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Mars to Earth at an average of 29 kbits/s

mars.jpl.nasa.gov

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Re: Mars to Earth at an average of 29 kbits/s

#71

Post by [deleted] »

hrayr wrote: post #16
Achshar wrote: post #11

Earlier quoted context omitted.

> It's awesome that they've been involving the public so much in the details of how the rover mission really works. It must be mission critical to spread awareness since their budget cuts are getting worse and one way to correct that is to get people excited about space exploration. They now put a considerable effort in PR, involving people in the mission, sharing most of the information and making professional video…

"And curiosity was named after an essay written by a student in a competition organised by NASA for school students." Nasa has been doing this for some time now, Sojourner[1], and MERs (Spirit & Opportunity) have also been named by student competitions. [1] http://mars.jpl.nasa.gov/MPF/rover/name.html

[deleted]

Re: Mars to Earth at an average of 29 kbits/s

#73

Post by alinajaf »

eupharis wrote: post #65
mkramlich wrote: post #64

Earlier quoted context omitted.

> In particular, we are going to need to have a local cache of the internet on Mars. I predict somewhere today at Google an engineer just got an idea for his 20% project. "Red Cache"

I hope so. The trick would be, after there is a cache of the Internet on Mars, to only have to send the changes, not the whole Internet again. Straight snapshots would probably be the only viable option though. And maybe make the policy, once a decade do a complete update. And every year, do "any webpage accessed by colonists in the past year will be updated. And the top 5-15% of webpages by popularity on Earth." And…

The only thing your plan doesn't account for is how we get the updates from the web developers on Mars :-)

Re: Mars to Earth at an average of 29 kbits/s

#75

Post by [deleted] »

nitrogen wrote: post #56
pothibo wrote: post #51

Earlier quoted context omitted.

We're not talking about your average data. We're talking about optimized data. Of course there's an overhead. EDIT: removed specific type of data

I'm not sure what you mean by "optimized" data. Edit: my very rudimentary understanding of information theory tells me that there's no "average" or "optimized" data, only varying amounts of entropy (AKA compressibility). My limited knowledge of radio and electrical transmission says that transmitted data is encoded to make effective use of the transmission medium (e.g. 8b/10b encoding, 8-to-14 modulation, TMDS). So,…

[deleted]

Re: Mars to Earth at an average of 29 kbits/s

#76

Post by pothibo »

nitrogen wrote: post #56
pothibo wrote: post #51

Earlier quoted context omitted.

We're not talking about your average data. We're talking about optimized data. Of course there's an overhead. EDIT: removed specific type of data

I'm not sure what you mean by "optimized" data. Edit: my very rudimentary understanding of information theory tells me that there's no "average" or "optimized" data, only varying amounts of entropy (AKA compressibility). My limited knowledge of radio and electrical transmission says that transmitted data is encoded to make effective use of the transmission medium (e.g. 8b/10b encoding, 8-to-14 modulation, TMDS). So,…

At first, I wouldn't have thought that they would use encoding to maximize efficiency. But now that I think about it, their goal isn't efficiency but rather consistency. So yeah I was wrong.

Maybe I thought this was more primitive than what it really is :/

Re: Mars to Earth at an average of 29 kbits/s

#77

Post by nitrogen »

pothibo wrote: post #76
nitrogen wrote: post #56

Earlier quoted context omitted.

I'm not sure what you mean by "optimized" data. Edit: my very rudimentary understanding of information theory tells me that there's no "average" or "optimized" data, only varying amounts of entropy (AKA compressibility). My limited knowledge of radio and electrical transmission says that transmitted data is encoded to make effective use of the transmission medium (e.g. 8b/10b encoding, 8-to-14 modulation, TMDS). So,…

At first, I wouldn't have thought that they would use encoding to maximize efficiency. But now that I think about it, their goal isn't efficiency but rather consistency. So yeah I was wrong. Maybe I thought this was more primitive than what it really is :/

You seem to be trying to say something, but it's not coming across. What is primitive? How is it primitive? How do you describe the difference between efficiency and consistency in your usage? Is English not your primary language?

