Specification • Unless otherwise specified, the JAS mechanical structure shall meet these specifications during or after exposure to all environmental conditions specified in the Environmental specification. All of the intended application’s performance parameters must be considered to determine if the mechanical design can withstand the impacts of all environments.
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Error Detection
Specification • Packet errors shall be detected by adding a CRC to each packet transmitted, checking it at the receiver, and discarding any erroneous packet.
Ethernet
Specification • Ethernet comprises a family of networking technologies with numerous media types and standards; 100Base-T (IEEE 802.3-2008:section 8) and 1000Base-T (IEEE 802.3-2008:section 40) the most popular in use today.
Factors of Safety
Specification • The JAS mechanical structure shall have strength margins of safety greater than zero when calculated from analytically derived structural loads. The factors of safety (FS), shown in the first table below, and test load factors, shown in the second table below, shall be applied to the limit loads. All laminated...
Fatigue
Specification • The JAS mechanical structure metallic elements shall be designed to withstand the effects of cyclic load condition caused by the design environment. The design environment includes all ground handling transportation, testing, launch and on orbit operational environments indicated in the Environmental Specification. MSFC-HDBK-505 Chapter 7 shall be implemented for fatigue...
Functional Description
Specification • The JEEP provides efficient, best-effort delivery of packets. In-order delivery is only guaranteed if there are no transmission errors over the SpaceWire link, e.g., bit errors or dropped packets, and there are no routing options which could cause a segmented packet to be transmitted or received out of order. JEEP...
Fundamental Frequency
Specification • The first mode of the JAS mechanical structure shall be greater than 500 Hz when mounted to a rigid surface.
Gasketing
Specification • The JAS mechanical structure shall use EMI gasketing to reduce EMI emissions as appropriate for the intended application.
Gravity Release Impact
Specification • The JAS mechanical structure shall remain within given displacements as applied by determining gravity release impacts on the mechanical structure.
Grounding
Specification • Grounding provisions are required for the mechanical design to eliminate the potential for ESD charging on floating metal. Any component members with surface areas greater than 20 cm2 shall have a grounding provision. Bolted fittings are acceptable as grounding provisions if the joint meets the electrical resistance requirement for bonding....
Header
Specification • JRDDP Packet Format Destination Address The first byte of the header shall contain the Destination SpaceWire Logical Address (SLA) field that is associated with the destination TEP to which the packet is being sent. Protocol ID The second byte of the header shall contain the SpaceWire Protocol ID field and...
Humidity Impact
Specification • The JAS mechanical structure shall maintain the electronics/PCBs within given displacements as applied by determining humidity impacts on the mechanical structure. If composite structures are used, the humidity should remain between a saturated composite at nominal 60% RH test area and a dry composite at 0% RH humidity vacuum environment...
Interface Control
Specification • The JAS mechanical structure shall be designed to a prescribed Interface Control Drawing (ICD) as required by the application. Requirements called out in the ICD should include an answer to most of the design considerations in this specification.
JAS Command Packet
Specification • JAS Command Packet All fields are shown in bits. The variable length application data field must be an integral number of bytes for the packet error control calculation. Spare bits may be used for padding purposes at the end to ensure the packets are an even number of bytes in...
JAS Efficient Exchange Protocol
Specification • The JAS Efficient Exchange Protocol (JEEP) uses the lower level SpaceWire data link layer to provide data delivery services to one or more higher level application processes. This document specifies the functional requirements for JEEP but does not specify the interfaces to the lower or higher level processes, which may...
JAS Packet Definition
Specification • The JAS Packet is built upon CCSDS and PUS packet standards. Some modifications were made to enforce a layered architecture in order to promote reuse of applications. The following sections will highlight these differences in more detail.
JAS Packet Service
Specification • Error: unable to migrate element with tag="" The CCSDS/SOIS subnetwork packet service standard can be referenced if a generic packet service is needed. The JAS Packet Service is an implementation of the CCSDS/SOIS packet service, specifically tailored for the JAS packet. The following diagram shows how the JAS Packet Service...
JAS Packets
Specification • Applications require a messaging format to allow them to communicate with each other. Legacy programs may already have a messaging format that they prefer to use. There is nothing that precludes any of the JAS communication protocols or data links from supporting these formats. The JAS Packet was developed for...
JAS Reliable Data Delivery Protocol
Specification • The JAS Reliable Data Delivery Protocol (JRDDP) uses the lower level SpaceWire data link layer to provide reliable packet delivery services to one or more higher level host application processes. This document specifies the functional requirements for JRDDP but does not specify the interfaces to the lower or higher level...
JAS Specific Services Definitions
Specification • The JAS specific services will be based on the PUS service concept. Most PUS services were created for communication between onboard applications and ground systems. JAS adds additional services to support more onboard payload functions. [Placeholder: Additional development is needed to define the JAS specific services to support onboard payload...
JAS Telemetry Packet
Specification • JAS Telemetry Packet All fields are shown in bits. The variable length application data field must be an integral number of bytes for the packet error control calculation. Spare bits may be used for padding purposes at the end to ensure the packets are an even number of bytes in...
JEEP Packet Format
Specification • All JEEP packets shall include a fixed length header, followed by a variable length payload. The figure below shows how the JEEP packet is embedded within the standard SpaceWire packet. Note that while a SpaceWire packet may have zero or more destination addresses before the JEEP header, the JEEP requires...
JRDDP Packet Format
Specification • All JRDDP packets shall include a variable length header, followed by a variable length payload, followed by a 2-byte CRC Trailer. The figure below shows how the JRDDP packet is embedded within the standard SpaceWire packet. Note that while a SpaceWire packet may have zero or more destination addresses before...
Life
Specification • The JAS mechanical structure shall be constructed of materials capable of performing for the necessary mission life time (for example, 3 years storage in an inert atmosphere and 10 years on orbit). This analysis will require extensive parts and materials screening and processing.
Logical Connections
Specification • Upon initialization all TEPs shall be in the CLOSED state. OPEN/RESET Command When a transmit TEP transitions to the ENABLED state (as commanded by the host), it shall send an OPEN/RESET packet to its receive TEP and initiate an acknowledgement timer. CLOSE Command When a transmit TEP transitions to the...
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