LISA Pathfinder Sheet : 1

Transcription

1 Pathfinder Sheet : 1 Issue : A Date : Inputs to LISA Pathfinder Space-Ground Interface Document (SGICD) - Part 2, Baseband. CI CODE: Prepared by: Date: Robin Ashencaen Checked by: Date: Kevin Gould Approved by: Date: Neil Dunbar Authorised by: Date: Astrium 2005 The contents of this document are the copyright of Astrium and shall not be copied in whole, in part or otherwise reproduced (whether by photographic, reprographic or any other method) and the contents thereof shall not be divulged to any other person or organisation without the prior written consent of Astrium.

2 Pathfinder Sheet : 2 Issue : A Date : INTENTIONALLY BLANK

3 Pathfinder Sheet : 3 Issue : A Date : Table of Contents 1 INTRODUCTION Purpose Scope 5 2 DOCUMENTS Applicable Documents Reference Document 6 3 ABBREVIATIONS 7 4 TELECOMMAND STRUCTURE Telecommand Segments ( =TC Frame Data Unit) Packet Aggregation in the Segment Data Field Telecommand Frame Bypass and Control Command Flag Spacecraft ID Virtual Channel ID Frame Length Frame Data Unit TC Frame Sequence Number TC Frame Error Control 14 5 TELEMETRY STRUCTURE (DRAFT) Telemetry Source Packet Source Packet Header Packet Data Field Telemetry Transfer Frame Transfer Frame Format 19

4 Pathfinder Sheet : 4 Issue : A Date : Table of Figures Figure Telemetry Source Packet Fields...15 Figure Data Field Header in Packets...17 Figure Transfer Frame Format...19

5 Pathfinder Sheet : 5 Issue : 1 Date : INTRODUCTION 1.1 Purpose <To be provided by ESA> 1.2 Scope <To be provided by ESA>

6 Pathfinder Sheet : 6 Issue : 1 Date : DOCUMENTS 2.1 Applicable Documents The following publications form a part of this document to the extent specified herein. Unless an issue is quoted for a document, the current issue is deemed to apply. When an issue is quoted, that issue, and no other, must be used. [AD-1] Telemetry and Telecommand Packet Utilization, ECSS-E-70-41A 30, Jan 2003 [AD-2] LISA-PATHFINDER/SMART-2 Operations Interface Requirements Document (OIRD), S2-ESC- IRD-5001, Issue 2, Revision 0. [AD-3] CCSDS B-4, Packet Telemetry, Blue book, Issue 4, Nov [AD-4] [AD-5] System Requirements Document, CSI-PJ-EST-SRD Spacecraft Requirement Specification, S2.ASU.RS [AD-6] CCSDS B-3, Telecommand Part 1 Channel Service, Blue book, Issue 3, June 2000 [AD-7] LISA Pathfinder Packet Utilisation Standard (LPF-PUS) S2.SYS.ICD.2001 [AD-8] SGICD Part Reference Document The publications listed below contain background information relating to the subjects addressed. [RD-1] Packet Telemetry Standard, ESA PSS /1. [RD-2] Packet Telecommand Standard, ESA PSS /2. [RD-3] Telemetry Channel Coding Standard, ESA PSS /1. [RD-4] CCSDS B-1 Lossless Data Compression, Blue book, Issue 1, May 1997 [RD-5] LISA-Pathfinder Acronyms List, S2.ASU.LI.1006, Issue 1, April 2004

