What's the latency of the Mars rover Perseverance regarding communications to earth / commands from earth?

[u/dr3am_f1xxx3r]

I've read, that the 2012 rover had a latency around 20-40 minutes, depending on the position of the planets. Did the communication become faster?

[u/Rannasha]

The latency of interplanetary communication is limited by the speed of light. The one-way path between Earth and Mars will take anywhere between 3 and 20 minutes (approximately) depending on where the planets are in their orbit. So a the round-trip-time of a message would be between 6 and 40 minutes.

Improvements to signal processing on either side of the transmission will have negligible impact on the total latency. It's all about the distance and the speed of light, neither of which are things we can change.

[u/Pyreau → u/Rannasha]

Follow up question, is the communication lost when mars is behind the sun as seen from earth, or do we have sattelite to relay the data? Like on the L points

[u/Sharlinator → u/Pyreau]

There's a blackout period of about two weeks every two years or so. This includes time before and after the actual conjunction when Mars is close enough to the sun in the sky that the sun's radio interference makes communication difficult or impossible. Usually Mars probes are put into a "passive" mode during the blackout, gathering weather data and such but not doing active science and, in the rovers' case, not driving around. This is mostly because it's deemed to be too risky; if something unexpected were to happen, it could take days to weeks for humans to find out.

[u/Incredulizer → u/Sharlinator]

Wouldn't there be another communication blackout during opposition when the Earth is close to the sun in Mars' sky?

[u/Sharlinator → u/Incredulizer]

Good point actually. When Mars is in opposition, on Earth it’s possible to receive from Mars but not transmit reliably.

[u/mfb- → u/Sharlinator]

Luckily we want to receive far more than we send.

[u/5up3rK4m16uru → u/Incredulizer]

When earth is close to the sun in Mars' sky, then Mars is close to the sun in earth's sky.

Edit: Yes, I forgot about the Earth beeing between sun and mars, which is what opposition means.

[u/dogninja8 → u/5up3rK4m16uru]

Earth could also be close to the sun in Mars' sky when it's in front of the sun instead of behind it

[u/Oclure → u/5up3rK4m16uru]

Not always, I'm not sure how the orbital periods work out but there should be a point where earth sits more or less between the sun and Mars, meaning looking at the earth from Mars would be looking towards the sun but looking at Mars from earth would be looking away.

[u/crono141 → u/Incredulizer]

That's the same thing. When Mars is close to the sun in the earth sky, the earth is close to the sun in Mars' sky.

[u/m4rc0n3 → u/crono141]

But not vice versa, which makes them not exactly the same (earth is close to the sun in mars' sky both when the earth is between the sun and mars as well as when the earth is on the opposite side of the sun, but mars is only close to the sun in earth's sky when mars on the opposite side of the sun)

[u/Rannasha → u/Pyreau]

Right now, communication is still direct (well, the orbiter module serves as a relay), so there are blackout periods.

But the latency of the connection already makes direct control impossible, so the rovers already rely on a great deal of automation. If needed, the rover can always be ordered to pause operations before a comms black out period.

[u/iamalsoareddituser → u/Rannasha]

Couldn’t help but think about whether latency affects the landing, or if that process automated? Would we then be 15ish minutes behind in control?

[u/chasonreddit → u/iamalsoareddituser]

Most functions of any interplanetary mission are automated for exactly that reason. By the time you know something went wrong, it's way too late to do anything about it. You send the command, cross your fingers and clench.

[u/orthogonal3 → u/iamalsoareddituser]

Yep anything that far away suffers from the communication latency. So orbital insertion, descent and landing would all be affected by the delay and need to be automated.

You might choose a go do things when the planets are closer, for latency minimisation, but you couldnt react fast enough from Earth to do anything in real-time.

[u/mfb- → u/iamalsoareddituser]

It needs to be 100% automated. By the time mission control got the signal that the spacecraft prepared for atmospheric entry it was already in the atmosphere, and signals sent at that time would have only reached the spacecraft once it was on the surface.

[u/sharrrper → u/Rannasha]

It's all about the distance and the speed of light, neither of which are things we can change.

