JPL D-71987 Discovery Program GRAIL Telemetry Dictionary (TD) Gravity Recovery Processor Assembly ( GPA ) Flight Software Rev. E (Telemetry dictionary documentation extracted from JPL D-49059) Prepared by: _____________________________________ _________________ GRAIL GPA Software Lead: Tim Rogstad date Approval: _______________________________________ _________________ Flight System Engineer: Kevin Barltrop date ________________________________ _________________ Payload Manager: Bill Klipstein date 27 August 2012 GRAIL Telemetry Dictionary Document Change Log See PDF version of document for table. Table of Contents 1. INTRODUCTION 1 1.1 Identification 1 1.2 Overview 1 1.3 Document Scope 1 1.4 Method 2 1.5 Notation 2 1.6 Controlling Documents 2 1.7 Applicable Documents 3 2. SPACECRAFT TELEMETRY COMMUNICATION 3 2.1 Spacecraft Bus Architecture 3 2.2 Telemetry System Bus Transaction Protocols 3 2.3 Telemetry Philosophy 4 2.4 Telemetry Message Formats 4 Table 4. Telemetry Format Template 5 3. TELEMETRY PROCESSINg 5 3.1 Telemetry Timestamps 5 3.2 Telemetry Checksums 5 3.3 Telemetry Rates 5 3.4 Telemetry Counters 5 4. TELEMETRY CAPABILITIES 6 Table 5. Telemetrys Packets 7 5. TELEMETRY CONSTRAINTS 7 6. TELEMETRY DETAILED DESCRIPTION 7 6.1 Observables 7 6.2 Tone Status 9 6.3 Track Descriptor 10 6.4 Receiver Management 12 6.4.1 ADC 12 6.4.2 ADCFixedPoint 13 6.4.3 DirTable 13 6.4.4 Command Ack 15 6.4.5 LogMessage 16 6.4.6 GrailHealthStatus 16 6.4.7 Configuration 17 6.5 Time 18 6.5.1 PPSTime 19 6.5.2 External Event Time 19 6.6 Navigation 20 6.6.1 TimeTransfer 20 7. APPENDICES 22 7.1 BlackJack Protocol CRC Lookup TAble 22 7.2 ACRONYMS 23 1. INTRODUCTION 1.1 IDENTIFICATION This document is the Telemetry Dictionary for the Gravity Recovery Processor Assembly (GPA) Instrument of the GRAIL Project. It applies to all telemetry sent between the Project spacecraft and the Instrument. This document contains the telemetry dictionary contents of the project document Command and Telemetry Dictionary (JPL D-49059) 1.2 OVERVIEW By mapping the lunar gravitational field globally to unprecedented accuracy and resolution, GRAIL will peer deep inside the Moon to reveal its internal structure and thermal history. Knowledge acquired about the Moon from GRAIL will be extended to understand the broader evolutionary histories of the other rocky planets in the inner solar system: Earth, Venus, Mars, and Mercury. Indeed, the Moon is a linchpin for understanding how the terrestrial planets evolved. GRAIL is the lunar analog of the successful GRACE (2002) twin-spacecraft terrestrial gravity recovery mission that continues to operate. GRAIL will be implemented with a science payload derived from GRACE and a spacecraft derived from the (2005 launch) LM Experimental Small Satellite-11 (XSS-11). GRAIL will place twin spacecraft (represented as GRAIL-A and GRAIL-B in Figure D.1-2) in a low-altitude (50 km), near circular, polar lunar orbit to perform high-precision range-rate measurements between them using a Ka-band payload. Subsequent analysis of the spacecraft-to-spacecraft range-rate data provides a direct measure of the lunar gravity. Each of the two GRAIL satellites carries an LGRS system that is a single frequency Kaband-only version of the dual frequency GRACE KBRS. The LGRS contains an instrument called the Gravity Recovery Processor Assembly (GPA) that process the Ka-band ranging data, and the S-Band time-transfer system data. The GPA will be built at JPL from the primary flight proven components of the GRACE processor. Sufficient quantities of these are in stock at JPL and available for use in the GPA including the TurboRogue ASIC, 603e PowerPC CPU, and AMD Flash Memory. The required FPGAs are available from Xilinx. With these components available, design and flight software modifications over the GRACE design will be minimal. 