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NASA Mars Science

NASA Creating Laser Communication System For Mars 104

techtribune writes "NASA is in the process of developing a new technology under project Laser Communications Relay Demonstration or LCRD which will allow them to provide faster means of communications from Mars. The Mars Reconnaissance Orbiter (MRO) currently can only send at speeds of around 6 Mbps or about like a DSL modem here on Earth. At this rate, it can take upwards to 90 minutes to transmit a single high resolution image to Earth from Mars. With the MRO outfitted with the new technology it would be able to transmit the same high resolution image back to Earth at over 100 Mbps and only taking about 5 minutes to do so."
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NASA Creating Laser Communication System For Mars

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  • Just don't mis-aim the laser. I'd hate for my city to blow up like in Sim City 2000 when the orbiting solar plant's beam goes off-kilter...

    • by Anonymous Coward

      Those mis-aimed beams in Sim City 2000 were microwave, actually. Which is what we use today for such interplanetary communications. So I daresay this will only make us safer!

    • by PPH ( 736903 )
      Think of the poor amateur astronomers looking at Mars through their backyard telescopes.
      • Hey, you need a solar filter to look at the sun, now you'll just have to buy a Mars-laser filter to safely look at Mars! It's a business opportunity!

  • by symes ( 835608 )

    What if it's cloudy?

  • That's still faster than most connections in the US! That's not bad at all!
  • From the summary:

    At this rate, it can take upwards to 90 minutes to transmit a single high resolution image to Earth from Mars

    At least part of this 90 minute transmission time is due to the maximum speed of light, not the date rate. According to NASA, it takes 10 to 20 minutes [nasa.gov] to get a signal from Mars to Earth:

    How long does it take for a signal to be sent from Earth to Mars?

    Signals to/from Mars travel at the speed of light (186,000 miles per second, or 300,000 kilometers per second). It takes between 10 and 20 minutes for a signal to travel from Earth to Mars, depending on the relative position of the planets at that time.

    • by Anonymous Coward

      Math is hard, please help me.
      6Mbps ~ 600KBs
      600KB/s * 60 seconds/min * 90 minutes == ~3.2GB

      So if the image is a raw 32 bit TIFF we're looking at at image of 28k x 28k pixels. Me thinks someone should introduce them to JPG compression.

      • I'm just speculating, but a risk-averse JPL may be concerned about using a JPEG because the extra work of compressing the raw image to a JPEG would be one more failure item on already very-complicated space probes.

        Like I said, that's just my theory -- a quick google of "space probe image compression" didn't turn up anything for me; maybe others would have luck.

        Discrediting my theory is a note on the Galileo Wikipedia entry [wikipedia.org] regarding the use of data compression to improve throughput after the high-gain anten

      • by AndrewBuck ( 1120597 ) on Wednesday August 24, 2011 @06:33PM (#37197904)

        Science images are NEVER EVER compressed in JPEG. In fact they probably don't even use the TIFF format either. Almost all science images in astronomy are done in the FITS [wikipedia.org] format which I think was developed by NASA. This is because not only does the image need to be lossless raw data in order to be used for proper scientific measurements, but also much metadata must be included with the frame for some kinds of science observations.

        Common metadata will include the position of the camera (where the orbiter was when the picture was taken), the camera's orientation (which way it was looking at the time), the exact time when the image was taken, the image exposure time, the camera's CCD temperature, whether on-chip binning has been carried out, the camera's readout noise, the camera's gain, etc. All of this information is necessary for some kinds of science and therefore NASA doesn't want to lose any of this information.


        • by serviscope_minor ( 664417 ) on Wednesday August 24, 2011 @07:02PM (#37198336) Journal

          . This is because not only does the image need to be lossless raw data in order to be used for proper scientific measurements, but also much metadata must be included with the frame for some kinds of science observations.

          Pedantically speaking, TIFF also allows for arbitrary metadata. And all sorts of other bizarre crap. FITS is a much older format and part of the reason it is used is historical.

          The main reason it is used is that it is a format specifically designed for archival use. It is a very simple format and one can easily write an image parser and writer from scratch which will happily accept and be accepted by most systems (so that ignores the more obscure non image options). I have done so.

          NASA quite rightly expect FITS images to be readable in 100 years time. This is reasonable since you could probably write that parser in a couple of days without even having access to the spec. TIFF by comparison is not a simple file format.
          t's also not a bad format. Lossless compression will get you at most 3x on a natural image with 8 bits per channel, but more like 1.5-2, and often is not worth the bother, especially as support for TIFF compression is somewhat spotty once it moves into more than 8 bits per channel.

          one marginally irritating thing about FITS is that it is in column-major format (yay @ fortran) rather than row major, where as most capture hardware and other image formats are row-major. So, loaading/saving FITS images often requires a quadrupal for-loop (endian/channels/rows/cols) to rearrange the data.

