Specification • For all components that will be in the vicinity of an optical payload and anywhere that contamination at the molecular level is an issue, all parts and materials must comply with ASTM E 595 for less than 1% Total Mass Loss (TML) and 0.1% CVCM. Thermal bake-out of all components...
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Molecular Thermovac Testing
Specification • Thermovac temperature testing is required to determine dissipation at full power modes. A test plan needs to be developed and coordinated with the System Engineer.
Mounting Distortion Impact
Specification • The JAS mechanical structure shall maintain the electronics/PCBs listed below within given positions with distortions less than expected for the intended application.
Multicast/Broadcast
Profile • SpaceWire doesn’t inherently support a multicast or broadcast capability. There is a time-code distribution function but it is limited in the amount of user information that can be distributed. An approach has been developed for a broadcast capability through custom router and endpoint modifications. It uses a set of dedicated...
Multiplexed Logical Channels
Specification • The protocol shall support multiple simultaneous logical connections over a single SpaceWire link.
Network Discovery
Profile • When probing for routing switches, early network discovery techniques typically relied on each routing switch’s configuration port to respond to identification requests to confirm the routing switch’s presence. A request packet was typically dispatched to the configuration port, and a response packet provided confirmation of existence. This same request/response approach...
Network Topologies
Other • The selection of network topology is a critical component when developing multi-node or multi-point system architectures. A good choice of topology will require less power, have less complexity, higher reliability, and will orchestrate network traffic smoothly and quickly between nodes. Conversely, a poor choice of topology will introduce complex and...
Networks
Profile • Each JAS node should contain a SpaceWire Router per the SMAC Profile which allows for extensive scaling of the network. A network is made up of a number of links, nodes (endpoints) and routing switches. Links provide the means for passing packets from one node to another. Nodes can be...
Nominal Case
Specification • In the nominal case the close packet is immediately acknowledged by the receive TEP and the transmit TEP transitions to the CLOSED state. The receive TEP transitions to the CLOSED state after the expiration of its timer. The purpose of the receive TEP’s delay in the CLOSING state is to...
Obscuration
Specification • All JAS mechanical structure components shall be placed to prevent obscuration of the system view of space if the JAS electronics box will be used to radiate. Structural elements shall be kept an appropriate distance away from the JAS electronics housings.
Operating Temperatures
Specification • Operational temperatures are provided in thermal study for the nominal orbit. Excursions from predicted operational temperatures shall be increased by 11C (bilateral) when these temperatures are utilized in all fatigue analysis. For the purposes of fatigue the temperature excursion within an orbital season may be considered. For the purposes of...
Operational Vibrations
Specification • The JAS housing shall meet all of the displacement budgets, while subjected to the operational environment produced by the acceleration in file, TBD. These shall be used as base inputs.
Orientation
Specification • The JAS housing shall meet mechanical alignment performance specifications in any direction.
Overall Functional Description
Specification • This protocol describes the mechanism for reliable transfer of data packets over a SpaceWire connection and adds the following capabilities to a SpaceWire link: Multiplexed Logical Connections Reliable Delivery Missing packet detection Out of sequence packet reordering Buffer fragmentation and reassembly
Packaging for Thermal Dissipation
Specification • The preliminary JAS mounting details are defined by the baseplate details in ICD drawing xxxxxx. The JAS electronics box is meant to mount through the blue baseplate shown in the figure below. The figure shows a nominal 3x3 stack in an exploded view. JAS Mounting Exploded View Conducted Self-radiated panels...
Packet Addressing and Routing
Specification • Packets will be identified and routed in the system using the SAPID, DAPID, ST, and SST. Applications shall provide these fields to the JAS Packet Service to create the stream of packets that will be sent across the communication channel. Communication channels and addresses, such as a SpaceWire address, can...
Packet Error Control
Specification • Even though JAS network protocols offer a guaranteed delivery option, there still exists the possibility of an error being introduced into a packet while it is being created or transferred from memory to the communication channel. To provide an additional layer of error detection all JAS packets shall contain a...
Packet Sequence Numbers
Specification • An 8-bit sequence number shall be assigned to each packet transmitted.
Packet Sequencing
Specification • The use of the packet sequencing fields within the JAS packet is different from the definition in the CCSDS and PUS standards. The original intention of the packet sequence counter was to provide two functions. First, it was used in combination with the sequence flags to reassemble data sets that...
Packet Service
Profile • A packet service is used to send messages between applications. JAS assumes that each processing element has one packet service for each packet format that is defined. In order to promote reuse, a layered architecture is used whereby applications are abstracted from the packet format details. The packet service contains...
Packet Service Definitions
Specification • [Placeholder: services reserved for and specific to JAS; this is a lead in to describe the services. Contact SNL if immediate support is needed with this topic. Content will be developed for JT 2.0.]
Packets
Profile • The basic form of a SpaceWire packet is shown below. More details about SpaceWire packets can be found in the Communication Specification. The format contains the following: One or more 8-bit addresses that allow the packet to be routed through the network An 8-bit protocol identifier which allows multiple protocols...
Particulate Contamination
Specification • Internal Cavities will be wiped clean with isopropyl alcohol and allowed to air dry for 30 minutes prior to close out; the structure will be covered during the drying process. The surfaces will be visibly clean. Visibly clean is defined as no contamination visible when viewed from 6-18 inches away...
Payload
Specification • JRDDP Packet Format Secondary Header (Optional) The presence of the optional secondary header is indicated by the Secondary Header Flag in the Packet Control field. If a secondary header is present, its contents and format are implementation dependent and shall be documented in a program specific document. The secondary header...
PCI Express
Specification • PCI Express, or PCIe, is another multi-lane high speed serial interconnect technology. Each lane is a full-duplex data stream comprised of two differential signaling pairs, one for transmitting and one for receiving.
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