AIUI, bandwidth of the link between Perseverance on Mars and us here on Earth means we’ll get plenty of still images, but not much video. Why is bandwidth so limited? How would the rover (or its orbiting comm relay) have to be modified to get a meaningfully higher data rate? Does the antenna get unwieldy, or the power supply, or both?
Earlier thread on a similar topic (coming from the same OP, incidentally): why do astronaut audio transmissions from orbit still sound so bad?
My guess is the same as it was in the other thread: The certified technology is rather old but tried and tested, and getting new technology with higher bandwidth tested and certified for spaceflight is an arduous process. The main purpose of Perseverance is taking and analysing geological samples, and the bandwidth is sufficient for that; the images are a by-product, and it’s not worth jeopardising the main mission by installing higher-bandwidth but untested communications technology for a video feed.
Nonetheless, the Martian wind will make a hell of a ring tone.
I am looking forwards to seeing the descent.
I can speak to this with some authority as I worked on an (unsolicited) proposal for a interplanetary telemetry system. Although there are certainly power limitations on the Mars Relay Network (MRN) satellites and the Perseverance rover itself, the real limitations are with the NASA Deep Space Network (DSN), which despite the name sounding like it should be in orbit is comprised of three communication complexes here on Earth: Goldstone in California (US), Madrid (Spain), and Canberra (Australia). These do use what is now fairly obsolescent technology (although it has been upgraded through the years to support deep space and interplanetary missions) but the real limitations are the restricted bandwidths to avoid interference and the fact that the stations have to rotate along with the Earth, which means they have to trade off or delay communications, with each station only able to access a portion of the sky for ~8 hours.
The MRN could potentially receive and retransmit higher bandwidth video by buffering it but at the expense of restricting transmission of other scientifically more valuable data. There isn’t much highly dynamic activity that occurs on Mars other than the occasional dust storm so high rate data is of little value in comparison to atmospheric readings, soil composition measurements, et cetera. And of course the DSN doesn’t just receive data but also has to transmit commands, which do not take up a lot of bandwidth but they are of high priority and have to be confirmed.
In the future, for larger and multiple interplanetary missions we will absolutely need a space-based, solar-orbiting data relay system; this is especially a prerequisite for any crewed mission where high data rate video communications and medical telemetry is required. Ideally this would be a high bandwidth system that retransmits to the existing Tracking and Relay Data Satellite System (TDRSS) or some other communication network that relays via Ka- and Ku-band high rate ground stations. The cost of doing this, while more expensive than any single uncrewed interplanetary mission, is not extraordinary and frankly has probably gone done relative to inflation compared to the concept we proposed in the early 2000s, especially as deployable flexible solar arrays are now a potential option instead of relying on RTGs or compact nuclear fission generators for power.
If you could somehow stand unprotected on the surface of Mars during a peak gust of a windstorm, the amplitude of the sound it produces would be more quiet than a whisper, and it would barely shift your hair. The atmosphere on Mars is thick enough to carry suspended particles and, with the low gravity, just barely enough to fly a specially designed helicopter, but it is tenuous even compared to the highest latitudes on Earth.
Video may not have much scientific value, but ISTM it would have immense PR value and might lead to increased public support (and funding) for future missions. Example, they made room for this fantastic video which arrived today:
I hope we get some more cool footage from the rover and the helicopter in the weeks and months ahead. If they can do that, I won’t complain if they ask for more money in the future.
What would the subject of the video be? Apart from the occasional dust storm, and the equipment that we send up there, nothing really moves on Mars. A 5-minute video of some rocks wouldn’t be very compelling.
While NASA certainly has a significant public relations presence (and has a mandate and specific budget for public education), it isn’t as if this publicity is something that translates into more budget or support in Congress. People may get excited about the Mars rovers or a mission to Titan, but almost nobody is making their decision about who to vote for on the basis of whether they support space exploration. Funding for missions, and indeed, the entire space program, is largely focused on where the work goes (i.e. to important districts with powerful congresspeople on critical budget committees) and actively pushed a handful of genuine space enthusiasts in Congress like John Culberson (who, despite his climate change denialism was a big supporter of outer planets missions).
The supposed “PR value” of space exploration, and particularly crewed exploration, is vastly overstated by enthusiasts. Despite what a technical triumph and (mostly) bloodless victory it was for the United States to be the first (and still only) nation to land people on the surface of the Moon, the Apollo program never enjoyed the support of even a majority of Americans. That it was cut short of even the planned J-class mission by the Nixon Administration despite the fact that the majority of hardware was built and crews were training was a fait acomplis, notwithstanding Nixon’s hatred for having to continue a legacy of Kennedy and Johnson.
