Requirements for the Star Tracker Parallel Science
Programme
Rømer System Definition Phase 2000/2001
Document no.:
Date:
Prepared by:
Checked by:
Authorized by:
Classification:
MONS/IFA/PL/RS/0003(1)
22.04.2001
Hans Kjeldsen and Tim Bedding
Jørgen Christensen-Dalsgaard
Jørgen Christensen-Dalsgaard
Open: The document is unclassified and there are no
restrictions in circulation.
Requirements for the Star Tracker Parallel Science Programme
Requirements for the Star
Tracker Parallel Science Programme
Teoretisk Astrofysik Center, Institut for Fysik og Astronomi, Aarhus Universitet
This document may only be reproduced with permission of TAC/IFA, except within the Rømer project where
any type of reproduction is allowed.
MONS/IFA/PL/RS/0003(1)
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Requirements for the Star Tracker Parallel Science Programme
DISTRIBUTION
This document is for internal use by the Rømer project. All Rømer key persons will be able to access the
document via the DSRI webpage: http://www.dsri.dk/roemer/pro.
MONS/IFA/PL/RS/0003(1)
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Requirements for the Star Tracker Parallel Science Programme
Contents
1. SCOPE
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2. APPLICABLE DOCUMENTS
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3. STAR TRACKER PARALLEL SCIENCE REQUIREMENTS
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3.1 Assumed detector properties
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3.2 Assumed read-out electronics
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3.3 Assumed optical system
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3.4 Required readout procedure for parallel science
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3.5 Output data produced
3.5.1 Data volume and rate
MONS/IFA/PL/RS/0003(1)
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Requirements for the Star Tracker Parallel Science Programme
1. SCOPE
This document specifies the requirements for the Parallel Science Programme on the Rømer Star Trackers.
The document has been prepared by the Theoretical Astrophysics Center and the Institute of Physics and
Astronomy at Aarhus University as a contribution to the Rømer System Definition Phase (The Danish Small
Satellite Programme).
MONS/IFA/PL/RS/0003(1)
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Requirements for the Star Tracker Parallel Science Programme
2. APPLICABLE DOCUMENTS
AD1: Rømer Science Mission Specification
MONS/IFA/MIS/RS/0001(1)
AD2: MONS Payload Requirements Specification
MONS/IFA/PL/RS/0001(2)
AD3: MONS Field Monitor Requirements Specification and Parallel Science
MONS/IFA/PL/RS/0002(1)
AD4: MONS Payload Electronics Requirement Specification
TERMA # 255503 DT
AD5: MONS Field Monitor System Definition Phase Design Report
MONS/AUS/PL/RP/0002(1)
MONS/IFA/PL/RS/0003(1)
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Requirements for the Star Tracker Parallel Science Programme
3. STAR TRACKER PARALLEL SCIENCE REQUIREMENTS
The Attitude Control Subsystem on the Rømer platform will include two Star Trackers in order to provide the
needed attitude information for calibrating the ACS. The ACS update frequency will be 1 mHz.
In order to increase the science output of the Rømer mission, we are planning a parallel science programme
aiming at surveying the field of view for variable stars. We also plan to collect integrated images of the whole
field of view in order to allow more general programmes in cosmology, solar system work and stellar physics.
