At great risk of being thwapped with a clue bat, I'm going to ask this newbie sort of question that may seem stupid but it has me stumped.
I read/hear about satellites being in eclipse for too long and running out of battery/shutting down/whatever. Now, since most of the LEO satellites are in orbits of 100 minutes +/-, I don't understand how they could be in eclipse for more than ~50 minutes. So the question is...
For the satellites that have this eclipse issue, is it that their batteries are essentially expired and can't power the satellite for ~50 minutes (that makes sense to me) based on the charge they get from having the solar panels exposed for ~50 minutes, or is there some mechanism that is totally non-obvious to me that allows a LEO satellite to be in the dark for periods of time much longer than half of each orbit thereby creating a situation where the batteries have to power it in the dark for a very long period of time relative to the orbital period?
If it's the former, well, that's obvious enough I guess. If it's the latter, could someone draw me a picture or point me to a URL that explains how that is possible?
Thanks.
Darin VE3OIJ
Hello Darin,
The eclipse period depends upon the orbit of the satellite. In the last AMSAT Journal I had a graph of the changing eclipse period of AO-51. The ability to charge the batteries depends upon the surface area of the satellite that has solar cells, how efficient the solar cells are, the length of time the solar cells are exposed to sunlight and the angle of the sun on the solar cells.
With AO-51 we can set the TX output power level for both transmitters. In my role of managing the satellite I am constantly monitoring the total power consumption of the satellite and making sure that the satellite batteries will sustain that power level during each eclipse period. The batteries are recharged each time the satellite is in the sun. Determining the TX power levels and what modules are on at any particular time and factoring in the eclipse time and sun time plus sun angle are all part of managing the satellite and part of being a command station. Some smaller satellites may not have space to add the additional control circuitry, it is a trade off.
AO-51 has gone from periods of nearly half an hour of eclipse each orbit to no eclipse period over the last 3.5 years.
Essentially it goes back to the basic design of the satellite. Knowing the basic orbit the satellite will be in, how much surface area is needed to support X amount of TX power during Y long eclipse periods. Then designing a battery charger/regulator to support this and provide the ability to alter whatever is needed to maintain an operational satellite.
If you interested in the actual systems AMSAT offers a book on AO-51 with descriptions of all the hardware systems and specifications.
73, Gould, WA4SXM AO-51 Command Station
----- Original Message ----- From: "PDC" [email protected] To: [email protected] Sent: Tuesday, January 15, 2008 3:19 PM Subject: [amsat-bb] Satellite in eclipse
At great risk of being thwapped with a clue bat, I'm going to ask this newbie sort of question that may seem stupid but it has me stumped.
I read/hear about satellites being in eclipse for too long and running out of battery/shutting down/whatever. Now, since most of the LEO satellites are in orbits of 100 minutes +/-, I don't understand how they could be in eclipse for more than ~50 minutes. So the question is...
For the satellites that have this eclipse issue, is it that their batteries are essentially expired and can't power the satellite for ~50 minutes (that makes sense to me) based on the charge they get from having the solar panels exposed for ~50 minutes, or is there some mechanism that is totally non-obvious to me that allows a LEO satellite to be in the dark for periods of time much longer than half of each orbit thereby creating a situation where the batteries have to power it in the dark for a very long period of time relative to the orbital period?
If it's the former, well, that's obvious enough I guess. If it's the latter, could someone draw me a picture or point me to a URL that explains how that is possible?
Thanks.
Darin VE3OIJ _______________________________________________ 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
I'm going to ask this newbie sort of question... since most of the LEO satellites are in orbits of 100 minutes +/-, how can they be in eclipse for more than ~50 minutes.
They cant, but it is never 50% because the satellite is high, so it sees over the horizon. Thus for a 100m orbit, we get about 65 minutes in the sun and about 35 minutes in the dark.
Here is our LESSON LEARNED on PCSAT1. Its not the "eclilpse" that kills us, but our inability to charge enough during the 65 minutes to make it through the next 35 min eclipse. That is why PCSAT works on every orbit after it has entered the sun. After about 20 minutes it has charged up enough to work. But in the remaining 45 minutes it cannot accumulate enough charge to then fully make it through the next 35 minute eclipse.
Thus, it dies 14 times a day, and resets back to the defaults, which enables back up receiveers and transmitters to assure recover from the ground. It is that extra load that prevents enough charge to make it. Only 3 times a year when the sun is right, it can stay up long enough for us to send the command to turn off the extra receivers and transmitters, then let it charge up fully, and then it runs fine for a month or so until something happens and it resets.
Just a lesson learned. *** Make sure you can charge up enough in ONE pass in the sun, to survive the next eclipse.
Bob, Wb4APR
I operate Geo-stationary satellites for a living, and I agree with Bob on this. Geo-stationary birds have even shorter eclipses due to their increased altitude (approx 22,300 miles) Those eclipses are at most 72 minutes at the peak of eclipse season (equinox). Towards end of life the solar arrays can degrade and the problem becomes recharging the batteries enough to make it through the next eclipse 24 hrs later. We have in the past reduced the transponder load on spacecraft when the arrays couldn't support charging the battery enough to handle the full load through the eclipse.
Mark KK7CU
On 1/16/08, Robert Bruninga [email protected] wrote:
I'm going to ask this newbie sort of question... since most of the LEO satellites are in orbits of 100 minutes +/-, how can they be in eclipse for more than ~50 minutes.
They cant, but it is never 50% because the satellite is high, so it sees over the horizon. Thus for a 100m orbit, we get about 65 minutes in the sun and about 35 minutes in the dark.
Here is our LESSON LEARNED on PCSAT1. Its not the "eclilpse" that kills us, but our inability to charge enough during the 65 minutes to make it through the next 35 min eclipse. That is why PCSAT works on every orbit after it has entered the sun. After about 20 minutes it has charged up enough to work. But in the remaining 45 minutes it cannot accumulate enough charge to then fully make it through the next 35 minute eclipse.
Thus, it dies 14 times a day, and resets back to the defaults, which enables back up receiveers and transmitters to assure recover from the ground. It is that extra load that prevents enough charge to make it. Only 3 times a year when the sun is right, it can stay up long enough for us to send the command to turn off the extra receivers and transmitters, then let it charge up fully, and then it runs fine for a month or so until something happens and it resets.
Just a lesson learned. *** Make sure you can charge up enough in ONE pass in the sun, to survive the next eclipse.
Bob, Wb4APR
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 (4)
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Gould Smith
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Mark Lockwood
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PDC
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Robert Bruninga