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Juno - Jupiter Orbiter
Guest_Analyst_*
post Mar 13 2007, 06:02 PM
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QUOTE (djellison @ Mar 12 2007, 01:56 PM) *
What I want to know is what the downlink will be like smile.gif


With 500 watts total power this should not be an issue during downlink. Voyager works today with less than 300 watts and has a quite powerful telecom system. With a 2.5m high gain it should be possible to have 32 to 64 kbits/s in X-band for Juno. Like New Horizons or better. Should give us some pictures smile.gif

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NMRguy
post Mar 13 2007, 10:03 PM
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As far as I can tell, the Juno team has always planned to include X-band radio frequency capabilities. Does the addition of the Italian Ka-band transponder add a new dimension to the gravity science experiment, or has NASA just outsourced development of that instrument to Italy?

In more general terms, there are a multitude of radio frequencies available for gravity science. Do most space agencies choose X and Ka-bands because of their extensive communications development and because they both just pass through the atmospheric radio frequency window, or are there additional reasons? [Ka-band seems to be the shortest wavelength to still transmit through the atmosphere.]

Finally, are Doppler shifts measured concurrently for both frequency bands to achieve signal redundancy, or can we actually improve signal to noise rations with a combined analysis (or something like that)?

Im really looking forward for this bird to get off the ground.
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edstrick
post Mar 14 2007, 09:35 AM
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Early deep space missions (not including REALLY early pre-Mariner stuff, which I think tended to use lower frequencies) used S-band. X-band and Ka-band let you focus your spacecraft transmitted power (say 20 watts RF) onto smaller and smaller targets surrounding the Earth. The beam-spots are essentially diffraction limited and cover a vastly larger area than the Earth. You just try to have pointing accurate enough that Earth is in the near-center of the beam-spot. The result of higher frequencies is more bits of data per transmitted watt per hour.

Drawbacks include more precise antenna pointing required at the spacecraft and opacity of heavy precipitation on Earth to the shorter wavelengths.

With 2 or 3 frequencies, you can play valuable games increasing precision in ranging and doppler measurements. Space is NOT empty, it contains ionized plasma, as does Earth's ionosphere, and planetary ionospheres crossed during radio occultations. Earth also has an atmosphere, containing various vertical temperature and humdity profiles. All these have effects on the radio transmission. With one frequency, you just model them as best as you can. With more frequencies, you can start to separate out plasma effects and atmosphere effects and maybe variable column water vapor abundance effects -- directly from the data.

Plasma/ionospheres have more effect at long wavelengths... look at HF (strong) VHF (usually weak) and UHF (minimal) ionosphere bounce of radio transmissions on Earth. Gasses have different frequency dependent effects. Mariner 5 carried a radio RECEIVER for a dual frequency occultation experiment at Venus. Stanford university transmitted a dual frequency carrier wave at the spacecraft which measured the signal strength (and maybe doppler shift, I can't remember) of each signal as it went behind the planet. JPL, meantime, did a Spacecraft-to-Earth S-band occultation like Mariner 4 did at Mars. It turned out the low frequency occultation data (C band? L band?) was so strongly refracted that below certain altitudes, refracted raypaths crossed and there were "caustiics"... mirages... in the signal and it could not be uniquely interpreted. Similar experiments have not flown since on deep space missions. It would still be useful for things like Io ionosphere and trace atmosphere occultations.
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Phil Stooke
post Mar 15 2007, 03:35 AM
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Ed, the Mariner 5 dual-frequency occultation experiment
involved one UHF and one VHF signal (can't remember their frequencies); and
the "phase" (ie. Doppler shift) of the signals was indeed measured along
with their signal strength. In fact this experiment was carried largely
because its phase-detection capability made it lots more sensitive to
electron layers in Venus' ionosphere than the S-band occultation was. (I
think I mentioned before that there was a feud over whether to carry this
experiment at all on that hastily jury-rigged planetary mission. JPL
recommended a copy of the Mariner 4 TV camera, with one visible and one UV
filter, instead; but NASA HQ overrode them. Decades later, I'm still seeing
fights over the decision in science papers.)