1.3 DOCUMENT SCOPE In order for the Flight Software for the GPA Instrument to meet its requirements, scientific and engineering information must be sent to the Ground in the form of telemetry packets. This document describes to the bit-level the contents and definitions of telemetry packets. 1.4 METHOD The telemetry formats of the GRAIL Instrument are direct adaptations of those of the predecessor mission, GRACE. 1.5 NOTATION When this document refers to the Instrument, it is referring to the GRAIL/GPA Instrument. When this document refers to the Flight Computer, it is referring to the Flight Computer specified by the Project. Alternately, the terms Flight Processor and Gravity Recovery Processor Assembly may be used. Abbreviations for these terms are FC, FP, and GPA, respectively. The term, TBD, refers to items that are "to be determined". By FSW, it is meant the GPA flight software that executes in the Flight Computer specified by the Project. The GRAIL/GPA FSW is an adaptation of the FSW from a predecessor mission called GRACE. In this document reference to the Predecessor Project or the Inherited Project will mean the GRACE Project. The term, Ground, is meant to include all software, hardware, and operational activities supporting the sending of commands and the reception of telemetry to and from the Spacecraft and Instrument. The GRAIL Spacecraft minimally interacts with the command and telemetry of the Instrument other than to store the same for opportune moments to conduct appropriate uploads and downloads. 1.6 CONTROLLING DOCUMENTS See PDF version of document for table. 1.7 APPLICABLE DOCUMENTS 1. Gravity Recovery and Interior Laboratory (GRAIL) Project Software Management Plan (PSMP) D-38908 2. Gravity Recovery and Interior Laboratory (GRAIL) Instrument Software Management Plan, Rev B (SMP) D-44366, April 13, 2010 3. BlackJack Data Link Protocol, Interface and Implementation Description (JPL D-20675) 4. GRAIL Command and Telemetry Dictionary, Rev E (CTD), October 6, 2011 (JPL D-49059) 2. SPACECRAFT TELEMETRY COMMUNICATION 2.1 SPACECRAFT BUS ARCHITECTURE Telemetry is returned to the Spacecraft over a dedicated RS-422 link operating at 19.2 kiloBaud. This data port carries science data to be archived and forwarded to the ground. A second port (operating at 57.6 kiloBaud) is used for receiving telemetry during pre-flight operations. 2.2 TELEMETRY SYSTEM BUS TRANSACTION PROTOCOLS The telemetry system bus is a standard RS-422 serial communication line. The data rate is 19.2 kiloBaud. The order in which bits within bytes are transmitted is per the definition of the physical link layer. In multi-byte numeric quantities, the most significant byte and bit shall be transmitted first. Floating point numbers are represented using the ANSI/IEEE Standard 754-1985 for Binary Floating-Point Arithmetic. For ASCII strings, the first byte transferred is the leading byte of the string with subsequent characters following sequentially. 2.3 TELEMETRY PHILOSOPHY Telemetry bears all the information produced by the Instrument. The FSW has a certain flexibility in that not all telemetry packets need be sent at any time. Certain telemetry packets are always sent. Others may be requested. Return rates of telemetry packets may vary. Telemetry packets are of six distinct types: 1. Observables 2. ToneStatus 3. TrackDescriptor 4. Receiver Management 5. Configuration 6. Time These correspond to functional libraries or modules within the FSW. The formats of these packets are based on a common standard which is described below. 2.4 TELEMETRY MESSAGE FORMATS All packets emitted by the spacecraft have a common header type. A sequence of arguments of varying types may follow the header. A single packet type may have various lengths usually due to a single variable string argument at the end of the command. The Observables packet has a variable format, where the definition of the packet varies according to the states of certain parameters or conditions. The length of the packet, as coded in the header, allows for correct parsing as the varying states have unique lengths. The standard telemtry packet format is as follows: Table 4. Telemetry Format Template See PDF version of document for table. 