Deep-space communications relay stations

[adoucette]

Are you also getting a lot of static from Voyager, now that it's 110 AU away from us?

No

How easy is it to listen to a radio station broadcasting from Los Angeles if your radio is in New York City?

Different conditions, radio bands and technologies entirely.

This is a radio tower and it broadcasts in 360 degrees.

We listen to Voyager with the Deep Space Network, using 70 meter antenna.

Voyager broadcasts in the X-Band on a 3.7 meter high gain DIRECTIONAL antenna. (Voyager also listens to us on the S-Band)

And we are doing it at ~113 AUs from Earth and at only about half the original power (nominal about 200 watts are available for transmitting now)

It is much much further than the distances you have been discussing and so it appears you are trying to solve a problem that doesn't actually exist.

Arthur

 

[Rhaedas]

I agree that the problem isn't one we have yet. Relay satellites won't be used for talking to probes, but rather facilitating communication between two points that both cannot broadcast strong enough signals or receive weak ones. Exactly why we have cell towers, but didn't before we had cell phones, or communication satellites in geosyn orbit.

 

[leopold]

I didn't "miss" it, I simply made an amateur calculation that the benefit of a multi-watt communication of data outweighed the slight loss of time involved in the use of a network of comm satellites.

you missed my point.
i am not talking about propagation delay (the time needed to pass through the relay).
i am talking about the hours needed for EM waves to traverse the distance to the probe.

Here's the bottom line, as far as I'm concerned. If a deep-space probe arrives at its' destination and gets more static on it's comm link to us than useful information (like course changes or changes to its' computer program), or if it puts out more static than useful data from it's experiments, what good is it?

NASA gets around this by sending data in triplicate.
this reduces the bandwidth but it does allow reasonable accuracy.

 

[BennyF]

a further refinement of my original idea

"Here's the bottom line, as far as I'm concerned. If a deep-space probe arrives at its' destination and gets more static on it's comm link to us than useful information (like course changes or changes to its' computer program), or if it puts out more static than useful data from it's experiments, what good is it?"

- me, yesterdeay

you missed my point.
i am not talking about propagation delay (the time needed to pass through the relay).
i am talking about the hours needed for EM waves to traverse the distance to the probe.

NASA gets around this by sending data in triplicate.
this reduces the bandwidth but it does allow reasonable accuracy.

Then I think that a comm link (aka "deep-space communications relay station") would improve the accuracy of the data at a cost of launching the relay station and maybe having it malfunction or be damaged by a comet. This cost would, in my opinion, be outweighed by the benefit of a better signal-to-noise ratio.

I have another refinement of my original idea, too. When a deep-space probe is launched, NASA sends out a signal to whichever relay satellite will be closest to it when the probe arrives at the destination. This signal tells the relay satellite to turn on its' own propulsion system and to plot a course for a spot near the probe's destination. If the probe will be headed for a spot beyond Saturn, the signal may have to go through a chain of relay satellites before it reaches the last comm link, but passing information from one comm link to another one is what they are designed and built to do.

When the probe arrives at its' destination, there's a nuclear-powered relay station waiting for it, close enough to ensure more accuracy in its' signal-to-noise ratio than the probe could alone. If technology has advanced enough to permit a transfer of energy from the nuclear-powered comm link to the battery-powered probe, then such a transfer is made.

After the two satellites have "shook hands", the probe conducts its' experiments. When they're finished, if the probe has a secondary destination, the comm link does another energy transfer and the probe starts moving towards it . If not, the comm link simply turns on its' own propulsion system and moves back to its' original position.

At no time during this "meeting" do the two satellites have to dock. They just have to be close enough so that the distance from the comm link, the one with the nuclear power supply and a laser beam output, to the probe, the one that is equipped with a set of batteries and the technology to accept a laser beam input, can be small enough to result in a minimum threshold of accuracy in aiming the laser beam and hitting the target.

 

[adoucette]

Again you are solving a problem that doesn't exist.

More to the point, you are adding significant expense and complexity into a system that is working just fine without it.

Voyager, using technology from 40 years ago communicates with us daily from a distance of over 110 AU, it is past all the planets and is in the process of leaving the Solar System behind. We talk to it each day even though it takes 32 hours for signals to transverse that huge distance.

http://www.jpl.nasa.gov/news/news.cfm?release=2011-128

A more modern spacecraft, Cassini orbits Saturn at ~10 AUs from the Earth or nearly a billion miles, and gives us an enormous amount of data:

http://www.tecca.com/news/2011/03/15/saturn-fly-by-video/

See any problem with Signal to Noise?