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edstrick
post Mar 15 2007, 08:31 AM
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I'm an images type of guy, but with 20-20 hindsight, I think the experiments were a tossup. A Mariner 4 type camera -- IF -- it could have taken full disk and quarter-disk photos might have given them a good first clue on the atmospheeric circulation, but a Mariner 4 type, kilometers resolution, single-image-swath across the disk would have been nearly useless.

Occultation was a completely new technique that had been tested once with spectacular results but was still underdeveloped. The Stanford experiment turned out to be rather redundant, but it was a learning experience.

And it gave confidence in the overall occultation results. Combined with the Venera-4 descent data (till it was crushed at about 25 atmospheres pressure), and an (at the time debated) correction to the Venera radar altimetry point, it fixed the radius of the planet and determined the probably atmosphere surface pressure and temperature.

With 20-20 hindsight, what ***I*** would have carried on Mariner 5 was a simple but scanned infrared radiometer. Similar to that on Mariner 6/7, 9 and 10 but with an internal stepper to scan a crude raster across the planet. Mariner 2 saw, in it's very limited zig-zag pass of the IR radiometer field of view (boresighted with the microwave radiometer), depressed temperatures at the now known location of the polar high-altitude ring-cloud that surrounds the double-vortex. They would have seen that and maybe other interesting structures, though in 10-20 micrometer IR, you don't see the atmosphere windows to under the clouds.
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tedstryk
post Mar 15 2007, 01:48 PM
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I would add that until Venus was nearly frame filling, it is questionable whether the data would have been able to tell us anything that we couldn't tell from earth (that Venus had some bright and dark clould markings in UV, but nothing about their nature).


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Guest_AlexBlackwell_*
post May 4 2007, 08:41 PM
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QUOTE (AlexBlackwell @ Jul 17 2006, 03:53 PM) *
Again, I apologize for reviving a dormant thread; however, has anyone noticed this particular Juno website?

Has anyone noticed this website has been updated? It now has a Juno favicon, too biggrin.gif

This post has been edited by AlexBlackwell: May 4 2007, 08:55 PM
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JRehling
post May 6 2007, 09:19 PM
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QUOTE (AlexBlackwell @ May 4 2007, 01:41 PM) *
Has anyone noticed this website has been updated? It now has a Juno favicon, too biggrin.gif


Someone with my math skills and slightly more gumption (hint-hint) might want to calculate the minimum distance between Juno's orbit and the big five satellites. It seems like we'll get a few snaps of the satellites, and I'm curious at what resolution. Sometime between now and 2016, it would be interesting to know that.
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edstrick
post May 7 2007, 07:43 AM
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"...Venus was nearly frame filling, it is questionable whether the data would have been able to tell us anything that we couldn't tell from earth ..."

Wrong. Earthbased data by the early 70's was poor due to seeing limitations and the need to image the atmospheric features at near UV wavelengths where seeing is worse than terrible even if it's pretty decent at near-IR/Red wavelengths. While the Mariner 4 camera was pretty limited, a well targeted series of UV images with the disk exactly filling the field of view would have provided a first real look at the cloud patterns.

But you're right after all...
My limited understanding was that any camera that might have flown on Mariner 5 would have been a minimally modified version of the Mariner 4 cam, including a 1 axis scan platform that could position the camera left-right (sort of) in azimuth as the spacecraft's trajectory took it's fixed-elevation narrow angle view across the planet. A dozen-ish frames of vague, low contrast streaky and mottled uv absorber features would have been a pretty minimal result for a major experiment. Whatever they are, the UV markings on Venus rapidly lose contrast as you zoom in on them for finer and finer details. 30% contrast at 100 km scale drops to say 3% contrast at 10 km and perhaps 0.3% contrast at 1 km scale. (I'm making up the numbers but they are the right sort of idea and probably in the ballpark estimates.)

They could see a persistent "Y" and "PSI" shaped cloud pattern aligned with the apparent equator and that it often repeated with about a 4 day period. Real cloud patterns and dynamics and meteorology was entirely beyond earthbased observation.

