I noticed over the years that satellite beacon downlinks transmit their telemetry in a form that must be translated by a telemetry app to their engineering values. Since the information is transmitted from the satellites why not provide the engineering values in the downlink without the extra step having to be done on the ground? What is the logic of doing this?
Dave Marthouse N2AAM [email protected]
David,
It is much more efficient in terms of the information transmitted, hence power and bandwidth, to use the raw binary/hex for transmission. It also saves the programming and memory in the satellite CPU. The combination frees up resources which can be otherwise used. It works well given the almost universal availability of personal computers. I recall, vaguely, there have been a few birds with some "quick look, real people" data, but I may be in error.
73s,
Alan WA4SCA
<-----Original Message----- <From: [email protected] <[mailto:[email protected]] On Behalf Of Dave Marthouse <Sent: Monday, December 09, 2013 7:35 AM <To: [email protected] <Subject: [amsat-bb] General Telemetry Question < <I noticed over the years that satellite beacon downlinks transmit their <telemetry in a form that must be translated by a telemetry app to their <engineering values. Since the information is transmitted from <the satellites <why not provide the engineering values in the downlink without <the extra <step having to be done on the ground? What is the logic of doing this? < < < < < <Dave Marthouse N2AAM <[email protected] < < <_______________________________________________ <Sent via [email protected]. Opinions expressed are those of <the author. <Not an AMSAT-NA member? Join now to support the amateur <satellite program! <Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb <
On 12/9/13, Alan [email protected] wrote:
David,
It is much more efficient in terms of the information transmitted, hence power and bandwidth, to use the raw binary/hex for transmission. It also saves the programming and memory in the satellite CPU. The combination frees up resources which can be otherwise used. It works well given the almost universal availability of personal computers. I recall, vaguely, there have been a few birds with some "quick look, real people" data, but I may be in error.
ARRISat transmitted some of its operating data on FM using a voice synthesizer.
73s
Bernhard VA6BMJ @ DO33FL
<snip>
Hi All,
Just to confuse ..FUNcube-1 transmits some telemetry in RAW and some in human readable format. The latter comes from the GOMspace EPS which is powering our baby!
cheers
Graham G3VZV
-----Original Message----- From: Alan Sent: Monday, December 09, 2013 2:44 PM To: 'Dave Marthouse' ; [email protected] Cc: CC Subject: [amsat-bb] Re: General Telemetry Question
David,
It is much more efficient in terms of the information transmitted, hence power and bandwidth, to use the raw binary/hex for transmission. It also saves the programming and memory in the satellite CPU. The combination frees up resources which can be otherwise used. It works well given the almost universal availability of personal computers. I recall, vaguely, there have been a few birds with some "quick look, real people" data, but I may be in error.
73s,
Alan WA4SCA
<-----Original Message----- <From: [email protected] <[mailto:[email protected]] On Behalf Of Dave Marthouse <Sent: Monday, December 09, 2013 7:35 AM <To: [email protected] <Subject: [amsat-bb] General Telemetry Question < <I noticed over the years that satellite beacon downlinks transmit their <telemetry in a form that must be translated by a telemetry app to their <engineering values. Since the information is transmitted from <the satellites <why not provide the engineering values in the downlink without <the extra <step having to be done on the ground? What is the logic of doing this? < < < < < <Dave Marthouse N2AAM <[email protected] < < <_______________________________________________ <Sent via [email protected]. Opinions expressed are those of <the author. <Not an AMSAT-NA member? Join now to support the amateur <satellite program! <Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb <
_______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Answer: Engineering efficiency..
There is far more computing power on the ground than the satellite. Also, KISS principle. Also, calibration can be done without modifying flight code. And finally, it is far more compact to send binary or hex than human readable decimal.
Bob, WB4aPR
-----Original Message-----
why not provide the engineering values in the downlink without the extra
step having to be done on the ground? What is the logic of doing this?
To follow up on Bob's comment. If you send the raw analog sensor data to the ground you can - Fix mixed up channels if you got them wrong before launch. This happened with the 1990 AMSAT Microsats and I've seen it since then in other birds. - Change calibration values if found to be wrong after launch. I've seen this most often with ACS systems where the sign of a magnetometer or torq rod is backwards. - Change cal equations if an analog sensor or its system partially fails. Most recently I've seen this with a science mission cubesat that has been in orbit about 6 months and suffered a partial failure. Adjusting the equations on the ground allowed for a continued science mission. - Save downlink characters, hence time. You can get more data down in a shorter packet. Example: To send human readable ASCII for a telemetry value like "A=3676 " takes 7 bytes. If you just send the number and a space it's 5 bytes. The same value in binary is two bytes (long int in C language). - Get all values in a single AX.25 frame with a single and common time stamp. In binary you can get about 225 values in a frame (with a time stamp, ID, etc.). In ASCII you can only fit about 50ish. A typical cubesat has more than 50 TLM values (although some have less). A typical microsat may have as many as 200. - When downloading science or sensor data the amount you can get to the ground is often the limiting design factor. With current technology you can usually store as much as you want in the sat. But to get it to the ground you need to be as efficient as possible. Binary is most often used, but that's not efficient enough for some missions and further compacting the data is needed - using one or more of several other techniques.
Jim
On 12/9/2013 7:44 AM, Robert Bruninga wrote:
Answer: Engineering efficiency..
There is far more computing power on the ground than the satellite. Also, KISS principle. Also, calibration can be done without modifying flight code. And finally, it is far more compact to send binary or hex than human readable decimal.
Bob, WB4aPR
-----Original Message-----
why not provide the engineering values in the downlink without the extra
step having to be done on the ground? What is the logic of doing this? _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Hi,
In the case of FUNcube the on board sensors give their readings as n bit values when they are interrogated. This data is agregated into a data frame for transmission using forward error correction to improve the s/n ratio.
The problem with on board conversion is that you would have to store the scaling/offset/logarithmic values for all channels on board, in rom.
These are usually only characterised during thermal cycling / illumination testing etc and would have to be uploaded to the satellite rom. Not necessarily a simple task.
It is easier to do it on the ground where we can tweak the calculation factors.
73
Dave, g4dpz On 9 Dec 2013 13:52, "Dave Marthouse" [email protected] wrote:
I noticed over the years that satellite beacon downlinks transmit their telemetry in a form that must be translated by a telemetry app to their engineering values. Since the information is transmitted from the satellites why not provide the engineering values in the downlink without the extra step having to be done on the ground? What is the logic of doing this?
Dave Marthouse N2AAM [email protected]
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
participants (7)
-
Alan -
B J -
Dave Marthouse -
David Johnson -
Graham Shirville -
Jim White -
Robert Bruninga