| 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 at:
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, ExoMars2016, BepiColombo,
Solar Orbiter and Rosetta missions, and all of NASA's solar system
exploration missions. 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 Venus Express SPICE data set has been produced by
Semenov, B. (NAIF/JPL)
Diaz, J. (ESAC/ESA)
Vazquez, J.L. (ESAC/ESA)
Barthelemy, M. (ESAC/ESA)
Heather, D. (ESAC/ESA)
Costa, M. (ESAC/ESA)
Escalante, A. (ESAC/ESA)
and archived by
Vazquez, J.L. (ESAC/ESA)
Costa, M. (ESAC/ESA)
Escalante, A. (ESAC/ESA)
3. The Venus Express SPICE data set
================================
The Venus Express SPICE data set consists of several SPICE kernels,
organised as follows:
* CK: These kernels contain information about
orientation of the space vehicle or any articulating
structure on it. More information on the CK kernels in this
data set is provided in CKINFO.TXT.
* EK: These kernels contain spacecraft and science
instrument event related information. More information on EKs
in this data set is provided in EKINFO.TXT.
* DSK: These kernels contain information about the shape of the
Venus Express spacecraft structures. More information on DSKs
in this data set is provided in DSKINFO.TXT.
* FK: These kernels contain 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, mission targets, and the
spacecraft and its instruments. More information on FKs in this
data set is provided in FKINFO.TXT.
* IK: These kernels contain instrument information, such as field of
view or internal timing specifications. There are IKs provided
for most of the Venus Express spacecraft instruments. More
information on IKs in this data set is provided in IKINFO.TXT.
* LSK: These kernels contain a table with the leapseconds used to
convert between ET and UTC. If there are multiple LSKs in this
data set, the latest kernel supersedes the previous ones. More
information on LSKs in this data set is provided in LSKINFO.TXT.
* PCK: These kernels provide information about Solar
System bodies orientation and shape, and possibly parameters
for gravitational, atmospheric or rings models. The data set
contains PCK kernels for the planets and their satellites.
More information on the PCK kernels in this data set is
provided in PCKINFO.TXT.
* SCLK: These kernels contain data needed for conversion between ET
and spacecraft clock. If there are multiple SCLKs in this
data set, the latest kernel supersedes the previous ones. More
information on SCLKs in this data set is provided in SCLKINFO.TXT.
* SPK: These kernels contain ephemeris data (position and velocity)
of the spacecraft and solar system bodies. The data set provides
kernels with such information for the planets, the Sun, the Moon,
Venus, ground tracking stations, and the Venus Express spacecraft.
More information on SPKs in this data set is provided in SPKINFO.TXT.
3.1 - Origin of the kernels.
a) Generic kernels such as PCKs, LSKs and some of the SPKs are
provided by NAIF.
- Frames kernels for ground stations.
b) Other kernels provided by NAIF.
- The Venus Express frames kernel has been created by B.
Semenov, in collaboration with the ESA SPICE Service.
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.
d) Kernels created by the ESA SPICE Service, alone or in
collaboration with the instrument teams. These include:
- The instrument kernels (IK) have been developed by
the ESA SPICE Service, in collaboration with the
instrument teams and NAIF.
- Kernel with mission independent frames, created by the
ESA SPICE Service.
- CK kernels with orientation of the Venus Express s/c
as defined by the quaternions provided by the housekeeping
telemetry.
- CK kernels with orientation of the Venus Express Solar
Arrays.
- Kernel with orientation of the MAG boom.
- The digital shape kernels (DSK) have been developed by
the ESA SPICE Service.
e) Kernels from other sources. These include:
- CK kernels describing the motion of the ASPERA scanner,
produced by the ASPERA team.
- CK kernels describing the motion of the VIRTIS scanner,
produced by the VIRTIS 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 and extended.
This data set covers the cruise and nominal phases.
The ORVM product provided by Flight Dynamics covers the complete
mission, from cruise phase to the end of mission. There is only one
ORVM product.
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. Provided attitude data
usually is predicted, although kernels with reconstructed
data are present in the data set 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 Venus Express mission. This information allows the
conversion between the Venus Express S/C Clock time and UTC
time.
ESOC always provide predicted and reconstituted orbit data,
but only predicted attitude data. These products are the
source of the CK and SPK kernels.
ESOC generated time correlation data records and stored them in
the telemetry server. These records were the source for the SCLK
kernel.
An automated system, called ADCS (Automatic Data Conversion
System) was responsible for the generation of CK, SPK and SCLK
kernels from the ESOC flight dynamics data file products and
telemetry server SCLK records. ADCS detected when a new product
was generated or a new time correlation packet was available, and
ran a series of processes in order to create the proper kernels.
ADCS used the SPICE Toolkit in order to fulfill its task. It ran
on a server physically located at ESTEC until December 2007;
after that date, the server was located at ESAC.
3.3 - Using the SPICE kernels.
At least a basic knowledge of the SPICE system is needed in order
to use these kernels. The SPICE Toolkit provides versions in
Fortran (SPICELIB), C (CSPICE), IDL (icy), Matlab (Mice), and
Java (JNISpice) and the user can choose any one that suits
him/her.
The SPICE routine FURNSH can be used to load a kernel file into a
SPICE-based application to make kernel's data usable with SPICE
APIs.
In the case when two or more kernel 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).
3.4 - Meta-kernels
A metakernel file, called 'VEX_Vvv.TM', can be found under the
``EXTRAS/MK/'' directory in this data set. This file can be used
with a SPICE-based application running on a UNIX workstation to
load Venus 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.
|
.png)
.png)