Mariner 10
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tedstryk
post May 8 2007, 01:45 PM
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Based on what I have read, the Mariner-R (the design that became Mariners 3-5), with the R standing for "runt," carried a camera that was designed primarily to test conditions for future cameras. One has to remember that the Mariner-R design being used in the 1964 launch was simply due to limited rocket capability. The originally planned probes would have had much better cameras. It was more of a backup that could be flown should they have to depend on the Atlas/Agena. And it served its purpose quite well - even beyond the light leak problem, the Martian surface proved to exhibit much less contrast than expected. This discovery aided Mariners 6 and 7. And of course it made interesting scientific discoveries, such as the lack of albedo/topographic correspondence on Mars, as well as the better known spotting of craters and pretty much killing the canals. But such images of cloudtops, while they would have been more detailed than those of earth, would, as edstrick indicated, not taught us all that much for a major experiment.


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Paolo
post May 8 2007, 06:33 PM
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QUOTE (tedstryk @ May 8 2007, 03:45 PM) *
Based on what I have read, the Mariner-R (the design that became Mariners 3-5), with the R standing for "runt,"


As far as I know, Mariner-R (for Ranger) were Mariner 1 and 2, Mariner 3-5 were originally called Mariner C, I think


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tedstryk
post May 8 2007, 08:27 PM
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QUOTE (Paolo @ May 8 2007, 06:33 PM) *
As far as I know, Mariner-R (for Ranger) were Mariner 1 and 2, Mariner 3-5 were originally called Mariner C, I think

Yes, you are right. Mariner-C was at times called "runt" as a pejorative. I made the mistake of linking this to Mariner-R. Oops.


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edstrick
post May 9 2007, 08:12 AM
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I have a xerox of an article from some journal like a major pub of the Geological Society of America or some such from the early 60's... maybe 1964 or 3. It's a carefully considered review of geological possibilities to look for during the exploration of Mars. It's thoughtful, well reasoned, raised essential questions regarding the possibility of finding folded mountain belts, volcanic features, erosional patterns.... etc. It totally missed the possibility of impact craters and the possibility of large areas with terrains that resulted from having minimal internal geologic activity for the majority of the planet's lifetime.

The overwhelming science results from Mariner 4 boiled down to three items.

1.) Some of the surface is REALLY old with lunar like cratering, probably impact craters. (whatever really old is).

2.) The surface pressure is confirmed by occultation to be at about 1/200'th atmosphere, as suggested by recent spectroscopy, and not the 1/10'th atmosphere most recent analyses had suggested the last couple <?> decades. Accordingly, the atmosphere must be mostly CO2 (enough to explain the spectra)

3.) There is minimal if any global magnetic field and thus no radiation belts. Thus the core is not molten or not driven to provide an active dynamo.


Pretty impressive results for such an early mission.
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JRehling
post May 10 2007, 08:31 PM
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QUOTE (JRehling @ May 6 2007, 02:19 PM) *
Someone with my math skills and slightly more gumption (hint-hint) might want to calculate the minimum distance between Juno's orbit and the big five satellites. It seems like we'll get a few snaps of the satellites, and I'm curious at what resolution. Sometime between now and 2016, it would be interesting to know that.


I finally took the leap.

For the Galileans, Juno's closest flyby possibilities will be as it flies directly over one pole on the apojove portion of the orbit. Those distances are:

Io: 264,000 km
Europa: 355,000 km
Ganymede: 444,000 km
Callisto: 408,000 km

Amalthea will be closest, potentially, at perijove, at 105,000 km. Amalthea's distance from the polar looking view will be as little as 150,000 km.

Io and Europa's encounters will be about as far as Cassini was from Dione when THIS

http://photojournal.jpl.nasa.gov/jpeg/PIA08856.jpg

images was snapped. Of course, the Galileans are much bigger than Dione.

We should get some nice satellite images from JunoCam...
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volcanopele
post May 10 2007, 08:43 PM
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What's the field of view of JunoCam and what is the size of an image?


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