[amsat-bb] Digital Satellites Question

Phil Karn karn at ka9q.net
Sun Jul 27 05:58:17 UTC 2014

On 07/22/2014 08:41 AM, Dave Marthouse wrote:

> A digital satellite would imply loads of processing power on the
> satellite.  I would assume that with this additional activity that there
> will be more
> hardware on the bird with more complexity as this won't be a bent pipe
> system.

Not necessarily. Yes, it will rely on onboard computers -- but so do the
many analog satellites that use them for command and control. When the
IHU memory on AO-10 failed after 3 years in a high radiation orbit, the
analog transponder continued to operate but there was no way to repoint
the antennas and solar panels or to change the operating mode or power
system setpoints.

> With more physical hardware of much more complexity in orbit what about
> the radiation hazards to this more complex and physical hardware heavier
> system?  Wouldn't a software based system be prone to radiation induced
> hardware and software glitches?
> What about shielding etc?

Radiation usually isn't a serious problem in LEO, though relatively
simple precautions like error-corrected memory are still a good idea.
With 14-16 day-night cycles per day, the usual problem is battery wearout.

And for low altitude cubesats, atmospheric drag usually trumps
everything else. Small objects tend to have small ballistic coefficients
making them more susceptible to drag. Even ARISSat-1, which was larger
and heavier than a cubesat, decayed in only a few months. Most cubesat
launch opportunities are to low altitudes, partly because that's where
the ISS flies, and partly because of the increasing pressure to minimize
space debris by keeping them out of the longer-lived altitudes.

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