  We present the development of Linear Astigmatism Free - Three Mirror System
(LAF-TMS). This is a prototype of an off-axis telescope that enables very wide
field of view (FoV) infrared satellites that can observe Paschen-$\alpha$
emission, zodiacal light, integrated star light, and other infrared sources. It
has the entrance pupil diameter of 150 mm, the focal length of 500 mm, and the
FoV of 5.5$^\circ$ $\times$ 4.1$^\circ$. LAF-TMS is an obscuration-free
off-axis system with minimal out-of-field baffling and no optical support
structure diffraction. This optical design is analytically optimized to remove
linear astigmatism and to reduce high-order aberrations. Sensitivity analysis
and Monte-Carlo simulation reveal that tilt errors are the most sensitive
alignment parameters that allow $\sim$1$^\prime$. Optomechanical structure
accurately mounts aluminum mirrors, and withstands satellite-level vibration
environments. LAF-TMS shows optical performance with 37 $\mu$m FWHM of the
point source image satisfying Nyquist sampling requirements for typical 18
$\mu$m pixel Infrared array detectors. The surface figure errors of mirrors and
scattered light from the tertiary mirror with 4.9 nm surface micro roughness
may affect the measured point spread function (PSF). Optical tests successfully
demonstrate constant optical performance over wide FoV, indicating that LAF-TMS
suppresses linear astigmatism and high-order aberrations.
