GSFC/NGIMS-FSW-22 Flight Software High-Level Requirements Document for CONTOUR/NGIMS September 22, 2001 Version 1.3 Co-Investigators: ___________________________________ ____________ Dr. Hasso B. Niemann ___________________________________ ____________ Dr. Paul Mahaffy Instrument Manager: ___________________________________ ____________ I INTRODUCTION This document delineates the high level requirements for Flight Software (FSW) for the CONTOUR/ NGIMS instrument. These are flight software requirements at the highest level, and as such are often somewhat ambiguous; further, unambiguous and verifiable clarification of requirements is provided in other more detailed specifications. The Neutral Gas and Ion Mass Spectrometer (NGIMS) experiment is a quadrupole mass spectrometer that employs two ion sources, each optimized for a specific set of measurements. NGIMS will measure the abundance and isotope ratios for many neutral and ion species in the coma of each comet during the flyby. Using these two sources, NGIMS Flight Software (FSW) must rapidly switch between measurements of the cometary neutral gas and ambient ions from the coma as the CONTOUR spacecraft flies by the nucleus. There is an acronym list on the last page. NGIMS Functions. Direct Gas Sampling in the Open Ion Source: The open source of the NGIMS minimizes gas/surface interaction effects by directly sampling gaseous species that are formed into a beam before the ionization region by collimating lenses; the FSW must control the voltages on these lenses. The open source measures ambient particle density directly for all neutral species. High Sensitivity Sampling in the Closed Ion Source: The closed ion source will use ram density enhancement to provide measurements of higher accuracy and sensitivity for the more inert atomic and molecular species than provided by the open source. The sensitivity enhancement is achieved by sampling the ambient gas through an orifice into an enclosed antechamber. Open Source Sampling of Thermal and Medium Energy Ions: Ion species present in the coma within the mass range (1 to ~300 AMU) will be sampled through the open source. These ions are created by photoionization, electron ionization, and other processes acting on gases in the coma. Ion Source Selection in the Quadrupole Deflector: Ions are sequentially directed to the mass analyzer from the selected ion source by changing the potentials on the quadrupole deflector. This electrostatic device allows FSW to focus either Ion Source into a common exit lens system. The Quadrupole Mass Analyzer: The quadrupole (QP) mass analyzer consists of four hyperbolic rods mounted in a rigid mechanical assembly. The transmitted mass-to-charge ratio and the filter resolution are controlled by FSW by variations in RF and DC electric fields between adjacent rod pairs while opposite rod pairs are kept at the same potential. Three fixed frequencies are selected to cover the mass range. The Dual Detector System: The detector system counts ions transmitted through the quadrupole analyzer to produce a mass spectrum; counts are collected by FSW and sent in TM to ground. The system is redundant and configured for a wide dynamic range. Control of the QP and switching lenses is performed via DACs (Digital-to-Analog Converters). In this document, reference to "tuning" means that the FSW must compute a set of DAC values for the QP rods and switching lenses to perform a certain analysis and sample the pulse counts with the detector system. NGIMS also has two valves that the FSW must open and close, as well as various other "digital controls" (DCons) such as pressure gauge on/off control, EM (Electron Multiplier) select, Filament on/off control, etc. NGIMS communicates with the S/C via 1553 interface. II BACKGROUND During initial stages of instrument FSW development, the requirements, design and implementation had been documented via a "MOU" method -- Memorandums Of Understanding have been passed between instrument groups. After general agreement, detailed specifications were then generated specifically for the programming personnel. This document delineates flight software requirements at a high level for all personnel, and essentially places them under configuration control. III REQUIREMENT NUMBERING For reference purposes, each requirement is designated with a requirement number, e.g., "HLR-01" (High-Level Requirement number 01). Any modifications to this document that add or delete requirement will still maintain original requirement numbering by using a decimal suffix, e.g. to add a requirement after HLR-01, the number would be HLR-01.1. Any statement in this document which is not accompanied by a requirement number of that form is thus not a requirement, but is merely provided for explanatory purposes. Sub-requirements are sometimes specified, describing the main requirement in more detail. For every mission and subsystem, the "cheaper faster better" doctrine that NASA has adopted always carries something beyond essential functional requirements: a concept called "stretch goals." For this instrument FSW, stretch goals are indicated as "optional" requirements, signified by "(O)" in this document. IV FSW REQUIREMENTS 1. Sampling 1.1 General. HLR-01 Mass Sampling and TM transmission thereof shall be autonomous during encounters. Note that autonomous operation via commanding scripts in the S/C is acceptable. References to "onboard sequencing" or "autonomous" events can be implemented either within the instrument FC or onboard the S/C, time-sequenced relative to MET (Mission Elapsed Time) or Tzero (Time Of Closest Approach). HLR-01.1 (O) A Stored Command Processor and time-tagged Command Sequence shall reside onboard the FC. An "Auto-start Sequence" is a requirement for the FSW to handle an unexpected FC reboot during comet encounter because in the absence of such requirement, a reboot any time during a comet encounter is catastrophic for instrument