Space-Track has cataloged two payloads from the Dec 19 Falcon 9 launch, USA 312 and USA 313 (without orbital data of course). This implies the Falcon 9 second stage was deorbited.
看到了吧？原来NROL-108这一发是两颗卫星！

Radio observers have located the NROL-108 payload (USA 312) on orbit:http://satobs.org/seesat/Dec-2020/0105.html51.35 degree inclined, 520 x 540 km orbit.
SSO倾角大于90°，这颗侦察卫星跟SSO无关……