Given that the shuttle beams down live color video (i.e. they have plenty of bandwidth) why does the audio always sound worse than a telephone?
Just a WAG until somebody who knows what they’re talking about comes in. I would assume something in the atmosphere is causing some type of interference. If I get a chance, I’ll try looking it up.
Maybe nobody cares about the audio? We have transmitters with stereo, hi-fidelity sound, enhanced bass and sub-woofers. We listen to them on our own high-quality stereos in our cars. But you won’t find this stuff in your typical private plane. Listen to your local “Eye in the Sky”. I haven’t taken a survey, so I can only answer for myself. When I’m flying, all I care about (communication-wise) is that I can understand who I’m talking to, and they can understand me.
Because their direct phone line gets disconnected after the first orbit.
That’s why France hates us: 30,000 miles (48,000 kg) of phone cable snaps back and lands on them after every shuttle launch. :D:D
Hm. WAG here.
The shuttle people like systems that are reliable and foolproof. They just recently started overhauling the main control panels, which were of mid 70’s vintage. I’d say the radio setup is something they know will work, know how to repair them in their sleep, and can repair them easy. Of course it’s not modern. I would assume using more modern electronics would involve chips and stuff that are subsceptible to radiation and the like. You can take a PIII laptop into orbit, but get ready for it to reboot randomly all the time.
So what does all this boil down to? They like systems that are built to last. They aren’t concerned about audio quality that much right now.
This is my favorite Q in this forum! I’m dying to know the right answer because I’ve often wondered this myself. Meanwhile I’ll share a story that’s sort of related – and maybe even contains a germ of the right answer:
A few years back I heard an interview with a veteran radio newsman who, I believe, worked here in NYC when they “invented” fly-over traffic reporting back in the 50s or early 60s; whether he was the actual traffic reporter or was merely on-staff at the time, I don’t recall – but he was an eye witness to this story.
Because the fly-over idea was unproven and unprecedented, the station agreed to do it on a trial basis; they did it using the existing equipment they had on hand. They owned a small remote transmitter – meant to broadcast live events like concerts, parades and sporting events – which they loaded into the helecopter (or I think it was a small plane at first… I don’t recall).
Long story short: The concept was a spectacular success – and spawned the entire fly-over traffic reporting industry that exists coast-to-coast today. However there was one hitch in the trial. Because the concept was so new, and because the reports were so crystal clear (the original remote transmitter was built to give excellent sound quality) many listeners thought it was a hoax – they simply did not believe the reporter was really flying overhead. So the station purposely replaced or modified the transmitter and/or mic to give it that noisy, tinny sound quality we now associate with live remote broadcasts.
Sounds like an UL to me.
I’ve worked with small portable mobile radio transmitters. Unless you have a good full unit which needs a truck to carry it around, it sounds pretty bad.
My guess as to why the audio sounds poor on the space shuttle is that they compress it to save bandwidth. I don’t think the video is of all that high a quality either. Considering all of the data that is constantly going to and from the shuttle, It’s not all that surprising that they would want to conserve as much bandwidth as possible.
well, there’s plenty of small portable mobile radio transmitters that sound crystal clear. i’ve worked in radio, and the only time we’ve had problems is when we’re broadcasting from a building where we don’t get a good antenna location. these are decent size transmitters (breadbox size), but they don’t need a truck to broadcast from, just a wall plug. and 15 miles away sound fine, 30 miles isn’t unheard of.
video takes up much more bandwidth than the audio; however, if the technology thing that Saint Zero brought up isn’t right, i’d go with the frequency that the Space Shuttle transmits at has some interference. now, i don’t know what frequency it does broadcast at, but it’s possible that there’s more interference at the frequency the audio is broadcast at than the video, or maybe the video transmitter has more power. we come to expect color nowadays, and anything less is unprofessional.
Great question, sorry I can only WAG. I agree about only the proven equipment goes up, and perhaps good mikes of that vintage are heavy.
