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Almost every single space enthusiast is excited about a Mars mission and when we are sending our scientists there. But from the communications point of view, are we ready to test the recent advancement to the technology? If not, are we looking for an alternate solution (lasers)?

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    $\begingroup$ I assume you mean a manned Mars mission? The question would benefit greatly from some indication of why this would need different communications than the numerous unmanned missions. $\endgroup$ – Nathan Tuggy Apr 14 '17 at 4:15
  • $\begingroup$ Yes, I meant Manned Mars mission only. The reason I used the word Scientist because we will be sending our scientist first and then the ordinary people as it's not to reach the red planet. I was looking at some papers and found that we have some limitations and that's the reason the thought came to my mind. What do you think? $\endgroup$ – Pras4 Apr 14 '17 at 5:58
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    $\begingroup$ My point wasn't about the word choice of "scientist", but about the fact that at the moment there are no fewer than eight active Mars missions sending back scientific data. $\endgroup$ – Nathan Tuggy Apr 14 '17 at 6:01
  • $\begingroup$ Maybe STARGATE is an example of planned research into additional means of communications? Dunno, so far no answer here. $\endgroup$ – uhoh Apr 16 '17 at 7:43
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    $\begingroup$ Are we ready to test what recent advancement to what technology? What are you talking about? $\endgroup$ – Mark Adler Apr 16 '17 at 13:23
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The current DSN could be enough, depending on what the crewed mission requirements are. If you just want to communicate with voice and moderate-rate engineering and science data, then sure. If your requirements are to send back many channels of continuous 8K ultra-high definition video, then no. You would at least need to upgrade the DSN receivers to handle those kinds of data rates. With a big enough antenna and power amplifier on Mars, you could, in principle, transmit those data rates at current DSN radio wavelengths.

However, it would be much more efficient to use laser communication to meet those sorts of requirements, in terms of power and aperture. It is quite feasible to do so. There is no insurmountable problem with pointing, as speculated in another answer here. We lack only the money and the mission impetus to build such systems. Space and ground systems for Mars-Earth laser communications have been designed and proposed for decades, and a technology development effort is currently underway to prepare for the mission that might someday demand it.

Considering the other rather large expenses of crewed missions to Mars, it seems extremely likely that the small investment would be made in laser communications to support those missions and to provide better entertainment value from the mission back here on Earth.

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  • $\begingroup$ Is there no inherit issue with time availability of the DSN? $\endgroup$ – ChrisR Apr 16 '17 at 21:34
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    $\begingroup$ There's usually one DSN antenna pointed at Mars already, which should be enough. You can have multiple receivers on one antenna. $\endgroup$ – Mark Adler Apr 16 '17 at 21:50
  • $\begingroup$ The possible data rate using DSN depends also on the transmitter power used at Mars, the antenna size there and the changing distance between Earth and Mars. A very low noise preamplifier would help to increase uplink rate. More power at Mars would increase the possible downlink data rate. But on Earth a 20 kW transmitter could be used, using more than the usual 20 W on Mars is difficult. $\endgroup$ – Uwe Jan 10 '18 at 9:13
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Probably not.

Back in 2014, NASA issued a Request for Information concerning the use of commercial solutions for Mars relays. One of the key limitations outlined in this RFI was the very limited bandwidth of the current relay infrastructure.

In addition, the DSN is used for many other interplanetary missions (if not all, I don't have the data on this). Therefore, there is an inherent scheduling issue if one wants to maintain permanent communication with a crew on Martian soil, or in transit.

As pointed out by Mark Adler, the main barrier to laser communication from Earth to Mars may be the lack of money and mission requirement to continue developing this. Briefly looking this up, it seems ESA has reached a Technology Readiness Level of 6 for their LEO to Earth systems. NASA was at least planning to reach a TRL of 6 for their deep space laser communications by Mars 2017.

Concerning the pointing situation, a GEO spacecraft, which is only about 36,000 km above Earth, would shift its radio-frequency coverage projection by 700 km if its pointing is off by 1 degree. Lasers have a much more narrow beam than a typical reflector (or antenna). So the pointing constraint is even more stringent. I suspect that the solution we'll end up choosing in a few years is "plain-old" radio communication but at a higher frequency: the higher the frequency, the more power is needed to generate that signal, but the bandwidth is also increased. In any case, a Mars mission would surely have several redundant communication systems.

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    $\begingroup$ I have a hunch you are right - though at some point people will start nit-picking if THz or millimeter wave "is" radio or optical, until it's pointed out that a lot of radio people have already been calling what they are looking at "light" for a while now. Certainly an array of THz emitters could unfold to dozens of meters in size quite easily, and since each element can have a phase shifter, it would not have to be a particularly stable framework at all. $\endgroup$ – uhoh Apr 16 '17 at 7:56
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    $\begingroup$ Telescopes in space "point" the pixels of their focal planes to sub-arc second stability and knowledge, and with bright Mars as a guide star, this can be in real time. There needs to be special active optical stabilization, but that's do-able with some combination of lenses, mirrors, and fibers and some piezo actuators. You might want to add the size of the airy disk at Mars. An arc second is about 5E-06 radians, so with an 850nm wavelength and a 1.7 meter aperture you get 0.1 arc seconds theoretical, but you don't get 20 kilowatts of laser power into that beam, more like 2 watts. $\endgroup$ – uhoh Apr 16 '17 at 7:58
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    $\begingroup$ I don't think you'd need to go as high as THz though. Up until relatively recently the DSN only supported S, C and X bands (resp. 2-4 GHz, 4-8, 8-12 GHz). They added Ka (26.5 -40) but NASA still requires all interplanetary spacecraft to transmit on another lower band than Ka. If they supported Ka for everyone, we'd already see drastic increases in bandwidth. (There's a reason why GEO operates with K and Ka.) $\endgroup$ – ChrisR Apr 16 '17 at 8:02
  • $\begingroup$ Good point concerning space telescopes. However, the receiver and/or emitter would need to compensate for the rotation of both planets and any other perturbation, and that would require great planetary models (is that already supported in SPICE?). In addition to the 2 watts of power you get, isn't the signal also potentially very noisy? Not to mention when Mars and Earth are in conjunction or close to conjunction, but that causes problems even for radio coms. $\endgroup$ – ChrisR Apr 16 '17 at 8:07
  • $\begingroup$ @Yep, yep, and yep! Good points one and all. I'd love to read more about this, I don't even know enough to ask a good question yet. If I think of something I'll flag it here as well. $\endgroup$ – uhoh Apr 16 '17 at 8:12

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