Oh, sure, having some video is good for what they call EPO (Education and public outreach). So, they have some video. But it’s not like they need a continual live webcam: You can probably meet almost all of the demand with less than an hour, total, for a mission that’s probably going to last years. That doesn’t take much bandwidth at all.
@Stranger_On_A_Train, surely the public relations helps to get those genuine space enthusiasts in Congress like Culberson? A small audience is still an audience.
Not really. I doubt than one person out of fifty people randomly drawn could name all five rovers that NASA has put on Mars, how many landers NASA has sent to Venus, and even most avowed space enthusiasts couldn’t accurately tell you how many Apollo missions there were or what happened on them other than Apollo 11 and Apollo 13 (and the they’d get details wrong). For the vast majority of the population, the US space program is Chuck Yeager, John Glenn, Neil Armstrong on the moon, Steve Austin, the Voyager flyby of Jupiter (or was it Saturn?), Sally Ride, that teacher who died in the Challenger ‘explosion’, John Glenn (again), Tom Hanks, the astronaut who went crazy and tried to kidnap her romantic rival while wearing Space Depends, and Matt Damon playing a ‘space pirate’…so, basically a bad karaoke rendition of “We Didn’t Start The Fire”.
Actual space exploration occupies such a tiny portion of public awareness that most people can probably more of the cast of any random Star Trek series than of the Mercury 7 astronauts. Most people believe that NASA has a gigantic annual budget to rival the Pentagon instead of a relatively slender budget that is less than 10% of what California spends on education. What really helps is that NASA has research centers, programs, and subcontractors represented across the United States in every key district from Virginia to California and from Ohio to Texas. So, money that goes into NASA programs eventually goes into these districts, creating jobs that can’t be outsourced or easily eliminated. Back when I followed policy reviews on the space program, almost all of the discussion in Congress pertained not to any scientific merit or educational value but about where the money would go and how it would be divvied out to support aerospace contractors.
Anyway, Culberson is gone (and good riddance to him; aside from his support for interplanetary missions he was onerous and largely anti-science) and the space program will proceed apace, albeit not ever proceeding at the pace that it could be with consistent budget and mission. What would make more sense is to focus the program not upon flashy missions and “PR” events but on developing an infrastructure and technology that bootstraps the capabilities for space exploration such that longer and more complex (and eventually crewed) missions beyond Earth orbit are a logical consequence rather than a massive effort to get funding and develop mission-specific technology, which is what the bulk of NASA programs aside from the crewed program do, albeit in piecemeal fashion.
Could someone with the right equipment pick up the signal in their back yard (assuming they knew “where” to “look”) (so to speak)?
A few months ago I read about a Mars mission that was going to scoop up samples and then, through a years-long complicated relay process, eventually get them back to Earth. Is this part of Perseverance’s mission, or am I thinking of something else?
Although the telemetry stream has to be decommed the signal is not encrypted, so provided you have something similar to the Goldstone 70m antenna in your backyard and the patience to figure out the data encoding formats, sure, you could pick up and read the signal.
Perseverance is going to pick up soil samples, store them in hermetically sealed tubes, and deposit them at sites designated by the mission team as sample cache depots. An as-yet undefined Mars sample return mission will fly to the surface, collect them, and ascent back to an Earth return vehicle to send them back for analysis by terrestrial laboratories. You can find information about this and there aspects of the Perseverance rover and Mars 2020 Mission at the site below:
I’ve been puzzling over why the core samples are being left on the surface like breadcrumbs rather than just kept on an easily extractable cassette on the rover. Leery of weight gain, perhaps, as the empty tubes are filled with rock?
It sounds like concern that something goes wrong with Percy, and it cannot extract the samples.
Bring a can opener.
The primary reason for this is that the samples can be left in a location that is easy for a lander to land at and retrieve. If the rover ends up getting stuck or disabled going up the rim of Jezero Crater it may be inaccessible to a lander.
To be clear, I didn’t mean that EPO helps get folks like Culberson elected. I meant that EPO helps elected folks like Culberson become space nuts. Even if only one person in 50 follows NASA news, that’s two Senators and eight or nine Representatives, which could certainly be enough to tip a close vote.
I read NASA’s caching strategy for the soil samples and they say that with the orbiter and rover cameras they will be know the location of the samples within centimeters. But the weather is terrible on Mars and the sample tubes will be on the surface for several years. Wouldn’t they be buried in dust or scattered in a dust storm? Is the power of dust storms on Mars less than I imagined, or is the cache location somehow sheltered from the wind?
Because of the extremely low pressure of the atmosphere, the force of the wind in even the most powerful dust storms would be like a light breeze on Earth. The reason the dust storms are so opaque is because the dust on Mars is extremely fine like deconsolidated silt (which is probably exactly what it is) and the low gravity allows even the light winds to carry it high into the atmosphere. The sample canisters aren’t going anywhere.