PART III IMPLEMENTATION OF THE MASTER SCIENCE PLAN

Transcription

1 MASTER SCIENCE PLAN OVERVIEW DOCUMENTATION (MEX-EST-PL-11912, Draft Issue 1.5) PART III IMPLEMENTATION OF THE MASTER SCIENCE PLAN Planetary Missions Division Research and Scientific Support Department

2 : 2 Document Issue Record Prepared by Affiliation Issue P. Martin SCI-SB, ESTEC Issue May 2003 P. Martin SCI-SB, ESTEC Draft Issue November 2004 Checked by Affiliation PST ESTEC August 2004 Mission Manager ESTEC September 2004 Applicable and Reference Documents Both applicable and reference documents provide additional supportive information for a better understanding of the information given in the present documentation. Applicable and reference documents are listed in Annex 1 and 2, respectively. Cross-references to applicable and reference documents are indicated throughout this document by a combination of a letter code and sequential numbers, such as ADxx for applicable documents and RDxx for reference documents. 2

3 : 3 Table of Contents 1. Building the Introduction How to Implement the MSP Scope of this Release General Constraints and Conventions Plan Start Plan End Guidelines for Data Acquisition Payload Commissioning Coordination with Orbital or Landed Mars Missions Time Convention Orbit Numbering Spacecraft Geometry Planetary Constants Use and validation of auxiliary data; SPICE kernels

4 : 4 1. Building the 1.1. Introduction The (MSP) is aimed to be a compilation of payload objectives and consolidated high-level operation timelines for each orbit of the Mars Express mission. The implementation of the MSP constitutes the start of the scheduling, at MTP level, of the acquisition of science data by the Mars Express spacecraft in a way that is consistent with both the scientific objectives of the mission and the resources available for that data collection. Those resources (e.g., power, OBDH bandwidth, on-board data storage, telemetry bandwidth, spacecraft visibility from the ESA New Norcia (NNO) or NASA DSN ground stations, available bandwidth between NNO/DSN and ESOC) constitute important constraints on the planning and on the operations, as they shall be sufficiently dimensioned to allow the mission and payload scientific objectives to be achieved during the time that Mars Express will be operational. The Mars Express science data acquisition periods will be distinctly defined on an orbitby-orbit basis, allowing flexibility in the implementation of the science operations of the mission. Although each orbit might end up being different from any other, which may imply time-consuming planning activities, the goal is to optimize the science data acquisition without altering the available flexibility. This can be achieved by, for instance, planning sequences of orbits for which the observations to be performed by one or several instruments repeat themselves for a certain number of orbits (e.g., to fulfill the global mapping objective). This is also certainly achieved by developing powerful planning tools that will greatly facilitate the detailed planning activities and reduce the time spent for conflict resolution. The is the result of that optimization, the core of the MSP being materialized by the orbit-based, harmonized MIRA request files. During the Mars Commissioning phase, the Commissioning and Verification Plan constitutes the driving document for the payload operations. The becomes the driver of the science operations during the routine operations phase. The Flight Operations Plan (FOP) is always used as reference for all operations How to Implement the MSP The MSP shall contain the science windows and approved science observation periods, the payload instruments pointing requirements, and the corresponding selected instrument main science observation modes as imposed by the mission operations conditions (e.g., global data return, pericentre illumination, occultation and eclipse seasons). Due to the limited onboard (storage capacity) and ground (contact time) resources together with 4