3. TELEMETRY PROCESSING 3.1 TELEMETRY TIMESTAMPS Only certain packets contain a timestamp. Precise timestamps are returned when Science values are returned in the packet and the time of science or engineering acquisition is important for ground processing of the packet contents. For other, non-timestamped packets, the time of acquisition by the spacecraft is adequate to interpret the packet contents. 3.2 TELEMETRY CHECKSUMS Checksums are not used for any GRAIL telemetry packets. 3.3 TELEMETRY RATES For those packets emitted regularly, typical rates are given in the following table: See PDF version of document for table. 3.4 TELEMETRY COUNTERS Packet counters are not employed for any GRAIL telemetry packet. 4. TELEMETRY CAPABILITIES Table 5. Telemetrys Packets See PDF version of document for table. 5. TELEMETRY CONSTRAINTS The GPA will not send data that is known to be bad or unusable. No data is sent if the necessary RF signal is not "locked," or if the SNR is too low to produce reliable data. In the event of a sensor-specific outage, data from the functioning sensors will continue to be processed. Housekeeping data is always sent. For S-Band phase and pseudorange tracking, and for Ka-Band tone tracking, the local oscillator frequency is not detrended from phase measurements. When the phase count exceeds 1e10 cycles (positive or negative), a constant 1e10 cycles is removed from the count in order to maintain precision. 6. TELEMETRY DETAILED DESCRIPTION 6.1 OBSERVABLES See PDF version of document for table. 6.2 TONE STATUS See PDF version of document for table. 6.3 TRACK DESCRIPTOR See PDF version of document for table. 6.4 RECEIVER MANAGEMENT 6.4.1 ADC See PDF version of document for table. 6.4.2 ADCFixedPoint See PDF version of document for table. 6.4.3 DirTable See PDF version of document for table. 6.4.4 Command Ack See PDF version of document for table. 6.4.5 LogMessage See PDF version of document for table. 6.4.6 GrailHealthStatus See PDF version of document for table. 6.4.7 Configuration See PDF version of document for table. 6.5 TIME 6.5.1 PPSTime See PDF version of document for table. 6.5.2 External Event Time See PDF version of document for table. 6.6 NAVIGATION 6.6.1 TimeTransfer See PDF version of document for table. 7. APPENDICES 7.1 BLACKJACK PROTOCOL CRC LOOKUP TABLE Example: If the lookup key, ( ( CRC >> 8 ) XOR NewByte ), is 0x68, the lookup value is 0xEDAE. See PDF version of document for table. 7.2 ACRONYMS ACC Accelerometer AOCS Attitude and Orbit Control System ASIC Application-Specific Integrated Circuit CHU Camera Head Unit CG Center of Gravity CR Condition Register CRC Cyclic Redundancy Check CTD Command and Telemetry Dictionary ECI Earth-Centered Inertial EMC/EMI Electromagnetic Compatibility/Interference FC Flight Computer FP Flight Processor FPGA Field Programmable Gate Array FSW Flight Software GPA Gravity Recovery Processor Assembly GRACE Gravity Recovery And Climate Experiment GRAIL Gravity Recovery and Interior Laboratory IS Instrument System KBRS K-Band Ranging System LGRS Lunar Gravity Ranging System LO Local Oscillator MWA Microwave Assembly OBDH On-Board Data Handling System OCC Occultation (antenna) PCDU Power Conditioning and Distribution Unit POD Precision Orbit Determination (antenna) PPS Pulse Per Second PSMP Project Software Management Plan RF Radio Frequency SMP Software Management Plan SNR Signal to Noise Ratio SPU Signal Processing Unit TBD To Be Determined TML Total Mass Loss TR TurboRogue USO Ultra Stable Oscillator VCML Volatile Condensable Material Loss