SECCHI Consortium Meeting, Paris - March 2007 Heliospheric Imagers – Instrument Status Chris Eyles...
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Transcript of SECCHI Consortium Meeting, Paris - March 2007 Heliospheric Imagers – Instrument Status Chris Eyles...
SECCHI Consortium Meeting, Paris - March 2007
Heliospheric Imagers – Instrument Status
Chris Eyles
Space Science & Technology Department (RAL)
Richard Harrison, Chris Davis, Danielle Bewsher, Steve Crothers and Jackie Davies (RAL)
Jean-Philippe Halain (Centre Spatiale de Liege)
Dan Moses and Jeff Newmark (Naval Research Laboratory)
Chris Eyles
Space Science & Technology Department
HI Design Requirements
• Geometrical requirements:– To view the Sun-Earth line
with unbroken coverage from Corona to Earth orbit
– Opening angle of 45º governed by average CME width over equator
• Brightness levels:– Need to achieve rejection to
< 3x10-13 and < 10-14 B/Bo to detect CME signal
– Have to contend with contributions from the F-Corona, planets, stars, the Earth and Moon
Chris Eyles
Space Science & Technology Department
HI Specifications
HI-1 HI-2
Direction of centre of FOV 13.98º 53.68º
Angular field of view 20º 70º
Angular range 3.98º – 23.98º 18.68º – 88.68º
CCD pixel size 35 arcsec 2 arcmin
Image array (2x2 binning) 1024x1024 1024x1024
Image bin size 70 arcsec 4 arcmin
Spectral bandpass 630-730 nm 400-1000 nm
Nominal exposure time 12-20 s 60-90 s
Nominal exposures per image 70 50
Nominal image cadence 60 min 120 min
Brightness sensitivity (Bo = solar disk) 3 x 10-15 Bo 3 x 10-16 Bo
Straylight rejection (outer edge) 3 x 10-13 Bo 10-14 Bo
Chris Eyles
Space Science & Technology Department
Early Mission Summary (1)
• Launched on 25 Oct 2006
– Decontamination Heaters switched on few hours later
• SECCHI Electronics and HI Cameras switched on 27 Oct
– Electronics checks, dark images, Cal LED images
• Outgassing until 22 Nov
– Decontamination Heaters switched off
– CCD cooling curves and dark charge measurements (see later)
– Cal LED and dark images
• HI-A Door deployment and first light on 13 Dec
• First Lunar swing-by and heliospheric insertion of STEREO-A on 15 Dec
– HI-2A images of Moon !!!
Chris Eyles
Space Science & Technology Department
Early Mission Summary (2)
• HI-B Door deployment and first light on 11 Jan
– HI-1B images of Comet McNaught !!!
• Second Lunar swing-by and heliospheric insertion of STEREO-B on 21 Jan
• A reduced synoptic observing programme began late-Dec (for HI-A)
– Summed sequences of 25 x 24 sec exposures for HI-1 and 50 x 50 sec exposures for HI-2, both every 2 hours
– Interspersed with various calibration activities, including S/C off-points and rolls
• Various calibration and commissioning activities over period Dec – date
– HI straylight off-point calibrations (see later)
– SCIP stepped calibration rolls
– Open Door exposure time linearity sequences
– Open Door Cal LED images (LED + sky; sky only)
Chris Eyles
Space Science & Technology Department
Early Mission Summary (3)
• Just starting routine synoptic observing programme (see later)
• HI-A/B calibration rolls planned for 13 and 15 Mar
– 90/270 deg simultaneous rolls; spacecraft are rolled so that HI-A and HI-B view same area of sky to North and South of ecliptic