7 Pathfinder Sheet : 7 Issue : 1 Date : ABBREVIATIONS The abbreviations used in this document are listed in RD-5.

8 Pathfinder Sheet : 8 Issue : 1 Date : TELECOMMAND STRUCTURE 4.1 Introduction The telecommand structures defined here are based closely on the ESA PSS standard [RD-2]. The following data structures are defined: a) A TC packet, which is the fundamental user data unit. The TC packet is used to exchange data between a source application process on the ground and its associated application process on the spacecraft. The LISA pathfinder source packets are defined in AD-7. b) A Telecommand Segment The telecommand packet is used to multiplex source packets from several source application processes on the same data communications channel. A Segmentation mechanism exists in the standard, whereby very long packets may be broken up into manageable chunks. Segmantation is NOT used on LISA Pathfinder, but the TC segments are still implemented for their multiplexing aspect. c) A Transfer frame which is the link protocol data unit, is used to transfer the source data through the ground to spacecraft communications path. The transfer frame also provides a mechanism by which the data link can be time shared between functionally distinct scources by creating logical virtual channels. d) The Transfer frames are broken up into CLTUs by the coding layer. These are modulated onto the RF uplink. As segmentation is not used in LISA pathfinder, a typical TC message s bits can be illustrated by the figure () below.

9 Pathfinder Sheet : 9 Issue : 1 Date : Lisa Pathfinder Telecommand Transfer Frame Structure Figure 1 TC Frame Header (5 Octet) TC Frame Data Unit TC Segment Data field TC Frame Version Bypass Flag Number (=0) Control Command Flag Spare (=0) Spacecraft ID (=52 hex) Virtual Channel ID Frame Frame Length Sequence TC Segment Header Number TC Packet Header Packet Data field Header TC Packet Data field Error Control (CRC) Sequence flag MAP ID Version Nr Type Packet ID Data field header flag APID PID PCAT sequence Sequence flag control Sequence count Packet Length (of TC source packet data field) CCSDS Secondary header flag TC PUS version no. Execution Completion Progress of Execution ACK (n ot use d) Start of Execution (not used) Acceptance Service Type Service subtype Source ID Application data Packet CRC bits max 16 2 Octet 2 Octet 1 Octet 2 octet 2 Octet 2 Octet 4 Octet 6 O c t e t 232 o c t e t m a x TC Frame Header (5 Octet) 1 octet TC S e g m e n t D a t a f i e l d 248 O c t e t m a x i m u m T e l e c o m m a n d F r a m e m a x i m u m L e n g t h 256 O c t e t 228 octet max 2 Octet 2 Octet

10 Pathfinder Sheet : 10 Issue : 1 Date : Lisa Pathfinder Telemetry Transfer Frame Structure Figure 2. Attach TM Transfer Frame Primary Header ed Synch Master Virtual Frame Data Frame Identification ron - Chann Chann field status isation Versio S/C ID Virtual Operati el el Secon Sync flag (=0) Packet Segme First Marke n channe on Frame Frame dary order nt header r (= Numbe l ID control Count Count Header flag length pointer 1A CF r (=0) filed flag (=0) ID FC 1D flag (=0) (=11 hex) bin) Version Nr TM T r a n s f e r F r a m e D a t a F i e l d - m a x I m u m L e n g t h Octret TM S o u r c e P a c k e t D a t a F i e l d TM S o u r c e P a c k e t H e a d e r TM D a t a f i e l d H e a d e r Packet ID Packet sequence control Packe t Lengt APID h (of TM sourc e PID PCAT packet Type Data field header flag Grouping Flags Source Sequence count data field) filler (=0) TM PUS version no. filler (=0) Service Type Service subtype filler (=0) Time Application data TM Packet error control Operati TC onal Frame Control Error Field Control (Contai (CRC) ns CLCW) 8504 bits max 16 4 Octet 2 Octet 2 Octet 2 Octet 2 octet 2 Octet 2 Octet 4 Octet 1063 octet max 2 Octet 4 Octet 2 Octet TC Frame Header (5 Octet) 6 O c t e t o c t e t m a x T e l e m e t r y F r a m e m a x i m u m L e n g t h O c t e t R e e d - S o l o m o n D a t a S p a c e Reed Solomon check symbols 160 octet

