASA have identified a new mission scenario in order to solve the Huygens radio communications problem and fully recover the scientific return from the Cassini-Huygens mission to Saturn and its giant moon Titan. After six months of investigations and analysis by a Joint ESA/NASA Huygens Recovery Task Force (HRTF), senior management from the two space agencies and members of the Cassini-Huygens scientific community have endorsed several modifications to the mission. These will allow a return close to 100% of the Huygens science data, with no impact on the nominal prime Cassini tour after the third Titan encounter. The modifications have been introduced because of a design flaw in the Huygens communication system. This problem meant that the Huygens receiver was unable to compensate for the frequency shift between the signal emitted by the Probe and the one received by the Orbiter, due to the Doppler shift. (The Doppler shift is a measure of the difference in tone between an emitted and a received wave (for example, radio) when the transmitting source and the receiver move one with the respect to the other.) This would have resulted in the loss of most of the unique data returned from the Probe during its descent through Titans dense atmosphere. In order to ensure that as much data as possible is returned from the pioneering Probe, the Huygens Recovery Task Force proposed a new schedule for Cassinis first orbits around Saturn. The agreed scenario involves shortening Cassinis first two orbits around the ringed planet and inserting an additional orbit which provides the required new geometry for the Huygens mission to Titan. Under the new scenario, the arrival at Saturn on 1 July 2004 remains unchanged. However, Cassinis first flyby of Titan will now occur on 26 October, followed by another on 13 December. The Huygens Probe will <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

brellis · Jul 28, 2007

Thanks MW. Fuel is a precious commodity indeed. The new mission scenario will have some impact on Cassinis propellant supply, consuming approximately one quarter of the Orbiters estimated fuel reserve by the end of the four-year mission. Dragon remembered correctly, just dragging Huygens around for a couple of months spent a lot of surplus fuel. It was definitely worth it, though! btw, I'm now remembering which spacecraft still has quite a bit of fuel remaining: the Voyager craft are projected to have enough juice until at least 2020. Depending on where and when they send Cassini for her final act, the Voyagers might outlive the big Saturn bus! <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

3488 · Jul 30, 2007

Hi MeteorWayne, Yes, it was quite a serious clanger that had been dropped by ESA, for not ensuring that the receiver on board Cassini, could not cope with therange of Doppler changes, from Huygens. I was furious when that first leaked out, during the pre Saturn arrival tests that the two could not communicate. Is this the sort of thing that prelaunch tests should have ironed out? As MeteorWayne correctly said, they did find an ingenius solution. One problem I did hear about was because of the nature of the new line up, not only was an early release crucial, but Huygens did pass reasonably close to Iapetus post release. This was fortunately accounted for during the calculations. I know the other embarrassing thing was someone forgot to switch on the A channel of the reciever aboard Cassini. Good job the B channel was the default channel, so that was already on. All in all, a huge success, but very nearly did not happen. But then that is what a learning curve is. Hi brellis, yes that is quite an oxymoron,. The Voyagers have outlived Galileo & as you say, could well outlive Cassini too. AFAIK, the jury is still out on what to do with Cassini, when she can no longer return useful results & / or when the maneuvering thrusters get low on fuel. I have heard of three things. 1). Deorbit Cassini into Saturn (as had happened to Galileo at Jupiter). 2). Use several close Titan encounters, to allow Cassini to escape the Saturn system & to be put in a 'graveyord' orbit between Saturn & Uranus. 3). Similar to 2, but going the other way, to impact Cassini into Jupiter. Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

vogon13 · Jul 30, 2007

My rather dramatic choice for 'disposing' of Cassini is to use it to put a crater into Cassini Regio on Iapetus. Subsequent spacecraft to Saturn can observe the crater and study the thickness of the (presumed) coating and also observe if the dark material is 'reforming' or 'regenerating'. Having a subsequent rover explore the crater would be extremely interesting . . . If we have to dispose of Cassini, it might as well be put to use for one last experiment. <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

3488 · Jul 30, 2007

I second your proposal. Not only that Vogon13, if the cameras are still working, great approach shots, in real time, especially from the narrow angle!!!!!! Great idea, I like it. Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

vogon13 · Jul 30, 2007

Make it happen . . . <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

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