SPICE is an imaging spectrometer operating at vacuum ultraviolet (VUV) wavelengths, 70.4 – 79.0 nm and 97.3 - 104.9 nm. It is a facility instrument on the Solar Orbiter mission, which carries 10 science instruments in all, to make observations of the Sun’s atmosphere and heliosphere, at close proximity to the Sun, i.e to 0.28 A.U. at perihelion. SPICE’s role is to make VUV measurements of plasma in the solar atmosphere. SPICE is designed to achieve spectral imaging at spectral resolution >1500, spatial resolution of several arcsec, and two-dimensional FOV of 11 x16arcmins. The many strong constraints on the instrument design imposed by the mission requirements prevent the imaging performance from exceeding those of previous instruments, but by being closer to the sun there is a gain in spatial resolution. The price which is paid is the harsher environment, particularly thermal. This leads to some novel features in the design, which needed to be proven by ground test programs. These include a dichroic solar-transmitting primary mirror to dump the solar heat, a high in-flight temperature (60deg.C) and gradients in the optics box, and a bespoke variable-line-spacing grating to minimise the number of reflective components used. The tests culminate in the systemlevel test of VUV imaging performance and pointing stability. We will describe how our dedicated facility with heritage from previous solar instruments, is used to make these tests, and show the results, firstly on the Engineering Model of the optics unit, and more recently on the Flight Model. For the keywords, select up to 8 key terms for a search on your manuscript's subject.
SPICE is a high resolution imaging spectrometer operating at extreme ultraviolet wavelengths, 70.4 – 79.0 nm and 97.3 -
104.9 nm. It is a facility instrument on the Solar Orbiter mission. SPICE will address the key science goals of Solar
Orbiter by providing the quantitative knowledge of the physical state and composition of the plasmas in the solar
atmosphere, in particular investigating the source regions of outflows and ejection processes which link the solar surface
and corona to the heliosphere. By observing the intensities of selected spectral lines and line profiles, SPICE will derive
temperature, density, flow and composition information for the plasmas in the temperature range from 10,000 K to
10MK. The instrument optics consists of a single-mirror telescope (off-axis paraboloid operating at near-normal
incidence), feeding an imaging spectrometer. The spectrometer is also using just one optical element, a Toroidal Variable
Line Space grating, which images the entrance slit from the telescope focal plane onto a pair of detector arrays, with a
magnification of approximately x5. Each detector consists of a photocathode coated microchannel plate image
intensifier, coupled to active-pixel-sensor (APS). Particular features of the instrument needed due to proximity to the Sun
include: use of dichroic coating on the mirror to transmit and reject the majority of the solar spectrum, particle-deflector
to protect the optics from the solar wind, and use of data compression due to telemetry limitations.
A hot, magnetized plasma such as the solar corona has the property that much of the physics governing its activity takes place on remarkably small spatial and temporal scales, while the response to this activity occurs on large scales. Observations from SMM, TRACE, SOHO and Yohkoh have shown that typical solar active regions have loops ranging in temperature from 0.5 to 10 MK, and flares up to 40MK. The spatial and temporal domains involved have been heretofore inaccessible to direct observations from Earth, so that theory has relied heavily on extrapolations from more accessible regimes, and on speculation. The RAM Solar-Terrestrial Probe consists of a set of carefully selected imaging and spectroscopic instruments that enable definitive studies of the dynamics and energetics of the solar corona.
We discuss a mission concept (ESSEX) for probing energy and mass transport in the solar atmosphere. The primary instrument on ESSEX is a high-speed EUV imaging spectrograph designed to extract plasma diagnostics from the small-scale, rapidly varying events that are thought to heat the solar atmosphere. We argue that spectral resolution is required to determine the physics that underlies the spectacular solar coronal images returned by TRACE and other EUV imaging telescopes. Previous and current spectrographs are severely limited in time resolution, and we present two rapid imaging spectrograph designs that are optimized for different tasks: the ESSEX spectrograph, intended as a pure science instrument to identify the physical mechanisms of energy and mass transport in generic solar features; and a synoptic spectrograph, intended as an operational instrument to quantify momentum and energy release in coronal mass ejections and filament liftoff events. If flown, ESSEX will provide high cadence observations required to trace the flow of energy through reconnection and wave motion in the solar atmosphere. It will achieve sub-arcsecond resolution in the transition region and corona with both spectroscopy and imaging over a continuous temperature range from 10,000 K to 10 million K, and will sample chromospheric wave motion at frequencies over 100 Hz.