11 Pathfinder Sheet : 11 Issue : 1 Date : Telecommand Packets Are defined in [AD-7] these form the Data field for the next layer, The segmentation layer. 4.3 Telecommand Segments ( =TC Frame Data Unit) The Telecommand Segment defined in [RD-2], and shown below, shall be used as TC Frame Data Unit (i.e. the data unit transferred from the Segmentation Layer to the Transfer Layer to be inserted in the Frame Data Field of the Telecommand Frame). The telecommand segment may be uplinked using either the AD or BD service defined in [RD-2] Telecommand Segment Header The Segment Header contains the following two fields: Sequence Flags (Bit 0 and 1) Multiplex Access Point (MAP) Identifier (Bits 2 through 7) Sequence Flags There shall be no command packet segmentation for LISA Pathfinder, so the sequence flags shall be set to 11 BIN. even if several packets are aggregated in a single command segment (see section MAP ID MAP IDs shall be used to route the telecommands from the decoder depending on the type of handling required for the command e.g. the OBC software or the OBC Command Pulse Distribution Units (CPDU). MAP IDs shall not be used to define which OBC processor the TC is sent to this will always be the currently active one.. For LISA Pathfinder the following MAP IDs are allocated : 0 dec from Decoder-1 to CPDU-1 or from Decoder-2 to CPDU-2

12 Pathfinder Sheet : 12 Issue : 1 Date : dec from any Decoder to active OBC-processor Segment data field The data in the segment data field will be one or more Telecommand Source packets. These are defined in AD Packet Aggregation in the Segment Data Field For telecommand segments NOT addressed to a CPDU, it shall be possible, but not mandatory, to pack a set of TC packets into a single telecommand segment such that they are all encoded and transmitted in the same transfer frame / CLTU. After unpacking the command segment by software, all contained commands shall be sent for execution in the same order as contained in the segment. Note: in addition to the maximum segment length, the only restriction to this shall be that all commands aggre-gated in the same segment are destined to the processor software MAP ID and use the same transmission mode (AD / BD).

13 Pathfinder Sheet : 13 Issue : 1 Date : Telecommand Transfer Frame The Telecommand Frame must conform to the structure defined in [RD-2] Version No. Always set to Bypass and Control Command Flag The specifications as defined in [RD-2] shall apply Spare Always set to Spacecraft ID The following Telecommand Spacecraft Identification on the uplink has been assigned to LISA Pathfinder: Bin = 52 Hex TBC Virtual Channel ID Two Virtual Channel Identifiers shall be used addressing the two on-board decoders. The values are: 0 for decoder 1 63 dec for decoder 2 These two values shall be consistently used in the CLCWs Frame Length This 10-bit field contains a length count "C" which equals one fewer the total octets in the TC Transfer Frame. The count is measured from the 1st bit of the FRAME HEADER to the last bit of the FRAME ERROR CONTROL Field:

14 Pathfinder Sheet : 14 Issue : 1 Date : "C" = (Total Number of Octets) 1 For LISA Pathfinder, the maximum length of a Telecommand Frame is 256 octets (i.e. C <= 255) Frame Data Unit The content of a TC Transfer Frame data unit is the TC segment defined in section 4.3 Refer to section TC Frame Sequence Number The specification as defined in [RD-2] shall apply TC Frame Error Control Annex D of [AD-1] provides the specification of the CRC method to be used for LISA Pathfinder Coding SGICD pt 1 specifies that the uplink bit stream shall be coded in accordance with RD-2. In this process the bit stream resulting from the Telecommand Transfer Frame defined above is partitioned into 56 bit code blocks, to which are added 8 bits of error correction, making a total of 64 bits in a code block. The total length is configuarble for a given mission: 8 octets long codeblocks are selected for Lisa Pathfinder. The code blocks are then assembled into Command Link Transmission Units (CLTUs). Each CLTU starts with a 16 bit start sequence of EB90 hex, followed by a variable number of codeblocks, and then the tail sequence, which is hex. The tail sequence will fail the check which will indicate the end of the CLTU Uplink Modulation The uplink modulation etc. is defined in part 1 of the SGICD,[AD-8]

