| Description |
Data Set Overview ################# This data set includes the complete set of ancillary information for the Mars Express spacecraft in the form defined by ESOC (European Space Operations Centre). The ESOC auxiliary data contains geometric and other ancillary data needed to recover the full value of science instrument data. In particular ESOC data files provide spacecraft ephemerides, orientation and time correlation information, and sequence of events. Additionally pointing request information and star occultation events are provided in separate files. This data set is contained in a single virtual volume including data from all mission phases and covering from launch, 2003-06-02T19:18:21.799, through the end time of the latest spacecraft trajectory file supplied in the data set. Until the end of the spacecraft or mission lifespan, this data set is accumulating with new data added approximately every three to six months. Data Types ########## This data set contains the following data types: ATNM: file describing pointing, containing a transformation traditionally called the C-matrix which is used to determine time-tagged pointing (orientation) angles for a spacecraft. Instead of storing the C-matrix, the Mars Express attitude file contains discret quaternions. The attitude file is located under the DATA/ATNM directory in this data set. CMH: TBW EVTM: file type containing the most up to date events consistent with the orbit data form the ORHM and ORMM file types. For each event, one line of information is given. The event files are located under the DATA/EVTM directory in this data set. ORHM and ORMM: files containing ephemerides for the Mars Express spacecraft during the cruise phase and around Mars. They provide position and velocity, given in a Cartesian reference frame. Orbit data files are located under the DATA/ORBIT directory in this data set. PTR: files containing a complete definition of the attitude pointing of the S/C for the covered period. Only the pointing during S/C manteinance window remains undefined in the PTR. The Pointing Timeline Request are located under the DATA/PTR directory in this data set. STOM: files containing star occultation events for a set of starts provided by the SPICAM experiment. Star occultation files are located under the DATA/STOCC directory in this data set. TCORR: binary table containing the Time Correlation coefficients packets that contain the on-board calibration data required to perform a mapping between the Universal Coordinated Time (UTC) and the spacecraft ephemeris time (SCET). Time Correlation data file is located under the DATA/TCORR directory in this data set. Data Type Characteristics and File Details ########################################## Attitude Data (ATNM Type) ========================= General information about ESOC Attitude Data for Mars Express ------------------------------------------------------------- Attitude data are provided for all mission phases apart from safe modes. Except for initial launcher separation and for backup modes the attitude is contorlled in one of the following ways: - The S/C takes a fixed inertial attitude commanded by ground. - The S/C follows a time dependent attitude profile commanded by ground - The S/C x-axis is Earth Pointing, the S/C y-axis is nearly to the ecliptic. Time dependent inertial Earth and Sun direction profiles are commanded by ground. The attitude information in this file is based on command profiles. There is no distinction between cruise phase and operational orbit as for orbit ephemeris, since that is not necessary in terms of attitude. The attitude is provided in segments, each covering a specific time span. These segments have no overlap. There may be gaps between the segments and even gaps in the segments. Attitude data have been provided for the past and near future during the operational mission. Predicted vs. Reconstituted Attitude Data ----------------------------------------- Except special cases, no reconstituted data have been provided for Mars Express attitude information. Despite that originally it was stated that reconstituted attitude data would be provided for certain pointing modes as a Flight Dynamics official product, this was denied and removed from the official documents after the Near Earth Verification (NEV) Review even when these data were requested several times by the Principal Investigator (PI) teams and it was flagged as something the scientist would need. The reason to not provide reconstitution for the attitude data can be sumarized in the following points: - The attitude estimation from the S/C onboard filter could not be improved on ground with the available Attitude and Orbit Control System Telemetry. - The divergence on the pointing of the onboard estimated attitude from the Flight Dynamics provided predicted attitude in the DDS is below the specified requirements and in the order of the measurement noise. Representation of Attitude Data ------------------------------- The attitude of the S/C refers always to S/C frame (also called S/C reference frame) with respect to the reference frame J2000. The pointing of a Mars Express spacecraft is described by the rotation of the S/C reference frame with respect to the J2000 reference frame. This rotation is usually represented by a 3x3 matrix, called C-matrix which is used to perform the transformation of the three components of a vector in the J2000 frame to components expressed in the spacecraft reference frame. The attitude of a payload instrument can be derived by applying the rotation between the instrument frame and the S/C frame. So, it is possible to obtain the orientation of any instrument by matrix multiplication. The rotation matrix can be represented by a quaternion, which is a four-dimensional vector that represents a unit vector (3 components) and an angle. The vector represents the axis of rotation, and the angle the rotation magnitude. Attitude Data Access. Data Storage. ----------------------------------- Attitude data have to be stored in a binary direct access data file in a format that is tailored with respect to numerical accuracy, access performance and storage requirements. This applies to the S/C predicted attitude (and in special cases, reconstituted). Although the low level architecture of data storage is quite sophisticated the retrieval of data is made very easy by the use of a simple access software. The attitude file contains attitude information at discrete times. The corresponding epochs are not equidistant in time but are chosen by numerical integrator. Attitudes for arbitrary epochs are derived by interpolation. The whole attitude is partitioned into blocks which comprise a mission phase or a part of it. For each block and for the whole file there is additional information stored in block headers and the file header. All data are stored in logical records containing either attitude, block header or th file header information. The logical records are in turn grouped together into the physical records of the binary direct access file. The access software (archived within this data set) reads the data only from binary direct access files. To allow the transfer of data between machines which are not binary compatible, attitude data have been made available in ASCII format together with a FORTRAN utility for conversion into the required binary format on the target platform. This ASCII files have been archived in this data set as well as the FORTRAN program. To access an attitude at a certain epoch from a FORTRAN application program, a library is provided together with the attitude data. This software is described in the SOFT.CAT catalogue. ASCII Version of the attitude file ---------------------------------- Although content and structure of the ASCII file is completely transparent to the user (only the conversion with AS2BIN is required to create a valid binary attitude file), a short description follows. The ASCII file contains several blocks of data. Each block has a leading descriptive part, called meta data, consisting of a list of keyword value pairs surrounded by the identifying META_START and META_STOP keywords and the attitude data part proper. The following keywords appear in the meta data: - CREATION_DATE Date and time of file creation - OBJECT_NAME Identification of object (MARS EXPRESS) - TIME_SYSTEM always TDB, i.e. barycentric dynamical time - REF_FRAME reference frame, always EME 2000 = mean Earth equator of J2000 - START_TIME start of time interval covered by the following block of data - STOP_TIME end of time interval covered by the following block of data - FILE_TYPE always ATTITUDE FILE - VERSION_NUMBER indicates the version of the file format - VARIABLES_NUMBER always 4 - DERIVATIVES_FLAG always 0 The proper attitude data are just lines providing at discrete time steps epoch of the state and the quaternion describing the rotation from the inertial to the S/C frame. Orbit Data (ORHM and ORMM