          But back on topic: 6mpbs over 400e6 km is amazing!

        • There are plenty of lossless image compression techniques. There are even standardized file formats that could be used. For instance JPEG2000 can use CDF 5/3 wavelet compression (lossless) and supports user defined XML metadata boxes. In other words 100% reversible image compression plus whatever metadata payload they wanted to include.
      • by Gib7 ( 2445652 )
        Math looks good (although upper case "K" is Kelvin - you need lower case "k" for kilo...), but I suspect there's a large dose of redundancy and Error-correction information included in that 6Mbps. It's not like you can have an efficient retry protocol with a 20 minute ping time. So, there'd be less than 3.2GB of useful data sent. Probably between 50% and 70% would be actual image.
      • Yeah, let's decide a compression algorithm what's an important detail on extraterrestrial pictures.

    • Wrong. The 10 to 20 minutes you speak of is the latency, however this 90 minute figure is probably arrived at by taking the size of the image and dividing by the 6mbps transfer rate. It will take 10-20 minutes after the first bits leave Mars and arrive at Earth, however after Earth sees the first bit they will still have to wait 90 minutes to see the last bit.


    • by Co0Ps ( 1539395 )
      No TFS is right. You're talking about latency. The summary talks about bandwidth. Latency and bandwidth are two completely different things. The time it talks for the recipient to download the image from transfer start to end is 90 minutes, no matter if you send the image from mars, jupiter or alpha centauri. Unless you use TCP.
    • 6Mbps * 60 sec = 360 Mb/m = 45 MiB/min * 60min = 2.7GiB/hr. Are they saying they're transmitting images that exceed 2.7GiB per image? Assuming 8 bits per "color" and a 6 channel "color", that's a 450M-pixel image. Even at 12b/channel, it's a 300M-pixel image, or 20K x 15K (4:3 aspect ratio) resolution image. Call me skeptical, but I think there has been a mistake.
    • Um, Unless you were kidding, the transit time is a measure of LAG, not transfer speed. The original statement, that it can take 90 minutes to transmit an image to Earth, is a measure of the transfer speed, IE, when the message finishes leaving the orbiter. When Earth actually receives it is a different question. So the 10 to 20 minute speed of light lag would be in addition to the the 90 minute estimate.

    • they clearly aren't including the limit considering the new one takes 5 mins instead of 90.
  • The speed isn't the issue. A sufficiently well focused and powerful laser (or multiple lasers) could probably push as much bandwidth as you need. The problem is the latency.

    The distance between Earth and Mars varies from between roughly 56 and 399 million kilometres. That's a minimum round-trip time of ~374,000ms and a maximum round trip time of ~2,600,000ms, ignoring the speed of light in atmosphere. Somebody's going to make a killing selling Squid boxes when we get around to colonizing the place.

    • No. The issue here is not the latency. Latency is a problem (it is a major issue with the rovers. Trying to direct them where to go and then waiting to see if they run into problems is a big nuisance). But here the total problem is bandwith. The total bandwith is low, so it takes a very long time to send data from Mars to Earth. We get far more data on Mars than we can even send back to the Earth. Even with this new system that will still be the case but if it works it won't be nearly as bad. This will impr
      • Actually, I think the bandwidth is pretty darn high. 6mbps is pretty impressive given the distance. I had no idea they could pump data that fast between planets.

        • Well yes, it is high for most purposes. It is very low compared to how much data is being produced.
      • by Guspaz ( 556486 )

        I meant that while the new system makes a big improvement in bandwidth, it can't do anything about the latency due to the speed of light.

    • Bandwidth is an issue. Telemetry is extremely tightly budgeted on a mission like this, and being able to get more back would vastly increase the available science data as well as simplify operations.

      And a high-powered laser is not a trivial task. First, all the power comes from solar cells, which are themselves heavy and they try to keep them minimized. Second, when you're pumping a lot of energy through a laser, you end up with a lot of heat that is difficult to discard. You can't bleed it off through

    • by Anonymous Coward

      Somebody's going to make a killing selling Squid boxes when we get around to colonizing the place.

