Back in the days of the Apollo missions, NASA was working with 1960s analog radio equipment, so it’s not surprising that the audio quality of their transmissions to ground control was even worse than that of a landline telephone call.
In the 50 years hence, there have been some improvements in technology. I can place a VOIP phone call to someone on the far side of the earth and enjoy remarkably high audio fidelity, courtesy of digital compression and transmission; to my ear, it sounds like something close to the full frequency range of human hearing, with perhaps minor digital compression artifacts being apparent.
So why do astronauts in orbit still sound like shit? Is computing power and transmission bandwidth really that limited? That seems doubtful, since there are often video connections between ground and the astronauts on the ISS. What’s the deal?
Can you point out a recording where it sounds bad? Like you say, there is two-way bandwidth of tens to hundreds of megabits/second between the station and the ground. There are also VHF telephones, which aren’t going to sound that good if there is interference, so it depends on which system the recording was made from.
The phone calls you’re placing never have to punch through the entire atmosphere. They mostly go through wires, except maybe for a cell call, which only has to traverse a few miles in the air.
Good question; I was just discussing this with my wife. Practically every transmission from space that I’ve heard sounds like its going through a megaphone or a cupped hand. Nowadays, I’d expect a broadcast from space to sound as clear as a Saturday Night Live sketch on TV.
I read somewhere that the Space Shuttle, for instance, used 32 kbps digital audio on S-band, so even in the best case that will not sound crystal-clear unless some form of compression is used. Still, it’s not that low.
Here’s the entire recent all-female spacewalk. Audio from GC sounds clear as a bell (presumably the recording was made at GC), but if you click around and look for transmissions from the astronauts, they sound just like the Apollo days.
The cost of the ISS was somewhere around $150B, so as far as cost is concerned, ISTM that VOIP-quality audio would have been a drop in the bucket.
The ground does not sound to me clear as a bell: I swear I can hear digital compression, but that could be my imagination. As for the spacewalking people, apparently EVA comms use VHF, and, granted, there should not be too much interference since they are right next to the radio relays in the space station, but that’s exactly the same type of narrow-band FM radio technology used in the Apollo days, so why should it sound different.
As to why they use it instead of something more high-tech? Good question, but it’s a relatively simple technology, and it works.
I would assume that the considerations are similar to a Bluetooth headset.
The time it takes to compress is too long for conversation, which is why your headset doesn’t work with mp3.
I would wager that video is of a lesser immediate importance than live audio transmission, so especially for external activities the delay is just too much to allow for.
Just a WAG, but for an astronaut on an EVA you want extremely reliable communications with minimum lag. Analog degrades gracefully, digital (especially with high degrees of compression) is either there or not.
As they say in French: that’s a negative, good buddy.
Modern compression—audio, video, or generic zlib stream compression—is easily done in real time. A headset might use an ASIC for that, I guess, but an FPGA or even an older general-purpose CPU is fast enough for real-time audio compression.
Also, MP3 compression implementation was limited much more often by patent issues than by processing power. Fraunhofer’s patent (USPTO 6,009,399) expired less than three years ago. IIRC, Fraunhofer often required a per-device licensing fee for MP3 compression, and many non-audio-player device manufacturers decided the fee wasn’t worth it.
One explanation worth considering: NASA’s audio quality is a throwback for the same reason most commercial aircraft entertainment systems are a throwback: certification for flight is very expensive.
In other words, current voice quality is acceptable and no one has the time or money to certify the electronics required for modern compression algorithms.
I’ve worked on plenty of instruments with chips/boards designed in 1982. They look like they belong in an Atari 2600. And my employer kept them in place as long as those chips were available because getting new chips/boards certified was prohibitively expensive and time consuming.
One of the factors is that the microphones are fitted to the astronauts caps (which are different sizes for each astronaut) inside a closed helmet and can’t be adjusted easily - or at all if the astronaut is on an EVA. The caps and microphones can shift around inside the helmet and their sweat and other moisture can affect the equipment. The next generation of space suits is probably going to address this by making the microphone a part of the space suit itself.
The problem may be entirely at the space station end. Crappy, poorly placed mics. Lousy signal between mic and the transmitter to ground. Stuff like that.
One complication may be the multiplexing system used to allow people to talk and be heard within the space station.
The space station to ground might have tons of capacity to carry digital audio but the local system may be limited, esp. if they don’t want a ton of stray radio cruft messing with more sensitive stuff.
The spacesuit currently used by NASA astronauts is the Extravehicular Mobility Unit, developed for the Space Shuttle program and first used in 1981. So it’s 1970s technology, with only minor improvements since then.
It’s all marketing. People expect a voice transmission from space to sound awful, helps convince people that we need to keep spending money on human space travel.
I’m not an engineer, but I’m willing to bet this is the reason, akin to the reason why the Omega Speedmaster is still the only watch certified for EVA. Surely the technology would be there - high-bandwidth internet access via satellites is a commercially available off-the-shelf product, and there, too, the signals have to punch through the atmosphere (with a much longer distance between ground and geostationary satellites than between ground and the ISS). But before you instal something of that sort on the ISS, you need to get it approved, and for that purpose you need to get the technology certified. Which is an arduous bureaucratic process. The existing certified solutions are not so unsatisfactory as to create a pressing need to get a successor technology certified.