5 : 5 conflicting instrument observation requests, the building of the MSP is extremely complex and time-consuming (see Part IV about assumptions and constraints). To prepare the, one must first specify the relationships between the mission goals and the detailed scientific objectives of each payload experiment. Then the scientific objectives agreed for a given science sub-phase representing a specific period of the mission lifetime shall be implemented and tuned according to the payload operating requirements and operational constraints. The major payload requirements are pointing requirements, instrument activity modes, duration of data acquisition periods, and selectable instruments data rates. This specification of operating requirements is to be checked against spacecraft and subsystems capabilities and iteratively revised until being a good match with the available resources. Power usage, science/communications consolidation and OBDH bandwidth usage are the major constraints of the Mars Express mission. The main information that is needed by PST and POS to build the MSP is the instrumentspecific information (e.g., objectives, requirements, priorities, target lists, constraints) and the assumptions and constraints for operating the spacecraft and ground systems. The Mission Planning System Operations Constraints and Budget Document (OCD; RD25), together with the PID-B (RD31) and instrument Flight User Manuals constitute the primary source of instrument-specific information that is to be used as input for science operations. Assumptions and constraints compiled for the Mars Express mission are summarized in Part IV. Other documents such as the CREMA (RD2) provide further detail on the mission operations profile and constraints. Detailed planning constraints and assumptions are also listed in the Mission Planning Concept (RD24 and RD44). The planning and implementation of the MSP is based on material and parameters prepared or known before the launch of Mars Express, such as the frozen ground track orbit configuration, or on information known following launch, Mars orbit insertion or even resulting from unforeseen events (e.g., power anomaly, MARSIS deployment delay). Therefore, a key issue is to check that the payload scientific timelines and the corresponding resulting scientific measurements and surface coverage match all predicted parameters. Re-planning of payload operations may be necessary for various reasons, at least in the form of refinement of the previous planning, in order to ensure that the science objectives of the mission are reached. This may likely take place during the medium-term planning, but could in some cases be done at a higher level of the scientific planning. The high-level science planning and implementation of the is characterized by the definition of a number of science sub-phases and a planning rationale linked to the scientific goals of Mars Express, combined with the adoption of a dedicated science planning policy and strategy that shall streamline the conflict resolution process. Part VI brings this rationale, policy and strategy forward. 5

6 : 6 2. Scope of this Release Issue 1.0 of the MSP documentation was released at the time of the launch of the Mars Express mission, and therefore did not include updated information with regard to a number of decisions or events such as the selection of the eq100 orbit, the changes in the planning concept resulting from the approval of a second ground station or from the power subsystem anomaly, or the commissioning and routine detailed planning scheme and strategy (with delayed MARSIS antenna deployment). This released Issue 1.5 of the overview documentation includes all the relevant and up-to-date information, covers the payload commissioning phase including the initial scientific operations conducted in this phase, gives further details on the post-commissioning planning when the Payload Operations Service was phased in, and covers the beginning of the routine phase of the nominal mission. The orbit-by-orbit planning of the payload operations that is laid out in Annexes 8 and 9 of this release spans the time from early payload operations (January 2004) until about January The next issue of this MSP documentation is expected to cover a period of 24 months from the time of MOI, corresponding to the entire duration of the nominal mission. This document will be updated if and when necessary with new data or due to changes of constraints. In this release are specified and/or updated: The general constraints and conventions The assumptions, mission operations profile and operational constraints The scientific data downlink process, planning rules and constraints The payload detailed scientific rationale and objectives The payload scientific targets of interest The declared payload scientific priorities The payload contingency plans The special events and targets of opportunity The payload operating requirements and configuration The definition of science phases and sub-phases The science planning policy and strategy The orbit-based payload operations timelines * * May be specified for the period covered, orbit by orbit: The graphic representation of the orbit configuration/geometry The spacecraft pointing profile The consolidated timeline of payload events The information on each scientific observation (goal, target) 6

