PROBA-3 is a mission devoted to the in-orbit demonstration (IOD) of precise formation flying (F²) techniques and technologies for future ESA missions. The mission includes two spacecraft. One of them will act as an external occulter for scientific observations of the solar corona from the other spacecraft, which will hold the ASPIICS coronagraph instrument, under CSL responsibility.<p> </p>The ASPIICS instrument on PROBA-3 looks at the solar corona through a refractive telescope, able to select 3 different spectral bands: Fe XIV line @ 530.4nm, He I D3 line @587.7nm, and the white-light spectral band [540;570nm]. The external occulter being located at ~ 150 meters from the instrument entrance, will allow ASPIICS to observe the corona really close to the solar limb, probably closer than any internally or externally occulted coronagraph ever observed.<p> </p>This paper will present the straylight model and analyses carried out by CSL. A first specificity of the analysis is that the scene on the useful Field of View (FOV) is the solar corona which has a brightness dynamic range as high as 10<sup>3</sup> between the close corona, close to 1 solar radius (Rsun), and the “distant” corona around 3RSun. The specifications are very stringent for this type of instrument. A consensus was found and will be presented regarding the expected straylight within the FOV. It will also be shown that to achieve realistic estimations it is required to take into account the exact location of the created straylight as well as the entrance field.<p> </p>The second specificity that had to be analyzed is that the diffraction from the solar disk by the external occulter enters the instrument un-obstructed until the internal occulter, and with a brightness 100 times higher than the close corona (~1RSun) brightness. The simulation of this diffraction as well as its propagation inside the ASPIICS telescope creating additional straylight, had to be carefully established in order to give realistic results of its impact on the performances while being actually possible to compute.
The ESA formation Flying mission Proba-3 will y the giant solar coronagraph ASPIICS. The instrument is composed of a 1.4 meter diameter external occulting disc mounted on the Occulter Spacecraft and a Lyot-style solar coronagraph of 50mm diameter aperture carried by the Coronagraph Spacecraft positioned 144 meters behind. The system will observe the inner corona of the Sun, as close as 1.1 solar radius. For a solar coronagraph, the most critical source of straylight is the residual diffracted sunlight, which drives the scientific performance of the observation. This is especially the case for ASPIICS because of its reduced field-of-view close to the solar limb. The light from the Sun is first diffracted by the edge of the external occulter, and then propagates and scatters inside the instrument. There is a crucial need to estimate both intensity and distribution of the diffraction on the focal plane. Because of the very large size of the coronagraph, one cannot rely on representative full scale test campaign. Moreover, usual optics software package are not designed to perform such diffraction computation, with the required accuracy. Therefore, dedicated approaches have been developed in the frame of ASPIICS. First, novel numerical models compute the diffraction profile on the entrance pupil plane and instrument detector plane (Landini et al., Rougeot et al.), assuming perfect optics in the sense of multi-reflection and scattering. Results are confronted to experimental measurements of diffraction. The paper reports the results of the different approaches.
We report on the current status of the KORTES project – the first sun-oriented mission for the International Space Station to be launched in 2016-2017. KORTES will comprise several imaging and spectroscopic instruments that will observe solar corona in a number of wavebands, covering EUV and X-Ray ranges. A brief overview of the instrumentation of KORTES, its’ layout, technical parameters and scientific objectives is given. An additional attention is given to the design of multilayer optics and filters to be employed in EUV instruments of KORTES.
We report measurements of the reflection spectra of (i) concave (spherical and parabolic) Mo/Si, Mg/Si, and Al/Zr
multilayer mirrors (MMs) intended for imaging solar spectroscopy in the framework of the TESIS/CORONAS-FOTON
Satellite Project and of (ii) an aperiodic Mo/Si MM optimized for maximum uniform reflectivity in the 125-250 Å range
intended for laboratory applications. The reflection spectra were measured in the configuration of a transmission grating
spectrometer employing the radiation of a tungsten laser-driven plasma as the source. The function of detectors was
fulfilled by backside-illuminated CCDs coated with Al or Zr/Si multilayer absorption filters. High-intensity second-order
interference reflection peaks at wavelengths of about 160 Å were revealed in the reflection spectra of the 304-Å Mo/Si
MMs. By contrast, the second-order reflection peak in the spectra of the new-generation narrow-band (~12 Å FWHM)
304-Å Mg/Si MMs is substantially depressed. Manifestations of the NEXAFS structure of the L<sub>2, 3</sub> absorption edges of
Al and Al<sub>2</sub>O<sub>3</sub> were observed in the spectra recorded. The broadband Mo/Si MM was employed as the focusing element
of spectrometers in experiments involving (i) the charge exchange of multiply charged ions with the donor atoms of a
rare-gas jet; (ii) the spectroscopic characterization of a debris-free soft X-ray radiation source excited by Nd laser pulses
in a Xe jet (iii) near-IR-to-soft-X-ray frequency conversion (double Doppler effect) occurring in the retroreflection from
the relativistic electron plasma wake wave (flying mirror) driven by a multiterawatt laser in a pulsed helium jet.