The Solar Probe mission is an unprecedented exploration of the inner heliosphere, which will achieve unique science by flying over the pole of the Sun and as close to the Sun's surface, through the solar corona, as is technologically feasible today. It will first travel to Jupiter for a gravity assist, leave the ecliptic plane, fly over the Sun's poles to within 8 solar radii, and reach perihelion over the equator at 4 solar radii. A unique aspect of the Solar Probe orbit is that the trajectory is orthogonal to the Sun-Earth line during perihelion passage so that there is continuous radio contact throughout the flyby. Two perihelion passes are planned, the first near the 2014 solar minimum and the second near the 2019 solar maximum. This orbit ensures that the mission will probe both the high speed solar wind streams and the equatorial low-speed streams.
Although NASA recinded the 1999 Solar Probe Announcement of Opportunity (AO 99-OSS-04) in early 2001, Solar Probe is still very much alive and community support for the mission is strong. In the fall of 2001, Congress earmarked $3M for Solar Probe and instructed NASA to consolidate the Solar Probe management within the existing SEC/LWS program. The Johns Hopkins University Applied Physics Laboratory (JHU/APL) is currently reviewing the mission and conducting an Engineering Assessment Study to be released later this year. Both the NRC Decadal Survey Committee and the SEC Roadmap Committee have strongly endorsed Solar Probe and recommended that it be "implemented as soon as possible".
Two successful sounding rocket flights were launched on May 15, 1997 and November 2, 1998 with an objective of providing inter-calibration with several of the instruments on board SoHO and TRACE. We will discuss here the results of the inter-calibration between the SwRI/LASP rocket imaging instruments and the Extreme-UV Imaging Telescope (EIT) on SoHO. The MXUVI sounding rocket instrument is a multi-layer mirror telescope equipped with a special internal occulter and light trap to provide full disk imags of Fe IX/X 17.1 nm and off-limb observations of He II 30.4 nm. The SoHO/EIT instrument is also a full disk multi-layer imager with four channels, Fe IX/X 17.1 nm, FE XII 19.5 nm, Fe XV 28.4 nm and He II 30.4 nm. By comparison with the EIT observations taken at the same time we can quantify the sensitivity degradation of the EIT detector, as well as measure the off-limb stray- light characteristics of the two instruments.
SOPHIE (Solar Photometric Helium Imaging Experiment) is a design for a new space-borne EUV multi-layer reflecting coronagraph to obtain full coronal field-of-view (solar disk and 1.1 to 3.0 solar radii above the limb) observations in He II 304 angstrom, and to measure the coronal helium abundance as a function of structure and time in the corona. Knowledge of the coronal helium abundance is fundamental to understanding the dynamics of the solar wind acceleration region, yet its value is not well known. SOPHIE will open up a new observational domain by providing full field-of-view coronagraph observations of helium, as opposed to electrons observed with traditional white light coronagraphs. Moreover, it has been recognized in the last several years that time variable phenomena is important and relevant to every aspect of the transition region and corona.
The instrument SUMER (solar ultraviolet measurements of emitted radiation) is designed to investigate structures and associated dynamical processes occurring in the solar atmosphere from the chromosphere through the transition region to the inner corona, over a temperature range from 104 to 2 multiplied by 106 K and above. The observations will be performed, on board SOHO (solar and heliospheric observatory) scheduled for launch in November 1995, by a scanning, normal-incidence telescope/spectrometer system in the wavelength range from 500 to 1610 angstrom. Spatial resolution requirements compatible with the pointing stability of SOHO are less than 1000 km corresponding to about 1-arcsec angular resolution. Doppler observations of EUV line shifts and broadenings should permit solar plasma velocity measurements down to 1 km s-1. We report here on some specific features of this instrument related to its pointing as well as its spatial and spectral resolution capabilities.
The SUMER (solar ultraviolet measurements of emitted radiation) instrument on the SOHO (solar and heliospheric observatory) satellite is sensitive to the state of polarization of the incident radiation primarily due to two optical elements, the scan mirror and the holographic grating. The angle of incidence of light striking the scan mirror varies from roughly 73.3 to 81.6 degrees (with respect to the mirror normal), which causes the mirror reflectance to be sensitive to the state of polarization of the incident radiation. Therefore, the measurement and characterization of this polarization sensitivity as a function of wavelength was performed using the engineering model optics (scan mirror and grating) and synchrotron radiation, which is nearly 100% linearly polarized, from the SUPERACO (Super Anneau de Collisions d'Orsay) positron storage ring in Orsay, France. The polarization sensitivity or modulation factor of the SUMER instrument was found to be between 0.4 to 0.6, depending on the wavelength and the angle of incidence of light striking the scan mirror, and agrees with the calculated polarization properties based on the measured optical constants for silicon carbide (SiC).
Metric nonlinearities in microchannel plate detectors have been mapped using a small spot of UV light scanned across the detector. The centroid of the detected image is accurately located, and corrections to the wavelength scale are made to determine the precise absolute Doppler shifts of the solar emission lines. The possible causes of the observed nonlinearities are briefly discussed.