      Not Squid on Linux - net/ipv4/tcp_timer.c

      /* Increase the timeout each time we retransmit. Note that
      * we do not increase the rtt estimate. rto is initialized
      * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests
      * that doubling rto each time is the least we can get away with.
      * In KA9Q, Karn uses this for the first few times, and then
      * goes to quadratic. netBSD doubles, but only goes up to *64,
      * and clamps at 1 to 64 sec afterwards. Note that 120 sec is
      * defined in the protocol as the maximum pos

      • by vadim_t ( 324782 )

        FTP would be a bad protocol for file transfer to Mars with so much talk back and forth.

        I figure they'd use HTTP POST or something similar.

  • If Comcast or a cell phone company manages it, they could pay for the space station from the profits on bandwith!
  • At those speeds, I cant imagine that there isnt some lost/corrupted data. Does retransmission factor into the 90 minute time, or are they using so many redundant signals that theres no need for a TCP-like packed received ack? Whenever communication between Earth and Mars comes up I just have to wonder how long it's going to be until we find a way to communicate faster than light using something like quantum nonlocality. Otherwise were going to need two internets once we finally colonize that rusted out w
    • I think it's safe to use UDP on this one. They're pictures. Mostly. A bit lost here. A bit lost there. No worse than a few dropped pixels. Sorta like Rick Perry or Palin. Just a little fuzzy around the edges.

      • by grumling ( 94709 )

        Lose a bit here, a few dropped pixels there and you end up with the "Face On Mars." [sciencemaster.com]

        I'd like us to get as much non-corrupted data as possible. Helps keep the kookie insane theory folks from getting any traction.

        • Helps keep the kookie insane theory folks from getting any traction.

          Ha ha ha! Yeah right! Okay, maybe a little bit, but it's kinda like dropping a single sandbag of rationality on your front porch as the tsunami of crazy comes barreling towards shore.

          At least that's how I felt once I saw that there were some theories going around that the SDO had proven that there were alien spaceships shootin' lazors at the sun, and Jupiter-sized comets in the inner solar system, based on the noise in single images.

      • Well there's no point is using IP at all, IP is designed to allow for four billion addresses. What you need in this case is a point-to-point, like a serial cable, not a network stack. Having a network stack would seriously add to the overhead.

        And you certainly don't need UDP, or FTP running inside it. Dropped data is a no-no, I believe, but there's no reason you can't just send commands and return data in the raw, then ask for corrupted blocks from the data to be sent again.

        It would look like this:

        E: Send m

        • Given their rather long latencies from speed-of-light delays, they might be using forward error correction to fix errors ahead of time. This works more or less like PAR files in that if less than a given fraction of the bits are corrupted, the data can still be recovered without problem, and that would seem to be much quicker than having to do a SYN/ACK type "Hey, these don't CRC out right, give me them again" scheme.
        • Sounds like TCP to me. Oh, and IPv6 has plenty of addresses.
          • Well yes, sort of, but the 'receive window' is the size of the data to be transmitted. TCP is designed to give reliability in near real-time, this kind of application needs nothing like that.

    • by Co0Ps ( 1539395 )

      You calculated the expected noice and simply add enough error correcting redundancy to deal with it. You can use this for example:


    • While I do not recall all that was done, TCP was re-written slightly to handle that. It really proves the power of abstraction thinking.
  • If they can make it faster, I'd be pretty impressed. That dang light speed limit really bugs me.

  • by tetrahedrassface ( 675645 ) on Wednesday August 24, 2011 @06:35PM (#37197920) Journal

    Nice planning on the communication system. Nice to see good solid planning, development and R&D. It's what NASA is good at. They also design pretty good rockets, rockets that used to take us places. Now that we have a better network, lets build the SLS and quit relying vaporcraft to get us there. Let,s quit cutting funding, and make it a priority to travel to are causing a brai Mars. We put a human on the moon and can do it again. The SLS can get us there.. we still have the brain power to go to Mars, but our politicians and misguided and overly hopeful privatization plans.... Less than one tenth of one percent of our budget is spent on space... For all of you wanting to save money, if privatizing space makes sense, why not privatize our national security, epa, and social security?? We need a heavy lifter!

  • So we have finally realized that lasers make sense for long-distance communications. Isn't this likely to have been realized by aliens a long time ago? I think this is why SETI hasn't found alien signals. The aliens use laser or possibly something better. We are unlikely to detect any civilizations more advanced than our own over radio.

    • You can't take back what you broadcast. Radio wave communication is sufficiently simple that it's not all together unlikely other civilizations wouldn't have at least used it at some point. Sure, eventually they may move beyond it. However, if we're receiving their radio signals just now, it's quite plausible they are now far more advanced than us. But, at the same time, in the time it takes for the signals to reach us (assuming they're even powerful enough to not get lost in the background) they could have
  • Higher bandwidth doesn't mean faster, it means more data over the same time. Both means are still limited by the speed of light.