Types) ================================ General information about ESOC Orbit data for Mars Express ---------------------------------------------------------- Orbit determination has been a batch least squares procedure taking into account range and Doppler measurements from the European Space Agency 35m antenna at Perth. During critial mission phases tracking data have been additionally provided by ESA/Kourou and NASA/DSN stations. The dynamical model of the S/C motion refers to the J2000 inertial reference frame with Barycentric Dynamical Time (TDB) as independent variable. In addition to the Newtonian attraction of the planets and the Moon, the model includes: - Relativistic corrections to the gravitational fields. - Perturbations of the Earth and Mars gravitational fields due to oblateness. - Solar radiation pressure forces. - Orbit manoeuvres. - Small forces due to gas leaks or uncoupled control jets. The centre of integration depends on the mission phase. Near Mars the orbit is integrated with respect to the planet. During cruise phase the centre is the Sun. The ephemerides of the planets and Moon are taken from the latest version DE4005 of the Jet Propulsion Laboratory (JPL) export ephemerides files. Range and Doppler measurements are corrected for several effects: - Transponder delay. - Signal delay due to the troposphere and ionosphere of the Earth. - Signal delay due to interplanetary plasma. The result of the least squares prcedure are best estimates of the state vector of the S/C and of severalmodel parameters plus statistical information. The accuracy depends on the mission phase. The number and frequency of batchs runs for the orbit determination depends on the mission phase and the availability of tracking data. For the cruise phase has been done tipically every month (at least once) while for Mars Orbit phases the process is executed once a week. Two types of orbit data have been provided for the Mars Express mission. One, named ORHM type, covered the cruise phase from launch to Mars Orbit Insertion (MOI), the second, called ORMM type, the operational orbit around Mars after orbit insertion. For all types, the reference plane is the Earth mean equator of J2000. The orbital data have been provided during cruise phase as heliocentric states, in the operational orbit as Mars centric states. Data of the first type (ORHM) is contained in a single file. With each new orbit determination and/or manoeuvre optimisation, a new version of the file has been created. Only the latest version of the file (00038) has been archived in this data set. Data of the second type (ORMM) have been distributed over several files due to the large amount of data. The name of the file contains the start time YYMMDDhhmmss of the interval which is covered by the file. As there are no gaps between files, the corresponding end tyme of a file is given by the start time of the next file. The time interval is tipically about one month. The start time in the file name has been given to an accuracy of a day (i.e. hhmmss = 000000) and is accurate to one day compared to the actual time spancovered by the data in the file. For example, the file with YYMMDDhhmmss = 040309000000 contains data starting at any time between 08/03/2004 and 10/03/2004. This has been done in order to keep some freedom in the choice on the actual separation of data in time. This separation has taken into account operational conditions like correction manoeuvres. Predicted v. Reconstituted Orbit Data ------------------------------------- The orbit prediction uses the same dynamic model and similar integration techniques as for orbit determination (described in the previous chapter -- General information about ESOC Orbit data for Mars Express). But instead of fitting the S/C orbit in the past with received tracking data the future S/C orbit is integrated using the best estimate of the last orbit determination and optimized with respect to fuel consumption and mission constrains by suitable insertion of manoeuvres. Reconstituted data have been delivered with every update of the files. Although these files, when delivered to the PI teams contained both predicted and reconstituted orbit data, the latest version (archived in this data set) of each file contains only reconstituted data. Orbit Data Access. Data Storage. -------------------------------- Orbit data have been stored in a binary directo data access file in a format that is tailored with respect to numerical accuracy, access performance, common application interface and storage requirements. This applies to the S/C recontructed and predicted orbits (not available). Although the low level architecture of data storage is quite sophisticated the retrieval of data is made very easy by use of a simple access routine. The orbit files contain orbital information at discrete times. The corresponding epochs are not equidistant in time but have been chosen by the numerical integrator. The whole orbit is partitioned into blocks which comprise a mission phase or a part of it. For each block and for the whole file there is additionalinformation stored in block headers and the file header. All data have been stored in logical records containing either orbital, block header or file header information. The logical records are in turn gruoped together into the physical records of the binary direct access file. The access software (archived within this data set) reads the data only from binary direct access files. To allow the transfer of data between machines which are not binary compatible, orbit data have been made available in ASCII format together with a FORTRAN utility for conversion into the required binary format on the target platform. This ASCII files have been archived in this data set as well as the FORTRAN program. Read access has been established by a layer of low level FORTRAN subroutines on top of which a very simple FORTRAN access subroutine resides. This subroutine is described in the software catalogue of this data set (SOFT.CAT). ASCII Version of the orbit files -------------------------------- Although content and structure of the ASCII file is completely transparent to the user (only the conversion with AS2BIN is required to create a valid binary orbit file), a short description follows. The ASCII file contains several blocks of data. Each block has a leading descriptive part, called meta data, consisting of a list of keyword value pairs surrounded by the identifying META_START and META_STOP keywords and the orbit data part proper. The following keywords appear in the meta data: - CREATION_DATE Date and time of file creation - OBJECT_NAME Identification of object (MARS EXPRESS) - TIME_SYSTEM always TDB, i.e. barycentric dynamical time - REF_FRAME reference frame, always EME 2000 = mean Earth equator of J2000 - CENTER_NAME Identificiation of central body, e.g. SUN, MARS. - START_TIME start of time interval covered by the following block of data - STOP_TIME end of time interval covered by the following block of data - FILE_TYPE always ORBIT FILE - VERSION_NUMBER indicates the version of the file format - VARIABLES_NUMBER always 6 - DERIVATIVES_FLAG always 1 (state and state derivative provided) The proper orbit data are just lines providing at discrete time steps epoch of the state, the state (position in km, velocity in km/s) and the state derivative (with respect to time scale in days). Events Information File (EVTM Type) =================================== General Information about ESOC Events Information File ------------------------------------------------------ The EVTM type file contains the most up to date events consistent with the orbit data form ORHM and ORMM files. During the mission lifetime this file contained events up to the near future. The file archived in this data set contains the most up to date events as happened during all the mission phases (cruise and opperational orbits). For each event, one line of information is given. The events occur in ascending order in time. Event File Format ----------------- The following table shows a description of the collumns of the event file: _______________________________________________________________________ NAME | DESCRIPTION | --------|--------------------------------------------------------------| EVTTID | Event Type Identification | --------|--------------------------------------------------------------| EVTCNT | Event Count | --------|--------------------------------------------------------------| PREREC | Single character flag indicationg whether event is predicted | | (P) or reconstituted (R) | --------|--------------------------------------------------------------| EVTTIM | Start Time of Event in the format YY-DDDThh:mm:ss.dddZ | --------|--------------------------------------------------------------| EVTDUR | Duration of event in seconds. | --------|--------------------------------------------------------------| EVTDES | Description of