Atlas V 541 - NROL-42 - VAFB SLC-3E - Sep 24, 2017 05:50 UTC (Sep 23 2250 PDT)

[jcm]

I hadn't spotted this before or seen discussion about it: the Enhanced Polar System USAF comms package EPS-2
probably flew on this mission

https://govtribe.com/project/sources-sought-recapitalization-of-enhanced-polar-system-eps-satellite-communications-system

(text attached)

SMC plans to purchase two additional EPS EHF XDR payloads to prevent a MILSATCOM
mission gap in the Polar region. SMC is pursuing a near-term hosted payload
option to be launched in Calendar Year (CY) 2022 to satisfy EPS mission
requirements...

Global protected SATCOM will be provided in the near-term by two complementary 
space systems. The Advanced Extremely High Frequency (AEHF) system currently 
provides protected SATCOM services for both tactical and strategic users in
mid-latitude regions (65°S to 65°N). The EPS will soon provide protected SATCOM
for a small number of tactical users in the North Polar Region (65°N to 90°N).ng
Both AEHF and EPS provide protected SATCOM employing XDR payloads utilizing the
EHF band.

EPS payloads are currently hosted on another organization's space vehicle. EPS-1
is currently on orbit and EPS-2 will be available for testing in late CY17. The
EPS ground segments includes a payload control and mission planning element
located at Schriever AFB and a Northern Tier SATCOM Gateway located at Clear AFS,
which provides DoD Information Network (DoDIN) connectivity via the Camp Roberts
Teleport.

I think we may conclude that EPS-1 was on NROL-35 and EPS-2 on NROL-42.
We know the IPS (Interim Polar System) flew on earlier TRUMPET type missions