16
$\begingroup$

With the approach of InSight to Mars today, and the two cubesats watching it, much is being made about seeing "Live Video" from the cubesats. I'm pretty sure that simply can't happen, but I'm wondering if the technology to broadcast live video actually exists, if there was a camcorder on one of the missions already at Mars. Could live video be transmitted (IE, is there a capability to get the required bandwidth at a distance of Mars), and received on Earth in a legible format (After speed of light transmission delays, of course)

If not, then what would it take to make this actually happen?

Improve this question
$\endgroup$
6
  • 3
    $\begingroup$ It depends on what the meaning of "exists" is. By exists, do you mean you'll allow for a few years to put it into a new satellite and put it in orbit around Mars or on the surface, or that it would have to use the satellites and landers already present at Mars? $\endgroup$
    – uhoh
    Nov 26, 2018 at 16:20
  • 10
    $\begingroup$ What do you mean? Are you asking about bandwidth? Speed of light? Power? Nyquist–Shannon? Compression? -1 for asking an extremely unclear question then answering it yourself with the answer you were looking for without give others clear direction as to what you were looking for. $\endgroup$
    – Sam
    Nov 26, 2018 at 18:42
  • 1
    $\begingroup$ Mostly the bandwidth. $\endgroup$
    – PearsonArtPhoto ♦
    Nov 26, 2018 at 18:46
  • 2
    $\begingroup$ The two cubesats allow for live telemetry relay, not video. Useful, especially if something were to go wrong during descent. (Without the cubesats, InSight would've had to save its telemetry and upload after a successful landing.) $\endgroup$
    – ceejayoz
    Nov 26, 2018 at 21:34
  • 6
    $\begingroup$ Agree with @Sam. I can't even guess what information you might possibly be looking for just from reading. Youd don't clarify what limitations you have in mind, you don't clarify what you expect to happen, you don't clarify what research you've done on the issue. There's just nothing in the question that gives anyone context to answer. Would happily downvote if I could and have flagged for closure as Unclear. $\endgroup$
    – jpmc26
    Nov 27, 2018 at 1:20

3 Answers 3

Reset to default
21
$\begingroup$

It turns out that for the closest that Mars is to Earth, MRO can transmit at 4.0 Megabits/ second on Ka band. That is enough for standard definition video. So something a bit bigger then MRO could easily transmit video, although only when the two planets are close to each other.

Improve this answer
$\endgroup$
5
  • $\begingroup$ MRO high-gain antenna is 3m in diameter - mars.nasa.gov/mro/mission/spacecraft/parts/antennas $\endgroup$
    – Jacob Krall
    Nov 26, 2018 at 20:04
  • 2
    $\begingroup$ With enough CPU power for video compression (h.264, h.265, or VP9), good quality 1280x720p30 is very possible at that bitrate. Or depending on how compressible the video is (jerky hand-held imagery with lots of detail in focus tends to be the most difficult), 1080p is also possible. The more CPU time you spend, the better the quality-per-bitrate tradeoff is. This can come at some cost in latency, but that's totally negligible vs. the speed-of-light delay. You could totally break live video up to encode 15-second chunks in parallel, encoding at 1/4 real-time on 4 computers for high quality. $\endgroup$
    – Peter Cordes
    Nov 27, 2018 at 1:12
  • $\begingroup$ From a cubesat with a limited power / CPU budget, a fixed-function hardware video encoder like you find in modern video cards and cell phones could do a reasonable job at 4Mbps for 720p content. Presumably the scene would be fairly low motion (and/or consistent motion of everything, so motion vectors for one block predict motion for neighbouring block), so be easy-ish to encode (not take a lot of bitrate for good quality). Depending on the scene, 1Mb/s can be sufficient for youtube quality levels. $\endgroup$
    – Peter Cordes
    Nov 27, 2018 at 1:14
  • 2
    $\begingroup$ @PeterCordes right, although I wonder how an off-the-shelf hardware video encoder with no radiation hardening or anything would still work after the journey to Mars! That in itself (for such a non-critical part of the mission) would be interesting to see. $\endgroup$
    – leftaroundabout
    Nov 27, 2018 at 11:23
  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – called2voyage ♦
    Nov 28, 2018 at 16:22
8
$\begingroup$

For example, this answer shows the math behind the Voyagers being noise limited with a ~1 kHz bandwidth at 20 billion kilometers. At 100 million km, a Voyager sized antenna with a few Watts would make a signal at earth 46 dB stronger, so you would be noise-limited around (40 MHz) with the 70m dish and receiver with a NEP of 20 Kelvin. These are handwavingly rough numbers, but some kind of reasonable video is possible with existing and not even new technology. But the logistics of making it happen is still a challenge.

The noise-limited bandwidth scales roughly linearly, so if you had 100 W to transmit for 7 minutes, in that case no problem!

Improve this answer
$\endgroup$
7
4
$\begingroup$

Worth mentioning that it takes 3 to 22 minutes for light to reach one of these planets from the other.

And no transmission can exceed light speed, barring a huge overhaul of Physics as we know it.

No equipment ever could have the signal here in less than three minutes.

Any affirmative answers are using a definition of "live" that allows for minutes-long delays.

Improve this answer
$\endgroup$
4
  • 4
    $\begingroup$ This is true, I didn't mean to include speed of light delay to preventing live. I meant video that is sent in real time from the spacecraft, of course it can't be received in real time. $\endgroup$
    – PearsonArtPhoto ♦
    Nov 26, 2018 at 18:36
  • $\begingroup$ Or a coordinate system in which light travels from Mars to Earth instantaneously. $\endgroup$
    – Acccumulation
    Nov 26, 2018 at 21:46
  • 14
    $\begingroup$ Using this answer, to be pedantic, there's no such thing as "live" anything, as it takes a finite amount of time for a photon to travel so much as one plank length. $\endgroup$
    – Phil
    Nov 26, 2018 at 22:10
  • $\begingroup$ @Phil since this also applies to witnessing an event in person, one reasonable definition of "live" would be an audiovisual experience equivalent to being there. $\endgroup$
    – Emilio M Bumachar
    Nov 27, 2018 at 12:37

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.