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.