On May 20, 2020, the prime contractor of the Argos-4 HoPS mission, General Atomics (GA), hosted a major milestone, its Delta Critical Design Review (CDR) virtually for its customers. In attendance was NOAA, the U.S. Air Force, and Aerospace Corporation. The purpose of the Delta CDR was to capture final updates to the spacecraft design to incorporate the change of primary payload from a reflectometry instrument (ReSI) to a Radiation Monitor (RADMON) and to address residual actions and liens from the initial CDR held in December 2019. In addition, the Argos-4 Assembly, Integration and Test (AIT) plan was presented to customers. GA also discussed changes to the payload launch vehicle, an updated Electromagnetic Control Plan, mechanical design analysis, and reviewed risks. The following day, GA held a Quarterly Review with OPPA leadership in attendance to be debriefed. The Argos-4 program is looking forward to its next milestone- acceptance of the flight payload from Europe later this summer!