Your larger point about backup being required is very salient, however it is no longer the case that GPS can be turned off or impaired by DOD. When SA was turn

Your larger point about backup being required is very salient, however it is no longer the case that GPS can be turned off or impaired by DOD. When SA was turned off in 2000 it was irrevocable. GPS satellites designed since that date do not carry the SA feature capability.