The Multiple Payload Ejector carrier system has been built by Wallops Flight Facility as a modular structure designed to carry multiple segments that support smaller individual payloads.
MPE can accommodate multiple payload classes, ranging from over 400 pounds to under 10 pounds. The MPE envelope and orbital insertion mass are consistent with the DARPA Falcon demonstration launches. A Falcon demo is likely to be the first launch of the MPE.
There are three payload classifications for MPE payloads - Primary, Secondary, and Tertiary. The payload organization may request a specific classification based on desired priority, services, and volume and mass. NASA has the final determination on payload classification.
Primary Payloads: There is only one primary payload per mission. Primary payloads will have priority in determining mission parameters such as orbit altitude, ejection options, cleanliness requirements, and other system level parameters. The mass and volume available for the primary payloads is greater than secondary and tertiary payloads.
Secondary Payloads: The number of secondary payloads depends on the number of MPE segments. Services are available to secondary payloads with less input toward mission parameters. Secondary payloads can be manifested in the primary slot when a primary payload is not available, however a secondary payload in a primary slot does not have the privileges of a primary payload.
Tertiary Payloads: Tertiary payload slots are typically available in the 2 and 3-segment configurations. There is a maximum of 4 slots per segment. Tertiary slots are designed to accommodate a P-POD Mark 2 ejection system or equivalent.
Tertiary payloads are considered low priority in determining mission parameters and providing services. Tertiary payloads can be manifested in a secondary slot.