– 180 deg rolls; each spacecraft in turn rolled so that HI-A and HI-B view same area of sky centred on ecliptic
Chris Eyles
Space Science & Technology Department
HI CCD Cooling and Dark Charge
HI-1A CCD Dark Charge vs Temperature
0,01
0,10
1,00
10,00
100,00
1000,00
-80,00 -60,00 -40,00 -20,00 0,00 20,00
CCD Temperature (deg C)
Da
rk C
ha
rge
(D
N/p
ixe
l/se
c)Dark Charge (DN/pixel/sec)
HI-1A HI-2A HI-1B HI-2B e2v value*
+20ºC 505.7 392.0 496.5 402.0 1300
-80ºC 0.0018 0.0014 0.0017 0.0014 -
Fitted dark charge vs T relationship -
Idark = A T3 exp(6400/T) (T in deg K)
* Based on 20000 e/pixel/sec and 1 DN = 15 e
Chris Eyles
Space Science & Technology Department
HI Thermal Status
CCD vs Lens Barrel Temperature Correlation
-85,0
-80,0
-75,0
-70,0
-65,0
-60,0
-30,0 -20,0 -10,0 0,0 10,0 20,0
Lens Barrel Temperature (deg C)
CC
D T
empe
ratu
re
(deg
C)
HI-1A
HI-2A
HI-1B
HI-2B
HI-A HI-B
Structure -70 to -23ºC
-68 to -29ºC
S/C Interface -1ºC 0ºC
HI-1 CCD -83ºC -80ºC
HI-2 CCD -80ºC -76ºC
HI-1 Lens Barrel
-15ºC -29ºC
HI-2 Lens Barrel
-15ºC -15ºC
CEB Internal -13ºC -13ºC
Wax Actuator -72ºC -71ºC
• All temperatures are well within operating limits• HI-1B Lens Barrels stabilized at -29ºC with Operational Bus Heater• CCD temperatures are very satisfactory
Chris Eyles
Space Science & Technology Department
HI-A Straylight Off-Point Calibration (HI-1)
HI-1A Measured F-Corona Versus Off-Point Angle - 30 Jan 2007
1,0
10,0
100,0
1000,0
10000,0
2,0 6,0 10,0 14,0 18,0 22,0 26,0
Degrees from Sun Centre
DN
per
Bin
per
Sec
on
d
Nominal PointingFitted R^(-2.38)+1.0 deg Off-Point+0.5 deg Off-Point-0.25 deg Off-Point-0.5 deg Off-Point-0.75 deg Off-Point-1.0 deg Off-Point
• Spacecraft off-pointed in steps in HI pitch:
– 0.25º, 0.5º, 0.75º, 1.0º and 1.5º towards Sun
– 0.5º and 1.0º away from Sun
• Stars removed with median filter, then measured F-corona intensity at a number of points across centre-line of FOV
• Values plotted against angle from Sun centre allowing for off-point
• Rn profile fitted to nominal pointing values
• 1 DN/sec ~ 1.2 x 10-13 B/BO for HI-1
– Straylight rejection better than 2 x 10-13 B/BO over most of FOV
• Margin of at least 0.5º in off-pointing from Sun
HI-1A (Measured - Profile) Versus Off-Point Angle - 30 Jan 2007
-20,0
0,0
20,0
40,0
60,0
80,0
100,0
2,0 6,0 10,0 14,0 18,0 22,0 26,0
Degrees from Sun Centre
DN
per
Bin
per
Sec
on
d
Nominal Pointing
+1.0 deg Off-Point
+0.5 deg Off-Point
-0.25 deg Off-Point
-0.5 deg Off-Point
-0.75 deg Off-Point
-1.0 deg Off-Point
Chris Eyles
Space Science & Technology Department
HI-A Straylight Off-Point Calibration (HI-2)
HI-2A Measured F-Corona Versus Off-Point Angle - 30 Jan 2007
1,0
10,0
100,0
1000,0
15,0 25,0 35,0 45,0 55,0 65,0 75,0
Degrees from Sun Centre
DN
per
Bin
per
Sec
on
d
Nominal PointingFitted R^(-1.85)+1.0 deg Off-Point+0.5 deg Off-Point-0.25 deg Off-Point-0.5 deg Off-Point-0.75 deg Off-Point-1.0 deg Off-Point
HI-2A (Measured - Profile) Versus Off-Point Angle - 30 Jan 2007
-10,0
0,0
10,0
20,0
15,0 25,0 35,0 45,0 55,0 65,0 75,0
Degrees from Sun Centre
DN
per
Bin
per
Sec
on
d
Nominal Pointing
+1.0 deg Off-Point
+0.5 deg Off-Point
-0.25 deg Off-Point
-0.5 deg Off-Point
-0.75 deg Off-Point
-1.0 deg Off-Point
• Rn profile fitted to nominal pointing values
– Value of n is very different for HI-1 and HI-2, 2.38 and 1.85 respectively, difference in spectral response?