My exposure to this stuff is limited to a few exercises in a Matlab class years ago, plus what I read on HN and Wikipedia. Based on what I understand, from a data transmission perspective, there is no difference between efficiency and consistency. There is a theoretical maximum amount of data that can be transmitted using a given medium, bandwidth, and error rate. The only goal is to get as close to that maximum as possible.

Also, there's no shame in admitting you're wrong. In fact, every opportunity to be wrong is an opportunity to learn.

Re: Mars to Earth at an average of 29 kbits/s

#78

Post by pothibo »

nitrogen wrote: post #56
pothibo wrote: post #51

Earlier quoted context omitted.

We're not talking about your average data. We're talking about optimized data. Of course there's an overhead. EDIT: removed specific type of data

I'm not sure what you mean by "optimized" data. Edit: my very rudimentary understanding of information theory tells me that there's no "average" or "optimized" data, only varying amounts of entropy (AKA compressibility). My limited knowledge of radio and electrical transmission says that transmitted data is encoded to make effective use of the transmission medium (e.g. 8b/10b encoding, 8-to-14 modulation, TMDS). So,…

I do have a question however. I just read about 8b/10b encoding and I think we can agree that 8b/10b has around 20-25% overhead. This means that for the same throughput (29k/sec) we have 21.75k/sec of data.

Since TMDS is a superset of 8b10b than it's a fair assumption to think it has the around the same overhead.

Now I know we're only talking encoding here, not encryption but still, I wonder:

What kind of encoding are they using, because smaller the encoding is, the weaker the encryption is (Unless I got this wrong...)?

Now if all my assumptions are correct could it be possible that they use an encoding that makes encryption useless?

Re: Mars to Earth at an average of 29 kbits/s

#79

Post by pothibo »

nitrogen wrote: post #77
pothibo wrote: post #76

Earlier quoted context omitted.

At first, I wouldn't have thought that they would use encoding to maximize efficiency. But now that I think about it, their goal isn't efficiency but rather consistency. So yeah I was wrong. Maybe I thought this was more primitive than what it really is :/

You seem to be trying to say something, but it's not coming across. What is primitive? How is it primitive? How do you describe the difference between efficiency and consistency in your usage? Is English not your primary language? My exposure to this stuff is limited to a few exercises in a Matlab class years ago, plus what I read on HN and Wikipedia. Based on what I understand, from a data transmission perspective,…

Yeah, english isn't my primary language and I haven't spoken it in a long time so sorry if I can't make my point across :)

I'm not ashamed for being wrong. If that'd be the case I would have been ashamed my whole life heh.

When I said consistency I was referring to low-error rate in the signal. I should have said that but couldn't find the correct word for it.

Efficiency meant efficiency in the bandwidth usage.

So in that sense, there's always a tradeoff between efficiency (use 100% of the bandwidth to transmit real data) and consistency (make sure that 100% of the sent data is error-free)

Now, when I first wrote my comment. I had the feeling that communication was very basic commands. like a 2 bit integer for movement direction (00 up, 01 down, 10 left, 11right). So if you'd use such a scheme to communicate instruction to the rover, there would be an obvious overhead (encoding 2 bit into 4, 10, etc).

But now that I really think about it, instruction sent to the rover are probably very complex, which increase entropy, which in the end, made my first assumption wrong, is this clear? I hope it is ;) If not, I can rephrase !

Re: Mars to Earth at an average of 29 kbits/s

#80

Post by zokier »

TheAmazingIdiot wrote: post #68
rubberbandage wrote: post #44

Earlier quoted context omitted.

Absolutely, this seems like one of the most amazing in a long string of incredible things. There’s only enough energy to power two 60w light bulbs, and yet it can transmit all the way to earth while also powering the computer running the thing.

You'd be amazed what you can do just with a watt of radio power. If a transmitter and a receiver is in space, what's the furthest distance the receiver can go away from and have a 1 watt signal still above the noise floor? Assume the transmitter is a perfect omnidirectional. About 9200 miles.

9200 miles is not very much in space. That's like 0.006% of the distance between Earth and Mars.
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