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In article . com,
"dexx" wrote: Is it true that Huygens ceased transmission less than 2 hours after touchdown? Whilst it was a magnificent achievement to travel so far and land perfectly, it seems a great shame that the probe was so short lived. I'm suprised the designers didnt make it rugged enough and powered enough to survive several days. You need to understand the mission a little more. The probe was designed to measure the atmosphere on Titan. The landing part was a bonus. The probe ran on batteries. Batteries only last so long, especially in the cold. To make the probe run much longer, it would have required an RTG (nuclear battery). That would have made the probe far heavier, causing all kinds of mission compromises from launch, number of instruments, and its chances of survival coming through the atmosphere. Next, the probe only had so much power, so it needed the Cassini to record the data and retransmit it back to earth. Cassini was moving, and it was out of view of the probe within 2 hours of the probe landing. There was no easy way to keep Cassini in view of Titan for much longer without totally redesigning the Saturn mission. As it is, the probe worked great and proved the technology. There isn't too much more the Cassini/Huygens team could have gotten without doing a much more complex mission that would have sampled the surface looking for life. Maybe next time. -john- -- ================================================== ==================== John A. Weeks III 952-432-2708 Newave Communications http://www.johnweeks.com ================================================== ==================== |
#12
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"dexx" wrote in message ups.com... Is it true that Huygens ceased transmission less than 2 hours after touchdown? Whilst it was a magnificent achievement to travel so far and land perfectly, it seems a great shame that the probe was so short lived. I'm suprised the designers didnt make it rugged enough and powered enough to survive several days. Cassini will not return to Titan for about a month as it is in orbit round Saturn, not the moon. With a given mass budget, you have to trade off more batteries against losing an instrument. The optimum design was probably to last as long as Cassini would be above the horizon plus a little bit spare. George |
#13
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"dexx" wrote in message ups.com... Is it true that Huygens ceased transmission less than 2 hours after touchdown? Whilst it was a magnificent achievement to travel so far and land perfectly, it seems a great shame that the probe was so short lived. I'm suprised the designers didnt make it rugged enough and powered enough to survive several days. There is also the issue that transmission had to be relayed via the Cassini spacecraft - meaning that Cassini had to be close to Titan and also had to be above the horizon as fas as Huygen is concerned If you have a look at the animation applet on the ESA website http://www.esa.int/SPECIALS/Cassini-...6E2VQUD_0.html you can see that Cassini's path isn't really favourable for that. I reckon the 'above the horizon' condition won't be met for almost 2 weeks, by which time Cassini will be about 2 million miles from Titan. The next Titan flyby isn't until 15th Feb. |
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"dexx" wrote:
Is it true that Huygens ceased transmission less than 2 hours after touchdown? Whilst it was a magnificent achievement to travel so far and land perfectly, it seems a great shame that the probe was so short lived. I'm suprised the designers didnt make it rugged enough and powered enough to survive several days. Well, all that costs weight, and the probe was designed to be an _atmosphere_ probe, not a surface rover. Unlike you, the ESA community were overjoyed with the two hour survival, they'd planned for three _minutes_ of surface lifetime. And now that the space explorer types have pulled this one off in such grand style [my message to them was "please accept a standing ovation from the entire planet"], can't you hear them planning to drop a "ruggedized Huygens" into the atmosphere of one of the gas giants? Or is that probe already en route? xanthian. -- Posted via Mailgate.ORG Server - http://www.Mailgate.ORG |
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On 16 Jan 2005 06:18:31 -0800, dexx wrote:
Is it true that Huygens ceased transmission less than 2 hours after touchdown? Whilst it was a magnificent achievement to travel so far and land perfectly, it seems a great shame that the probe was so short lived. I'm suprised the designers didnt make it rugged enough and powered enough to survive several days. Even if it had more power the signal has to be relayed to Cassini. Cassini kept it's focus on the Huygens probe for 2 hours then turned toward earth to relay the temetry. Form earth you could barely pick up the carrier signal. Since Cassini continues on it's route through the saturnian system you wouldn't be able to get a continuous transmission anyhow. Besides the most important part of the mission was a spectral analysis of Titan't atmosphere. The surface pictures were really just gravy. -- Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/ |
