| DATA_SET_DESCRIPTION |
Data Set Overview
=================
This dataset contains data from COSIMA instrument in the Rosetta
spacecraft. The set covers the substrate history from the
calibration period of the instrument starting 2002-05-29 up to the
payload checkout #8 2008-11-17.
Note that Version 2.0 is the first version archived for this
dataset. Version 1 was never archived.
During the calibration period the instrument was operated with
several software versions and for test purposes the operations
were not always nominal. The substrate histories are anyway
considered to be complete.
During the first commissioning period from 2004-03-02 to
2004-06-06 the substrates from the target holder #D8 covering the
dust inlet was stored.
During the second commissioning period from 2004-09-06 to
2004-10-16 the first ever in space secondary ion mass spectra were
generated. These can be found from the substrate #1C2 data.
During the passive payload checkouts (PC) no science data was
generated. The target holder #C2 was to be lifted to test the
target manipulator unit. This failed in PC1 and PC3 due to
hardware anomaly. Due to spacecraft telemetry problem, this
history is not available from PC2 either.
Test images from empty COSISCOPE slot were taken in all payload
checkouts. All the substrates were also imaged in space to be used
later as initial reference images.
During the active checkouts the main operational concentration was
to heal the baddly behaving ion emitter A. During those operations
some spectra was acquired, but without intention to generate
really scientifically usable background spectra from the
substrates.
Parameters
==========
The primary measured parameter is the time of flight mass spectrum
of a grain, ion events collected for 131072 time bins, each
1.953125 ns in length. For data selection purposes, three
individual time windows can be selected for each generated
spectrum. In addition or instead, a peak list separating the
organic and inorganic peaks can be generated. For quantitive
analysis and gain optimisation, instead of individual time bins,
a sum of events in three time windows can be collected. These are
called scans in the COSIMA system.
Grains in the substrate are searched with the COSISCOPE camera.
COSISCOPE main task is to generate grains list of the prominent
features on the substrate surface. The images itself can also be
generated.
Processing
==========
The spectrum time of flight ion data is mass calibrated with the
same procedure as is used in space for the peak data. The
calibration should be used only as rude starting point and for
scienctific analysis each calibration must be checked.
The housekeeping data covering the data aqcuisition period is
calibrated to physical units and statistically analyzed were
applicable to support the evaluation of the data quality.
Data
====
COSIMA generates the following PDS products
spectrum
--------
The spectrum is generated by bombing the comet grains collected
on the substrate by indium ions. The seconday ions are measured
by time of flight mass spectrometer. The spectrometer collects
individual ion arriving times to an array of 131072 bins, each
1.953125 nanosecond in size. From accumulated ion data, peaks
are detected and from the assumed mass scale and detected peak
positions a mass is given to each time bin. This calibration
is automatic and the user must check the scale for real use.
The spectrum can be divided in time to at most tree different
subspectrums to reduce the amout of data to be transmitted.
The product files have the naming convention
CS_YXX_YYYYMMDDTHHMMSS_SP_Z.TAB, where the Y is either 1 for
top, 2 for middle and 3 for bottom substrate. The XX is target
holder number in the range C1 to D8, counting in hexadecimal
number base. The YYYYMMDDTHHMMSS gives the start year, month,
day, hour, minute and second. The Z is P for positive and N for
negative ion spectrum.
peaks
-----
Generated as the spectrum, but the spectrum mass scale is
established onboard COSIMA. The list of 300 first organic and
inorganic peaks is transmitted. For higher masses, the total of
count hits for a mass range is given.
The product files have the naming convention
CS_YXX_YYYYMMDDTHHMMSS_PK_Z.TAB, where the Y is either 1 for
top, 2 for middle and 3 for bottom substrate. The XX is target
holder number in the range C1 to D8, counting in hexadecimal
number base. The YYYYMMDDTHHMMSS gives the start year, month,
day, hour, minute and second. The Z is P for positive and N for
negative ion spectrum.
scan
----
Used for instrument calibration and gain optimisation. Currently
no PDS product available, as the spectrum window limits are very
difficult to find to all the scans made. Produces total sum of
the event counts over three possible time windows.
spectrum housekeeping
---------------------
There's three kind of housekeeping information.
