HECOR (HElium CORonagraph) is a coronagraph designed to observe the solar corona at 30.4 nm between 1.2 and 4
solar radii. The instrument is part of the Herschel sounding rocket payload to be flown from White Sands Missile Range
in December 2007. Much like for neutral hydrogen, the residual singly ionized helium present in the corona can be
detected because it resonantly scatters the intense underlying chromospheric radiation. Combined with the simultaneous
measurements of the neutral hydrogen corona made by SCORE, the other coronagraph of the Herschel payload, the
HECOR observations will provide novel diagnostics of the solar wind outflow. HECOR is an externally occulted
coronagraph of very simple design. It uses a triple-disc external occulting system, a single off axis multilayer coated
mirror and a CCD camera. We present measurements of the EUV mirror roughness and reflectivity, tests of the image
quality, and measurements of the stray light rejection performance. The mirror uses a novel multilayer design with three
components that give HECOR a high throughput.
The Heliospheric Imager (HI) is part of the SECCHI suite of instruments on-board the two STEREO observatories
launched in October 2006. The two HI instruments provide stereographic image pairs of solar coronal plasma and
coronal mass ejections (CME) over a field of view ranging from 13 to 330 R<sub>0</sub>.
The HI instrument is a combination of two refractive optical systems with a two stage multi-vane baffle system. The key
challenge of the instrument design is the rejection of the solar disk light by the front baffle, with total straylight
attenuation at the detector level of the order of 10<sup>-13</sup> to 10<sup>-15</sup>. Optical systems and baffles were designed and tested to
reach the required rejection.
This paper presents the pre-flight optical tests performed under vacuum on the two HI flight models in flight temperature
conditions. These tests included an end-to-end straylight verification of the front baffle efficiency, a co-alignment and an
optical calibration of the optical systems. A comparison of the theoretical predictions of the instrument response and
performance with the calibration results is presented. The instrument in-flight photometric and stray light performance
are also presented and compared with the expected results.
The Heliospheric Imager (HI) forms part of the SECCHI suite of instruments aboard the two NASA STEREO spacecraft
which were launched successfully from Cape Canaveral AFB on 25 Oct 2006 (26 Oct UTC). Following lunar swingby's
on 15 Dec and 21 Jan respectively, the two spacecraft were placed in heliocentric orbits at approximately 1 AU - one
leading and one lagging the Earth, with each spacecraft separating from the Earth by 22.5° per year.
Each HI instrument comprises two wide-angle optical cameras - HI-1 and HI-2 have 20° and 70° fields-of-view which
are off-pointed from the Sun direction by 14.0° and 53.7° respectively, with the optical axes pointed towards the ecliptic
plane. In this way the cameras will for the first time provide stereographic images of the solar corona, and in particular of
Coronal Mass Ejections (CMEs) as they propagate outwards through interplanetary space towards the Earth and beyond.
The wide-field coverage of HI enables imaging of solar ejecta from 15 to about 330 solar radii whilst the other SECCHI
instruments (2 coronagraphs and an EUV imager) provide coverage from the lower corona out to 15 solar radii.
This paper briefly reviews the design and performance requirements for the instrument. The various activation, checkout
and calibration activities before and after opening the instrument's protective cover or door (instrument 'first-light') are
then described and it is shown that the instrument has met the design requirements, including CCD and camera imaging
performance, correction for shutterless operation of the cameras, straylight rejection and thermal requirements. It is
demonstrated from observations of a CME event on 24-25 Jan 2007 that the instrument is capable of detecting CMEs at
an intensity of 1% of the coronal background. Lessons learnt during the design, development and in-orbit operation of
the instrument are discussed.
The Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) developed for the NASA Solar Terrestrial
Relations Observatory (STEREO) mission is a suite of optical telescopes that will, for the first time, observe the entire
inner heliosphere from the solar surface out to the vicinity of Earth from twin spacecraft. SECCHI was developed by an
international consortium led by the Naval Research Laboratory (NRL). The primary objective of the STEREO mission is
to understand the Coronal Mass Ejection (CME) phenomenon, discovered in 1971, and most recently extensively
observed by the NASA/ESA Solar and Heliospheric Observatory (SOHO). The SECCHI telescope suite is returning
unprecedented views of the Sun and inner heliosphere. The SECCHI instruments on each of the two STEREO spacecraft
observe CMEs from their initiation, through the corona, and into interplanetary space beyond the Earth's orbit. We
present an overview of the development and early operations of the SECCHI experiment.
The Extreme Ultraviolet Imager (EUVI) is part of the SECCHI instrument suite currently being developed for the NASA STEREO mission. Identical EUVI telescopes on the two STEREO spacecraft will study the structure and evolution of the solar corona in three dimensions, and specifically focus on the initiation and early evolution of coronal mass ejections (CMEs). The EUVI telescope is being developed at the Lockheed Martin Solar and Astrophysics Lab. The SECCHI investigation is led by the Naval Research Lab. The EUVI’s 2048 x 2048 pixel detectors have a field of view out to 1.7 solar radii, and observe in four spectral channels that span the 0.1 to 20 MK temperature range. In addition to its view from two vantage points, the EUVI will provide a substantial improvement in image resolution and image cadence over its predecessor SOHO-EIT, while complying with the more restricted mass, power, and volume allocations on the STEREO mission.
The Solar Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory will characterize the dynamical evolution of the solar plasma from the chromosphere to the corona, and will follow the connection of plasma dynamics with magnetic activity throughout the solar atmosphere. The AIA consists of 7 high-resolution imaging telescopes in the following spectral bandpasses: 1215Å. Ly-a, 304 Å He II, 629 Å OV, 465 Å Ne VII, 195 Å Fe XII (includes Fe XXIV), 284 Å Fe XV, and 335 Å Fe XVI. The telescopes are grouped by instrumental approach: the MAGRITTE Filtergraphs (R. MAGRITTE, famous 20th Century Belgian Surrealistic Artist), five multilayer EUV channels with bandpasses ranging from 195 to 1216 Å, and the SPECTRE Spectroheliograph with one soft-EUV channel at OV 629 Å. They will be simultaneously operated with a 10-second imaging cadence. These two instruments, the electronic boxes and two redundant Guide Telescopes (GT) constitute the AIA suite. They will be mounted and coaligned on a dedicated common optical bench. The GTs will provide pointing jitter information to the whole SHARPP assembly. This paper presents the selected technologies, the different challenges, the trade-offs to be made in phase A, and the model philosophy. From a scientific viewpoint, the unique combination high temporal and spatial resolutions with the simultaneous multi-channel capability will allow MAGRITTE / SPECTRE to explore new domains in the dynamics of the solar atmosphere, in particular the fast small-scale phenomena. We show how the spectral channels of the different instruments were derived to fulfill the AIA scientific objectives, and we outline how this imager array will address key science issues, like the transition region and coronal waves or flare precursors, in coordination with other SDO experiments. We finally describe the real-time solar monitoring products that will be made available for space-weather forecasting applications.
The ability to derive physical parameters of the Sun from observations by the Solar and Heliospheric Observatory (SOHO) Extreme Ultraviolet Imaging Telescope (EIT) greatly increases the scientific return of the mission. The absolute and time variable calibration of EIT therefore is of extreme interest. The NRL EIT Calibration Sounding Rocket (CalRoc) program was initiated to provide well calibrated, contemporaneous observations in support of SOHO EIT. These observations provide three benefits to the SOHO EIT data, absolute calibration points, temporal and spatial information of the EIT EUV response variability in flight via flat field information and clues to the physics of the degradation. Details of the bandpasses of the multilayered optics and the total telescope photometry are presented. Comparisons are shown with the contemporaneous images from SOHO EIT. Plans for the second CalRoc flight are discussed. Loss of reflectivity in the multilayer mirrors has been identified as a new component to the SOHO EIT and CalRoc degradation.