The NRO sometimes has a spare satellite in production, so if one failed somehow, the replacement could be ready relatively quickly, if it was vital to national

The NRO sometimes has a spare satellite in production, so if one failed somehow, the replacement could be ready relatively quickly, if it was vital to national security. The NRO has transferred surplus hardware to NASA for science missions. Google Terra Bella (aka Skybox) uses SmallSat (~100 Kg) imaging satellites, and the NRO could use a similar for priority uses where a launch failure wouldn't be as painful as loosing a $1Bn spy satellite. A SmallSat wouldn't be as capable as the larger ones, but has advantages. The purpose of the EELV program is more about assured access to launch vehicles to get to space, than individual missions being near 100% success.