That is interesting and makes sense. A 1U CubeSat has about the same volume to dedicate to power as a typical laptop. 

Having to keep a power reserve for 6 weeks on a secondary type battery without charging for 6 weeks is difficult. And the analogy fits as laptops do this as well. 

One option might be to include a watchdog. A primary battery with an low power microcontroller to switch from the primary (and therefore shelf stable) to turn on secondary power along with the rest of the CubeSat. Once power is latched through a mechanical relay for the satellite, it could shut down and not drain power. Today there are space rated microcontrollers that drain as little as 0.4uA on standby, shut down 0.02uA on shutdown.

Dimitrios
VA3DSZ

On Sun., Jan. 31, 2021, 13:59 Ashhar Farhan, <farhanbox@gmail.com> wrote:
Having built four missions and launched two, I can say that the main challenge of cubesats is their really small power budget. The rest of the risks just multiply because of that. 
Very often, the time from insertion into the ppod to launch is  more than six weeks. The batteries drain off, as the batteries drain off, the entire system is browned out. it is a miracle to put up back again. very often, the analog circuitry that would have charged the batteries through solar panels is replaced by software on OBC. But the OBC is unavailable, the analog state is undetermined. There is a colossal fight among schrodinger's cats inside the box. 
On the other hand, why does the AO-7 continue to work? because it has an all analog design that will turn on the transponder as soon as power is applied and the oscillators can oscillate. If they fail to boot up on one orbit, there is always another orbit to bet on.
This  is also compounded by the cubesat/IARU specification that insists the satellite should have a way to switch itself off under ground control. This means that unless the CPU decides to wake up the radio, it will remain silent. If the CPU has browned out, then bye, bye, bluebird!
- f
 


On Sun, Jan 31, 2021 at 10:06 PM Dimitrios Simitas <va3dsz@gmail.com> wrote:
CubeSats enjoy a up to a 39% industry average failure rate. From most common to least, CubeSat failure (21%), launch failure (12%), and not ejected and not specified are tied at 2% each.


Successful deployment made up 61% of the 848 CubeSat launches between 2005 and 2018. So the Fox line has met industry standards (3 of 5 deployed successfully).

The hardware, even if purchased to be space tolerant, is still assembled and ground based testing in a educational or not for profit environment is limited compared to the big commercial companies. It's the reason why Es'hail 2's amateur component was built commercially using AMSAT specifications.

There is also the issue that as secondary payload CubeSats have been developed to not use active means of deployment. Such as hoping their solar cells, and antennas release. Which is suspected to have caused many failures as has been pointed out. 

Even so, SpaceX is seeing a 5% failure rate on their $2.5 million Starlink Satellites and even NASA's $4 billion Hubble had issues. Space can be unforgiving. And due to size and weight constraints of CubeSats, unlike larger commercial satellites, it's nearly impossible to build redundant systems to keep the satellite functional after any system failures. 

The term acceptable failure rate in engineering comes to mind. And expecting perfection out of a CubeSat just isn't going to happen. 

Dimitrios
VA3DSZ

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