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Telemetry Made Simple: Rocket Phone Home
UserID 3.14 writes "This article from science daily talks about a communications module that will be strapped to the rockets of a shuttle or other payload delivery vehicle. It can be used to provide constant telemetry by making a cell phone call using the Globalstar Network. Does this mean that if you use a cell phone in space, even there people will ask you to step outside?" See NASA's web page about the Flight Modem, which seems to be very much a work in progress
Just so long as they don't try to WAP-enable the launch vehicles, I think we'll be juuust fine...
"Hey, it looks like booster rocket #4 made $500 worth of calls to a 900 line..."
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If you ever drop your keys into a river of molten lava, forget 'em, because man, they're gone. -- Jack
I regularly participate in amateur rocket competitions. For telemetry I find it quite simple to attach a Nokia 5100 (with detached Honey Orange faceplate) and wire it to a microprocessor that will send varying volumes in different audible frequency bands to indicate different values, scaled into audible ranges. For example, altitude, airspeed, latitude and longitude (as calculated by GPS and communicated to the uP). I simply record on DAT tape the audio on another cell phone. When I return home I play the audio into my computer as a WAV file, and then run spectrum analysis on it and scale and filter frequency analysis into raw telemetry data that I can then plot. (This is easily done with Matlab).
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Know someone who is stealing cable? Report them!
It can be used to provide constant telemetry by making a cell phone call using the Globalstar Network.
- sea-level.- sea-level, will you accept charges?
May I humbly suggest a cost-saving measure:
Rocket: I'd like to make a collect call please.
Operator: Who may I say is calling?
Rocket: Bob I'm-at-23.494923N-82.293823W-3042.4293-feet-below
Operator: One moment please.
*Somewhere in a control room, a telephone rings*
Chart Plotter: Hello?
Operator: I have a collect call from Bob I'm-at-23.494923N-82.293823W-3042.4293-feet-below
Chart Plotter: Wrong number.
*Chart Plotter hangs up*
Operations Manager: Who was that?
Chart Plotter: The rocket. It's over Cuba.
NO CARRIER
Ground Control to Major Tom
Ground Control to Major Tom
Charge your mobile phone and put your hands free on.
Ground Control to Major Tom
Commencing dialup, cell-phone on
Check phone number and may ATT's love be with you
(spoken)
Ten, Nine, Eight, Seven, Six, Five, Four, Three, Two, One, Liftoff
This is Ground Control to Major Tom
You've really been connected
And the papers want to know whose telco you use
Now it's time to use the hands free if you dare
"This is Major Tom to Ground Control
I'm stepping through the door
And my cell phone's floating in a most peculiar way
And your voice sounds very different today
For here
Am I sitting in a tin can
Far above the world
My cell-phone's been cut off
And there's nothing I can do
Though I'm past one hundred thousand miles
I'm feeling very still
And I think my cell-phone knows which tower to use
Tell customer support I love them very much - they know"
Ground Control to Major Tom
Your cell phone's dead, there's something wrong
Can you hear me, Major Tom?
Can you hear me, Major Tom?
Can you hear me, Major Tom?
Can you....
"Here am I floating round my tin can
Far above the Moon
my cell phone's been cut off
And there's nothing I can do."
NASA is willing to strap a cell phone to their tres expensive rockets filled with sensitive custom electronics, but Continental won't let me use my cell phone in the air. "Oh no, it might interfere with the aircraft's avionics. Besides, you can't use cell phones in flight because they'll see too many cells at once from way up there. Use our AirPhone instead, only $19.99/second!"
I'll bet astronauts don't have to put their seat backs and tray tables in their full upright and locked positions, either. Lucky bastards.
The traditional way of doing this is to put an inertial platform and navigation unit on the rocket. That is what is used on most lauch vehicles.
Telemetry data is usually downlinked as a synchronous serial stream composed of fixed length telemetry frames. Reed-Solomon and convolutional error correcting codes may be used to improve the bit-error-rate and link margins. Nobody, that I know of, uses IP for any air-to-ground communication links. IP is widely used for transferring data between ground stations and control centers.
One problem with the "rocket phone" is the low bit rate. Most launch vehicles have telemetry data rates in the 200 kbps to 600 kbps range.
Range safety is an important issue. Most range safety systems use multiple sources of data, such as launch vehicle telemetry, tracking antenna angle encoders, multiple C-band radar systems and optical trackers. You have to know where the rocket is, where it is heading, and whether the engines and other systems are working properly.
Mea navis aericumbens anguillis abundat
It used to be that NASA had to have a string of ground stations and ships around the world to get continuous data from space vehicles. This is still an issue for countries like China, and the logistics have impacted their space program. NASA does now use a lot of custom relay satellites, but the communications hardware is still $100k+ one-offs for each application. Using $5k of commercial equipment that is probably better developed is indeed a good thing. The articles also lumped together with the LEO sat communication aspect the increasing use of GPS to augment and eventually replace dedicated radar for positioning. John Carmack