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Terrell Miller wrote:
dexx wrote: Is it true that Huygens ceased transmission less than 2 hours after touchdown? Whilst it was a magnificent achievement to travel so far and land perfectly, it seems a great shame that the probe was so short lived. I'm suprised the designers didnt make it rugged enough and powered enough to survive several days. one design limitation factor was the length of time that Cassini would be "over the horizon" wrt the lander. Huygens doesn't have powerful enough transmitters to relay the datastream directly to Earth, so having longer batt life wouldn't do anything but waste money and resources if it couldn't see its mothership and thus transmit data. Building enough transmitter power to send to Earth directly would very likely have major scalability issues, which in turn would have a direct impact on other mission profiles (maybe they could have had a powerful transmitter but little or no instrumentation to feed it data, f'rinstance). Mission planning for any tpye of space vehicle is a series of tradeoffs between various things: time, money, propellant, payload, *type* of payload, mission duration, mission capability, etc. etc. Bottom line: for any launcher and any vehicle and any mission profile, there's only so much you can include. Add more of thing X and you have to take away from things Y, Z and A'. Perhaps more importantly, the more things you put in, the more effort to integrate it all, the more effort needed to shave weight, and the more potential for a mission-threatening screwup. How many missions have failed, or even failed to get funded, because they were too ambitious? -- John Halpenny A cluttered desk is the sign of a cluttered mind. I’m so glad my desk isn't empty. |
#17
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"OG" wrote in message ... May I just briefly say that when I started replying this thread only had 1 reply ;-) OG |
#18
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They were hoping for ~30 minutes of surface
data; I believe some early predictions said only a few seconds. Ben |
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dexx wrote:
Is it true that Huygens ceased transmission less than 2 hours after touchdown? Whilst it was a magnificent achievement to travel so far and land perfectly, it seems a great shame that the probe was so short lived. I'm suprised the designers didnt make it rugged enough and powered enough to survive several days. A lot of people have responded already, but I haven't seen the single most critical point made yet. There was no certainty as to what type of surface lay under the clouds. We knew there were light and dark areas, what the temperature and pressure probably were. But we didn't know if it was liquid or solid, how much topology was there, whether it was smooth or rough with rocks or ice boulders, etc. Designing a probe to survive the landing with high confidence, across the wide range of possible conditions, was just too hard. ESA weren't entirely sure if Huygens was going to survive landings on soil, rocks, or liquid surface anyways. One of Ralph Lorenz' early focus areas was a paper quantifying the impact parameters and survival chances for the various possible impact surfaces. See: http://www.lpl.arizona.edu/~rlorenz/huygensimpact.pdf -george william herbert |
#20
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Henry Spencer wrote:
[snip] It would have greatly increased the cost and complexity, unfortunately, because it would almost certainly have required an RTG. Moreover, several days is not enough -- it'll be a month or two (I forget exactly) before Cassini goes past Titan again. You can't really do a long-lived Titan surface mission without better communications support, that is, either a Titan orbiter or a lander that's big enough and heavy enough to carry its own high-power transmitter and steerable high-gain antenna (plus the power source needed to run them). To be fair, an RTG powered lander might very well have had enough power to send data directly back to Earth. At low bit rate certainly, but probably fast enough to be workable. Galileo was able to operate at pitiful data rates, with spectacular results, for example. However, the surface science capabilities of the probe didn't justify massive expenditures to increase the return for that portion of the mission. A new probe with different instruments and a different design, perhaps, but not Huygens. Also, I believe that it would have been enormously difficult to design Huygens and provide a large enough RTG to keep it operating in the event of a landing in liquid hydrocarbons, which was, and still is, a substantial possibility for a Titan lander. Considering how long ago Huygens was built, and that it was the first foray into a virtually unknown world, I think it did spectacularly well. We can do better next time, but partly that's because of the extraordinarily valuable data Huygens has provided. |
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