15 Pathfinder Sheet : 15 Doc No. S2.SYS.ICD.2001 Issue : A Date : TELEMETRY STRUCTURE 5.1 Introduction The telemetry structures defined here are based closely on the ESA PSS standard [RD-1]. The following data structures are defined: a) A TM Source packet, which is the fundamental user data unit. The TM packet is used to exchange data between a source application process on the ground and its associated application process on the spacecraft. The LISA pathfinder source packets are defined in AD-7. b) A TM Transfer frame which is the link protocol data unit, is used to transfer the source data through the ground to spacecraft communications path. The transfer frame also provides a mechanism by which the data link can be time shared between functionally distinct scources by creating logical virtual channels. c) The Transfer frames are Reed Solomon encoded and Convolutional coded by the coding layer. d) These are modulated onto the RF uplink. A typical TM message s bits can be illustrated by the figure (2). 5.2 Telemetry Source Packet All telemetry packets must conform to this structure, which is defined in the PUS [AD-7] Figure Telemetry Source Packet Fields

16 Pathfinder Sheet : 16 Doc No. S2.SYS.ICD.2001 Issue : A Date : Source Packet Header Packet ID Version Number: The version number must be set to 0 as specified in [AD-1] Type: For telemetry source packets, the type must be set to zero. Data Field Header Flag: This indicates the presence or absence of a Data Field Header and must be set to 1 except for Idle and OBC High Priority telemetry packets where it is set to 0. Application Process ID (APID): The Application Process ID uniquely identifies the on board source of the packet. The APID is structured into two fields: The Process ID (PID) which defines the application which is the source of the telemetry packet. The Packet Category which identifies different categories of packets to be processed by the addressee The choice of APID values across the spacecraft subsystems and instruments can be derived from the PID allocation and Packet category information given in section Error! Reference source not found Packet Sequence Control Grouping Flags: The grouping flags in all telemetry source packets must be set 11 BIN to indicate that the telemetry source packet is "unsegmented". Source Sequence Count: For Telemetry packets the Application ID (APID) shall be divided into Process ID (first 7 bits) and Packet Category (last 4 bits). This implies that independent Packet Source Sequence Counters are generated by the same on-board packet terminal (Process ID) for each Packet Category. Ideally, this counter should never re-initialise, however under no circumstances shall it short-cycle (i.e. have a discontinuity other than to a value zero). The counter wraps around from to zero, and shall start at zero at power on of the unit or on start of the application generating the packet Packet Length The packet length field is used to point to the beginning of the next packet for purpose of extraction from the transfer frame. The Packet Length field specifies the number of octets contained within the Packet Data Field. The actual length of the entire Source Packet will implicitly be 6 octets longer, since the standard 48-bit Packet Header always precedes the Packet Data Field. The number is an unsigned integer C where

17 Pathfinder Sheet : 17 Doc No. S2.SYS.ICD.2001 Issue : A Date : C = <Number of octets in Packet Data Field> - 1 The number is limited by the 2 octets length of this packet field. Maximum size of Source Packets for LISA Pathfinder: C max = = (= max possible size for the 2 octet Packet Length field) Packet Data Field Data Field Headers Data field headers are provided for all telemetry packets except for time packet TM (9,2), Idle and OBC High Priority telemetry packets. The data field header is preceded by the source packet header and followed by source data and error control. Figure Data Field Header in Packets PUS Version Number: This field indicates that a Packet Error Control field is at the end of the Packet Data Field and is set to 1 (001 BIN ) for LISA Pathfinder. The error control code is CRC Service (Packet) Type This indicates the category to which the telemetry source packet relates. Service (Packet) Sub-type: Together with the Type, the Sub-type uniquely identifies the nature of the telemetry contained within the telemetry source packet.

