8 ms·
Mars to Earth at an average of 29 kbits/s
- ryusage 14y agoIt's awesome that they've been involving the public so much in the details of how the rover mission really works. I'd actually been wondering about this exact question, since it seems to be one of the limiting factors for the quality of images and such. From a physics standpoint, sending data is clearly a lot more complicated than I'd previously assumed.
- keithpeter 14y agoYes, the clue is in the comparison to 'home modems'. The technology was finalised 2004, which means design around 2000 or so? I'm impressed with the reception technology that allows 'direct to home' communication at all given the power levels available.
- rubberbandage 14y agoAbsolutely, 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.
- jeza 14y agoThis probably has more to do with the massive antenna (also known as a radio telescope) here on earth that are used to pick up the signal. Fortunately a few such antenna exist around the globe, so Mars should be in view of one of these antennas at all times. According to Wikipedia (http://en.wikipedia.org/wiki/Deep_Space_Network http://en.wikipedia.org/wiki/Deep_Space_Network), radio telescope complexes used by NASA are located at: Goldstone Deep Space Communications Complex near Barstow, California, USA Robledo de Chavela near Madrid, Spain Canberra Deep Space Communications Complex near Canberra, Australia
- TheAmazingIdiot 14y agoYou'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.
- zokier 14y ago9200 miles is not very much in space. That's like 0.006% of the distance between Earth and Mars.
- TheAmazingIdiot 14y agoI well realize that. I was assuming absolute worst conditions, at 1 watt PEP. With hardware noise reduction, we can drop easily to .1 watt and still keep everything else consistent. Next, if we choose a directional antenna, we can also greatly magnify directed output. No sense in directing energy in the ground, is there? We can also have receiver systems (dish arrays) that can provide great gains in reception and transmitting.
- Achshar 14y ago> 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 videos. And i believe this is why we see twitter accounts of most astronomers, satellites, rovers and other NASA properties. The NASA's ustream has been very popular lately and they have presence on every major social network. And curiosity was named after an essay written by a student in a competition organised by NASA for school students.
- hrayr 14y ago"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 http://mars.jpl.nasa.gov/MPF/rover/name.html
- deleted 14y ago[deleted]
- ericHosick 14y agoIn general, space travel is very risky. It's not like they can iterate. Pulling something off like landing on Mars is very impressive. Keeping this in mind, I feel it was actually quite risky that NASA streamed the landing live. I think NASA should receive big kudos for taking that real risk.
- Dylan16807 14y agoSo those are the lander->earth and lander->sat speeds. How fast can the satellites transmit to earth? If we somehow always had a sat in reach of the lander, how much data would we be able to send? Edit: Did the research. MRO's antenna can handle .5 to 4 megabits depending on the distance between planets. Wow, having to wait for flybys is a huge bottleneck. http://mars.jpl.nasa.gov/mro/mission/communications/commxband/ http://mars.jpl.nasa.gov/mro/mission/communications/commxban...
- zhoutong 14y agoI wonder if it's possible to launch an orbiter in Mars synchronous orbit. That'll eliminate the bottleneck.
- waterlesscloud 14y agoWouldn't just a higher orbit achieve the same thing? You'd be in sight for longer periods, right? Without locking you into a location the way synchronous would. The current orbiters are primarily for imaging, so it makes sense that they're as low as possible. If you were always going to have several surface missions, it might make sense to have higher orbiters primarily tasked with communication relay.
- danielweber 14y agoAs someone explained to me on another thread, the orbiters they have now are in polar orbits. A more equatorial orbit would create very frequent uplinks. One thing is that they didn't know Gale Crater was where they were going to land until pretty soon before launch. There were a number of other sites. And if they chose one further from the equator, that satellite wouldn't necessarily be in the right place.
- Sharlin 14y agoWould have been nice if Mars Telecommunications Orbiter [1] had flown. In addition to a higher orbit more suitable for communications, it would have included an experimental high-bandwidth laser link to Earth. Alas, the project got cancelled for budgetary reasons. [1] http://en.wikipedia.org/wiki/Mars_Telecommunications_Orbiter http://en.wikipedia.org/wiki/Mars_Telecommunications_Orbiter
- darkstalker 14y agoWhat's the latency of that data connection?
- ntkachov 14y agoI asked this question on quora, about 14 minutes. http://www.quora.com/Curiosity-Mars-Rover-1/What-is-the-bit-rate-at-which-curiosity-sends-data-back-to-earth/answer/Andy-Mcfarland?__snids__=51092015 http://www.quora.com/Curiosity-Mars-Rover-1/What-is-the-bit-...
- Achshar 14y agoThe latency is about 14 minutes, which is funny because we consider 100 ms latency a bad thing here on earth.
- sp332 14y ago14 minutes one-way, so a "ping" would take 28 minutes.