event. | --------|--------------------------------------------------------------| EVTTID is a alphanumeric string of lenght 4 which is unique for each event type. EVTCNT is a running number for each event type. It will always be in ascending consecutive order. The format of EVTTIM is YY-DDDThh:mm:ss.dddZ where YY are the last two digits of the year, DDD is the day of the year and hh, mm, ss and ddd are hours, minutes, seconds and millisecons of the day. All other symbols are fixed character constants. The provided numerical accuracy of EVTTIM depends on the event type. For pericentre passages, the event time is provided with a numerical accuracy of 3 decimal digits. For all other events, the provided numerical accuracy is reduced to 1 second, i.e. the three decimal digits ddd are 000. EVTTIM is always given in UTC. If there is no duration related to the event (e.g. pericentre passage) then EVTTIM referes just to the time of the event rather than the start time of the event and EVTDUR contains 0. Although the end of events can be derived from the start time of the event and its duration, the end of the event is additionally given for convenience. In this case EVTTIM refers to the end of the event and EVTDUR contains also 0. Event Types in the file. ------------------------ The tables at the end of this section show all event types. The event types AxxH and LxxH refer to the event whenthe ^ation of the line of sight from the Ground Station to the S/C rises above or falls below the horizon mask. The horizon mask defines, depending on the azimuth, the minimum required ^ation of the antenna for reception of a signal. In the event description, the ^ationof the horizon mask is given in degrees as nn. The ^ation for AxxH and LxxH may differ from each other. For the event types AxxH, AxxT, LxxH and LxxT the xx and XXX in the EVTTID and EVTDES indicate the Ground Station (G/S) antenna and complex as follows: _________________________________________ | xx | XXX | G/S Antenna | (EVTTID) | (EVTDES) | -------------------|----------|----------| Perth | 73 | PER | -------------------|----------|----------| New Norcia | 74 | NN0 | -------------------|----------|----------| Kourou | 75 | KOU | -------------------|----------|----------| DSN Goldstone 34m | 13 | GDS | -------------------|----------|----------| DSN Goldstone 70m | 14 | GDS | -------------------|----------|----------| DSN Goldstone 34m | 15 | GDS | -------------------|----------|----------| DSN Goldstone 34m | 24 | GDS | -------------------|----------|----------| DSN Goldstone 34m | 25 | GDS | -------------------|----------|----------| DSN Goldstone 34m | 26 | GDS | -------------------|----------|----------| DSN Madrid 34m | 54 | MAD | -------------------|----------|----------| DSN Madrid 34m | 61 | MAD | -------------------|----------|----------| DSN Madrid 70m | 63 | MAD | -------------------|----------|----------| DSN Madrid 34m | 65 | MAD | -------------------|----------|----------| DSN Canberra 34m | 34 | CAN | -------------------|----------|----------| DSN Canberra 34m | 42 | CAN | -------------------|----------|----------| DSN Canberra 70m | 43 | CAN | -------------------|----------|----------| DSN Canberra 34m | 45 | CAN | -------------------|----------|----------| The event types AxxH, AxxT, LxxH, LxxT indicate when the line of sight to the S/C reaches the given ^ation at the G/S. These events do not indicate whether a TM/TC link is possible, as further events have to be consider like occultation, opposition or conjunction. The event types ALHM and LLHM refer to the event when the ^ation of the line of sight from the lander to the S/C rises above or falls below the horizon mask. The horizon mask defines, depending on the azimuth, the minimum required ^ation of the orbiter direction for reception of a signal. In the event description, the ^ation of the horizon mask is given in degrees as nn. In the beginning, the horizon mask is not known and nn will always be zero. If a horizon mask derived from actual visibility times becomes available, it is used for this events. In that case, the ^ation for ALHM and LLHM may differ from each other. AL10 and LL10 are given, when the ^ation of the line of sight rises above and falls below 10 degrees. The entry XXX in EVTDES of types ALHM, AL10, LLHM and LL10 gives the identification for the lander. BE2 is used for Beagle-2, MRA and MRB for Mars Exploration Rover A and Mars Exploration Rover B. The event types ALFn and ALRn refer to the event when the forward link (i.e. Mars Express Melacom to Beagle2) or return link (i.e. Beagle2 to Mars Express Melacom) become available and, at the same time, the aspect angles on both antennas (i.e. line of sight from Beagle2 to Mars Express with respect to Beagle2 antenna boresight and line of sight from Mars Express to Beagle2 with respect to Melacom antenna boresight) are below 70 degrees. Possible values for n are 1 to 7 for the return link (2^n kbps) and 1 and 3 for the forward link. Event types LLFn and LLRn are the corresponding end events, i.e. correspond to the times when the forward or return links become unavailable. The events are computed based on a default S/C nadir poining attitude and on a Beagle2 antenna pointing direction towards the local zenith. In the events descriptions, bit rate in kbps (x=2, 4, 8, 18, 32, 64 and 128), range in Km (rrrrr) and line of sight direction from lander to S/C as azimuth in degrees (zzz.z) and ^ation in degrees (ee.e) at the corresponding event time are provided. Type MOCS and MOCE refer to the event, when the line of sight from the centre of the Earth to the S/C starts and ends to be occulted by Mars. With MOCS some additional parameters are given: - rrr.rr,ddd.dd are right ascension form 0 to 360 and declination from -90 to +90 in degrees of the line of sight from the centre of the Earth to the S/C at start or end of occultation. - xxx.xx,yyy.yy are planetocentric longitude from 0 to 360 degrees eastward and planetocentric latitude from -90 to +90 degrees of the occulted Mars point. This is the point where the line of sight is tangential to the martian surface at start and end of occultation. - zzz is the Sun zenith angle in degrees for the occulted Mars point at start or end of occultation. Types MO2S and MO2E refer to the event, when the smallest distance between the surface of Mars and the line of sight from the centre of the Earth to the S/C drops below or rises above 200 km. Additional parameters are given: - rr.rr,dd.dd are right ascension and declination in degrees of the line of sight from the centre of the Earth to the S/C at event time. - xxx.xx,yyy.yy are planetocentric longitude from 0 to 360 degrees eastward and planetocentric latitude from -90 to +90 degrees of the point on the line of sight where the distance to the surface of Mars is 200 km. - zzz is the Sun zenith angle in degrees for that point at event time. Types LTCS and LTCE refer to the event, when the telecommand link between the G/S and the S/C is interrupted due an occultation by the Earth Moon. Types LTMS and LTME refer to the event, when the telemetry link is interrupted due an occultation by the Earth Moon. The G/S of the event is given as XXX in the event description with the same meaning as for the AOS/LOS events. Type POCS and POCE refer to the events, when the line of sight from the centre of the Earth to the S/C starts and ends to be occulted by the Mars Moon Phobos. Types DOCS and DOCE refer to the events, when the line of sight from the centre of the Earth to the S/C starts and ends to be occulted by the Mars Moon Deimos. For the computation of the evente, a spherical shape of the Mars Moons is assumed. The radius is an estimate of the semi major axis of the body ellipsoid (13.4 km for Phobos, 7.5 km for Deimos) augmented by an error radius of 30 km for Phobos and 100 km for Deimos to account for uncertainties in the moons positions. For details on the computation of the events, see reference TBD_1. Types PENS and UMBS refer to the event, when the S/C enters the penumbra and umbra of the body indicated by xxx. The entry xxx can be either MAR for Mars, PHO for Phobos or DEI for Deimos. The events PENE and UMBE indicate the exit from penumbra and umbra. For the computation of the events, a spherical shape is assumed. For Mars, the radius is equal to the equatorial radius of the ellipsoid. For Phobos and Deimos an augmented radius is used as defined in the description to the event types POCS, POCE, DOCS, DOCE (see above). Types SCDS and SCDE refer to the event, when the Sun/Earth/Spacecraft angle (SESC) falls below the limit where saf TM downlink is guaranteed. The nominal value for this estimate is 3 degrees according to refernce TBD_2. The actually used n value is provided in the event description This event type is provided on the G/S when the S/C is near the Earth. Far from the Earth, only one event type refering to the centre of the Earth has been provided. This is indicated by the acronym XXX which is either a G/S (same