**2. Existing satellite systems, related interfaces and standards**

**Figure 2** describes an overview of existing satellite systems, consisting of a satellite Bus, a mission PL and a typical set of interfaces between the Bus and PL using a standard data Bus. A typical set of interfaces between the satellite Bus and a mission PL includes seven interface types, namely: (i) Physical & Mechanical Interface, (ii) Electrical/Power/Cable Interface, (iii) Grounding Interface, (iv) Software & Data Interface, (v) Electromagnetic Compatibility (EMC)/ Electromagnetic Interference (EMI)/Electromagnetic Pulse (EMP) and Electro Static Discharge (ESD) Interface, (vi) Thermal Interface, and (vii) Frequency & Timing (F&T) Interface. This section focuses on satellite Bus and mission PL architectures and the data interfaces between them. Subsections 2.1 and 2.2 describe existing satellite Bus and mission PL architectures along with related interfaces and industry standards, respectively. Subsection 2.3 discusses existing standard 1553 data Bus and the pushes from space industry moving toward military standard 1553-B data Bus (MIL-STD-1553-B) and high-data-rate SpaceWire data Bus.

#### **2.1 Existing satellite bus, related interfaces and standards**

As described in Section 1, existing satellite Bus architecture includes typical 10 modular components, namely, BAS, BComRFS, BC&DHS, BTT&CS, BEPS, BTCS, BADCS, BPS, BCOMSEC and BS&MS. A functional description for each of these modular Bus components is also described in Section 1. **Figure 3** illustrates a notional block diagram for existing modular satellite Bus architecture. The figure

## *Future Satellite System Architectures and Practical Design Issues: An Overview DOI: http://dx.doi.org/10.5772/intechopen.92308*

#### **Figure 2.**

*Overview of existing satellite Systems using standard 1553 data bus.*

#### **Figure 3.**

*Existing notional modular satellite bus architecture.*

shows that space industry has used the modular design concept to architect the satellite Bus, where common functions are group together and then isolate or separate from the other group of functions. As an example, BAS consists of a group of antenna components and control functions (e.g., antenna pointing, beamforming, etc.), which is separated and isolated from BComRFS. It is important to note that the figure also shows how these satellite Bus components are connected together, i.e., the lines with arrows connecting them. These lines represent the interfaces among the Bus components, where the interface can be any of the seven interface types described above. Below is a list of some of the existing interfaces and associated standards for existing satellite Bus based on National Aeronautical and Space Administration (NASA), European Space Agency (ESA), U.S. DOD and international Consultative Committee for Space Data System (CCSDS) standards [19–26]:

	- Satellite Bus shall protect its own electrical power system via overcurrent protection devices on its side of the interface.
	- Satellite Bus shall deliver a maximum transient current on any Power Feed Bus of 100% (that is, two times the steady state current) of the maximum steady-state current for no longer than 50 ms.
	- Bus Survival Heaters, which are elements of the Bus thermal subsystem, shall be required to have power to heat certain satellite Bus components during off-nominal scenarios when the BEPS power is not fully energized.
	- Power line conducted emissions for satellite Bus equipment shall meet the EMC interface specification specified in SMC Standard Handbook, SMC-S-008, Section 6, 6.01, 6.02, 6,03, 6.04, 6.05, 6.06, 6.07, and 6.08.
	- Power line conducted susceptibility for satellite Bus equipment shall meet the EMC interface specification specified in SMC Standard Handbook, SMC-S-008, Sections 6, 6.10, 6.11, 6.12, 6.13, 6.14, 6.15, 6.16, 6.17, 6.18 and 6.19.
	- ESD susceptibility for satellite Bus equipment shall meet the EMC interface specification specified in SMC Standard Handbook, SMC-S-008, Section 6, 6.43.
	- EMP susceptibility for satellite Bus equipment shall meet the EMC interface specification specified in SMC Standard Handbook, SMC-S-008, Section 6, 6.45.
	- Satellite Bus EPS should ground in a way that reduces introducing stray currents or ground loop currents into the satellite Bus components.
	- Satellite Bus ground interface shall follow NASA single-point ground or multiple-point ground architecture.
	- A conductive heat transfer of 15 W/m2 or 4 W shall be considered small enough to meet the intent of being thermally isolated.
	- Satellite Bus command and telemetry data formats shall be NASA Unified S-Band (USB)/CCSDS standards or U.S. DOD Space-Ground Link Subsystem (SGLS) standards. Note that (i) most of NASA and ESA standards are CCSDS compliance for interoperability purpose, and (ii) some military systems have both USB and SGLS capabilities.

*Future Satellite System Architectures and Practical Design Issues: An Overview DOI: http://dx.doi.org/10.5772/intechopen.92308*


For military applications, majority of satellite Busses are usually designed using contractor's custom designed interfaces and very tightly couple together to reduce weight, size and power. It is for this reason, current military satellite BTT&CS component also include the COMSEC component. For commercial applications, satellite developers are also concerned with weight, size and power reduction, but they are also concerned with component refresh and upgrade without redesigning the satellite Bus, hence commercial satellites tend to use modular Bus components and widely accepted interface standards to connect the internal Bus components. Industry views on the "open" and "close" interfaces will be addressed in Section 4.
