Advances in Space Imaging
Russell A. Howard
Naval Research LaboratoryNSF Workshop on Small Missions, 15-17 May 2007
Outline
• Overview of the STEREO Mission
• Overview of SECCHI instrument and its capabilities
• Some early observations/results
• Thoughts on miniaturizing this type of instrumentation
STEREO Science Objectives
Understand the origins and consequences of CMEs
Determine the processes that control CME evolution in the heliosphere
Discover the mechanisms of solar energetic particle acceleration
Determine the 3-D structure and dynamics of corona and interplanetary plasmas and magnetic fields
STEREO Instruments
• Remote Sensing
– Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) PI: Russell Howard, Naval Research Laboratory
– STEREO/WAVES (SWAVES) PI:Jean Louis H. Bougeret, Centre National de la Recherche Scientifique, Observatory of Paris
• In Situ
– In situ Measurements of Particles and CME Transients (IMPACT) PI: Janet G. Luhmann, University of California, Berkeley
– PLAsma and SupraThermal Ion and Composition (PLASTIC) PI: Antoinette Galvin, University of New Hampshire
SCIP
STEREO Spacecraft (Behind)
HI
SWAVESBoom (3x)
Plastic
IMPACTBoom
SWAVESBoom (3x)
SWAVESBoom (3x)
STEREO Orbits
Sun SunEarth
Ahead @ +22/year
Behind @ -22/year
Heliocentric Inertial Coordinates(Ecliptic Plane Projection)
Geocentric Solar Ecliptic CoordinatesFixed Earth-Sun Line
(Ecliptic Plane Projection)
Ahead
Behind
Earth
1 yr.
2 yr.
3 yr.
4 yr.
1yr.
2yr.
3 yr.4 yr.
SECCHI Science Overview
021104-06SECCHI_CDR_Science.8
COR/HI Overlap Regions
Fields of View
COR2 (Black)
HI-1 (Red) and HI-2
(Blue)
SECCHI/EUVI First Light ImagesFe IX, Fe XII, Fe XV, He II
EUVI Enhanced Images
• This is an example of wavelet enhanced EUVI (Fe XV, 284A) images of a solar rotation in March• They reveal the off-limb structures out to the edge of the field of view (1.7 Rsun)•Similar movies in Fe X and Fe XII also show the XUV structures to the FOV edge•This enables us to couple the white light structures in the COR1 coronagraph with an inner limit of 1.4 Rsun to the disk.
SECCHI/COR2 and LASCO/C2/C3
Image of Moon from SECCHI/HI-2 During STEREO-A Flyby 12/15/2006
Comet McNaught Movie HI-1
HI-2B Comet McNaught Receding
Earth’s Moon (Saturating The CCD Pixels)
Comet McNaught
TO SUN
Milky Way
Earth Occulter
StrayLightFromEarth
HI 1A: 2007 Feb 1-15
Venus and optical system ghost artifact
Mercury
Streamer relocates to a higher latitude
Putting All the A-Telescopes Together
0 4º15 R
24º96 R
65º260 R
90º360 R4R ≈ 1º
CME observed in All Telescopes (24 Jan 2007)
Ecliptic
Plane
0 4 24 55 90DEGREES
EUVI, COR1, COR2: 9 Feb 2007
Outer Limit= 15 Rsun
Cropped on West Limb
COR2, HI-1, HI-2: 9 Feb 2007Running Differences & Additional Filtering
SECCHI – Early Results:COR2 Observations
• Apparent limiting magnitude: at least m11
– Lots of stars
• Observed comets:
– Surprisingly few!
– Over 40 “SOHO” Kreutz have passed through COR2
- We have seen just four of them
- This is due to the bandpass of COR2 relative to LASCO/C2
Comet Encke
Miniaturization Thoughts (1)
• NRL/Solar Physics has been involved in all classes of instruments from small rocket payloads to very large shuttle class instruments.
• Solar Imaging requirements
– Pointing system to point the payload at the Sun. The trend now is for very accurate pointing with low jitter (sub arc sec pointing)
– Spinners are possible but 3-axis stabilized platforms much better
– Large apertures/long focal lengths for highest resolution, shortest exposure times
– Monitoring instruments (e.g. for space weather) could relax these requirements, thereby reducing the size/mass.
– If cadence permits, images can be summed on-board to increase the number of photons collected. The SECCHI/HI-1/2 accumulate respectively 50/100 images to achieve ~30/60 minutes of exposure
• The size of the SOHO/LASCO was reduced to save mass, but C3 reduction hit practical limits in the size of overlap and could not be reduced any further.
Miniaturization Thoughts (2)
• Can any of the STEREO be minimized?
– Consisted of 2 spacecraft,
– Each S/C ~450 kg dry mass, ~500 kg wet.
– Instrument complement
- ~95 kg each S/C
- SECCHI
- 5 telescopes, electronics box, interconnect harness ~50 kg
- One subsystem: Heliospheric Imager (HI) ~12 kg shown on left. Most of the mass is the CCD passive cooling system
- The optical system itself is quite small.