definition as in the event description for acquisition and loss of signal is used) or EAR for Earth. For details of the involved algorithms see reference TBD_3. Types SCUS, SOUS, SCUE and SOUE refer to the event, when the Sun/Spacecraft/Earth angle (SSCE) falls below the limit where safe TC uplink via HGA or MGA is guaranteed. The nominal value for this estimate is 5 degrees. The actually used value is provided in the event description. As for SCDS and SCDE, this event type is given either with respect to a G/S or the Earth depending on the S/C-Earth distance. The event types MPER and MAPO refer to the event when the S/C crosses the line of apsides. This event is defined by the time when the osculating true anomaly measured from -180 degrees to +180 degrees changes sign. For a detailed description of this event type refer to TBD_4. The number nnnn in the event description provides the current orbit number. Orbit numbers are incremented by one with each apocentre passage starting from the first apocentre after orbit insertion. For each event of type MPER, also the subsatellite point (xxx.xx,yyy.yy) in planetocentric longitude from 0 to 360 degrees and planetocentric latitude between -90 and +90 degrees and the Sun zenith angle zz of the subsatellite point in degrees are given. Types KMDS and KMAS, x km descend and x km ascend, refer to the event when the height of the S/C position above the Mars reference ellipsoid drops below or rises above x km. Events are provided for heights of 800 km, 1200 km, 2000 km and 4000 km (i.e. x i either 800, 1200, 2000 or 4000). All events of type AxxH, LxxH, AxxT, LxxT, MOCS, MOCE, POCS, POCE, DOCS, DOCE, SCDS, SCDE, SCUS, SCUE, SOUS, SOUE refer to a purely geometrical situation. All considerations concerning related start and end times of TM and TC have to take into account additionally the one way light time. Types NPSS and NPNS indicate the times in the mission when the pointing of the x-axis has to switch from North to South (NPSS) or from South to North (NPNS) in order to avoid Sun incidence on the S/C -x face in nadir pointing mode around Mars. In nadir pointing mode, with the x-asis perpendicular to the ground track, the angle between the S/C -x axis and the Sun direction varies around the pericentre by some degrees (e.g. at the switching time around mid March 2004 about 5 degrees). This means that there is not a single data and time to switch to correct x axis pointing or, conversely, depending on the duration of the nadir pointing, it might therefore not be possible, to avoid Sun incidence on the S/C -x face during a complete pericentre passage in nadir pointing mode (neither with North nor with South pointing option). Instead, the duration of the nadir pointing has to be reduced or a small Sun incidence must be tolerated. The events are calculated as follows: At the beginning of the mission the S/C x axis was North pointing, i.e. close to the orbital North pole. The Sun incidence on the S/C -x face was the calculated at each pericenter assuming nadir pointing mode and the first pericentre is noted when the x axis has to switch from North to South pointing to avoid Sun incidence on the -x face exactly at pericentre. An event NPSS is then inserted at the time of the preceding apocentre that indicates the required switch from North to South. The event NPNS for switching back to North is inserted at the apocentre time before the pericentre where the switch back to North is required. Type EPSS indicates the date and time where the S/C y axis direction has to change from ecliptic North to South in order to minimise Sun incidence on the S/C +z face. There is a considerable time span around the switching time where a small Sun incidence angle can not be avoided, neither with North nor with South pointing option. The event is calculated such that the option with the smallest incidence angle is chosen. The computation of the event time is based on the direction of the ecliptic pole which is used by the AOCMS onboard software, not on the true ecliptic pole. Types NPSS, NPNS and EPSS refer only to the corresponding geometrical conditions as described above. The times may differ from the actual switching times as commanded by the Flight Control Team. _______________________________________________________________________ EVTTID | Event Type | --------|--------------------------------------------------------------| AxxH | Acquisition of Signal at ground station with ^ation angle | | nn. | --------|--------------------------------------------------------------| AxxT | Acquisition of Signal 10 degrees at ground station. | --------|--------------------------------------------------------------| ALHM | Acquisition of signal at landing site from orbiter with | | ^ation angle nn. | --------|--------------------------------------------------------------| AL10 | Acquisition of signal 10 degrees at landing site from orbiter| --------|--------------------------------------------------------------| ALFn | Acquisition of Beagle2 forward link with 2^n kbps. | --------|--------------------------------------------------------------| ALRn | Acquisition of Beagle2 return link with 2^n kbps. | --------|--------------------------------------------------------------| OMAS | Orbit Manoeuvre start | --------|--------------------------------------------------------------| SMAS | Slew manoeuvre start | --------|--------------------------------------------------------------| WOLS | Wheel offloading start | --------|--------------------------------------------------------------| FPAS | Entry into FPAP | --------|--------------------------------------------------------------| FPIS | Entry into FPIP | --------|--------------------------------------------------------------| MO2S | Mars Occultation 200 km start. | --------|--------------------------------------------------------------| MOCS | Mars occultation start | --------|--------------------------------------------------------------| POCS | Phobos occultation start | --------|--------------------------------------------------------------| DOCS | Deimos occultation start | --------|--------------------------------------------------------------| LTCS | Start of TC link interruption due to Earth Moon occultation | --------|--------------------------------------------------------------| LTMS | Start of TM link interruption due to Earth Moon occultation | --------|--------------------------------------------------------------| PENS | Penumbra start | --------|--------------------------------------------------------------| UMBS | Umbra start | --------|--------------------------------------------------------------| SCDS | S/C conjunction (SESC n degrees) start | --------|--------------------------------------------------------------| SCUS | S/C conjunction (SSCE n degrees) start | --------|--------------------------------------------------------------| SOUS | S/C opposition (SSCE n degrees) start | --------|--------------------------------------------------------------| KMDS | x km descend | --------|--------------------------------------------------------------| MPER | pericentre passage | --------|--------------------------------------------------------------| MAPO | apocentre passage | --------|--------------------------------------------------------------| LxxH | Loss of signal at ground station with ^ation angle nn. | --------|--------------------------------------------------------------| LxxT | Loss of signal 10 degrees at ground station. | --------|--------------------------------------------------------------| LLHM | Loss of signal at landing site from orbiter with ^ation | | angle nn. | --------|--------------------------------------------------------------| LL10 | Loss of signal 10 degrees at landing site from orbiter. | --------|--------------------------------------------------------------| LLFn | Loss of Beagle2 forward link with 2^n kbps | --------|--------------------------------------------------------------| LLRn | Loss of Beagle2 return link with 2^n kbps | --------|--------------------------------------------------------------| OMAE | Orbit manoeuvre end | --------|--------------------------------------------------------------| SMAE | Slew manoeuvre end | --------|--------------------------------------------------------------| WOLE | Wheel offloading end | --------|--------------------------------------------------------------| FPAE | exit from FPAP | --------|--------------------------------------------------------------| FPIE | exit from FPIP | --------|--------------------------------------------------------------| MOCE | Mars occultation end | --------|--------------------------------------------------------------| MO2E | Mars occultation 200 km end. | --------|--------------------------------------------------------------| POCE | Phobos occultation end | --------|--------------------------------------------------------------| DOCE | Deimos occultation end | --------|--------------------------------------------------------------| LTCE | End of TC link interruption due to Earth Moon occultation. | --------|--------------------------------------------------------------| LTME | End of TM link interruption due to Earth Moon occultation. | --------|--------------------------------------------------------------| UMBE | Umbra end. | --------|--------------------------------------------------------------| PENE | Penumbra end. | --------|--------------------------------------------------------------| SCDE | S/C conjunction (SESC n degrees) end. | --------|--------------------------------------------------------------| SCUE | S/C conjunction (SSCE n degrees) end. | --------|--------------------------------------------------------------| SOUE | S/C opposition (SSCE n degrees) end. | --------|--------------------------------------------------------------| KMAS | x km ascend. | --------|--------------------------------------------------------------| NPSS | x-axis pointing switch from North to South | --------|--------------------------------------------------------------| NPNS | x-axis pointing switch from South to North | --------|--------------------------------------------------------------| EPSS | y-axis pointing switch from North to South | --------|--------------------------------------------------------------| _______________________________________________________________________ EVTTID | EVTDES | --------|--------------------------------------------------------------| AxxH | XXX_AOS_nn | --------|--------------------------------------------------------------| AxxT | XXX_AOS_10 | --------|--------------------------------------------------------------| ALHM | xxx_AOS_nn | --------|--------------------------------------------------------------| AL10 | xxx_AOS_10 | --------|--------------------------------------------------------------| ALFn | BE2_AOS_TC_xKBPS_/_RN_rrrrr_/_AZ_zzz.z_/_ELV_ee.e | --------|--------------------------------------------------------------| ALRn | BE2_AOS_TM_xKBPS_/_RN_rrrrr_/_AZ_zzz.z_/_ELV_ee.e | --------|--------------------------------------------------------------| OMAS | ORB_MAN_START | --------|--------------------------------------------------------------| SMAS | SLEW_MAN_START | --------|--------------------------------------------------------------| WOLS | WHEEL_OFFL_START | --------|--------------------------------------------------------------| FPAS | FPAP_START | --------|--------------------------------------------------------------| FPIS | FPIP_START | --------|--------------------------------------------------------------| MO2S | OCC_MARS_200KM_START_/_RA_rrr.rr_/_DE_ddd.dd_/_ | | OMP_(xxx.xx,yyy.yy)_/_SZA_zzz | --------|--------------------------------------------------------------| MOCS | OCC_MARS_START_/_RA_rrr.rr_/_DE_ddd.dd_/_ | | OMP_(xxx.xx,yyy.yy)_/_SZA_zzz | --------|--------------------------------------------------------------| POCS | OCC_PHOBOS_START | --------|--------------------------------------------------------------| DOCS | OCC_DEIMOS_START | --------|--------------------------------------------------------------| LTCS | XXX_OCC_MOON_TC_START | --------|--------------------------------------------------------------| LTMS | XXX_OCC_MOON_TM_START | --------|--------------------------------------------------------------| PENS | xxx_PENUMBRA_START | --------|--------------------------------------------------------------| UMBS | xxx_UMBRA_START | --------|--------------------------------------------------------------| SCDS | XXX_CON_START_SESC_n | --------|--------------------------------------------------------------| SCUS | XXX_CON_START_SSCE_n | --------|--------------------------------------------------------------| SOUS | XXX_OPP_START_SSCE_n | --------|--------------------------------------------------------------| KMDS | x_KM_DESCEND | --------|--------------------------------------------------------------| MPER | PERICENTRE_PASSAGE_nnnn_/_SSP_(xxx.xx,yyy.yy)_/_SZA_zzz | --------|--------------------------------------------------------------| MAPO | APOCENTRE_PASSAGE_nnnn | --------|--------------------------------------------------------------| LxxH | XXX_LOS_nn | --------|--------------------------------------------------------------| LxxT | XXX_LOS_10 | --------|--------------------------------------------------------------| LLHM | xxx_LOS_nn | --------|--------------------------------------------------------------| LL10 | xxx_LOS_10 | --------|--------------------------------------------------------------| LLFn | BE2_LOS_TC_xKBPS_/_RN_rrrrr_/_AZ_zzz.z_/_ELV_ee.e | --------|--------------------------------------------------------------| LLRn | BE2_LOS_TM_xKBPS_/_RN_rrrrr_/_AZ_zzz.z_/_ELV_ee.e | --------|--------------------------------------------------------------| OMAE | ORB_MAN_END | --------|--------------------------------------------------------------| SMAE | SLEW_MAN_END | --------|--------------------------------------------------------------| WOLE | WHEEL_OFFL_END | --------|--------------------------------------------------------------| FPAE | FPAP_END | --------|--------------------------------------------------------------| FPIE | FPIP_END | --------|--------------------------------------------------------------| MOCE | OCC_MARS_END_/_RA_rrr.rr_/_DE_ddd.dd_/_ | | OMP_(xxx.xx,yyy.yy)_/_SZA_zzz | --------|--------------------------------------------------------------| MO2E | OCC_MARS_200KM_END_/_RA_rrr.rr_/_DE_ddd.dd_/_ | | OMP_(xxx.xx,yyy.yy)_/_SZA_zzz | --------|--------------------------------------------------------------| POCE | OCC_PHOBOS_END | --------|--------------------------------------------------------------| DOCE | OCC_DEIMOS_END | --------|--------------------------------------------------------------| LTCE | XXX_OCC_MOON_TC_END | --------|--------------------------------------------------------------| LTME | XXX_OCC_MOON_TM_END | --------|--------------------------------------------------------------| UMBE | xxx_UMBRA_END | --------|--------------------------------------------------------------| PENE | xxx_PENUMBRA_END | --------|--------------------------------------------------------------| SCDE | XXX_CON_END_SESC_n | --------|--------------------------------------------------------------| SCUE | XXX_CON_END_SSCE_n | --------|--------------------------------------------------------------| SOUE | XXX_OPP_END_SSCE_n | --------|--------------------------------------------------------------| KMAS | x_KM_ASCEND | --------|--------------------------------------------------------------| NPSS | NADIR_POINTING_X_N_TO_S_SWITCH | --------|--------------------------------------------------------------| NPNS | NADIR_POINTING_X_S_TO_N_SWITCH | --------|--------------------------------------------------------------| EPSS | EARTH_POINTING_Y_N_TO_S_SWITCH | --------|--------------------------------------------------------------| _______________________________________________________________________ EVTTID | Duration until | --------|--------------------------------------------------------------| AxxH | XXX_LOS_nn | --------|--------------------------------------------------------------| AxxT | XXX_LOS_10 | --------|--------------------------------------------------------------| ALHM | xxx_LOS_nn | --------|--------------------------------------------------------------| AL10 | xxx_LOS_10 | --------|--------------------------------------------------------------| ALFn | BE2_LOS_TC_xKBPS_/_RN_rrrrr_/_AZ_zzz.z_/_ELV_ee.e | --------|--------------------------------------------------------------| ALRn | BE2_LOS_TM_xKBPS_/_RN_rrrrr_/_AZ_zzz.z_/_ELV_ee.e | --------|--------------------------------------------------------------| OMAS | ORB_MAN_END | --------|--------------------------------------------------------------| SMAS | SLEW_MAN_END | --------|--------------------------------------------------------------| WOLS | WHEEL_OFFL_END | --------|--------------------------------------------------------------| FPAS | FPAP_END | --------|--------------------------------------------------------------| FPIS | FPIP_END | --------|--------------------------------------------------------------| MO2S | OCC_MARS_200KM_END_/_RA_rrr.rr_/_DE_ddd.dd_/_ | | OMP_(xxx.xx,yyy.yy)_/_SZA_zzz | --------|--------------------------------------------------------------| MOCS | OCC_MARS_END_/_RA_rrr.rr_/_DE_ddd.dd_/_ | | OMP_(xxx.xx,yyy.yy)_/_SZA_zzz | --------|--------------------------------------------------------------| POCS | OCC_PHOBOS_END | --------|--------------------------------------------------------------| DOCS | OCC_DEIMOS_END | --------|--------------------------------------------------------------| LTCS | XXX_OCC_MOON_TC_END | --------|--------------------------------------------------------------| LTMS | XXX_OCC_MOON_TM_END | --------|--------------------------------------------------------------| PENS | xxx_PENUMBRA_END | --------|--------------------------------------------------------------| UMBS | xxx_UMBRA_END | --------|--------------------------------------------------------------| SCDS | XXX_CON_END_SESC_n | --------|--------------------------------------------------------------| SCUS | XXX_CON_END_SSCE_n | --------|--------------------------------------------------------------| SOUS | XXX_OPP_END_SSCE_n | --------|--------------------------------------------------------------| KMDS | x_KM_ASCEND | --------|--------------------------------------------------------------| MPER | n/a | --------|--------------------------------------------------------------| MAPO | n/a | --------|--------------------------------------------------------------| LxxH | n/a | --------|--------------------------------------------------------------| LxxT | n/a | --------|--------------------------------------------------------------| LLHM | n/a | --------|--------------------------------------------------------------| LL10 | n/a | --------|--------------------------------------------------------------| LLFn | n/a | --------|--------------------------------------------------------------| LLRn | n/a | --------|--------------------------------------------------------------| OMAE | n/a | --------|--------------------------------------------------------------| SMAE | n/a | --------|--------------------------------------------------------------| WOLE | n/a | --------|--------------------------------------------------------------| FPAE | n/a | --------|--------------------------------------------------------------| FPIE | n/a | --------|--------------------------------------------------------------| MOCE | n/a | --------|--------------------------------------------------------------| MO2E | n/a | --------|--------------------------------------------------------------| POCE | n/a | --------|--------------------------------------------------------------| DOCE | n/a | --------|--------------------------------------------------------------| LTCE | n/a | --------|--------------------------------------------------------------| LTME | n/a | --------|--------------------------------------------------------------| UMBE | n/a | --------|--------------------------------------------------------------| PENE | n/a | --------|--------------------------------------------------------------| SCDE | n/a | --------|--------------------------------------------------------------| SCUE | n/a | --------|--------------------------------------------------------------| SOUE | n/a | --------|--------------------------------------------------------------| KMAS | n/a | --------|--------------------------------------------------------------| NPSS | n/a | --------|--------------------------------------------------------------| NPNS | n/a | --------|--------------------------------------------------------------| EPSS | n/a | --------|--------------------------------------------------------------| Star Occultations File (STOM Type) ================================== For a list of stars provided by the SPICAM experiment, star occultation events are given in a separate file. Four types of events are considered: - 200 km descend This event refers to the time when the minimum distance of the line of sight between S/C and star from the Mars reference ellipsoid drops below 200 km. - start occultation This event refers to the time when the line of sight starts to be occulted by the Mars reference ellipsoid. - end occultation This event refers to the time when the line of sight ends to be occulted by the Mars reference ellipsoid. - 200 ascend This event refers to the event when the minimum distance of the line of sight between S/C and star from the Mars reference ellipsoid rises above 200 km. All events are sorted in ascending order in time. For each event one line of description is given. The meaning of each collumn in the star occultation is as follows _______________________________________________________________________ Collumn | Field description | =========|=============================================================| 1 | Orbit number, counted from first apocentre after orbit | | insertion. | ---------|-------------------------------------------------------------| 2 | Event time in UTC in the format YY-DDDThh:mm:ssZ (for the | | format description, please refer to the EVTTIM parameter in | | the previous section of this document) | ---------|-------------------------------------------------------------| 3 | Time until next pericentre in the format hh:mm:ss | ---------|-------------------------------------------------------------| 4 | Time since last pericentre in the format hh:mm:ss | ---------|-------------------------------------------------------------| 5 | True anomaly in degrees between -180 and +180 degrees. | ---------|-------------------------------------------------------------| 6 | Bright Star Catalogue star number | ---------|-------------------------------------------------------------| 7 | Event description, one of the following four entries: | | 200 km, descending | | start occultation | | end occultation | | 200 km, ascending | ---------|-------------------------------------------------------------| 8 | Occultation point in the format (xxx.xx,yyy.yy) where | | xxx.xx is planetocentric longitude in degrees from 0 to 360 | | eastward, and yyy.yy is planetocentric latitude in degrees | | from -90 to +90 degrees. | ---------|-------------------------------------------------------------| 9 | Solar zenith angle, i.e. the angular separation in degrees | | between the Sun direction and the direccion of the | | occultation point as seen from the centre of Mars. | ---------|-------------------------------------------------------------| 10 | Local time, i.e. the difference in longitude in degrees | | between occultation point and Sun direction from -180 to | | +180 degrees. | ---------|-------------------------------------------------------------| For the format definition of the collumns, please refer to the product label of the star occultation files. For a detailed description of r^ant algorithms and model assumptions (e.g. reference ellipsoid, rotational elements) refer to TBD_5. Time Correlation File (TCORR Type) ================================== In this data set, only the Time Correlation Coefficient Packets are archived. These packets contain the information necessary to enable the UTC time of a packet to be obtained from its OBT. The following contains a description of the end-to-end processing involved in generating the time correlation packets, as well as a description of the packet contents. The procedures for carrying out Spacecraft Time correaltion are specified in the ESA Packet Telemetry standard TBD_6 and the r^ant section reproduced hereafter. Spacecraft Time Correlation Procedures -------------------------------------- On board the spacecraft, the contents of the Spacecraft Elapsed Time clock are sampled at the instance of occurrence of the leading edge of the first bit of the Attached Synchronisation Marker of that telemetry Transfer Frame of Virtual Channel 0 with a Virtual Channel Frame Count 0. This time sample shall then be placed into the standard Spacecraft Time Source Packet and telemetered to ground before the Frame Counter of Virtual Channel 0 has counted 255 more frames, so as to avoid ambiguity. Should this sampling rate (intervals of 256 Frames of Virtural Channel 0) prove too low for the mission requirements, it is permisible to sample clock contents at intervals of 128, 64, 32, 16, 8, 4, 2 or 1 frame(s) of Virtual Channel 0, by choice. Consequently the time sample shall be telemetered to ground before the selected number of Frames of Virtual Channel 0 have elapsed (128, 64, 32, 16, 8, 4, 2 or 1, all counts starting from Virtual Channel Frame Count 0). The ground data capture system shall: a) accurately time-tag the instant of reception of the same first bit of the Attached Synchronisation Marker of the Virtual Channel 0 Transfer Frame with a Virtual Channel Frame Count 0. The time standard used will be the CDS-coded UTC. b) extract the standard Spacecraft Time Source Packet and collect the CUC-coded time sample. Thus, a correlation between the Spacecraft Elapsed Time and the UTC reference on ground shall be established which can be used: - on ground, to transform the Spacecraft Elapsed Time information contained in the source Packets into UTC information. - on board the spacecraft, to achieve directly the same service as on the ground. Mars Express Implementation --------------------------- The design of the Mars Express spacecraft onboard systems is such that it is possible to select the sampling rate at which the standard Spacecraft Time Source Packet is generated to be one of every 256, 128, 64, 32 or 16 VC0 frames. All telemetry frames on reception at the groundstation are time stamped with the current UTC (obtained from the station clock which is synchronised with UTC), this is called the Earth Reception Time (ERT). These frames are then routed to the control system at ESOC. On arrival the packetiser (i.e. the application responsible for extracting the source packets from the received time frames) extracts the ERT timestamp of every VC0 zeroth frame (i.e. the frame at whose leading edge bit the timestamp contained in the next standard Spacecraft Time Source Packet was generated). The extracted ERT then has 3 correction factors applied to it: 1) the first is to remove the delay between the downlinked frame arriving at the antenna and it actually reaching the equipment where the ERT is timestamped on the frame. This correction is composed of two elements, a fixed delay (which varies between groundstations and it determined by measurements) and a variable delay which depends on bit rate and is the same for all groundstations. 