**2.2 Existing mission payload, related interfaces and standards**

As pointed out in Section 1, existing mission PL architecture consists of 14 modular components, but there are three PL components that rely on the satellite Bus' design, namely, PL EPS, PL ADCS and PL PS. Therefore, the mission PL architecture usually has 11 modular components, including PL AS, PL Com-RFS, PDPS, PL C&DHS, PL TT&CS, PL TCS, PL COMSEC, PFTS, PL TRANSEC, PL SMS and PL S&MS. A functional description for each of these mission PL modular components is also provided in Section 1. **Figure 4** presents a notional block diagram for existing modular mission PL architecture. Similar to the satellite Bus

#### **Figure 4.**

*Existing notional modular Mission payload architecture.*

design, the space industry has also applied the modular design concept to architect the mission PL. Below is a list of some of the existing interfaces and associated standards for existing mission PL leveraged from NASA, ESA, U.S. DOD and international CCSDS standards [19–26]:

	- Sizing all components of the mission PL power harness, such as the wires, connectors, sockets, and pins to the peak power level shall be required by the mission PL equipment in addition to satellite Bus to prevent damage to the power harnessing.
	- PL Survival Heaters shall be required to have power to heat certain mission PL components during off-nominal scenarios when the BEPS power is not fully energized.
	- The mission PL thermal design should be decoupled from the satellite Bus at the mechanical interface between the satellite Bus and neighboring mission payload to the maximum practical extent.
	- A conductive heat transfer of 15 W/m2 or 4 W shall be considered small enough to meet the intent of being thermally isolated.
	- Mission PL command and telemetry data formats shall be NASA USB/CCSDS standards commercial applications or U.S. DOD SGLS standards for military applications. Some military systems have both USB and SGLS capabilities.
	- PL "Safe Mode" is a combined mission PL components hardware and software configuration that shall be designed to protect the PL components from possible internal or external harm while making minimal use of satellite Bus resources (e.g., power).
	- PL Command SAFE Mode shall be required to protect and preserve mission PL components under anomalous and resource constrained conditions.
	- Mission PL components shall respond to uplink commands from Mission Control Center (MCC) to suspend and resume the transmission of the mission PL components.
	- Mission PL shall be responsible for on-board mission data storage capabilities.

For most commercial applications, the MCC can be merged with the SOC, and the mission PL TT&CS (PTT&CS) and PL CD&HS (PCD&HS) components can be incorporated into satellite (i) Bus TT&C (BTT&CS) and (ii) Bus CD&HS (BCD&HS) components, respectively. Similar to the satellite Bus interfaces design, for military applications, the mission PL components are tightly coupled using contractor's custom designed interfaces. For commercial applications, the mission PL components are loosely coupled using widely accepted open interfaces.