Arthur

 

[BennyF]

A more modern spacecraft, Cassini orbits Saturn at ~10 AUs from the Earth or nearly a billion miles, and gives us an enormous amount of data:

http://www.tecca.com/news/2011/03/15/saturn-fly-by-video/

See any problem with Signal to Noise?

Arthur

I own a number of calendars with photographs made by Ansel Adams. They're beautiful to look at, and some of the prints made by him directly from his own negatives have sold at auction for thousands of dollars. These are just black-and-white photographs of southwestern landscapes.

Only people who have carried a groundglass view camera on their back (like me) can appreciate the effort it can take to make a photograph like that, and only people who have worked in a black-and-white darkroom (like me) can appreciate how much effort it can take to produce something that beautiful from large and sometimes imperfect black-and-white negatives, especially when some of his negatives measured eight inches wide and ten inches long. That was the measurement for just one negative, and he carried several in individual light-proof negative carriers. I used similar light-proof negative carriers, but my negatives only measured four inches wide and five inches long, but I still had to deal with imperfect images when I got them back into the darkroom.

It wouldn't surprise me one bit if the images from Voyager looked very different when they first arrived than the way they do in the animation you kindly linked to.

 

[adoucette]

I own a number of calendars with photographs made by Ansel Adams. They're beautiful to look at, and some of the prints made by him directly from his own negatives have sold at auction for thousands of dollars. These are just black-and-white photographs of southwestern landscapes.

Only people who have carried a groundglass view camera on their back (like me) can appreciate the effort it can take to make a photograph like that, and only people who have worked in a black-and-white darkroom (like me) can appreciate how much effort it can take to produce something that beautiful from large and sometimes imperfect black-and-white negatives, especially when some of his negatives measured eight inches wide and ten inches long. That was the measurement for just one negative, and he carried several in individual light-proof negative carriers. I used similar light-proof negative carriers, but my negatives only measured four inches wide and five inches long, but I still had to deal with imperfect images when I got them back into the darkroom.

Again, totally different technology.
None of these probes use film, they use CCD senors, and the data is in digital format.
So now digital images of interesting events can go VIRAL and be forwarded from person to person to person, such that when you get it, it may have been forwarded 100 times, and yet it is IDENTICAL to the original.

It wouldn't surprise me one bit if the images from Voyager looked very different when they first arrived than the way they do in the animation you kindly linked to.

First of all those pictures were from Cassini, second of all we live in a digital world and we know how to send data, even compressed, with NO LOSS and we can send authentificaton data to be sure that what is received is what was sent.

http://en.wikipedia.org/wiki/Lossless_JPEG
http://www.google.com/patents?hl=en...rection&printsec=abstract#v=onepage&q&f=false

Those pictures of Saturn are exactly what Cassini took.

Arthur

 

[BennyF]

Again, totally different technology.
None of these probes use film, they use CCD senors, and the data is in digital format.
So now digital images of interesting events can go VIRAL and be forwarded from person to person to person, such that when you get it, it may have been forwarded 100 times, and yet it is IDENTICAL to the original.



First of all those pictures were from Cassini, second of all we live in a digital world and we know how to send data, even compressed, with NO LOSS and we can send authentificaton data to be sure that what is received is what was sent.

http://en.wikipedia.org/wiki/Lossless_JPEG
http://www.google.com/patents?hl=en...rection&printsec=abstract#v=onepage&q&f=false

Those pictures of Saturn are exactly what Cassini took.

Arthur

I own a film camera (Minolta SR-T model, almost as old as I am) and a digital camera. Believe me, I know the difference between the two technologies. I'm glad the data transmission technology is so advanced that you can check it to make sure that it's accurate.

I still worry, as an amateur, about the "noise" that could potentially interfere with the signals that are sent to and from any deep-space probe, something that is so far away from us, the distances must be measured in astronomical units. What sources of noise exist in our solar system, and does their existence affect NASA's choices for mission locations or travel routes?

Benny, a pseudonym, chosen to honor Mr. Franklin



P.S. I have an unfinished patent application on my computer. If it's approved, I believe it will be placed into Class 320, Subclass 166, the class and subclass for charging a capacitor.

 

[adoucette]

I own a film camera (Minolta SR-T model, almost as old as I am) and a digital camera. Believe me, I know the difference between the two technologies. I'm glad the data transmission technology is so advanced that you can check it to make sure that it's accurate. [/quota]

Deep space transmission of software updates to probes couldn't be done without it, but it's something NASA routinely does.