7 : 7 3. General Constraints and Conventions 4.1. Plan Start The start of long-term science planning activities as established in this release of the MSP overview documentation is constrained by the mission operations profile. The start of the payload operations planning is set at the beginning of the scientific involvement in the mission once the spacecraft has arrived safely and is in a stable orbit around Mars. The first in-orbit scientific activities on Mars Express started at the beginning of January Early after Mars orbit insertion, interleaved Mars commissioning activities (spacecraft, payload) and initial payload operations took place to fulfill the mission s scientific goals and in preparation of the phasing-in of the routine operations. The payload commissioning and early scientific activities at Mars were planned as part of the Commissioning and Verification Plan (RD14) Plan End This release covers (i) the initial payload operations that took place during the first few months of the mission at Mars (during Mars Commissioning Phase) and (ii) the first 10 months of routine payload operations until end of March 2005, planned using the MTP planning cycle scheme with the Payload Operations Service (POS) fully involved and operational. The complete MSP documentation shall be constituted of the cumulated LTP and MTP payload timelines covering a number of defined science sub-phases (see Part VI), the total of which corresponding to the entire duration of the nominal mission Guidelines for Data Acquisition The allocation and regulation of scientific data acquisition is constrained by mission operations parameters (e.g., mission profile, spacecraft and ground resources, spacecraft safety) and by the planning rules and guidelines advised by the Payload Support Team and the MOC, in consultation with the SOWG and SWT. Planning rules and guidelines are established with respect to: Time, frequency, duration and priority of science data acquisition Pointing requirements Instrument data rate Data volume shares and data downlink Communication versus observation periods Power usage Spacecraft maintenance and commanding 7

8 : 8 Part IV of this MSP documentation is dedicated to giving some insight into the various assumptions, constraints and rules that have been established to regulate and optimize the planning of the Mars Express payload operations. Some of these rules may need to be revised as experience is gained during the mission and depending on the occurrence of unforeseen events or changes in the spacecraft or payload configuration Payload Commissioning The payload checkout, calibration and commissioning activities are described and planned in the Commissioning and Verification Plan (RD14). The latter document specifies the goals and constraints for all payload-commissioning activities during the Near-Earth Verification Phase, the Cruise Phase and the Mars Commissioning Phase. It also indicates the activities required at spacecraft platform and ground segment level. The Commissioning and Verification Plan is the driving document for all operation activities at the beginning of the mission, until the Mars Express Commissioning Results Review (CRR) declares the spacecraft and its scientific payload ready for routine operations. The payload commissioning activities at Mars are compiled in this MSP documentation as they play a critical role in the understanding of the payload instruments (e.g., their performance) and in the preparation of the routine science mission. Initial payload observations acquired during the Mars Commissioning Phase are to be taken as part of achieving the scientific objectives of the mission. Indeed, the first few weeks of the inorbit mission are critical from a scientific point of view as the ground track coverage and observation conditions lead to nearly unique opportunities for scientific data collection. The commissioning activities in orbit around Mars take place under various operational conditions, leading to the definition of 6 commissioning sub-phases. These sub-phases are defined in Part VI of this documentation. The relevant payload operations timelines are distributed in Annex Coordination with Orbital or Landed Mars Missions This planning documentation is intended to deal with the data acquisition from the Mars Express orbiter instruments. As such, it does not generally take account of requests to coordinate the data acquisition from Mars Express with the data acquisition from other spacecraft missions (such as NASA orbiter and landed missions) or from Earth-based experiments. However, coordinated science operations between the Mars Express orbiter instruments and the instruments onboard the NASA Mars Exploration Rovers (MER) Spirit and Opportunity have been undertaken and more are foreseen. These operations are therefore planned as part of the regular MSP activities. See Part V and Annexes 8 and 9 that give 8

9 : 9 further detail regarding the relevant coordinated scientific objectives and payload operations timelines. Coordination is also foreseen in terms of communication data relays between the Mars Express telecommunication subsystem MELACOM and the MER rovers or Mars Odyssey spacecraft. The planning of the relevant communication sessions appears in the MSP/MTP timelines, as the required spacecraft resources (pointing, power, data) influence the planning of operations by the scientific payload onboard Mars Express. Several such coordinated communication sessions have been successfully conducted, demonstrating the capabilities of having for the first time a network for communications around another planet. For information, the interfaces of the Mars Express mission in the context of the international collaboration are given in Figure 18 below. The coordination of the Mars Express lander science operations with the orbiter payload operations was to be part of this documentation as well, and was preliminarily described in the Coordination of Mars Express and Beagle-2 Science Operations Document (RD32). Following the fate of Beagle-2, this activity did not take place. 9