The baseline for the Star Tracker parallel science programme is a standard TERMA Star Tracker, which
consists of the following major parts:







Optics
Mounting interface to the spacecraft
Baffle
Radiator for cooling the detector
CCD Detector Unit
Read-out Electronics Unit
Data Processing Unit (Rømer main computer - CDH)
3.1 Assumed detector properties
CCD chip:
Image:
Image Area Size:
Frame transfer Operation:
Pixel Size:
CCD Operating Temperature:
CCD Temperature Stability:
CCD Temperature Measurement
Accuracy (Telemetry):
MONS/IFA/PL/RS/0003(1)
Marconi Applied Technologies
CCD 47-20 Front Illuminated (AIMO CCD Sensor)
1024 x 1024 pixels
13.3 x 13.3 mm2
1024 x 1024 pixels Storage area
13 um square
-10 degC
5 degC (RMS)
1 degC (RMS)
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Requirements for the Star Tracker Parallel Science Programme
3.2 Assumed read-out electronics
Saturation Level:
A/D-Conversion:
Conversion factor:
Readout noise:
Readout Frequency
Integration Time:
Accuracy of Integration time:
Read-out Modes:
Read-out time:
30.000 e/pix
8 bits or better
35 e/ADU (soft saturation: 8960 e)
20 e/pix
1 MHz
25 msec - 2 sec programmable
1 usec (RMS)
Full frame and window read-out
1 usec/pix (1 MHz)
Full frame: 1049 msec
6.0 usec (0.166 MHz)
380 nsec/pix (2.6 MHz)
Full frame: 398 msec
7 x 13 x 13 pixels:
42 msec
28 x 13 x 13 pixels:
149 msec
64 x 13 x 13 pixels:
332 msec
630 x 630 pixels:
494 msec
1024 x 1024 pixels:
1049 msec
Vertical shift time:
Horizontal shift time:
Read-out per field:
3.3 Assumed optical system
Lens Aperture, D
Focal Length, f
f-ratio
Image scale at detector:
Field of view:
Pixel-Size:
FWHM (star)
Transmission Efficiency:
incl. CCD:
Optical Bandpass:
No. of photons V=5
Saturation V=5:
Saturation
43 msec:
150 msec:
332 msec:
336 msec:
497 msec:
MONS/IFA/PL/RS/0003(1)
24 mm
35 mm
f/1.46
0.61 mm/deg
22 deg x 22 deg
77 arcsec/pix
2.5 arcmin (2 pix)
50 % (no filter)
20 %
400 nm - 800 nm (no filter)
36,000 e/sec
exp=1 sec
V = 1.6
V = 2.9
V = 3.8
V = 3.8
V = 4.2
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Requirements for the Star Tracker Parallel Science Programme
3.4 Required readout procedure for parallel science
5 sec procedure:
Time: (msec)
EXPOSURE:
READ OUT:
0000 - 0149
0150 - 0156
0157 - 0488
0489 - 0495
0496 - 0992
0993 - 0999
150 msec (STR1)
7 msec transfer
332 msec (1)
7 msec transfer
497 msec (2)
7 msec transfer
1000 - 1149
1150 - 1156
1157 - 1488
1489 - 1495
1496 - 1992
1993 - 1999
150 msec (STR2)
7 msec transfer
332 msec (3)
7 msec transfer
497 msec (4)
7 msec transfer
149 msec - 28 stars (497 msec exp)
2000 - 2149
2150 - 2156
2157 - 2488
2489 - 2495
2496 - 2992
2993 - 2999
150 msec (STR3)
7 msec transfer
332 msec (5)
7 msec transfer
497 msec (6)
7 msec transfer
149 msec - 28 stars (497 msec exp)
42 msec - 7 stars (43 msec exp)
332 msec - 64 stars (150 msec exp)
494 msec - 630 x 630 pix (332 msec exp)
332 msec - 64 stars (150 msec exp)
494 msec - 630 x 630 pix (332 msec exp)
332 msec - 64 stars (150 msec exp)
494 msec - 630 x 630 pix (332 msec exp)
3000 - 3149
3150 - 3156
3157 - 3492
3493 - 3499
3500 - 3542
3543 - 3549
3550 - 3999
150 msec (STR4)
7 msec transfer
336 msec (7)
7 msec transfer
43 msec (8)
7 msec transfer
9 x 43 msec (9-17) + 9 x 7 msec transfer
149 msec - 28 stars (497 msec exp)
4000 - 4149
4150 - 4156
4157 - 4492
4493 - 4499
4500 - 4542
4543 - 4549
4550 - 4999
150 msec (STR5)
7 msec transfer
336 msec (18)
7 msec transfer
43 msec (19)
7 msec transfer
9 x 43 msec (20-28) + 9 x 7 msec transfer
42 msec - 7 stars (43 msec exp)
MONS/IFA/PL/RS/0003(1)
332 msec - 64 stars (150 msec exp)
42 msec – 7 stars (336 msec exp)
9 x 42 msec – 9 x 7 stars (9 x 43 msec exp)
332 msec - 64 stars (150 msec exp)
42 msec – 7 stars (336 msec exp)
9 x 42 msec – 9 x 7 stars (9 x 43 msec exp)
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Requirements for the Star Tracker Parallel Science Programme
3.5 Output data produced
5 sec. procedure:
5 x 150 msec:
3 x 332 msec:
3 x 497 msec:
2 x 336 msec:
20 x 43 msec:
33 exposures
STR-frames:
630 x 630 pix IMAGE:
64 stars (NO SCIENCE)
235 stars
(V > 3.8)
28 stars:
(V > 4.3)
7 stars:
(V > 3.8)
7 stars:
(V > 1.6)
Stellar classes:
Magnitude limit
Exposures:
Number of stars:
Class-I:
Class-II
Class-III
Class-IV
V > 1.6
V > 3.8
V > 4.3
V > 3.8
20 x 43 msec
2 x 336 + 3 x 332 msec
3 x 497 + 3 x 332 msec
3 x 332 msec
7
7
28
200
Photometric precision per minute for the star trackers used for parallel science.
