Specification • The receiver shall send a positive acknowledgment (ACK) packet for each DATA packet received without error.
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Allocation of Service Types and Subtypes
Specification • The PUS provides a standard set of services that are targeted for communication between spacecraft and ground systems. Many of them may not be applicable to on-board communication between applications. However, nothing precludes their use in a JAS-based system. The PUS can be extended to add additional functionality to existing...
Backplane Connectors
Specification • JAS electrical design should utilize commercial connector standards when applicable. The VPX plug-in module to backplane connector is a Tyco Electronics MultiGig RT2 connector system which was chosen for its rugged mechanical performance and high-speed electrical performance, rated to 6.4 Gb/s and demonstrated to support data rates greater than 10...
Backplane Topology
Specification • The backplane is a key element in achieving high-speed connections between the plug-in modules or nodes in the case of a JAS system. VPX compliant backplanes support a minimum signaling rate of at least 3.125 Gbps on any differential point-to-point connection. There are a small number of required signals on...
Buckling and Crippling
Specification • Evaluation of buckling strength shall consider the combined action of primary and secondary stresses and their effects on general instability, local or panel instability, crippling, and creep.
Buffer Fragmentation and Reassembly
Specification • In cases where a higher-level transmit application (or higher layer in a communications stack) must transmit a buffer of data that exceeds the JRDDP MTU size, the buffer must be fragmented into a series of JRDDP packets and then reassembled at the receive TEP before returning the buffer to the...
Buffer Segmentation and Reassembly
Specification • In cases where a higher-level transmit application, or higher layer in a communications stack, must transmit a buffer of data that exceeds the JEEP MTU size, the buffer must be segmented into a series of JEEP packets and then reassembled at the receive TEP before returning the buffer to the...
CCSDS Telecommand and Telemetry Format Packet Standard
Specification • CCSDS Space Packet The CCSDS packet format consists of a packet primary header and packet data field. The header provides routing information for the packet and metadata that describes the packet. The data field is intended to be a user-defined field that can be customized for applications. Details of how...
Channel Closing Process
Specification • The following sections present the interactions (in the form of UML Sequence Diagrams) between transmit and receive endpoints while closing a channel. Various error conditions are presented in order to show nominal, delayed, and worst case scenarios. The hexagonal icons represent the TEP states while the dashed green lines represent...
Channel Independence
Specification • Each transport channel shall operate independently from other transport channels.
Channel Operations
Specification •
Cleanliness
Specification • Cleanliness is an important design consideration which can be mitigated by the mechanical structure and processes. Systems adjacent to an optical payload may have more strict cleanliness requirements than non-optical payload. The following sections describe the requirements which deal with Cleanliness considerations for the JAS mechanical structure.
Coating Surface Resistivity
Specification • The thickness of all chemical film treatments need to be controlled to provide low surface resistivity. Surface resistivity shall be less than 1 x 109 ohm/ square.
Coating Volume Resistivity
Specification • All paints and coatings shall have a volume resistivity less than 1 x 109 ohm-cm.
Communication Data Links
Specification • JAS nodes should communicate through one or more standard communications protocols. Serial communication protocols are the recommended approach but JAS does not preclude the use of parallel communication protocols. JAS also does not preclude the use of custom or legacy based communications.
Communication Specification
Specification • The Communication Specification provides details about network interfaces, communication services, and packet structures that were described in the Communication Profile. The figure below provides context of where the Communication Specification resides in the JAS standard. JAS Standard Hierarchy
Coordinate Definition
Specification • The JAS mechanical structure shall implement a coordinate system as a reference point for the design. The mounting of each component should be considered as the coordinate reference. The coordinate frame can originate on a pin-and-slot mounting. [Placeholder: Defining a coordinate frame helps to determine center of gravity, mass, envelopes...
Custom Communications
Specification • Custom communications specifications by definition are not described by any single specification. The electrical parameters will be determined by the components involved in the design. For example, if the communications utilize gigabit (GTX) transceivers in an FPGA then the electrical requirements will be prescribed by the GTX specifications.
Data Transmit Queue
Specification • When packets from more than one channel are available for transmit, packets shall be transmitted in the order in which they are queued and in accordance with the transmit priority described above.
Data Types
Specification • The JAS standard does not require a specific length or encoding format for data types. Systems can define these based on what best suits their needs. Sizes, endianness, byte ordering, and bit ordering are typically driven based on the processing and memory architectures that are used. However, in order to...
Delayed Case
Specification • A delayed but recoverable scenario occurs when a receive TEP receives at least one CLOSE packet but the transmit TEP does not receive any ACK packets as shown in Figure 3. In this case the receive TEP will eventually transition to the CLOSED state via the timeout and the transmit...
Design Constraints
Specification • The following sections define some important design constraints that the program will levy on the system. The constraints will drive many of the choices in designing the mechanical system.
Design Thickness
Specification • For strength and buckling analyses, minimum material thickness shall be used. Minimum thickness is defined as the nominal thickness minus the lower tolerance and applies to metallic and nonmetallic structural elements. For modeling purposes and stiffness calculations, use nominal or expected values. For flexures the Maximum blade thickness shall be...
Design Ultimate Load
Specification • The JAS mechanical structure shall have sufficient strength to simultaneously withstand design ultimate loads, the corresponding temperature, pressure and accompanying environmental phenomena without failure.
Design Yield Load
Specification • The JAS mechanical structure shall withstand design yield loads, the corresponding temperature, pressure and associated environmental phenomena without permanent deformations, or permanent misalignments, of all components.
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