2) the second correction is to remove the propagation delay, i.e. the time taken for the signal to travel from the spacecraft to the groundstation antenna. The appropriate correction is obtained from the predictions contained in the Flight Dynamics One Way Light Time (OWLT) file. 3) the third is to remove the delay in processing the frame on the spacecraft. This correction is composed of two elements: a fixed delay plus a variable delay which is a bit-rate dependent. After the above corrections have been applied to the ERT what is obtained is effectively the UTC at which standard Spacecraft Time Source Packet was generated onboard the spacecraft. This time is then stored internally by the Packetiser. When the next standard Spacecraft Time Source Packet arrives the Packetiser uses this, along with the stored, generation UTC to create a Time Telemetry Packet which contains both the spacecraft time and the UTC at which it was generated. These packets are then distributed to the system and filed. The actual generation of the Time Correlation Coefficients packet is instigated manually by the Flight Control Team who have the ability to specify a time range from which the Time Telemetry Packets should be used to obtain a correlation. Once the applicable Time Telemetry Packets from the specified time range have been extracted from the archive a least squares fit is calculated to obtain the coefficients necessary to convert the OBT in the source packets to UTC. Once the appropiate coefficients have been calculated the FCT can the either reject the obtained correlation, or accept it. If the obtained correlation is accepted a validity start time is specified which is the time from which that correlation is valid, i.e. is used to derive the UTC timestamps from the OBT time contained in the source packets. A time correlation remains valid until the next time correlation packet is generated. It should be noted that as data can be stored on board the spacecraft the time correlation used to timestamp any particular packet is not necesarily the current correlation since the system will actually use the correlation that was valid for the OBT contained in the source packet. For Mars Express, the gradient of the obtained time correlation should be nominally 1, in practise there will be samll deviations form this. Any time correlation packet which is found to contain a gradient substantially different from 1 should be treated with caution. Time Correlation Packet Structure --------------------------------- It must be noted that the Time Correlation Packet is NOT a spacecraft source packet since it is generation internally by the control system. Consequently the structure of this packet does not conform to that of spacecraft generated telemetry packets. The structure of the packes is as shown in the following diagram, note that the byte order is big-endian, i.e. the most significant byte has the lowest address (the word is stored big-endian-first): ___________________________________________________ | | | Time Correlation Packet Data Field (Fixed) | | | |-------------------------------------------------| | | | | | | Gradient | Offset | Std | Gen Time | | | | | | |-------------------------------------------------| | | | | | | 64 bits | 64 bits | 64 bits | 48 bits | | | | | | |-------------------------------------------------| | | | 256 bits | |-------------------------------------------------| The meaning of the various fields are as follows: ______________________________________________________________________ | | | | Filed Name | Description | | | | |---------------------------------------------------------------------| | Gradient | Gradient value of the Coefficients Pair. | |---------------------------------------------------------------------| | Offset | Offset value of Coefficient Pair. | |---------------------------------------------------------------------| | Std | Standard Deviation value associated witht the | | | Coefficients pair. | |---------------------------------------------------------------------| | Gen Time | Generation Time of the Coeficients in CCSDS CUC format.| | | The format of this is as described in TBD_2 | | | where there is no p-field and the t-field is composed | | | of 4 bytes coarse time and 2 bytes fine time. | |____________|________________________________________________________| It should be noted that for the Time Correlation Coefficient packet, the SCET contained in the header contains the time at which the contained time correlation became valid. About the Time Correlation File contained in this data set ---------------------------------------------------------- This binary table is made of the Mars Expres Time Correlation Packets generated by the Mission Control System. These packets are archived with their DDS header where the applicability time is contained. Once the appropiate coefficients have been calculated the Flight Control Team can the either reject the obtained correlation (considering this as a wrong Time Correlation coefficients packet), or accept it. Several of this wrong Time correlation packets have been accepted and delivered on the DDS. These packets have been removed from this file since they should not be used. The following table shows a list of the TC packets delivered and which ones have been removed: =================================================== |Time Correlation Coefficient Packet | | | Applicability Time (DDS HEADER) | Archived? | =================================================== | 2 Jun 2003 15:45:00 | NO | |-------------------------------------|-----------| | 2 Jun 2003 19:47:41 | YES | |-------------------------------------|-----------| | 3 Jun 2003 03:17:52 | NO | |-------------------------------------|-----------| | 3 Jun 2003 09:55:09 | YES | |-------------------------------------|-----------| | 3 Jun 2003 15:05:05 | NO | |-------------------------------------|-----------| | 3 Jun 2003 17:10:36 | YES | |-------------------------------------|-----------| | 4 Jun 2003 02:16:24 | NO | |-------------------------------------|-----------| | 4 Jun 2003 05:27:00 | YES | |-------------------------------------|-----------| | 4 Jun 2003 06:37:38 | NO | |-------------------------------------|-----------| | 4 Jun 2003 16:58:30 | YES | |-------------------------------------|-----------| | 5 Jun 2003 04:38:32 | NO | |-------------------------------------|-----------| | 5 Jun 2003 17:30:00 | YES | |-------------------------------------|-----------| | 7 Jun 2003 16:51:06 | YES | |-------------------------------------|-----------| | 14 Jun 2003 18:44:08 | YES | |-------------------------------------|-----------| | 17 Jun 2003 15:52:00 | NO | |-------------------------------------|-----------| | 17 Jun 2003 16:09:36 | YES | |-------------------------------------|-----------| | 12 Jul 2003 01:26:56 | YES | |-------------------------------------|-----------| | 18 Jul 2003 15:30:13 | YES | |-------------------------------------|-----------| | 21 Aug 2003 11:34:25 | YES | |-------------------------------------|-----------| | 8 Sep 2003 13:23:27 | YES | |-------------------------------------|-----------| | 15 Dec 2003 09:00:00 | YES | |-------------------------------------|-----------| | 28 Apr 2004 06:09:55 | YES | |-------------------------------------|-----------| | 19 May 2004 09:41:09 | YES | |-------------------------------------|-----------| | 3 Jun 2004 06:25:43 | YES | |-------------------------------------|-----------| | 28 Jun 2004 16:04:15 | YES | |-------------------------------------|-----------| Software ######## ESOC provides along with the auxiliary and ancillary data a software toolkit to convert the attitude and orbit ASCII files into binary format and access the data. The software has been archived within this data set and it is properly described in the Software catalogue object in a separate file in this data set (SOFT.CAT). |
| Mission Description |