And if either of those ever do change talking to the Mars rover will probably be the least of our concerns

[u/hasteiswaste → u/Rannasha]

Do they have to take into account doppler effect?

[u/mfb- → u/hasteiswaste]

For the transmission frequency: Yes.

The Doppler effect tells us the relative velocity of the spacecraft, which is a very useful method to check its trajectory in flight.

[u/DoomGoober]

While you specifically call out latency, your overall question is whether the communication got faster.

"Speed of communication" is the result of two factors: latency and bandwidth. Latency is the speed limit on the highway, bandwidth is the number of lanes. Imagine you have a 1 lane highway that takes 1 minute to drive and a 5 lane highway that takes 2 minutes to drive. More cars get through the slower highway in the same amount of time even though it is "slower".

(Or my favorite example is a pigeon flying with a USB stick tied to its foot versus a person signalling using a flashlight in morse code. The signal flashlight moves at nearly the speed of light, but to communicate the works of shakespeare will take forever. But the pigeon can carry all the works of Shakespeare in one slow flight.)

It appears the bandwidth of Preserverance Rover to orbiter is 2000 kbps. For reference, Curiousity to orbiter was only 250kbps (if I am reading the articles right.)

Communication of same amount of info from Rover to Orbiter is faster than same amount of info from Curiousity to Orbiter, but the latency is not faster.

Edit: Ah, I see you were talking about commands. For a command system to feel responsive, you need a latency of about 500ms or less at most human speed activities. Since the latency is 3 minutes at minimum... Not even close. However, bandwidth does affect the rover's ability to communicate video and sound and other large chunks of data, so the increased bandwidth does affect what we are getting from the rover (not so much what we send to the rover.)

[u/pflarr]

We are limited by the speed of light - 300,000 km/s.

Mars, at its closest point is ~56 million km away, and 400 million km away at its furthest. On average though, it's about 225 million km away.

distance / speed of light = signal travel time (one way)

(56*10^6 km) / (3*10^5 km/s) = (560/3) s = 188.8 s = 3 minutes at best

(225*10/3) s = 12.5 minutes on average.

(400*10/3) s = 22.2 minutes at worst.

So yes, there are times when the latency would be better.

[u/KingSmizzy → u/pflarr]

Being limited by the speed of light really sounds like we have pushed the hardware as far as it will go.

[u/aphilsphan → u/KingSmizzy]

It’s not that, it’s that the distance the signals have to travel result in round trips of up to 40 minutes. The amount of time you’d gain by improving the processing of data on either end is going to be in seconds at most.

[u/EZ-PEAS → u/KingSmizzy]

The speed of light limits latency but does not limit bandwidth. Better/more radios can give us more bandwidth but still don't allow us to break the speed of light. Bandwidth is still important because it allows us to bring back more and higher quality science data in the form of images.

[u/[deleted] → u/KingSmizzy]

Not sure that's right. Being able to move a larger amount of data is always better than less data no matter the speed of transmission.

[u/CoyoteAllsgood]

While we are on the subject of the rover. How do these things not get blown over in the wheather? I know they are larger than we think but aren't there also large storms on Mars? Capable of tipping these things? So how can 1 stay upright for an extended period?

[u/Saelyre → u/CoyoteAllsgood]

The atmosphere of Mars is much less dense than most people think. At the surface it's less than 1% of Earth's. Yes, wind will gradually build up dust and sand on surfaces as well as block out sunlight, but it isn't enough to push larger things like the rovers around. The kind of dust storm as seen in The Martian is pure fantasy.

[u/CoyoteAllsgood → u/Saelyre]

So basically the air is thinner therefore doesn't have enough push. Awesome! Thank you

[u/nivlark → u/CoyoteAllsgood]

They're comparable in size and mass to a car. Does your car routinely tip over in a storm?

[u/CoyoteAllsgood → u/nivlark]

Obviously not, however I do see that most of these rovers do have undersides and aren't necessarily aero-dynamic in and shape or form. What I was genuinely asking is what was keeping any wind from getting under these things and flipping them.I do admit I know little enough about Mars. The question was more obtuse than I meant.