First, the minimum, maximum, mean and standard deviation of the
analog data, temperatures, voltages and currents, is calculated
for the period of the measurement.
Second, the used time to digital converter timing for the ion
beam chopper, bunchers and ion optics is given.
Third, the time to digital converter temperature calibration for
the delay line is given. The calibration is needed to adjust the
delay line so, that the 16 bin hardware event counter gets even
bin distribution over the sampling period.
The product files have the naming convention
CS_YXX_YYYYMMDDTHHMMSS_S_HK.TAB, where the Y is either 1 for
top, 2 for middle and 3 for bottom substrate. The XX is target
holder number in the range C1 to D8, counting in hexadecimal
number base. The YYYYMMDDTHHMMSS gives the start year, month,
day, hour, minute and second.
grains
------
The grain list is taken by the COSISCOPE camera from the
substrate surface. The orientation of the substrate is
calculated from the reference dots on target holder. The
binding box of the substrate feature is given in substrate
coordinates, which has origo at lower left corner and is 10000
times 10000 micrometers. The grain quality, based on the
brightness is given as relative number from 0-255.
The product files have the naming convention
CS_YXX_YYYYMMDDTHHMMSS_GR__.TAB, where the Y is either 1 for
top, 2 for middle and 3 for bottom substrate. The XX is target
holder number in the range C1 to D8, counting in hexadecimal
number base. The YYYYMMDDTHHMMSS gives the start year, month,
day, hour, minute and second.
image
-----
The image take by the COSISCOPE camera. The image has 1024*1024
pixels resolution with 10 bit brightness information. The PDS
product uses 16 bits for brightness storage.
The product files have the naming convention
CS_YXX_YYYYMMDDTHHMMSS_IM_Z.IMG, where the Y is either 1 for
top, 2 for middle and 3 for bottom substrate. The XX is target
holder number in the range C1 to D8, counting in hexadecimal
number base.The YYYYMMDDTHHMMSS gives the start year, month,
day, hour, minute and second. The ZX is P for right (plus) side
and N for left (minus) side led illumination.
The image files can be viewed only with software, that
understands PDS data formats, like 'NASAView', available from
PDS.
COSISCOPE housekeeping
----------------------
For the COSISCOPE housekeeping the operating temprature mimimum,
maximum, mean and standard deviation is calculated for the
operation time period. In addition, the COSISCOPE operation
setup parameters are given. Also the subsrate orientation
information is given.
The product files have the naming convention
CS_YXX_YYYYMMDDTHHMMSS_G_HK.TAB, where the Y is either 1 for
top, 2 for middle and 3 for bottom substrate. The XX is target
holder number in the range C1 to D8, counting in hexadecimal
number base.The YYYYMMDDHHMMSS gives the start year, month, day,
hour, minute and second.
Ancillary Data
==============
Other data required to interpret this data, especially if it is
not included in the dataset (for example, laboratory calibration
values)
Coordinate System
=================
COSIMA substrates are exposed 3 at a time to the +Z side of the
spacecraft. The dust funnel has 20 * 34 degree field of view.
^
| direction of
| flight
|
^ +Xcosima (down-track)
|
|
--- +---------|---------+
^ | | |
| | | |
| | | |
| | | |
| 20 deg | x-------------> +Ycosima (cross-track)
| | +Zcosima |
| | |
| | |
V | |
--- +-------------------+
| 34 deg | Boresight (+Z axis)
|<----------------->| is into the page
| |
No S/C geometry is calculated for the data.
Software
========
All the data can be used by PDS tools or any ASCII reading software.
Media/Format
============
The data is delivered as PDS standard compliant electronic files.
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