Rosetta, Philae and Comet 67P/Churyumov-Gerasimenko.

[Geneborg]

Laser communication is in experimentals, as far as i know they have done some successful tests form orbit, thats about it. All space communication is slow, and its far from trivial. But thats outside of common knowledge of course, ppl think they have far better stuff then we have on our cellphones...thats not the case, spacetech usually lags 10 years behind, rosetta was launched 10 years ago, meaning the tech is 15-20 years behind from what we have NOW

[K^2]

Is this is purely a power usage concern? Couldn't they use direct laser communication for both things? (Would that require a dedicated new satellite?)

It basically is, and laser would make it way worse. Not only wouldn't it improve your ability to direct a beam from that distance, but you'd be losing a whole bunch of power in conversion.

[O-Doc]

I think GregA believes that Philae and Rosetta will find evidence to support electric universe theory, and that this will unlock secrets to such things as dark matter. Just smile and nod...

I agree. Clearly what we are seeing in this picture is rotten ice.

[eRe4s3r]

Thank you both, gotta admit that puts the images we have and the speed of information delivery into perspective o.O

[Kinglet]

Philae is asleep. The power reserves were exhausted during the last data transmission to earth, and the solar panels are in the shade.

[GoSlash27]

*snip* So at 20m, you'll be expecting ~4nW of power, which seems like too weak of a signal to detect.

K^2,

I'm an avionics tech and we play around with these sorts of figures all the time. I have no idea what signal levels are expected in this case, but I do know that a decent antenna and receiver can easily pick up a signal at 4nW. That's about -54dBm. I have worked on TACAN receivers using 1/4 wave antennas that need to be intentionally adjusted to reject signals below -98dBm, since it could potentially cause navigation errors. That's down in the hundreds of femtowatts range.

The GPS receiver in your phone can detect signals down to -125 dBm or even lower.

HTHs,

-Slashy

Edited November 16, 2014 by GoSlash27

[Aningaaq]

Well, I found this excellent paper about the CONSERT: ftp://ftp.eorc.jaxa.jp/cdroms/EORC-061/data/f_papers/ceos006.pdf

I can't understand half of it but it might be enlightening to some of you.

[K^2]

K^2,

I'm an avionics tech and we play around with these sorts of figures all the time. I have no idea what signal levels are expected in this case, but I do know that a decent antenna and receiver can easily pick up a signal at 4nW. That's about -54dBm. I have worked on TACAN receivers using 1/4 wave antennas that need to be intentionally adjusted to reject signals below -98dBm, since it could potentially cause navigation errors. That's down in the hundreds of femtowatts range.

The GPS receiver in your phone can detect signals down to -125 dBm or even lower.

HTHs,

-Slashy

Unexpected. But thanks for making me work through some of these. I guess, I was expecting cosmic background and/or solar to be more significant. As it turned out, the entire band of solar radiation from 86MHz to 94MHz only adds up to 1.1x10^-13W/m². The base sensitivity of instrumentation wasn't really a question in my mind.

The GPS being able to pick up a fraction of pW/m² is really impressive. How is that not drowned out in all sorts of noise?

[vitekc45c]

Just in case anyone has trouble imagining the size of 67P

[Technical Ben]

Unexpected. But thanks for making me work through some of these. I guess, I was expecting cosmic background and/or solar to be more significant. As it turned out, the entire band of solar radiation from 86MHz to 94MHz only adds up to 1.1x10^-13W/m². The base sensitivity of instrumentation wasn't really a question in my mind.

The GPS being able to pick up a fraction of pW/m² is really impressive. How is that not drowned out in all sorts of noise?

Short answer? Maths.

Long answer? (I've no idea, but could not resist the joke... sorry. I know you know much more about it than I do! )

More seriously, as far as I know, a lot of signal processing is done these days to remove "noise" and find a signal. Are they using just maths and signal processing here?

Edited November 16, 2014 by Technical Ben

[lajoswinkler]

Just in case anyone has trouble imagining the size of 67P

https://scontent-b-cdg.xx.fbcdn.net/hphotos-xap1/t31.0-8/s960x960/1962154_1521814644742572_3694304396633875450_o.jpg

Because those things' sizes are obvious to anyone.

[GoSlash27]

Unexpected. But thanks for making me work through some of these. I guess, I was expecting cosmic background and/or solar to be more significant. As it turned out, the entire band of solar radiation from 86MHz to 94MHz only adds up to 1.1x10^-13W/m². The base sensitivity of instrumentation wasn't really a question in my mind.

The GPS being able to pick up a fraction of pW/m² is really impressive. How is that not drowned out in all sorts of noise?

I actually know the answer to this, but it's pretty far off- topic. The short version is that the GPS signal is below the noise floor. Rather than detecting the signal itself, the receiver detects the signal's effect on the randomness of the background noise.

Longer version:

As a crude example, say the background noise floor is a series of coin flips. We sample 1,000 flips and expect 500 heads if there's no signal, and our signal might skew that a bit, like 524 heads.

If we get a result that's consistently non- random, then we lock onto the frequency and start tracking whether we're getting more heads or more tails. We expect the results to flip heads to tails or vice-versa at regular intervals and we compare how accurately the changes track with each of our satellite's unique fingerprint (the PRN code).

