| 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
end of the escort phase 3 2015-10-20. See the MISSION.CAT for
a more detailed operations description.
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.
During the prelanding phase, the COSIMA instrument was
commissioned.
The TOF-SIMS related voltage settings were optimised and
COSISCOPE focused using the D8 substrates.
From 2014-08-11 onward dust collection and the TOF-SIMS
analysis was carried out with the D0 substrates. The TOF-SIMS
measurements were done on selected dust particles on all D0
substrates. The particles coordinates were established manually
from the COSISCOPE images. The substrate coordinate system applied
for the TOF-SIMS has some extra offsets due to mechanical
tolerances, particle heights and ion paths being different for
positive and negative SIMS. These offsets can only be established
by analysing the TOF-SIMS and image data.
As of 2014-10-23 the ion optics was not operable anymore within
the nominal operation parameter settings and the TOF-SIMS and the
spectra got scientifically useless.
The TOF-SIMS data during the 2014-10-23 - 2015-03-10 period is
more or less instrument test data. Some of the tests were done
across particles and the data may be usable, but the spectra are
out of the nominal parameter range, containing shadow peaks and
instrument effects.
While the instrument was tested with different ion optics
parameter setups, the CF substrates were exposed first time to
collect dust on 2014-12-12. The particle collection worked
nominally. The C7 substrates were exposed for the first time on
2015-02-14.
From middle of the March 2015 a parameter setup was established,
that recovered the TOF-SIMS part of the instrument. Searching for
a new ion path optimum was a slow process, as there was the
potential of permanent damage due to Indium deposition on ion
optics. The SIMS was carried out mainly with C7 and CF.
D1 was exposed on 2015-04-10 and CD on 2015-05-30. CD, CF and D1
were analysed by TOF-SIMS during May 2015 and CF and D1 in the
June 2015. In July 2015 C7 was measured again, while CD was
exposed for particle collection and TOF-SIMS up to October.
D2 was exposed on 2015-10-11.
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 from the COSISCOPE images.
Although COSISCOPE can generate the grains list on board, most
of the grain analysis is done manually on ground from the images.
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
history
-------
The substrate history product contains information about
substrate storage and expose periods, cleaning and heating
actions, COSISCOPE camera images and grains lists and any
spectra taken. The history starts from the moment substrates
were installed in the COSIMA flight instrument.
The product files have the naming convention
CS_YXX_SUBSTRATE_HISTORY.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.
Note that although there is an action entry in the table, the
spectrum, image or housekeeping data may be marked as missing,
usually due to telemetry downlink problems.
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 position given as X and Y does not necessarily match the
X and Y established on the substrate image due to mechanical
and ion path reasons and differs for the positive and negative
data. This offset can only be solved by analysing the TOF-SIMS
data.
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. For the definition of
the peak separation see the EAICD document.
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, gain optimisation or when
moving over the substrate, to make a measurement matrix.
Produces total sum of the event counts over three possible time
windows.
The product files have the naming convention
CS_YXX_YYYYMMDDTHHMMSS_SCAN.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.
heat
----
The substrate can be heated to clean it or to analyse volatile
dust. The product contains the heating curve.
The product files have the naming convention
CS_YXX_YYYYMMDDTHHMMSS_HEAT.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.
clean
----
The single substrate position can be cleaned by the Indium ion
beam. The product contains the emitter tip current housekeepin
statistics.
The product files have the naming convention
CS_YXX_YYYYMMDDTHHMMSS_SCAN.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.
Note that so far this have never been done in with the COSIMA.
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 of either
CS_YXX_YYYYMMDDTHHMMSS_S_HK.TAB for spectrum,
CS_YXX_YYYYMMDDTHHMMSS_SCHK.TAB for scan or
CS_YXX_YYYYMMDDTHHMMSS_CLHK.TAB for cleaning, 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.
Note that there are calibration images and thus calibration
grain lists, which can be identified from a fixed pattern,
typically with 103 detected grains.
Note that consecutive grain lists may have different content
due to variations in the mechanical positioning and
illumination.
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.LBL, 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 right (plus) side
and M for left (minus) side led illumination.
The LBL file points to simlarly named FIT file, where the FIT
refers to the FITS image standard. FITS (Flexible Image
Transport System) format is defined in 'Astronomy and
Astrophysics', volume 376, page 359;
bibcode: 2001A&A...376..359
Note that there are calibration images, which can be identified
from a fixed squares pattern.
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 and the mask used to pick up subimages.
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 a 13 * 20 degree field of view for
a distinct dust particle.
^
| direction of
| flight
|
^ +Xcosima (down-track)
|
|
--- +---------|---------+
^ | | |
| | | |
| | | |
| | | |
| 13 deg | x-------------> +Ycosima (cross-track)
| | +Zcosima |
| | |
| | |
V | |
--- +-------------------+
| 20 deg | Boresight (+Z axis)
|<----------------->| is into the page
| |
The distance from the funnel inlet to the exposed
(10+1+10+10)mm*10mm substrates is 162 mm. The dimensions of the
funnel inlet are 58mm*40mm.
-------------
----------------- ^
------------ 20
5 v
<------------------ 162 ----------------->
5 ^
------------ 20
----------------- v
-------------
-------------
----------------- ^
------------ 29
16 v
<------------------ 162 ----------------->
16 ^
------------ 29
----------------- v
-------------
No S/C geometry is calculated for the data.
The substrates have a coordinate system, defined in micrometers
from 0-10000 in X and Y direction, starting from the lower left
corner. There's a second coordinate system, named XM substrate
in the FITS-file, which tries to compensate on the mechanical and
ion path difference from the COSISCOPE to the TOF-SIMS analysis
position.
The spectrum position given as X and Y does not necessarily match
the X and Y established as XM substrate coordinates. This offset
is different for positive and negative spectra and can only be
solved by analysing the TOF-SIMS 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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