Mission Overview ================ Mars Express was the first flexible mission of the revised long-term ESA Science Programme Horizons 2000 and was launched to the planet Mars from Baikonur (Khazakstan) on June 2nd 2003. A Soyuz-Fregat launcher injected the Mars Express total mass of about 1200 kg into Mars transfer orbit. Details about the mission launch sequence and profile can be obtained from the Mission Plan (MEX-MMT-RP-0221) and from the Consolidated Report on Mission Analysis (CREMA)(MEX-ESC-RP-5500). The mission consisted of (i) a 3-axis stabilized orbiter with a fixed high-gain antenna and body-mounted instruments, and (ii) a lander named BEAGLE-2, and was dedicated to the orbital and in-situ study of the interior, subsurface, surface and atmosphere of the planet. After ejection of a small lander on 18 December 2003 and Mars orbit insertion (MOI) on 25 December 2003, the orbiter experiments began the acquisition of scientific data from Mars and its environment in a polar elliptical orbit. The nominal mission lifetime for the orbiter was 687 days following Mars orbit insertion, starting after a 5 months cruise. The nominal science phase was extended (tbc) for another martian year in order to complement earlier observations and allow data relay communications for various potential Mars landers up to 2008, provided that the spacecraft resources permit it. The Mars Express spacecraft represented the core of the mission, being scientifically justified on its own by investigations such as high- resolution imaging and mineralogical mapping of the surface, radar sounding of the subsurface structure down to the permafrost, precise determination of the atmospheric circulation and composition, and study of the interaction of the atmosphere with the interplanetary medium. The broad scientific objectives of the orbiter payload are briefly listed thereafter and are given more extensively in the experiment publications contained in ESAs Special Publication Series. See NEUKUM&JAUMANN2004, BIBRINGETAL2004, PICARDIETAL2004, FORMISANOETAL2004, BERTAUXETAL2004, PAETZOLDETAL2004 and PULLANETAL2004. The Mars Express lander Beagle-2 was ejected towards the Mars surface on 19 December 2003, six days before the orbiters capture manoeuvre. The probe mass was limited to about 70 kg by the mission constraints, which led to a landed mass of 32 kg. The complete experimental package was weighed in approximately at 9kg. The landers highly integrated scientific payload was supposed to focus on finding whether there is convincing evidence for past life on Mars or assessing if the conditions were ever suitable. Following safe landing on Mars, this lander mission would have conducted dedicated studies of the geology, mineralogy, geochemistry, meteorology and exobiology of the immediate landing site located in Isidis Planitia (90.74deg E, 11.6deg N), as well as studies of the chemistry of the Martian atmosphere. Surface operations were planned to last about 180 sols or Martian days ( about 6 months on Earth), see SIMSETAL1999. As no communication could be established to the BEAGLE-2 lander, it was considered lost in February 2004 after an extensive search. A nominal launch of Mars Express allowed the modify the orbit to a G3-ubeq100 orbit. The G3-ubeq100 orbit is an eliptical orbit, starting with the subspacecraft point at pericenter at the equator and a sun ^ation of 60 degrees. At the beginning of the mission, the pericentre moves southward with a shift of 0.54 degree per day. At the same time the pericentre steps towards the terminator which will be reached after about 4 months, giving the optical instruments optimal observing conditions during this initial period. Throughout this initial phase lasting until mid-May 2004, the downlink rate will decrease from 114 kbit/s to 38 kbit/s. After an orbit change manoeuvre on 06 May 2004 the pericentre latitude motion is increased to guarantee a 50/50 balance between dayside and nightside operations. With this manoeuvre, the apocentre altitude is lowered from 14887 km to 13448 km, the orbital period lowered from ~7.6 hours to 6.645 hours, and the pericentre latitude drift slightly increased to 0.64 degree per day. After 150 days, at the beginning of June 2004, the South pole region was reached with the pericentre already behind the terminator. Following, the pericentre moves northward with the Sun ^ation increasing. Thus, the optical instruments covered the Northern Mars hemisphere under good illumination conditions from mid-September 2004 to March 2005. During the next mission phase, lasting until July 2005, the pericentre was again in the dark. It covered the North polar region and moves southward. Finally, throughout the last 4 months of the nominal mission, the pericentre was back to daylight and moves from the equator to the South pole, and the downlink rate reached its highest rate of 228 kbit/s. The osculating orbit elements for the eq100 orbit are listed below: Epoch 2004:1:13 - 15:56:0.096 Pericentre (rel. sphere of 3397.2 km) 279.29 km Apocentre (rel. sphere) 11634.48 km Semimajor axis 9354.09 km Eccentricity 0.60696 Inclination 86.583 Right ascension of ascending node 228.774 Argument of pericentre 357.981 True anomaly -0.001 Mission Phases ============== The mission phases are defined as: (i) Pre-launch,Launch and Early Operations activities, including (1) science observation planning; (2) payload assembly, integration and testing; (3) payload data processing software design, development and testing; (4) payload calibration; (5) data archive definition and planning; (6) launch campaign. (ii) Near-Earth verification (EV) phase, including (1) commissioning of the orbiter spacecraft; (2) verification of the payload status; (3) early commissioning of payload. (iii) Interplanetary cruise (IC) phase (1) payload checkouts (2) trajectory corrections (iv) Mars arrival and orbit insertion (MOI) (1) Mars arrival preparation; (2) lander ejection; (3) orbit insertion; (4) operational orbit reached and declared; (5) no payload activities. (v) Mars commissioning phase (1) final instrument commissioning, (2) first science results, (3) change of orbital plane. (vi) Routine phase; Opportunities for dawn/dusk observations, mostly spectroscopy and photometry. This phase continued into a low data rate phase (night time; favorable for radar and spectrometers). Then daylight time, and went into a higher data rate period (medium illumination, zenith, then decreasing illumination conditions). Observational conditions were most favorable for the optical imaging instruments at the end of the routine phase, when both data downlink rate and Sun ^ation are high. (vii) MARSIS Deployment The dates of the MARSIS antenna deployment is not known as of writing this catalogue file. (viii) Extended operations phase A mission extension will be proposed in early 2005 to the Science Programme Committee (SPC). (ix) Post-mission phase (final data archival). Science Subphases ================= For the purpose of structuring further the payload operations planning, the mission phases are further divided into science subphases. The science subphases are defined according to operational restrictions, the main operational restrictions being the downlink rate and the Sun ^ation. The Mars Commissioning Phase and the Mars Routine Phase are therefore divided into a number of science subphases using various combinations of Sun ^ations and available downlink bit rates. The discrete downlink rates available throughout the nominal mission are: - 28 kbits/seconds - 38 kbits/seconds - 45 kbits/seconds - 57 kbits/seconds - 76 kbits/seconds - 91 kbits/seconds - 114 kbits/seconds - 152 kbits/seconds - 182 kbits/seconds - 228 kbits/seconds The adopted Sun ^ation coding convention is as follows: - HSE for High Sun Elevation (> 60 degrees) - MSE for Medium Sun Elevation (between 20 and 60 degrees) - LSE for Low Sun Elevation (between -15 and 20 degrees) - NSE for Negative Sun Elevation (< -15 degrees) The science subphase naming convention is as follows: - Science Phase - Sun Elevation Code - Downlink Rate - Science Subphase Repetition Number The following tables gives the available Science Subphases: NAME START END ORBITS BIT SUN RATE ELE ---------------------------------------------------------- MC Phase 0 2003-12-30 - 2004-01-13 1 - 16 MC Phase 1 2004-01-13 - 2004-01-28 17 - 58 114 59 MC Phase 2 2004-01-28 - 2004-02-12 59 - 105 91 69 MC Phase 3 2004-02-12 - 2004-03-15 106 - 208 76 71 MC Phase 4 2004-03-15 - 2004-04-06 209 - 278 57 51 MC Phase 5 2004-04-06 - 2004-04-20 279 - 320 45 33 MC Phase 6 2004-04-20 - 2004-06-04 321 - 475 38 22 MR Phase 1 2004-06-05 - 2004-08-16 476 - 733 28 -13 MR Phase 2 2004-08-16 - 2004-10-16 734 - 951 28 -26 MR Phase 3 2004-10-16 - 2005-01-07 952 - 1250 28 16 MR Phase 4 2004-01-08 - 2005-03-05 1251 - 1454 45 63 MR Phase 5 2004-03-05 - 2005-03-24 1455 - 1522 76 16 MR Phase 6 2004-03-25 - 2005-07-15 1523 - 1915 91 0 The data rate is given in kbit per seconds and represents the minimal data rate during the subphase. The sun ^ation is given in degrees and represents the rate at the beginning of the subphase. Detailed information on the science subphases can be found in MEX-EST-PL-13128. |