10 : 10 Figure 18: Telecommand and telemetry flow in international collaboration around Mars. 10

11 : Time Convention For planning purposes, most information provided by the instrument teams is specified and supplied as orbit number and time offset from pericentre. The purpose of this is to allow for a slight drift in the time of orbit events between planning and actual execution. This is essentially the case for all inputs to the MIRA planning tool. and time information is given in UTC in some cases. The format used is the following: YY-DDD'T'HH:MM:SS Z YY are two characters to specify the last two numbers of the year. DDD are three characters to specify the day within this year T00:10:10Z specifies the 10th day of the year 2003 (see CRID; RD28). All date and time information in the MSP will use this format. All date and time information in the PIOR will use this format (See POS Commanding Scenario; RD23). Orbit and Attitude files use TDB as time standard with the following format: YYYY-MM-DDTHH:MM:SS.sssssss. On board the spacecraft, all telemetry data are packetised in source packets. Each source packet is time-tagged with the OnBoard clock Time (OBT). The field in the TC packet containing the OBT has 6 bytes (48 bits). This field contains the SCET (SpaceCraft Elapsed Time; DDID; RD29), which represents the number of seconds elapsed from the last reset of the clock. This field is coded as follows: 4 bytes for seconds and 2 bytes for fractions of second (up to fractions of a second). This time corresponds to the OBT time when the data were measured by the instrument onboard the spacecraft. On reception, the TC packets are wrapped with a header to be distributed via the DDS. The contents of the packet are unprocessed, and only that header is attached to its beginning. The header contains the SCET time in UTC format (the UTC when the data were measured by the instrument onboard the spacecraft). The time correlation coefficients are employed to calculate the UTC time of the DDS header from the data acquisition start time in OBT. The time format used to code the UTC in the DDS packet header is the Sun Modified Julian Time, as standard on Sun Solaris UNIX platforms. It corresponds to the number of seconds since 00:00:00 UTC on 1 st Jan 1970 with leap seconds taken into account. The time correlation coefficients are produced on the ground station, using a procedure involving data from the spacecraft. The onboard spacecraft clock is sampled on the spacecraft, placed into the standard spacecraft time source packet in CUC format (4 bytes for seconds, 2 bytes for fractions of second) and transmitted to ground. On reception, all 11

12 : 12 packets are time-tagged with the current UTC (obtained from the station clock which is synchronized to UTC) and routed to the control system at ESOC. This time is called Earth Reception Time (ERT). The ERT is extracted and several corrections are applied to obtain the onboard time in UTC format. The ERT is corrected for the delay introduced in the ground station (transmission from the antenna to the equipment where the ERT is time-stamped on the frame), propagation delay (the time taken for the signal to travel from the spacecraft to the ground station antenna) and the delay in processing the packet on the spacecraft. The result of all these corrections is a time correlation packet that contains both UTC and OBT formats, i.e., the same event measured in the two time scales. All these time correlation packets are used to calculate the time correlation coefficients by a least square fit. The time correlation between the spacecraft onboard clock and the UTC time shall be updated on a regular basis (e.g., every couple of weeks). In case the instrument teams want to correlate their instrument time counter values to an appropriate UTC time, the relevant chapter in the DDID explains the usage of the time correlation file (TCF) Orbit Numbering It is expected that the Mars Express spacecraft will execute 2293 orbits around the planet Mars during the nominal mission. The nominal injection sequence has been addressed and presented by ESOC (see RD2 and Figure 19). As a result, the numbering convention that has been chosen is such that Orbit 1 is the first closed orbit after MOI (from the first apocentre to the second apocentre). A certain number of orbits were performed to reach a stabilized polar elliptical orbit with a 7.5-hours orbital period around the planet. The Eq100 mapping orbit was reached on 28 January 2004, at the orbit number 57. During the entire nominal mission, the spacecraft starts a new orbit number as it passes through the apocentre. All predicted data from the MOC are based on this concept. The Mission Planning Concept (RD24) gives further information on orbit numbering. 12