I still worry, as an amateur, about the "noise" that could potentially interfere with the signals that are sent to and from any deep-space probe, something that is so far away from us, the distances must be measured in astronomical units. What sources of noise exist in our solar system, and does their existence affect NASA's choices for mission locations or travel routes?

Doesn't appear to be an issue.

Arthur

 

[leopold]

First of all those pictures were from Cassini, second of all we live in a digital world and we know how to send data, even compressed, with NO LOSS and we can send authentificaton data to be sure that what is received is what was sent.

http://en.wikipedia.org/wiki/Lossless_JPEG
http://www.google.com/patents?hl=en...rection&printsec=abstract#v=onepage&q&f=false

compressing an image with no loss is not the same as transmitting that image with no loss.

i do not think NASA will go the "checksum" route to insure data validity because of transmission time.
the major snafu will be in course corrections.
pictures and other data such as magnetometer readings probably will not be affected like course corrections would.

interesting subject actually.

 

[adoucette]

compressing an image with no loss is not the same as transmitting that image with no loss.

i do not think NASA will go the "checksum" route to insure data validity because of transmission time.
the major snafu will be in course corrections.
pictures and other data such as magnetometer readings probably will not be affected like course corrections would.

interesting subject actually.

But when you compress a digital image and then you get data corruption, the image becomes useless.

Clearly looking at the Cassini imagaes that's not the case.

Clearly NASA is not having a problem sending or receiving accurate data from exceedingly long distances.

 

[MacGyver1968]

Other than the sun...what other sources of potential interference are there in the solar system that could affect transmission?

 

[leopold]

Other than the sun...what other sources of potential interference are there in the solar system that could affect transmission?

attenuation of signal will account for most of the problem.
radio noise from other objects such as black holes and the planets themselves.
jupiter is a strong radio emitter.
when the signal strength drops to about the radio noise level is when you start having problems.
the only real solution in my opinion would be triple or even quadruple transmission.

 

[leopold]

But when you compress a digital image and then you get data corruption, the image becomes useless.

not necessarily useless.
a few pixels dropped or miscalculated will not render a picture useless.

 

[billvon]

It wouldn't surprise me one bit if the images from Voyager looked very different when they first arrived than the way they do in the animation you kindly linked to.[/SIZE][/FONT]

Digital images look exactly the same before and after transmission. Error detection and correction protocols ensure this.

 

[adoucette]

not necessarily useless.
a few pixels dropped or miscalculated will not render a picture useless.

Really?

Make a copy of a JPEG image. (Don't do the following except to the copy!)

Open the Copy with your favorite JPEG viewing program, and amire the image.

Close the file.

Take Notepad and set it to "all files" and open the copied JPEG image.

Randomly change ONE byte within it to a space.

Save the file with the one byte changed.

Try to open the copy with your JPEG viewing program.

Arthur

 

[adoucette]

For those who are interested:

NASA's Exploration and Space Communications (ESC) Division at Goddard Space Flight Center

http://esc.gsfc.nasa.gov/157.html

 

[Rhaedas]

Really?

Make a copy of a JPEG image. (Don't do the following except to the copy!)

Open the Copy with your favorite JPEG viewing program, and amire the image.

Close the file.

Take Notepad and set it to "all files" and open the copied JPEG image.

Randomly change ONE byte within it to a space.

Save the file with the one byte changed.

Try to open the copy with your JPEG viewing program.

Arthur

Not saying your point isn't a good one, but I also don't think they use JPG format, and given they have experts at image processing, they probably use a format that wouldn't break like that.

 

[leopold]

Really?

Make a copy of a JPEG image. (Don't do the following except to the copy!)

Open the Copy with your favorite JPEG viewing program, and amire the image.

Close the file.

Take Notepad and set it to "all files" and open the copied JPEG image.

Randomly change ONE byte within it to a space.

Save the file with the one byte changed.

Try to open the copy with your JPEG viewing program.

Arthur

probably some sort of thing microsoft built into windows.

take the same image in paint and make a few random changes to various pixels and the picture is still discernible.
as a matter of fact you will be surprised at how many pixels you can change and still be able to discern the image.

 

[adoucette]

probably some sort of thing microsoft built into windows.

take the same image in paint and make a few random changes to various pixels and the picture is still discernible.
as a matter of fact you will be surprised at how many pixels you can change and still be able to discern the image.

Not the same thing.

One is dealing with an uncompressed image and simply changing a few pixels in the visible image.

The other is changing data in a data stream (same as errors in the transmission) that causes the decoding algorithm to fail completely.

The point is, we KNOW how to transmit digital data and ensure that what we received is what we sent.

The digital age we live in sorta relies on that and NASA has known how to do that for decades.

Arthur