Curves for the four different stellar classes are show. Saturation for class I is at
V=1.6, for class II and IV at V=3.8 and for class III at V=4.3. In order to estimate
amplitudes for coherent oscillations that can be detected at S/N=4 using the Star
Tracker, one should multiply the scatter by 0.037. We will therefore be able to
detect oscillations with amplitudes below 30 ppm for the brightest candidate stars.
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Requirements for the Star Tracker Parallel Science Programme
The following table shows the noise for stars of different magnitude observed using the four different
exposure times.
Stellar magnitude
V = 1.6
V = 2.0
V = 3.0
V = 3.8
V = 4.0
V = 4.3
V = 5.0
V = 6.0
V = 7.0
V = 8.0
V = 9.0
V = 10.0
20 x 43 msec
0.00159
0.00209
0.00446
0.00868
3 x 332 msec
2 x 336 msec
3 x 497 msec
0.00406
0.00464
0.00573
0.00968
0.0220
0.0529
0.130
0.325
0.813
0.00493
0.00563
0.00695
0.0117
0.0237
0.0640
0.158
0.393
0.984
0.00423
0.00693
0.0152
0.0359
0.0876
0.218
0.544
Based on this table we can estimate the noise per min for the four different types of exposure sequences
(stellar classes).
Stellar magnitude
V = 1.6
V = 2.0
V = 3.0
V = 3.8
V = 4.0
V = 4.3
V = 5.0
V = 6.0
V = 7.0
V = 8.0
V = 9.0
V = 10.0
Class I (7 stars)
0.00046
0.00060
0.00129
0.0025
Class II (7 stars)
0.00090
0.00103
0.00128
0.0022
0.0047
0.0118
0.029
0.072
0.181
Class III (28 stars)
Class IV (200 stars)
0.00098
0.00163
0.0036
0.0086
0.021
0.052
0.131
0.00117
0.00134
0.00165
0.0028
0.0064
0.0153
0.038
0.094
0.23
Finally we may estimate the amplitude of modes that can be detected by the Star Tracker after 30 days of
observing (duty cycle = 85 %). The table below indicate amplitudes that can be detected at S/N=4.
Stellar magnitude
V = 1.6
V = 2.0
V = 3.0
V = 3.8
V = 4.0
V = 4.3
V = 5.0
V = 6.0
V = 7.0
V = 8.0
V = 9.0
V = 10.0
Class I (7 stars)
17 ppm
22 ppm
48 ppm
92 ppm
Class II (7 stars)
33 ppm
38 ppm
47 ppm
81 ppm
170 ppm
440 ppm
0.11 %
0.27 %
0.67 %
Class III (28 stars)
Class IV (200 stars)
36 ppm
60 ppm
130 ppm
320 ppm
780 ppm
0.19 %
0.48 %
43 ppm
50 ppm
61 ppm
100 ppm
240 ppm
570 ppm
0.14 %
0.35 %
0.85 %
Milli-magnitude oscillations can be detected in stars down to magnitude V=8.
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Requirements for the Star Tracker Parallel Science Programme
3.5.1 Data volume and rate
We will produce data for 242 stars per minute (each in 2 apertures), plus housekeeping (e.g., pitch, yaw, roll
and background estimates). The total data rate will be 1050 bytes per minute. This means 636 kbytes per
orbit and 1.27 Mbytes per 24 hr. + 25% margin: 1.6 Mbytes/24 hr.
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