Lantern is poorly described in the website. This should simply be fixed.
Not knowing the exact specs of the device is a poor excuse for the
lack of clarity on this.
As of Nov 30, 2014, the highest capacity SD card I can easily find on the web
is 256GB. It costs $97, quantity 1.
look up PNY-Elite-Performance-256GB on amazon.
If we stick with spending $100 for hard drives,
3Tbytes costs $100
Look up hard drives at Microcenter.
If we are designing for a year from now (Nov 2015) , we expect prices to fall, and we'll be ordering in
quantity. On the other hand, you want reliability so the absolute max capacity
isn't the best. But let's estimate we'll be able to get double those
capacities for $100, so that's 512Gbytes sd (maybe use 2 cards!) or
6Tbytes of magnetic hard disk, (SSD disk costs about the same as
Wikipedia English XML compressed is only 10GBytes.
We can uncompress on the fly.
SD is more expensive per byte but has many advantages:
- lower power so less solar panel expense to support it
- more reliable as no moving parts
- much faster so can serve more people quicker with a given processor.
- generates less heat so keeps other parts cooler and thus more reliable,
and necessitating less fan so again less expense and area for solar panels.
and Wikipedia takes up only 2% of it, so let's go with the SD memory.
Note that when a Lantern is shipped, it can be pre-loaded with Wikipedia, etc.
so the satellite to Lantern data transmission only needs to be the updates.
For any large, relatively persistent body of knowledge, updates per month
will be a tiny fraction of the total knowledge size, probably less than 1% per month.