success. During comet encounters, an FC reboot shall : HLR-01.2 Cause the instrument to, at a minimum, automatically begin some "nominal" science sequence (automatic setting of the lens voltages and scanning) HLR-01.3 Enter a "turn-on" sequence where the QP is generating and detecting ions HLR-01.4 Perform the above turn-on sequence in a "safe" (timed) manner; and guard against entering dangerous "Auto-turn-on" modes (for example, as a result of simple operator errors) HLR-01.5 Cause Muxes to be sampled, HK to be generated, and resume transmitting science & HK telemetry HLR-01.6 Cause FSW to continue in said nominal science mode and await any further commands (from the S/C C&DH, or from within any NGIMS stored commanding); and, if/when received, heed such commands. HLR-01.7 Indicate in TM that such an "Auto-start" sequence was indeed (or was not) performed. HLR-02 The FSW shall provide the capability to tune the quadrupole to specified AMU values, sample the pulse counters at that tuning, and return the counter values and associated data in TM. HLR-03 The FSW shall sample from 0 AMU to ~300 AMU. 1.2 Sampling controls An "Integration Period" (IP) on the order of 22 ms will be implemented in the electronics; the IP is the basic (and smallest) unit of sampling. HLR-04 The FSW shall provide the capability to tune the quadrupole at the IP rate to the following basic modes: HLR-05 Sampling with Unity mass resolution at unity AMU steps HLR-06 Sampling with Unity mass resolution at any 1/10 AMU value HLR-07 Band & Totals (mass resolution wider than 1 AMU) HLR-08 Support for energy scans (tuning of selected DACs to any, including "off-center" values) HLR-09 The FSW shall provide the capability to tune all DACs at the IP rate to a new value to support the above quadrupole tuning. HLR-10 The FSW shall provide these tuning capabilities with autonomous compensation for RF drift (on certain DACs) and temperature change (on all DACs). HLR-11 FSW shall provide these tuning capabilities for QP and all DACs with autonomous compensation for changing S/C potential. HLR-11.1 FSW shall provide these tuning capabilities with autonomous compensation for changing S/C attitude (within acceptable values of pointing angle) using angle data provided by S/C. HLR-12 The FSW shall provide the capability to change between Open Source and Closed Source at the IP rate. HLR-13 The FSW shall provide the capability to change between Ion Mode and Neutral mode the IP rate in the Open Source. HLR-14 The FSW shall provide the capability to "overlap" frequencies - that is, to be able to tune the QP to certain masses using either the nominal frequency or an alternate frequency. 1.3 Scanning The FSW should maximize science return: HLR-15 The FSW shall allow scanning within selectable pre-defined AMU ranges (a "mass table" concept) with periodic changing between modes and algorithms (a "round robin" scanning concept). HLR-16 The FSW shall implement the "Adaptive Scanning" algorithm that has been prototyped in the GSFC Code 915 laboratory, with the ability to disable the algorithm interactively via commanding. HLR-17 Via sequencing (from the S/C or onboard the instrument), the FSW shall allow autonomous control of the sampling parameters (AMU ranges, resolution, Source, modes). 1.4 Calibration and Tuning. HLR-18 The FSW shall provide robust support for calibration & tuning via commands, scanning modes, and general operation. 2. COMMANDING HLR-19 Commands shall be supported for a minimum of the following functions: HLR-19.1 Scanning Control HLR-19.2 Valve Control HLR-19.3 DCON Control HLR-19.4 Standby Mode HLR-19.5 Memory Modification HLR-19.6 Memory Dump HLR-19.7 Reboot HLR-19.8 DAC Overrides HLR-20 The FSW shall support a method for a pressure test sequence. (?) HLR-21 The FSW shall support a "Baseline Checkout" sequence. HLR-22 (deleted) HLR-23 (deleted) 3. TELEMETRY A Science TM channel, HK TM channel, and non-packetized TM (NPTM) channel are available. HLR-24 Science and HK in telemetry shall be CCSDS packets, time-tagged, unambiguous and complete. Telemetry shall include, at a minimum: HLR-24.1 Data collected every Integration Period: (a) High and Low Sens Counts (b) One Mux and data describing the data (metadata) to the extent that the Scanning Sequence (see 1.3) can be reconstructed: (c) Scan Mode information (d) AMU (e) Frequency (f) Source (g) Mass Resolution HLR-24.2 Pertinent HK and Health/Status data HLR-24.3 Memory Dump data (when requested) HLR-25 The Science and HK telemetry generation rate shall not exceed 4.5K bits per second on average. HLR-25.1 HK telemetry shall include acknowledgment of commands received. 4. FSW IMPLEMENTATION Maximum re-use of flight software is desired (e.g. from Cassini GCMS and INMS). HLR-26 (deleted) HLR-27 Each detailed FSW requirement shall be testable and verifiable. HLR-28 The FSW shall comprise a robust & fault-tolerant system as Category IV software as defined by NASA-GB-1740.13-96. HLR-29 The FSW shall support modification (application of memory patches) via TC including the ability to reprogram all of EEPROM (128KW) and RAM (64KW). HLR-29.1 A default load image of the FSW in EEPROM shall be supported; a FSW version in PROM shall be used as a fall-back image in the event the EEPROM image is bad, or not desired. HLR-30 Primary tuning and calibration parameters shall be documented, and allocated to a contiguous section of flight computer memory for ease of modification. HLR-31 Each release of the software shall be identified by version or build number, which shall be placed in computer memory. ACRONYMS AC Alternating Current AMU Atomic Mass Unit DAC Digital to Analog Converter DC Direct Current EM Electron Multiplier FC Flight Computer FSW Flight Software GSE Ground Support Equipment HLR High-Level Requirement HK Housekeeping IP Integration Period MOU Memorandums Of Understanding QP Quadrupole RF Radio Frequency S/C Spacecraft SC Stored Command TC Telecommand TM Telemetry 6