When we get an exact match, we know which satellite we have and we know that it's telling us a data "1". If our result is exactly wrong, OTOH, we know that it's the same satellite, but it's sending us a data "0" because the satellite sends zeroes by inverting it's PRN code.

That's the gist of how the receiver works. If you want to know how we work out all our fancy results from that, hit me up on PM. I don't mind sharing it, but it's way off- topic for this thread.

Best,

-Slashy

Edited November 16, 2014 by GoSlash27

[GregA]

I think GregA believes that Philae and Rosetta will find evidence to support electric universe theory, and that this will unlock secrets to such things as dark matter. Just smile and nod...

You don't have to go full electric universe theory to suggest that space has an electrical charge.

For example, here is a peer reviewed paper published in a scientific journal that is admittedly a preliminary discussion on the matter. But then, it has never been explored before.

http://arxiv.org/abs/1409.3096

It is a really simple to understand theory as well. The chaos of the galactic core ejects negatively charged protons giving the galaxy an overall charge. The same process happens with the solar wind from the sun, giving the outer solar system a negative charge. Comets after spending millions or billions of years in the interstellar spaces of the galaxy develop massive negative charge, as they approach suns, they become anodes resulting in the coma and tail.

[Kryten]

That would explain why Philae was immediately destroyed by massive electrical discharge upon touching down.

[GregA]

That would explain why Philae was immediately destroyed by massive electrical discharge upon touching down.

Yes, because aerospace engineers have no concept of electrical charges potential to damage their craft. Thats why launch pads are not surrounded by lighting suppressors, airplanes don't universally have static discharge antennas, and the Pioneer space craft is not anomalously accelerating exactly as predicted by these models.

/rolls eyes

[Kinglet]

That would explain why Philae was immediately destroyed by massive electrical discharge upon touching down.

Ironically, it's doomed right now because of the exactly opposite reason: Low electric charge.

[GregA]

Ironically, it's doomed right now because of the exactly opposite reason: Low electric charge.

Boy it sure would be neat if future comet explorers just needed to erect an antenna a few dozen feet to get unlimited electric charge while they were in inner solar system.

[Technical Ben]

... snip mid blowing stuff...

Best,

-Slashy

Wow, nice. It's kinda "on topic" in that no doubt such ideas still work with space exploration and getting a signal back when it's really hard (Voyager perhaps?). I think they also use similar ideas in particle detectors and other statistical analysis of data. I may have seen a post about the GPS before, but had forgotten. Thanks for the info.

[Kryten]

Yes, because aerospace engineers have no concept of electrical charges potential to damage their craft. Thats why launch pads are not surrounded by lighting suppressors, airplanes don't universally have static discharge antennas, and the Pioneer space craft is not anomalously accelerating exactly as predicted by these models.

'Pioneer anomaly' is due to asymmetric radiation of heat, the rest has nothing to do with this. Philae doesn't have lightning suppressors or lightning discharge antennae last time I checked, there should have been a massive, damaging discharge if your model was right. There wasn't.

[GregA]

'Pioneer anomaly' is due to asymmetric radiation of heat, the rest has nothing to do with this. Philae doesn't have lightning suppressors or lightning discharge antennae last time I checked, there should have been a massive, damaging discharge if your model was right. There wasn't.

Heh, look again at the harpoons that failed to fire. See all that fibrous metal? This is about perfect if you wanted to make a static charge suppressor.

LOL.

[Kryten]

I'm starting to think you don't know what any of these words mean. You claim the comet is very highly negatively charged. There is no mechanism for Philae and/or Rosetta to have achieved the same level of charge. Uncharged object+massively charged object, negatively or positive=Zap. A 'static charge suppressor' would make this situation worse, not better.

[GregA]

'Pioneer anomaly' is due to asymmetric radiation of heat, the rest has nothing to do with this. Philae doesn't have lightning suppressors or lightning discharge antennae last time I checked, there should have been a massive, damaging discharge if your model was right. There wasn't.

There is a theory. The experiment has neither a control nor has it been rigorous at this point. We will have a better idea once New Horizons is on its way out of the Solar System.

[Technical Ben]

That would have made a "bang" in the news had there been a static charge. I doubt most of the equipment would transmit or work.

[Kryten]

There is a theory. The experiment has neither a control nor has it been rigorous at this point. We will have a better idea once New Horizons is on its way out of the Solar System.

When a better model of the radiation is applied, the effect goes away; we don't need a control for that, any more than we need a control to show the discrepancies in the precession of Mercury are explained by GR.

[GregA]

I'm starting to think you don't know what any of these words mean. You claim the comet is very highly negatively charged. There is no mechanism for Philae and/or Rosetta to have achieved the same level of charge. Uncharged object+massively charged object, negatively or positive=Zap. A 'static charge suppressor' would make this situation worse, not better.

http://www.freepatentsonline.com/3968405.pdf

There you go a "static electricity suppressor" patent for. An antenna witch relieves built up charge.

I am starting to think you are just playing semantic games, and are not actually interested in a discussion.