• 1 DN/sec ~ 2 x 10-14 B/BO for HI-2
– Straylight rejection better than 2 x 10-14 B/BO over most of FOV
• Margin of at least 0.5º in off-pointing from Sun
Chris Eyles
Space Science & Technology Department
Synoptic Observing Programme (1)
HI-1 HI-2
Exposure Time 24 sec 50 sec
Exposure Cadence 30 sec 60 sec
Number of Images in Summed Sequence 50 99
Duration of Exposure Sequence 25 min 99 min
Summed Sequence Cadence 40 min 2 hr
Observing Duty Cycle 50% 67%
• In addition take full-resolution single images at regular intervals– One every 2 days for HI-1– One every 4 days for HI-2
Chris Eyles
Space Science & Technology Department
Synoptic Observing Programme (2)
• Exposure times selected on dynamic range considerations
– 24 sec exposure for HI-1 gives maximum F-corona signal ~ 60% of dynamic range; very few saturated stars in HI-1 (~ 0 – 1)
– 50 sec exposure for HI-2 gives ~ 3 – 6 saturated stars
• Exposures at multiples of 30 sec simplifies scheduling
• Duration of exposure sequence results in drift of stars by ~ 1 bin
– Minimal smearing of star images
• Summed sequence cadences constrained by telemetry allocation but matched to respective plate scales and typical velocity of coronal ejecta
Chris Eyles
Space Science & Technology Department
HI Instrument Health and Status
• The HI instruments are performing superbly
• HI CEB and other electronics performance entirely nominal
• Thermal performance nominal
– All temperatures within operating temperature limits
– CCDs operating at ~ -80ºC; dark charge negligible, high tolerance against radiation damage effects
• No new issues or problems since launch
• Calibrations of flat fields, pointing offsets, etc proceeding well
Chris Eyles
Space Science & Technology Department
HI Instrument Issues
Three issues were known about pre-launch:
• Thermal leak in HI-1B Lens Barrel
– Very minor, requires operating set-point of HI-1B Optics to be -29ºC rather than -15ºC
– No impact on performance whatsoever
• Off-axis PSRF of HI-2B inferior to HI-2A
– Also minor, issue was found late in programme
– No significant impact on Level 1 science; star removal from images will be more challenging
• Bright Earth in HI-B
– Issue arises from fundamental orbital mechanics and the consequent (and inevitable) mission design.
– Dynamic range of cameras is excellent
Chris Eyles
Space Science & Technology Department
• First solutions from fitting to star-fields show plate-scales, distortion parameters, etc consistent with pre-launch values
• PSFs consistent with pre-launch values
Values in pixels –
• Tests during AIV showed that HI-2B PSF problem is not a simple focus setting error– No significant impact on Level 1 science– Star subtraction more challenging; stellar photometry may be somewhat
compromised– Images not so photogenic
HI Imaging Performance
Pre-Launch PSF On-Orbit PSF
FWHM HEW FWHM est
HI-1A 3 – 4 3 – 4 ~ 3 – 4
HI-2A 3 – 6 3 – 6 ~ 3 – 8
HI-1B 3 – 4 3 – 4 ~ 3 – 4
HI-2B 3 – 10 3 – 12 ~ 3 – 12
Chris Eyles
Space Science & Technology Department
HI-B Bright Earth Issues (HI-1)
• Earth first produced significant stray light effect on HI-1B on day 98 (Jan 30)– Sun-Earth angle was 34.5º
• Earth will leave HI-1B FOV (Sun-Earth angle 24º) around day 150 (Mar 23)• Sun-Earth angle will return to 34.5º around day 169 (Apr 11)
– Guarantees that Earth will cease to be an issue for HI-1B by mid-Apr– In fact will be significantly earlier because Earth irradiance is more than an order
of magnitude lower than on day 98
A recent HI-1B image (25 Feb):
Surface brightness < 10% of F-corona locally
Chris Eyles
Space Science & Technology Department
HI-B Bright Earth Issues (HI-2)
• Earth signal is ~ 5 x 1010 photoelectrons per pixel (in 10 sec)– ~ 2.5 x 105 x CCD full-well depth!!!– Also ~ 2.5 x 105 x system dynamic range
• By mid-June Earth irradiance will be order of magnitude lower– Spacecraft separation still only 13º– Success of on-going modeling and background subtraction studies will determine
how much earlier Earth will cease to be an issue.
HI-2B image (10 sec exposure) from 6 Feb:
Surface brightness < 10% of F-corona locally
Chris Eyles
Space Science & Technology Department
The Lunar Transit in HI-B
19 Feb 2007
0100 UT(full-res image)
28 Feb 2007
0100 UT(full-res image)
Chris Eyles
Space Science & Technology Department
HI Instrument Status Conclusions
• The performance of the instruments is excellent
• No new issues or problems since launch
• The Bright Earth will cease to be an issue for HI-1B by mid-April or earlier and for HI-2B by mid-June or earlier
• Excellent progress with calibrations– First flat-fielding results– First star-field fitting results– Pointing information being implemented in FITS headers
(CRPIX, CRVAL, PCj_i, PV2_1, initially with nominal off-points, soon with updated values from star fields)
• HI is well placed for start of mission science phase