- dantotheman 14y agoThe real question is if its has an IPv6 address yet or if its still stuck using IPv4?
- vitno 14y agoIt doesn't use IP... it uses a protocol called CCSDS
- waterlesscloud 14y agoIt varies. As others have said, it's currently just under 14 minutes. But it can be as low as 3 minutes or as high as 21 minutes, depending on the distance from Earth to Mars. Which of course varies as they orbit the sun.
- sillysaurus 14y agoRound-trip latency is the time it takes a signal to travel from Earth to Mars and back. As Mars and Earth orbit around the sun, their distance relative to each other is constantly changing. The minimum distance from Earth to Mars is 35,000,000 miles, and the maximum is 249,375,000 miles. Since light travels at 670,000,000 miles per hour in a vaccuum, we can calculate the minimum and maximum round-trip latency: Minimum round-trip latency = (2 * 35,000,000 miles) / (670,000,000 miles per hour) = (0.167164 hours) * (60 hours per minute = 10.0299 minutes Maximum round-trip latency = (2 * 249,375,000 miles) / (670,000,000 miles per hour) = (0.744402 hours) * (60 hours per minute = 44.6642 minutes
- DanBC 14y agoUsing Sloppy to view websites gives a reasonable idea of how slow this is. (http://www.dallaway.com/sloppy/ http://www.dallaway.com/sloppy/)
- graue 14y agoVery cool concept. Unfortunately, this only proxies the starting hostname and doesn't rewrite absolute URLs, so on most modern websites, image/CSS/JS resources (being served from subdomains or S3 etc.) will load unproxied and not get slowed down.
- fsiefken 14y agoDoes anyone know more about the architecture of this space radio network? For example does it use tcp/ip on top over radio or is it packet switched as with amateur packet radio?
- vbtemp 14y agoGenerally they use the CCSDS specifications, CCSDS is an international body with the space agencies of each major country contributing. Google for CCSDS, they have a bunch of open standards. Space networks really aren't quite at the level of fully mature, layered, multi-hop packetized networks... It's a Hard Problem. Basically, TCP/IP doesn't scale to meet the constraints of deep-space networks (high latency, asymmetric data rates, intermittent connectivity). It just breaks down. That's why there's a lot of active research in DTN (delay/disruption tolerant networking and ad-hoc networking protocols). ION (Interplanetary Overlay Network) is the JPL implementation of the DTN protocols, and has been flown in a demonstration capacity on some extended-mission/end-of-life Deep Space missions. Much of it has been open sourced at this point.
- gchang 14y agoHere's some publicly available technical information about how the DSN works: http://eis.jpl.nasa.gov/deepspace/dsndocs/810-005/ http://eis.jpl.nasa.gov/deepspace/dsndocs/810-005/
- Irishsteve 14y agoUp in Sweden they have DTN's for reindeer farmers. A helicopter which brings food supplies acts as the data transfer relay. DTN book for anyone interested in the area. http://www.amazon.com/dp/1596930632 http://www.amazon.com/dp/1596930632
- noselasd 14y agoHere's the protocol stacks http://public.ccsds.org/publications/default.aspx http://public.ccsds.org/publications/default.aspx , here's source code for some higher layers https://ion.ocp.ohiou.edu/ https://ion.ocp.ohiou.edu/
- oleyb 14y agoIt's faster than my work's connection!
- barking 14y agoYou are joking but in 2003 I had to live with 6 kbps (yes SIX KILOBITS) at a time when my monopoly telco was advertising broadband speeds.
- vladd 14y agoI'm wondering how do they prevent non-NASA entities from sending commands to the rover - are they using some sort of cryptographic signatures when sending the commands?
- iwwr 14y agoYou need access to the big Deep-Space Network of radio dishes.
- vbtemp 14y ago1. You can hack into the DSN, and try to do it that way. 2. Set up an 80-meter dish in your back yard, with a team of NASA RF experts. With step (2), the authorities will zero in on you in a second, so the emphasis is definitely on the cyber security of the ground infrastructure and not on SSL-over-space-link-communication.
- vladd 14y ago(2): there are plenty of third world countries or foreign government agencies where placing a 80-meter dish is not a problem. Although the process seems a bit intimidating - http://deepspace.jpl.nasa.gov/dsn/features/dsnbuilt1.html http://deepspace.jpl.nasa.gov/dsn/features/dsnbuilt1.html
- vbtemp 14y agoNot just assembling the dish - you also have to know the ephemeris schedule, bit coding scheme (it changes based on circumstances), packet formats, software infrastructure... In the great scheme of things, my friend, Cuba or Zimbabwe secretly erecting an 80 meter dish just to f--k with a rover on mars isn't really a concern. Even though ESA or China or Japan might conceivably have the theoretical capability to do this... there are other things to worry about.
