Multi object spectrograph of the Fireball balloon experiment

Fireball is a NASA/CNES balloon-borne experiment to study the faint diffuse circumgalactic emission in the ultraviolet around 200 nm. The field of view of the 1 meter diameter parabola is enlarged using a two-mirror field corrector providing 1000 arcmin(2) at the slit mask. The 0.1 nm resolution Multi Object Spectrograph is based on two identical Schmidt systems sharing a reflective aspherical grating. The aspherization of the grating is achieved using a double replication technique of a metallic deformable matrix. We will present the F/2.5 spectrograph design and the deformable matrix process to obtain the Schmidt grating with elliptical contours.