    • by danlip ( 737336 )

      So you don't say that your network is "faster" or "slower" when it has more or less bandwidth? Most people do. Faster means it takes less time to communicate the same amount of data. Lag/ping time is important to, and you are right that this doesn't help those numbers, but I think it can still be called faster.

  • We don't even know if the Martians use big-endian encodings yet.

  • I'm not sure what the big deal is. I've seen this decades ago.
    Granted the end points were stationary relative to each other and the distances were slightly shorter.

    But all you'd really need is a 50MW laser and a phase-conjugate tracking system.

    • When you work out where to get 50MW from when you are solar powered and in orbit around Mars let me know. I'd love some of that action for my roof :)

      • by danlip ( 737336 )

        Tsk tsk, it was a 5 MW laser. And the energy comes in chemical form, but it's a one shot thing. Put simply, in deference to you, it's like lasing a stick of dynamite.

    • The thing about space (besides that its big) is that it makes almost everything harder. Every spacecraft is power starved, so simply adding power is not usually a possibility -- the key is going to be getting a higher data rate for the same amount of energy, mass and operational complexity compared to radio comm.

      Even more importantly: high powered lasers put off a lot of heat. On Earth, we've gotten pretty good at disposing of heat -- convection or conduction work great. Unfortunately, in space, you can

  • by istartedi ( 132515 ) on Wednesday August 24, 2011 @07:08PM (#37198468) Journal

    Any possibility of licensing spectrum to the Russians, the Chinese, or other countries that want to send probes to Mars? Fractional T-1 to Mars in exchange for a Soyuz ride or something...

    • You dont need a license to transmit laser light for data transmission.

      • You dont need a license to transmit laser light for data transmission

        You do need a license to relay weaker signals from the surface of the planet up to an orbital platform controlled by a 3rd party.

        If your probe can send signals up to an orbital platform you don't need as much power (lasers do attenuate over distance). There might be a significant weight penalty for a direct Earth-Mars laser with each probe. If you save the weight, you can send more probes to different locations instead of launching you

      • by Shatrat ( 855151 )
        I believe he means to lease a dedicated circuit. Too many wireless stories have confused Slashdot readers about how telecom works.
    • That's not a bad idea, actually. Put one transmitter on Earth and one relay around Mars* and pool the resources of the transmitting nations on improving bandwidth and reliability. Then the Mars relay switches to high-bandwidth (relatively) short-range radio for the last leg.

      *Realistically, a redundant set

  • My home Internet connection is still only 4 Mbps. I'm totally jealous of those Martians right now. Also, "in about like"? Seriously, who edits these summaries? A twelve-ye... never mind.
  • Anyone have a link to the details? I'd love to see how they solved problems like atmospheric disturbances and dispersion. A cartoon of a satellite doesn't tell us jack shit about how it works.

    • by Anonymous Coward

      The details in the proposal are probably
      a) still proprietary, until the task order is issued
      b) probably, to a certain extent, subject to export controls

      But, in general, Space Laser Comm has been around quite a while (Lincoln Labs at MIT has done a lot of work for USAF on this).

      They use pulse position modulation and avalanche/single photon kinds of detectors. It doesn't take a very big telescope on either end (and especially for Dave's project, where they're in LEO)

  • Is this bi-directional? If I'm going to spend a year going out there I'm sure as hell going to download some "images" from earth!
    • My mod points just expired. You are SOOOOOO right on the money. If we are going to the moon, asteroids, Mars, etc, we really need big 2-way comm (will not be fast, but pipe can be big).
  • latency will suck though

  • I haven't read the article, but I'm pretty sure the 5 minutes only refers to how long it will take the data to be be sent, not received. Latency on interplanetary communications is a bitch.

    Average distance between Earth and Mars: 230 * 10^6 km (from Wikipedia)
    230 * 10^6 km / c = 12.78 minutes (via Google)

  • These crosscutting flight demonstrations were selected because of their potential to provide tangible, near-term products and infuse high-impact capabilities into NASA's future space exploration and science missions. By investing in high payoff, disruptive technologies that industry does not have in-hand today, NASA matures the technologies required for its future missions while proving the capabilities and lowering the cost for other government agency and commercial space activities.

    OIC, they've hired an M

  • Great Mars has internets that are four times faster than my home connection now. I wish I was martian.
  • Who would have figured that packet collisions will likely be caused by asteroids and meteorites.

"Yeah, but you're taking the universe out of context."