For the purpose of this RFI, NASA is seeking ideas for one large payload up to 13,200 pounds (6,000 kilograms) or smaller, stackable payloads up to 661 pounds (300 kilograms) each. Payloads could be mounted in any number of configurations within the adapter, which sits between the Orion spacecraft and rocket’s upper stage. Actual mass allocations on the flight would depend on the flight trajectory and payload capacity after the primary mission is satisfied.
A fully-loaded extended Cygnus would be a little bit over 11,000 pounds. Seems like the logical fit for this mission, given its flight plan. Except for this part of the release:
Current EM-2 mission concepts assumes that any co-manifested payloads would deploy from SLS and have no further interaction with the rocket or Orion spacecraft. NASA would provide the launch opportunity, and the payload provider would assume all payload costs.
It certainly doesn’t sound like NASA is ruling out the idea that the payload would interact with Orion. They wouldn’t say anything close to “current mission concepts assume” if they weren’t open to that change. Orbital ATK has certainly shown other ideas on what EM-2 could do with a Cygnus involved. My bet is that EM-2 will look an awful lot like the afore-linked video.