- stephengillie 14y ago
- kayoone 14y agoNice, just like my first modem back in 1996. Now let me host a dedicated QuakeWorld Server on Mars!
- mistercow 14y agoYou might find that the 1700 second round trip latency is a tad higher than your modem in 1996.
- rwhitman 14y agoI read this the other day and found it interesting: http://en.wikipedia.org/wiki/Interplanetary_Internet http://en.wikipedia.org/wiki/Interplanetary_Internet Apparently NASA had plans for launching an orbiter specifically as an optical communications hub for Mars but scrapped it in 2005: "As of 2005, NASA has canceled plans to launch the Mars Telecommunications Orbiter in September 2009; it had the goal of supporting future missions to Mars and would have functioned as a possible first definitive Internet hub around another planetary body. It would use optical communications using laser beams for their lower ping rates than radiowaves."
- jk4930 14y agoNow it's ESA's turn to try it: http://www.esa.int/esaMI/ESOC/SEMM5IHWP0H_0.html http://www.esa.int/esaMI/ESOC/SEMM5IHWP0H_0.html (OT: Note the picture at the bottom, the astronaut is one of ours: Austrian Space Forum, a private space R&D org.)
- ChuckMcM 14y agoSo one wonders at what point you uplink to a satellite with ejectable flash drives which, when full, detach, make a gravity sling shot pass to leave orbit and then burn for a rendezvous with earth 9 months later. If I did the math right a 1TB drive returned from Mars in 9 months would be an effective bandwidth of 470K bits per second (or 47K bytes per second)
- zandor 14y agoSounds like a modern take on the Corona satellites. http://en.wikipedia.org/wiki/Corona_(satellite) http://en.wikipedia.org/wiki/Corona_(satellite)
- rodion_89 14y ago470K bits == 58.75K bytes (assuming 8-bit bytes)
- bluesmoon 14y agoyou also need parity bits
- ChuckMcM 14y agoTypically bytes are coded 8N1 (or 1 start bit, one stop bit, and 8 data bits) so 10 baud gets you 1 byte. Hence the nominal divide by 10 (this is 8b/10b encoding) But in a pedantic sort of way, the computation should add extra bits for ECC since the drive has ECC bits already embedded in it, so a 1TB drive probably has more than 10 Tbits it is probably closer to 15 - 20 terabits.
- arrrg 14y agoLatency matters, too. Often all the data is necessary to make decisions so (for example) only immediately transmitting a limited subset of the data is not really an option. It’s not like that rover is driving around autonomously. It has some autonomy, but it can’t decide what’s interesting and what’s not, what has to be investigated and what not.
- 14y ago
- bluesmoon 14y agoI love this statement (from the Preventing Busy Signals page): "The Deep Space Network (DSN) communicates with nearly all spacecraft flying throughout our solar system."
- Florin_Andrei 14y agoSo, it's basically like dial-up back in the day.
- nemilar 14y agoThis may be a silly question, but I don't understand why the bandwidth is so low. I understand the latency will be high, since you're limited by the speed of light; but wouldn't you be able to get more bandwidth just by increasing the spectrum of light used, as well as the baud of the transmitter/receiver?
- accountoftheday 14y agoEven with optimal coding you are still limited by achievable signal over noise due to the Shannon limit.
- diminish 14y agowhat if they open sourced all of their components on github..
- bwr 14y agoI'm guessing there is a lot of data that never gets sent to earth. Do they send thumbnails of the images to determine what is interesting? Is there a software tool available that creates a thumbnail and then creates a copy of the original image that is dependent on the thumbnail to be recreated. If you can't tell I wasn't really sure how to word that last sentence. Basically, less data would be required to transmit because you are only sending the data required to reconstitute the real image. Depending on the size of the thumbnail this might result in a negligible difference. For example, a very naive implementation might create a thumbnail from every pixel where x or y is odd and then when/if you want the original image you can get the data required to put the image back together (it would be a similar sized thumbnail but with the even pixels) For this naive approach the thumbnail would likely be much larger than you want and would not help at all :)
- 205guy 14y agoThere must be some amateur radio people out there able to receive these signals, no? With the protocol stacks mentioned in the other comments, I wonder if they're able to extract the encrypted data. Which leads me to think there have got to be people/governments trying to figure those out.
- ck2 14y agoThe high gain system they have for curiosity has an upper end of 2Mbps - to the orbiter. The orbiter can talk to earth at up to 6Mbps depending on how far away we are at that time. 6Mbps at that distance is a staggering feat of engineering.
- drumdance 14y agoA friend of mine used to work at JPL on transmissions from one of the older explorers. Maybe Voyager? Anyway, he compared the energy used to transmit from the probe to that of a flower petal falling from a height of six feet.
- xfhai 14y agoMy suggestion is a satellite going around the Sun between Earth and Mars, so that there would be more visibility.