| DATA_SET_DESCRIPTION |
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.CAT
2. 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.
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