From a scientific standpoint, there's really no value in downlinking video as opposed to still images. It costs several multiples worth of scarce downlink bandwidth, for a tiny gain in what there is to see of the same rocks at slightly different angles. Same reason we didn't have New Horizons at Pluto or the various Mars rovers do any video.

There might be some scientific value for taking video. One measurement where video might be valuable is measuring the saltation threshold, or the wind speed at which grains begin to move, of the surface using rotor downwash. These measurements are important to understand the dune pattern on Titan. This could be pretty weird as the dust on titan is believe to be made of something similiar to moth balls, which could stick to each other like packing peanuts due to frictional electrostatic charging.

[0]https://www.jhuapl.edu/techdigest/TD/td3403/34_03-Lorenz.pdf [1]https://www.news.gatech.edu/2017/03/27/electric-sands-titan

Why is bandwidth so scare still? Satellites in geosynchronous orbit on earth can do terabit/sec of total capacity now.

Obviously latency is going to be extremely high, but I can't really understand why data rates are still so low?

Inverse square law. For the same transmit power, your received signal strength diminishes with the square of the distance

That received signal strength is what determines channel capacity (C) which is the upper limit on the bit rate you can get.

see Friis and Shannon's channel capacity

[0] https://en.wikipedia.org/wiki/Friis_transmission_equation

[1] https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theore...

Yes, I get that. But it seems that performance has barely improved since the 1970s despite the massive gains in telecommunication efficiencies since then. Or is the SNR so poor that even 1970s era technology was able to be close to the limit?

These are physical restrictions, not technological.

What about the laser technology NASA is developing? That should be a lot faster than current radio based technology?

Titan has smog in the visible spectrum. Details matter! The technology is also not that mature, yet.

Focusing a laser at that range requires a rather large diameter heavy set of optical components.

You will need a blinding-strong laser.

Because the signals have to travel so much farther and are so much weaker when they arrive. It's amazing that any data at all can be extracted from a radio signal that travels a billion miles.

Spacecraft transmit power and antenna size is limited. This means the amount of power that arrives at earth is rather low because microwaves spread out quite a bit with distance. The other issue is that NASA only has so many big radio dishes in the deep space network[0] to gather this small amount of power and extract a signal. Technology has improved, but in order to get much higher bandwidth we'd need bigger dishes. We also need at least three around the globe to get continuous coverage. Although perhaps by the time this mission lands we could have multi-kilometer aperture receivers on the ground or in space. Laser communication could allow for much higher bandwidth, because lasers have a shorter wavelength they don't spread out as much with distance. However, laser space communication is in its infancy and would not work well on Titan due to the smog.

[0]https://en.wikipedia.org/wiki/NASA_Deep_Space_Network

Maybe workaround transmission power by reflecting and modulating a signal over an existing power source. Like a very big mirror with an LCD pixel in front of it.

"one over r-squared"

Latency is high, but the power you have to pump through an antenna / laser to get enough watts on the receiver goes up really fast with distance.

Here's a summary that touches on it if you'd like to learn more: http://www.qrg.northwestern.edu/projects/vss/docs/Communicat...

And here's a detailed derivation for voyager. https://space.stackexchange.com/questions/24338/how-to-calcu...

I don’t think you realize just how far away the outer solar system is.

Low transmit power. Long distance. Very low SNR at receiver.

Don't get your hopes down! It's still very possible that we'll get some good, if not real-time, video out of this!

Ah, we likely will not get real time video. Maybe APL has some tricks I'm not privy to. Source: I asked a DSN coms engineer.

There will be at least an hour delay. Saturn is pretty far

10 seconds of video from Titan would change the world. It's shame we don't have this from Mars already. So it would take a few weeks to transmit - we got time.

Now figuring out which 10 seconds to select and send to earth... that'll be interesting. An on-board cache of x GB data storage, with key frames taken every 30 minutes, would probably be able to select some pretty compelling 10 second segments.

What about the world would be different after getting a 10 second video from Titan?

It would be inspiring for me at least.(Assuming something was moving)

Send them all, just pick a likely-nice one for sending while the eyes of the world are on Mission Control.

Caching everything then sending it at leisure is working nicely for New Horizons.

No 4K flyovers for Instagram?

I mean sure, eventually, over many down link cycles. But not real time.

Space travel just makes it utterly clear there is on such thing as real time. Computing is constantly running up against the speed of light.

It's not about latency, it's about power required to transmit. From far away, you need to push lots of power through to get a readable signal on the receiver side. It's kinda-sorta like seeing a flashlight.

In a sense tho, at-the-speed-of-light is real time, as it's the maximum speed of anything.

If, as clock A nears the speed of light it appears that stationary clock B is slowing down, doesn't that mean that at the speed of light is no time? Does a photon in a vacuum arrive instantly at its destination? If a photon looks at another photon, does the other photon appear not to be moving at all, or... Ouch my brain.

> If, as clock A nears the speed of light it appears that stationary clock B is slowing down, doesn't that mean that at the speed of light is no time?

If clock A could reach the speed of light (which it can't), then, yes, clock B would appear to be 'frozen in time'.

> Does a photon in a vacuum arrive instantly at its destination?

From the perspective of any possible observer, no, it always appears to be traveling at the speed of light. If an observer could travel at the speed of light (which it can't), then, yes, it would appear as if it arrived instantly in the sense that clocks at both its source and destination would appear to be not running at all.

> If a photon looks at another photon, does the other photon appear not to be moving at all, or... Ouch my brain.

Yeah, this is tricky. Photons can't look or see – what could that mean as looking/seeing involves detecting photons (or, in the sense that something like echolocation is 'seeing', detecting a pattern of matter, e.g. sound)? In a sense, not moving at all or both moving at the same maximum speed don't seem to be much different, from the 'perspective' of a photon.

Somewhat related, this video describes how, if one could travel on a vehicle that could accelerate at a constant rate continuously for decades, one would eventually see the cosmic microwave background radiation as a rainbow ring because traveling closer and closer to the speed of light would shift the apparent frequency of the radiation first into the visible spectrum (and then beyond it).

My comment was mostly tongue in cheek, I know photons don't have eyes. :)

Not completely related, but you reminded me of something interesting I remember hearing about neutrinos. Apparently (HN physicists please correct me if I'm wrong), neutrinos have an extraordinarily tiny objective lifetime, and the only reason we can detect them is that, because they travel so close to the speed of light, they experience almost no passage of time in while in flight.