Presentation on theme: "An all-sky heliospheric imager All-sky coverage (when two are employed) 0.1% differential photometry Robust, light-weight design Low background-light contribution."— Presentation transcript:
An all-sky heliospheric imager All-sky coverage (when two are employed) 0.1% differential photometry Robust, light-weight design Low background-light contribution –When bright background-light contributors are kept away from FOV and –optics do not protrude from protected volume
Basic concept – see models here A smooth corral blocks stray light from background sources below FOV –Light must multiple-diffract over surface to reach protected volume Non-protruding optics provides a virtual image of a hemisphere of sky A conventional CCD camera views virtual sky Two such cameras placed on opposite sides of a spacecraft provide whole-sky coverage
Corral concept: laboratory tests
Principal corral features Lightweight, simple, robust (resembles a foxhole rather than a castle…) Does not depend upon high-tech surfaces, nor is surface performance subject to normal contamination Precise alignment is unnecessary when corral surface extends a bit beyond minimum required ~ 1 m size permits viewing within 2° of Sun
Principal optics features Non-protruding design Toroidal mirror covers most of sky That portion of sky occulted by mirror separately covered by lens in center Virtual image of sky recorded by conventional CCD camera system Stray light residue controlled by field stop, Lyot stop and final imaging system
Cutaway schematic of corral/optics (left) Conventionally turned optic (right)
Hemispherical-Imager Mirrors Conventionally turned & polishedDiamond-turned A diamond-turned lightweight mirror has been fabricated with the tool moving in a circular path, that avoids the “jaggies” that ordinarily plague such strongly curved mirrors. Manufactured by Bach Research, who also made the SMEI diamond-turned mirrors.