9.4 Design Methodology
313
9.4.4 Bus Network Design
There are many devices on the spacecraft to exchange data and control information.
The bus is the carrier to connect all information nodes and transmit data. Each device
and component involved in the exchange of data information is connected together
via a bus, which sets up an onboard information network. Usually centered on the
onboard computers, the data and commands communication between subsystems and
related payload devices is realized on the onboard data bus. In the interior of OBDH
subsystem, the bus is also necessary for data exchange because of the distributed
architecture.
As the carrier and hub of data communication, the spacecraft bus has not only the
function of data transmission, but also the ability to work in real time, high reliability
in complex space environment and adapt to the requirements of data transmission
service. Therefore, the spacecraft bus is not simply the same as the common data I/O
cable.
The data bus can be classified into two categories: serial and parallel. Up to date,
the serial bus is widely used in spacecraft. Some of the buses used in spacecraft were
developed specifically for military and aerospace applications, such as the MIL-STD1553B bus, the SpaceWire bus, and etc. Some are industrial or commercial buses that
have been used in other fields, such as CAN bus, RS422/485 general line, Ethernet,
IEEE1394, LVDS and etc. It can be selected according to the scale, speed, power
consumption and distance of data transmission.
The MIL-STD-1553B bus (hereinafter referred to as 1553B) was first proposed
by the United States military. It was a standard bus for military aircraft. It was a
digital command-response time-division multiplexed serial bus. The bus controller
was responsible for the bus scheduling and the management control of up to 31
terminals for data communication. The bandwidth was 1 Mb/s. Since 1970s, standard
bus had been developed as well as standardized bus communication protocol, and the
mechanism of bus communication was standardized, then redundant configuration
of hardware and prevention of terminal short-circuit fault were designed. Because
of its high reliability, it was widely used in the aerospace field. Now it was a mature
spacecraft bus, which was applied in many spacecraft all over the word.
The 1553B bus was applied in the Chang’E-3 lunar lander as the main channel of
information. The double redundant hot backup design was applied, and the interface
was transformer-coupled. The terminal signal output terminals had isolation resistors,
and the minimum non-response timeout time was set. The communication timeout
process could avoid the failure of a node of the bus network from affecting the
security of onboard data communication, so as to ensure reliable data transmission
and non-proliferation of faults.
LVDS (Low Voltage Differential Signaling) was a general peer-to-peer physical
interface technology that is suitable for high-speed data transmission with low power
consumption. The technology was based on the ANSI/TIA/EIA-644 LVDS interface
standard. It had the advantages of high speed, low power consumption and low noise.
The LVDS had 330 mV low voltage differential signal and fast transition time. It
313
9.4.4 Bus Network Design
There are many devices on the spacecraft to exchange data and control information.
The bus is the carrier to connect all information nodes and transmit data. Each device
and component involved in the exchange of data information is connected together
via a bus, which sets up an onboard information network. Usually centered on the
onboard computers, the data and commands communication between subsystems and
related payload devices is realized on the onboard data bus. In the interior of OBDH
subsystem, the bus is also necessary for data exchange because of the distributed
architecture.
As the carrier and hub of data communication, the spacecraft bus has not only the
function of data transmission, but also the ability to work in real time, high reliability
in complex space environment and adapt to the requirements of data transmission
service. Therefore, the spacecraft bus is not simply the same as the common data I/O
cable.
The data bus can be classified into two categories: serial and parallel. Up to date,
the serial bus is widely used in spacecraft. Some of the buses used in spacecraft were
developed specifically for military and aerospace applications, such as the MIL-STD1553B bus, the SpaceWire bus, and etc. Some are industrial or commercial buses that
have been used in other fields, such as CAN bus, RS422/485 general line, Ethernet,
IEEE1394, LVDS and etc. It can be selected according to the scale, speed, power
consumption and distance of data transmission.
The MIL-STD-1553B bus (hereinafter referred to as 1553B) was first proposed
by the United States military. It was a standard bus for military aircraft. It was a
digital command-response time-division multiplexed serial bus. The bus controller
was responsible for the bus scheduling and the management control of up to 31
terminals for data communication. The bandwidth was 1 Mb/s. Since 1970s, standard
bus had been developed as well as standardized bus communication protocol, and the
mechanism of bus communication was standardized, then redundant configuration
of hardware and prevention of terminal short-circuit fault were designed. Because
of its high reliability, it was widely used in the aerospace field. Now it was a mature
spacecraft bus, which was applied in many spacecraft all over the word.
The 1553B bus was applied in the Chang’E-3 lunar lander as the main channel of
information. The double redundant hot backup design was applied, and the interface
was transformer-coupled. The terminal signal output terminals had isolation resistors,
and the minimum non-response timeout time was set. The communication timeout
process could avoid the failure of a node of the bus network from affecting the
security of onboard data communication, so as to ensure reliable data transmission
and non-proliferation of faults.
LVDS (Low Voltage Differential Signaling) was a general peer-to-peer physical
interface technology that is suitable for high-speed data transmission with low power
consumption. The technology was based on the ANSI/TIA/EIA-644 LVDS interface
standard. It had the advantages of high speed, low power consumption and low noise.
The LVDS had 330 mV low voltage differential signal and fast transition time. It