You really are obsessed with that Simpsons episode Hail Ants.
picmr
One reason, I suspect, why the audio quality sucks is because the dang thing is moving so fast. A direct-to-ground transmission would only be viable for a few minutes before the Orbiter is over the horizon. So the signal is most likely relayed via sattelite, and the transmission is probably non-directional (once again because everything from the Orbiter is a moving target). That would disperse the signal, and would probably require amplification by the relayer, ground or sattelite.
Furthermore, the Shuttle operates in a fairly narrow area between electromagnetically active “belts”, but that’s not my bag so I’m not going to mess with that end of it.
This might prove interesting.
http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts-ovcomm.html
The complete reference to the shuttle’s communications systems. Wowsers.
good point
also a good point. New equipment requires lots of testing…the first of which is the ability to withstand the stress of launch. This is why the Hubble was recently fitted with a 486 processor instead of the latest Pentium (or G3 ). The testing takes years.
Another possible reason why the video quality is so much higher than the audio is that the video typically isn’t real-time, like the audio is. Think about how much video you’ve ever seen from the Shuttle: One or two clips per mission, lasting about five seconds each. Heck, maybe each of those clips took 30 minutes (WAG) to download, to get that kind of quality. The audio, on the other hand, is running continuously, so they have to accept whatever they can transmit at that rate.
Yeah, come to think of it, I remember seeing a live broadcast transmission from the shuttle (was it during a Super Bowl?) and it was… not good. The picture quality resembled that of a small-town local cable television ad, and it still sounded bad.
Interestingly, the interview (or whatever you call it) was rather awkward, because there was about a one-second signal delay. You could see the astronauts still listening once the interviewer had concluded the question. Being the geeks that we are, we did a little bit of math and guessed must be bouncing through so many relays and geosynchronous satellites that we were seeing a speed-of-light delay. I don’t know if we were correct.
Here’s my WAG: The sound quality sucks because the transmissions are relayed via satellite to the ground, and those satellites have minimal bandwidth and use old technology.
Remember, VHF communication is line-of-sight, and the space shuttle is orbiting the earth something like once every 90 minutes.
Back in the early days of the space program, NASA had a series of tracking and communication stations all around the globe. As a spacecraft orbited, communications would be handed off from one ground station to another. It was a logistical nightmare, and still left blind spots over oceans, etc. So NASA eventually put up some communications satellites in Geosynchronous orbit, spaced so that a shuttle or any other spacecraft could maintain constant communication. These things were put up decades ago, and are so expensive that they probably carry a zillion channels of telemetry, voice, and other stuff. This would limit the bandwidth for each channel.
Another possible reason: High bandwidth requires more power, and/or bigger antennas. This adds weight to the shuttle. NASA may have spec’d out the communication system to provide the barest of intelligble communication, so that it used the least amount of power.
read the link I provided, the explain the whole setup in there. But you are right, the signal bounces off satellites, ground stations… it looks like 5 different stations and the like. No wonder it sounds bad.
Just read the link.
The Orbiter uses 32Kbps voice channels, encoded as a digital stream. This is plenty of bandwidth for high-quality voice. For comparison, your telephone’s bandwidth is only about 3500hz, and could be encoded without much loss in about 14 kbps without compression. Remember your MP3 files? If you want to see what kind of quality you can get at 32kbps, record yourself talking into a mike and encode an MP3 at that data rate. I don’t think you’ll be able to hear much difference. Music would suck, but voice transmissions don’t need anywhere near as much bandwidth.
The poor quality probably has to do with the huge number of intermediate steps the audio goes through. From astronaut mike through the radio system to A/D encoder, to the transmitter, TDRS satellite, ground station, D/A conversion, transmission through god knows how many patches and cables before it’s finally amplified and you hear it. The shuttle’s electronics have to be lightweight, so you’re not going to have Hi-Fi stereo gear onboard. You’ll have the minimal amount of equipment required to do the job.