1. SPICE System Overview : SPICE data contain geometric and other ancillary information needed to recover the full value of science instrument data. In particular, SPICE kernels provide spacecraft and planetary ephemerides, instrument mounting alignments and spacecraft orientation. Data needed for relevant time conversions is also included. SPICE was designed by the Navigation and Ancillary Information Facility (NAIF) to aid scientists and engineers with ancillary and engineering data. This data comes from a wide range of sources such as the spacecraft, the mission control center and the designers of the spacecraft and its instruments. The ancillary data comprises information on data acquisition; position and orientation of the spacecraft at the time of acquisition; information on the target, such as location, shape and orientation; reference frame specifications and time conversion data. The primary SPICE data sets are often called 'kernels' or 'kernel files'. These kernels are composed of ancillary information, which has been created in such a way as to allow easy access and correct usage by the space science and engineering communities. In addition to the kernels, there is software provided, known as the SPICE toolkit, along with standards, documentation and software support. The SPICE toolkit and documentation can be found on: http://naif.jpl.nasa.gov/naif/ The SPICE toolkit was freely offered to the worldwide space science and space mission engineering communities at the time this data set was released. The few rules governing its use are posted on the ''Rules'' page of the NAIF website: http://naif.jpl.nasa.gov/naif/rules.html SPICE is used on a number of space missions, such as ESA's Mars Express, SMART-1, Venus Express and Rosetta missions; NASA's Mars Global Surveyor, Stardust, Cassini, Mars Exploration Rovers, Mars Reconnaissance Orbiter and Deep Impact. The SPICE system has been produced and is maintained by Caltech's Jet Propulsion Laboratory under contract to the U.S. National Aeronautics and Space Administration. For an additional explanation of the SPICE system, please consult SPICE_INST.CAT2. Data Producers and Other Key Personnel : The Mars Express SPICE data set has been produced by Acton, C. (NAIF/JPL) Bachman, N. (NAIF/JPL) Semenov, B. (NAIF/JPL) Vazquez, J.L. (RSSD/ESA) Heather, D. (RSSD/ESA) and archived by Vazquez, J.L. (RSSD/ESA)3. The Mars Express SPICE dataset : The Mars Express SPICE dataset consists of several SPICE kernels, organised as follows: * CK kernels. This kernels contain information about orientation of the space vehicle or any articulating structure on it. More information on the CK kernels in this dataset is provided in CKINFO.TXT. * FK kernels. Reference frame specifications. Definitions of, and specifications of, relationships between reference frames (coordinate systems). Among the frames kernels included, there are kernels that specify reference frames related to the earth and the spacecraft. More information on the FK kernels in this dataset is provided in FKINFO.TXT. * IK kernels. Kernels that hold intrument information, such as field of view or internal timing. There is a different kernel for ASPERA, HRSC, PFS and OMEGA. More information on the IK kernels in this dataset is provided in IKINFO.TXT. * LSK kernel. This kernels hold a table with the leapseconds used to convert between ET and UTC. If there are multiple LSK kernels in this dataset, the latest kernel supersedes the previous ones. More information on the LSK kernel(s) in this dataset is provided in LSKINFO.TXT. * PCK kernels. These kernels provide information about Solar System bodies orientation and shape, and possibly parameters for gravitational, atmospheric or rings models. The dataset contains PCK kernels for the planets, their satellites, and the asteroids Lutetia and Steins. More information on the PCK kernels in this dataset is provided in PCKINFO.TXT. * SCLK kernel. This kernel (spacecraft clock coefficients) allows for conversion between ET and spacecraft clock. If there are multiple LSK kernels in this dataset, the latest kernel supersedes the previous ones. More information on the SCLK kernel(s) in this dataset is provided in SCLKINFO.TXT. * SPK kernels. Kernels with information about ephemeris (position and velocity) of the spacecraft and solar system bodies. The dataset provides such information for the planets, the Sun, the Moon, the New Norcia tracking station, several DSN tracking stations, and the spacecraft. More information on the SPK kernels in this dataset is provided in SPKINFO.TXT. 3.1 - Origin of the kernels. a) Generic kernels provided by NAIF. - Binary and text PCK and LSK kernels. - Some SPK kernels with ephemeris of the solar system bodies. - SPK kernels for ground stations. - Frames kernels for ground stations. b) Other kernels provided by NAIF. - The instrument kernels (IK) have been developed NAIF, the intrument teams and RSSD/ESA. - The Mars Express frames kernel has been created by NAIF, in collaboration with RSSD/ESA. c) Kernels generated with ESOC Ancillary Data. - ESOC ancillary data are the main source of information required to create SPICE kernels for attitude (CK), orbit (SPK) and time (SCLK) information for the Spacecraft. - Also, ESOC ephemeris data are used in the creation of SPK kernels for martian satellites. See next chapter (3.2) for a more detailed explanation on how these kernels are generated. d) Kernels created by the Mars Express SGS (Science Ground Segment), alone or in collaboration with the intruments teams. These include: - CK kernels with orientation of the Mars Express Solar Arrays. - RSSD frames kernel. - ESTRACK_V01.BSP and ESTRACK_V01.LBL. These kernels contain respectively position and frame information for the ESA ESTRACK network ground stations. The user must be aware that the data in these kernels are low accuracy. e) Kernels from other sources. These include: - Ephemeris kernels provided by Royal Observatory of Belgium. They contain spacecraft position information, calculated independently of ESOC ancillary data. - CK kernels describing the motion of the ASPERA scanner, produced by the ASPERA team. 3.2 - Creation of SPK, CK and SCLK kernels from ESOC Ancillary Data. Orbit Data. ---------- In terms of orbital data, the mission can be divided in three different phases: cruise phase, nominal phase and extended phase. This dataset provides all the available orbit data at the moment the dataset was compiled. Several different types of data products are provided by ESOC: ORHM and ORMM. The ORHM product covers the cruise phase from launch to the Mars Insertion, and provides the orbit data as heliocentric states. There is only one ORHM product. During the nominal and extended phases, new ORMM files are provided on a regular basis, each of them covering a month period. The orbital data contained in these files are states with respect to Mars. MARSAT_ESA products are created using ESOC ephemeris, and give ephemeris information for the martian satellites, from 2004 until the end of 2007. Creating MARSAT_ESA kernels for further dates is not foreseen. Attitude Data. ------------- Attitude data for the spacecraft are provided for all mission phases except for safe modes, for the past and the near future. The attitude is provided in several records, called segments, each covering a specific time span. These segments have no overlap, but there may be gaps between the segments, and even gaps in the segments. The available attitude data is usually predicted, although kernels with reconstructed data are present in the dataset if needed (for time intervals for which the predicted attitude is known to be not accurate enough). Time Correlation Data. --------------------- Time Correlation is one of the most critical pieces of information needed for the use of the SPICE system within the Mars Express mission. This information allows the conversion between the Mars Express S/C Clock time and UTC time. ESOC always provide predicted and reconstituted orbit data, but only predicted attitude data. Only SPK kernels with reconstructed data are archived. ESOC delivers time correlation data which are the source for the SCLK kernel. An automated system, called ADCS (Automatic Data Conversion System) is responsible for the generation of CK, SPK and SCLK kernels from the ESOC flight dynamics data. ADCS detects when a new product was generated or a new time correlation packet was available, and run a series of processes in order to create the proper kernels. ADCS uses the SPICE toolkit in order to fulfill its task. It runs in a server physically located at ESAC. 3.3 - Using the SPICE kernels. At least a basic knowledge of the SPICE system is needed in order to use this kernels. The SPICE toolkit provides versions in Fortran (SPICELIB), C (CSPICE), IDL (icy) and MATLAB (mice), and the user can choose any one that suits him/her. The SPICELIB routine FURNSH, CSPICE function furnsh_c, and icy routine cspice_furnsh load a kernel file into the kernel pool as shown below. CALL FURNSH ( 'kernel_name' ) furnsh_c ( ''kernel_name'' ); cspice_furnsh, 'kernel_name' In the case when two or more files contain data overlapping in time for a given object, for binary kernels, the file loaded last takes precedence. If two (or more) text kernels assign value(s) using the ':' operator to identical keywords, the data value(s) associated with the last loaded occurrence of the keyword are used -all earlier values have been replaced with the last loaded value(s). Loading Kernel Files into a SPICE-based Application : A metakernel file, called 'MEX_Vvv.TM', can be found under the /EXTRAS/MK directory in this dataset. This file can be used with a SPICE-based application running on a UNIX workstation to load Mars Express SPICE data provided in this data set together (note that the logical path provided in the PATH_VALUES keyword and pointing to the volume root directory should be changed to the actual path of the volume root directory on the system where the volume is mounted). When there are two or more kernels that cover the same time interval (as is the case here for the .BSP and .BC kernels) the last kernel loaded is the one used by the SPICE software for computations in the interval or overlap.

The SPICE kernels in this dataset are either provided by NAIF (for instance, kernels containing parameters describing the planets, or the LSK kernel containing information about leapseconds) or calculated from the orbit and attitude data information generated by ESOC. In both cases the archive team are confident that the SPICE data is correct and accurate within the precision provided by the software and the instruments at the time the data was archived