# Designing a satellite power system

#### JulianTech5

Joined Jul 5, 2018
9
I am currently developing a concept picosatellite project launched by a pocketqube that is in a very early development phase, to be completely honest I have very basic electrical engineering experience when it comes to power systems and want to make sure what i'm doing this fine, the processing and communications part of the satellite are already sorted out and I just need help regarding power management. I am currently designing the power management for 2 separate devices, a small 26x26mm board satellite and a larger pocketqube. More or less to have an idea of the sort of power needs we are talking about here, the board satellite will only consume about 60mw at max and the pocketqube will probably consume about 170mw at most. The smaller board satellite will have no batteries and will use passive attitude control to point at the sun, while the pocketqube will have a small Li-ion battery and will most likely have active attitude control.
I have currently decided to use the SPV1040 MPPT integrated regulator for charging the battery, this will then be combined with some sort of off the shelf overcharge/overdischarge protection circuit. I am hoping to use a TPS62120DCNR switching regulator to regulate the power directly coming from the batteries in the pocketqube and the solar cells in the board sats. The current prototype uses a linear voltage regulator but I would like to increase the efficiency of the regulator.
There is quite a bit of stuff to take in mind and this is sort of an open discussion, feel free to ask me anything about the project and any input and collaboration are really appreciated since I'm working on this on my own.

Julian

#### dl324

Joined Mar 30, 2015
9,344
Welcome to AAC!

Thank you for organizing your thoughts in paragraphs. A few extra blank lines would have been appreciated.
1. What are the solar panel ratings?
2. What are the battery specs?
3. What is your assumption for hours of daylight?
4. How long does the device need to operate in total darkness?
5. What environmental control do you have?
6. What voltage does the regulator need to provide?
7. What is the spacing between the two boards? Is it just one satellite with 2 boards? You mentioned "board sats, so it's unclear.

#### JulianTech5

Joined Jul 5, 2018
9
Welcome to AAC!

Thank you for organizing your thoughts in paragraphs. A few extra blank lines would have been appreciated.
1. What are the solar panel ratings?
2. What are the battery specs?
3. What is your assumption for hours of daylight?
4. How long does the device need to operate in total darkness?
5. What environmental control do you have?
6. What voltage does the regulator need to provide?
7. What is the spacing between the two boards? Is it just one satellite with 2 boards? You mentioned "board sats, so it's unclear.
1. Voltage (Open Circuit) 2.62V Voltage (Max Power)2.33V Current (Max Power)14.6mA Power (Max Power)34 mW Efficiency 28%
2. it completely depends on the beta angle of the orbit and other parameters but for example a standard LEO orbit would have just above 45m of daylight out of a 90m orbit.
3. Approximately 30-45m, same as last question
4. None, basic insulation on the pocketqube and just a bare board on the board satellites. (Seems risky and not appropriate for a Li-ion but batteries have been tests in nearly exact situations on previous missions)
6. 3.3v
7. It is a mothership pocketqube launching smaller board based satellites, sorry for my bad explanation.

Im more than happy to explain anything from this project, thanks for your reply

#### be80be

Joined Jul 5, 2008
1,963

#### JulianTech5

Joined Jul 5, 2018
9
Thanks for the info! However I am hoping to design and create the pocketqube myself, not buy parts. (Price tag is also a little prohibitive )

#### dl324

Joined Mar 30, 2015
9,344
7. It is a mothership pocketqube launching smaller board based satellites, sorry for my bad explanation.
The smaller satellites have no power source? Are they tethered to the larger satellite? How do they get their power? How long do they need to operate?

Does passive attitude control mean none?

You didn't give battery specs. Charging Li-ion batteries is not recommended below freezing or above around 120F. What are the temperature extremes you expect?

#### be80be

Joined Jul 5, 2008
1,963

Thanks

#### JulianTech5

Joined Jul 5, 2018
9

#### be80be

Joined Jul 5, 2008
1,963
Back years ago I seen where they used Li-ion battery it put in a case and used resistor to keep it warm so it could charge these was launched from high altitude balloon.

#### JulianTech5

Joined Jul 5, 2018
9
Back years ago I seen where they used Li-ion battery it put in a case and used resistor to keep it warm so it could charge these was launched from high altitude balloon.
Indeed some satellites use nichrome wire and other heaters to maximize the charging and output of the batteries however people have successfully avoided this before.

#### be80be

Joined Jul 5, 2008
1,963
They had to heat it some how because you cant change the fact that 1000 mA li-ion battery will only put out 500 mA at 18C
and it drops fast from there the colder you get you'd be lucky to get 100mA -15 and like above 500 at 20C

#### JulianTech5

Joined Jul 5, 2018
9
They had to heat it some how because you cant change the fact that 1000 mA li-ion battery will only put out 500 mA at 18C
and it drops fast from there the colder you get you'd be lucky to get 100mA -15 and like above 500 at 20C
indeed, tests will obviously have to be carried out, but so far it looks like it still falls under the required power constraints.

#### JulianTech5

Joined Jul 5, 2018
9
Does anyone have experience with switching regulator circuit design and using the SPV1040? I'm pretty set on those devices and just want to make sure im designing the circuit well.

Thanks