13 : Spacecraft Geometry Figure 19: Nominal injection sequence. The spacecraft geometry (AOCS reference frame) is as follows in Figure 20, with indication of the axes of rotation used by Flight Dynamics. Characterization of the pointing modes with respect to the various rotational axes is described in the Mission Planning Concept (RD24). For further information, Figure 21 shows in detail the layout of the payload platform in the mechanical reference frame used by the prime contractor EADS-Astrium. From the convention used for the AOCS and mechanical spacecraft reference frames, the X axis is equivalent to the Xb axis, the +Z axis is equivalent to the Zb axis, and the Y axis is equivalent to the Yb axis. 13

14 : 14 Figure 20: Spacecraft geometry (AOCS frame) with rotational axes. From RD2. Figure 21: Mars Express payload platform layout and spacecraft mechanical frame. 14

15 : Planetary Constants The use of planetary constants for the Mars Express mission is such that: The IAU 2000 cartographic convention is adopted for Mars Express. The planning tools MIRA and MAPPS have been converted to run with this agreed convention. There is an agreement between JPL and ESOC to use the same planetary constants as applicable for the Mars Exploration Rovers (MER) and Mars Reconnaissance Orbiter (MRO) missions. The document to be used as reference document is the Planetary Constants and Models document (RD33). Minor differences with the constants to be used by JPL on its missions are stated in the ESOC/JPL Navigation ICD (RO-ESC- IF-5011; RD34) and are related to navigation. The Phobos and Deimos ephemeredes is understood to be different from the one used by JPL. The Mars gravity field will be used inside the sphere of influence of Mars Use and validation of auxiliary data; SPICE kernels The files giving access to orbit, event and attitude data for the Mars Express spacecraft and the original software used to produce and process this data are delivered by ESOC (DDID; RD29 and RD30). Following requests made by several PIs, ESA decided to offer the ancillary data of Mars Express in SPICE format, in addition to the original ESOC format. SPICE (Spacecraft, Planets, Instrument, C-Kernel, Events) is a toolkit maintained by the Navigation and Ancillary Information Facility (NAIF) at JPL/NASA, which aims to offer a common information system that allows scientists and engineers to access navigation and other ancillary spacecraft data from many planetary missions. The primary SPICE data sets are called "kernels" or "kernel files". There are several types of kernel files: SPK for spacecraft and planets ephemeris data, CK for attitude data, FK for reference frames, SCLK for time correlation, IK for instrument information, PCK that contains the planetary constants and LSK with time conversion constants and leap seconds. During the Mars Express pre-launch activities, the NAIF team has developed the software and kernels to be used for the mission, supported by all instrument teams and the PST. The SPK and CK kernels are generated at ESTEC in real-time during the mission, without human intervention, the process being supervised by PST. These files are generated from the ESOC orbit and attitude data respectively. LSK and PCK files are created by NAIF whenever it is required (due to updates in the constant s values or introduction of new leap seconds by the International Earth Rotation and reference system Service). The PST generates SCLK kernels every time a new time correlation packet is released by MCS (this process shall be automated at medium-term). An FK file 15

16 : 16 containing all the mission specific frames has been created and it shall be updated if required. An IK file is produced for each instrument describing its sensor s characteristics and special features. The use of different data sets requires careful and accurate validation of all data and planning tools produced for the Mars Express mission. The auxiliary data conversion into SPICE kernels and the relevant data distribution is explained in RD35. 16