The Solar EruptioN Integral Field Spectrograph

Abstract

The Solar eruptioN Integral Field Spectrograph (SNIFS) is a solar-gazing spectrograph scheduled to fly in the summer of 2025 on a NASA sounding rocket. Its goal is to view the solar chromosphere and transition region at a high cadence (1 s) both spatially ( ${0.5}^{″}$ ) and spectrally (33 mÅ) viewing wavelengths around Lyman alpha (1216 Å), Si iii (1206 Å), and O v (1218 Å) to observe spicules, nanoflares, and possibly a solar flare. This time cadence will provide yet-unobserved detail about fast-changing features of the Sun. The instrument is comprised of a Gregorian-style reflecting telescope combined with a spectrograph via a specialized mirrorlet array that focuses the light from each spatial location in the image so that it may be spectrally dispersed without overlap from neighboring locations. This paper discusses the driving science, detailed instrument and subsystem design, and preintegration testing of the SNIFS instrument.

Keywords: Chromosphere, active; Flares; Instrumentation and data management; Sounding rocket; Spectrograph; Spicules.

Figure 1

Synthetic Ly-$\alpha$ spectra as a function of time (a)–(d) as forward modeled using the RADYN and RH1.5D codes for nanoflare simulations with 10 s heating by electron beams with energy cut-off E_C of 8 keV and energy flux of $5\times {10}^8$ (a), $8\times {10}^8$ (b), and $1.2\times {10}^9$ (c) ergs cm⁻² s⁻¹; as well as thermal conduction only (d) for a coronal loop with half-length $L/2=15$ Mm and initial loop top coronal temperature of 1 MK. Negative (positive) velocities indicate blue (red)-shifts. The panels on the right side show Ly-$\alpha$ spectra every 1 s during the first 20 s of each simulations.

Figure 2

The SNIFS Instrument layout: (a) a top view of the payload; (b) a side view of the payload. The left two sections contain the telescope and spectrograph elements, while the right section contains telemetry and housekeeping elements. Light enters through a shutter door on the left of the payload. The primary bulkhead is located center left of the payload with optical benches mounted to it. The telemetry bulkhead is located center right on the payload carrying the large heatsink, electrical, and vacuum equipment.

Figure 3

Photos of one of the mirrorlet arrays: (a) view of the array’s face. The individual mirrorlets can be seen as a reflective grid; (b) the back of the mirrorlet array, with tweezers for scale.

Figure 4

A simplified version of how a mirrorlet array works, showing how an image at a focal plan is converted into spectra and back into a datacube. Adapted from Westmoquette et al. (2009).

Figure 5

SNIFS optical design: (a) the top view, (b) the side view. Light enters from the left side of the image (not shown). The optical elements, in order, are: Primary Mirror, Secondary Mirror, Tertiary Mirror, Mirrorlet Arrays, Focusing Mirror, Grating, and Detector. After the third optical element, the optics split off into two different fields of view in order to view two different regions on the Sun.

Figure 6

A heat-rejection baffle was placed at the first focus of the primary mirror. This view shows the baffle mounted on a cutout of the front optics bench. The invar plate (yellow) restricts the FOV. The light grey baffle also acts as a heatsink.

Figure 7

Block diagram showing the commands and connections which pass through the SNIFS Arduino boards.