[angry_octet]

While amateurs can do an amazing job of detecting satellites, I think it is pretty likely that there are smaller satellites which are operating in extreme low power mode, waiting until a conflict where they are required. Whether there are enough to replace GPS and comms lost due to anti-satellite attacks and resulting debris is a bigger question.

[nradov]

It isn't physically possible to get useful GPS service from a small satellite. This is just basic physics. Calculate the power required to transmit the necessary signals. You need some fairly sizable solar panels. No way to hide those.

[mlyle]

I get crummy GPS fixes inside my house with 30dB+ of attenuation of the signal by structure and parts of the sky absolutely masked, while using absolutely crummy antennas.

To me, this seems to imply you could make a useful system today with orders of magnitude less transmit power.

[orestarod]

Maybe I do not understand something. But you get these readings, through all these conditions, with the help of the present, powerful and energy hungry satellites. A mini, less powerful satellite would not perform the same under the same conditions.

[sciurus]

The military doesn't need GPS to work from inside a house.