SECCHI Consortium Meeting, Paris - March 2007 Heliospheric Imagers – Instrument Status

1. SECCHI Consortium Meeting, Paris - March 2007Heliospheric 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)

2. 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

3. HI Specifications

4. 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 !!!

5. HI-A First Lights

6. HI-A Lunar Swingby

7. 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)

8. Comet McNaught (HI-1A 11-18 Jan 2007)

9. SCIP-B Stepped Calibration Roll

10. 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

11. HI CCD Cooling and Dark Charge Fitted dark charge vs T relationship - Idark = A T3 exp(6400/T) (T in deg K) * Based on 20000 e/pixel/sec and 1 DN = 15 e

12. HI Thermal Status • All temperatures are well within operating limits • HI-1B Lens Barrels stabilized at -29ºC with Operational Bus Heater • CCD temperatures are very satisfactory

13. HI-A Straylight Off-Point Calibration (HI-1) • 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 • Rn 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

14. HI-A Straylight Off-Point Calibration (HI-2) • Rn 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

15. Synoptic Observing Programme (1) • In addition take full-resolution single images at regular intervals • One every 2 days for HI-1 • One every 4 days for HI-2

16. 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

17. 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

18. 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

19. HI Imaging Performance • 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

20. 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

21. 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

22. The Lunar Transit in HI-B 19 Feb 2007 0100 UT (full-res image) 28 Feb 2007 0100 UT (full-res image)

23. 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