18 Pathfinder Sheet : 18 Doc No. S2.SYS.ICD.2001 Issue : A Date : The same Service Type and Subtype definitions shall apply to all applications. Time Fields: All telemetry source packets shall have a time field. Time1 ( 5 octets ): This time format is 5 octets long. It shall be used for all telemetry source packets. It s format is defined in the PUS, [AD 7] Source Data The packet source data constitutes the data element of the telemetry reports to the ground Packet Error Control The purpose of the Packet Error Control field is to transport an error detection code so that the receiving application on ground can verify the integrity of the complete packet. The type of error control algorithm shall be CRC. The error control shall be calculated over the complete packet less the final 16 bits Packet Error Control field. For LISA Pathfinder all telemetry packets except the Idle and OBC High Priority Telemetry packets shall have this field. 5.3 Direct TM source packet Format is TBD. 5.4 Telemetry Transfer Frame LISA Pathfinder uses the following Reed-Solomon encoding scheme: Encoding with an interleaving depth of five, as specified in [RD-1] Transfer Frame Length Due to the Reed-Solomon encoding, the only allowed frame length (before encoding) shall be 1115 octets.

19 Pathfinder Sheet : 19 Doc No. S2.SYS.ICD.2001 Issue : A Date : Transfer Frame Format Figure Transfer Frame Format Transfer frame Data field The TM source packets described above become the Data field for the Transfer frame. Alternatively, for direct TM, the data field shall be a direct TM source packet Transfer Frame Primary Header Version No. Always 00. Spacecraft ID The following Telecommand Spacecraft Identification on the downlink has been assigned to LISA Pathfinder: Bin = 52 Hex TBC Virtual Channel ID Data sources on-board are allocated a virtual channel number to identify them to the ground processing facilities as follows (values given in decimal): Direct TM (from the hardware) 0 real time TM (from the OBSW) 2 TBC stored TM (from the mass memory) 5 TBC idle packets 7 Operational Control Field Flag

20 Pathfinder Sheet : 20 Doc No. S2.SYS.ICD.2001 Issue : A Date : This flag shall be set to 1 and a Command Link Control Word (CLCW) shall be inserted in the Operational Control Field for all frames. Master Channel Frame Count Field Contains a sequential binary count (modulo 256) of each transfer frame transmitted. A resetting of this count before reaching 255 shall not take place unless it is unavoidable. Any case when it is unavoidable shall be documented in the LISA Pathfinder Flight User Manual. Virtual Channel Frame Count Field Contains a sequential binary count (modulo 256) of each transfer frame transmitted through a specific Virtual Channel. A resetting of this count before reaching 255 shall not take place unless it is unavoidable. Any case when it is unavoidable shall be documented in the LISA Pathfinder Flight User Manual. Secondary Header Flag The Flag shall be set to 0, indicating that a secondary header is not inserted in the frame. Data Field Synchronisation Flag This flag shall be set to zero; i.e. octet-synchronised and forward-ordered Telemetry source Packets or Idle data shall be inserted in the Transfer Frame Data Field. Packet Order Flag Shall be set to zero. The Packet sequence count order shall be forward. Segment Length Identifier As the Data Field Synchronization Flag set to zero, the Segment Length Identifier shall be set to 11 BIN. First Header Pointer Being the Synchronization Flag set to zero, the First Header Pointer shall contain information on the position of the first Telemetry Source Packet within the Transfer Frame Data Field; i.e. the binary representation of the location of the first octet of the first Packet Primary Header. The locations of any subsequent headers within the same Transfer Frame Data Field will be determined by calculating these locations using the Packet Data Length Field. If no Packet Primary Header starts in the Transfer Frame Data Field, the First Header Pointer shall be set to BIN. For Idle Frames the First Header Pointer shall be set to BIN Transfer Frame Trailer contains the Operational control field and the frame error control Operational control field This contains the Command Link Control Word (CLCW) Frame error control This has a 16 bit CRC calculated over the entire frame. 5.5 Coding Layer

21 Pathfinder Sheet : 21 Doc No. S2.SYS.ICD.2001 Issue : A Date : TBW 5.6 TM Compression TBW Intentionally blank

22 Pathfinder Sheet : 22 Doc No. S2.SYS.ICD.2001 Issue : A Date : DOCUMENT CHANGE DETAILS ISSUE DATE RELEVANT INFORMATION/INSTRUCTIONS A Initial Issue DISTRIBUTION LIST INTERNAL EXTERNAL LISA-PF team ESA Configuration Management Library